# Plywood vs OSB



## MJW

So tell me, why would you worry about it getting wet in the first place? 

I probably haven't seen as many roofs as some here, but I have seen enough. Almost every roof we have ever torn off with plywood, we have to renail it down or resheath it. Maybe it is just our climate here. I'm sure others from MN will tell you that plywood just isn't used anymore. Yes, it could be due to price, but most will tell you that plywood delaminates, curls, bows, breaks.....much easier than OSB.

I only remember one OSB sheathed house that we had to replace the sheating on. That was on a garage that a guy heated with no insulation. The sheathing just crumbled because of all the moisture in it.

Studies don't mean squat to me. Everyone knows real world experience is where the answers are. Isn't that why you posted your question? If you already had your data and had no intention of hearing other views, why would you ask?


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## Ed the Roofer

MJW,

Sheathing and the nails penetrating it and the insulation on the floor of the attic all can get wet way beyond what a periodic rain storm prior to covering the decking can do from a lack of a proper balanced attic ventilation system. This internal humidity, which never ventilates and dries out the interior, is what more readily affects the deck sheathings.

From personal experiences, I have seen much more substantial deterioration and swelling on even 10 to 20 year old osb vs much older cdx plywood.

You also mentioned earlier about an osb product that lasts for 50 years on interior floors. Is this the real life achievment of the product or just the manufacturers stated expected life cycle? 

I wasn't aware that any osb product has been available for at least 50 years yet, but maybe I am wrong.

Also, I should further qualify that statement that some codes used to and still do allow 3/8" decking. When this thinner 3-ply version of plywood is used, I believe that product also is garbage. But, when a 4-ply 1/2" or better cdx is used, I do not see such a short life cycle for functionability, especially where proper balanced ventilation has been installed.

I also agree that practical hands on experiences are more valid than laboratory conditioned experiments and testing, but when the test results are done in an unbiased scientific method, those results should not be discounted.

Also, on another forum, many builders on that other site heavily promoted another product called Advantech, which I am unfamiliar with unless it also goes by another name.

You really should download the articles from the link I provided earlier, especially the technical one from Georgia Pacific, if you at least would be open to examining the tests done and the results obtained.

Ed


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## Grumpy

Ed, I've no problem using the thinner 3/8 3 ply cdx when we are sheathing over spaced decking. However if the plywood were only supported by the rafters, I agree it'd have to be 4 ply.


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## Ed the Roofer

I still use the 4-ply 1/2" C.D.X. on skip sheathing as a rule. 

The codes can be interpreted differently by the building inspectors. They may deem that the original 1" x 6" spaced board decking plus the new 3/8" sheathing qualifies to meet the typical 1/2" minimum requirement, but they also may view the new decking as the only decking. In Elgin, they list 5/8" as the minimum requirement, yet I have never seen any other contractor do so. 



I know, I am splitting hairs, because when the heck does a building inspector ever check that out. (One formerly from East Dundee and one currently in South Elgin does though)

Ed


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## AaronB.

They get out of the trucks there? LOL


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## Ed the Roofer

Yes Aaron, there actually is one guy that does an extremely diligent job. On many occasions in the past, he required the homowners to do even more additional work, such as a chimney housing replacement or additional sheathing replacement.

He is the exception rather than the rule though. Mostly, they do a drive by just to make sure a permit is in the window and thats it.

Ed


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## PlainPainter

permits for roofing is a scam. Andover, MA is the most strict town in terms of building codes in the whole country - and I have yet to hear of them checking up on roofers - they do collect the permit fees though!

-plainpainter

p.s. I wouldn't stand on roof decking that was only 3/8 - heck 1/2 seems kind of skimpy to me. But I guess since you aren't hosting ball dances on a roof - who cares.


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## AaronB.

IBC and UCC say it's cool.


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## Grumpy

PlainPainter said:


> permits for roofing is a scam. Andover, MA is the most strict town in terms of building codes in the whole country - and I have yet to hear of them checking up on roofers - they do collect the permit fees though!


I enjoy working in towns where permits are required. Scam or not they do protect the consumer. Why? The unliscenced and uninsured laborers who decide to be roofers for a day don't get a permit to do the job... which highly reduces the likleyhood they will bother trying. 

Yes very few villages around my are actually do inspections, however the village is doing the due dilligence for the customer nad making sure they are hiring roofers to repalce their roof.


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## A Good Roofer

Be careful when walking on old OSB. I had someone who almost fell through the roof. He steped on a spot at the bottom of a valley that had been leaking for a long time. The OSB just pulverized from the water. Th roofers foot went through the ceiling and I had to repair the drywall. The customer refushed to pay for the additional work on the ceiling and said we should give it to our insurance company. Our dedutable was $1,000, so we just ate the cost.


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## PlainPainter

Personally - if the roof decking is rotting in that way - that's homeowners responsibility for the drywall repair - that ain't contractor negligence. And I certainly will remember to put a clause in my next roofing contract that customer is held liable for any damages as a result of faulty roof decking, and that customer maintains the deck is in good condition for the purposes of setting up roofing equipment and will hold up to normal working conditions - and that any and all damages as consequence of these assumptions will be paid by said customer - except for workers comp. 

It's one thing if you are ripping off the old decking and putting down new decking and someone by accidents steps through some board. But I remember one job we did where we had to walk on some flat roof and perhaps place some ladder to get on some rake side gable - everything was done professionaly - and then there was a leak which ruined the ceiling. Of course the homeowner blamed my boss at the time - and he ended up putting a $1,000 ceiling for free. Which I felt was kind of scummy - because as painters we had to 'trust' her structure in order to put equipment up there - otherwise how would we paint some tricky parts of her house? All the procedures were well within normal painting practices. My thoughts were that the roof was very near the end of service cycle - and would have gone by itself eventually and ruined the ceiling anyways. 

My thoughts are that a customer has to agree beforehand to a certain convention of practices when it comes to equipment, scaffolding, setup, and working practices. And any and all consequences for these actions are on the customer. If I crawl around some dormer to paint it - and a whole bunch of roofing shingles come loose because they have been there 35 years - that ain't my fault! I have to follow a certain guideline of working norms in order to get a job done - not every job is without some damage. Contrary to popular opinion, I haven't invented an anti-gravity machine that allows me to float effortlessly around customers homes and do my thing without worry.

I just feel very strongly about customers blaming us for everything - when I feel it isn't our fault - we're just trying to make a living - not looking for wet spots in crap OSB decking, that shouldn't be there to begin with, to step through.

-plainpainter


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## AaronB.

Well, many people get their roofing replaced because its old and leaking.


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## Ed the Roofer

Aaron,

Whos fault or liability is it, if when one of your workers is walking across the roof before the tear off starts and their foot and leg break through the shingles and decking and puts a hole in the drywall ceiling below, not assuming any injury to the worker.

Remember, he is not doing anything irresponsible and not carrying any excess weight such as a bundle of shingles, just walking up the slope of the roof to the ridge to get started.

Is this contractor negligence? Should the contractor and their general liability insurance pay for the repairs?

Or, is this neglected condition caused and perpetuated by the homeowners lack of taking timely maintenance and repairs?

How do you guys feel about this scenario? 

Oh, and lets presume, for the sake of argument, that you have a $ 1,000.00 deductible and the total cost of damages is $ 1,500.00 for drywall repair, mudding, taping, and repainting the whole ceiling, as the example.

Ed


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## PlainPainter

That is so totally not contractor negligence - to the point this shouldn't even be discussed. If some contractors here have to think on this - it's a sad thing. Customer pays me to put on new roof - I don't pay customer to have new ceiling - I am an invited guest to do a certain task. Now if customer said roof has weak spots on it - and wants it in writing that no damage will result of it. Then it's our responsibility to either comply with the person or turn the job down. But we have to start with a reasonable assumption that the roof is walkable in order to commence work on it. Why should I pay for someone's sheetrock repair - because they didn't hold their end of the bargain by supplying a good solid roof decking. If homeowners want to have this silly attitude like they have the right to get everything fixed for free - then they can go up their own blasted ladders and rip their own blasted roofs off. Anything you do that falls within the norm of procedures to get your job done - makes you off the hook for any mishaps. When I scrape windows and remove old glazing - I make customers sign that I am not liable for glass damage - because you break alot of glass sometimes, though it's not negligence - it's just how it is. And I refuse to pay for new glass - when in the normal procedure of removing old paint and old glazing you knock a little bit on old rickety window glass - there is always failure. Now if some dooby on my crew let go a ladder and it smashed through a window - that is negligence! 

-plainpainter


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## AaronB.

yEAH, i KNOW ABOUT ALL THE GREY AREAS, BUT i ALSO KNOW THAT IF IT GETS TO COURT, ITS ANYBODY'S GUESS WHAT THE JUDGE WILL DECIDE....I.E. i HIRED A TREE GUY ONCE TO CUT TREES, HE NEVER FINISHED, SO i DIDNT PAY HIM. i LOST IN COURT...DONT KNOW HOW, DONT KNOW WHY, I HAD PICTURES AND EVERYTHING, BUT STILL LOST AND HAD TO PAY THE FULL CONTRACT PRICE (sorry for the caps) plus interest and court costs for naked trees (no leaves or limbs left)

now, when anyone asks me if I know a tree guy, I make sure to relay the message. FWIW.


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## PlainPainter

Courts ain't about who is right and who is wrong - it's about legal procedure. We as contractors decide what we feel is right - and certainly I have decided that homeowners have to own up to certain
responsibilities. I mean if you want to get real technical, if a homeowner hires you out directly - they are acting as the G.C. subbing out your services, and are responsible for any mishaps and accidents that may happen - i.e. they can get sued if someone falls off their roof!
Now some contractors carry insurance be it by law or by peer pressure - as a way to relieve homeowners from any liability. Because afterall they shouldn't have to pay if a roofer falls off their roof - well, whatever - I guess so - then again if they fall because of structural failures - then I think the homeowner is liable. What if you pile a bunch of bundles on the peak - and the whole roof structure collapses under the weight of the roofing bundles - and people die and what not? Carrying liability insurance is a service contractors provide clients so as not to hold customers liable - but then again I have never had serious accidents happen - and who's to say my insurance company doesn't go after the homeowners insurance if it's a severe structural failure on the part of the homeowner? Certainly my liability is not there to be abused by homeowners who think I should pay for sheetrock repair because there roof was substandard.

And getting back to the courts - if you think you shouldn't be held liable for certain things - it's your responsibility to word your contracts as such and then pay a lawyer to go over the language to make it all legal. It's called playing the game - and when you play the game, and your lawyer has made everything legit - then the courts will rule in your favor. If a lawyer can't make something legit - then you'll know at least in a court of law you will lose - so that will be have to added to your costs of 'doing' business - and your estimates will have to go up.

-plainpainter


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## Grumpy

A Good Roofer said:


> Th roofers foot went through the ceiling and I had to repair the drywall. The customer refushed to pay for the additional work on the ceiling and said we should give it to our insurance company. Our dedutable was $1,000, so we just ate the cost.


I wouldn't have dreamed of asking the customer for payment for damage we caused.


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## Grumpy

A Good Roofer said:


> Th roofers foot went through the ceiling and I had to repair the drywall. The customer refushed to pay for the additional work on the ceiling and said we should give it to our insurance company. Our dedutable was $1,000, so we just ate the cost.


I wouldn't have dreamed of asking the customer for payment for damage we caused. Grey area, contrator negligence, or otherwise.


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## MKECONTRACTOR

*My 2 cents*

When plywood gained popularity there were old timers that said it was crap and would never use anything but 1x's. "Glued together garbage". The same has/ is happening with OSB vs. ply now. 

Show me a hundred studies that show ply is better and I will show you 100 that say OSB is better. I spent a few hours researching it a few months ago and found a study that seemed really independent and reliable. Damn thing is I can't find it now to post a link to it! Anyway, the jist of what they said is this:

Water resistance- OSB is actually better than ply, except for the edges. The edges have to be sealed, and are from the factory. (The red/yellow/whatever paint is on the edges for that reason, not to differentiate thickness or any other reason.) The problem is that piece you cut and install and then gets rained on before you can get things sealed up. 

Nail holding-Ply beat OSB by a hair. 

Consistancy- OSB beat ply by a mile. You will not get very few pieces of OSB that are not square, flat, or have weakspot due to knots being present in the center of the board.

Strength-OSB beat ply. They ran like 5 different tests, striking it, twisting it, bending it, pulling it, etc.

My overall take on the article was OSB is a better product, as long as it stays dry. I use OSB, and would use it building my own house, with one exception, the subfloor. 
I don't care about the price, if ply costs x amount more, I would just charge my customers that much more. I use it because of the consistency, no knots, no delaminated pieces. 

So in my opinion in comes down to your preference. Hopefully the guys that use ply really believe they are delivering the best product, and so do the guys that use OSB.


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## Ed the Roofer

MKEContractor,

Please, Thoroughly read my post # 8. Also, after reading that post, click on the link I provided. It has 6 articles debating the merits of each product, both pro and con for each product. I believe you may find the article you previously referenced amongst that batch.

You are certainly in your rights to have your opinion, but I respectfully disagree with your conclusions.

Ed


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## PlainPainter

The thing about 1x's - is that they don't buckle and warp like many plywood sheathed roof decks. They breathe much better than continuous sheathing roofs like osb or plywood. They don't rot in the same way - they'll show leaks sooner than later as water will come through the cracks and not just soak the plywood - more buckling. And it's easier to repair damaged 1x's. I am not advocating going back to that kind of construction - but heck let's not knock a product that I have seen on roofs that are 100, 200, and 300 years old - with all it's deficiencies - will either plywood and osb last so long so reliably?

Let's not delude ourselves as to quality vs. modern construction techniques - but If I was building my own home - using rough sawn 1x's as my roof sheathing, and cedar shakes as my 'starter' row on the bottoms of my roof would probably be a reality - my friend who is a carpenter - who recently redid his roof, used shakes instead of drip edge on his dormer roofs - and I think it's a great look - not that either of us would do that for a customer.

-plainpainter


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## A W Smith

thom said:


> I'm a firm believer in osb. Though with substantial weather it will start to flake off, the structural integrity will not be impaired. Plywood, even cdx, will delaminate and loose its structural integrity with water.
> 
> Plywood has structural strength in only one direction, osb in two.


 
Actually that is not true. OSB stands for Oriented Strand Board. This means that the strands are oriented mostly in the long direction of the board product. This gives OSB more strength in the long direction that the short direction. the same as conventional plywood. I prefer to use Douglas fir cdx plywood for sheathing because of its superior nail holding properties. OSB was once made from Aspen trees hence the early market name for OSB, "Aspenite'


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## dougger222

I'm with MJW on this one. Perhaps it's a Minnesota thing?

Doing tear offs with a lot of both I like doing roofs with OSB better than plywood unless the plywood was never damp and it's got h-clips.

Torn off a lot of roofs 10-15 year old with OSB and the decking was in mint condition. Torn off a lot of roofs with plywood 15-20 years old and it was in horrible condition. I'm sure there's more at work like Ed has mentioned but this is from personal experiances. I hate tearing off roofs with plywood and no h-clips because it buckles at the horizontal butts so much. My Dad likes to step the seams together and shoot Senco PW staples and it's worked very well for many years afterwards.

In the past 10 years only worked for one builder who used plywood for decking and on steep roofs it was tough to walk on.

What I like more about plywood is the nails bite better than OSB. Nothing is easier than tearing off a 10 year old roof with staples and OSB!!!


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## pgriz

*OSB vs. plywood vs. boards*

Thank you to Ed for doing the extensive research. I'll chime in with my own experience. In roofing, some customers act proactively, but most wait until something goes wrong before they think about changing the roof. However it started, it usually means moisture on and in the roof sheathing. By the time the problem is apparent, the sheathing often has been wet persistently. So what happen?
Wood planks (1x4 or 1x6 T&G) get wet, and eventually will start to rot if the wetting is persistent, but once the wetting is stopped, dry to their "normal" shape. It takes lots of water and lots of time before wood planks are no longer fit to be used.
3/8 plywood has only two glue layers holding the three plies together. If persistently wet, the glue tends to dissolve (although not evenly), and the plies delaminate. When walking on these roofs, you can often hear the cracking as the remaining glue breaks under the tension of your flexing the wood with your weight. However, it really is too thin to use as roof sheathing (even though codes allowed it in the past). When we have to redeck, it is usually because the decking is 3/8 plywood that has delaminated past the point of any useful structural strength.
1/2 inch plywood has four plies, and three glue layers. Better than 3/8, in resisting water damage since water penetration is not even across the glue layers, and not all the plies delaminate at the same rate. When we have to replace 1/2 inch plywood, it is usually localized damage.
5/8 inch plywood has five plies and four glue layers. Again better than 1/2 inch. Almost never have to replace it, except in cases of long-term leakage in the same spot.
1/2 inch OSB is my least favorite roofing material because any place where leakage happened, the board is quite weak and even if it dries again, it doesn't appear to have the same strength. Any place which experiences leakage means that board has to be replaced. 

Now I've had contractors tell me that I'm living in the past and the new engineered materials are far more cost-effective. My observation to them is that is true as long as everything works as it is supposed to, with no leakage or condensation. But when things start to go wrong, I'd like to see a material that can cope with persistent moisture and not fall apart. Then the repair costs are not huge (replace the gyproc, wet insulation, and defective roof covering). Otherwise, especially with "cheap" construction, we have to propose expensive repairs. I'm OK with using OSB in walls or floors, but not as roof sheathing.


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## Ed the Roofer

I was at my office till 5:00 am this morning, sorting through the photos I had my secretary upload onto my computer, so that I could meet todays Yellow Page deadline, because I am changin the ad slightly and adding a work in progress photo and a finished view.

The benefit of burning the candle all night, was that I had the opportunity to review about 2,500 photos from this past year.

I can tell you with a certainty, by seeing so many photos all at once, that PGRIZ is right on with all of his comments just made. It is amazing the amount of damaged deck sheathing I have replaced in the course of one year. Sure, I know that I purchace about 20 to 25 bunks of plywood, but when you see all of the photos of all of the roofs that need decking replaced, it still astounds me of the poor home owner maintenance and crappy workmanship issues which led to these results.

The other reason for going through the photos, was to pick which ones I want to use as a photo gallery on my website being developed. 

Also, as a clear and definitive assurance, these photos convincingly proved beyond any resonable doubt, how vital a balanced ventilation system is. The amount of mold growth on the underside of the deck sheathing was astounding. 

I look forward to compiling the photos to share the whole gamut with you all.

Ed


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## whitewolf woodworks

I'm not that old, but wasn't plywood rejected by carpenters when it first came out? Lots of old timers saying, "I'd never use that crap, use solid boards instead!" Just as sheetrock was rejected by the plaster trade when it first came out. And Pex? some day all houses will be plumbed with pex. How about Tyvek vs. tar paper. I think, that with OSB v plywood, either of them is a mess when they get wet, so, install them correctly and don't let them get wet. Also, isn't OSB actually stronger than plywood?


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## RooferJim

exterior grade CDX plywood is 1000x better than any OSB. I have reroofed many an OSB house that sagged between the rafters. I rip that garbage out and put real plywood down, They only use it for the price.

RooferJim
www.jbennetteroofing.com


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## 2ndGen

jjcold417 said:


> I'm not that old, but wasn't plywood rejected by carpenters when it first came out? Lots of old timers saying, "I'd never use that crap, use solid boards instead!" Just as sheetrock was rejected by the plaster trade when it first came out. And Pex? some day all houses will be plumbed with pex. How about Tyvek vs. tar paper. I think, that with OSB v plywood, either of them is a mess when they get wet, so, install them correctly and don't let them get wet. Also, isn't OSB actually stronger than plywood?


Hi JJ, 

Of course there might always be some reservation at using anything that's new
(like how I didn't like and still don't like torch-down roofing or fake slates). 

But when it's a justifiable concern, it is what it is. 
In my case(s), I was right about not liking those two particular materials.
And, I feel the same about OSB. 

When ply get's wet, at least it can recover. 
When OSB gets wet, it's shot and has to be removed. 

Plywood has at least proven itself to be a reasonable replacement for boards.
OSB (in my opinion) has not proven itself to be a reasonable replacement for ply. 

I believe that OSB may be stronger in certain conditions, but not on a roof. 
There's what can be simulated in a laboratory and real world conditions. 
I just think that OSB is an inferior product for roof sheathing when compared to plywood (especially 3/4").

Personally, if I were building a home or replacing my decking, I'd go with T&G .


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## Just a Roofer

I have walked on osb after a tearoff where everything looks ok until my foot went through a dry rotted spot that appeared to look perfectly normal. Makes me think twice when osb decking is on the job. 

Personally, i think osb is crap & would never recommend it and like others have said it tends to dip in between the rafters. Jmo


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## RooferJim

OSB Sucks !!! Period. only the cheap builders and the ignorannis will attempt to argue otherwise. Use 5/8" exterior CDX Plywood.


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## MJW

I would say 95% of newer homes up here have 1/2" OSB, 24" on center rafters, and clips. Haven't heard of any huge masses of homes having a problem even with our weather and heavy snow/ice.

Personally, anything heavier or stronger is just overkill, in this area anyhow.

BTW, most of the sub-flooring here is OSB also.

I've seen more plywood fail than I have OSB. Although, never seen any 5/8" CDX look too bad. Sure, it's great, but overkill for the average home.


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## loneframer

I've framed hundreds of homes in the last 25 years and have seen OSB get steadily better while 4/5 ply CDX fir gets continually worse in quality. With the advent of Advantech and the Zip wall/roof products, I don't think twice to recommend OSB products. At least I know when I rip a sheet in half, it's not going to open up like a clam.

Anyone who points blame at OSB because the roofing/siding/flashing/ventilation details were half-a$$ just doesn't get it anyway.:no:


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## calhomeremodel

I have yet to use osb on a roof, and just do not see it happening.


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## echase

Pardon the non-roofer question: 

Would plywood fans replace bad OSB boards with plywood, or is mix-and-and match a no-no?


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## 2ndGen

loneframer said:


> I've framed hundreds of homes in the last 25 years and have seen OSB get steadily better while 4/5 ply CDX fir gets continually worse in quality. With the advent of Advantech and the Zip wall/roof products, I don't think twice to recommend OSB products. At least I know when I rip a sheet in half, it's not going to open up like a clam.
> 
> Anyone who points blame at OSB because the roofing/siding/flashing/ventilation details were half-a$$ just doesn't get it anyway.:no:


Anything that can't stand moisture (whether from exterior or interior sources) shouldn't be in a place that waterproof a structure.

Failed roofing details or improper installation is going to allow damage to any substrate regardless of what it is (OSB, plywood, metal, T&G board, etc...). 

The proper context in comparing OSB to ply in that particular situation is which better withstands the moisture? In that case (which is what we're talking about here), OSB is inferior to plywood. 

A plywood deck that gets wet can be left intact provided that is is dried out sufficiently. An OSB roof that gets wet is trashed. There is no saving an OSB roof. Regardless of how it gets wet (whether by improper roof install, uncontrollable circumstance [like clogged gutter, pest damage, etc...], etc...), the better deck is the one that doesn't degrade upon getting wet. 

Plywood is proven (over a century in use). 
OSB just got here (barely since the 70's). 

While there are tons of articles online regarding the pros & cons of ply/osb, I think this article is probably the best researched and offer references from the industry. 

http://www.prosalesmagazine.com/industry-news.asp?sectionID=432&articleID=134260&artnum=1

Ultimately, there is no reason for a Roofer to use OSB other than to save a few bucks on a job. It's an inferior product. It's more prone to damage if it should get wet. It doesn't hold nails as well as plywood. It's heavier. And so on...

I can't speak about it's performance for sheathing walls, but it's discouraged by manufacturers for use in sub-flooring or in wet areas.


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## 2ndGen

Great info here too: http://www.contractortalk.com/f15/plywood-vs-osb-18291/index3/


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## 2ndGen

echase said:


> Pardon the non-roofer question:
> 
> Would plywood fans replace bad OSB boards with plywood, or is mix-and-and match a no-no?


I would replace all OSB decking with plywood. 
Besides, once you rip off a roof from an existing OSB deck, it's shot. 
I wouldn't mix inferior products with superior products. 
Your deck would only be as strong as your weakest link.


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## 2ndGen

calhomeremodel said:


> I have yet to use osb on a roof, and just do not see it happening.


Then you'll never have the same problems with OSB that others have had. 

I'm not saying OSB doesn't have it's place in other applications (it might, I just don't know), 
but I don't know why anybody would gamble with it if it isn't as proven as plywood.


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## Cyle

Around here you won't find plywood on the floor, walls, or roof. 99% osb atleast. Never had a problem with it so do not see the problem. And here plywood is 3x the price, so what's the benefit? There is none. Redid plenty of roofs with osb 20+ years old without any issue.


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## bretth0214

I just looked at a roof yesterday on a 5 year old house that had 1/2" osb on it. The reason I was looking at the roof is because the shingles are blowing off of it in two places. Now I know who the builder was and to call him a hack would be an understatement so I am not surprised that the shingles were blowing off. What I was surprised about was that there was osb on a roof, around here that isn't too common at least I have never see it. 

While I was walking around on the roof I was afraid I would fall through the roof deck it was really spongie and sagging between every truss. To compile the problem there was no underlayment at all on the roof. So long story short it looks like we will be ripping off all of the osb and replacing it with plywood and a properly installed roof.


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## MrRoofer

It seems to me where you get your OSB might be a large factor in things. Or maybe not so much anymore :laughing:. I remember growing up we had to keep OSB in the shed at home or it would blow up if it got a drop on it. Not anymore.

There are very few plywood buildings here anymore, and it has been that way the entire time I have been in the trades (pretty close to 20 frickin years) IMO OSB is stronger, and weathers better. It is not uncommon for a roof to sit under snow for a month before it gets shingles, with no adverse effects. The only people who use plywood nowadays are known as the overkillers. I'm not saying there is anything wrong with that, just sayin'.


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## mikebooth

*mikebooth*

I have strated using Zip System, this does not require 30# felt. You tape the joints. It is a one step operationa and has a texture that helps to protect from falls. :thumbup:


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## Red Adobe

I skimmed the post and heres my .02 worth

OSB back in 80's and 90's had problems as i saw several post. Better glues and production has made it alot better nowdays.

If you look most OSB is marked for exterior or general.......general is what you put behind sheetrock in a rental so when an idiot punches the wall he breaks his hand.....exterior is for decking and sheeting

I use OSB 90% of the time. 
The last few times I have used cdx it had lots of cracks and defects.

One last thing.....here in the SW alot of lumber is kept in HUTs at the yards and if you look at a stack of osb it may have a little hump while a stack of plywood is all curled up and a mess. we can go from 90% humidity one rainy day to 6% and windy the next. So like so much in our trade there is a time and a place for different products


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## 2ndGen

Red Adobe said:


> I skimmed the post and heres my .02 worth
> 
> OSB back in 80's and 90's had problems as i saw several post. Better glues and production has made it alot better nowdays.
> 
> If you look most OSB is marked for exterior or general.......general is what you put behind sheetrock in a rental so when an idiot punches the wall he breaks his hand.....exterior is for decking and sheeting
> 
> I use OSB 90% of the time.
> The last few times I have used cdx it had lots of cracks and defects.
> 
> One last thing.....here in the SW alot of lumber is kept in HUTs at the yards and if you look at a stack of osb it may have a little hump while a stack of plywood is all curled up and a mess. we can go from 90% humidity one rainy day to 6% and windy the next. So like so much in our trade there is a time and a place for different products


Hi Red.

I would imagine that in Texas, you guys don't have much humidity consistently?


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## 2ndGen

MrRoofer said:


> It seems to me where you get your OSB might be a large factor in things. Or maybe not so much anymore :laughing:. I remember growing up we had to keep OSB in the shed at home or it would blow up if it got a drop on it. Not anymore.
> 
> There are very few plywood buildings here anymore, and it has been that way the entire time I have been in the trades (pretty close to 20 frickin years) IMO OSB is stronger, and weathers better. It is not uncommon for a roof to sit under snow for a month before it gets shingles, with no adverse effects. The only people who use plywood nowadays are known as the overkillers. I'm not saying there is anything wrong with that, just sayin'.


I'm all for regional performance (osb doing better in some places, ply in others). 

That brings something to mind. 
A sheet of 1/2" osb weighs in at about 78#. 
A sheet of 3/4" ply weighs in at about 75#. 

As long as osb doesn't get wet, it's ok. 
But I can't build for perfection. 
I build for failure...or "just in case". 
"Just in case" that decking gets wet,
I want my customers to have a solid substrate. 


Ply, lighter and stronger and thicker (holds nails better). 
Easier to handle. Easier to cut. More jobs site proof 
(won't crumble if corner hits floor or is hit with anything). 

There are just so many reasons why for Roofing, 
plywood is superior to osb. 

In my framing class, I was told that osb is best for walls.
It's make up makes it structurally sound in either direction. 
But while the instructor (who had 35 years in the trade,
I by the way have 26 years) acknowledged that osb was 
being used more for roofing, he preferred ply for roofing. 

I guess this is the ultimate test...what would we put on our homes?
Well, actually, I'd "overkill" it ( :lol: ) and use T&G Boards!
But if I had to use sheet goods, 3/4" CDX Plywood and sleep well at night.


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## echase

What's the preferred method of sealing cuts in OSB when used for decking in a high-humidity environment? 

Can Killz take the heat?


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## caybound

For me, our humidity makes OSB a no-go, but also, I HEAR that you can get (borate) treated OSB, but I haven't seen it. No treatment, no use for it here.


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## jdc313

ed the roofer is wrong.... osb flakes and plywood delaminates because there is not proper ventilation from the soffit to the ridge... if you dont have a soffit you use venting drip edge... plywood wont delaminate and osb wont flake if it is ventilated and kept dry... both are fine to use...


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## jdc313

osb wont dip when you have h clips installed... its all about ventilation ventilation ventilation!!!!


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## jdc313

RooferJim said:


> exterior grade CDX plywood is 1000x better than any OSB. I have reroofed many an OSB house that sagged between the rafters. I rip that garbage out and put real plywood down, They only use it for the price.
> 
> RooferJim
> 
> 
> Jim,
> I bet that osb sagged either because it wasnt originally installed properly and didnt have h clips... also... when a house isnt ventilated properly, condensation builds and causes the osb to expand and contract, and causes plywood to delaminate. We always pull the bottom row of wood to make sure baffles are in place, and the insulation is not touching the plywood down by the soffit. We also almost always install more soffit vents to help ventilation... the best way to ventilate a house is with with a 1.5 inch gap at the ridges, baffles installed, gable vents blocked off, and soffit wide open. Block off the gable allows air to be pulled from eave to ridge without interruption.


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## jdc313

osb is also always straighter and flatter... a lot of plywood i see at the store is always warped and knotted


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## bluebird5

Old thread, but I used 5/8 osb today for the first time. I have always used 5/8 ply, but I could not afford it on this job. One thing I noticed is it was sooo much easier to get into the plywood clips. I did notice some sheets were thicker than others. I still like ply better, but the osb was definitely easier to lay. Rafters were on 16 inch centers.


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## buildr7

Do you use osb against tile or plywood.


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## Rio

bluebird5 said:


> Old thread, but I used 5/8 osb today for the first time. I have always used 5/8 ply, but I could not afford it on this job. One thing I noticed is it was sooo much easier to get into the plywood clips. I did notice some sheets were thicker than others. I still like ply better, but the osb was definitely easier to lay. Rafters were on 16 inch centers.


Did you use Advantech?


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## Morning Wood

Rio said:


> Did you use Advantech?


Advantech on a roof? Zip wall yes.


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## Rio

Morning Wood said:


> Advantech on a roof? Zip wall yes.


Is it normally not used on roofs? Don't know but have heard a lot of good about it on this site, apparently it's a really good product.


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## tenon0774

Rio said:


> Is it normally not used on roofs? Don't know but have heard a lot of good about it on this site, apparently it's a really good product.


Good for subfloors.

I have Never used advantech on the roof.


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## jlsconstruction

Rio said:


> Is it normally not used on roofs? Don't know but have heard a lot of good about it on this site, apparently it's a really good product.


I wouldn't want to carry them on the roof. They are heavier than regular osb. 


But we use zip for roofs, same brand.


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## Tinstaafl

Advantech is great for subfloors, because you're practically guaranteed to get them rained on a time or three before you're dried in. Not much point in using it for roof sheathing, since once that's down you're about 15 minutes from dry-in. 

Never been in a position to use zip, but it sure seems like that'd be the cat's meow.


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## schaefercs

We used 5/8 advantech on a roof once, maybe 5 years ago. It was pretty slick to walk on because the wax like finish they used to treat the material. Would love to use zip


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## Tinstaafl

Advantech is the cat's meow when it comes to moisture resistance. I've left chunks of it out in the weather for 3-4 years and it... turns gray. Edges swell slightly with that kind of exposure, but structurally it's way more intact than plywood would be.

Get a floor rained on a couple times before it's dried in, and you'd have a tough time telling it.


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## TimNJ

Warren said:


> The treatment goes throughout the product. The edge has a waxy feel after you cut it. The stuff is amazing.


I wondered if that stuff was after the fact applied, or was it all the way through.


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## TimNJ

How is its holding power such as nailing hardwood floor?


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## EricBrancard

TimNJ said:


> I have never used it.
> I would be curious to hear from anybody that does.
> If you have a cut edge is it more vulnerable?


I have pieces of it that have been outside for a few years that I would rather use than a brand new sheet of 3/4" Ply.


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## EricBrancard

Tinstaafl said:


> Advantech is the cat's meow when it comes to moisture resistance. I've left chunks of it out in the weather for 3-4 years and it... turns gray. Edges swell slightly with that kind of exposure, but structurally it's way more intact than plywood would be.
> 
> Get a floor rained on a couple times before it's dried in, and you'd have a tough time telling it.


Yup. The grey discoloration doesn't go far either. I ran an RO150 over it and it comes right back to the new color. The water pretty much beads off of the stuff.


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## jlsconstruction

I've been using dry guard and really like the stuff.


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## Tinstaafl

TimNJ said:


> How is its holding power such as nailing hardwood floor?


I don't have any personal experience with that, but my gut feeling is that it would do just fine.


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## Calidecks

So wouldn't it be fair to say the only thing that makes advantech different is the waterproofing? And also why don't they use regular plywood, it can be waterproofed? Advantech made a decision to use osb, I wonder why that is. It's a serious question, by the way.


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## Nick R

*Plywood Vs OSB*

I was at a trade show sponsored by huber. Advantech is made of much thinner flakes then regular osb, and each flake is completely coated with the same type of glue that gorilla glue is (forgot the name). It's then compressed. The result is much more dense and greater strength in deflection as osb, and does not wick water like the veneers of plywood would.

Edit: I think it was MDI glue.


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## hdavis

TimNJ said:


> How is its holding power such as nailing hardwood floor?


Better than ply. Takes more to drive the nail in, too.

I've kept scraps around outside for years, they hold up well. I have a cold frame in ground contact made out of advantec for 6 years. You get some edge swelling, but that's from the wood starting to decompose.

Heavy stuff, it's stiffer than ply and rated for longer spans.


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## Calidecks

I've worked on many framing jobs out here and I've never used it or even seen it at the lumberyard. I'm sure it's more popular in wetter climates. However it's been awhile since I've been on a framing job.


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## jlsconstruction

*Plywood Vs OSB*



Californiadecks said:


> So wouldn't it be fair to say the only thing that makes advantech different is the waterproofing? And also why don't they use regular plywood, it can be waterproofed? Advantech made a decision to use osb, I wonder why that is. It's a serious question, by the way.



My understanding is its easier to waterproof a million little pieces vs 7 laminations like plywood. Also it's cheaper to use because it's made from scrap lumber like stumps and branches. Also it's stronger, small pieces lock together like gravel in concrete


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## TNTRenovate

Californiadecks said:


> If plywood was so much superior than why don't they use it for TJI's and Advantech?


If OSB is so great why did they have to come up with Advantech?


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## jlsconstruction

I do like dry ply to, but hardly use it, sometimes when I'm just doing a bathroom remodel. It's coated dug fer ply


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## hdavis

Californiadecks said:


> I've worked on many framing jobs out here and I've never used it or even seen it at the lumberyard. I'm sure it's more popular in wetter climates. However it's been awhile since I've been on a framing job.


IMO, it's a must in baths. I love the stuff, I just don't like lugging it around.


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## Nick R

jlsconstruction said:


> My understanding is its easier to waterproof a million little pieces vs 7 laminations like plywood. Also it's cheaper to use because it's made from scrap lumber like stumps and branches. Also it's stronger, small pieces lock together like gravel in concrete



Right I think they were getting at the veneer of plywood acting as straws, where the flakes are much smaller straws. Also the greater number of laminations in ply yields a stiffer panel, so the thin flakes compound that, but cheaper like you said.


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## jlsconstruction

hdavis said:


> IMO, it's a must in baths. I love the stuff, I just don't like lugging it around.



90 pounds a sheet


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## hdavis

jlsconstruction said:


> 90 pounds a sheet


Feels like it, but I never weighed one or checked the specs....


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## jlsconstruction

*Plywood Vs OSB*



hdavis said:


> Feels like it, but I never weighed one or checked the specs....



Our lumber yard has weights on the invoices, so the drivers don't over load the trucks, that's at least what they say


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## hdavis

1/2" is 57 lbs per sheet, so 90 for 3/4" is about right. Taking it solo up narrow stairs and making corners is a pain, but it's worth it.


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## Calidecks

TNTSERVICES said:


> If OSB is so great why did they have to come up with Advantech?


Advantech is modified osb.
It didn't replace it. It made osb better.


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## TNTRenovate

Californiadecks said:


> Advantech is osb.


Right, but if osb is so great why did they need to improve it.


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## jlsconstruction

TNTSERVICES said:


> Right, but if osb is so great why did they need to improve it.



Why don't they improve plywood? Or at least stop degrading it?


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## Calidecks

jlsconstruction said:


> Why don't they improve plywood? Or at least stop degrading it?


Cost is always entered into the equation.


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## Calidecks

What I can say is osb sure does lay flatter. They are both rated for shearwalls as long as they are struct 1


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## Calidecks

I called my engineer and ran that question by him. He said as long as the exterior walls get rapped right away or don't get wet, either is just as strong. Here in Cali we can go months without much moisture or rain.


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## TNTRenovate

jlsconstruction said:


> Why don't they improve plywood? Or at least stop degrading it?


I don't have an issue with it. I made a temp ramp out of some 3/4" cdx for my shed. Unfinished it has lasted 3 years. Not saying that's normal but no way osb would have lasted one season change without falling apart.

Maybe it is area related.


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## Calidecks

TNTSERVICES said:


> I don't have an issue with it. I made a temp ramp out of some 3/4" cdx for my shed. Unfinished it has lasted 3 years. Not saying that's normal but no way osb would have lasted one season change without falling apart.
> 
> Maybe it is area related.


Osb isn't made to be exposed. It's made to work with a building rap.


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## TNTRenovate

Californiadecks said:


> Osb isn't made to be exposed. It's made to work with a building rap.


Strike 1


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## Calidecks

TNTSERVICES said:


> Strike 1


How is that a strike? So plywood doen't make good exposed decking material is that strike one? I mean if using something for what it isn't designed for constitutes a strike, then the strikes would be infinite. :laughing: come on Rob, your getting rusty. :laughing:


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## jlsconstruction

*Plywood Vs OSB*



TNTSERVICES said:


> I don't have an issue with it. I made a temp ramp out of some 3/4" cdx for my shed. Unfinished it has lasted 3 years. Not saying that's normal but no way osb would have lasted one season change without falling apart.
> 
> Maybe it is area related.



We had a shed build with bare osb that was still standing after 16 years, it ended up at about 1/4". 





If cars were so great in 1885 why did they improve them?


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## TNTRenovate

Californiadecks said:


> How is that a strike? So plywood doen't make good exposed decking material is that strike one? I mean if using something for what it isn't designed for constitutes a strike, then the strikes would be infinite. :laughing: come on Rob, your getting rusty. :laughing:


It's a bit tongue and cheek. I did say that it's not normal.

Point really being is osb and plywood have their place and some is just personal preference, some is obviously market related (due to the varied experience), and some is application.

I'm just a plywood guy. For what I do it's a better fit and what I am used to. We don't have any quality issues here that I have run into. I can't stand prepping OSB for tile.


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## TimNJ

TNTSERVICES said:


> I don't have an issue with it. I made a temp ramp out of some 3/4" cdx for my shed. Unfinished it has lasted 3 years. Not saying that's normal but no way osb would have lasted one season change without falling apart.
> 
> Maybe it is area related.




The thing is you can't compare OSB to plywood, you would compare Advantech to plywood for your ramp.

I am also a plywood guy: Doug fir all the way. 3/4 T&G subfloor, 1/2 wall sheathing, 5/8 roof sheathing. I have never had D/F delaminate on any of my jobs, however I could see where Advantech would have its own benefits.


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## TNTRenovate

TimNJ said:


> The thing is you can't compare OSB to plywood, you would compare Advantech to plywood for your ramp.
> 
> I am also a plywood guy: Doug fir all the way. 3/4 T&G subfloor, 1/2 wall sheathing, 5/8 roof sheathing. I have never had D/F delaminate on any of my jobs, however I could see where Advantech would have its own benefits.


I don't think that's fair at all. Advantech is coated, plywood isn't.


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## jlsconstruction

TNTSERVICES said:


> I don't think that's fair at all. Advantech is coated, plywood isn't.



They have coated plywood


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## TNTRenovate

jlsconstruction said:


> They have coated plywood


No chit! But that isn't what he said. He just said plywood. I could have said the same about OSB. That's why this is a bit silly.


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## jlsconstruction

I guess I'm completely lost. It's just like anything else, use the correct product in the correct place


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## TNTRenovate

jlsconstruction said:


> I guess I'm completely lost. It's just like anything else, use the correct product in the correct place


He said that I couldn't compare plywood and osb for exposure, that it would be more like plywood versus advantech. I disagree because plywood doesn't have a coating and advantech does. If he had said a treated plywood and advantech then that would be apples to apples. That was my point.


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## Warren

TimNJ said:


> The thing is you can't compare OSB to plywood, you would compare Advantech to plywood for your ramp.
> 
> I am also a plywood guy: Doug fir all the way. 3/4 T&G subfloor, 1/2 wall sheathing, 5/8 roof sheathing. I have never had D/F delaminate on any of my jobs, however I could see where Advantech would have its own benefits.


Our #1 contractor used DF plywood for years. About 5 years ago, we started to see a decline in the quality. He now uses Advantech on all decks, osb on walls and roof. We cover the roof with ice guard and synthetic paper immediately after we sheath.


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## TimNJ

TNTSERVICES said:


> He said that I couldn't compare plywood and osb for exposure, that it would be more like plywood versus advantech. I disagree because plywood doesn't have a coating and advantech does. If he had said a treated plywood and advantech then that would be apples to apples. That was my point.


You take D/F plywood subfloor and compare it to Advantech subfloor.
I think that is fair. They are both designed for subfloor use. So presume that both would be susceptible to standing water until dry in.


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