# Which is the proper roofing felt to use?



## CSinMa (Mar 4, 2012)

I have read many posts on many topics in these forums and have wondered which is the proper felt to use on different projects. 
I see many contractors use 15 lb for roofing. (doesn't that stuff bubble up from the hot roof and make the roof wavy?)

Where I come from (mass) we use 30 lb felt for roofing underlayment and 15 lb felt for exterior walls under some types of siding and under hardwood floors. :thumbsup:

So which IS the proper material to use where you come from?


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## Tom Struble (Mar 2, 2007)

better question than what is why


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## CSinMa (Mar 4, 2012)

not quite sure what that means Tom, what IS why?


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## TNTRenovate (Aug 19, 2010)

15# for walls and shed roofs, and 30 for homes roofs.


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## katoman (Apr 26, 2009)

Why? To protect the roof in the event water should penetrate the shingles.

Here anything over an 8/12 pitch does not require underlayment.

I have moved to "roof gaurd". No more tar paper. This gives you usually only one seam instead of all the seams in tar paper. It also is great in that you can put this on right after the sheathing goes on.

Then the roof is protected untill the roofer can get to it. It is not ruined like tar paper is if it rains. Here's a pic,


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## Randy Bush (Mar 7, 2011)

katoman said:


> Why? To protect the roof in the event water should penetrate the shingles.
> 
> Here anything over an 8/12 pitch does not require underlayment.
> 
> ...


This would be a good picture to sent to OHSA :thumbup:Although i have done much of the same myself.

Rarely use felt anymore, to much wind here, but when did it was #30.


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## katoman (Apr 26, 2009)

Randy Bush said:


> This would be a good picture to sent to OHSA :thumbup:Although i have done much of the same myself.
> 
> Rarely use felt anymore, to much wind here, but when did it was #30.


The roofer was a sub. But after that pic I supplied them with my and my guys harnesses. They didn't want to use them, but I told them they didn't have a choice in the matter.

Honest.


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## Randy Bush (Mar 7, 2011)

katoman said:


> The roofer was a sub. But after that pic I supplied them with my and my guys harnesses. They didn't want to use them, but I told them they didn't have a choice in the matter.
> 
> Honest.


 Was also thinking about the guy on the ladder, way to much angle. Anymore I prefer to use a harness, never have came off of a roof and don't plan too. Getting to old for those type of risks.


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## woodchuck2 (Feb 27, 2008)

I dont do too many roofs but i alway ice/water shield everything. I used to use 30lb felt but it slips/slides when having to walk on it and is merely a moisture barrier. The ice/water seals the roof IMO, less chance of water leaks down the road.


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## katoman (Apr 26, 2009)

woodchuck2 said:


> I dont do too many roofs but i alway ice/water shield everything. I used to use 30lb felt but it slips/slides when having to walk on it and is merely a moisture barrier. The ice/water seals the roof IMO, less chance of water leaks down the road.


Yes, we ice and water the start. Sometimes two rows. But you are not supposed to do the whole roof. This will trap moisture and lead to the sheathing rotting.


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## CSinMa (Mar 4, 2012)

katoman said:


> Yes, we ice and water the start. Sometimes two rows. But you are not supposed to do the whole roof. This will trap moisture and lead to the sheathing rotting.


you have brought up a good point Katoman. I have gotten different opinions on water and ice barrier over the entire roof, some say as you say, but others claim it stops the dry rotting on roof boards. personally I like to only put it 6 ft up the roof, in valleys, around roof perimeter and under step flashing. The house has got to breath somehow, after the way they over insulate everything today. There is good reason why the houses built in the 1800's-early 1900's are still standing. Heck they insulated with newspaper


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## Yankee Framer (Feb 20, 2012)

I have heard that 15lb felt will void the warranty on some shingles. This is just hearsay as I have never read anything on it. Though I would just suggest you use what ever the manufacturer of the product you are applying tells you to use under said product. Can't go wrong there.


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## superseal (Feb 4, 2009)

Imagine the tear off when it's all I/W :no:


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## TNTRenovate (Aug 19, 2010)

superseal said:


> Imagine the tear off when it's all I/W :no:


That was my first thought, but he did say that he doesn't do many, so why would he care.

Tar Paper, Felt and the like have multiple purposes.

It protects the roof prior to shingling, I hadn't heard that rain would ruin it, quite the opposite, it's the sun that will ruin felt. Felt is a moisture barrier, thus rain would not ruin it or get to the roof if it is installed.

It also protects the roof in driving wind and rain. In any event anytime rain gets past a shingle there are a million nail holes that water can penetrate.

And the final reason is tear off. It allows one to remove the shingles from the roof with little effort.


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## hdavis (Feb 14, 2012)

CSinMa said:


> you have brought up a good point Katoman. I have gotten different opinions on water and ice barrier over the entire roof, some say as you say, but others claim it stops the dry rotting on roof boards.



I'd say stopping dry rot would be a poor trade off for replacing the decking due to real rot. Lots more expensive, and some added risk, so I only go 2 up, valleys, etc.


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## Tinstaafl (Jan 6, 2008)

Rain alone will not wrinkle roofing felt. It's the combination of rain and sun that does. 15 lb is fine if you're going to get the shingles on immediately, but in many cases that doesn't happen--so it's a good idea to go with 30 lb "just in case". It won't deform quite as quickly.

Technically, there's no reason a properly shingled roof should need felt at all. And there are many 100 year old roofs doing just fine without any ice & water shield.


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## Warren (Feb 19, 2005)

30# felt is almost the same price as the synthetic paper here now. We have used almost exclusively synthetic paper since 2005. No rips, tears, or pieces have blown off EVER. Can't say that about felt. I tell people who insist on felt that the roofer needs to be there the same day we finish the framing. If they use #30, he should still be there within the week.


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## TNTRenovate (Aug 19, 2010)

Warren said:


> 30# felt is almost the same price as the synthetic paper here now. We have used almost exclusively synthetic paper since 2005. No rips, tears, or pieces have blown off EVER. Can't say that about felt. I tell people who insist on felt that the roofer needs to be there the same day we finish the framing. If they use #30, he should still be there within the week.


Slick as crap though when wet, not saying that it would deter me from using, just saying!


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## ohiohomedoctor (Dec 26, 2010)

I remember watching a mexican about fall off a roof in front of a costa rican roofing crew. I never have seen a mexican turn that red again.


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## Warren (Feb 19, 2005)

TNTSERVICES said:


> Slick as crap though when wet, not saying that it would deter me from using, just saying!


Lighter, faster to install, easier to cut, stays on, doesn't wrinkle, doesn't tear, etc...

It is a bit slippery, but after I install it, I am done up there forever!


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## Tinstaafl (Jan 6, 2008)

Many of the synthetics actually offer far more traction when wet than felt, and are tear-resistant as well. The only downside is that they do tend to be more expensive, so a lot of builders elect to save a kopeck or two.


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## Tom Struble (Mar 2, 2007)

CSinMa said:


> not quite sure what that means Tom, what IS why?


why is what you want an underlayment to do,whether wind resistance, walkabiliy,exposed durability, air infiltration etc.. then choose it accordingly


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## CSinMa (Mar 4, 2012)

isn't felt paper of any kind just for expansion and contraction of different materials, to make sure nothing buckles, binds or gets snagged?


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## Tom Struble (Mar 2, 2007)

if thats what you need to do then any paper will do,even rosin

but lets think about this for awhile..what else would be important on a roof?


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## jmiller (May 14, 2010)

Tom Struble said:


> but lets think about this for awhile..what else would be important on a roof?


The most important job (on shingle roofs) of the [underlayment] is being a secondary drainage plane- in case of blow offs, or an ice dam backs up under the shingles, or the roofers didn't do the valley right, etc.


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## ohiohomedoctor (Dec 26, 2010)

Unfortunately tar paper of any kind was considered optional around here for years. Going to be tons and tons of roofs to do in a few more years.


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## Groutface (Jan 20, 2011)

Not a roofer at all but I do my own and it doesn't leek. I used tar paper under the whole install.....good or bad..


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## katoman (Apr 26, 2009)

Groutface said:


> Not a roofer at all but I do my own and it doesn't leek. I used tar paper under the whole install.....good or bad..


That's good. :thumbsup:


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## Gary H (Dec 10, 2008)

back in the 80's builders found a loop hole to not use felt. I always wondered what those plywood sheets look like now?


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## Splinter hands (Aug 31, 2011)

For me personally I never use 15# 30# is min. and prefer synthetic if the H.O will go for the extra cost. TNT mentioned it being slick and it is slicker than felt if it is wet, real slick, but when it is dry most of it is nice and grippy to walk on and it wont tear out on you. The extra cost is worth the grip on a steep roof. Another thing to remember is to not be a cheap a** and cover up the Ice shield with felt or the syn. felt also, otherwise if it's a hot day when you go to tear off the old shingles those last few rows sometimes stick to the I&W like superglue.


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## Splinter hands (Aug 31, 2011)

Gary H said:


> back in the 80's builders found a loop hole to not use felt. I always wondered what those plywood sheets look like now?


What was the loophole? Curious what the excuse was.


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## CSinMa (Mar 4, 2012)

Here's the real purpose of the felt paper under shingles. 
As warm moist air rises, it passes through the sheetrock ceiling in your home and up through the attic.
The felt paper allows the moist air to pass through, but if some of the moisture condenses on the underside of the shingle, the felt paper keeps that condensed moisture from touching the wood. 
If the condensed moisture were to be in contact with the wood, over time the wood would be damaged.

The other reason for the felt underlay is to provide a simple barrier between the asphalt in the shingles and the wood sheathing. The sap in the wood isn't good for the shingles.
On the low pitch roofs, under 4:12 but over 2:12, a double underlayment is required. 
not double thickness, like going from 15 lb to 30 lb. But two actual layers.
It also doesn't mean a complete covering of one layer of underlayment, and then another layer of underlayment over the first one.
It means that after one row of felt paper is layed down, the next row needs to start at the halfway point on that first row, not at the top edge of the first row.


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## TNTRenovate (Aug 19, 2010)

CSinMa said:


> Here's the real purpose of the felt paper under shingles.
> As warm moist air rises, it passes through the sheetrock ceiling in your home and up through the attic.
> The felt paper allows the moist air to pass through, but if some of the moisture condenses on the underside of the shingle, the felt paper keeps that condensed moisture from touching the wood.
> If the condensed moisture were to be in contact with the wood, over time the wood would be damaged.
> ...



http://arrowheadroofing.com/news/roofing-felt-its-real-purpose/

Hmmmm? Google search much? :laughing:


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## Tom Struble (Mar 2, 2007)

i don't buy that condensation won't form under the felt

most synthetics are actually vapor barriers


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## jmiller (May 14, 2010)

CSinMa said:


> As warm moist air rises, it passes through the sheetrock ceiling in your home and up through the attic.
> The felt paper allows the moist air to pass through, but if some of the moisture condenses on the underside of the shingle, the felt paper keeps that condensed moisture from touching the wood...


Warm air passing through the drywall will condense on the underside of the sheathing, NOT on the shingle side (cold side/top) of the sheathing.


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## Handyman3970 (Nov 21, 2010)

Hmmm, if these guys are worried about condensation I think they should be adding some ventilation not more layers of felt. 
Am I wrong?


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## TNTRenovate (Aug 19, 2010)

Handyman3970 said:


> Hmmm, if these guys are worried about condensation I think they should be adding some ventilation not more layers of felt.
> Am I wrong?


If their is adequate ventilation, then more won't do anything to prevent the moisture. You really need to address the heat loss at the source. Sealing all areas of penetration would be the first step.

But even at that. Am I supposed to believe that the moisture is going to penetrate the sheathing and tar paper before resting on the underside of the shingles?


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## skcolo (May 16, 2009)

Almost every attic is under ventilated. Code is 1sf of ventilation for every 150sf of space. Note: A 8" hole for a 1 sf vent doesn't count as 1 sf.


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## TNTRenovate (Aug 19, 2010)

skcolo said:


> Almost every attic is under ventilated. Code is 1sf of ventilation for every 150sf of space. Note: A 8" hole for a 1 sf vent doesn't count as 1 sf.


It would if it were 8x18


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## skcolo (May 16, 2009)

Then it wouldn't be an 8" hole. :no:


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## 1985gt (Dec 10, 2010)

CompleteW&D said:


> No.... not at all. The price of 15# and 30# felt is generally the exact same price. But the 15# has four squares and the 30 # two squares. It costs TWICE as much.


You will have to forgive me. We do almost all low slope so I don't know shingle felts off the top of my head. I happen to go look at our local Menard website. 12.94 a roll of either 15 or 30. 15 has 432 sf and 30 is 200. 

We will say this roof is 30 squares. 

So 7 rolls of #15. $90.58
or 15 rolls of #30. $194.10.

I'm thinking Gbigbuck should learn the insurance game if he is going to play it. Eat the $103.52... :whistling


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## CompleteW&D (May 28, 2011)

No worries at all. But you're right about the insurance thing. You get those approvals BEFORE you do them or forget getting any coin on them....


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## tnt specialty (Apr 19, 2007)

If your're relying on the felt for any type of "water-tightness", your not very confident in your craftsmanship as a shingler.....Spend your energies learning how to install shingles/proper flashing techniques.....Felt/underlayment in a shingle roof assembly is a mere divorcing layer separating shingles from raw wood substrate......Been doing this a very long time - Put on thousands of roofs in many states, in every kind of climate.....my $.02


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