# Can 2x12 tongue and groove expand & tear 15-lb tar paper?



## DeanL (May 23, 2011)

DeanL

I have an old roof deck made of tongue and groove 2x12s. It's currently covered with tar & gravel and want to change to Asphalt shingles. Due to it's low pitch I planned to use standard 15lb tar paper with a 17" overlap, Another contractor mentioned that the expanding & contracting of the tongue & groove could rip the 15-lb paper. He says I should use 30-lb, or even better yet go over the whole roof with plywood 1st. What's your thoughts? San Diego, CA


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## PA woodbutcher (Mar 29, 2007)

What is the pitch of the roof?

Just out of curiosity, how are you going to get the tar and gravel off the roof?


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## DeanL (May 23, 2011)

*DeanL*

2 1/2 pitch, Shovel & broom.


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## kage (Aug 17, 2008)

Why you want shingles on a flat roof?? and if your going to do that I would put I&W on NOT 15#


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## DeanL (May 23, 2011)

*DeanL*

Pitch= 2 1/2 x 12 it's not flat


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## Jason-F (Jul 4, 2009)

minimum use a full coverage of ice & water.


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## Chris Johnson (Apr 19, 2007)

When I was in Cali there were lots of shingles on really low slope roofs and I&W was what I saw over the whole roof


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## Grumpy (Oct 8, 2003)

2/12 is as good as flat imo. Shingles are not to be used below 3/12. Well some manufacturers may let you but I have only done it a handfull of times at the demand of the customer who didn't want a low slope membrane.

Last spec I read for this application called for a minimum of a double layer of 15# felt or full coverage of ice shield. I'm on the fence about full I&W as I have heard it lead to condensation problems, but maybe that's because the ventilation wasn't proper. I did have this problem once with a full coverage of ice shield, but though the ventilation was proper, there was a heater in a connecting attic space which put a huge ammount of moisture into the attic. We blocked that air flow and installed additional ventilation, and haven't had any problems since. So I gues the moral of this story is make sure the ventilation is better than perfect. 

Then again you said it's a flat roof with T&G, which in my kneck of the woods means the ceiling is exposed roof deck, which means there is not going to be ventilation, which means you need to build up a false roof deck, which means the cost of the job will double, which means Just install single ply.


FWIW I wouldn't use 15#, regardless of slope. I use 30# or fiberglass reinforced felt only.


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## kage (Aug 17, 2008)

DeanL said:


> Pitch= 2 1/2 x 12 it's not flat


In my neck of the woods that is considered flat, way to low for shingles.


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## GettingBy (Aug 19, 2010)

DeanL said:


> Another contractor mentioned that the expanding & contracting of the tongue & groove could rip the 15-lb paper.


What percent does wood expand at right angles to the grain, from kiln dry to soaking wet? This is a few percent IIRC.

How much stretching can tarpaper do without tearing? Possibly zero but that info has got to be somewhere closeby. I'll find it.


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## kage (Aug 17, 2008)

DeanL said:


> DeanL
> 
> Another contractor mentioned that the expanding & contracting of the tongue & groove could rip the 15-lb paper.


This I would say is a myth.


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## GettingBy (Aug 19, 2010)

He may be right
http://books.google.com/books?id=wF...esnum=3&ved=0CCUQ6AEwAjgK#v=onepage&q&f=false
but this book is from 1920.

I'd contact the tar paper manufacturer and ask for elasticity data. It's probably very temperature-sensitive.


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## PA woodbutcher (Mar 29, 2007)

The reason I asked what the pitch was because I have never seen anyone go from a tar and gravel to shingles. Tar and gravel mostly being reserved for either very low slopes or flat. Most people I know of discourage use of shingles below 4/12. With proper precautions, such as I&W or double felt it can be done to 3/12.

You list your trade as roofing, but I suggest you try the DIY and get some schooling


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## Tom Struble (Mar 2, 2007)

most flat grained lumber will change in size across the grain 1 percent for each 4 percent change in moisture content

so a 12'' board will change about 1/8'' through out the season

can that rip felt? i dunno:blink:


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## GettingBy (Aug 19, 2010)

Cut a 1/8" wide strip of felt 12" lg fresh out of your freezer [0 F to 10 F] and see if you can stretch it 1/8" without tearing.

Since paper has a grain, cut another strip at right angles to the first and try it again.

Do again at room temperature.

Post results. Have a Bud.


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## roof-lover (Sep 19, 2008)

2x12 TG??? I would have to see it to believe it! And if it was true, than that means exposed ceiling. Which means no ventilation. Which means no ICE/water sheild. Which means no, do not put on shingles. Install a low-slope roofing product only. Hire a roofer..


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## DeanL (May 23, 2011)

*DeanL*

Roof-lover - you seem to get the picture as it really is -felt is supposed to breath - which would be some ventilation - more felt or a felt alternative would breath less - the condensation could be held below the shingles (not good). The rest of the neighborhood has already changed from Tar & gravel to Asphalt.
Thank you all for your input.


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## old roofer (May 10, 2011)

i may be wrong shingle manufactor will not warranty shingle installed over decking wider than 6" WIDE


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## Tom Struble (Mar 2, 2007)

DeaL said:


> Roof-lover - you seem to get the picture as it really is -felt is supposed to breath - which would be some ventilation - more felt or a felt alternative would breath less - the condensation could be held below the shingles (not good). The rest of the neighborhood has already changed from Tar & gravel to Asphalt.
> Thank you all for your input.


none of this is right:no:...well except maybe the neighborhood part


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## seeyou (Dec 12, 2008)

old roofer said:


> i may be wrong shingle manufactor will not warranty shingle installed over decking wider than 6" WIDE


I'd never heard that one, so I just checked two installation manuals. No mention of board width - just thickness.


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## DFW Roofing (Mar 4, 2011)

seeyou said:


> I haven't been able to find anything like that in Certainteed's warranty or installation instructions. Got a link to back that up?


No link, it is in CertainTeed's "Shingle Applicator's Manual" in the chapter on roof decks. It is also in the GAF Steep Sloped Roofing Field Guid.

I have had insurance pay for a new deck on a claim before, but I had to copy and send the pages to the adjuster.


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## thorcctx (Nov 20, 2009)

there's low slope instructions on the back of every bundle ,just did one last week 2.5 on 12 double your first course and then double lap your paper,six nails a shingle paper over metal at eaves under on gables but Don't take my advice follow manufactures spec's


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## seeyou (Dec 12, 2008)

DFW Roofing said:


> No link, it is in CertainTeed's "Shingle Applicator's Manual" in the chapter on roof decks. It is also in the GAF Steep Sloped Roofing Field Guid.
> 
> I have had insurance pay for a new deck on a claim before, but I had to copy and send the pages to the adjuster.


Here's a GAF tech bulletin (4/11):
http://www.gaf.com/Documents/Deck_R...g_Deck_Boards_-_Steep_Slope_Tec-43-793-v2.pdf

The only relevant reference is the statement that "Standard decks include: Wood planking… Nominal 1” thick (min.) x 6” wide (max.) wood planking, with a maximum 1/8” 
spacing at the ends and sides." There is no disallowing of any other 1X width. 

What is the date on your Certainteed SAM?

Mine only says:
"THE ROOF DECK* MUST BE AT LEAST:
3⁄8" (9.5 mm) thick plywood, or 7⁄16" (11 mm) thick non-veneer, or nominal 1" (25 mm) thick wood deck.


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## roof-lover (Sep 19, 2008)

Dean, You sure do know alot about this homeowners electricity bills and the neighbors and their roofs. :thumbsup:


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## MJW (Jan 27, 2006)

seeyou said:


> Here's a GAF tech bulletin (4/11):
> http://www.gaf.com/Documents/Deck_R...g_Deck_Boards_-_Steep_Slope_Tec-43-793-v2.pdf
> 
> The only relevant reference is the statement that "Standard decks include: Wood planking… *Nominal 1” thick (min.) x 6” wide (max.) wood planking*, with a maximum 1/8”
> ...


If you talk to a Rep, they will tell you the reasoning for that.....It eliminates roofing on rough sawed boards. Anything wider than 6" is typically rough sawed.


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## seeyou (Dec 12, 2008)

MJW said:


> If you talk to a Rep, they will tell you the reasoning for that.....It eliminates roofing on rough sawed boards. *Anything wider than 6" is typically rough sawed.*


Must be a regional issue. 

We've got kiln dried 1x8, 1x10, and 1x12 a plenty. I haven't seen a house built in the last 50 years with any rough sawn lumber in it except for cosmetics.


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## MJW (Jan 27, 2006)

seeyou said:


> Must be a regional issue.
> 
> We've got kiln dried 1x8, 1x10, and 1x12 a plenty. I haven't seen a house built in the last 50 years with any rough sawn lumber in it except for cosmetics.


We have plenty of that lumber available also, but not used on roofs anymore. When 1x boards were used and larger than 1x6, they are usually rough sawn. I agree, it would be a regional thing though just like everything else.


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## DeanL (May 23, 2011)

*DeanL*

There just seems that no matter what I say some people just decide that they know what my roof deck is made of, and that I don't seem to know what I'm talking about. If you are sure that my roof deck is made of something other than what I have told you (2x12) please don't bother with the input. 
Yes this is my own home here in San Diego, my 20+ years contracting experience has been mostly in Minneapolis. 
California does not require I&W in much of the state.
A little more specific the house has LR, DR, Kitchen, & 3 BRs. with vaulted 2.5/12 ceilings (not rough sawed). The 2x12 is used even in the few areas that have sheet rock/plaster ceilings. The attached garage has 1/2 plywood over all of it except it's 5' over hang. The roof deck different levels - look like hell - but what can you expect from the builder who skipped insulation in the walls. 
I'm smart enough to know a 2x12, I'm smart enough to know that a vaulted ceiling with no insulation in it's design is just looking for condensation problems. I plan to follow the manufacturer's recommendations but the roof is (50+years) existing and I doubt that my ceiling fan is what they have in mind for ventilation. That's why I had questions.


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## JWRoofing (May 5, 2011)

High velocity wind code states that 2 in 12 and below is "low-slope", anything above 2 in 12 is considered "steep slope". Now the NRCA does not recommend Shake or Tile on roofs under 4 in 12. 

So even the "experts" disagree.

________
JW Roofing
Energy Star Roofing - Miami Roofing


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