Replies

1. 
   webby | Mar 28, 2009 08:33pm | #1

   Bump.

    

   Why? Is it for insulating purposes? Seems to me It would be detrimental in one way or another to the shingle life. I.e. if something fell on the roof, or foot traffic during maintenence, heat buildup in the summer? Would probably void the shingle warranty.

   Webby 

    

   
   

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   Edited 3/28/2009 1:35 pm ET by webby

1. 
   jAndy | Mar 28, 2009 10:26pm | #2

   Yeah it is for some insulating value. As for denting it...I don't see that as a problem, for it is fairly dense alone, and under the shingles should be impervious to damage, I would think?

2. 
   Piffin | Mar 29, 2009 12:19pm | #8

   almosty no makers void warrantee for hot roof any more. There is a decrease in shingle lifespan but it is so minimal as to be negligible - a few months in the course of the roof. 

    

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1. 
   webby | Mar 29, 2009 06:39pm | #11

   Sorry, I didn't mean it to sound like they would void the warranty for a hot roof, but just for the shingles applied directly to the foam if a claim was ever filed. What I get for being in a hurry.Webby 

    

1. 
   Piffin | Mar 29, 2009 07:14pm | #12

   In this case, that's what the definition of a hot roof is. 

    

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1. 
   webby | Mar 29, 2009 08:05pm | #13

   Ahh, learnt something new. thanksWebby 

    

2. 
   xxPaulCPxx | Mar 28, 2009 10:32pm | #3

   Do you mean 3/4" thick?

   FHB just had an article on this.  They had the foam layer on the bottom, then blocking to fasten the sheathing too, then the sheathing.  The blocking also provided a ventalation path to a ridge vent.  This gives you a good nailing surface on the outside, insulation on the inside, and if you seal the foam panels correctly you have an extra waterproof layer shedding water out the eaves if you have a leak in the sheathing.  You can then pack the underside of the rafter bays full of insulation (batts or cellulose) and drywall to the rafters.

   Tu stultus es
   Rebuilding my home in Cypress, CA
   Also a CRX fanatic!

   Look, just send me to my drawer.  This whole talking-to-you thing is like double punishment.

3. 
   Danno | Mar 28, 2009 11:31pm | #4

   I would NOT put foam sheets right under shingles. Dow, here in Midland, tried that a while ago and it was a major fiasco. If you have leaks, you can't tell where they are originating (and you will have leaks). There were other problems too. My Dad's lady friend bought a house that was done that way and water was leaking down inside the exterior walls and into her windows and everything.

   I would question having roofers tromping around on Styrofoam and trying to nail shingles through it into anything that would hold the shingles in place. You'd have to have long nails and everything would be moving around.

   I would definitely recommend that you do a LOT of research before going ahead with this idea. I think it is a bad one! Styrofoam under the roof sheathing may be not as bad. May actually be okay.

4. 
   jr40 | Mar 29, 2009 03:13am | #5

   Like you I had extra sheets of foil backed 1" foam boards.  I applied them to the underside of the roof sheeting and I think it makes a heck of a difference in heat escaping through the roof in the cold months and heat gain in the summer.  I have thick butt cedar shakes on the roof here.  You might think about it.

5. 
   bcarpentry | Mar 29, 2009 07:13am | #6

   Hey,
   I'm would definitely never ever put foam directly under shingles and on top of the sheathing. I would rip it to widths that fit snug between the rafters on the underside however. I live in upstate NY as well and yeah we want our roofs to be insulated well. But you don't want to compromise the integrity of your shingles by putting foam under them. Ever <shudder>. And I don't think I'm overreacting. But that is just my opinion. G'luck

6. 
   Piffin | Mar 29, 2009 12:17pm | #7

   You will need another layer of sheathing to nail the shingles to on top of the foam sheets.

   Where did you get foam that is two thirds of an inch thick?

    

    

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   Taunton University of Knowledge FHB Campus at Breaktime.
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1. 
   jAndy | Mar 29, 2009 05:40pm | #9

   Actually I mis-spoke (mis-wrote?)the size is only 3/8".
   Because of all the warnings I'm getting I think I may go with one, maybe 2, layers.
   These boards are stiff with plastic coating. I don't see them causing any appreciable movement to the nails.
   And I'm going to use 35 year shingle, which I guess can take the extra heat? It's the same shingle they use in the south isn't it? it never goes over 100 deg. here.

1. 
   Piffin | Mar 29, 2009 06:33pm | #10

   by the time you add the second ply of sheathing over the foam for nailing, 3/8" is not worth what you'd get out of it. I've done this with 2" to 4" of foam, but wouldn't waste my time on it for less than an inch.do it without sheathing and put the shingles directly on the foam like you are thinking and you waste both time and money while voiding shingle warrantee 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!