Foam Board Over Or Under Type X Drywall On Exterior? - General Discussion - Contractor Talk

Foam Board Over Or Under Type X Drywall On Exterior?

 
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Old 12-25-2015, 11:37 PM   #1
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Foam Board Over Or Under Type X Drywall On Exterior?


I'm using 1" foil faced foam with a 6.00 r value to get a total r 20 to meet code. The exterior walls are 2x4. I have 3/4 inch plywood on the exterior connected directly to the studs. Do I install foam board over or under the exterior grade (using 5/8" denshield) type X drywall? I need a 1 hour fire barrier because I am within 5' of the property line. There is vinyl siding covering the structure.
Thanks!
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Old 12-26-2015, 05:20 AM   #2
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


Type x on the outside and foam underneath... you need to protect the foam.

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Old 12-26-2015, 07:16 AM   #3
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


thanks, I have an issue where a relative of the homeowner who installs denshield is saying not to put foam board on underneath because the nails could bend. I can see this happening on the side we are putting two 5/8" layers, but not on the side with only one. I would use galvanized 16d nails and nail it through the studs. If I don't use the foam, I have to find another way to get my wall up to an r-20.
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Old 12-26-2015, 08:04 AM   #4
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


Under as stated above - if worried about nails bending maybe look into Zip Systems insulated sheathing or others like Dows or...
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Old 12-26-2015, 08:18 AM   #5
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


Let me bring up another issue.

Last time I checked, if you put vinyl siding over foil faced insulation, it voids the warranty for the vinyl siding. The heat from the foil is enough to warp the vinyl siding. I don't have it in writing. I can't send you to a link. But, I have been paid to remove and replace vinyl siding along with the foil faced insulation underneath. I can remember 2 houses in particular. Both instances were the west side only. It was probably about 25 years ago. I haven't seen anyone use foil faced since then. The next year it went to an R-board that was tan in color and had a semi-hard facing.

If it were me, I would put the foam on the outer side of the drywall. If you try to put plywood over the foam, there will be places that pull in further than other places. The foam will compress more in some areas than others.

I would also double check to make sure the building inspector approves this. He will most likely say to follow the blueprint, but what if he says the drywall has to be the outermost product, closest to the siding.
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Old 12-26-2015, 09:22 AM   #6
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


You can always use 1 1/2" Roxul Comfortboard over the type X.
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Old 12-26-2015, 12:43 PM   #7
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


Quote:
Originally Posted by builditguy View Post
Let me bring up another issue.

Last time I checked, if you put vinyl siding over foil faced insulation, it voids the warranty for the vinyl siding. The heat from the foil is enough to warp the vinyl siding. I don't have it in writing. I can't send you to a link. But, I have been paid to remove and replace vinyl siding along with the foil faced insulation underneath. I can remember 2 houses in particular. Both instances were the west side only. It was probably about 25 years ago. I haven't seen anyone use foil faced since then. The next year it went to an R-board that was tan in color and had a semi-hard facing.

If it were me, I would put the foam on the outer side of the drywall. If you try to put plywood over the foam, there will be places that pull in further than other places. The foam will compress more in some areas than others.

I would also double check to make sure the building inspector approves this. He will most likely say to follow the blueprint, but what if he says the drywall has to be the outermost product, closest to the siding.
no..foil faced foam is not excluded under any vinyl siding warranty today,you may find a very old one from the old nailite panel but warpage from reflective foam really doesn't happen,what you may have experienced was a defective panel or possibly defective dual pane window issue idk

the other type of foam with the ''tan'' facing is kraft paper and is the one not recommended because the paper tends to absorb water
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Old 12-26-2015, 01:18 PM   #8
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


What is the set back on the foundation? Sounds like your really bulking up the exterior. Better off using mineral wool batt insulation in stud bays, one layer of 5/8" type x on the inside. That with the 3/4" plywood should get you your hour. If not, you can use fire rated paint sprayed on the plywood as well. The more layers of finishes you use the more that can go wrong in the long run. Here in Ontario your allowed to use longer fasteners to go through the foam board and into something solid behind it with vinyl siding, not sure about your area though

Last edited by carp.addict; 12-26-2015 at 01:21 PM.
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Old 12-26-2015, 05:18 PM   #9
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


Nope. The foil faced foam board caused the siding to warp, bad. I was the second contractor to replace it. I removed the foil faced insulation board and replaced it with the Kraft faced (or whatever it was). At that time, that is all that was available. I remember it was hard. You could I kcal put an extension ladder on it without going through.
It didn't warp after that.
I remember the siding company refused to reimburse the homeowner. The lumber yard hired me and paid me.
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Old 12-26-2015, 05:33 PM   #10
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


nope what?show me a siding manufacturer that specifically states they won't honor a warranty issue because of reflective underlayment

i have checked, there are none,know why?cause it doesn't happen

reflective foil under siding cannot generate more heat,not how it works
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Old 12-26-2015, 10:53 PM   #11
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


I don't think you read all of my post. I said I didn't have it in writing. I said the vinyl manufacturers wouldn't pay to replace it.

The siding rep said it voided the warranty and they wouldn't pay for it. The siding company didn't. I would assume that is why the lumber yard paid to replace it.

Why can't you believe a silver reflective surface doesn't reflect heat? There are a lot of blue tarps that have a silver side. Concrete insulation blankets have a black side and a silver side. Do you think it is just for decoration.

I'm not going to argue it. I was told it wasn't under warranty because of the foil facing. I removed it and it fixed the problem.

As far as a window causing the problem? 1 window from, I assume a neighbor's house, wouldn't warp the siding on the entire side of the house. An area yes, The entire side, no. Also, at that time, a low e coating was very rare. As I think about it, there wasn't even a house next door. At that time it was a vacant lot.

I think we need to get back to the subject. What order do you think he should apply the foam.
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Old 12-27-2015, 12:04 AM   #12
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


Just to throw out another point in whole mess is, if the foil does not have about 1 - 1 1/2" of air gap to the next layer of material then it is useless to use the foil anyway.

Also, you need to find a UL listed 1 hour assembly to show the AHJ, something like on THIS page.

I would think about the UL U327.

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Old 12-27-2015, 12:05 AM   #13
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


I think the order should be plywood to studs for shear if no other reason, foam , densglass and finally the siding with the size, type and attachment schedule dependent on the siding type and the thickness and density of the foam.

I've attached a link to an interesting and informative reference put out by the Foam Sheathing Coalition on the subject. It has a detail showing the order of installation.

http://fsc.americanchemistry.com/Bui...-Coverings.pdf

Last edited by Rio; 12-27-2015 at 12:20 AM.
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Old 12-27-2015, 12:15 AM   #14
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


Quote:
Originally Posted by ScipioAfricanus View Post
Just to throw out another point in whole mess is, if the foil does not have about 1 - 1 1/2" of air gap to the next layer of material then it is useless to use the foil anyway.



Also, you need to find a UL listed 1 hour assembly to show the AHJ, something like on THIS page.



I would think about the UL U327.



Andy.

Exactly where I was going with my comment.

What's the assembly show? A layer of 5/8" does not a rating make. The system functions as an assembly.


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Old 12-27-2015, 12:38 AM   #15
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


Quote:
Originally Posted by ScipioAfricanus View Post
I would think about the UL U327.

Andy.
UL 330 is pretty close to what he's doing. No type X at all.
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Old 12-27-2015, 06:32 AM   #16
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Re: Foam Board Over Or Under Type X Drywall On Exterior?


Ok. I thought about this last night. The vinyl siding was not covered under warranty. It was because of the heat reflected by the foil faced insulation. And yes, this is covered in the warranty.
"Distortion or melting of the Vinyl Siding Products due to external heat sources, including but not limited to, barbeque grills, fires or as a result of reflection from windows, doors or other objects;" - Certainteed.

The two words, "or other objects" is where it is at. In those 2 cases the siding manufacturer determined the foil faced insulation was causing distortion of the siding. It only applied to the west side of the houses. Nothing else was distorting. Maybe that wasn't the case. Maybe, like you said, it was a defective panel. Or all of them on the west side. Whatever the case, it wasn't covered because of the foil faced foam and replacing it with another product solved the problem.

Really, if you think about it, almost all building materials have this in their warranties. I have come across a lot of "contractors" that will tell customers, "spray foam around replacement windows, voids the warranty." This is not true. Spray foam does not void the warranty. If, however, the spray foam is the reason the window doesn't work, then the is not covered because outside influences are causing the window to fail. I should add, there was a time people were using the regular spray foam around windows and not the foam for windows and door.

So back to the original post. There have been some very good posts. I've given my input. What's yours?

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