Drywall over foam board insulation

[clemsonfor]

I am wanting to know if what my title says has been done by anyone (the blue stuff, foam that is not drywall)? I did breif reasearch on the net and have heard both. Several with no nail pops or trouble, others say that you cant do it cause of a moisture barrier. But i see no difference than blue foam under drywall vs the plastic vapor barrior, both will trap moisture behind the drywall as both will have insulation behind them in this case?

What im proposing. In a remodel of my upstairs i want to atleast put the ridgid foam on the ceiling before i put my drywall over it. I have those ceiling tiles on it now, the 12" by 12" kind. I really dont want to pull them down so was just gonna rock over them but thinking about getting more insulation i was thinking blueboard first. There is 6" batt insulation in the void now, half the room has the ceiling attached to the roof joists and the middle is a flat part with ceiling joists (if this makes any sense). Meaning that half the room is slanted like the roof and the other has attic space over it.

I also want to think about doing it on the walls?

What are you guys thoughts?

 

[bp fick]

Me? Since you're gonna have to re-hang the drywall anyhow? I'd just demo the old stuff and be done with it. Jam extensions, outlet boxes all set wrong, what a pain. With a tear out, you can then be sure everything is right. Or, call Mike Holmes of Holmes on Homes, and listen to him crab for awhile.

The demo cannot be THAT bad. I'd just tear 'er out and do it like a new build.

 

[davedj1]

You should have no problems doing what you desire. Just make sure that the screws don't get driven too deep (easy to do over foam). I don't want to alarm you but the fumes from the foam are extremely toxic in the event of a fire. We've used Hi-R sheating under the drywall too, you get a higher R rating with less thickenss. I don't have the figures here at the moment but you can look up the R rating for 1" blueboard and compare it to 1/2" Hihg R. The thinner you make the inslulation the easier it will be to screw the sheetrock over.

Don't mind the spelling errors, I'm under the influence of muscle relaxers at the moment:licking:

 

[tmajor]

Well, I've done exactly what your proposing, regarding the insulation under sheet rock With 2 exceptions: My house is "double plank", so it breathes pretty well. The other thing is, I used the white insulation with the foil on one side. I haven't had any problems. ... with condensation or nails popping, however, I did use screws. I believe the insulation was 1".

With your upstairs ceiling, you HAVE to have an airspace between the insulation and the roof boards or you'll get condensation, you can't imagine. I'm referring mostly to the part, which runs with the roof.

 

[RRILEY]

If you already have 6 inches of insulation in there why the blue board? And how thick are you talking about for that? Are you in South Carolina? I have rental property and you will regret just covering up a problem and not fixing it right, especially for your own home.

 

[RRILEY]

Like Tmajor said the roof decking needs air flow to vent and dry out to prevent rot and mildew and stink and water stains etc. etc. etc.

 

[BHD]

I have done similar, using the foil faces foam, (now our house was boarded up on the inside, with ship lap lumber,

one mistake I felt I made was not putting some wood striping around the windows, for some thing solid to nail to,

makes some things hard to work with, with the thickness of not any thing solid, to work with,

I would do it again tho knowing what I know, but would most likely use 3/4 thickness, and fur out the windows and a 1x4 on the floor and would not hurt to put something at the ceiling for some thing solid to nail/screw to,

I use what was called a box extension, a small sheet metal thing with tabs where the screws are, and it slipped inside the box in the wall, and held with longer screws in the receptacles,
this was what I used, Inspired Remodeling & Tile | Nashville, TN | Peter Bales, Contractor | Play it Safe With Outlet Extensions
it appears they make a plastic version of it as well,
PVC Electrical Box Extenders for Tiled Backsplash - Brings your outlets out flush with the wall.

 

[tmajor]

My house, being "double plank" had no problems nailing or hitting wood, unless you hit a crack between boards. There were no receptacles in the walls, due to the planks and the house was built before electricity was available. So, I had to cut into the first plank for part of the box depth and the insulation took care of the rest. The wires were run up the cracks between the planks.

 

[clemsonfor]

Me? Since you're gonna have to re-hang the drywall anyhow? I'd just demo the old stuff and be done with it. Jam extensions, outlet boxes all set wrong, what a pain. With a tear out, you can then be sure everything is right. Or, call Mike Holmes of Holmes on Homes, and listen to him crab for awhile.

The demo cannot be THAT bad. I'd just tear 'er out and do it like a new build.

I am gonna do the ceiling most likely the walls, Maybe? So the only boes i have to worry about is 2 ceiling boxes, not a big deal.

 

[clemsonfor]

You should have no problems doing what you desire. Just make sure that the screws don't get driven too deep (easy to do over foam). I don't want to alarm you but the fumes from the foam are extremely toxic in the event of a fire. We've used Hi-R sheating under the drywall too, you get a higher R rating with less thickenss. I don't have the figures here at the moment but you can look up the R rating for 1" blueboard and compare it to 1/2" Hihg R. The thinner you make the inslulation the easier it will be to screw the sheetrock over.

Don't mind the spelling errors, I'm under the influence of muscle relaxers at the moment:licking:

Yea, im not to worried about fumes in a fire, id hope id be outta there at that point, if not i have more to worry a bout.

 

[magicheater]

Drywall does better being affixed to a solid member. Putting foam in between introduces a tension factor which can lead to screw pops and other negative effects. Better to have a nailing/screwing strip for final application of drywall. Using foam is not a bad idea but it needs to be applied correctly for subsequent substrates to perform as intended and without fail.

 

[RRILEY]

were, or are there strips of wood installed on the original ceiling for your 12 inch square ceiling tiles to be stapled to? Are the original walls plaster? Do you have gable vents for the roof or the vented ridge cap?
A lot of things to consider here.

 

[RRILEY]

Don't hang pictures with hammer and nail or heavy objects.

 

[RosseauK]

Have you thought about putting the foam up then strapping it for the drywall??
Make sure you take down the current vapor barrier as the blue foam acts as one.

 

[clemsonfor]

Im not really trying to go over a problem or take the easy way out. The easy way would be no foam and keep the existing insulation and just go over it all. Im thinking of keeping the celing tiles as an extra bit of insulation.

I agfree if there is no air gap there is a problem according to you. But i thought that 6"/R19 insulation went into a 6"void, weather it be a ceiling or a wall.

I will tear some more tiles off to measure the rafter size (could just go in attic) as well as to see a label on the insulation or just measure it to see how thick it is. This room has been the way it is since the late 60's or early 70's. I know if it was done wrong then that still dosent make it right.

And like i said im not trying to cover anything up. Now is the time to fix it. Im just looking for more of a buffer between this bedroom and the hot southern sun 8"s over my head!

 

[forgeblast]

what about sprayfoam, and then just drywall over it.

 

[clemsonfor]

what about sprayfoam, and then just drywall over it.

That would work, but i would have to still remove all the old tiles(im not opposed to this im and just saying) pull the glass insulation, then pay to have it sprayfoamed (i already have insulation). Then there still is the problem in the center of the room (part with the flat celing thats not with the roof line) once i pull the tiles and insulation down, there is no backer for the sprayfoam, i would have to lay plywood as a floor in the attic space as a floor so that you have a backer to shoot spray foam onto in this area. I like the idea of sprayfoam, i just dont think it would work the best here. I could though pull the batt insulation from the slanting parts of the ceiling, spray those parts and then lay extra batt insulation into the attic space over top of the current insulation.

Keep the though coming guys.

 

[clemsonfor]

were, or are there strips of wood installed on the original ceiling for your 12 inch square ceiling tiles to be stapled to? Are the original walls plaster? Do you have gable vents for the roof or the vented ridge cap?
A lot of things to consider here.

Looks like they used cheap paneling that was nailed to the joists and stapled to that? I have no idea how they held as that seems flimsy, but the ceiling is strong and tight as is.

I have gable vents and with the new roofs instalation in a few weeks will also have ridge vents.

 

[clemsonfor]

Have you thought about putting the foam up then strapping it for the drywall??
Make sure you take down the current vapor barrier as the blue foam acts as one.

Vapor barrior Ha. This is an old house in the south they dont use those. The closest thing would be the paper back on the insulation.

But a serious question, say i did have a proper plastic vapor barrior behind the tiles against the studs/joists. Why would it hurt to put foam (with taped joints) over that. There would be 2 barriors, similar to a double layer of plastic? I guess the only thing is if moisture gets between the 2 it would never leave.

 

[Rustyiron]

I would check out another forum called greenbuildingtalk.com and find the apropriate section for your question. I knew a guy that did that many years ago but I have not spoken to him in quite a while, last I knew he had no problems.