Helping In Friend's Attic Mess

Terrence

By trade, I am a painter.
So that is why I'm stopping in to ask such an elementary question.

This is with a friend who already started the job in his attic. The attic roof framing is 24" oc, pretty standard around here, and he is putting up 1/2" drywall to make the attic into useable space.

He has already put in insulation (and I will spare telling you that he chose to use the rigid blue foam stuff instead of the faced batten stuff you staple in, and his tales of woe about getting it to stay put). He has already drywalled the short vertical walls (about 24" tall before the rafters), and has started on the rafter part (I believe it is a 12/12 roof).

Here's the question:
Is it kosher to use 1/2" drywall at 24" spacing on a 45 degree ceiling, or is this going to sag? My guess is it will sag, but I have never done this this way. I would love to help him out by stopping him before he regrets all this hard work if it is a bad idea.

Would you guys use thicker drywall, or some form of cross-bracing, or what is a good solution in this case?

Many thanks in advance.

steve1

The ceiling should be strapped 16'oc then there wont be any issues.The truss framing for the roof is no different then any other ceiling.

Joe Carola

Terrence,

He should be using 5/8" sheetrock. You don't need any cross bracing or strapping. Here in NJ, whether we frame 16" o.c. or 24" o.c. we don't use strapping.

What size rafters does he have and did he use insulation baffles?

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Joe Carola

Project53

Ok I don't get the rigid blue foam stuff....that makes no sence. But anyway , yes he needs 5/8 sheet rock.
But back to the blue stuff....If he just pushed this up against the roof sheithing...then he didn't insulate anything. Did he somehow get this to be right against the sheet rock? This stuff is only like at the most 2" thick. If thats what he did, I don't think he needs a rafter vent?
Even with a 2x4 roof truss.
My guess is he used this stuff because he thought he could save $$$$$
Depending on how he did it....it may be a complete waste of money.

InsulPro

He definately didn't save any money on that 2" blue dow. That stuff is expensive.

clampman

No kidding insulpro. Plus that stuff would be miserable to fit between rafters.

If it was me, I'd strap the celing and use 1/2 inch. Chances are he could have moist air up there - if not down right water condensing on the dow blue, then runing in rivulets. But even moist air alone weakens the paper and the rock itself and it likes to sag then (and the screws don't hold for sh*t either). If you get a little condensation on fiberglass, it doesn't run. It just sits there till it dries out.

I'm not big on that dow blue myself, after discovering it is the favorite stuff of carpenter ants to make nests in when they hibernate during the winter. Same with that expanded polystyrene behind the fake stucco.

What do you think of that stuff , Insulpro?

Regards,
Jimc

InsulPro

Sounds good Clampman.
So I was just wondering is your friends attic is a full vault or a scissor truss?

BULLHART

I'd just upgrade to 5/8". WOrks great on 24" o/c IMO.

Terrence

Yes, he used the Blue Dow boards, and he said it was next to impossible to get them to stay in place (keep falling out). He cut little wedges to wedge them in.

I was rolling my eyes on that one and thinking that won't insulate a thing... but didn't want to say anything because I am not an insulation pro... Although I DID say he MIGHT need to replace that with fiberglass batten insulation.

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joe thanks

8" rafters, and rigid board, not baffles (as baffling as that may be...)

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Yeah I think it was a waste from what I have just read here...

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So I was just wondering is your friends attic is a full vault or a scissor truss?

Full vault

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Sounds good. Luckily he has only done one piece of 1/2 so far, so I will tell him to get 5/8" (Too bad he had to cut all the rock inhalf to get it up there...

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This was a clear case of one HO telling another HO how to do something (completely wrong), and Home Depot providing the support for that.

I don't know what the Blue DOW costs, but maybe I should get him to do that right too... He's been calling me to help him for 3 months, but I've been too busy. I think he really wanted my opinion about the insulation though since it was so difficult for him.

Anyway, thanks for your help, guys.
Expensive or not, at least he can get it right now.

Mbskye

They do make a 1/2" rock that is raited for ceilings, Ive never used it but Ive seen it used & it didint seem to cause any problems. but once again its made for ceilings & not just standard 1/2" rock.

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" Second place, is the first loser."

d.janvrin

Im With the strapping 16 oc then stagger sheet rock end joints along with strapping saves time money and tapeing , Good Luck !!

I wouldn't even try the rock without strapping unless every thing is square ,plumb and exactly 24"oc witch is not even done in most new construction !!!!!!!!!!!!!!!!

747

Why didn't he just put a few big dabs of liquid nails on the back of the insulation. That would have held it in place. Or is that CONTRAINDICATED.

karma_carpentry

He should have ventilation channels unless he insulates with open cell sprayed in foam.

Code descriptions from Washington state, check the sixth and 8th bullet point. My state, section 1210.1.

72chevy4x4

[quote=karma_carpentry;147134]He should have ventilation channels unless he insulates with open cell sprayed in foam.

are you indicating the open cell foam can be sprayed in w/o ventilation channels? what about higher density/closed cell foam?

karma_carpentry

A hydrophobic open cell foam like Icynene can definitely be sprayed in with no ventilation channels in a cathedral ceiling, without condensation forming.

I don't know the answer regarding closed-cell foams, but I suspect it would be the same, because they are, effectively, a vapor barrier. Open-cell foam is a vapor retarder (5 inched of Icynene is rated at 10 perms), enough to still let framing members breathe, but low enough to prevent condensation buildup.

You still might want to check your local codes or give a call to the inspector, I don't know how fast these changes have diffused. I know the inspectors have been fine here in Boston with a couple of recent sprayed-in cathedral ceilings I've worked on.

thom

We hang 1/2" rock at 24" ctrs in NM all the time. Sags aren't an issue. Maybe because it's dry here, I don't know, but I do know that stuff built 30+ years ago with 1/2" on a ceiling at 24" ctrs is fine.

karma_carpentry

I think the issue is more that the spacing isn't always accurate so you can't guarantee you'll land on a rafter with the edges of the sheets.

Last time I worked on something like this, we ran horizontal straps at 19.2", then sprayed in Icynene. Then 1/2" rock.

You also get the chance to shim out the strapping to plane out the ceiling if you use strapping. Those rafters often sag differently, and some of the timbers are sometimes up to 1/2" wider than others.

thom

Well Karma, that makes sense. Of course 16" ctrs would have the same problems so the spacing is not an issue and should have been left out of the initial question.

Chris G

At 45 degrees, I think you're fine to use 1/2". I'm with Karma, you will have an easier time and a better looking ceiling if you strap it. If he hasn't closed it in yet, tell him to put some battens in there. He'll get his money back in the long run with heat/ac savings.

And make raft with the old blue stuff.