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Discussion Starter #1
Getting ready to install insulated ceiling in my garage. The firewall between house and garage goes floor to ceiling with no exposed 2x4 on which to attach the insulation, or drywall. So I have to put up a 2x4 up and attach it.
Question is, can I mount it (with long screws) on top of the existing drywall, or should I cut the drywall out and mount the 2x4 directly to the underlying wood?

I know the drywall is extra thick and fire retardant. (a 2 hour wall as I understand it), so I don't know if I can legally break through the drywall, or if there is some appropriate way to handle this?
 

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Have you considered removing the existing drywall and insulating, then putting new drywall in? Usually, 2 hour firewalls are 5/8" drywall on both sides of the wall, but sometimes contractors will use two layers of 1/2" on the garage side to gain the necessary thickness. I would think that it would be much easier to install insulation in the existing stud cavity instead of tacking on an additional 2x4 frame to hold the insulation/drywall...

If you do make cuts into the existing drywall, the holes need to be well sealed with mud to prevent hot gasses from entering the attic space. Those holes can cause a small fire in the garage to move into the attic and burn off the roof. I saw that more than a few times over the years...
 

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Do NOT cut into the drywall, Tom!!! I mentioned a couple of years back, about an arsonist in my neighbourhood, back then,.
He'd started a fire in the rear of a four-plex and the fire was so hot that it consumed everything in it's path...but it was stopped dead in its tracks by the 5/8" 'Fireguard' drywall. Man, was I impressed!
Dan (above) is absolutely correct, but getting rid of old drywall has become a bit of a p.i.t.a., and if you can live with losing 4" of floor space go with the new framed wall...just my personal choice.
Not necessary to anchor it to the existing wall. Nail it through to the ceiling framing and the floor, same as you would with any other partition wall. Run your wiring then insulate and board. If you can get some help, use 12' sheets or whatever works for your wall length, horizontally! I know stick thinks vertical is the way to go, but taping and filling a 4' high seam at waist height and maybe one or two vertical joints beats a bunch of 8' high joints all to Hell! :)
 

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We maintain firewalls in construction. Maintain existing You can screw 2's to the corresponding studs if you want 1 1/2" cavity. Why insulate an interior wall? soundproofing?
 

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We maintain firewalls in construction. Maintain existing You can screw 2's to the corresponding studs if you want 1 1/2" cavity. Why insulate an interior wall? soundproofing?
I agree, why are you insulating the wall, Tom?
I like the suggestion of 1 1/2" furring and foam bat insulation from Lowes, if it is necessary to insulate.
Are you talking about the wall separation in the attic?
Herb
 

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Hold on? if it's a firewall between the house and the garage the walls already insulated
 

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"Hold on? if it's a firewall between the house and the garage the walls already insulated"

;)...you can never have too much insulation, right, Rick?
Agreed . I only have one piece of insulation that Honest John sent me , and it's still pretty darn cold in there :fie:
 

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Discussion Starter #13 (Edited)
We maintain firewalls in construction. Maintain existing You can screw 2's to the corresponding studs if you want 1 1/2" cavity. Why insulate an interior wall? soundproofing?
I think I am talking about putting up a ledger board.

I am insulating the ceiling, not the wall, then putting up drywall on the ceiling to enclose the insulation up there. The garage walls are already insulated and drywalled.

Just need to know whether to cut through the drywall parallel to the other beams, and attach a new 2x4 ledger board to the existing framing underneath the existing drywall, or to mount that 2x4 kedger through the drywall into to wood on the other side with some really long screws. I will staple the insulation to this new 2x4 ledger and attach the last 2 feet of the drywall to it. It won'd be bearing much weight. This is all on the house side of the garage. I'm putting in the insulation, but hiring someone to put up the ceiling.

I am not going to put in a frame, just a ledger board.

Putting up R38 insulation up there. Tired of freezing in winter, baking in summer.
 

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Tom as I understand it, you can insulate/drywall the ceiling, but when you get close to the interior wall, you have nothing that you can attach the insulation/drywall to - is that correct?

How do your joists run - are they parallel to the interior wall or perpendicular?
 

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Discussion Starter #15
Tom as I understand it, you can insulate/drywall the ceiling, but when you get close to the interior wall, you have nothing that you can attach the insulation/drywall to - is that correct?

How do your joists run - are they parallel to the interior wall or perpendicular?
Exactly on the first point. And the joists run parallel to the interior wall. I think I confused everyone because I didn' t have the labels right.

I have done this on an exterior wall, but not on a fire wall with drywall already on it.
 

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OK, what is the distance between the interior wall and the closest joist? How long are the joists or what is the distance front to back? What is above the joists - is it an attic or open space and do you plan to put anything up there?
If the distance between the wall and first joist isn't that great I would consider building a bulkhead, attached to the first joist, butted against the wall without fasteners. If the distance is excessive, you couldn't do that because it would likely sag at the wall. The alternative is to extend a some two bys, across the top of the first two joists towards the wall and attach the bulkhead to the joist and to those extensions. Does that make sense?
 

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Discussion Starter #17 (Edited)
OK, what is the distance between the interior wall and the closest joist? How long are the joists or what is the distance front to back? What is above the joists - is it an attic or open space and do you plan to put anything up there?
If the distance between the wall and first joist isn't that great I would consider building a bulkhead, attached to the first joist, butted against the wall without fasteners. If the distance is excessive, you couldn't do that because it would likely sag at the wall. The alternative is to extend a some two bys, across the top of the first two joists towards the wall and attach the bulkhead to the joist and to those extensions. Does that make sense?
I think you are talking about something like outriggers. Span several 2x4s across the existing joists. The distance between joists is 24 inches on center.

The distance between the wall and the first joist is almost the same. So that's why I think a ledger board is the best solution. BUT MY QUESTION REMAINS THE SAME: Can I mount the ledger board on top of the drywall, or do I need to cut the drywall away and mount the ledger board directly on the underlying wood?

The minor problem I see with outriggers is that it may interfere with installing the insulation. But I guess I could suffer through that for two 25 foot lenghts. I'll just itch a little more.

I would want the outriggers to span at least two joists, but I think I would still want a ledger board suspended from the outriggers to attach to the wall as well.

So even with outriggers, I still have the same problem, cut through the drywall or drill through it?

Thanks for the suggestion Vince. Best bet so far.
 

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Tom
Just go ahead and screw or nail a Ledger board to the drywall,just find the studs in the wall you will have use longer nails or screws, you might want to also use liquid nail.
If it around 24" from the last truss to the wall you'll be fine
 

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Discussion Starter #19
Tom
Just go ahead and screw or nail a Ledger board to the drywall,just find the studs in the wall you will have use longer nails or screws, you might want to also use liquid nail.
If it around 24" from the last truss to the wall you'll be fine
Cool, that's what I hoped would work. I think if I use some 4 or 5 inch screws, hit the studs or the joist on the other side of the drywall, then the weight (insulation and 1/4 sheet of drywall) will be OK. I think it would be smart to do the outriggers as well. At least, that's the plan for now.
 

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What John said. Still trying to figure out what you are calling outriggers.

I try to avoid using screws in framing if I can. I see Mike Holmes do it all the time but I still think it's a bad idea in most cases. The reason why is all the screw failure I saw when I lived in northern Alberta on my front steps. They were a set of steel risers with boards screwed down from underneath and I kept getting broken screws. It finally dawned on me why. Screws are tempered to be hard enough so that you can drive them and without stripping the heads out prematurely. This tempering also makes them brittle so that they don't tolerate much flexing before they snap off.

Nails on the other hand are quite soft and will flex back and forth quite a few times before there is enough metal fatigue to cause them to fail. Nails are old school but I still think they are the best choice in framing because most framing moves as time and seasons change.
 
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