Insulation / Vapor Barrier Question

[I-Hate-Hulse]

I've got a double garage that is attached to the neighbor's double garage. However, these are not attached to the house itself. (it's a detached, attached garage...confusing I know)

I'm currently heating and insulating/drywalling my half of the grage structure. Currently both halves of the garage have uninsulated and unfinished exterior walls. However, by code, a finished dividing wall exists between our two halves of the garage. The dividing wall is like 10inches wide, has lots of insulation in it (about 8" of batt) and is sheeted with fire rated drywall on each of our sides of the wall.

Here's the problem - they never vapor barriered the drywall behind my side of the wall. My neighbor has no plans to heat / or finish their half of the garage. My questions are:

1) Do I have to vapor barrier the dividing wall?

- my instinct says yes, other wise there will be leakage to the unfinished side

2) Can I put Vapor Barrier over the existing firerated dywall on the dividing wall (without tearing it out) and resheet over it with a new layer of drywall?

- or will I get some moisture issues in the fire rated drywall layer?


Thanks!

[bluntus logicimus]

1.) Yes
2.) No

[You Need a Thneed]

I'm just wondering about expansion/contraction issues if one side is heated, and the other side is not. Will you end up cracking drywall, and putting extra stress on the structure?

[GoinAllTheWay]

Originally Posted by bluntus logicimus

1.) Yes
2.) No

You sure about that? I was under the impression that a vapour barrier was only needed on an exterior wall. This is a wall that devides two garages and is not exposed to the exterior.

[EVERLAST]

Originally Posted by bluntus logicimus

1.) Yes
2.) No

I agree with this #2 but do not see you having an alternative...regardless of what side its on the framing should have never occured after the firewall without vapour barrier

[bluntus logicimus]

Originally Posted by You Need a Thneed

I'm just wondering about expansion/contraction issues if one side is heated, and the other side is not. Will you end up cracking drywall, and putting extra stress on the structure?

No more an issue than the exterior walls of any dwelling exposed to weather elements. Even less so in this case as the attached unheated structure provides for a measure of moderation of temperature fluctuation.

[Ne7en]

Originally Posted by GoinAllTheWay

You sure about that? I was under the impression that a vapour barrier was only needed on an exterior wall. This is a wall that devides two garages and is not exposed to the exterior.

Yes it certainly requires a vapour barrier. The original poster stated his neighbor was not planning to heat his/her side of the garage, therefore it is treated as exterior.

HEATED SIDE - gypsum wall board/ vapour barrier /stud & insulation/ air barrier/ gypsum wall board - COLD SIDE

[bluntus logicimus]

Originally Posted by GoinAllTheWay

You sure about that? I was under the impression that a vapour barrier was only needed on an exterior wall. This is a wall that devides two garages and is not exposed to the exterior.

Play it safe and install the vapour barrier. Moisture build-up may or may not be an issue although I would think that in the dead of Winter, the unheated garage could be sitting at near freezing and the heated garage at a comfortable +18. I would think that to be enough of a difference to create the potential for moisture build-up. There is also the issue of some heat loss which the vapour barrier would mitigate.

To the OP . . . it's a garage. Does it need to look pretty inside? If not, pulling down drywall and reinstalling with 6mil is a fairly simple job.

[GoinAllTheWay]

Makes sense. Besides, for the cost of a vapour barrier, why the heck not I guess.

[Ne7en]

Originally Posted by bluntus logicimus

Play it safe and install the vapour barrier. Moisture build-up may or may not be an issue although I would think that in the dead of Winter, the unheated garage could be sitting at near freezing and the heated garage at a comfortable +18. I would think that to be enough of a difference to create the potential for moisture build-up. There is also the issue of some heat loss which the vapour barrier would mitigate.

To the OP . . . it's a garage. Does it need to look pretty inside? If not, pulling down drywall and reinstalling with 6mil is a fairly simple job.

Or when the neighbor opens the overhead door in the dead of winter -35 out and your garage is sitting at +16. No question you should have a vapor barrier. Sorry to cause a headache but you'll be dealing with allot worse issues if you don't.

[Shazam]

Originally Posted by Ne7en

Yes it certainly requires a vapour barrier. The original poster stated his neighbor was not planning to heat his/her side of the garage, therefore it is treated as exterior.

HEATED SIDE - gypsum wall board/ air barrier /stud & insulation/ vapour barrier/ gypsum wall board - COLD SIDE

What? NO.

VB ALWAYS goes on WARM SIDE!!!!!!!

[Ne7en]

Originally Posted by Shazam

What? NO.

VB ALWAYS goes on WARM SIDE!!!!!!!

Agh, my mistake. Thanks for spotting that.

[speede5]

I doubt anyone will agree with me but if there are no outlets on this wall and the tops and sides are sealed you will never have a problem. A couple good coats of oil based paint will make the entire wall a vapor barrier. Water vapour travels in the moving air through holes (outlets). It will not travel through firerated drywall in any capacity capable of causing harm. if you can see the base of your wall, run a bead of acoustic sealant along the sill, make sure there are no moisture paths throught the top and sides and relax. Also if there are no outlets, there is no reason (unless there is a code out there I don't know of) you couldn't vapour barrier over the firerated drywall and cover with another layer. The second layer is only going to increase your firerating.

[I-Hate-Hulse]

Thanks everyone. I was sure VB woud be required but my lazyman's approach to not taking down the existing drywall and putting VB/DW over it sounds bad. Cost and time isn't that much more so really....suck it up and do it right sounds like the best way to go. I'll probably only have my side heated to +5 or so, unless I'm actually doing something in the garage.

Acoustical sealant question here - applying it to the top and bottom plate is definately what I'm going to do, but how many of you actually apply it to the studs when you're overlapping VB to make seams? This is in additional to Tuck taping the seam of course.

[THE SCUD]

tuck tape those seams. acoustic on top/bottom plate.

[Bindair Dundat]

Originally Posted by speede5

I doubt anyone will agree with me but if there are no outlets on this wall and the tops and sides are sealed you will never have a problem. A couple good coats of oil based paint will make the entire wall a vapor barrier. Water vapour travels in the moving air through holes (outlets). It will not travel through firerated drywall in any capacity capable of causing harm. if you can see the base of your wall, run a bead of acoustic sealant along the sill, make sure there are no moisture paths throught the top and sides and relax. Also if there are no outlets, there is no reason (unless there is a code out there I don't know of) you couldn't vapour barrier over the firerated drywall and cover with another layer. The second layer is only going to increase your firerating.

That's what I was just about to add to the thread; glad I read all the way to the bottom...
You'll actually get the same effect (without the mess/stink of oil) if you just use a couple of coats of a high quality semigloss 100% Acrylic (i.e. "kitchen and bath") over a standard drywall primer. The "mistint" section of the local paint store is your friend for such a purchase...

5/8" "Type X" drywall is bulletproof in comparison to 1/2" "standard".

If you're worried about plugs, buy those foam rubber seals that fit under the faceplates of the outlets...they work both ways. The demising wall (as described) is almost certainly a proper firewall, with 2 staggered 2 x 4 walls, each batted with R-14 rockwool insulation (with an air gap between these two walls). Such a wall construction will outperform a "standard" 2 x 6 exterior wall (and by a considerable margin) thermally.

Problem solved.

[I-Hate-Hulse]

Originally Posted by Bindair Dundat

That's what I was just about to add to the thread; glad I read all the way to the bottom...
You'll actually get the same effect (without the mess/stink of oil) if you just use a couple of coats of a high quality semigloss 100% Acrylic (i.e. "kitchen and bath") over a standard drywall primer. The "mistint" section of the local paint store is your friend for such a purchase...

5/8" "Type X" drywall is bulletproof in comparison to 1/2" "standard".

If you're worried about plugs, buy those foam rubber seals that fit under the faceplates of the outlets...they work both ways. The demising wall (as described) is almost certainly a proper firewall, with 2 staggered 2 x 4 walls, each batted with R-14 rockwool insulation (with an air gap between these two walls). Such a wall construction will outperform a "standard" 2 x 6 exterior wall (and by a considerable margin) thermally.

Problem solved.

Unfortunately, I forgot to mention that the dividing wall is not mudded or taped, just boarded, so there are open seams between the sheets. I assume that isn't going to be enough. Between taping these or tearing it out I think I'd rather do the latter.

Is Roxul/rockwool code for a dividing firewall? The batt material there appears to be while John Mansville fiberglass. House is about 9 years old.

[Bindair Dundat]

Originally Posted by I-Hate-Hulse

Unfortunately, I forgot to mention that the dividing wall is not mudded or taped, just boarded, so there are open seams between the sheets. I assume that isn't going to be enough. Between taping these or tearing it out I think I'd rather do the latter.

Is Roxul/rockwool code for a dividing firewall? The batt material there appears to be while John Mansville fiberglass. House is about 9 years old.

Mineral fiber batts are most often used in these applications, but fiberglass is also acceptable under the code provisions.

Taping is required for all fire rated demising walls...methinks that this must have "snuck" through the inspection process at some point in time.

Tearing off and replacing the board (in this case) would be a needless expense.

The coatings system (as I described above) will deliver a "perm" rating in the ballpark of 1.0>1.8, more than suitable for the situation, as the wall construction will dramatically mitigate the temperature differential between the two sides; moreso yet if your intent is to only keep your side a few degrees above freezing during the heating season.

Tape the wall (or get it taped, if you're hiring a Drywall contractor for that aspect of your finishing process), paint as described above, and buy beer with the $ you saved.

If you "tear off", you will have to replace the board with "Type X"...and it's a whole lot more a sheet (almost double the price) as is 1/2" standard.

Also...if the paper on the wallboard has been sitting exposed for 9 years then yes, prime it with alkyd (enamel) undercoater. You can finish with S/G Acrylic right over top of the oil primer with no worries.