I have some extra rigid foam panels and a wall surrounding an unheated garage that needs insulation. It is not practical to use the panels outside the studs, where drywall already is up inside the garage
Is there any reason I would not want to cut the panels to fit inside the 2×4 stud bays?
In this situation, what about a vapor barrier? I’m in a mid-Atlantic “mixed” heating zone.
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Replies
>>a wall surrounding an unheated garage that needs insulation.<< Is this a partition wall between the house and the garage, or is it an exterior garage wall.
>> It is not practical to use the panels outside the studs, where drywall already is up inside the garage << Are you saying the partition wall between the house and the garage is already insulated and drywalled? Or is this a detached garage?
You don't say what kind of foam it is, but if you do some research on that specific kind, I think you will find that it is a vapor barrier.
None the less, putting foam in the stud bays is fine, but it must fit tight, or otherwise will be pretty much useless. The best way to make it fit tight is to foam it in place with some spray foam. Be aware though that the foam needs to be covered with drywall for fire safty reasons.
All:
When I read a lot of these initial posts I find them very confusing as far as what the poster is working on and/or what they want to do.
I'm not trying to pick on this guy, but does his initial description not make total sense or is there something wrong with me? OK - that opens me up for "pot shots" but, just for a minute I'm being serious here. :-) Maybe I'm just not any good at reading between the lines? Maybe when I see something that I can't understand, I should just pass over it, even if I do know some good stuff about the subject?
No, you're not wide of the mark; I can't quite visualise what the OP's trying to do, either.
It sounds to me like he's just trying to use up some surplus material, but it makes no sense that the drywall's already up and he's thinking of sticking the foam into those stud bays.
We're going to have to wait for him to come back and clear it up.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
>>a wall surrounding an unheated garage that needs insulation.<< Is this a partition wall between the house and the garage, or is it an exterior garage wall.
>> It is not practical to use the panels outside the studs, where drywall already is up inside the garage << Are you saying the partition wall between the house and the garage is already insulated and drywalled? Or is this a detached garage?
It's a detached, unheated 2x4 framed garage, with fiberglass insulated walls and drywall on the interior. I'm adding a heated timberframe workshop in an L outside 2 of the garage walls. I'm tearing the siding off the outside walls of the existing garage. This will be replaced by T&G pine panelling between the timber frame and the garage stud walls.
A lot of the existing fiberglass has been tunnelled by mice. The foam I have is 1" and 2" thick extruded polystyrene, extra from when I insulated under the new slab floor.
I am able to cut the foam board to fit snugly and precisely inside the stud bays, as long as they were framed square and plumb, which sometimes they weren't. In that case I can squirt some caulk or foam sealant into the gaps.
It seems to me, as I fit a few pieces into narrow bays around a door opening, that the foam board has an added advantage of strengthening the stud frame. My question is, is it likely to create moisture problems with condensation forming on either the inside or outside plane? It does not seem to be breathable as fiberglass is. I'd be filling the whole bay with 3.5" thick foam, about R 15-20. Eventually I may get around to removing the drywall from inside the garage and putting up foam sheathing plus a new layer of flame retardant drywall.
As for the oddity of having insulation in the existing walls of the unheated garage, that's just the way it was built. I don't know if there was a code requirement or what. It has had the advantage of helping to keep the garage interior nice and cool during the summers. There is unfinished space above the garage, maybe the builder expected someone to eventually finish it off as living space.
Anyway, sorry for not providing enough detail. My question really is about the wisdom of using rigid foam board BETWEEN studs. All the information I find on the Internet assumes builders are using it as thermal sheathing on the exterior, between frame and siding. Which makes sense to me. So I'm wondering if there is any reason people don't use it between studs, other than cost? Fitting it is sort of a pain, because builders don't build like cabinet makers and maintain exactly 14.5 " between studs and the foam is not sold in those widths anyway. But the gap problem really exists with batts, too, if it's not very carefully installed.
Tom
why not put the panels across the wall prior to installing the t&g siding. No fitting and a whole lot better R value without leakage?
>> why not put the panels across the wall prior to installing the t&g siding. No fitting and a whole lot better R value without leakage?Yes, I understand that.
To make a long story short, there is no extra clearance to do it that way.If I do use the foam, the idea would be to fit the entire 3.5" cavity (or 3" for R15, anyway).I can cut the foam with a jigsaw and rail guide. The kerf idea sounds good but I do not have a table saw here.
Why not score the foam with a utility knife and snap it like you do with drywall? Seems like it would be easier and faster than using a saw to cut it.
tables saw is th eeasy way
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Tom,
When the local school district re-roofed the High School, the contractor took off the 1-1/2" thick ridged foam sheets that were 4X8'. All the contractor wanted was to have the old insulation removed.... I rented an open U-Haul trailer and brought home more than 90 sheets.... practially Free!!
That said, I insulated our 1958 garage/well house's outside walls with the ridged foam, cutting it with a simple drywall handsaw. To seal the rough edges, I bought 2 or 3 cans of expanding foam, but the kind that's the low expanding version and filled any rough gaps around the foam sheets' edges. About an R-8 per sheet, you can get a lot of R-value in a wall, not to mention the economy of "Free" insulation.
As a side bar to that experience, I have a 4" thick concrete tilt-wall building with a 9ft. wall. Great for strength, but once all that mass gets cold or heated from direct sunlight, it says that way for DAYS.... So, I attached 2X4's to the interior surface of the North and West walls. While loading the old foam sheets, the ground was littered with 3" diameter stamped metal washers and 7" long, hex-head screws. I placed one layer of the foam sheeting in between the wood lath strips, then alternated seams on the next 3 layers. The metal washers and the long Hex-head screws screwed into the 2X4's held all four layers against the wall. I had to cut 1' sections to add cover the top of the 9' wall, so I also used several cans of that low volume-expanded foam to fill any chips or voids in the foam sheeting.
By luck and a kind deed for another site superintendent, I was given enough foil-faced 6" thick fiberglass insulation taken out of a suspended ceiling. So, I added a 2X6 stud wall from used lumber from the same site, on 2' centers, in front of the foam sheeting. Using a vapor barrier and soffit 4X8' sheets of Hardiboard as interior dry wall, my North and West walls are now a foot thick and have an R-value of over 50....
So, use that ridged foam sheeting!!
Bill
I would cut it with a skilsaw or a tablesaw, 1/4" to 1/2" undersize, tack in place with a couple of nails, and use cans of expanding foam to seal it to the studs.
Trying to fit the foam perfectly will be an exercise in frustration. A little space around the rigid foam helps the expanding foam to adhere.
Tom,
Make sure you try the "score and snap" method mentioned by Danno. I've done this lots of times with rigid foam. It works well; some brands/types of rigid foam are easier to work with than others.
Make sure you have a new blade in your knife and give it a go.
In my experience, cutting the pieces to the exact dimension (that is, don't "burn an 1/8" or whatever) of the measured opening makes a piece that fits in nice and tight -- sometimes a few taps with a mallet helps.
My question really is about the wisdom of using rigid foam board BETWEEN studs.
There is nothing wrong with the addition of foamboard between the studs in that it is better than nothing.
The question of validity arises with the excessive amount of labor involved producing a tight shell by this method
and the fact that you are still leaving a portion of the wall pratically uninsulated by the volume of the studding
which can add up to a somewhat large area when one imagines the total number of 1 1/2inch wide 2x4 lumber widths of the garage lined up beside each other.
The foamboard insulation far exceeds the value of fiberglass batts in insulation properties.Before I had done I was more the friend than the foe of the pine tree, though I had cut down some of them, having become better acquainted with it. Sometimes a rambler in the wood was attracted by the sound of my axe, and we chatted pleasantly over the chips which I had made. -Thoreau's Walden
> Fitting it is sort of a pain, because builders don't build like cabinet makers and maintain exactly 14.5 " between studs and the foam is not sold in those widths anyway.One way to deal with this is by kerfing the pieces by running them through a tablesaw, about an eighth of an inch in from the edge, on both sides.
I would do it.
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A garage that is framed and drywalled, but no exterior sheathing or siding?
Whatever it is, your explanation/description leaves a lot out.
Joe H
like matt, I ama bit confused.
If this is an unheated garage, why insulate it?
And you speak of placing foam board between the studs but maake it sound like the sheet rock is already up.
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Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Like others have said. Kind of confusing on how you plan on putting foam between studs with sheetrock already installed. No exterior sheathing?
Those questions aside, the insulation has no value if the space is not conditioned. Kinda like putting an airconditioner on your open porch. And the vapor barrier is immaterial if there is no temp. or humidity difference from inside to out.
the insulation has no value if the space is not conditioned..
I'm not sure what you mean by that, exactly. However, I can point out that the insulation will help reduce the temperature extremes the workshop would otherwise experience. That is, it will passively remain cooler in the summer and warmer in the winter than it would without the insulation.
>> That is, it will passively remain cooler in the summer and warmer in the winter than it would without the insulation. <<
And it can work against you too. Many times I have worked on a sunny morning after a cold night in a sheetrocked and insulated but unheated house and had it be colder in the house than it is outside.
I'm not sure what you mean by that, exactly. However, I can point out that the insulation will help reduce the temperature extremes the workshop would otherwise experience. That is, it will passively remain cooler in the summer and warmer in the winter than it would without the insulation.
An insulated unconditioned building will just lag behind the ambient temp. But I don't see how any passive cooling will be gained unless a radiant barrier is used.
The coolness Matt speaks of is obviously the lag in temp. change just as holding any gained heat later in the day.
If it were truly only a temperature lag, as you suggest, the inside of the building would experience the exact same temperatures as the outside -- the only thing that would be different is the time.
Think of the temperature in a cave --- it is always around 50-some degrees. All the earth around it insulateds it from the extremes experienced on the surface. Temperatures in the cave do not reach freezing temperatures, nor do they ever get that hot.
The OPs insulated shed will qualitatively perform the same way: the insulation will act to filter out the high and low temperature spikes and move it towards a mathematical average. Of course, he only has R10 or R15 (or whatever), so although the shed won't perform as well as the cave on a quantitative basis, it will follow the performance on a qualitative basis.
I had an uninsulated to be enclosed carport in N.Fl that I used the 2",4x8 foam on the ceiling,between the rafters because I didn' want to install drywall with 3" screws, and then covered that with 3/4 sheet foam across the rafters to seal the edges.I probably should have used the spray foam but like billjustbill some of this stuff was free. I will be hanging drywall next? I used one of those japanese thin hand saws to cut my stuff and it went through like butter. I can really feel the temp. diff.from the main house, so I think mine was a success.