How can I insulate an old garage without wrap?

[diyer_]

Hello,

I live in Chicago and have a detatched garage. As far as I can tell, it's vinyl siding and then horizontal wood, please see picture below. I've lived here for 3 years and no water seems to intrude. I want to start insulating my garage with foam boards but I'm trying to understand how I can allow air between the foam boards and horizontal wood. I don't want the wood to rot. Could I use some thin strips of wood placed on the horizontal wood, then glue the foam boards to that? Then use foam spray to seal around the foam board?

The closet thing I found was this youtube video where they use something called Delta Dry and then another layer of some sort of stretchy material to cover that, then they foam sprayed it. Since this is a garage, I want to do it right, but maybe a cheaper method... thoughts?

Here's the video -

 

[kaymccampbell]

Why don't you just use rockwool? It should breathe enough.

 

[diyer_]

Why don't you just use rockwool? It should breathe enough.

I forgot to mention. The studs are original 2x4 (they are actually 2x4 before the downsized them) and they don't follow any 16 or 24 inch spacing. They are all over the place... , like 15, 23, 30, etc...

 

[kaymccampbell]

Rockwool cuts with a serrated bread knife. I'm assuming you're going to line the garage with some kind of drywall or paneling. If not, you could always run the rock wool horizontally. Otherwise it stuffs into the studs like fiberglass. Which you could also use, but it's not as rigid.

 

[jack stand]

From what I understand is you want 2" (minimum) of foam in order to have the average "dew point" happen within the foam and therefore no moisture problems. This is for living spaces where much more water vapor is created just by normal living activities.
This is very different (lower) for a garage with the possible exception of parking a snow packed vehicle inside. It's also important to seal the foam to the framing around all edges.

 

[jblnut]

Always that guy that says spray foam ....

So I'll be that guy ...

How about spray foam ? No need to worry about oddly spaced studs then and it'll insulate like crazy while sealing tight to everything it touches so no air gaps between things to rot wood

 

[diyer_]

Always that guy that says spray foam ....

So I'll be that guy ...

How about spray foam ? No need to worry about oddly spaced studs then and it'll insulate like crazy while sealing tight to everything it touches so no air gaps between things to rot wood

I got a quote from a couple places and it was near 5 grand... .

 

[diyer_]

From what I understand is you want 2" (minimum) of foam in order to have the average "dew point" happen within the foam and therefore no moisture problems. This is for living spaces where much more water vapor is created just by normal living activities.
This is very different (lower) for a garage with the possible exception of parking a snow packed vehicle inside. It's also important to seal the foam to the framing around all edges.

Thanks, would the foam boards be glued directly to the horizontal wood? I fear it will rot due to that?

 

[diyer_]

Rockwool cuts with a serrated bread knife. I'm assuming you're going to line the garage with some kind of drywall or paneling. If not, you could always run the rock wool horizontally. Otherwise it stuffs into the studs like fiberglass. Which you could also use, but it's not as rigid.

If I do it horizontally, I'd just tape the edges? From what I researched, I thought mold could happen due to my setup...

 

[Toomanytools?]

What is the use of the garage, working shop area or car storage? If you went with 3" rigid (R15) held it flush with inside stud, nail sideways or friction fit or spray foam to hold it. That would leave a 1/2" air gap, but at a cost of $124/ 4x8 sheet for R15, that's $3.90 a square foot. Rockwool/Ruxol R15 is around $1/sqft.

 

[diyer_]

What is the use of the garage, working shop area or car storage? If you went with 3" rigid (R15) held it flush with inside stud, nail sideways or friction fit or spray foam to hold it. That would leave a 1/2" air gap, but at a cost of $124/ 4x8 sheet for R15, that's $3.90 a square foot. Rockwool/Ruxol R15 is around $1/sqft.

It's going to be a working shop (car repairs during winter / wood work) / extra office. I work from home and have a child and a couple crazy dogs so I wanted the option of working out there anytime of the year if it starts getting annoying at home .

 

[u2slow]

In my cool/damp climate, VB goes on the inside; over the batt insulation, before wallboard.

 

[jblnut]

I got a quote from a couple places and it was near 5 grand... .

How large is the garage ? How thick was the foam quoted ? Ceiling done or just walls ? Open or closed cell ? Without a bearing on size and details the $5k could be a screaming good deal or an absurd price. If you hire spray foam done you'd likely be able to use it sooner and it'll be insulated better than anything you're going to install yourself. That is not meant to be snarky or anything like that so don't read it that way please.

That all being said .... The only place I have spray foam on the property is around the perimeter of the house in the floor joists as the rest of the house is foam (SIP Built) so I figured why not. Foam does wonders .... when it's sunny and 20-25F outside with very little wind the furnace/infloor heat will not call for heat from 10am until dark. Quite crazy really. Foam does wonders .... Spendy up front but works well.

If I were to do something else in your case I'd get rolls of fiberglass batt insulation and piece it in there. Vapor barrier on the inside and wall covering stuff over the whole works. The plastic is behind everything in every building we have here in Central MN so I'd imagine it'd work fine.

I helped a buddy insulate an old shed a while back and he insulated with fiberglass between the studs then put 1-1/2" blue foam board over the studs and taped the seams, VB over the foam and put 1/2" plywood over the foam. You can heat that shed with a candle and he almost does. Just a little rocket heater in there will sweat you out. Just another idea depending on how well you want it insulated. Think about when you've ever seen a house with foam around the outside under the siding .... it's that but in reverse. Not sure if it's GJ approved but that was a long time ago and we resided it last summer and nothing was rotten that we could find ....

 

[Idle Serge]

I, too, had some odd spacing in my detached 18X24 garage. I didn't want to deal with the mess of measuring, cutting and fitting accordingly so I got a quote and had it done. I live in the PNW and got it installed for just shy of $2,200. I thought that was a bargain, considering how much work it was going to take to get it done - granted, a 2 man team got it done in an 8 hour day.

20221128_152045 by Sergio Zapien, on Flickr

Even did along the rafters - R15 all the way around:

20221128_152123 by Sergio Zapien, on Flickr

 

[jack stand]

Thanks, would the foam boards be glued directly to the horizontal wood? I fear it will rot due to that?

In theory, if you're foam is thick enough the dew point (where the warm inside air meets the colder outside temperatures) is taking place within the foam AND there's no exterior water penetrating the wall, you don't need an airspace.
Provided that you seal the edges you have an equivalent to a "spray foam" job.
The foam, every inch of it IS you moisture barrier.
With a little patience and effort used foam from commercial re roofing jobs shows up on c/l and marketplace. There's also "outlets" that have access to and sell "seconds" and from my experience it's only a thickness variation. Unimportant in your application.
Here's a quick guide to the 3 rigid foam insulation panels.

Rigid Foam Insulation Types | EPS, XPS, ISO | Insulfoam

Not all rigid foam performs the same. Compare differences between expanded polystyrene (EPS), extruded polystyrene (XPS) and polyisocyanurate (ISO) insulation.

www.insulfoam.com

 

[PoorUB]

There has been some talk of spray foam and wood framing being a problem. The foam will allow some moisture to get behind the wood sheathing and it stays wet because it can not breathe.

IMO, without house wrap I would want my outer layer of insulation to breathe and let any moisture evaporate.

I would go with fiberglass or rock wool and a vapor barrier.

 

[diyer_]

There has been some talk of spray foam and wood framing being a problem. The foam will allow some moisture to get behind the wood sheathing and it stays wet because it can not breathe.

IMO, without house wrap I would want my outer layer of insulation to breathe and let any moisture evaporate.

I would go with fiberglass or rock wool and a vapor barrier.

Thanks.. So the order would be

Vinyl Siding --> Horizontal wood --> Rock wool / fiberglass --> Vapor barrier --> drywall

And this would enable the the Horizontal wood and Rockwood cavity to breathe.

 

[diyer_]

I, too, had some odd spacing in my detached 18X24 garage. I didn't want to deal with the mess of measuring, cutting and fitting accordingly so I got a quote and had it done. I live in the PNW and got it installed for just shy of $2,200. I thought that was a bargain, considering how much work it was going to take to get it done - granted, a 2 man team got it done in an 8 hour day.

20221128_152045 by Sergio Zapien, on Flickr

Even did along the rafters - R15 all the way around:

20221128_152123 by Sergio Zapien, on Flickr

Nice.. I assume you did the electrical before hand? What height are your outlets at?

 

[diyer_]

How large is the garage ? How thick was the foam quoted ? Ceiling done or just walls ? Open or closed cell ? Without a bearing on size and details the $5k could be a screaming good deal or an absurd price. If you hire spray foam done you'd likely be able to use it sooner and it'll be insulated better than anything you're going to install yourself. That is not meant to be snarky or anything like that so don't read it that way please.

That all being said .... The only place I have spray foam on the property is around the perimeter of the house in the floor joists as the rest of the house is foam (SIP Built) so I figured why not. Foam does wonders .... when it's sunny and 20-25F outside with very little wind the furnace/infloor heat will not call for heat from 10am until dark. Quite crazy really. Foam does wonders .... Spendy up front but works well.

If I were to do something else in your case I'd get rolls of fiberglass batt insulation and piece it in there. Vapor barrier on the inside and wall covering stuff over the whole works. The plastic is behind everything in every building we have here in Central MN so I'd imagine it'd work fine.

I helped a buddy insulate an old shed a while back and he insulated with fiberglass between the studs then put 1-1/2" blue foam board over the studs and taped the seams, VB over the foam and put 1/2" plywood over the foam. You can heat that shed with a candle and he almost does. Just a little rocket heater in there will sweat you out. Just another idea depending on how well you want it insulated. Think about when you've ever seen a house with foam around the outside under the siding .... it's that but in reverse. Not sure if it's GJ approved but that was a long time ago and we resided it last summer and nothing was rotten that we could find ....

I can't located the quote but I believe it was closed cell, walls and under the roof. The size is a typical 2 car garage in Chicago. I'd have to get the measurements. It didn't feel like a good deal to me.. Again, the garage is really old and not straight. I don't want to sink in that kind of money if I can do it myself another method. Even if it's 90% as good as foam or whatever percentage. If I can sustain working in there, then its done its job.

 

[u2slow]

Nice.. I assume you did the electrical before hand? What height are your outlets at?

Fwiw, I felt wall boarding was more advantageous than an exhaustive electrical rough-in. Now I can piecemeal exactly what i want - in conduit - as i decide I need it.

 

[larry4406]

With proper tools, vinyl siding is actually pretty easy to remove and then reinstall. Once removed, you could apply any exterior WRB (tyvek, etc) of your choice.

Just throwing this out there so you think thru all options.

 

[duneslider]

Just add roofing felt in the cavities before insulation. It works great as an air barrier but will still let vapor movement happen so stuff will dry to the outside in the summer. Its easy to work with and cheap. You could do the same thing with other wraps. Taping it to the studs would be best but I think the benefits of just stapling it in would be fine. I would cut it wider by a couple inches so you can overlap the studs a little and have room to staple.

 

[Idle Serge]

Nice.. I assume you did the electrical before hand? What height are your outlets at?

Correct - electrical was in fact done before hand; I placed them at 48".

 

[stevied916]

I would use rockwool. It cuts extremely easily and is not effected by moisture in the way fiberglass is.