garage insulation ideas

[franklin40]

hi everyone. for those who have done their own insulating of their garage/shops maybe you could offer me some advice. I have a double detached garage that is unfinished on the inside. I am looking to insulate it so I can work in there in the winter (Canada prairie winter). I'm not wanting to heat it all the time just when working out there. I am toying with the idea of blow in insulating for the walls covered by drywall but don't know what I should do with the roof. I'd like to keep the rafters open for storage. would using foam insulation between the rafters be a bad idea? anyone have experience with this that can give pros and cons? any venting suggestions? I'd likely run an electric heater but maybe propane. thanks.

 

[PAToyota]

This is what I did in my workshop with adequate soffit and ridge venting. I have a woodshop on the second floor of my workshop, so I was concerned about how much it would heat up during the summer.

The foil faced foam reflects the heat from the underside of the roof deck and the airspace carries the heat up to the ridge vent. It works better than I had expected.

I'm guessing that in Canada you won't have quite the same worries about summer heat, but airspace under the roof deck would still be recommended. If you do something like this for the airspace, then you can "fill" the rest of the space with cheaper batt insulation.

 

[KLF]

My garage is also uninsulated now, I have storage above in the rafter space that I access via a drop-down attic stair. Still, I have 11+' ceiling height in my garage. I don't really see a need to keep the storage space above warm.

My plan is to use plywood on the walls, much more durable than drywall and you can easily take it back off if you need to change anything. Then I was gonna hang 1" foil-faced polyisocyanurate foam from the bottom of the ceiling joists, foil side down, with the joints taped. This will provide a reflective surface to bounce lighting back down. Then I was gonna blow chopped cellulose in the walls and above the ceiling.

I have good soffit vents but no ridge vent yet, so I need to install that first. I also installed a high CFM gable fan at one end to suck out the heat and fumes/smoke with I'm running the welder.

 

[WarDamnEagle]

I would also vote for either plywood or OSB on the walls vs. sheetrock.

 

[FJ40-GARAGE]

Then I was gonna hang 1" foil-faced polyisocyanurate foam from the bottom of the ceiling joists, foil side down, with the joints taped. This will provide a reflective surface to bounce lighting back down.

Thats the way, the foil should be always to the roomside, its a vapor barrier, if done the other way around it will cause trouble with condensing water.

 

[PAToyota]

Thats the way, the foil should be always to the roomside, its a vapor barrier, if done the other way around it will cause trouble with condensing water.

Not necessarily true. First, the polyiso is closed cell, so the whole board is a vapor barrier. The foil is to reflect radiant heat, but it needs an air space to do so. If you put it directly against another material there is no chance for it to reflect heat and the heat transfer is by conduction. You might as well not have the foil at that point.

As my drawing above shows, the heat coming through the roof sheathing is reflected back into the airspace above it by the foil face. Then the air moving through the airspace carries the heat away.

But KLF was using the foil for light reflection, not heat. I would be concerned that the insulation boards would bow and let loose over time from the weight of the blown insulation they were supporting. They aren't really structural at all.

 

[AJP]

I'd go with foam ....everywhere.

Just finished my cottage on Lake Superior with "Pink" and based on my cousin's insight (he's in the business) if I were doing it again - I would use foam

 

[PAToyota]

If you do go with "solid" rigid foam, be sure to use expanding foam to seal alongside the foam boards next to the rafters so that you don't have a path for air to travel or you will get vapor/condensation issues.

 

[franklin40]

thanks for all the ideas. I think I will do the plywood on the walls. price isn't much different and you are right it is more durable which is nice, especially in the shop. I'll likely still do fiberglass in the walls and vapor barrier but the hard foam and sealer will be easier in the roof I think especially because I want the rafters open. do I need an air space above the hard foam in the roof if it is well sealed to the rafters? I have no soffit in the roof now anyways. my thinking is no because the spray in stuff would have no air space and is essentially he same think right?

 

[AJP]

this link is helpful ..
How to Insulate Cathedral Ceilings...Properly

I think if you are leaving the rafters exposed but want insulation against the roof - this offers some guidance

also why I still like the foam (not rigid) approach .... BUT must "declare" I have not actually used it myself. I'm still back at the Pink era although my basement forms where "SIP"

 

[BRUIN4]

Its INSIDE OUT!

I am sorry but you have it all wrong, not just you - the entire country. The insulation belongs on the OUTSIDE of the structure.

I have simplified it here but this is it.....

Most building scientists are just realizing that now, Canadians and Germans figured it out decades ago. Without going into a huge discussion on heat, vapor and air transmission and physics - simply put. installing all your control layers on the outside of the structure is the way to go in every climate.

Vapor control, thermal control and water control and air control properly placed outside of a structure will reduce the heating / cooling loads so dramatically that you wont believe it - OK not a very scientific answer but currently I am designing and building structures with no central cooling or heating plants in the northeast.

Think about it if you insulate on the outside you are doing two MAJOR things
1.Preventing the structure from heating up in the summer by keeping sun, heat outside
2. Preventing the structure from cooling off in the winter by using the thermal mass of the structure to hold the heat inside

Dont use a vapor barrier inside of a structure - long long discussion for another time.

We are moving towards UNVENTILATED compact insulated roofing systems (see SIPS panels) and right now I am installing 6" of polyiso on top of all roofs that I do or design - one owner saved 30% on his fuel bills the last two heating seasons without any other building mods. ( and before you ask we compare fuel consumption to Heating Degree Days ) so we know outside temps vs fuel usage

Its all about the air sealing and insulation. Polyisocyanurate rigid or XPS rigid sheets properly installed outside a structure works - also consider the garage FLOOR and if you are building new put at least 6" of XPS under the slab. This is a huge discussion but DO AN INTERNET SEARCH for insulated concrete forms and passivhaus and Energy recovery ventilator / heat recovery ventilator, SIPS panels.

Connect all the control layers together so the building is relatively airtight, air seal all penetrations window openings etc

Its a bit more to do it this way but its relatively easy. Attached here is a pic of what I mean - back ventilated wood cladding over polyiso that is used as the air control and water control layer - all joints taped and sealed. This place will never need to be repainted in 100 years.

 

[KLF]

I am sorry but you have it all wrong, not just you - the entire country. The insulation belongs on the OUTSIDE of the structure.

No argument here, but that's not practical for an existing structure, especially a garage that gets only occasional use in the winter.

As a professor in a Construction Technology program, I am a HUGE believer in some sort of foam on the OUTSIDE of the structure. Joe Lstiburek's "Cold Climate" book does a great job in explaining why it works so well. If I were building a NEW house, there is no question it would get 2" of XPS on the outside of the sheathing, taped, then strapping and siding. But, I can tell you that most contractors HATE putting foam on the outside... hell most of them hate doing ANYTHING different than what they've been doing for the last 30 years.

I also do a lot of work for Habitat for Humanity, and you wouldn't believe the fight I have to go thru on each project getting them to put foam on the outside. And, what makes it even crazier, we get the foam for FREE from Dow!

I'm hoping to attend a class this Fall on SIPs. I wanna learn how those things work.

But, it's not like you can retrofit an existing house. Believe me, I would if I could. Yes, it's possible, but it would be crazy expensive and I'd never get it back. My house has beveled ceder siding, and it's not like you can save it when you peel it off. Have you priced that stuff lately? All the doors and windows would have to come out, new jambs made inside, etc etc.

 

[cody c]

As a bit of a sidetrack to the two fella's who seem to know what they're talking about, what do you think about the foam/concrete blocks used to pour foundations for house construction? Ive heard from a couple people that if they did it again they would go all the way to the roof with it!

I like the idea of putting an air space between the siding and putting foam outside of the structure. I can see that if/when there is any condensation, that is the best place to let it breath. It seems to me that the biggest benefit of having poly under your drywall is to seal the insulation/dust out. I say that, as if there is any condensation, it will be trapped in your walls insulation at which point you'll have mold issues. I dont see that being the case with your vapour barrier outside of your insulation on the outside of foam.
This is just my perspective I dont have any formal training with this though.

I also like the idea of putting foam on the outer layer as you can gain some thermal mass that way, as your walls should carry a bit more heat. Which is kind of confusing about the concrete/styrofoam construction. Is the concrete part of the heat mass or not? It certainly isnt insulating. Why not have more insulation on the exterior and run your heating through a boiler or heat exchanger and then run glycol through lines in the concrete walls (maybe at the lowest part along each floor)? The heating of the house would be way more even than forced air and you could eliminate the ducting, which is kind of a pain for ceiling spaces etc.

What are your guys's thoughts, and a sorry for the sidetrack.

Edit: to the OP, your gonna lose most of your heat through the ceiling space, it may be difficult but if anything you should adress that first, and make sure there is a good airspace above it to prevent condensation. You may be fine to get the foam airspace channels, and then put fiberglass or roxul under it. If its 2x4 trusses and the insulation hangs too far below, I think you could suspend your poly below it, maybe with strips of wood along the truss to allow the insulation to sit below without tearing the staples through the poly.

As far as heating, a propane blower/heater works good enough to work in my little garage. Not hot, but warm enough to work under the cruiser in january, and fairly cost efficient.

If you have paint or batteries you store in there, Id suggest a metal paint cabinet and throw a small electric heater on the bottom shelf in it during the colder months.

 

[KLF]

As a bit of a sidetrack to the two fella's who seem to know what they're talking about, what do you think about the foam/concrete blocks used to pour foundations for house construction? Ive heard from a couple people that if they did it again they would go all the way to the roof with it!

These are called ICF construction (Insulated Concrete Forms). I have no direct experience with using it, although I did have a factory rep from Nudura (Insulated concrete forms | ICF | NUDURA USA and Canada) come to one of my classes once, very interesting. I might consider it for a foundation only, not the entire house though. Those things get kinda expensive. I think they apply well to commercial construction. There is a house not far from me that is 100% ICF construction, now that it's occupied for a couple of years I'd like to stop there and ask them how it's working out. One HUGE drawback is that even minor changes are a giant hassle, you have to jackhammer into the wall to do any electrical work. These are often heated with radiant floor systems.

The last house I worked on with Habitat (dedication this weekend), we used Thermomass walls for the foundation, which is a sandwich of concrete/foam/concrete. Very easy to setup the forms (we had a contractor do all this). I would probably use this system if I were building new. Make sure you also put foam UNDER the basement slab. Photo of the crew putting up the forms:

I like the idea of putting an air space between the siding and putting foam outside of the structure. I can see that if/when there is any condensation, that is the best place to let it breath.

This is called a "vented rain screen". We typically do this by putting strapping over the foam, with long (3") screws into the studs. Then you nail the siding to the strapping. You do need to make sure you put some sort of bug & critter screen at the bottom so they can't get up into the vented cavity. Very effective system, especially if you are using cedar or Hardie-Board siding.

You have to keep in mind that there is technically no such thing as a "vapor barrier". It is only a "vapor restriction". Even 6 mil poly has a permeability that water vapor can get through. And the other thing you should NEVER do is try to block moisture on BOTH sides of a wall cavity. Water vapor will eventually get in, then it can't get out, so it will start mold growth. Very bad thing!

I also like the idea of putting foam on the outer layer as you can gain some thermal mass that way, as your walls should carry a bit more heat. Which is kind of confusing about the concrete/styrofoam construction. Is the concrete part of the heat mass or not? It certainly isnt insulating.

In the Thermomass system, the concrete is there as a structural support and a durable outer layer. But concrete does have R-value, although very little.

If you have paint or batteries you store in there, Id suggest a metal paint cabinet and throw a small electric heater on the bottom shelf in it during the colder months.

I never store latex paint or rechargeable batteries in the garage during the winter. That's what basements are for.

 

[BRUIN4]

!! I know Joe Lstiburek well !!!??? , in fact Ill be seeing him next week for a few days up near Boston. I insulate existing structures from the inside all the time. Depending on your climate look into spraying closed cell or open cell foam, spray foam is not without its problems but a good spray foam applicator can make a big difference - that may be the best way out and will handle air control and thermal at the same BUT I love ridgid foam - polyiso - attached to the interior. If your ceiling is open then just screw it directly to furring strips on teh underside of the rafters and avoid all the cutting fitting and swearing

then tape all the seams and screw heads and your done - ( of course you may want to drywall it)

SIPS are Awesome - BUY Lstiburek's book on SIP's panel construction. The SIPS makers have come a long way in the past decade a 2000 sq ft house structure can be assembled in 2-3 days - on your foundation without finishes of course

 

[KLF]

LOL... Joe is kinda a "God" around here, a lot of what we teach is based on his writings and articles. I also read Fine Homebuilding a lot. Great magazine.

 

[BRUIN4]

I see you are in NH so of course you know Lstiburek and you must know Foard Panels. I have known Joe for years and I hope you have seen him speak and follow the info on his website...such a freekin strange small world.

Both Joe and John are great guys. I am a passivhaus builder - something they dont really have a big love for, but we are all on the same page.

I just built a garage ( for a clueless architect) it needed almost no heat or cooling - he refused to install an ERV! but his wife insisted on on installing a 24000 BTU split system...all they needed was a candle to heat the place and about 1000 btu of cooling - what a waste.


talk about short cycling!

 

[BRUIN4]

Sorry Cody...yes i love ICF's - (insulated concrete forms) - they are great, just like giant hollow leggo blocks made out of foam

One idea of mine is to use disposable coolers as ICF's - i see so many of these being thrown out - just check out a fish market, those styrofoam fish coolers all get thrown out! its more work but i bet you could use them as ICF's! and hey would be free

 

[KLF]

One idea of mine is to use disposable coolers as ICF's - i see so many of these being thrown out - just check out a fish market, those styrofoam fish coolers all get thrown out! its more work but i bet you could use them as ICF's! and hey would be free

Lol... Your idea reminds me of the guy I meet once that worked for a testing lab, he did all the concrete testing. He figured out how to get the test to pass but wouldn't actually break the cylinders. He started collecting them, taking them home, which his employer was fine with since cured concrete is expensive to get rid of. He ended up building a huge retaining wall out of them, then landscaped his whole yard with them, it was pretty cool.