Detached Unconditioned Garage--Insulation

[archy]

I am working on the design for a detached, unconditioned garage in a hot and humid environment (Zone 2). I was planning to insulate with spray foam, or at least batt insulation. I'm getting conflicting information on whether that is a good idea since it won't be air conditioned. This is what I am considering:

Vented Attic with Radiant Barrier
Closed cell spray foam insulation R-13 in walls and R-38 at attic floor. (I've also heard of doing 1" closed cell for air barrier at attic floor and then open cell or other kind of insulation on top of that.)

Is it a good idea to have it completely air sealed at walls and attic floor? Or will that not matter? Is spray foam too expensive for what I'm getting out of it?

Thanks.

 

[kj_mustang]

If you spray foam seal the interior, then there is no moisture transfer possible. Humidity levels inside will increase as you allow outside air in with each door opening. If you plan on just having windows open to help cool it, then it will be humid inside anyway.

 

[alxmlr789]

As far as my understanding of spray foam, is that when you seal the space, it needs to be conditioned or at least dehumidified.

 

[archy]

Oh, I see your point. There is nothing to dehumidify the space. Duh. There will be only one 3'x3' operable window.

So then should I use an unfaced batt insulation? Or no insulation? I plan to use Tyvec housewrap on the sheathing, which my understanding is breathable.

 

[kj_mustang]

If you never plan on conditioning the interior space, I would insulate with unfaced bats at the ceiling and walls and have a vented attic space. The insulation will help keep it cooler in that Texas heat.

 

[QwikKotaTx]

Asking here to avoid a new thread.

My garage is completely unfinished and I currently have a large blower attached to a roof vent. It keeps the garage about 3° hotter than outside. With it closed it pulls air in through the soffit vents and a small amount from around the garage door.

It's a lot better than what it was but will adding insulation to the ceiling make any real difference? The ceiling would be closed off from the attic area using plywood decking and insulation batts underneath, faced to keep them from falling apart. The fan would still pull in air from the soffits but the insulation cost would be at least $500 for R30 plus my time to install all of those items. Is it a waste of time and money?

 

[sweetk30]

the heat pushes down threw if there is no way to slow it down . my house garage is not insulated and by mid day is a hot box from hell . my shop outback is insulated walls and celing and if i keep the doors shut its great till late day early evening most of the time .

 

[b-boy]

My pole barn is insulated (R21 walls/R38 ceiling), and I'd say there is a 10F-20F difference between inside and outside temps on a hot day. Before I had insulation, I couldn't even stand to be in the barn in July/August.

 

[The Cobbler]

insulation definitely keeps the interior space cooler in summer, warmer in winter

 

[QwikKotaTx]

Thanks for the insight. I will keep an eye out for leftovers and try to cheaply insulate my garage. Definitely a winter project in Houston.

 

[Falcon67]

Having lived in Houston - good luck. On those 95F 85% RH or worse days, You're not going to get much relief without air movement or conditioning. I would try to keep as much air out of the wall cavities as possible because condensation will soak everything. I would talk to some local people about what works best. Or anyone along the coast - Baytown, NOLA, etc. It's all the same misery in the summer (that barely ever ends).

 

[QwikKotaTx]

Having lived in Houston - good luck. On those 95F 85% RH or worse days, You're not going to get much relief without air movement or conditioning. I would try to keep as much air out of the wall cavities as possible because condensation will soak everything. I would talk to some local people about what works best. Or anyone along the coast - Baytown, NOLA, etc. It's all the same misery in the summer (that barely ever ends).

Yeah, I am in Seabrook so crazy humidity. My friend said his Dad did very thick and complete insulation and was able to make his garage comfortable with a window unit which I have so I may go that route. Don't want my power bill to go up like crazy though. Mainly trying to justify spending $1k on batts not to mention my time and dealing with fiberglass.

 

[dcg9381]

Generally, they spray foam the roof deck, not the attic floor and don't install roof vents or soffit vents.

I assume you can't throw a ductless system in that thing?

I have a foam insulated steel building in Texas. You're building a refrigerator with no interior cooling system, which doesn't make a lot of sense. If you're not going to HVAC it, you could have a fan pull/push cool air in at night and shut it down as the day starts. You'll have to deal with the humidity.

There are lots of non-HVAC'd "shops" in Texas - I'm certainly aware of many of them at small airports.... The insulation certainly helps moderate the extreme weather, but after 25+ days of 100+ in Texas - it's going to get warm in there eventually.

 

[DC73]

It's a lot better than what it was but will adding insulation to the ceiling make any real difference?

Yes it will. If you could insulate the walls, that would help as well. We've had a week or so of over 100 degree temperatures. The maximum temp in my detached workshop on those days was 85 degrees. It's well insulated in both the ceiling and walls and I haven't ran the AC out there this week.

A fairly well insulated space without AC tends to settle somewhere around the average daily outdoor temperature if there are no heat sources inside.

My attached garage has attic insulation but the two exterior walls have none (the other two walls are common with the house and do have insulation). This garage stays cooler than the outdoor maximum temperature for the day until I park a vehicle with a hot engine inside. Then, the ceiling insulation holds the heat inside the garage.

Powered attic fans tend to use more energy than they save in air conditioning costs. That doesn't impact you since your garage doesn't have AC but once you get enough insulation in the ceiling, I doubt you'll notice much difference when the fan runs vs when it doesn't so you can probably turn it off and save some electricity costs.

DC

 

[QwikKotaTx]

Yes it will. If you could insulate the walls, that would help as well. We've had a week or so of over 100 degree temperatures. The maximum temp in my detached workshop on those days was 85 degrees. It's well insulated in both the ceiling and walls and I haven't ran the AC out there this week.



A fairly well insulated space without AC tends to settle somewhere around the average daily outdoor temperature if there are no heat sources inside.



My attached garage has attic insulation but the two exterior walls have none (the other two walls are common with the house and do have insulation). This garage stays cooler than the outdoor maximum temperature for the day until I park a vehicle with a hot engine inside. Then, the ceiling insulation holds the heat inside the garage.



Powered attic fans tend to use more energy than they save in air conditioning costs. That doesn't impact you since your garage doesn't have AC but once you get enough insulation in the ceiling, I doubt you'll notice much difference when the fan runs vs when it doesn't so you can probably turn it off and save some electricity costs.



DC

Thats good to hear on the insulation. I think I will persue finishing out my garage with R30 and OSB. I have a small window unit that I can fool with. Will try to use leftover jobsite materials if possible to save some coin.

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[QwikKotaTx]

Generally, they spray foam the roof deck, not the attic floor and don't install roof vents or soffit vents.

I assume you can't throw a ductless system in that thing?

I have a foam insulated steel building in Texas. You're building a refrigerator with no interior cooling system, which doesn't make a lot of sense. If you're not going to HVAC it, you could have a fan pull/push cool air in at night and shut it down as the day starts. You'll have to deal with the humidity.

There are lots of non-HVAC'd "shops" in Texas - I'm certainly aware of many of them at small airports.... The insulation certainly helps moderate the extreme weather, but after 25+ days of 100+ in Texas - it's going to get warm in there eventually.

Dont get me started on Houston shops. One July I worked in a South Houston warehouse INSIDE an enclosed pressure vessel with no a/c. It only had a top hatch and we were welding and grinding in there. OSHA field day. Crazy hot.

My thoughts on the attic fan are that it will drop the temp in the air space above the insulated surface a few degrees by pulling air in through the soffits. It will be on a thermostat.

Going to insulate garage door first as it is cheap and easy and gets several hours of full sun facing west.

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[sweetk30]

when i had my shop spray foamed they hit all 3 of my garage doors for 300 bucks extra total . 2-8x8 and 1-10x10 . cheeper and better than gluing on foam boards i think .

he told me a cool trick . skim off the panels high foam level with the door . go get a roll of coil trim as its the same with as door panels . secure the door springs and take tension off . then vise grip each panel so it wont fall off the door track . undo the hinges and cut the trim coil to length . lay it over and reinstall the hinges and ad a few extra self tap screws and bam your door is covered .

 

[dcg9381]

when i had my shop spray foamed they hit all 3 of my garage doors for 300 bucks extra total . 2-8x8 and 1-10x10 . cheeper and better than gluing on foam boards i think .

I'd like to see photos.. About to pay for $$ insulated doors in a residence. This might be a better option.

 

[sweetk30]

its just my work shop so no aluminum coil trim on them yet . . .

but this was the after job . 90% is flush or over height and needs trimmed down . the few low spots are still thick . it took longer for them to setup than to spray the doors . overspray pops right off with wire brush in hand . and the big door down low thats just dirty on the bottom from shop use . the foam holds up well with my shop facing the west and these 2 doors get full sun over 1/2 the day .

 

[MFolks]

Read up on the pros and cons of spray foam,I've read about lawsuits now making people sick who had their home sprayed,and are looking for compensation now. Formaldehyde outgassing was one chemical,probably others......

 

[DC73]

Read up on the pros and cons of spray foam,I've read about lawsuits now making people sick who had their home sprayed,and are looking for compensation now. Formaldehyde outgassing was one chemical,probably others......

Most of the outgassing problems and lawsuits were during the early years of spray foam and were primarily due to installer error. Find a good installer and there shouldn't be any issues. The spray foams are a two part foam that has to be properly mixed and sprayed at the correct temperature. If the installer doesn't get a complete and correct mix of the A part and the B part, and/or chooses to spray when the temperature is not ideal, the foam does not cure properly and that's when the outgassing occurs. It's not a trivial matter if it doesn't cure. It is difficult to remove and make right. I would never try to spray the foam myself and I wouldn't use just anyone. Pay a little more if you have to but make sure you have a good installer.

DC

 

[QwikKotaTx]

I would be worried about the weight of the spray foam and how the electric opener reacted.

 

[sweetk30]

about a half a wind more on my doors coils i did my self after and there good for a few years now and no real difference in the way they open / close by hand .

 

[dcg9381]

I would be worried about the weight of the spray foam and how the electric opener reacted.

I'm not sure that a few inches of (open cell) foam really adds much weight... Stuff is really light.