Insulation and A/C

[HaroRider]

Hey all, just got a new A/C Mitsubishi mini split installed in a 22×30x12ish garage. Its a 24k unit and while it works, during the sunny part of the day it struggles. Hot and humid nights, it works quite well. Seems like sun is the killer.

I have almost zero insulation in the shop so Im not surprised.

I have three 9x9 bay doors that are fully insulated. No windows, and 1 man door.

I was messing with my temp gun during an 85 degree sunny day (78ish in the shop) I saw my ceiling at 115ish degrees, the cinder block walls were around 80ish. (3 bay doors were around 80) The bay doors take on most of the sun. Block walls are on sides and rear with less sun.

If I was to insulate only the ceiling would that dramatically lower the temp in the shop? Or would I need to insulate the walls? (I dont want to lose the space insulating them)

Also what R value would I use? I am in Long Island NY.

Id be happy to get around 68ish in summer days.

Heating the shop isnt much of a problem as I dont really like too much heat, I have maintained 60ish in the winter and am more than happy with that. (I have an electric heater to use as a booster)

Thanks, Tom

 

[Jim greengo]

You might as well insulate it all while you're doing it.

 

[brewchief]

What type of ceiling? Is it open trusses, trusses with a drywall or metal ceiling? Or something else?

Honestly the more insulation the better up to a point.

Ceiling is probably the place to focus on to start.

 

[HaroRider]

Open trusses.

 

[HaroRider]

You might as well insulate it all while you're doing it.

Definitely, the issue is I dont want to lose the space. If I can be "happy" with the temperature. I rather that over losing more space.

 

[Dig Doug]

Definitely, the issue is I dont want to lose the space. If I can be "happy" with the temperature. I rather that over losing more space.

a few ideas -


Insulate the ceiling. Then see how the AC does. This will also help in winter

insulate the garage door also help in winter

add a ceiling fan or 2 to move / circulate some air - move the warmer air down and cooler air up (hot air rises, cold air settles) turn on the fan in the morning and let it go all day. Winter time reverse the fan direction and pull the warmer air down

add an exhaust fan ( like a Gable End fan ) on a temperature sensor to **** out the hot warmer air at the ceiling

if you work in the shop every day or for several days in a row - let the AC run to cool maintain in the mornings and evenings, set the thermostat !
it takes more energy to cool a space than it is to maintain a temperature

 

[HaroRider]

Thanks, I thought that an exhaust fan shouldn't be put in a conditioned space. Am I wrong thinking that?

I may try the fan idea, my ceilings are 10' to the cinder block but maybe 15' to the pitch (obviously very hot up there in summer)

I dont keep it conditioned 24/7 mostly weekends. Friday night I turn it on by Sat AM its pretty cool. But the temperature in the shop slowly rises during the day time. I could start Sat AM at 67 degrees and by 3:00 PM it could be 78 in the shop.

 

[racecougar]

Thanks, I thought that an exhaust fan shouldn't be put in a conditioned space. Am I wrong thinking that?

You're not incorrect. Either seal the building and condition the space or open it up and create a breeze. It doesn't make sense to expel your conditioned air and draw in unconditioned air.

As far as your situation is concerned, insulating the ceiling should make a very notable improvement. Is the roof vented?

 

[HaroRider]

No, roof is not vented.

 

[racecougar]

Would the plan be to install and insulate a ceiling and add roof venting or do a hot-roof style insulation install?

 

[HaroRider]

To be honest I never thought about it. (Hence why Im here)

Up in the "rafters" its storage, its hot up there and I see no use in conditioning the space. However, it would be a bit more work to sheetrock it off.

I've attached pictures of what Im working with.

 

[racecougar]

Ah, you have a hip roof, not trusses. Is there any soffit to speak of outside? Assuming not, the hot roof path is likely the path of least resistance here. If you were to install a ceiling, you'd end up with an unventilated attic, which can trap heat and moisture and become a real mess.

 

[dcg9381]

The path of least resistance is spray foaming that roof deck. No soffit or ridge vent. The whole thing becomes conditioned space.
It's also the fastest option. And the most expensive option per R value.

 

[racecougar]

Yep.

 

[billconner]

If you foam it, most codes would say you can't leave the foam exposed to the occupied space. There may be some that claim otherwise but make sure your local authority agrees.

 

[HaroRider]

Ok thanks, so spray foam and leave it open is the best bet?

I mean, I could put in an "attic" fan and close it off but it would probably be the more costly option. However less conditioned space, easier job for the A/C. Better results?

Why would I need to cover the spray foam? Its a detached 3 car, just curious? Fire reasons?

 

[crguy]

I would put an insulated sheetrock ceiling up, and put in some roof vents.

 

[HaroRider]

I dont have a ridge vent but it does have a small soffit.

The sun is the killer, today is very humid but a bit more cloudy and the A/C isn't bad, even with no insulation.

 

[billconner]

Ignoring for a moment using the space above the ceiling joists for anything, absolutely the simplest and least expensive approach is drywall or metal liner panel ceiling, blown in cellulose, eave vents, and some sort of higher vent. Put in a vapor barrier and keep the vents around 60% low and 40% high with 1/300th of the area of the ceiling.

But I appreciate your desire to maintain attic area for storage.

 

[HaroRider]

Please forgive my ignorance, eave vents are non mechanical vents?

Im guessing blown in insulation is much cheaper than spray foam? However making the space unusable?

I have a 3 car garage, however this is GJ and we know its never big enough (no pun intended) Thus, putting lesser used items up top is honestly a God send for me.

This is a bit of a situation for me to think about.

 

[HaroRider]

I have tool boxes, compressor and tons of stuff in here. How worried do I need to get about when getting the garage spray foamed? The cars can easily be removed, but the rest not so much.

If I pink stuff it, it would be cheaper. But possibly less efficient?

 

[billconner]

Eave vents - hole saw and


is easy. And blown in cellulose is way less dollars than spray foam. But I appreciate the storage. I'd price a storage shed or lean to addition + ceiling and blow in, etc. and see if it's not less than spray foam. It would be better storage.

 

[HaroRider]

Unfortunately, I can not touch/extend this garage since it is grandfathered in. (Doesn't meet modern day property setbacks) If its damaged, it has to be put back exactly the same. Spray foam/batt is my only option if I want to keep the space up top.

 

[thammel]

You need to insulate. My 28x32 is heavily insulated (and so are the doors) and my 18k btu minisplit has no problem whatsoever.

 

[theoldwizard1]

If I was to insulate only the ceiling would that dramatically lower the temp in the shop? Or would I need to insulate the walls? (I dont want to lose the space insulating them)

Yes !

Also what R value would I use? I am in Long Island NY.

As much as you can practically install and/or afford ! 6" minimum. 12" better.

If you have a South facing wall, do that second. 3"-4" acceptable.

 

[Copymutt]

I just hooked up the swamp cooler in the garage today. Coinkidink, I used my handheld to see wall & ceiling temps. It was 96 outside. The exterior wall temp in direct sun exceed 135* All interior walls were 84* as was the ceiling except for the SW area of the ceiling @ 92* I have a mix of R-13 & R 26 in the ceiling due to plywood on the joists for part of it. So it made no difference in the R value. The difference was due to strong sun exposure on the 2 sides for that hot corner. I’m not intending to add R value to attic walls or roof as the swamper is cheap to run & unlike NY humidity we’re @ single digits so it chills very well.

 

[billconner]

Unfortunately, I can not touch/extend this garage since it is grandfathered in. (Doesn't meet modern day property setbacks) If its damaged, it has to be put back exactly the same. Spray foam/batt is my only option if I want to keep the space up top.

So if you can't live without the storage spray foam - closed cell - seems to be answer. Too hard to get a really good air vapor barrier - critical to a "hot roof" - with batts.

 

[racecougar]

So if you can't live without the storage spray foam - closed cell - seems to be answer. Too hard to get a really good air vapor barrier - critical to a "hot roof" - with batts.

Agreed.

I have tool boxes, compressor and tons of stuff in here. How worried do I need to get about when getting the garage spray foamed? The cars can easily be removed, but the rest not so much.

I would pull everything out, but if that isn't possible, cover it all very well.

Im guessing blown in insulation is much cheaper than spray foam? However making the space unusable?

Yes.

Why would I need to cover the spray foam? Fire reasons?

Bingo.

 

[billconner]

Is there an option to do a raised ceiling in center and low - under ceiling joists - around perimeter - say 4'? Just a possible - with a little fussiness in framing raised ceiling - but allows venting roof deck and mostly blow in insulation, some batts in vertical between ceiling planes.

Easiest and most expensive, spray foam and try to get a spray coating approved for fire code or hard cover. I believe even ply or OSB covering meets code. (With a ready supply of rough sawn pine around me, I'd use that - cheaper than all but thinner OSB - and looks and smells good.)

 

[dcg9381]

Ok thanks, so spray foam and leave it open is the best bet?

IMHO, there is no real reason to enclose it if you don't have to.

I mean, I could put in an "attic" fan and close it off but it would probably be the more costly option. However less conditioned space, easier job for the A/C. Better results?

If you're using a ductless system with an air handler that's not in the attic, maybe decreasing the "volume" of the garage is better.. Decent idea. Attic space needs to be vented though.

Why would I need to cover the spray foam? Its a detached 3 car, just curious? Fire reasons?

Some areas require a "fire break" (drywall). If that's required the other work arounds are a spray on coating to make the foam compliant or using "fire rated" (typically closed cell) foam. We've had no issues leaving it exposed as it's not habitable space, but YMMV.

Reality is that you have to get spray foam pretty darn hot before it sustains ignition. Don't believe the "spray foam in a can" tests. Not the same stuff.

 

[TxSteve]

Spray foam.

For comparison - I built a barn last year here in north central Texas. All metal with 2" of closed cell on all walls and under the roof. The roof is painted white which I did on purpose for the heat mitigation. All doors and windows are insulated/double pane.

Yesterday was 96 and sunny. Laser thermometer showed 80 for the ceiling temp at 4:30.

Building is 40x50 with two 24k mini splits. Temp stays a comfortable 75-76 so far.

I'd not put in ceiling fans. Conditioned air naturally stratifies - cold air at the floor. Hot air at the ceiling. Put a box fan on the ground if you need air movement.

Talk to the installers. Talk about protecting the items in the building. They should cover everything.

 

[billconner]

as it's not habitable space,

Why is it conditioned if not habitable? I think I'd have a hard time convincing my building department - 1 person rural area - it's not habitable.

A lot of this depends on whether you want to or have to comply with building and fire codes. The IRC - likely what applies - requires foam plastic to be separated from the interior of a building - with some exceptions (your situation doesn't seem to allow) and allowances if the material passes certain tests (NFPA, FM, UL).

Not supposed to leave paper faced batts uncovered but lots do.

Just want you to be informed. For the single reason I think uncovered spray foam looks like $hit, I wouldn't want to work in a room with it
over me.

 

[TxSteve]

"habitable" is defined as a "space in a building used for living, sleeping, eating, or cooking"

garages, attics, crawlspaces, bathrooms, closets, porches, workshops, etc are not considered habitable space unless you've really angered the inspector.

 

[HaroRider]

Is there any worry about rotting the wood if I spray foam. I've read some horror stories, is this a real concern?

What do I need to look out for?

 

[dcg9381]

Why is it conditioned if not habitable? I think I'd have a hard time convincing my building department - 1 person rural area - it's not habitable.

Fair question. So insulate it first and air condition it later. It's going to depend on your local authority. Around here I don't need permits do my own insulation and air conditioning, but again, YMMV.

It's an interesting question, we had a thread on some authority that wouldn't allow a garage door being installed as ingres/egress to a home interior, but bars/restaurants do that all the time. I say a garage door does not make it a garage. And an air conditioner doesn't make it a house interior, but I'm not in charge...

Just want you to be informed. For the single reason I think uncovered spray foam looks like $hit, I wouldn't want to work in a room with it
over me.

I agree it could look nicer, but for what the amount of labor and materials required, I leave most of the shop open. You can paint it, but I've never gone that far either.

 

[billconner]

"habitable" is defined as a "space in a building used for living, sleeping, eating, or cooking"

garages, attics, crawlspaces, bathrooms, closets, porches, workshops, etc are not considered habitable space unless you've really angered the inspector.

If it's a shop or work space, than it's for "living", therefore habitable, even if labeled a garage.

 

[HaroRider]

Is there any worry of spray foam and wood rotting?

 

[bluedog225]

Ignoring for a moment using the space above the ceiling joists for anything, absolutely the simplest and least expensive approach is drywall or metal liner panel ceiling, blown in cellulose, eave vents, and some sort of higher vent. Put in a vapor barrier and keep the vents around 60% low and 40% high with 1/300th of the area of the ceiling.

But I appreciate your desire to maintain attic area for storage.

This is the 100 year solution. 100% reliable and pretty cheap.

 

[bluedog225]

Is there any worry of spray foam and wood rotting?

Yes

 

[billconner]

Yes

I think I'm with bluedog on this. Hard to imagine a perfect spray job that assures no interior air will reach sheathing anyplace and not condense. And if you do achieve perfection, you also have to be sure there is no leak letting rain in to sheathing. In either case, it won't dry. And the prospect of stripping roofing, sheathing, and foam is daunting. Now you may get by for 10 or even 20 years, if you're lucky.

All IMHO.