Insulating concrete block garage

4cylndrfury's post got me thinking this might be a place to turn to for advice. I've been trying to work out how to seal up and insulate my garage. It's a block garage, 22' x 30', built in the late 70's. It's got jalousie windows (the slat glass kind) that are obviously energy sinks, but beyond that the block and the few gaps in it are poor insulators as well. It's in good shape but block always has a few cracks and it's, what, R 0.5 on a good day anyway. The wiring is run in EMT conduit on the surface of the walls and the boxes are surface mounted. I want to both stop drafts and add R-value to the walls. I've got a huge moisture problem, and in the last year already killed one little dehumidifier. (The compressor would shut off maybe once a day for a few minutes. poor thing.) I would prefer to keep the block bare on the outside because it's got a nice coat of Boston ivy (the non-block-destructive kind) that looks good and provides sun shading in the summer. There are a couple big trees shading it overhead.

What is the best way to insulate a garage like this?

Whatever insulation method, I know the windows need replaced.

The best option I've come up with so far is to use foam board insulation, adhered to the block on the inside. Build the insulation up the 1.5" - 2" that the electrical boxes are deep. I could have wood strips every 16" to attach drywall (or drywall-like moisture resistant material) or adhere it directly to the foam using a spreadable adhesive. The former option reduces the effectiveness of the insulation, the latter runs the risk of adhesive letting go down the road. Is this crazy?

I wouldn't be able to do much insulating outside the garage because the roof overhangs are pretty small. I would only be able to go out enough for a single 1/4" or so layer plus siding before it became a problem.

Any advice? Am I missing something?

some insulating companies can pump an expanding foam into the walls, don't know if this is available in your area. Your moisture problem may be caused by the ivy growing on the walls holding moisture and allowing it to wick through the blocks. If you can see into the wall cavity you could pour a loose insulation into the cores.

Is the moisture issue simply condensation, or is it water leaking in from outside? If it's a leak, that has to be fixed before you put anything on the walls.

As for insulation, you need to insulate the ceiling as well - what kind of construction is overhead?

What about in the block itself, could you spray foam in there? No idea if it's a good idea or not.

You need to solve your moisture problem before you worry about warmth. Paint the interior of the blocks with a water inhibitor before you tack anything to the blocks or you'll just provide mold with a place to hang out.

If you really want warmth you'll likely need to give up some space in the garage. Hard foam insulation still has a pretty low R value so if you want to get serious you'll need to build the wall out for fiberglass insulation.

Until then get some spray expanding foam and seal any cracks, holes or crevices.

This article describes a method of using rigid foam to insulate block walls (I have the hard-copy issue):

http://www.finewoodworking.com/Workshop/WorkshopPDF.aspx?id=33746

You can get outlet box extensions to bring the receptacles out to the new wall surface.

But I agree you definitely need to diagnose and fix the moisture issue first.

When finishing my parents basement we covered the walls with thick poly sheeting for a moisture barrier, bolted 2x4 uprights to the wall, hung exterior wall insulation between the uprights, then hung drywall over that. It was effective, but not particularly cheap.

Spray foam insulation will solve all your issues. Would be interested in why the humidity is so high?

nderwater wrote: When finishing my parents basement we covered the walls with thick poly sheeting for a moisture barrier, bolted 2x4 uprights to the wall, hung exterior wall insulation between the uprights, then hung drywall over that. It was effective, but not particularly cheap.

+1 You will absolutely need a vapor barrier. Fasten 2x4s , using toggle bolts, and then fiberglass insulation. Fiberglass R value is a lot higher than rigid foam and costs a lot less. Drywall's O.K., but plywood is better, even if its thin. A can of spray foam to seal up around the receptacles and the framing for different windows, and you'll be able to heat it easily.

Foam board generally has a higher R-value than fiberglass batt: http://www.intechinsulation.com/rvalue_chart.html

Agree on the vapor barrier. Don't even bother with a habitable building if you don't have one.

Now, I may be spending too much time on those building shows. But I remember an episode where the house used a 10" thick monolithic poured concrete wall system. They placed the insulation on the OUTSIDE, to take advantage of the thermal mass the concrete structure allows. Now I know in this case the blocks are empty, but still, touch a block wall after the sun has been shining on it. How long does it retain that heat, hours after the sun is gone? There's still enough thermal mass there to take advantage of. It may help you maintain a constant temperature in there.

Hey, thanks for all the tips!

The moisture problem is just condensation, not actual leaks. I believe it's because of the shaded location (trees overhead, ivy on the walls) combined with the thermal mass of the concrete. It stays cool in there, and cool air holds less moisture, so it is just kind of damp. NOT condensing on all available surfaces kind of damp, just damp enough that tools want to rust and some unpainted particle board stored in it got mildewy.

I agree that I need a vapor barrier. I was thinking that the rigid foam board could be a vapor barrier, especially if the joints overlap. Say I do two layers, 1" each, staggering the joints both vertically and horizontally. Would that be a vapor barrier?

Failing that, I could wrap the garage in Tyvek and put vinyl siding on it.. but I really like the look of the block and ivy. My back yard is kind of an oasis with a pond and trees and shrubs, the ivy really helps make it look nice.

The roof is stick truss with R19 fiberglass between the trusses. I think it would help to drywall and insulate at the ceiling level instead of roof level but I use the truss space for storage shelving so I would lose a ton of storage in doing so.

I also agree that insulating outside the block would be awesome but the roof would have to be replaced to do that due to the small overhangs. I couldn't add 2" of insulation plus siding and have sufficient overhangs left. The roof is in very good shape and not very old.

Rigid foam board is R-5 per inch, so 2" of foam is R10, about the same as 4" of fiberglass.

Very true about a mass of concrete holding best. We know a guy who heats his shop with waste oil. One time the middle of winter, the heat went out. The slab that serves as the first floor ceiling and second floor main shop held heat so long he figured it was out for half a week before he noticed the heat was off.

Use 1-1/2" rigid foam insulation on the inside. Use 1-1/2" galvanized light gage metal Z furring. You can nailgun this directly into the block after painting the inside elastomeric block sealer. That gives you just the depth you need for junction boxes, etc. Run the furring and foam board vertically and the drywall horizontally. That way you can use impact-resistant drywall at the bottom 4 feet. Put the vapor barrier over the insulation and furring, under the drywall. Tape the seams.

Good luck!

I have nothing to suggest, but threads like this make my heart all warm and fuzzy for this forum.

DaveEstey wrote: Hard foam insulation still has a pretty low R value so if you want to get serious you'll need to build the wall out for fiberglass insulation.

This is incorrect. Rigid foam insulation has a much higher R value per inch than fiberglass batts.

If you're not gonna replace the windows, don't bother insulating. Your infiltration around the jalousie windows is so huge that you will not make up for the loss with a little bit of insulation. Think of it like insulating the ceiling of a room with no walls.

Insulate the block cores: bad idea. The webs of each of the blocks will make a thermal bridge from the cold outer face to the could inner face. Waste of money.

Insulate exterior: bad idea. It can be done well, but in your case the return will not be worth it.

Vapor barrier: important, but plastic is not gonna work for you. Total waste of time, and it may even trap moisture in the wall, deteriorating the framing more rapidly.

You gotta KNOW where the water is coming from. If it is a leak from outside, sealing the inside will not help. If it is condensation from heating the inside, good insulation can help.

Insulate interior: best idea. Now, with what...

Fiberglass: inexpensive to install, but minimal return. It needs a cavity to fill, which means it needs a frame. With your moisture problem, any type of framing could be subject to rot.

Rigid foam panel (your idea): excellent bang for the buck. Yes, it can act as a moisture barrier, but your gonna have to be careful about sealing all the joints, the top and the bottom. Stagger the laps and tape the joints in each layer. No nails or screws. Glue it all together.

The BEST system will be commercially sprayed medium density closed cell insulation. It will seal everything, act as a vapor barrier, give the highest R-value and the best performance. But it will be costly.

But you gotta plan to do the windows or anything else is a waste.

Take down the Ivy, paint the outside of your shop twice,replace the windows, insulate the ceiling.

I had forgotten you said jalousies. Yeah, the definitely need to go, even if you just put cheap all-vinyl replacement double-hungs.

I'm definitely planning on replacing the windows.

The outside of the block is painted, but I don't know what they used to paint it as it was before I moved here.

More later as I figure things out!