Condensation

[ezridr60]

I have a garage that is built in to a hillside. Condensation forms on the walls and I've been mulling over several ways to approach this. It would seem some sort of insulation is necessary on the walls. (Walls are concrete). What I was contemplating doing was putting a studded wall (treated 2X4's) up with foamboard insulation between the studs. Not sure if I should put some sort of a vapor barrier up before I applied drywall. Tyvek? Visqueen? I have already applied a coating on the walls to prevent water from getting in from outside, that is not the problem, nor was it ever. I did install a ceiling fan and keeping the air moving has helped tremendously. But it needs the insulation I think.

 

[yeldogt]

You have to eliminate the humidity -- and be absolutely sure you are not getting any water or moisture through the wall... even a small amount will cause problems.

Any insulation has to be thick enough to keep the inside surface above the dew point.

Plastic vapor barriers under drywall are nothing but trouble -- unless the wall can dry to the outside ... and yours obviously can not. Housewrap is water vapor permeable.

I have a space like yours and it requires a dehumidifier to keep the air humidity low enough so I don't have an issue ...

once the surrounding air is dry ....you will be able to dry out and confirm that the concrete wall has no moisture issues ... then the wall can be insulated as you would a basement... lots of possibilities.

You don't need as much insulation with buried walls as the ground provides a buffer.

 

[Chris705]

A couple of thoughts...the summer air in your garage is very humid and the cool concrete/masonry walls allow that humid air to condense on them....I have learned thru the years to keep my basement windows closed and de-humidifier running full time in the summer months. In your case it would probably be difficult to keep the air out with OH doors and such. So your thought about insulating the cool masonry walls is on track. I would suggest however a slightly different approach and that is to line your walls with a continuous layer of 2" rigid or something similar in thickness to prevent the moist air from ever getting the walls. They sell "Z" furring strips that you could run horizontally along with 2" rigid would allow you to fasten a covering of some sort on the face. And if you do you poly over the z strip and under your covering you would further prevent the moist air from getting to the cold walls and condensing. That is what you are trying to accomplish. The KEY is stop any air from getting thru what you construct to keep if away from the colder surface. So you have to be diligent about that or then you will eventually have possible rot/mold issues in places you can't see. The z strips fasten to the wall with masonry screws or powder fasteners and you lay the insulation and z strips up as you go....the other option would be to put 2x4's on the flat over the insulation. I would encourage you to tape the insul. joints if you proceed this way. And seal the lower sill plate with caulk or mastic to keep air from sneaking in underneath. Also sealing and returning insulation at the top of the wall to prevent air from getting in behind the insulation at the top would be required. Not sure how high grade is outside?

Good Luck!

 

[pattenp]

Chris705 has laid out the best solution.

 

[yeldogt]

If you are getting condensation and no water is leaking you are north of 70 RH

The only way to make this work with drywall without conditioning the space is to use spray foam -- no matter what you do .... some moisture will get in and around the sheet foam. And even at 70 RH you will have problems with drywall without lowering it.

The "z" strips with foam will work for insulation -- but you will still need to manage the humidity if you want to cover it with drywall.

I live in a valley -- everyone around me has had to devise a plan. Do it correctly or you will be ripping it out.

 

[ezridr60]

Sounds like there's a dehumidifier in my future. I'll check out the "Z" strips. I was thinking of 2" foam board, think that will provide enough insulation? Spray in is not an option, at least not here in the wilds of the U.P. The garage does have a heater in it, but I don't run it unless I plan on working out there. With the cost of LP it would be prohibitive to try and maintain any kind of temperature in the 50° range with outside temps -25° or colder. And thanks!

 

[yeldogt]

Around my way it would be -- but we don't get as cold as you. The problem with concrete is that it can hold a lot of moisture ... did you coat the inside of the concrete?


I'm propane also

 

[ezridr60]

Around my way it would be -- but we don't get as cold as you. The problem with concrete is that it can hold a lot of moisture ... did you coat the inside of the concrete?


I'm propane also

We did coat all exposed concrete with Muralo Acrylic Concrete Waterproof stuff. I say stuff cause it ain't paint, you almost had to trowel the stuff on and then brush into cracks and crevices with a stiff brush. And if cost is any indicator of performance, well let's just say the next time it rains for forty days and forty nights, this garage will be dry!

 

[sands35]

Another option not yet mentioned (I think), is to excavate and put insulation against the wall from the outside. That will keep the block warmer and avoid condensation that way.

EPS sheet is not *quite* as good as XPS - but is 1/2 the price. If there is no traffic and you protect any exposed EPS with some roll flashing, it will work fine.

Not sure if you want to take this on, but you can rent a mini-excavator for ~$300 a day and probably have it cleared out in a day, insulated and back-filled on day 2. It would also provide an opportunity to re-do the footer drains if needed.

 

[yeldogt]

ezridr60; did not want to sound like I did not believe you waterproofed!

We are up along the Delaware River -- so we can have humid cold days. The best way to proceed it to seal up the space and then run a dehumidifier -- see how much it will take to lower the RH - then after everything is dry ... it is easy to test the walls and floors for moisture. Do this before insulating.

Also most of the homeowner based dehumidifiers don't work in cool shops -- I have a Santa Fe unit ... not cheap .. but really works and runs efficiently .. my power is very $$ over .18 KW

 

[bochnak]

I've used PL300 adhesive on foamboard with good results. I used the special tape for joints.