Moisture on insulation
 

About a month or so ago I had built an addition onto our house. It is sitting on a concrete grade beam on 20ft piles. I poked by head in the crawl space today and I noticed a fair amount of moisture on the insulation that is in the floor joist cavities. The moisture is generally around the edge of the addition close to the outside walls. The vapour barrier is between the insulation and the subfloor.

I am guessing I am having some condensation issues as I live in Canada. To resolve the issue I am thinking of laying down some additional vapour barrier just on the ground and tacking it up along the grade beam walls.

Any other suggestions?

I would insulate the out side walls of the crawl space real good, plug off the out side vents for the winter time. Put good vapour barrier on the ground, Then take out the insulation that is in the floor before you lose your floor joist. Paul

If the insulation has already gotten wet, I would consider removing it if you haven't already. Beautiful spot for mold to start growing.

I hate to dissagree with Paul but you need air behind insulation, cross venting under the insulation in most parts of Canada is code. And yes dry out the insulation or repace it.

Improperly vented?

Conditioned air getting down there somehow?

Moisture on insulation
 

Let me see if i can understand this,( cross venting under the insulation in most parts of Canada is code) So to cross vent through the crawl space under the insulation, this air would come from outside? So he will be bringing in 20degrees
below zero air at times to vent his crawl space? Sure hope his pump and water lines aren't down there.
In Mi. we put 2" foam on block walls in the crawl space, plug off vents in the winter so the pump and water lines don't freeze. put plastic on the ground to stop moisture. No insulation in floor. Paul

Paul: That's a fair arguement except, it is winter and the insulation is wet!

Moisture on insulation
 

Yes he has moisture because he has the vapor barrier up in the insulation and not on the ground where it should be. If you stop it at the ground then it won't
get up in the insulation as much. Also he has some new construction which has a lot of moisture coming out of it and it will not be able to dry out because the insulation will be trapping it there. I have seen a lot of floor joist and floors rotted out because of insulation in the floor. Paul

He says he has vapour barrier on the warm side of the insulation so that dosn't count for much. I suppose we can agree the the moisture didn't come from inside the house, I'm hoping anyway. So we have a heat source in the crawl space that vapourized the moisture, then deposits it on the cooler surfaces near the outside of the house. I still say all the same arguements for a vented attic apply to a crawlspace.

thanks for the information and thoughts on this. The access to the crawl space is from the existing basement. I opened it up and put a little space heater in there and it has dried up nicely. I am thinking the moisture is coming from the ground so what I am going to do up put some poly on the ground and attach it to the STYROFOAM insulation on the inside on the concrete grade beam with some acoustic sealant.