Crawlspace Vapor Barrier

[Chris Brown]

I have recently had different people tell me that a plastic vapor barrier should be put down on the ground in a crawlspace and then add the gravel on top of it.

I think that the gravel should go down first on the ground and then put down the plastic on top.

What do you pros think, which way should it be.

[mehen]

In more budget remodels we will use 4" of gravel over compacted fill then poly vapor barrier with all joints taped. Also we include 2" rigid insulation mechanically fastened to the foundation wall down to the top of footing and continuing to the top of the wall (horiz) including the exposed concrete that is adjacent to the sill.

However most clients want to add a slurry pour on top of the vapor barrier for limited storage.

[Chris Brown]

Thanks Mark,

Are those foundations vented?

[mehen]

Nope. We are in Madison, Wisconsin and venting the crawlspaces is not typical unless the vents are connected to a automatic control tied into a heat recovery/air exchanger type unit.

I have found www.buildingscience.com a fantastic resource for different building types (walls, foundations, roofs) in specific geographic locations (climate zones). They offer many options for each zone and what r-value is attainable through different types of construction.

Sometimes they can be extreme....

High-R Foundation - 8" foundation wall, 4" rigid insulation, 2x6 furred wall with F/G insulation - R-45 - that's not too bad for a foundation wall !

[Alaskan Son]

Here in Alaska, that vapor barrier is extremely important. Most people just put it right over the ground without putting any sand or gravel down, but that can lead to tears. Ideally a layer of "fines" (sand or fine gravel) should go down first. And even more ideally another layer of fines on top of that to keep it all in place and well protected. Problem with the extra layer is that its a huge pain to spread out once the house is all closed in, and doing it before framing (which would be easiest) would essentially turn the crawlspace into a swimming pool till it was all dried in.

[Alaskan Son]

...and we always vent our foundations, either naturally or mechanically.

[mehen]

I will also add that in town we have had several tests come back with high radon tests. We have begun adding a passive radon detail in all additions with a very easy conversion to active if necessary. Taping the seams of the poly is imperative and as Michael mentions, tearing is quite easy.....thus the slurry coat.

Michael - How's the new mayor ?

[Alaskan Son]

Mark,

Is that a reference to Mrs. Palin??

[mehen]

No...Never....Just could not resist...Please don't hold it against me.

[Alaskan Son]

Okay then : )

[mehen]

To be honest - Between "Flying Alaska", "Buying Alaska" and "Alaska State Troopers" - I think Alaska seems like the greatest state in the union. I have my Private Pilot license - but no plane - That seems like a problem

[perryh]

Alaska is my favorite place on Earth

[briem]

In more budget remodels we will use 4" of gravel over compacted fill then poly vapor barrier with all joints taped. Also we include 2" rigid insulation mechanically fastened to the foundation wall down to the top of footing and continuing to the top of the wall (horiz) including the exposed concrete that is adjacent to the sill.

However most clients want to add a slurry pour on top of the vapor barrier for limited storage.

Ditto here in Michigan.