Vapor barrier on deck

[SustainableSerenityAcres]

So we are close to the point of the platform building that we need to figure out the

insulation

and vapor barrier thing. We are pretty sure we are going to go with a mix of roll

insulation

and rigid foam to get up to R30 on the floor. The hubby has asked me to look into where the vapor barrier should go or if we should not use a vapor barrier. We are up in central NH, so a pretty cold and wet climate up here to begin with. Mainly looking for suggestions on if we should use something like plastic sheeting or Tyvek and if so should it go up under the T&G flooring or down on the bottom of the platform on top of the OSB?

[tdsalad]

So I've been trying to learn more about this same subject. As I've been researching this (I'm no expert by any means), I'm finding that we have to think like stick builders, because that's what most of the info out there is written for in the building sciences.

So first you should consider the structure you're putting the yurt on... is it slab or whatever? You (like me) are thinking a wooden platform. So what is the equivalent in typical stick building? It would seem to me like it's almost a crawlspace.

Here are some links to discussions about issues with crawlspaces and what seems to be the best approaches to insulating them.

BSI-009: New Light In Crawlspaces - Building Science Information

and

3 Problems with Fiberglass Batt Insulation in Floors

and

Building Science 101

The approach that I've seen recommended the most is the encapsulated crawlspace (Crawl Space Encapsulation)... where the vapor barrier is on the walls and ground. But I suspect most of us won't be enclosing the platform of our yurts, so this isn't really valid. Instead, I'll be considering figure 7 at BSI-009: New Light In Crawlspaces - Building Science Information for now because I'll be building in MN and will also use radiant floor heat. This way we'll have insulation in the floor too.

But as the last link says... you need to consider your local climate and the system as a whole. Will you be cooling the interior of the yurt or

heating

it? That's going to matter.

I just found The best way to insulate a floor - GreenBuildingAdvisor.com too.

I'm sure there are others on the forum with more experience, but this is what I've found.

[Bob Rowlands]

I'm a carpenter by trade. Slightly off topic, but all crawlspaces need to be vented by building code. Even if you don't have a permit and an inspector signing off on the project, I know for a fact from experience that all enclosed house foundations need venting to exhaust

moisture

. I've worked on some really nasty crawl spaces redoing framing and insulation because of meager 'old school' thinking on venting. Nasty rot termites and ....and I won't give more details. Whatever you end up doing, make sure fresh air can EASILY get through the entire structure, or decay WILL set in. It's that simple.

Moisture

trapped in building materials is a key component in structural degradation.

[stephanwik]

Originally Posted by SustainableSerenityAcres

Mainly looking for suggestions on if we should use something like plastic sheeting or Tyvek and if so should it go up under the T&G flooring or down on the bottom of the platform on top of the OSB?

The standard way in Sweden is, from the inside -> out

1) T&G flooring

2) Plastic vapour barrier (the stuff I use is guaranteed for 50 years). 600mm overlap between rolls. This keeps the moisture inside the yurt from migrating down into the insulation. This is rolled on top of the floor joists.

3) Insulation (between the 600mm centre - centre joists). I use Earthwool.

4) Moisture permeable membrane (Tyvek will do just fine). This allows any moisture that might be taken up by the insulation to dry out.

5) OSB board (or some other board that is not sealed)