Need Crawlspace Solution/Opinions

[CBOY]

Hello everyone, this is my first post here.

I'm working on an 1880 brick hillside house (Northeast USA). It has a rubble foundation and there is bedrock exposed throughout most of the crawlspace. I think it will always have some water problems, as surface water uphill seeps in to the ground, hits the bedrock, then travels down hill. Unfortunately, there was a massive retaining wall and surface drain built across the back of the house, and I think ground water travels under this big concrete "gutter". This also makes installing a French drain nearly impossible.

My thoughts now are of letting the water flow through the crawlspace, down hill, but installing a vapor barrier to the bottom of the floor joists (sealed to the brick) to prevent moisture from corrupting the timber, and keep vapor from rising into the living space. Then I would attach foam insulation to the joists ("below" the vapor barrier). This would need to be well ventilated all year.

Here is a picture for clarity:
http://home.earthlink.net/~chriskellydesign/crawl.gif

Any suggestions?

 

[felix]

We probably do things differently here in the UK but the laws of physics are the same everywhere (according to Einstein).

How about putting air vents in your walls ABOVE your new vapour barrier. This will give you a 'false ground' which remains dry at all times. Any insulation below the vapour barrier will be wasted but you can put air permeable insulation between the joists instead.

 

[CBOY]

Thanks Felix.

I like your idea about the wall vents and "false ground," but I think I'd be worried about condensation and trapped moisture in the insulation. I guess that's why I thought of treating the floor like an exterior wall (plastic on the room side of the insulation). Why do you say that the insulation would be wasted? I was thinking of rigid extruded foam boards, like those that some people use on the ouside of the foundation, below ground.

Another chap had an idea: paper-backed insulation between the joists, with the paper up toward the subfloor, then siding, plywood, or "house wrap" across the bottom of the joists--no vapor barrier, and LOTS of ventilation. This is also like an exterior wall.

I guess my concern is more with keeping moisture out of the living quarters, less with the insulation.

Thanks for helping.

 

[felix]

I meant that insulation below the new false ground would be wasted because you have a free flow of cold, outside air above it. Over here it's standard practice to put a vapour barrier immediately behind plasterboard on walls and ceilings with the insulation in a vented space behind. I'm not so sure about a floor though. Wouldn't spilt liquid soak through to the underside and be trapped? I would use rock wool between the joists held up with perforated plastic sheet or mesh and leave the bottom edges of the joists exposed. Perhaps you should put your question in the Building forum for a more expert opinion.

 

[masona]

Is it not possible to have a soakaway to the sump then have a auto- pump to pump it away to drain?

 

[CBOY]

Great ideas guys.
I think a sump or interior perimeter drain is the way to go--fiberglass between the joists (barrier up), and LOTS of ventilation.

Thanks for the ideas.