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pjh3939 11-16-2011 03:47 PM

Crawl Space Insulation - Will this work?
I have an enclosed crawl space approximately 20" high. It is dirt floor, unheated, and gets a fair bit of moisture. I had planned to have it sprayfoamed but the contractor advises that the space is too restrictive to properly install and the price is too restrictive for me as well. My next thought is to install Roxul. Is this a good choice? The current finished floor is hardwood over 1" thick boards but the hardwood is not fit to be refinished. I plan to install laminate over the hardwood. Is it advisable to install plastic vapor barrier over the hardwood and under the laminate?
Thanks for your suggestions.

Jackofall1 11-16-2011 04:12 PM

Hello and welcome pjh, to the best darn DIY'r site on the web.

You say your crawl is enclosed, if totally enclosed (no vents) than you could use a minimum of 2" XPS on the walls, lay 6 ml plastic on the dirt and add a couple of heat registers to help dry the space out.

As for the flooring I would go with what is recommended by the manufacturer, I am not certain for laminate, but, hardwood underlayment can be 15 lb (roofing paper) felt paper.


pjh3939 11-16-2011 04:28 PM

Thanks for the reply. The space is totally enclosed with no vents. This is a 100+ year old home. The dirt floor is very uneven so laying plastic on the dirt would be quite difficult. There is also a concrete support base for the fireplace about in the middle of the space. When I say 20" high that is an average, some places may be 30", other areas 12" - 14". The location of the home and slope of the ground means that there is constant moisture. The product info for Roxul says it is moisture resistent so I thought it might be a good choice. I have always heard that vapor barrier goes on the "warm in winter" side of the insulation so that's why I thought it would be OK over the hardwood and under the laminate.
I'm located in eastern Canada so I'm trying to keep the floors a bit warmer in the winter.

Windows on Wash 11-16-2011 04:55 PM

You technically could lay a vapor barrier across the floor but you may have to deal with unintended consequences of that.

You will still have moisture diffusion and potentially bulk moisture coming through the dirt and roxul. It will get to the hardwood and will get through in many locations. I am never a big fan of plastic over hardwood flooring because you introduce the potential to trap moisture in a given space.

You can level out the floor and remove dirt where necessary. I think the first response from "Jackofall" is spot on. I would much rather see you insulate the walls of the crawlspace, seal up the floor, and supply some heat.

CrawlSpaceMoist 12-03-2011 09:36 AM

Agree. I wouldn't use a VB on top of the laminate...
Better to stop as much moisture as possible in the crawl. Either do it yourself or hire a laborer (or 2) to manicure the crawlspace until you can get a 100% coverage of at least a 6mil polyethylene down.
insulate the walls.
depending on how bit it is, you can add a register/damper to condition the space, or a dehumidifier.

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