Hello - (first post).

We live in the Washington DC suburbs and two years ago we purchased a home (1978/79 construction). For the past two winters we’ve noticed how absolutely cold the two rooms over the crawlspaces - lots of drafts from the floor.

The first crawlspace is under the master bedroom. It has exterior vents, so is considered a vented crawlspace. Most of the ground is covered with a layer of plastic – though it’s not taped together. There is no insulation against any of the interior or exterior wall surfaces. The floor has insulation (R19, I believe) with the moisture barrier (paper) facing the unheated main area of the crawlspace. I notice that there are portions of the floor which do not have insulation, so that’s clearly an area to work on but most of the area is covered. Some of the insulation has drooped (again) so I’ve used cut hangers to keep the insulation between the floor joists. Of course, the insulation paper isn’t flush against the floor joists for the most part so air can get between the joist and the edge of the insulation. Additionally there are holes in some of the paper (kfaft?) backing.

Our problem is that we can feel the cold air just emanating from the floor when we stand on it. I’m wondering if you think:

1. We should reverse the insulation – put the paper against the subfloor and re-attach
2. Add a layer of plastic (like house wrap) under the existing insulation (to better seal the entire space and keep the insulation up)
3. Add a layer of insulation perpendicular to the existing insulation and support with a netting system of some kind.
4. Replace the existing insulation completely but leave it installed in the same way.

The second space is under the family room. It does not have vents – though is not airtight by any means. It also does not have plastic sheeting on the floor. The insulation is oriented the same way (i.e. with the paper/moisture barrier facing towards the unheated crawlspace).

The question is the same as above – except with the lack of an open vent and plastic on the floor I don’t know if that changes the answer due to the requirement to mitigate any moisture build-up, particularly in the summer.

I’ve included a PDF document with drawings of both areas as I think ‘seeing it’ helps a lot.

For the record, I’ve reviewed the dept. of energy websites on this information but the majority of what is there says something like, “check with your local so-and-so as procedures in your area may vary”.


Thank you to all (in advance) for your advice.

Attached Images

CrawlspaceDrawings.pdf (9.7 KB, 212 views)

At the very least, you must reverse the insulation. Completing the plastic sheeting is a good idea.
If you had the money, I would recommend taking out all the insulation and having the entire floor area covered in spray on foam.

The spray foam seems awesome - though the cost is fairly prohibitive in the short term (it seems like in my initial calculations it is about $350 for the R19 fiberglass kraft batts versus about $2000 for the spray foam for approximately the same R value using the calculators I saw - e.g. Tiger.

It seems like DIY with the spray on foam is possible but not sure if that's actually a reasonable consideration.

Reversing the existing insulation is free. You can't put plastic under the insulation because that would trap any moisture between two vapor barriers. As I said "if you had the money" I know that stuff is pricey. I have worked on very old homes with field stone foundations. Please believe me that NOTHING stops drafts like foam and that is why I mentioned it.

Yup. Agreed. I'm thinking about trying the foam in the smaller crawlspace just to see how easy it is to use, how well it works, etc. Given the drafts that we have now, I'm thinking that a lower R value would be OK - or maybe that's just being "penny-wise, pound-foolish".

Do you have any recommendations with respect to whether I should put plastic over the dirt floor of the unvented crawlspace?

Thank you.

The cost of the plastic makes it no brainer. Keeping unwanted moisture out of a confined space is always a good idea.