How can I insulate a cramped crawl space?

Question

I have a home built in 1912 that I have been trying to find solutions to keeping the first floor warm in the winter for a few years. Heating for that floor is from forced air heat pump with ceiling vents and a recently installed gas fireplace insert. The main issue is how cold the floors get as well as the fireplace on warming the living room.

The crawlspace is tight to say the least. The joists have been repaired and supplemented over the years making the tight space even harder to navigate. The floors are dirt/ bedrock. It is vented and even though we are water adjacent we have not had any flooding or moisture issues in the 4 years we’ve been here. We have not had a professional look at it but homeowners of similar house in the area have been quoted $10-20k or had companies say they can’t do it.

I have good DIY experience and am willing to do the work. Are there any solutions that don’t involve encapsulating, which would be next to impossible?

Answer 1

Consider closing your crawlspace vents permanently. Here are some references:

To Vent or Not to Vent

Would you believe that many scientists now advocate removing crawl space vents altogether?

"What do you mean, take out the vents? We have to have venting - it's the only way the moisture has to escape!" This is typically what I hear when I tell a fellow contractor about getting rid of crawl space vents.

Yet a ton of new research indicates that rather than removing crawl space moisture, venting makes the problem worse. Building scientists have found consistently that when warm, moist outside air enters a crawl space, it instantly cools and drastically increases the relative humidity of the crawl space. When the relative humidity goes over 100 percent, the moisture is released into the crawl space atmosphere, with condensation accumulating on the walls, floors and building components.

Taking the Vents Out of Vented Crawl Spaces

To state it simply, using outside air to ventilate a crawl space only adds more moisture to the area — it does not dry it out. Furthermore, wall-vented crawl spaces allow condensation, surface mold growth, high wood moisture content and rotting wood to increase.

And more here:

• https://www.advancedenergy.org/crawl-spaces
• https://www.thisoldhouse.com/heating-cooling/21173202/should-crawl-space-vents-be-open-or-closed

Answer 2

Here are your options:

1. Insulate the floor.
2. Insulate the foundation from the inside.
3. Insulate the foundation from the outside.

2 would be the most difficult in your situation; not only would you have to work inside the crawl space, you'd have to excavate a ditch next to the foundation while inside the crawl space. So I think we can forget that.

If you can access all of the crawl space, then 1 might be a plausible DIY project. Get some fiberglass insulation rolls, stick them into the cavities between the joists, staple in place.

3 would require digging a ditch around the perimeter and putting some sort of sheathing over the insulation, so that would require more materials than the other options.

If you go with 2 or 3, it means that the crawl space would no longer be vented - in that case, I recommend sticking a dehumidifier in the crawl space.

Answer 3

You could insulate the floor joists. It will require the most insulation to do so. Depending on where you live you will need anywhere from R-13 to R-30. I'm originally from MD and when I built my house in the early 90s, R-19 was required as a minimum. That may have changed since then.

My suggestion would be to insulate the perimeter of the crawlspace with rigid foam. It will require digging down to the frost line (the amount that the ground freezes during the hardest winters to say it simply). That may or may not be easy to do in a crawlspace.

Add what you can to the walls of the foundation, that you can afford. 2" minimum, more the better. The only area of concern will be how to treat the vents. If they are standard 8X16", there are styrofoam plugs that will fit, or cut plugs from the foam used on the walls to fit from the outside.

Add the dirt back behind the foam to keep it pressed against the walls. The top of the foam should go to the subfloor/ to the top of the joists. Cut blocks of foam where the joists run into the walls perpendicular.

One other concern may be termites. The termites, if active in your area like they are MD will find a nice protected area to travel to the wood framing, between the foam and foundation.