What is the best way to insulate the ceiling of my crawl space?

Judy Mendel
Updated: Sept. 9, 2020

I have a concrete floor in my crawl space under an addition (the rest of the house is on concrete slab). There is no ductwork, there is a sump pump, and the wall joists above the foundation have spray-foam insulation. Since we moved in, I know that the addition's floor is very cold in the winter and in the summer we don't really have to use air conditioning because of the crawl space temperature. It is a wood floor on the other side of the crawl space ceiling. I haven't insulated because I read different articles and didn't want mold. But now I really need to do something, it's so cold in the winter. I'd like to do something ecologically good. I've been looking at a product called Reflectix, but not sure if this will be good. Any and all suggestions appreciated.

Responses (4)

Judy Mendel 4 years ago

Wow, great articles, I'd love to do rock wool, denim or hemp! ANyway, here are the additional facts you would like to know. I live just north of Chicago. I would say there is humidity in my crawl space because when I stored some boxes down there, they were a little damp when I went to use them. I just checked, and it was 71%. I bought a dehumidifier but it's a very large crawl space ( I don't have the measurements but it must be at least 40' by 13' ) and really wasn't sure if it had any affect so I unplugged it. I do have a sump pump, that I recently covered. I took a picture of my sump pump and I have no idea what I'm looking at. I'm also wondering if I created mold because two years ago, I covered it. I have pictures I could send you, but I don' know how to post them. Thanks!

Mike Reynolds 4 years ago

40 x 13 is 520 square feet and if it is short in height (as a crawl space is ) then that isn't a lot of volume so I bet it was actually doing its job. Is your dehumidifier set up to drain automatically or do you need to remove a bucket by hand? Easiest is if you have it drain from a hose so you can just forget about it. 71% RH is quite high, no surprise your boxes are soft with moisture and you are for sure at risk of mold forming. I'd say go plug the dehumidifier back in, then check it tomorrow and I bet you will notice a significant difference in the relative humidity. Its best kept under 50% if possible, and don't worry about the energy it consumes, since heating and cooling dry air is easier than heating and cooling humid air, so cheaper heating and cooling offsets the operational cost of the dehumidifier. 

A sump pump sits in a hole in the floor usually about 2 feet or so in diameter. Often their is a large plastic bucket with holes on the sides, that is what allows water to drain into it. A sump will have a float just like in the back of your toilet. With a toilet the float will shut off the water when it is full, where a sump pump will be activated by a rising float. Feel free to email pics to [email protected] 

Cindy Young 4 years ago

Hi , My house is an older modular home with crawl space and 24 inches plus or minus.. It has steel joist 8 ft x 7 1/2 . The ceiling of the crawl space is insulated with pink insulation with cardboard flex. The insulation is falling down and looks like I would say over half of the home. The floor is dirt.

Do I try and replace the foam or do I insulate the walls instead. Not vented.

what is the best product to use for either?