Crawlspace Insulation

I thought I would ask this question of all you wise and learned Inspectors:eek:
This house was built in the late 50’s. I called out the lack of insulation, as you can see in the pictures (sorry the one is sideways) there is no foundation insulation or any floor insulation.

The guy “flipping” the house agreed to adding foundation insulation. That would be good, but do you think it is better to add floor (Kraft face) insulation instead??

The excuse was that houses built then didn’t have floor insulation, which I suppose is true, but anyway would you have called out the lack of floor insulation anyway? They did agree to add a vapor barrier too though.

Thanks in advance for your answers!



I’d insulate the perimeter block wall, drop a vapor barrier down, close off the vents and let a heat run in the space.:wink:

If you are going to insulate the floor use batts without the kraft face since the vapor barrier needs to go up not down in Michigan.


Tell Larry “very funny”!

The 1st picture appears to be a foundation crawl space. Is the 2nd picture and Attic crawl space?


Second picture is of the crawlspace too. Picture of the floor with no insulation.

My Info could be outdated, but about 12 years ago I called The Pink Panther guys and spoke to the Tech’s not a sales rep.

He told me that (in Michigan) I should install a thick vapor barrier to the dirt floor of the crawspace, install bat insulation up the foundation walls down to the floor and continue across the floor 18-24". He told me (and repeated this three times) Do Not put any insulation between the floor joist or across the rest of the crawspace floor. I would be waisting my money.

He said you just want to cover the walls & the ground past the frost area. He went even farther and said that in an area that receives regular winds, like in Michigan you will lose more heat through uninsulated Wall then you will through an uninsulated conventional a frame roof. (The attic acts as a better insulator then a 2x4 wall.)

Again, things have changed in the world. I’m sure there are better ways to insulate now days.

Greg, floor insulation (as opposed to insulating the walls of the crawspace) is not a great idea for a number of reasons. After reading what I could find on building science and talking to building biologists here in Boulder, I never recommend insulating the floor and I don’t make recommendations about barriers or retarders unless I’m sure I understand how the home is working. Thermal, moisture and pressure gradients and the type of ventilation system they’re using…

A lot of good information from these people. The founding engineer, Joe Lstibureck, is speaking at the Energy Star conference in Denver next week. He’s one of the top minds in the country for this kind of thing. It’s a great opportunity. NACHI is giving education credits. Good one not to miss.


Thank you very much for the “building science site”. I love those kind of sites, and plan on reading this one.


Insulating the floor will vary from area to area. In warmer California, the code requires R19 insulation for raised floor construction.

As for existing housing, I make it a recomendation, not a repair issue if there is no floor insulation. Depending on when the house was built, floor insulation may vary from nothing to R19+. All perfectly legal at the time of construction.

Building science is one of those areas in which one size does definitely not fit all. Temperature, humidity, local building practices… look at posts from the guys from Florida about what happens when you have high humidty and someone gets the moisture barrier wrong. Houses melt like the Wicked Witch of the West. Drainage planes, vapor barriers and retarders, moisture barriers and retarders… the more you learn, seems like the less you know sometimes…

There are two basic theories on crawl space ventilation/insulation

  1. Insulate the floor, and have a well ventilated crawl space with a good ground surface vapor barrier (even better use a “rat slab”)

  2. Close off all vents, condition the space (cut in supplies on a forced air system), install a vapor barrier, and install perimeter insulation.

It really a toss up, but my preference is the sealed/condition space option if there is a forced air system.

JMO & 2-nickels … :wink:

Exactly, Robert, my preference too, in Michigan. :wink:

While thats my preference on the design side, wearing my inspectors hat I don’t get to chose, and I am just mindful that there tends to be more inspection/deterioration issues with ventilated crawl spaces (more common), and I always look a little closer with those types.

On one inspection, there was a house with an addition and crawl space foundations throughout. The original part of the house at the access was well ventilated with a good ground surface moisture barrier … everything looked fine.

That is until I crawled all the way across the house to the addition on the far side. No ventilation or ground surface moisture barrier in that area … and a plumbing leak to boot … very damp and stagnant conditions. My awl went completely through about the bottom 2" of the wood joists and main wood beams … :shock:

P.S. The crawl space addition with the problems also had the insulation installed wrong, with the vapor barrier on the bottom and the batts tabs stapled to the joist bottoms. A common mistake homeowners make when adding insulation to crawl spaces.

Insulation should always be installed with the vapor barrier on the “warm in winter side” … otherwise it can trap moisture in the joist spaces.

That, with the other conditions, was a red flag to peel back some insulation and probe the wood. I wasn’t to surprised when my awl went completely through the bottom parts of the framing members.

Also, here is a link to a pretty good discussion on crawl space ventilation …