Floor Joist Insulation

I live in Alaska, Juneau specifically. I just had an energy audit and the was told that I needed to have my crawl space insulated. I have a crawl space with a vapor barrier on the dirt floor, and closeable vents for air circulation. I installed solid foam insulation on the interior walls and solid foam insulation on the rim joist.

The fellow that completed my inspection told me he could install the recommended insulation of the floor joists. The work has been completed, but I am wondering if it was completed correctly.

Fiberglass batting without a vapor retardant was placed between the floor joists. Nothing is holding it in place except the resistance of the fiberglass to the wooden joists.

I have read that the proper method of insulation of the floor joist is to use fiberglass with a vaper retardant layer that is installed against the flooring. The insulation is held in place with netting, something called lighting rods, or clear plastic polyethylene sheeting - 6 mil.

I have not yet paid the fellow that completed the installation. He is also the state certified energy inspector. I really need some guidance.

Thanks so much for any assistance you might provide. This just does not seem to me to be a correct installation.

Happy Holidays!

Was a building paper/vapor barrier installed on the bottom of the floor prior to the batting being placed? You are correct in saying that thier should be something holding the batting from falling. Also be sure to where a resperator/mask if you should venture in there. Without a picture or further details it is hard to determine.


A vapor retarder (against the living area side) is definitely the best way to go when installing insulation in your floor joist cavities. The retarder will prevent moisture build-up on the floor sheathing where cold air is divided from the warm air.

It’s also best to have this insulation secured in place with chicken wire or some sort of single heavy gauge wire.

Never install polyethylene sheeting to hold the insulation in place. Poly is a vapor barrier (not a retarder) that will not allow condensation to leave the cavity and will cause a Mold build-up throughout the floor joist cavities.

In your type of climate, I also recommend closing your vents to the crawl space and simply condition it. Go HERE to see how I show all my HI clients how to insulate their crawl space.

Good Luck. I was stationed in Ft. Richardson Alaska and I love it out there. Especially the northern lights and the midnight sun.

The “heated crawlspace” in David’s link is, by far, my preference, too.

Mr. Valley, your instructions for a heated crawl space tell the homeowner everything except how to heat it. Without a source of heat, it cannot be considered a “conditioned” crawl space, and thus would be a code violation in most jurisdictions.

Who’s going to send expensive heat into a void that’s not being utilized?

Conditioning in my situation is simply keeping the cold air from entering this cavity in the first place. The warm floor will conduct minimum heat into this area. A direct heat supply to this cavity is indeed an option, but not necessary. That’s why I mention the pipe insulation.

**“Conditioning” **according to the code is either (1) the crawl space is used as a supply plenum for heated cand cooled air supply, or (2) contimuously operated mechanical ventilation is provided at 1 CFM per 50 sq. ft. of crawl space floor area, or (3) the crawl space is supplied with conditioned air.

Any sealed crawl space which is not conditioned in one of those three ways is a code violation in jurisdictions which have adopted the International Construction Code.

So, to answer your question, those who wish for their crawl space to meet the code definition of a “conditioned” crawl space will supply conditioned air to it. The code defines “conditioned”, not anyone else.

Please find something to do…Conditioned or un-conditioned crawlspaces is not a code violation because it’s not a living area. You either condition it or you don’t.

I went back down in my crawl space and took these images for further reference. No vapor retardant against the warm floor was installed. I also had foil quilt insulation that install in the fall and remove in the spring against the metal vents, just to reduce cold air coming into the crawl space. It has been removed. The current temp is 27 degrees outside and 42 degrees in the crawl space. Obviously, the crawl space is unheated. I am concerned that the pipes might freeze.

This fellow does state certified energy evaluations as well as weatherization. Now he wants to be paid for this, prior to the installation of new windows in the back of my house.

I don’t want to pay him for this work if it has not been done correctly. It does seem from the remarks so far that the work is not correct.

Please review photos.

Thanks all and Merry Christmas.

Gail Smith, Juneau, Alaska


A vapor retarder is required on that installation. Here is a link from Owens Corning.

Also, the pipes should be insulated to prevent freezing and bursting.

Maybe you should find something specific to do, such as reading the code. Who says that, because it’s not a living area, the code doesn’t apply? Start with Section R408.2.

Gail the work is substandard and should be corrected to prevent more damage. I would contact someone from the local office that has authority over this type of installation (different in a lot of states) and report the it. Did you have to pay for all the excess insulation laying in the crawl?