Floor Insulation Done

I rolled out the insulation, then just dragged it in as I installed it.

I’ve been putting off insulating the floor as long as possible. No one wants to crawl around under a house pushing itchy insulation up in between floor joists while sitting uncomfortably on gravel rocks. Also, the footprint of this house is 1600 sq ft, so it was a large area to cover.

Last year when it got cold (yes it gets cold here for a few weeks) – in the teens at night, I was excited to try out my wood stove. But I found that my feet got cold every time I went out there, even though the fire was blazing. As an experiment, I took off my boots and walked around in my socks – it was the floor! I started wearing wool socks when I had to work in the cold.

It didn’t make sense to insulate the floor over the summer with all the heat (“sweating” plus “fiberglass” is a terrible combination), and I was busy with framing, plumbing, and electrical in the Spring. With all that almost done, I ran out of excuses. Also, I was thinking of doing the insulation after I finished the HVAC plenum runs, but found out it would be more difficult to install insulation around the mechanical work.

I went with Kraft-faced (paper backing) almost 40′ rolls of R-19 insulation. The structure of my floor joists is 2×12’s spaced 16″ on center, perpendicular to two double 2×12 beams that span the entire floor (40′). This means there are basically three 13 foot sections of floor joists under the house. I say the rolls of insulation are “almost 40 feet”: they are about 39.37′. Why that length? I don’t know for sure, but with the rim joists and the double 2×12 beams, cutting the rolls into 13 foot lengths (13+13+13=39) made them fit perfectly between the joists.

Pushing it into place; working around drain pipe and electrical.

The weirdest part is they are held in place with spring steel wires. You push the bats in place, then push a steel wire up to hold it all in place every 16″. It seems to work just fine.

It took me 28 rolls to insulate. I just bought a few at a time – as many as I could carry:

You can fit more than you think in your wife’s car.

The whole process took about 8 hours, spread out over several days because my back needed a break from laying around under the house.

Installing insulation – “at night.”

Code says you can leave it open like this, so I will for now. After we move in, I want to go back and cover the insulation with plywood or hardware cloth to keep the critters out.

Next Steps

It’s either going to be electrical and sewer line trenching or HVAC. My brother-in-law owns an HVAC company and has a software tool to create designs for residential systems. He and two of my sisters and mom came out in July to take a look at the house to see how we could run the ductwork. We sent him a floor plan, and he sent me a detailed list of supplies needed – vent sizes, compressor size, etc. I took the plans to a sheet metal shop and they said the main plenum box – 20″x20″x20 feet long – would cost about $650 to make. Then I saw a video where a guy uses hand tools to build a sheet metal plenum box. I checked with a sheet metal supplier, and walked out the door with $400 in metal to make my own. I did a lot of “origami” as a kid – I think metal is a step up, but it’s not impossible.