Question for you! Love to hear about the good of spray foam. We are using a hybrid between spray and blown in cellulose. (I would have prefered all spray but DH.... well thats another story).

So Im assuming that the reason the small AC unit is able to maintain that temp is because of the very low air turnover of the house. With such a small amount of "leakage" do you have trouble with the humidity? I've been talking to the building inspector about spray foam and I had a concern of a tight house being tight enough to not allow the AC unit to run enough to extract the moisture from the air. One person I talked to said you downsize the unit - to make it work more.?. Most have said to incorporate and Air exchanger (or Heat Recovery Ventilation etc.)
Are you worried about moisture?
Thanks for the cool post.

Jen

water- congrats on building an efficient home. its good to see results and suggestions taken by the pros that offer it up on this forum.

Jen
Tight homes need to have correctly sized hvac for it. There are very few mechanical guys that know how to size units for tight homes with very low air leakage. Most "rule of thumb" sizing does not work. The large units short cycle and do not run long enough to extract the humidity out of the air like you mentioned. Smaller units will have longer run times, correct, but they will run at a much lower speed so the energy usage is lower and the house maintains better. My home is an ICF home with similar r value (r 28 average and r60 attic with some r50 foamed rafters) and air tightness with triple pane windows only uses a 2 ton AC unit. The square footage is about 3800 total conditioned space. In zone 6 with 7200 HDD, the furnace is a Lennox modulating that ranges from 22k btu to 70k. It runs around the 25k for most of the time in the winter at 0 and below. Rarely does it ramp up to full speed ever. The mechanical was carefully designed and selected, and there is also an HRV installed. The full mechanical, high end equipment and HRV only cost $12k for the home nearly 4k sqft. I have seen people post numbers on here that are over double that in dollars and sizing for the same square footage. This is due to some or all of: code min. home design and construction and/or oversized hvac.

Now, its great the spray foam is performing, but without starting the debate, I just want to be clear to any readers that they are other methods of achieving a tight home, high r, and the same results as the poster WITHOUT using spray foam, all at a reduced cost of spray foam.

And as always, put the money into the shell of the home, not the hvac! Increase the shell, decrease the hvac. Most cases, dollars are a wash or less and energy usage is lower for the life of the home!

Wow, I'm astonished! In a good way!

I also plan on putting foam in my home, and am very encouraged by your report. cheers!

Thank you very much for the update and congratulations on your project. Must feel good to do so much of the work yourself. I hope you offered to compensate energyrater for their time. Doing so would be highly ethical and increase the likelihood of other folks getting important help with their projects.

Have to point out that the exterior foam sheathing is the best bang for the buck for using foam for walls. I agree with lzearc that good results can be done without spray foam although I find open cell spray foam to be cost competitive with cellulose and sprayed fiberglass in our area for wall applications.

I think your stellar results have more to do with the time and effort you have put into the air sealing rather than the spray foam. I think spray foam in the walls has a very small impact on blower door tests for the most part. The roof deck on the other hand..

its really a good jod you are doing i will also try in my new house.........it was so good i have ever seen........

Here is a link that might be useful: vinyl siding baton rouge

I'm in a similar situation with a 4 year total DIY build, same reasoning (nearing completion and the 4 year anniversary on January).

The house is a concrete structure with EPS insulation (R64 on flat roof), triple pane windows, 16" thick exterior walls with Galvalume siding.

We installed our 2-ton AC two weeks ago, 100F +/-, humid days and now the house is a nice 72F with Typical construction here would use a 2 ton unit for the downstairs and a 3 ton unit for the upstairs for similar square-footage. I had that setup in my previous house and with duct-work in the super hot attic and leaky construction, the house never cooled below 78F during 100F days and we ended up with $600+ electricity bills. This was one of the main reasons to build something better because I got sick of burning cash on AC every summer.