Open cell foam insulation vs dense cellulose for Phoenix climate? (houses, new construction)

[HX_Guy]

Does anyone here have experience or input on what is better for the climate here?

For a new construction 2x6 house, there is an option for standard dense pack cellulose or an upgrade (~$12,000) of open cell foam insulation.

Reading online, the R-value of each is about the same, with dense cellulose actually edging it out a big in some articles Ive seen (3.8 vs 4.0). Cellulose seems to have better sound dampening between interior rooms as well, but foam I impinge can better insulate hard to reach corners and would be sprayed on the underside of the roof decking, making the attic much cooler vs blown in cellulose sitting on top of the ceiling deck.

[Hal Roach]

I would rather have a thermostatically controlled attic fan.

[maverick974]

Correct me if I'm wrong but I don't think most houses are built with insulation in the interior walls. Just the shell gets insulation..

[HX_Guy]

Originally Posted by maverick974

Correct me if I'm wrong but I don't think most houses are built with insulation in the interior walls. Just the shell gets insulation..

You are correct, the article I was ready talked about that but thats true, interior walls are typically not insulated (though we are doing the bathrooms and laundry walls for sound insulation purposes.)

[cactusland]

What insulation?

[Hal Roach]

I have seen the Germans bring the foam fad to BKK, and like a lot of German stuff it isn't cost effective, and rea!ly hasn't gained any traction. There is mostly no decking under concrete tiles here, and the foam was knocking the tiles out of alignment just enough to cause some hard to find leaks. Also, you are basically sealing the attic, and, as stated, ventilation is a better way to deal with the heat. Your windows are likely less than R-5, why would you spend 12,000 for space shuttle insulation in the attic?