Renovation - Spray foam or Batt Insulation! Advice please!
Thanks for the detailed reply! Was hoping you would see this!
Our contract has spray foam quoted, and it seems like he prefers to do spray foam. I’m not sure we will save any $ by going regular insulation. If so, any drawbacks by going with spray foam?
Foam is more money so if he's pricing the job based on a percentage of the cost, then he benefits by you spending 10k instead of 5, but that's probably not the whole answer.
Foam is better if it's done right, but imho only if the whole house is done.
Insulation is measured in R value which is essentially the measure of how long it takes heat to migrate through a certain space. Foam, rockwool, air, fiberglass and chopped paper all have different values. Where foam is better is that it stops air from passing through little cracks and crevices, but it costs at least twice as much per R value so if you're paying 10k to get r30 in your attic space instead of 5k you're paying too much.
It has some other benefits and drawbacks, as well. In the attic, you would typically spray the underside of the roof deck thereby making your attic semi-conditioned space. Your attic is cooler and neater because the heat is kept out, but you have to cool that space and circulate air or you'll end up with possible moisture issues. If the roof leaks, you can't find it as easily. When it leaks, the R value of the foam decreases. When you have a roof replacement it will compromised the foam. Voids and crevices decrease the effectiveness, but that's the installer and contractor's job to avoid.
The sprayed area would be less drafty, but basic construction quality would eliminate draftiness in new construction/addition anyway.
How big an addition are you talking and is there going to be a separate ac?
In most cases, I would hazard to suggest you'd be better off using batt or blown insulation for an addition and spending the savings vs foam on a high seer AC system.