My wife and I are building a home near Austin, TX. The ductwork will be placed in the attic of a low pitched roof. The roof covering will be standing seam metal. I would like to ask several clarifying questions regarding this:
1. My thought is to place open cell foam insulation against the roof deck with rigid foam on top to decrease the potential for condensation on the roof deck. Joe Lstiburek’s book suggests that you can also place closed cell foam directly against the roof deck instead of the other 2. This would seem to limit the ability of the deck to dry to the inside and is against other articles I have read. Can someone please explain what is the best design to go with and why?
2. Since the ductwork is in the attic, I read that it is best to condition this space. When I asked the HVAC designer regarding this, I was told that this is typically not done in residential construction. My builder also looked at me very funny. Am I being crazy by wanting the attic space to be conditioned, is the cost of this too high for the benefit given that the attic is already insulated?
3. Where should I put my water lines. Most people here put them under the slab, but given that the attic will be insulated, it would seem practical to put them there and avoid potential for having to break the slab in the future to fix a leak. The slab will form large part of the floor in our house and the look would obviously be destroyed if we had to have a big patch put in it. Any recommendations on this.
Thank you all for your help. I have read a lot on these topics over the past several months, but some of the things that seem to make sense aren’t what people are commonly doing and I appreciate your help with these dilemmas.