What kind of insulation would be best in the attic of an older Houston-area home?

Question

My house was built in 1963 just south of Houston, TX, and two inches of fiberglass insulation with a vapor barrier seems to have been considered adequate at that time. The roof of this house is at about 2:12 or 3:12 pitch. I am now interested in adding insulation to lower my heating and AC energy use. Here are my issues:

1) Does anyone know of a good insulation-need calculator out there?

2) The vapor barrier on the old insulation crumbles at a touch. Should I just rip it out and start over?

3) Does anyone knowledgeable have any thoughts on what kind of insulation would be easiest and best for me to work with (batts/blown in, cellulose/fiberglass)? I'm sort of looking for practical pros/cons of the various types here.

4) Many of the home repair books I have read recommend sealing the tops of the walls with caulk or 1:1 spray foam. Is this really necessary, or do I want the house to be able to breathe a bit more?

5) Any other thoughts/cautions would be appreciated.

Thank you.

Answer 1

House that old,I would check to see if you had any insulation in the walls. Mine didn't (built 1960-61, 290 & bw 8).

I cut my electric bill drastically by insulating walls, caulking windows, sealing all cracks and crevacies I could find.

Are you installing? Blown-in cellulose will do the job and you can rent the machine at Home Depot. But you can't blow fiberglas with it. Besides the glass fibers would probably end up all over the house, whereas cellulose is just dusty-vacuum it up. 6 inch (at least) perpendicular to existing batts blown-in or batts don't really matter.

You don't want to block the air flow from your eaves/soffits to whatever attic ventilation you have. On that subject the more the better. Caulk around your windows and doors. The fewer airleaks, the less money you spend heating/cooling.

Answer 2

The more the better.Your problem is that there probably isn't any in your walls. I'd put that foil backed foam(4'x8' sheets) up on the rafters and blown in (or fiberglass) at least 8" between the joists.Also make sure your attic has some ventilation(again the more the better.