jay040 said:
Can you explain that for me? Not doubting, just curious.
Quote:
If your exterior walls are not foam insulated, then it makes more economical sense to just use blowned-in insulation in the attic on top of the existing mat insulation already in the attic..
JMHO, and I may be off here, but this is my thinking...
I did a rennovation on my current house that I gutted to the studs throughout. I removed all the batt insulation in the walls that was rated at a R-13 value. In the reno process I used closed cell foam insulation in the walls that I did myself with Foam It Green to get an effective R-23 (3.25" x R-7/inch) to R-24 (3.5" x R-7/inch). That almost doubled the R value in the walls.
As far as the ceilings go, I didn't remove the ceiling in all the rooms so I left the batt insulation and/or the blown insulation in thoses areas. Since the living room area (largest and easiest access area in the attic) was gutted ceiling wise and I incorporated OSB decking in a good portion of that area for storage, I also used the spray foam to insulate that area. The ceiling joists are 2x6 joists so I got 5.5 inches of foam insulation giving me an effective R-38 before I decked the area.
The rest of the ceiling area I plan to just insulate with blown-in insulation on top of the existing stuff to get an effective R-49 when I'm through with the master bedroom, bath and closet area. I believe it's a lot cheaper and much easier to go this route than to remove all the batt and blown-in insulation and then replace it with closed cell insulation.
I just feel like the exterior walls with batt insulation at R-13 is your weakest link from an insulation standpoint and therefore going through all the labor, trouble and expense of foam insulating the attic in the OP's situation does not justify the significant labor and cost differential and therefore IMHO does not make economical sense!
On a side note, I will admit that I previously rennovated our old house (2 houses up the street) with R-13 batt insulation in the walls and about 15-16" of cellulose for a R-49 in the attic and I can definitely tell the difference between the two houses. IMHO, our current home is much better insulated.
Sorry for the long winded response jay040...