Saturday, December 22, 2007


Framing, electrical and plumbing are complete. The house has been insulated. Insulation used in the house is a combination of radiant barrier, spray-in foam, rigid foam board, and fiberglass batts.

Radiant Barrier

This house makes use of CBF Ultra radiant barrier insulation almost everywhere:
  • under roof shingles
  • under floors
  • under stucco in exterior walls
  • inside walls, just behind drywall
  • inside basement walls, just behind finish
CBF Ultra was used because it has a foil barrier with bubbles on both sides. It can be embedded in a wall, in concrete, under stucco, etc. and will always have the air gap necessary for radiant barrier to work. Radiant barrier dramatically reduces radiant heat transfer. Radiant barrier on the outside of the house reduces heat gain during summer, while radiant barrier on the inside of the house reduces heat loss during the winter. Radiant barriers under heated floors reflect heat back up.

Radiant barrier behind stucco has an added benefit: it introduces an air gap between the building structure (sheathing, studs, beams) and the stucco. This air gap reduces heat conduction between the building structure and the outside, effectively increasing the insulation value of the walls. This little bit of insulation makes a big difference in the overall insulation value of the wall because the studs and structure have much lower thermal resistance than a foam-filled stud cavity.

For example, consider a 6 inch wall of R25, whose structure covers 10% of the wall area, and is about R6. The wall has an effective R value of R = 1/(0.9*25 + 0.1*6) = R19. If the bubble adds R3.8 everywhere, then the wall's effective R value becomes R = 1/(0.9*(1/(25+3.8)) + 0.1*(1/(6+3.8))) = R24. So adding 1/4 inch of bubble increased the real R value of the entire wall by 20%!

Radiant barrier was the first insulation installed in the second floor of the house, prior to new roof shingles, in mid-summer. The difference was immediate and noticeable. The temperature in the second story dropped 15F, and it was cooler upstairs than it was outside - with no other insulation in place!

Icycene blown-in insulation

The bulk of the insulation is blown-in Icynene. Blown-in insulation does a great job filling areas between wires and pipes, and has no problems filling odd cavities where standard batts of insulation would need to be crammed in (poor insulation) or leave voids (no insulation). Spray-in practically eliminates drafts through walls and ceilings, and thereby substantially reduces problems associated with vapor permeating walls with its resulting condensation.

Rigid Foam Insulation

Rigid foam insulation is used where few interferences exisit: under floors above crawl spaces, under tiles floors over slab, and as insulation in basement walls. Under wood floors in the joist spaces, 3" thickness Dow Thermax board with radiant barrier is used. Its radiant barrier reflects heat back up to the radiant floors. Thinner 1" thickness Dow Styrofoam blue board in combination with CBF Ultra radiant barrier is used over slab floors and behind basement walls.

Fiberglass Batts

Fiberglass batts are used to fill larger dead spaces that don't have wiring or plumbing in them, such as cavities under roof walls.

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