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How do I insulate the attic of a 1941 Brick Cape?

My wife and I just bought a 1941 brick cape in Connecticut.
The 2nd floor (attic) is unfinished and the vermiculite insulation that was between floor joists has been removed so it currently has no insulation or floor in the attic - just open joists.
At the bottom of the floor joists is metal foil that was nailed to the underside of the joists.
We would like to insulate between the floor joists before winter sets in.
In the next two years, we plan to renovate the second floor and build a master bedroom suite and plan to install floor rediant heat (possibly warmboard).
1) What type of insulation do you recommend? If batt insulation, should it be faced or unfaced?
2) What r-value do you recommend?
3) What is the pupose of the metal foil that was nailed to the underside of the joists?
4) Do I need to install a vapor barrier?
5) When I eventually finish the second floor, do I need to remove the insulation I installed?

Thanks in advance to anyone who can share your expertise and advice!!

Re: How do I insulate the attic of a 1941 Brick Cape?

The metal foil was probably shiny at one time. A silver finish has a very low emissivity rating, that is it does not radiate heat very well so in theory, it should help hold heat.

Heat is lost in three ways, conduction, convection and radiation. Conduction is heat traveling through a medium, such as a piece of metal or a piece of wood. Convection is the circulation of air or other gas or even a liquid in some cases where the fluid medium (air) picks up heat from one surface through radiation and conduction (contact) and moves it to another surface where it is transfered again through conduction and radiation. Radiation is simply heat radiating off a surface (or absorbing heat) such as a stove. All surfaces radiate heat, it is just more noticeable from a stove.

For a low emissivity rating (low radiation) to work, it usually needs an air gap. Otherwise the low emissivity is offset by conduction. Years ago, there was a foil faced insulation on the market that was used with a foil backed sheetrock. The theory was to put the two foil surfaces facing each other with about a 3/4" gap and that would add about an R-3 to the value of the insulation. This was usually used on walls and the fiberglass batt insulation was only 2.75" thick. Turns out that an extra 3/4" of fiberglass is also worth almost R-3 and you can just use paper for the vapor barrier.

Because of that foil backed insulation, most people believe that all batt insulation should have a 3/4" gap between the vapor barrier and the sheetrock. Many codes require this, but for the best efficiency in using fiberglass batts, there should be NO gap between the fiberglass and the interior wall surface. Faced batts should have the wings stapled over the ends of the studs and not to the inside edges as most commonly done.

For your case, the foil is acting as a vapor barrier although attics are so well ventilated in most cases that a vapor barrier doesn't usually do anything, but it doesn't hurt either. I would recommend that you use fiberglass batts laid down between the joists for now. You can take them up and reuse them when you finish the second story.

The choice of whether to use faced or unfaced batts should be determined by what you plan on doing in the future. If you plan on using faced batts in the remodel, then go ahead and get them no and lay them with the faced surface down. Don't unfold the wings, just lay them in place and don't staple them down.

Re: How do I insulate the attic of a 1941 Brick Cape?


I ordered batt insulation based on your reply. Thanks so much for your advice!


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