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Cooling and Heating in an Attic Space

Topic: 
Insulation and Energy
Question: 

Our objective is to make our house warmer in the winter and cooler in the summer and lower our heating bill in the process. So, we are thinking of adding insulation to our attic. We live in a Cap Cod style house, built in 1942, with two bedrooms on the second floor, the kind with a finished attic, sloped ceilings and three foot pony walls. The unfinished parts of the attic (under the sloped part of the roof behind the pony walls) is insulated with about 4-6 inches of rock wool on the floor (it has most certainly compressed over time) and fiberglass bats, many of which have fallen off, on the walls. I'm pretty confident that new insulation will improve the comfort of our house. 1. Contractors are recommending blown fiberglass for the floor? and new bats for the walls. Are there any significant safety concerns to having blown fiberglass in the house? Any reason to consider bats for the floor? (For example, one day, we would like to build dormers. Will we need to remove the insulation for this remodel?) 2. Do we need to remove the rock wool before blowing in the new insulation or is it okay to blow the new stuff over the old? My understanding is that the rock wool will actually provide a vapor barrier. 3. (Most urgent question) Is it safe to blow fiberglass over knob and tube wiring? Should we have the wiring updated first? (If we did update the wiring, would we end up redoing it with a dormer addition?) Most of the knob and tube runs along the underside of the roof, but it runs down into through the floor in places. In addition there have been some more recent electrical additions that tie into the old knob and tube. I am concerned about creating a fire hazard if we cover the electrical with insulation. (If we do cover the electrical with blown fiberglass, have we created a nightmare if we ever want to update the knob and tube in the future?) 4. Another idea is to add some sort of ceiling venting at the top of the stairs on the second floor. I have read your site about operable sky lights. What about a fan that would vent the entire house to the outside? Would a fan be more effective? Especially on those summer nights when there is no breeze?

Answer: 

Matthew?

You are right about the concern with the tube and knob wiring. Such wiring depends upon free air circulation for cooling (and safety) and should not be covered with insulation. It also sounds to me as if there are some unsafe connections between old and new wiring. So, the first step is to bring in a licensed electrical contractor who can repair or replace the wiring and prepare the wiring for any insulation and modifications to the attic/roof.

For cooling purposes, an operable skylight tends to work much better than fans. The only time they don?t work is when you live in a noisy area and prefer to keep windows/skylights shut. I think that you will be very pleased by the summer cooling from an operable skylight.

Loose fiberglass insulation is a safe product if it is isolated from the rest of the house by walls etc. There maybe some argument about which loose insulation can have greater health considerations but the bottom line is that all loose insulation must be isolated from the living areas of the home.

The bad news about the insulation work is that 6? of new loose or batt insulation will not make a very big difference as far as winter heating. If at all possible, try using some high quality foam board siding (polyisocyanurate foam). But even that will not make a huge difference.

You might want to think about some zone heating in the attic. For example, you could ad some hot water heaters by using a dual purpose gas water heater.

George