Insulating attic and loft space must be done properly
Q. My 30-year-plus home has two rooms with mineral insulation, but my biggest concern is my third-floor loft. The temperature is always more extreme than the rest of the house. There is an attic space off this room, which has its original insulation only. Not too long ago I had a contractor come in to give me a price on reinsulating. He said he felt it was not necessary to do it and would be a waste of money. What’s your opinion?
A. Anytime you can add insulation, you will be reducing the amount of energy used to either heat or cool the home. In time, the costs of the insulation will be recouped in energy savings.
What you have to be careful about is not adding so much insulation that you prevent airflow through the attic space. The insulation should never touch the underside of the roof’s decking or block the vents at the soffits.
During the colder months, condensation can build up where insulation and decking meet and decay can form that would damage the roof and the attic floor.
However, you do want to minimize airflow through the insulation. When cold air passes through the fibers of the insulation, you lose a lot of the thermal resistance of the insulation, which is measured in R-values. The higher the R-value, the more thermal resistance the insulation offers.
An air barrier prevents unwanted airflow through the insulation. The higher the density of a material, the better it is at restricting airflow. Cellulose and spray-foam insulations have a much higher density than either fiberglass or mineral fibers and do a much better job at restricting airflow. By choosing the right product for each situation, you can see a dramatic reduction in energy use.
A loft indicates there are knee walls on either side of the room. When the knee walls are insulated, an air barrier of house wrap, cardboard, drywall, plywood, etc., should be applied to the attic side of the knee wall as well as to the openings in the floor joists under the knee wall. The remainder of the attic floor and the ceiling of the loft should be insulated with a thin layer of spray foam and then covered with loose-fill cellulose.
The foam gives you an air barrier and the limited area above and beside the loft can then be insulated with cellulose without having to compact the product or get too close to the roof and soffit areas. Check with local building officials or energy suppliers for the R-values required in your area.
Ÿ Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home improvement questions at d.Barnett@insightbb.com.
Scripps Howard News Service