Insulation for a Brick House
Avoid a fire hazard with Tom Silva's insulation advice
The plaster walls of my 1930s Tudor-style brick house get really cold in the winter, but I've been warned against insulating them because we have some old knob-and-tube wiring. Any suggestions on how to make my home warmer this winter? — Evelyn Bostic, Cincinnati
If that old wiring is still in use, then you're correct: Adding insulation would be a fire hazard. Knob-and-tube wiring has no jacket over the wires like modern cables do, so the bare wires were installed about 6 inches apart to prevent arcing and dissipate heat. If you packed insulation around those wires, they would get too hot.
Replacing the old wiring with new cables would not be difficult, but insulating the walls would be. And that insulation could actually make the brick more vulnerable to freeze-thaw cycles by reducing heat flow through the walls.
The best way to stay warmer in the winter—and cooler in the summer—is to upgrade the insulation in your attic. A house loses most of its heat though that space, and increasing its R-value will be easier and more cost-effective than insulating the walls.
In your climate, the code calls for attics to be insulated to a minimum R-value of 38. (For a list of insulation requirements by state, go to US Department of Energy Building Energy Codes Program.) A contractor who specializes in energy retrofits can determine whether your attic meets that standard and, if not, how much extra insulation it should have. He or she can also see if the attic has any old wiring that needs to be replaced. If more insulation is called for, make sure the contractor seals any air leaks into the attic at the same time.
After the attic is taken care of, focus next on the basement, on the sill where the house sits on the foundation. Hiring a contractor to seal that perimeter with a closed-cell spray foam will go a long way toward keeping cold air out.
Once those two critical areas are insulated properly, you'll probably find that your home is comfortable enough—and your heating and cooling bills low enough—to make wall insulation unnecessary.
— This Old House general contractor Tom Silva