Q. I’m remodeling a house that has two exposed 6x12 glulam beams that extend from the open-plan living space into an attached sunroom, which cools to near the outdoor temperature at night. Is there a good way to eliminate conductive heat loss through the exposed beams?
A. Steve Baczek, an architect in Scituate, Mass., responds: There are several ways to deal with the problem directly. For instance, you could insulate the beam on the inside to minimize its ability to take on heat from the indoor air, then box it in with some sort of finish material. That will reduce heat loss, though some or all of glulam’s top surface — where it makes contact with the floor joists above — will probably have to be left uninsulated. Also, the bulked-up appearance of the resulting beams may look awkward.
Another option would be to insulate the beams in the sunroom to prevent them from bleeding heat gained from the conditioned interior.
But the best solution — if the design of the structure permits — would be to physically decouple the outer and inner beams from one another where they pass through the wall, and separate the cut ends with pieces of 3/4-inch rigid foam. This approach would have to be designed by a qualified engineer.
However, before you do anything, you should consider how the thermal bridge fits into the bigger energy picture. Most homes have at least a few energy issues, and it’s best to start by tackling those that offer the largest return for the smallest investment. Conduction through the beams you’ve described here, for example, probably accounts for less heat loss than a 1- or 2-square-inch air leak in the building envelope. Simply air-sealing the beam penetrations through the outside wall might save more energy than insulating the beams themselves or engineering an internal thermal break — and at a tiny fraction of the cost.
