Attic & Roofline Insulation in Boston, MA

Attic and roofline insulation covers everything at the top of the house: the attic floor, the kneewalls and side attics of Capes and finished third floors, and the rafters of rooms built into the roof. Old Boston houses often have all three. Warm air leaks into these spaces through chases, wiring holes, light fixtures and the tops of walls, and the roof deck above gets warm enough to melt snow from below. The result is ice dams at the eaves and a top floor that is hot in July and cold in January.

Attic floors

Where there is a walkable attic, the plan is simple: seal every gap in the floor, add baffles at the eaves, and blow cellulose or fiberglass to depth. The Massachusetts stretch code summary lists R-60 for new ceilings, and loose fill reaches that depth for far less than foam.

Kneewalls and side attics

Capes and many Victorians have short kneewalls with small attic spaces behind them. The floor under those spaces is often open to the heated rooms below, and the kneewall itself may have nothing behind the plaster. We seal the joist bays under the kneewall, then insulate the kneewall or move the insulation up to the roofline so the side attic becomes part of the warm space.

Finished attic rooms and low-slope roofs

When a third floor has been finished, the insulation has to follow the roof. Closed-cell foam in the rafters seals and insulates in limited depth. On low-slope triple-decker roofs, the cavity can be shallow; sometimes loose fill can be blown in through a small opening, other times foam under the deck or insulation added during a re-roof is better.

Before covering anything

We check for roof leaks, bath fans venting into the attic, damp sheathing, rodent activity, vermiculite and live knob-and-tube wiring. City of Boston guidance notes that knob-and-tube was common until the 1940s and that an inactive system does not stop insulation work. A live one needs an electrician first.