Attic Air Sealing & Kneewall Insulation in Yonkers, NY

Attic air sealing and kneewall insulation fix the most common comfort problem in southern Westchester: a top floor that is too hot in July and too cold in January. Warm indoor air rises and escapes into the attic through gaps around chimneys, plumbing stacks, light boxes, bath fans, the attic hatch and the tops of interior walls. That leak pulls cold air in lower in the house and, in winter, warms the roof enough to melt snow that refreezes at the gutters. Sealing those gaps and then insulating to the right depth fixes both ends.

Kneewalls and half-story rooms

Many Capes, Tudors, bungalows and Colonials around Yonkers have bedrooms tucked under the roof. Those rooms are surrounded by short kneewalls with unheated attic space behind them, sloped ceilings with little room for insulation, and small flat attics above. Often the floor of the space behind the kneewall is open to the joists below, so cold air runs right under the second floor. We block and seal that floor, insulate and air seal the kneewall itself, and treat the sloped ceiling with dense-pack or foam depending on access. Where it makes sense, we move the insulation to the roof line instead so the whole space comes inside.

What the code calls for

The state energy code places Westchester County in Climate Zone 4 and lists R-49 for ceilings; NYSERDA's comparison of the 2020 code and the NYStretch supplement gives the same R-49 figure. Most older attics we open have a few inches of matted fiberglass or old loose fill, far short of that. On an open attic floor, R-49 is reached most cheaply with deep blown-in insulation after sealing. In sloped ceilings and kneewalls where depth is limited, closed-cell foam reaches more R-value per inch.

Ventilation and safety

Before insulation goes in we put baffles at the eaves so soffit vents stay open, keep insulation away from chimneys and flues with metal flashing and fire-rated sealant, and make sure bath fans vent outdoors rather than into the attic. Recessed lights that are not rated for contact with insulation get covered or replaced. If we find knob-and-tube wiring still in use, we stop and recommend an electrician before burying it.

Is it worth doing?

HomeGuide puts a typical attic insulation job at $1,000 to $2,700 and air sealing at $350 to $3,000. NYSERDA's Comfort Home program builds its base package around sealing and insulating the attic and rim joist, which says a lot about where the savings are. We put sealing and insulation on separate lines so you can see what each costs.