Dense-Pack Wall Insulation in Boston, MA

Dense-pack wall insulation is how most older Boston homes get their walls insulated without tearing out plaster. Many houses built before the middle of the 20th century have nothing between the plaster and the sheathing. That hollow bay lets heat out and lets cold air in through outlets, baseboards and window casings. Dense-packing fills each bay with cellulose at high density, so it slows air as well as heat and does not settle.

How it works

We drill a small hole in each stud bay, either from outside by lifting a course of siding or from inside through the plaster. A fill tube goes in, and cellulose is blown until the bay is packed tight. Then the hole is plugged and the siding replaced, or the interior patch is left ready for paint. On a typical older house, each floor's walls take a day or two.

Balloon framing and blocking

Many Victorians and triple-deckers are balloon framed, with studs running from the sill to the roof and no blocking between floors. Before dense-packing, those bays need to be blocked at the bottom so the cellulose does not fall into the basement, and ideally sealed at the top. We find and block those bays as part of the job.

Wiring and other checks

Boston's insulation barriers guidance notes that knob-and-tube wiring was common in homes until the 1940s, and that an inactive system does not stop insulation work. A live system needs an electrician before the walls are filled. We test outlets and look in the basement and attic for old wiring before quoting. We also check for water damage around windows and missing sheathing.

What R-value to expect

The Massachusetts stretch code summary lists R-30, or R-20 plus R-5 continuous, or R-13 plus R-10 continuous for new wood-frame walls in Zone 5. An existing 2x4 wall cannot reach those without exterior foam board, but filling empty bays is still one of the biggest comfort improvements an old house can get. If you are re-siding, adding rigid foam outside at the same time gets closer to the code values.