Major Surgery for a Failing Fat Wall

On the surface, an attractive 1980's-era Vermont country house. But inside the walls, trouble is lurking.

From the back yard, the home looks solid and well-built. And it is — except for a few major building science flaws.

A routine weatherization pre-inspction using a FLIR infrared camera revealed a major issue: the bright orange glow of uninsulated wall voids in the upper half of almost every wall.

An infrared scan from Jim Bradley's audit report, juxtaposed with a daylight photo of the same wall for the owner's information. The orange upper portion of the wall in the infrared scan shows where heat is leaking through the uninsulated wall cavities.

Another infrared scan of what should be a superinsulated foot-thick clear wall section shows settling of the insulation in the upper wall, and the clear image of a tunnel excavated by rodents.

On a cold day, infrared view from the heated indoors tells the same sad story: the cold purple area at the top of the wall shows the uninsulated void.

Ants infested this cement-parged polystyrene foundation insulation. Hearing the ants at work, birds attacked the foam in search of a six-legged meal.

Moisture building up in the cold wall cavities had degraded the OSB sheathing covering the outboard face of the outer stud wall frame.

Heavy with moisture, the loose-fill cellulose insulation has sagged in layers to the bottom of the wall cavities. The OSB sheathing has lost its integrity, and flakes off easily.

Bradley had originally planned to leave the building's existing Anderson windows in place. But damage to the OSB and framing behind the windows has led the owner to opt for window replacement instead.

The home's original builder was well-intentioned and did careful work, Bradley notes. For example, this outlet has been carefull air-sealed to the interior drywall. But a misunderstanding of building science and materials led to systemic wall failure.

After stripping off the sheathing, crew vacuums out the old cellulose insulation. Given the extensive infestation of the walls, Bradley says, he suspects that the original insuation was not borate-treated.

Connecting the vacuum hose to a filter bag in the rolloff dumpster.

A look at the filter bag inside the rolloff dumpster, collecting the spoiled cellulose insulation as the crew vacuums out the double-stud walls.

After insulating the inner wall stud bays with Roxul rock wool insulation, the crew applies and tapes Intello smart vapor retarder fabric to the inner wall from the outside.

The crew staples Insulweb open-weave fabric to the outside face of the stud wall, after installing interior Insulweb baffles to isolate each stud bay from its neighbors. This creates manageable-sized cavities for correct dense-packing, so the replacement insulation will not settle the way the original material did.

Stapling Insulweb open-weave fabric to the exterior wall framing.

Blowing cellulose dense-pack into the newly covered wall cavities.

A crew member cuts vapor-open exterior gypsum board sheathing for the insulated wall. This sheathing material will allow moisture to escape outward.

Sheathing the newly re-insulated wall with vapor-open gypsum board panels.

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