Insulation & air sealing · Larkspur Hollow and the Derwent Vale · Est. 1968
A house is a system. We insulate the whole of it.
Thistlewaite & Marsh has spent fifty-seven years in the attics and walls of the Vale — audit first, air-seal second, dense-pack third, test before we leave. Cellulose at 3.5 lb/ft³, attics settled to R-60, and a blower-door reading on file for every address we have ever finished.
Two CFM50 readings in every homeowner's file, one before and one after · fourth-generation dense-pack rigs · Est. 1968
The shop
Fifty-seven years of one idea
The first Thistlewaite blew rockwool into Vale walls with a machine he modified himself; his granddaughter runs the same trade with cellulose and a blower door, out of the same yard behind the corn exchange. We have never sold windows, financed furnaces or carried a product line — a house loses heat in holes and thin places, and that is the whole of what we fix.
The file travels with the house
Every job leaves with a binder: the audit sheet, the infrared photographs, the scope, and both blower-door readings. When the house sells, the file goes with it — solicitors in the Vale ask for it by now.
What we do
What we do to a house
The attic, to R-60
Dams around every recessed light and the hatch, baffles keeping the soffits breathing, then cellulose blown deep enough that the joists disappear. The attic is the cheapest heat you will ever buy back — two inches of the old mineral wool is not insulation, it is archaeology.
Dense-pack walls
Empty cavities filled through one 2-inch hole per bay, blown to 3.5 lb/ft³ so it cannot settle, plugged and patched the same day. The hollow-tile terraces of the Vale go from drum-sounding to dead-sounding in about six hours, and stay that way.
Cellar ceilings and rim joists
The rim gets two-part foam on the box sill and a bead where the plate meets the stone; the floor above gets R-38 dense pack with the ground vapor managed before it is covered. Cold floors over cellars are an air-leak problem wearing a sock disguise.
How it goes
Audit to test-out, ten working days
The same sequence on every job — the only variable is your project.
Day 1
The audit
Blower door and infrared camera, room by room, with the house cold and the sky cold behind it. You watch the walls stream purple where the heat is leaving. The written scope goes in the binder before we pack up.
Day 2
The seal
Every hole the camera found — top plates, chases, the chimney gap, the cellar ceiling — foamed or caulked. On a Vale terrace this is commonly two-thirds of the entire saving, and it is the day the drafts stop.
Days 3–6
The fill
Dense-pack in the walls, blow in the attic, foam on the rim. One crew, one van, dust sheets everywhere, holes plugged as the day advances. The house stays lived-in; we work a wall at a time.
Day 7
The test-out
The blower door comes back and the house speaks its second number. Both readings, the audit sheet and the infrared set go into the binder, and the binder goes to your address, not our filing cabinet.
The Vale, 2025 — 2026
Recent attics
Six jobs from the last year, photographed at handover with the insulation card still on the hatch. Nothing styled — an attic either holds R-60 or it does not.
The 1904 farmhouse at Hollow Mill tested 3,900 CFM50 in November — the audit sheet looked like a losing scorecard. They sealed it, dense-packed the walls and blew the attic, and the test-out read 1,450. The binder sat on the kitchen table at completion, and our buyer's surveyor rang them to ask where the work had been done. It had been done everywhere.
Audits booked within the week, valley-wide · (555) 011-6208 · desk@thistlewaitemarsh.example
Book the audit
Tell us the house — decade, walls, and which room loses January. The audit carries two blower-door readings and an infrared set, and everything it finds goes in the binder either way. desk@thistlewaitemarsh.example