Ground vapour barrier
Nothing else in a crawl space works until the ground is covered — IRC R408.3 treats it as the baseline, not an upgrade.
Shop the kit · Air sealing
Seal the leaks before you insulate
Insulation slows heat moving through a surface; it does almost nothing about air moving around one. A ceiling full of open top plates, flue gaps and wiring holes will keep losing heat under any depth of insulation — and once the insulation is down, every one of those gaps is out of reach. This is the work that goes first.
- 12 job-ready items
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What are you working on?
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How air sealing works
- Step 1
Find the leaks
Work on a cold, windy day. Look for dirty insulation, daylight and draughts around penetrations.
- Step 2
Match gap to sealant
Caulk for cracks, foam for irregular gaps, backer rod where the joint moves.
- Step 3
Seal before insulating
Everything you miss is unreachable once the insulation is down. There is no second pass.
Start with these 4
See everything →The four that change the outcome most, in the order a job actually needs them. Everything else on this page is worth having; these are the ones worth a second trip.
Vapour barrier seam tape
An untaped liner is a groundsheet. The laps are where the moisture comes back round.
Fire-rated expanding foam
Closes the big penetrations — flues, wiring, plumbing — that account for most of the leakage you can actually fix.
Acoustical or latex sealant
Does the top plates and the small gaps foam is too coarse for. You will use more tubes than you expect.
Which product for which gap?
Pick the gap in front of you. Matching the material to the joint is most of the skill.
Small crack, under ¼ in.
Caulk or acoustical sealant
Stays flexible and tools flush. Foam here just expands out of the joint and gets trimmed off.
Show me itMedium irregular gap, ¼–3 in.
Expanding foam
Fills a shape you cannot caulk. Use the fire-rated kind anywhere near a flue or chimney chase.
Show me themWide gap that moves
Backer rod, then sealant over it
The rod sets the joint depth so the sealant can stretch instead of tearing away from one face.
Show me themDuct seam or joint
Mastic, or foil tape
Not cloth duct tape — it fails within a couple of years in an attic. Mastic for anything awkward.
Show me themDoor or window edge
Weatherstripping
A compression seal on a moving edge. Caulk would bond the thing shut.
Show me themBare crawl-space floor
Ground vapour barrier, taped at the laps
Reinforced liner up the walls, pinned flat, every lap sealed. Code wants humidity control with it.
Show me themCore air sealing
On every job, whatever you are insulating afterwards.
Attic hatch weatherstrip kit
An uninsulated hatch undoes a surprising share of the work — it is a hole in the ceiling you just spent a weekend insulating around.
- Attic
Door and window weatherstripping
The leaks you can feel, and the cheapest ones to close. Worth doing at the same time as the attic, because the stack effect pulling air out up there is what pulls it in down here.
- Attic
- Doors & windows
- Garage
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Duct & HVAC sealing
Ducts running through an unconditioned space leak conditioned air straight outside.
Duct sealing mastic
If ducts run through the attic or crawl space, they are leaking conditioned air into a space that is effectively outdoors. Mastic over the joints beats tape, which lets go in a few years.
- Attic
- Crawl space
- Ducts
Foil HVAC tape
For duct joints and seams. Cloth duct tape fails within a couple of years in an attic; foil tape is what the name was supposed to mean.
- Attic
- Crawl space
- Ducts
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Specialty fixes
For the gaps the core kit cannot close properly.
Outlet and switch gaskets
Foam plates behind the cover of every socket and switch on an exterior wall. Individually tiny, collectively a real hole — and about the cheapest air sealing there is.
- Garage
Foam backer rod
For gaps too wide to caulk. Pack the rod in first and seal over it — sealant alone in a wide gap slumps, skins over and tears the first time the gap moves.
- Attic
- Crawl space
- Doors & windows
- +1 more
Foam board adhesive
Holds board to masonry. Use one rated for polystyrene — a solvent-based adhesive dissolves the board it is meant to be sticking.
- Crawl space
- Garage
- Masonry / foam board
Garage door bottom seal
Air leaking round the edges of a garage door loses far more than the panels do. Seal the perimeter before you spend anything on insulating the door itself.
- Garage
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Other categories
InsulationThe material itself. How much you need comes from your own measurements — coverage and pack sizes vary by brand, so the calculator gives you a bag or batt count rather than a guess.8 items
Safety gearFibreglass and attic dust are a genuine respiratory hazard. A respirator, sealed goggles and gloves belong on every project, whatever you are insulating.10 items
Measuring toolsGetting the area and the existing depth right is what decides whether the rest of the estimate means anything. Tape, laser, depth markers, moisture meter.23 items
Attic accessoriesThe small items that get forgotten and cost a second trip: baffles, depth markers, hatch weatherstrip, walk boards, support rods.9 items
Rechargeable headlampsHands-free lighting. Holding a phone torch is the usual reason a first attic trip ends early.3 items