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How to tape a vapour barrier

Updated: October 2026

The lap looked stuck at dusk and was hanging off the sheet in the morning. That is the usual way vapour barrier tape fails in a UK loft: dust, cold, a flexing membrane, or a joint asked to carry the weight of the sheet. This is how to tape a vapour barrier so the tape only closes a gap the sheet has already formed. The Products Compared editorial team used notes from A. Proctor Group, Novia and tesa, plus amazon.co.uk review signals dated 16 October 2026. A qualifying purchase can earn a commission at no extra cost to you. Which roll to buy sits on the [vapour barrier tape comparison](/hub/site-barriers/vapour-barrier-tape).

The lap looked stuck at dusk and was hanging off the sheet in the morning. That is the usual way vapour barrier tape fails in a UK loft: dust, cold, a flexing membrane, or a joint asked to carry the weight of the sheet.

Our top picks

tesa tesa 60077, 50 mm

Best overall

tesa tesa 60077, 50 mm
8.2/10about £30.84
View offer
DuPont Tyvek AirGuard 1310V, 60 mm

Rank 2

DuPont Tyvek AirGuard 1310V, 60 mm
8.6/10about £28.00
View offer
Ealyder Ealyder polyethylene, 100 mm

Best value

Ealyder Ealyder polyethylene, 100 mm
6.8/10about £17.99
View offer
On this page
  1. 1.Get the sheet flat before you look for tape
  2. 2.Stick the lap so it stays
  3. 3.Pipes, cables, tears and staples
  4. 4.When to stop
  5. 5.The lap, then the tape

Get the sheet flat before you look for tape

The sheet is the barrier. Tape on the wrong face does not move the vapour control layer to the warm side of the insulation. Lay the sheets against a firm background. A UK review of the Ealyder polyethylene roll says it held when the membrane was tight, clean and dry, and came unstuck where the membrane flexed. If the sheet billows between rafters, support it before you close the lap. Staples are not that support. They puncture the sheet. Novia's sequence is butyl in the joint, staples through the butyl, then a single-sided cover tape. Face tape over bare staples leaves the holes. The buying guide is where that two-tape decision belongs.

Stick the lap so it stays

Wipe the lap. Dust and a film of condensation are enough to make a tape look bonded and then let go. Use the temperature figure for the roll in your hand, and keep the roll in the house until you need it. Press, do not stretch. UK airtightness notes say no frost, no silicone, no tension, and rub the tape hard. A roller matters at reveals. Leave a test piece overnight on the long polyethylene roll. Two of the four UK reviews on that listing describe lift-off. Do not practise on the real lap with the red coating tape.
tesa tesa 60077, 50 mm

Testsieger

tesa tesa 60077, 50 mm
8.2/10about £30.84
View offer

Pipes, cables, tears and staples

A pipe wants a collar, not one straight strip. Keep the joint out of tension. A cable is easier to rush. tesa's UK note for 60077 uses two slit pieces so the tape lies flat either side of the wire, rather than one band that leaves tunnels. A small tear can take a patch of system tape pressed onto clean sheet larger than the hole. A long rip is a new sheet, not a collage. Staples are the hole people forget: face tape covers the crown and does not fill the puncture. If you have already stapled bare polythene, patch back to sound sheet or redo that bay with butyl. The foil tape page explains why a silver HVAC roll is not the shortcut.

When to stop

Stop when you cannot name both the warm-side sheet and the ventilation path the roof still needs. Taping every lap in a cold roof does not entitle you to close the eaves. That limit is on the loft page. A ring of tape is not a fire hood. Stop if this ceiling is the airtightness line for an air test, or if you cannot both seal a cold flat roof and keep the void ventilated.

The lap, then the tape

If the sheet is flat, clean and dry, press a single-sided tape on the lap the membrane maker specifies. If staples puncture it, put butyl in the joint first. If the hole is a pipe or a cable, collar it so the tape is not asked to bridge a gap. If you cannot name the warm-side sheet and the ventilation path, stop.

Common questions

Which side of the insulation does the sheet go?
On the warm side, the room side, for the usual UK roof cases described in guidance that cites BS 5250. The tape goes on that sheet, on the face the membrane maker tells you to stick. Tape on the cold side does not turn a breather membrane into a vapour control layer. If you cannot point at which side is warm, sort the build-up before you buy another roll.
How much should the sheets overlap?
Use the overlap printed for your membrane. Novia specifies 150 mm on its vapour control layers. A Passive House Systems UK guide for its own sheet says at least 100 mm. A 50 mm or 60 mm tape then sits on that overlap. It does not replace it. If your sheets only just meet, widen the lap before you look for a wider tape.
Do I need a roller?
You need pressure on every part of the strip. On a flat lap, a firm rub can do that. At a reveal or a pipe collar, fingers leave the edges unstuck, and Proctor asks for a roller there. Keep the joint out of tension. If you cannot press it, the tape is decoration until it lets go.
What if the loft is cold?
Warm the roll in the house and check the sheet. Proctor's window for its tapes is about 5°C to 30°C. DuPont allows 1310V above −5°C. A loft below the figure for your roll is a reason to wait, not a reason to press harder. Dust and condensation at low temperature are the combination that looks stuck and fails overnight.
How do I tape around a pipe or a cable?
Give a pipe a collar so the sheet meets a gasket, and keep that joint free of tension. For a small cable, tesa's 60077 note uses two slit pieces, each at least 110 mm long, so the tape lies on the sheet either side of the wire. One straight strip leaves tunnels. If the hole is large or the pipe moves, use the membrane maker's collar rather than a star of offcuts.
When do I stop and call someone?
Call when you cannot name both the sheet and the ventilation path, when spray foam is already in the rafters, when the ceiling is fire-rated, or when the sheet is the line for an air test. Also stop if downlights are still open and you were about to tape over the lamps. Those are design and fire questions, not a longer roll of tape.

Related pages

Best vapour barrier tape

Vapour barrier tape

Vapour barrier tape buying guide for sheet and width

Vapour barrier tape in a loft: leave the eaves open

Vapour barrier tape vs foil tape for a UK AVCL lap

Sources

Public UK sources from the research digest. Listing prices, stars, and review counts are the amazon.co.uk lines stored with these four ASINs. Page updated October 2026.

  1. Approved Document C — Requirement C2 and the vapour control layer (retrieved October 2026)
  2. BSI BS 5250:2021 — Management of moisture in buildings (retrieved October 2026)
  3. IKO note on BS 5250:2021 (retrieved October 2026)
  4. A. Proctor Group — installing air and vapour control layers (retrieved October 2026)
  5. Novia vapour control layers (retrieved October 2026)
  6. DuPont UK TDS, AirGuard tape 1310V (retrieved October 2026)
  7. tesa UK 60077 note (retrieved October 2026)
  8. Passivhaus Trust airtightness guide, June 2020 (retrieved October 2026)