DuPont Tyvek Supro Breather Membrane

In-Depth Look

Tyvek Supro is a breather membrane used as a pitched roof underlay or a timber frame wall membrane. A BBA certificate is independent evidence for stated uses, but building control still looks at the whole build-up.

Why Breathable Membranes Matter

Traditional roofing felt (Type 1F sarking felt) is a low-permeability membrane that traps moisture vapour inside the roof structure. As insulation levels in UK buildings have increased under Part L, more moisture is driven upward into the roof void, raising the risk of condensation on the underside of the felt and the top surfaces of roof timbers. A breathable membrane like Tyvek Supro is highly vapour permeable, allowing moisture vapour to escape from the structure while helping to keep driving rain out.

BBA Certification

The BBA (British Board of Agrément) certificate is independent evidence for stated uses. Building control still looks at the whole build-up, so check the certificate for your build-up.

Installation Guidance

Follow the BBA certificate and manufacturer instructions for laps, tapes and fixing, as these depend on the roof or wall design. On wall applications, the membrane is fixed to the structural frame before the outer cladding is applied. UV exposure before cladding is limited, so check the data sheet for your version. Supro is sold for roofs and for wall and floor applications, so check the certificate for your build-up.

Compliance

Tyvek Supro is CE-marked. Check the manufacturer’s data sheet for the standards it is tested to.

Verdict

Tyvek Supro is a breather membrane for roofs and walls. Its BBA certificate is independent evidence for stated uses, and building control still looks at the whole build-up.

How It Compares

DuPont Tyvek Supro is a breather membrane, a sheet that keeps wind and rain out of a building while letting moisture vapour pass through. The product information lists it as windtight and water resistant, highly vapour permeable, with a BBA certificate and an allowance for limited UV exposure during construction. Check the exact figures on the manufacturer’s data sheet for the version you buy.

Klober Permo, Proctor Roofshield and other roof underlays work on the same principle, and Wraptite and Visqueen sell membranes for walls. Their performance classes, certificates and permitted uses vary, so compare the current data sheet and certificate for each product rather than the headline description.

A BBA (British Board of Agrément) certificate is an independent assessment of a product for stated uses. It is useful evidence that the product suits those uses, but it is not an automatic pass at inspection. Building control looks at how the whole roof or wall is built and installed.

The product information describes Supro as both a roofing underlay and wall breather membrane. Because the certificate and uses can differ for each product and application, check that the version you buy is certified for your build-up. Roll widths and weights differ between versions of the product, so confirm the dimensions and specification against the data sheet before you order.

Whatever the building, the membrane should suit the build-up. The deciding factors are the type of roof or wall, the insulation, the ventilation and the manufacturer’s instructions.

Common Questions

What is the difference between a breather membrane and a vapour control layer? A breather membrane sits on the cold, outer side of the structure and lets moisture vapour escape while keeping rain out. A vapour control layer sits on the warm side and limits how much moisture vapour from inside gets into the structure. They work together as part of a design, and which you need depends on the build-up.

Do I need to leave a gap above the membrane, or tape the laps, on a roof? That depends on the roof design and the manufacturer’s instructions. Follow the BBA certificate and the manufacturer’s instructions for laps, tapes, battens and ventilation. The product information mentions sealing laps with tape for the windtight layer in some applications, but check the certificate for your particular roof.

Can I leave it exposed while the roof is being finished? Membranes are only designed to be left uncovered for a limited time, and the data sheet gives the maximum for your version. Treat that as a maximum, not a target. Wind can damage loose membrane, so fix it correctly and cover it as soon as practical.

What is the difference between roof underlays and wall membranes? Both control moisture and wind, but they sit in different places and face different conditions. A roof underlay lies under tiles or slates, supported on rafters or boarding. A wall membrane sits behind cladding. Certificates state which one a product is approved for, so check this before buying.