Tyvek® membranes are specially designed to minimise interstitial condensation and remove the need for ventilation in the insulation, providing a holistic solution to energy efficient warm pitched roof constructions. They permit water vapour in the roof space to permeate through to the batten space, where the natural movement of air through the roof covering disperses it into the atmosphere. The ability of Tyvek® membranes to provide this condensation control eliminates the need to ventilate between the underlay and the insulation, improving the overall energy efficiency of the construction.
As a secondary water-shedding layer, Tyvek® membranes also provide a barrier that minimises the wind load acting on the slates and tiles, and helps keep wind-blown snow and dust out of the roof construction.
Tyvek® and AirGuard® in Warm Roof Applications
Here, insulation is installed at rafter level, using rigid and/or semi-rigid insulation. Ideally, the insulation is positioned in a continuous layer above the rafters, so that the roof structure is in a ‘warm’ environment. However, certain roof specifications can involve installing insulation over, between or under rafters – or even a combination of all three.
Tyvek® and AirGuard® in Room in the Roof Applications
Room in the roof constructions frequently use a combination of warm and cold roof constructions, with varying types of insulation. Cold roof areas usually include ‘vapour-open’ fibrous insulation (e.g., mineral wool quilt); the sloping ceiling areas include closed-cell or foil-backed rigid board insulants, most of which are highly vapour-resistant. This variation in vapour resistance can create an imbalance in vapour drive. To solve this we recommend installing an air & vapour control layer (AVCL), such as DuPont AirGuard® Control, Smart or DuPont AirGuard® Reflective beneath the ‘vapour-open’ quilt insulation.
Meets Building Requirements
Non-ventilated pitched roof systems that use Tyvek® as rooﬁng underlay satisfy the requirement of Approved Document C2.
BBA certificate 08/4548 approves the use of Tyvek® & AirGuard® membranes in both warm and cold pitched roof constructions. These constructions are categorised as shown; the difference lies in where the insulation is positioned.