Installation guide

PERMAVENT must be installed the correct way up, this is, darker blue side with the lap indicators and PERMAVENT writing outward.

PERMAVENT should be unrolled along and parallel with the fascia (or eaves line) and held in place using the battens whilst working up the roof in the usual way. Laps should be a minimum of 100mm but we recommend 150mm and even 200mm on shallow pitch roofs of less than 20 degrees. Hips should be overlapped by 300mm and valleys should be under lapped by 300mm following the line of the valley. PERMAVENT-TAPE super strength double sided tape can be used to fix PERMAVENT to sarking or insulation boards such as in Scottish practice.

In all cases, although PERMAVENT is the only breather membrane with U.V. additives which enables a delayed finishing of the roof covering (up to three months), an eaves carrier tray (or tilting fillet) should always be installed to where the felt runs over the fascia and into the gutter.

Because of the high tech, lightweight design of PERMAVENT the laps should be taped and sealed using PERMAVENT-TAPE . When PERMAVENT is used on a cold non vented roof, taping and sealing of the roof laps and joins is essential to prevent moist or cold air and wind from entering the roof space.

As with all breather and lightweight membranes, if used with wide batten spacing or counter battens, there is a risk of flapping that could be noisy or even leak if the roof is not yet tiled in, especially if the pitch is shallow. Taping of the laps with PERMAVENT-TAPE as well as correct detailing will eliminate this risk.

Vent pipes, roof lights and apertures on the roof should be sealed with PERMAVENT-TAPE and any nail tears or damage must be repaired.

Cold vented roof (most common type) and Hybrid roof (or habitable roof space)

Place your PERMAVENT-TRAY eaves carrier over your facia ensuring that each carrier laps the next one by at least 75mm and is sealed together using PERMAVENT-TAPE . Ensure the ventilation is correctly installed.

Unroll the PERMAVENT-TAPE along the length of the PERMAVENT-TRAY eaves carrier about 50–100mm up from the back of the fascia and leave the protective tape in place. A strip of PERMAVENT at least 600m wide should now be installed up any valley section if, for example, preformed G.R.P Valleys are being used.

Unroll PERMAVENT along the line of the eaves with the bottom of PERMAVENT covering the eaves carrier and PERMAVENT-TAPE but not hanging over the fascia. PERMAVENT should not be pulled tight but allowed to slightly dip (about 5mm) between the rafters. Staple or nail the very top of PERMAVENT (this will be covered by the lap of the next run) and fix the battens at your required spacing.

Lift up the lower section to reveal the PERMAVENT-TAPE on the PERMAVENT-TRAY eaves carrier, peal off the protective tape, and stick PERMAVENT to the eaves carrier. Apply the PERMATAPE to the top of the newly laid PERMAVENT within the lap in the same way that it was applied to the eaves carrier. Repeat the previous actions and carry on up the roof battening and sticking the laps as you go. When you reach the ridge you should consider the other side of the roof and ensure that PERMAVENT is lapped over the ridge by the final roll and laps the other side fully. Ventilated ridge will have its own installation instructions that should be followed.

Where rafters/wall plates abut masonry that rises above the roof line, PERMAVENT should be extended up the abutment (wall/chimney etc) by at least 75mm. Provision should be made to guard against sagging.

Cold non-vented roofs (energy efficient roof)

This type of roof is laid in much the same way as a traditional roof but care must be taken to ensure the system is installed with good working practice.

This roof has no active ventilation of the roof space (no soffit, eaves or ridge vents) but relies on the PERMAVENT system of vapour control. It uses vapour barriers between the habitable rooms and the roof space (usually at ceiling level) with PERMAVENT keeping the roof dry and healthy. Because of the vapour escaping the roof space, advice should be sought as to counter battens or ventilation over the top of PERMAVENT

Warm Deck roofs (insulation between or over the rafters)

Fit an eaves carrier as before and lay on the first roll of PERMAVENT directly onto the insulation or rafters. Because PERMAVENT cannot dip between the rafters, in this type of roof, a counter batten of at least 10mm must be laid up and on top of the rafters. This counter batten will allow any rain or moisture to run under the normal roofing battens and off the roof. If the counter batten space is to be used for ventilation then advice should be sought*. Carry on up the roof as before using PERMAVENT-TAPE and counter battening and battening as you go.

* Warm Deck and Cold non-vented roofs

Information concerning whether or not you should ventilate the gap between Breather membranes and your roof covering (tiles etc) has not been fully defined by the controlling bodies. PERMAVENT works so well at releasing vapour from the roof space that interstitial condensation can form on the underside of the roof covering (slates etc). However, some coverings such as plain tiles allow sufficient air to pass through them as to clear any vapour that has escaped the roof and passed through PERMAVENT. Tightly fitting coverings such as manmade slates or steel sheet may trap this vapour causing interstitial condensation that can adversely affect them.

Ventilation should therefore be used over the fascia and at the ridge to clear it. You should check the advice of the tile, slate or roof covering manufacturer before you proceed without ventilation.

Vapour control

In order to combat condensation in the home the user should ensure the correct detailing of vapour control. A vapour control barrier should be installed behind the plasterboard at ceiling level (example: min 500 gauge DPM). Sealed loft hatches should always be used; pipes and apertures should be sealed. The top of the brick work cavity should be closed. Water tanks should be covered. Special attention should be given to recessed lighting that breaks the vapour control barrier.