Technical Support - Membranes

What is a roofing membrane?

A roofing membrane, sometimes referred to as underlay, provides a secondary layer of protection against water penetration beneath the primary roof finish (slate or tile).

How many types of membrane are there?

Membranes are either LR (low resistant) also known as vapour permeable (breather) or HR (high resistant) “non-breather”. Within the LR grouping we have Permo Air which is not only vapour permeable but also air open.

What is unique about Permo Air?

Permo Air is a low resistance air-open membrane. It is the ideal solution when there is a high risk of condensation forming in the roofspace. The difference with Permo Air is that it is both air open and vapour permeable further minimising the risk of condensation forming, particularly during the drying out period of a building. NHBC has officially recognised that the use of Permo Air eliminates the need for high level ventilation products in a Cold Roof.

Does Permo Extreme need ventilation?

Although Permo Extreme is Vapour permeable, under BS5250 it is classed as a HR underlay must require ventilation at low and high level in line with ventilation requirements applicable to your roof construction. 

Do I need ventilation with your other Membranes?

In most cases we would recommend ventilation. Your choice of membrane will depend on the roof construction. Whilst the use of  Permo Air eliminates the need for ventilation in cold roofs. Warm Roofs will require ventilations unless you are able to use a vapour control layer such as Wallint 50. Please note you cannot use a Vapour Control layer with Permo Extreme.

When should you use Permo Frame?

Permo Frame is designed to be used on Timber Frame Walls, Steel Frame Wall, Pre assembled Panels, On Site assembled frames and behind Vertical Cladding. It should be installed with the “fleece” side facing inward and the “smooth” side facing out toward the elements

What is a Vapour Control Layer?

It is a Layer designed to be installed on the warm side of insulation to aid in air tightness of pitched roofs and to control vapour and assist condensation control. In the Klober range there are two vapour barriers; Wallint 50 and Sepa Solar, which has a reflective surface which increases a construction's thermal resistance.

Can Permo Extreme be used with a Vapour Control Layer (VCL)?

Whilst Permo Extreme can be used with a Vapour Control Layer the roof will still require ventilation. This is due to the membrane being an HR product,

What is the best membrane for low pitched roofs?

Permo Extreme is engineered for low pitch roofs. For pitches of 12.5 degrees for profile tiles, 15 degrees for flat tiles and slates, 22.5 degrees for plain tiles.

What pitch can you go down with using Permo extreme?

You can go down 12.5 degrees which has an Interlock tile and Profile Tiles such as the Double Roman or Renown, 15 degrees for Flat Tiles and Slates and 22.5 degrees for plain tiles. Butylon tape is required to seal nail penetrations.

Why do I need an underlay support tray?

Over time, if left unsupported, membranes can sag between the rafters and cause water to pond at the bottom. This can be prevented by an underlay support tray. A modern and faster method than installing traditional timber fillets. Also the underlay support tray provides drainage from the underlay into the gutter (modern day underlays are only UV stable for up to 4 months, therefore should not be exposed).