Proctor Air - Air & Vapour Permeable Roofing Membrane

VAPOUR PERMEABLE
Proctor Air has an Sd-value of 0.015m and a vapour resistance of 0.075 MNs/g making Proctor Air one of the highest performing vapour-permeable membranes on the market.

FULLY AIR PERMEABLE
Air permeable membranes allow air movement through the roof, as well as allowing moisture to escape by diffusion. This means that condensation is far less likely to form on the membrane itself, and also allows the membrane to deal with much higher moisture levels within the building, for example during the drying out period.

WATER RESISTANT
Proctor Air is rated W1 under EN13859-1, and has a hydrophobic additive in all 3 layers. The membrane can be left exposed for up to three months to UV exposure, however for water resistance we recommend the exposure time is reduced to as short a time as possible. If leaving exposed we would advise a temporary cover such as a tarp, especially in inclement weather and in refurbishment projects (please refer to the FAQs in the Proctor Air brochure, page16-19). Proctor Air has a Hydrostatic Head of water of over 1m as recommended by NFRC Technical Bulletin 6. It is good practice not to leave the underlay exposed longer than necessary.

WIND UPLIFT RESISTANCE COMPLIES WITH BS5534
Based on fully independent 3rd party testing, Proctor Air can be utilised across the UK. This, in addition to no requirement for high level ventilation or the use of a vapour control layer, ensures Proctor Air remains the simplest and most cost effective method of achieving regulation compliance.

MORE UNIFORM AIRFLOW THAN VENTS
The air permeability of Proctor Air means a non-ventilated roof fitted with Proctor Air allows a more consistent air flow through the roof than a roof ventilated as per BS5250, without expensive and time consuming ventilation hardware fitted to the roof.

BBA CERTIFICATE 24/7147
Proctor Air is fully BBA certified for use in non-ventilated warm and cold roof applications.

SOLAR / PV PANELS
A unique feature of Proctor Air’s BBA certificate is the clarification that it can be used on roofs featuring solar PV. Consideration may be required with regards to specific installation criteria for the PV assembly being used. In line PV assemblies can be used, without any additional ventilation or counter battens, when installed with a minimum of two tile zones around the perimeter of the PV Assembly. Alternatively, at the ridge, the two tile zone can be replaced with a dry ridge system above the PV Panel. PV assemblies mounted above the slates or tiles do not require any additional consideration.

NO VCL REQUIRED
Installing Proctor Air means that a vapour control layer is not required for nonventilated cold pitched roof constructions.

15 YEAR WARRANTY
Proctor Air’s 15-year warranty provides peace of mind on any project.

ENERGY EFFICIENCY
Energy Loss by ventilation in conventionally ventilated cold roofs will be significantly reduced by the non-vented system.

How “Breathable” is Proctor Air?

While “Breathability” or breather membrane is a commonly used term, it is more technically accurate to refer to a material’s “vapour permeability”.
As Proctor Air is air permeable as well as vapour permeable, it can certainly be argued that it does breathe, as it allows air
movement, but this does not hold true for all “breathable” materials. In terms of vapour permeability, Proctor Air, with an Sd value 0.02m and a vapour resistance of 0.1MNs/g, is one of the most vapour permeable membranes on the market, as well as benefitting from the additional advantage of air permeability.

What difference does air permeability make?

Proctor Air, in addition to having one of the lowest vapour resistance available, is also air permeable. Industry research concluded that air permeability, combined with very low vapour resistance, inhibits the formation of condensation in a pitched roof to the point where it’s virtually impossible for condensation to occur under normal conditions.

Studies conducted by the BRE and Glasgow Caledonian University have concluded that not only does an air permeable roofing underlay outperform conventional airtight underlays, but may provide a higher air change rate than a roof ventilated according to the recommendations in BS5250.

Does Proctor Air suffer from “tenting”?

As anyone who’s slept in a cheap tent can tell you, some vapour permeable fabrics can lose their water resistance if anything happens to touch the underside. Where the use of underlays fully supported on timber sarking board is standard practice, ensuring Proctor Air does not suffer from this effect was always an important consideration for the A. Proctor Group. In fact while the first generation of VPUs suffered from this problem, most modern roof underlays are unaffected by this phenomenon.

So vents aren’t required?

The A. Proctor Group have undergone extensive testing to prove that ventilation is not required to the underside of the underlay.

The sole remaining situation where ventilation to the roofspace is required is in a cold roof with Plywood or OSB sarking. If in doubt, our team of technical experts can assist specifiers in achieving the most appropriate solution for their specific project.

How about high level vents?

Although non-ventilated roofs have been specified successfully for many years, recently BS5250, the NHBC technical standards and NFRC Technical Bulletin 6 have recommended that ridge only ventilation equivalent to 5mm per metre is used when vapour permeable underlays are specified. In both cases, the exception to this is where the underlay specified is both vapour AND air permeable.

Does Proctor Air “chatter” in the wind?

Wind blowing up into the eaves of a roof can cause a ‘chatter’ type noise with some types of underlay. Proctor Air is silent in such situations. As Proctor Air does not suffer from this problem, the membrane does not have to be pulled taut and does not have any special fixing instructions compared to that of some underlays. Counter battens can be provided to increase the air movement when used with close-fitting slates or tiles, or to provide drainage below the tile battens when used fully supported, but otherwise Proctor Air may simply be draped between the rafters as normal.

Can I use Proctor Air with timber treatments?

All three layers of the Proctor Air underlay have additives to increase the water hold out of the membrane. Timber treatments containing fungicides, insecticides and wood preservatives are extensively used in the building trade to protect rafters, sarking boards and tile battens. Treatments should be dry before installing Proctor Air.

What is the “drying out period”?

This is the period immediately after the building is completed, during which there are significantly higher amounts of moisture within the building. These include moisture in damp timber, from wet trades (concrete, plaster etc) and moisture that may have found its way in, prior to the building shell being wind and watertight. Although this moisture will eventually dry out, condensation is more likely to occur as it does so. This will usually be most apparent in the first winter when the building is heated. Proctor Air roofs are far less prone to this effect.

What about severe weather conditions?

The British Board of Agrément has also issued an Information Bulletin (No. 2) relating to good site practice when using permeable roof underlays. This highlights:-

• An underlay is not a total waterproof barrier and if used as a temporary waterproof covering then rain penetration may occur

• In certain conditions, particularly if there is heavy rainfall combined with subsequent severe freeze/thaw conditions, an underlay should not be exposed for more than a few days

BS 5534

APLR underlays should always been considered as water resistant membranes, based on their function as secondary protection below
slates or tiles.

As per section 4.9 Roofing Underlay and Clause 4.9.1 e) ‘provide temporary weather protection before the installation of the primary
roof covering. An exposed underlay is subjected to UV light which might lead to premature failure; therefore, the exposure periods
should be kept to a minimum. In certain conditions, particularly if there is persistent heavy rainfall combined with subsequent sever
freeze/thaw conditions, an underlay should not be exposed for more than a few days.

Note 2: If an underlay has to be left without a roof covering for a period of time when adverse weather rainfall and weather is expected,
a tarpaulin or similar protective sheeting may be used to protect the underlay until such time that the roof covering can be completed.’

A full copy of this BBA Information Bulletin No.2 – Permeable Roof Tile Underlay Guide to Good Site Practice is available from the BBA
web site: www.bbacerts.co.uk.