ROOFING MEMBRANE

Roofing membrane also referred to as 'roof underlay' is used to screen the building roof beneath the tiles to terminate insulation and rafters from being exposed to humid conditions, debris and dust. It can also help reduce noise in windy conditions. Membranes should also provide a clear path to the roof drainage system from the batten space for any water that may collect on their surface. They also act as temporary protection whilst the roof is being installed. In other words, roof breathable membrane will allow any moisture trapped in the wall cavity to escape, reducing the risk of damp in your home. Roof membranes come in various options such as felt, bitumen and polypropylene. The membrane is placed on the ‘cold’ side of the insulation, and will allow moisture to pass from the inside to the outside, and still allow air to circulate below, limiting the likelihood of damp and other moisture-related problems. Breathable roof membranes are typically used in constructions where external cladding or tiles are not completely water-tight or resistant to moisture. Being modern and lightweight, membrane is a great alternative to traditional styles of underlay products such as 1F roof felt. If your roof faces a lot of wind uplift, you should buy a membrane that is stronger and more durable - often made to manage the elements comfortably. A perfect example is Novia, which has all the benefits of lighter membrane with a higher tensile strength. On the other hand, your roof could be exposed to a high degree of condensation, so in this instance it would be more efficient to choose a highly breathable roof membrane that will successfully manage this problem. For a cheap option, it is recommended to use Novia, as it is a breathable membrane. All membranes can be supplied with or without self-adhesive tape. Breather membranes can also improve the thermal efficiency of a building’s external envelope and can provide temporary protection from the weather during construction or repair works.

TYPES OF ROOF MEMBRANES

Generally speaking there are two types of membranes – breathable membrane and non-breathable membrane. The main difference between non-breathable and breathable roof membrane is surround ventilation and how each tackles the problem of condensation.

Breathable roof membrane, as the name suggests, lets a building to breathe by allowing moisture to escape up through it and out of the building being located on the cold side of a pitched roof's insulation and beneath the battens which support the tile or slate. Breathable membrane allows vapour to travel through it easier, while non-breathable membrane doesn’t. Breathable roof membrane is newer and its popularity has soared in recent years. The most breathable types of membrane today are ‘air open’ and ‘vapour permeable’. These represent the cutting edge when it comes to breathability and are a result of extensive R&D on the part of the manufacturers. They’re especially useful in complex roofs, such as those found in extensions, skylight-equipped loft conversions and heavily partitioned apartment buildings where there are many breaks in the roof, and reduced opportunity for ventilation.

Non-breathable membrane on the other hand is not air permeable. This is not to say that non-breathable membrane is not suitable for new builds as non-breather membrane is still widely used and perfectly suitable on roofs where effective ventilation is already in situ. When non-breathable membrane is used below the slates or tiles, very little moisture makes its way into the batten space above. Non-breathable membrane is located on the cold side of the insulation. The best breathable roof membranes and non-breathable membrane will always be those that strike a balance between thickness and affordability.

There are two main types of membrane recognised by BS 5250 which is the British Standard for the Control of Condensation in Buildings:

High Resistance (HR)

HR membranes are impermeable underlays and will resist the passage of water vapour through the body of the membrane. HR membranes will always require additional roof space ventilation.

Low Resistance (LR)

An LR membrane will always have a lower vapour resistance figure and as such will allow an amount of water vapour to pass through the membrane by diffusion, lessening the risk of the build up of harmful condensation.
LR membranes are also known as vapour permeable membranes. The use of an LR membrane will therefore typically require less additional roof space ventilation than that of a HR membrane, although in accordance with BS 5250 the amount required will depend on the type of construction and whether a well sealed ceiling is present.

HOW LONG MEMBRANES LAST?

If a membrane doesn’t incur direct damage, it should last for several decades with minimal maintenance. If the membrane has been damaged, it will need to be repaired or replaced. In situations where big holes were made, a roof membrane repair kit may be required.

BRITISH STANDARDS FOR ROOF MEMBRANE

The low and high water vapour resistance tags given to breathable and non-breathable membranes respectively are classified so by British Standards. Some underlays will only be compliant with certain wind zones as outlined in BS5534. Thickness gives a good indication of resistance to wind and tearing, with thickness measured in grams per square metre. The BS5250 code of practice gives guidance for control of condensation on all different pitched roofing structures. BS 5534 ‘Code of Practice for ‘slating and tiling’ carries considerable implications for manufacturers as well as contractors, particularly in relation to membranes. Following an increasing number of problems with lightweight membranes ‘ballooning’, a new wind speed map of the UK was introduced in 2015, requiring manufacturers to provide information on packaging to show the zonal limit for each product. Membrane laps must be secured by a batten or by proprietary means such as a tape. If the latter, evidence will be needed from the manufacturer that this has been tested for wind uplift. Generally, breathable membranes for wall constructions do not have to be as high a specification as those in roof constructions. In roofs, breathable membranes are required to resist wind uplift so that tiles are not dislodged by movement of the membrane. Be sure to select the right length, width and then choose the desired gsm (grams per square inch). 

ROOFING MEMBRANE MANUFACTURERS

While standard grade membranes can be easily found in well known shops such as Wickes, Screwfix or B&Q, high quality membranes can only be spotted in online retailers like us. We are proud to offer top brands such as: Novia®, Tyvek®, Klober® and Cromar®. Here at InsulationGo we have the full range of products that protects the inside of a building against moisture build-up inside the house. Each section highlights the different products we offer catering for a variety of applications and requirements. 

NOVIA®

• Novia VC2T Scrim Reinforced Synthetic Laminate
• Novia Black 115GSM Roof and Wall Breather Membrane
• Novia Blue 4016 Type 2 Breather Wall Paper
• Novia FR Class B Fire Rated Breather Membrane
• Novia Reflex Reflective Roof and Wall Breather Membrane 
• Novia Ultra+ 95gsm Roof and Wall Breather Membrane
• Novia Black Construction Wrap Breather Membrane 

TYVEK®

• DuPont Tyvek Supro Breathable Membrane 
• Tyvek Housewrap Breather Wall Membrane from DuPont 
• DuPont Tyvek FireCurb Breather Membrane 
• Tyvek UV Facade Protective Membrane 
• Tyvek Supro Breather Membrane Felt Underlay

KLOBER®

• Klober Permo Extreme RS SK² Underlay 
• Klober Wallint 50 Vapour Control Layer 
• PERMO ECOVENT
• PERMO LIGHT
• PERMO FORTE
• PERMO AIR
• PERMO AIR
• SEPA LIGHT

CROMAR®

• Cromar Protect 1F Non-Breathable Membrane

Video credit:https://www.youtube.com/watch?v=OgBRjUD5CVA&t=53s

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