Welcome to the Waterproof Breathable Membrane category at Insulation4Less, where we provide a plethora of options to meet all your insulation and barrier needs. This range combines functionality, durability, and cost-effectiveness to facilitate top-tier building solutions.

Choosing a Waterproof Breathable Membrane

Breathable membranes sit on the cold side of insulation and help manage two different moisture risks. They form a secondary barrier against rain, snow and wind-driven moisture that gets past the outer roof or wall covering, while their low vapour resistance allows water vapour to move outwards. That is different from a vapour control layer, which normally sits on the warm side of insulation and is intended to restrict vapour entering the construction.

For pitched roofs, the underlay must be selected as part of the complete roof design rather than by roll weight alone. Wind uplift, roof pitch, exposure, support conditions, batten spacing and the tile or slate system all matter. Rooftec states that its breathable membrane is intended for fully supported and unsupported tiled or slate pitched roofs, warm and cold roof applications, Scottish sarking boards, and timber or metal framed construction.

Rooftec 95gsm, 120gsm or 140gsm: Which One Do I Need?

The three Rooftec options share the same basic purpose, roll lengths and application types. The practical difference shown on the product listings is membrane mass: 95g/m², 120g/m² or 140g/m². A heavier membrane can be easier to handle on demanding jobs, but gsm by itself is not a waterproofing class, wind-uplift classification or permission to use the product in every exposure zone. Check the relevant certificate and project specification before substituting one grade for another.

Construction Wraps and Breathable Membranes

Black+ Construction Wraps and ROOFTEC Breathable Membranes offer variants like the Black+ Ultimate 170GSM Roof and Wall Breather Membrane and different BBA certified options respectively. Specifically designed to provide a top-tier barrier against external elements while allowing water vapour to escape, these membranes safeguard your buildings against condensation and enhance the durability of the structure.

• Uses: Widely employed in walls and roofs, ensuring external elements such as water, wind, and dirt do not compromise the structural integrity.
• Selection Guide: Opt for GSM (grams per square metre) variants per the exposure level of your project to weather elements. Higher GSM often provides better protection against harsher conditions.

Radon Barriers and Kits

Products like 1600 Gauge Radon Barrier and Radon Barrier DIY Kit address a critical issue related to radon gas infiltration. A proper installation of these barriers prevents the harmful gas, which naturally emanates from the ground, from permeating into the living spaces.

• Uses: Imperative in areas known for radon presence, being used beneath the construction to thwart radon infiltration.
• Selection Guide: Gauge selection (thickness) should be dictated by the potential risk of radon gas in the area; the higher the risk, the thicker barrier you may need.

Accessory Tools: Tapes and Repair Kits

Single Sided Breather Membrane Lap Tape and Membrane Repair Tape come to your rescue whenever a robust, durable adhesive solution is needed. These tapes are designed to ensure that membranes remain securely in place, and any accidental damages can be promptly addressed.

• Uses: Generally utilised for sealing, repairing, and bonding membranes ensuring an airtight and waterproof seal.
• Selection Guide: Depending on whether you are bonding layers of membranes or performing a repair, select tapes designed specifically for the job to ensure maximum efficacy.

Which One Do I Need?

For a tiled or slated pitched roof, start with a roofing underlay whose certificate covers your roof build-up and wind zone. Rooftec 95gsm, 120gsm and 140gsm are the relevant roof membranes in this collection. Do not select solely by gsm. Confirm roof pitch, support condition, ridge height, altitude, exposure and batten arrangement against the current technical information.

For an insulated timber-frame or similar wall, choose a wall breather membrane. Novia Black+ is the stronger choice where W1 water resistance is required. Standard Novia Building Wrap is an entry-level W2 wall breather with a lower Sd value of 0.006m. For junctions and laps, use compatible membrane tapes rather than treating general-purpose tape as interchangeable.

For radon protection, use a specified radon barrier system. A radon barrier is not a substitute for a vapour-permeable roof or wall breather membrane. Likewise, external corners and repair tapes are system accessories, not membrane rolls.

How Much Membrane Do I Need?

Measure the actual roof slope or wall face rather than the floor plan. Multiply length by slope width or wall height to get the gross area, then allow for laps, ridges, valleys, abutments, openings and cutting waste. A 1m x 50m roll has a nominal sheet area of 50m² and a 1.5m x 50m roll has 75m², but installed coverage is lower because adjacent sheets overlap.

Does a Waterproof Membrane Mean It Is Completely Waterproof?

This is one of the most common questions around membrane products, and the useful answer is to look at the tested classification rather than the word “waterproof” on its own. A breather membrane is normally a secondary weather-resisting layer, not the finished roof covering. Rooftec 95gsm is classified W1 for resistance to water penetration. Novia Black+ is also W1, while Novia Building Wrap is W2. The tiles, slates or cladding remain the primary weathering layer.

Breathability does not mean the sheet has holes that freely pass rain. These products are engineered so water vapour can diffuse through while liquid water is resisted to the declared class. Performance still depends on correct laps, taped details where specified, intact sheets and suitable junctions around penetrations.

Laps, Fixing and Installation

Follow the membrane manufacturer’s current instructions and the roof or wall system specification. For Rooftec 95gsm, the data sheet states a minimum 20cm overlap at the ridge, a 15cm sheet overlap using the guide line, and at least 20cm overlap where the roof pitch is below 22°. It also says seams, butt joints and membrane damage can be treated with membrane adhesive tape, with suitable silicone or self-adhesive butyl tapes used at other substrates such as masonry.

The same Rooftec sheet gives stated suitability conditions including a well-sealed ceiling, ridge height no greater than 15m, roof pitch from 12.5° to 75°, site altitude no greater than 100m and no significant site topography. Those are product-specific conditions, not universal rules for every breathable membrane.

Frequently Asked Questions

What is a waterproof breathable membrane?

A waterproof breathable membrane is a vapour-permeable sheet used behind roof or wall finishes as a secondary weather barrier. It resists external liquid water while allowing water vapour within the construction to move outwards. The exact water-resistance and vapour-performance figures should be checked on the specific product data sheet.

What is the best membrane for waterproofing?

The correct membrane is the one certified for the specific roof, wall or ground application. For pitched roofing, check water-resistance class, wind-uplift suitability, roof pitch and support conditions. For walls, check EN 13859-2 performance. A radon or damp-proof barrier serves a different purpose from a breathable roofing membrane.

How thick should a waterproof membrane be?

Thickness is product-specific and is not a reliable stand-alone selection rule. Rooftec 95gsm is stated as 0.4mm thick in its data sheet, but performance is defined by tested properties such as W1 water resistance, vapour resistance and mechanical strength. Always select to the system specification rather than thickness alone.

What is the difference between a damp proof membrane and a waterproof breathable membrane?

A damp proof membrane is normally used to resist moisture from the ground and is designed as a barrier. A breathable membrane is generally used on the cold side of roof or wall insulation, where it resists external weather while allowing water vapour to escape. They are not interchangeable products.

Is breathable membrane waterproof?

A breathable membrane can be water-resistant to a declared test class while remaining vapour permeable. Rooftec 95gsm and Novia Black+ are declared W1 for resistance to water penetration. The membrane remains a secondary weather layer, so the roof tiles, slates or external cladding still provide the primary weather protection.

Do I need to tape breathable membrane overlaps?

Taping requirements depend on the product, exposure and airtightness strategy. Novia recommends a two-tape sealing system for its breather membranes, using double-sided tape between laps and a single-sided overlap tape to complete the seal. Rooftec also specifies membrane adhesive tape for seams, butt joints and repairs.

Can breathable membrane be used on walls?

Yes, where the product is declared for wall underlay use. Novia Black+ is suitable for insulated wall applications and meets EN 13859-2; Rooftec 95gsm is also declared to EN 13859-2 in its data sheet. Check cladding, cavity, fire and exposure requirements for the complete wall system.

Do I need a vapour control layer with a breathable membrane?

A breathable outer membrane and an internal vapour control layer perform different jobs and can be used in the same construction. Whether a VCL is required depends on the complete roof or wall build-up and condensation-risk design. Do not use the low vapour resistance of the outer membrane as evidence that an internal VCL is unnecessary.