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A construction waterproof breathable membrane used in house construction is a special type of building material designed to keep water (rain, snow, external moisture) out while allowing water vapor (humidity from inside the house) to escape. This balance helps protect the structure from water damage while maintaining a healthy indoor environment.
Building waterproof breathable membranes are typically made from polymer-based composite materials. Their structure usually includes the following layers:
1、Base Layer (Support Layer)
Polyester (PET) nonwoven fabric – higher tensile strength and better weather resistance.
Function: Provides mechanical strength and durability during installation.
2、Functional Layer (Core Membrane)
Polyolefin microporous films (PE or PP) – produced by stretching to form micropores that block water but allow vapor diffusion.
TPU (Thermoplastic Polyurethane) film – excellent waterproofing, flexibility, and durability, often used in high-end construction.
ePTFE (Expanded Polytetrafluoroethylene) membrane – superior breathability and weather resistance, but more expensive, used in demanding projects.
3、Composite Structure
Most membranes adopt a three-layer composite design:
Outer nonwoven layer (UV resistance, abrasion protection).
Middle functional waterproof-breathable film.
Inner nonwoven layer (strength reinforcement, easier handling).
4. Performance Principle
Waterproofing: Pore size is smaller than liquid water molecules, preventing rain penetration.
Breathability: Pore size is larger than water vapor molecules, allowing moisture to escape and reducing condensation and mold.
In summary, building waterproof breathable membranes are generally made from PP/PET nonwoven fabric combined with a microporous PE/PP film, TPU film, or ePTFE membrane
1、Waterproofing – Stops external liquid water (rain, snow, wind-driven moisture) from penetrating into the wall or roof.
2、Breathability – Allows water vapor inside the house to pass outward, preventing condensation and mold growth.
3、Air Tightness – Reduces unwanted drafts, improving energy efficiency.
1、Housewrap membranes (non-woven or woven) – Usually made of polypropylene (PP) or polyethylene (PE) films, laminated with breathable coatings (e.g., Tyvek®, Typar®).
2、Roofing underlays – Breathable membranes placed under roof tiles or metal roofing to prevent leaks but allow ventilation.
3、Wall membranes – Installed behind cladding (wood, fiber cement, brick veneer) to serve as a secondary weather barrier.
1、External walls – Behind siding, brick veneer, or cladding systems.
2、Roofs – Under pitched roof tiles or metal sheets
3、Timber frame and lightweight structures – To protect insulation and prevent dampness.
4、Energy-efficient buildings (like Passive Houses) – As part of air-tightness and moisture management systems.
Keeps walls and insulation dry, extends building life, improves energy efficiency, and ensures a healthier indoor climate.
1、Preparation
Make sure the sheathing surface (plywood, OSB, or other board) is clean, dry, and free of sharp edges or protruding nails.Check the weather: install in dry, calm conditions if possible.
2、Lay down the membrane
Walls: Roll the membrane horizontally, starting at the bottom of the wall and working upwards. This ensures overlaps shed water like roof shingles.
Roofs: Start at the eaves and roll upward toward the ridge.
3、Fixing the Membrane
Attach using staples, nails with plastic caps, or special fixing strips.Keep it taut but not overstretched to avoid tearing.For roofs, drape slightly between rafters to allow drainage.
4、Overlaps
Horizontal overlaps: at least 100–150 mm (4–6 inches).
Vertical overlaps: 150–200 mm (6–8 inches), preferably over studs or battens.
Always lap upper sheets over lower sheets (to shed water outward).
5、Sealing JointsUse
manufacturer-recommended tape to seal overlaps, corners, and penetrations.Seal around windows, doors, and service penetrations with flashing tape or prefabricated collars.Pay special attention to the bottom edge: ensure water drains to the outside, not behind the membrane.
6、Windows & Doors
Cut an inverted “Y” into the membrane where the opening will be.Fold flaps inside and tape securely to the frame.Add flashing tape or a preformed sill membrane to direct water outwards.
7、Final Layers
Walls: Cover the membrane with battens or cladding (wood, brick veneer, siding, etc.) with an air gap for ventilation.
Roofs: Fix counter-battens and battens before tiles or sheets are installed.
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