Roofing Membrane

Roofing waterproof membrane, also called roofing underlay, is the layer between your roof covering and the structure beneath. Eastopo makes both sides of the envelope: breathable LR underlays that let trapped vapour out (Sd 0.02–0.035m, EN 13859-1) and foil vapour barriers that keep humidity inside the warm room (Sd over 100m, EN 13984). One factory, both layers, in 1.5m x 50m rolls for wholesale buyers.

Where Breathable Membrane and Vapour Barrier Sit in the Building Envelope

Buyers often treat "membrane" as one product. It is not. The building envelope needs two different layers, each with its own standard and its own job. Specify the wrong one and the roof build fails quietly over years, not weeks.

The breathable layer — sold across UK merchants as breather membrane — is the roof's raincoat with vents. The vapour barrier, correctly called a vapour control layer (VCL), is the waterproof liner on the warm side. Fitting a vapour barrier where a breathable layer belongs — or skipping it entirely — is the most common spec error we see in timber frame and cold roof builds. Ordering both lines from one factory removes that risk at the purchasing stage: one supplier, two layers, one invoice.

Technical Data Trade Buyers Should Check Before Ordering

Retail pages list two numbers: Sd and water tightness. Wholesale buyers need the full matrix, because gsm, tensile and UV rating decide which product suits which site and which wind zone.

Read the range codes the way UK merchants do. LR120 and LR150 mean Low Resistance roofing underlay at 120 and 150 gsm; heavier gsm buys higher tensile and wider wind zone cover. Our LR 145–170g products sit in the same specification band as Klober Permo Forte 145 (Sd 0.03m, W1) — at factory-direct pricing, not merchant shelf pricing. Send your target gsm and wind zone and we match the grade for you.

What Happens When the Wrong Membrane Is Specified

Bad membrane choices rarely fail at handover. They fail at year two or three, when the snagging period is over and the roofer is long gone. Four failure modes to design out before you order.

Non-breathable layer over a warm roof. Lay bitumen felt without a vented void and condensation forms on its cold underside every night. The insulation wets out, R-value drops, and rafters develop black spot mould within 18 to 24 months. Contractors end up stripping and replacing whole roof decks — the cheapest membrane in the catalogue becomes the most expensive roof in the street.

Sd value on the wrong side. Put a high-Sd vapour barrier on the cold side and you seal moisture inside the structure instead of keeping it out. The dew point moves into the insulation, and condensation collects where nobody can see it until the ceiling stains.

Underlay left exposed too long. UV turns a standard membrane brittle. On the next windy day it splits along the lap line, and wind-driven rain enters above the insulation. Our 3–4 month UV rating covers a normal UK build programme when site slips; beyond that, protect the roll or order the UV-stable grade.

Lap and fixing shortcuts. Seal laps at 150mm minimum, and 200mm on pitches below 15°. Use compatible tape at every nail penetration. A 50mm lap saves two minutes per run and leaks for the life of the roof.

Range, Customisation and OEM

Both product lines ship in standard UK roll format — 1.5m x 50m at 75 m² per roll — and customise to order for distributors and OEM buyers.

Breathable membrane range

• Breathable Roofing Membrane — CE compliant Type LR underlay, Sd 0.02–0.035m, W1, wind zones 1–5
• Breathable Roofing Felt — 3-layer PO, budget-grade for cost-driven projects
• Breathable Membrane for Shed Roof — condensation control for sheds, log cabins and workshops
• Breathable Felt Membrane — air-open grade for high condensation risk pitches
• Breathable Building Membrane — wall and roof envelope applications
• Breathable Loft Membrane — loft and roofspace condensation protection
• Breathable Membrane Under Rafters — rafter-level installation for retrofit builds

Foil vapour barrier range

• Aluminium Vapour Barrier — Sd > 100m, 99% purity vacuum-deposited aluminium, ≥ 95% radiant heat reflection
• Vapour Barrier and Waterproof Thermal Insulation Aluminium Foil Membrane — vapour control, waterproofing and thermal reflection in one layer

Customisation. gsm from 100 to 220, roll width and length to order, printed branding on the selvedge, and private-label packaging for distributors. One factory, two layers, your brand on the box.

How Eastopo Manufactures Roofing Membranes

As a direct manufacturer of breathable membrane and vapour barrier rolls, Eastopo controls every step. The breathable range is a three-layer construction: spunbond polyolefin facings around a microporous core. The film is PE cast extrusion, then MDO-stretched — machine direction orientation — to open the micropores that give the layer its one-way breathability. Cast extrusion plus MDO stretching is what separates a membrane that holds its Sd value across the whole roll from one that drifts out of spec partway through production.

Every production batch is checked for Sd value, water tightness and tensile strength before it leaves the line, and roll weights are verified against the declared gsm. That is the difference between a quoted spec and a delivered one.

Packaging, Compliance and Delivery

• Compliance: breathable underlays to EN 13859-1 with water tightness Class W1; vapour barriers to EN 13984. Both product lines CE certified.
• Incoterms: EXW, FOB, CFR and CIF — our standard four, nothing hidden.
• Packaging: rolls in PE sleeve, carton or palletised per volume, labelled with spec and batch number.
• MOQ and schedule: depend on product line and whether rolls are stock or customised. Send your target gsm, roll size and quantity; we quote price, MOQ and lead time within one working day.

Frequently Asked Questions

Q1: What is the difference between a breathable membrane and a vapour barrier?
A breathable membrane sits on the cold, outer side of the roof and lets water vapour escape from inside while blocking wind-driven rain. A vapour barrier sits on the warm, inner side of the insulation and stops indoor humidity from reaching it. One lets moisture out, the other keeps it in. Most UK roof builds need both, fitted on their own side; using one product for both jobs fails.

Q2: Which side does a vapour barrier face?
Fit the vapour barrier on the warm side of the insulation — the indoor side. Its job is to stop humid room air diffusing into the insulation, where it would condense at the dew point. Fitted on the cold side, it traps moisture inside the structure and defeats its purpose. Seal every lap and penetration with compatible foil tape so the layer stays continuous.

Q3: Can a breathable membrane replace traditional bitumen felt?
Yes, on pitched and most warm roofs. Breathable LR underlays meet EN 13859-1 with water tightness class W1, outperform bitumen felt on vapour permeability, and are lighter to carry and cut. One condition applies: match the gsm to the wind zone and batten spacing, and never treat the membrane as primary waterproofing — tiles or metal sheet still carry that job.

Q4: What does the Sd value mean when comparing membranes?
Sd is the equivalent air layer thickness for water vapour diffusion, in metres. Low Sd, around 0.02 to 0.035m, means the layer breathes — what an outer underlay needs. High Sd, above 100m, means the layer is a near-total vapour barrier — what the warm-side liner needs. Compare Sd only within the same layer position; the two numbers mean opposite things on each side of the envelope.

Q5: Do you supply OEM rolls and private-label packaging?
Yes. We customise gsm from 100 to 220, roll width and length, and printed branding on the selvedge. Distributors can order private-label packaging so the roll carries their brand, not ours. Standard UK format is 1.5m x 50m at 75 square metres per roll. Send your target spec and we confirm feasibility and lead time within one working day.

Q6: What is your minimum order and lead time for wholesale membrane?
MOQ and lead time depend on the product line and whether the roll is stock or customised. Stock breathable and foil lines ship faster than bespoke gsm or printed rolls. Ask for a quote with your target gsm, roll size and quantity; we reply within one working day with pricing, MOQ and schedule.

Reviewed by the Eastopo Technical Team. Specification data verified against batch test results and current CE certification files.

Send us your roof spec — target gsm, wind zone, roll size and quantity — and we will match it to the right product within one working day. Email mj@eastopo.com ，WhatsApp +86 193 5725 8106 or use the inquiry form and ask for the membrane price list.

As one of the most professional roofing waterproof membrane manufacturers and suppliers in China, we offer a wide range of products with superior quality. Please rest assured to wholesale custom made roofing waterproof membrane from our factory. Good service and reasonable price are available.