Tyvek Solid is an external protective membrane that allows water vapour to pass through. A vapour barrier or vapour control layer is selected to limit the water vapour entering the building assembly. Using these two products interchangeably in a roof or façade project can change how the layers dry. Before ordering, establish what the membrane needs to do and where it will sit in the assembly.
What Does Tyvek Solid Do?
DuPont describes Tyvek Solid as a vapour-permeable, water-resistant membrane. It can serve as a secondary protective layer in timber, steel-frame and concrete wall systems. Here, “breathable” refers to water vapour transmission; it does not mean that the membrane ventilates the home.
A suitable membrane beneath the final roof covering helps manage water that may reach beneath that covering. On façades, it forms part of the protection behind the external cladding. The final covering, drainage and junction details must be designed separately. Review the application area on the Tyvek Solid product page and request the current technical document before obtaining a quotation.
What Do Vapour Barriers and Vapour Control Layers Do?
A vapour control layer restricts moisture moving from indoors into the building assembly to the level specified by the design. In many roof and wall details for heated buildings, it sits on the inside. When joints and penetrations are properly sealed, it also contributes to airtightness. DuPont's AirGuard explanation describes this layer's role on the internal lining side.
Products sold as “vapour barriers” and “vapour retarders” may have different resistance levels. Options with fixed or variable vapour resistance are available. The same membrane should not be recommended for every building without considering the climate, indoor moisture load, use of cooling and external layers together. AirGuard Reflective E in the ERK catalogue should likewise be treated as a separate product from the external membrane.
How Can You Tell the Two Membranes Apart?
| Check point | Vapour-permeable external membrane | Vapour control layer |
|---|---|---|
| Primary role | Protection against external water and wind, allowing outward drying | Controlling water vapour entering the assembly and air leakage |
| Typical position | Roof or façade layers outside the thermal insulation | Usually behind the internal lining in heated buildings |
| Information to find in the document | Watertightness, Sd value, exposure limit and intended use | Sd value or variable range, and the sealing system for joints and penetrations |
| Product example | Tyvek Solid | An AirGuard vapour control layer suitable for the project |
The table compares functions; it does not replace an assembly drawing. The project designer must determine the layer sequence, particularly for metal roofs, high-humidity spaces and continuously cooled buildings.
What Is the Sd Value and How Is It Read?
Sd expresses a material's resistance to water vapour transmission as an equivalent air layer thickness, in metres. A lower value indicates more open vapour transmission, while a higher value indicates greater resistance. This value alone does not describe watertightness or thermal insulation.
DuPont's published Tyvek Solid 1580B technical data sheet lists an Sd value of 0.025 m and a watertightness class of W1. These figures relate to the specified product in the document dated 11 August 2021; they should not be applied to other Tyvek models. Check the current data sheet and declaration of performance for the product being ordered separately.
Information to Prepare Before Selecting a Membrane
Send the supplier a drawing of the assembly instead of simply saying “I need a roof membrane”. The following information helps avoid confusing the external membrane with the internal vapour control layer:
- The province where the building is located and its intended use.
- The sequence of structural members, boards, thermal insulation and final covering in the roof or façade.
- Whether the roof space is heated and whether there are significant indoor moisture sources.
- How long the membrane will remain exposed during installation.
- The positions of window, chimney, pipe and cable penetrations.
- The required reaction-to-fire class and any ventilated cavity detail.
The quotation should show the accessory selection as well as the membrane. Request membrane joint tape, penetration collars and fixings suitable for the substrate as separate items. Do not assume that every tape performs equally on every surface.
Frequently Asked Questions
Can Tyvek Solid replace a vapour barrier?
Tyvek Solid is a vapour-permeable external membrane. It should not automatically replace a layer where the design requires high vapour resistance. Its role in the assembly and the required Sd value are the deciding factors.
Does a breathable membrane make ventilation unnecessary?
No. Indoor ventilation, ventilation of the roof void and water vapour transmission through a material are separate matters. Membrane selection does not remove the building's ventilation needs; whether the roof void requires ventilation depends on the system detail.
Can a Tyvek membrane be used as the final waterproofing on an exposed terrace?
Do not choose Tyvek Solid as the permanent exposed layer of a terrace simply because it is water-resistant. Its defined use is as a roof and wall underlay. An exposed terrace requires a separate system suitable for UV exposure, standing water, falls and service loads.
Requesting Products for a Roof or Façade
Send your building type, assembly drawing and approximate area to ERK İzolasyon to request a quotation for suitable membranes and accessories. For other parts of a timber building, see the timber building and tiny house waterproofing guide; for product groups, see the Tyvek membranes and tapes category.
Sources were checked on 25 September 2026. This article provides general information to support product selection; the application design and the manufacturer's current instructions take precedence.
