Tyvek® Housewrap

High spec. vapour-permeable membrane mainly for timber frame wall applications, but also suitable for steel-frame and concrete structures.

Tyvek® Housewrap is a high spec. vapour permeable membrane mainly for timber frame wall applications, but it is also suitable for steel frame and concrete structures. The membrane should be surface applied, fixed directly to sheathing ply or blockwork.

Product Properties

Composition Spunbonded polyethylene

Roll Size 2.8m x 100m; Weight 18kg; Coverage 270m2

Roll Size 1.4m x 100m; Weight 9kg; Coverage 130m2

UV exposure 4 months

Description

Tyvek Housewrap is manufactured by spinning strands of high-density polyethylene (PE-HD) and bonding them together with heat and pressure to form a flexible sheet.

The product has the nominal characteristics of:

Thickness (mm) 0.17

Weight (gm–2) 61

Roll length (m) 100

Roll width (m) 1.4, 2.7 or 2.8

Hydrostatic head (cm of H2O) >150

Colour to order.

Ancillary items for use with the product include:

Tyvek Acrylic Tape — a single-sided tape for sealing joints •

Tyvek Butyl Tape — a double-sided tape for sealing joints.

Quality control includes visual inspection, measurement of physical properties, thickness and roll weight.

Key Benefits

Technical specifications surpass BS4016 requirements

Membranes provide temporary weather protection during construction

Materials are easy to apply, cut and form around details

UKAS approved

General

Tyvek Housewrap is suitable for timber-frame constructions, either factory or site applied.

In the absence of other guidance, suitable timber-frame constructions are defined as those designed and built in accordance with NHBC Standards, Section 6.2.

The product meets the NHBC requirements for minimum water penetration resistance and minimum tear resistance in any direction for sites defined as very severe exposure (see section 14, Tables for Physical properties — directional and Physical properties — general).

The membrane may be damaged by high winds, careless handling or by vandalism and should not be left uncovered for longer than is absolutely necessary. Any damaged areas should be repaired or replaced before completion.

Damage to the membrane can be repaired prior to the installation of the external walls or cladding by laying another sheet over the damaged area and sealing it correctly, ensuring water is shed away from the sheathing.

Weathertightness

The product resists liquid water penetration and wind-blown snow and will protect the sheathing and frame from external moisture.

The period prior to the installation of the brickwork should be kept to a minimum. The membranes should not be used as a temporary waterproof covering during this time.

Risk of condensation

The product has a design resistance to water vapour transmission of less than or equal to 0.6 MNsg–1 and is defined as a ‘breather membrane’ in accordance with BS 5250 : 2002. Therefore, it will contribute towards minimising the risk of interstitial condensation in suitably designed walls.

The risk of condensation occurring within the wall of a timber-frame building will depend upon the properties and vapour resistance of other materials used in the construction, the internal and external conditions and the effectiveness of the internal vapour control layer.

Convective water transfer into the wall construction can be reduced by installing a continuous airtight sheet such as Tyvek SD2 behind the internal lining. This may also contribute to a successful pressure test by achieving the required design air permeability of 10 m3h–1m–2 in accordance with Approved Document L (see section 12.3 of this Certificate).

Strength

The product will resist the loads associated with construction and installation into timber-frame constructions.

The product is not adversely affected by water and will retain its properties when wet.

Properties in relation to fire

The product will have similar properties to polyolefin membranes in relation to fire, tending to burn and shrink away from the heat source. The product is unclassifiable in terms of the Building Regulations and this should be considered when assessing the overall fire risk.

Cavity barriers should be used to satisfy the requirements of the national Buildings Regulations.

Maintenance

As the product is confined within a wall construction it has suitable durability (see section 10), maintenance is not required.

Durability

The product will be virtually unaffected by the normal conditions found in a timber-frame wall and will have a life comparable with other similar elements of construction, eg vapour control layers.

Installation

Tyvek Housewrap must be installed in accordance with BBA Certificate No. 90/2548 instructions and the recommendations given in NHBC Standards, Section 6.2, where appropriate.

Procedure

Starting 300 mm from a corner, wrap the Tyvek® membrane completely around the external face of the sheathing board.

Make sure that the membrane overlaps the lowest timber member by 100 mm.

Normal practice is to unroll the membrane horizontally, but vertical application is also acceptable.

Fix the membrane with galvanised nails or stainless steel staples as follows:

Horizontal centres = max 600 mm

Vertical centres = max 300 mm Extend the Tyvek® membrane to cover window and door openings and staple or nail around the openings at 150 mm centres.

Any vertical laps formed in the membrane should be a minimum of 150 mm.

Horizontal laps between sheets and any laps onto cavity trays or flashings should be a minimum of 100 mm.

Sealing the laps with Tyvek® Tape is optional.

Once the Tyvek® membrane installation is complete cut an ‘X’ from corner to corner at window and door openings, fold inwards and staple/nail to reveals.

Make good to the corners with Tyvek® Tape. If windows and doors are already in place turn the membrane up against the frame to prevent water ingress.

Stud positions for wall ties can be easily marked by using an indelible marker pen.

Procedure for Lapping and jointing

The membrane should be fixed in such a way as to shed water away from the sheathing, and below the lowest timber. Upper layers should be lapped over lower layers.

Laps should be at least 100 mm and vertical laps 150 mm.

Vertical laps should be staggered wherever possible.

To assist in achieving the design air premeability the lap joints and penetrations through the underlay can be sealed with Tyvek Acrylic Tape or Tyvek Butyl Tape.

Fixing

The membrane must be secured at regular intervals with nails and staples to prevent damage by wind

Nails should be of galvanized or sherardized mild steel, austenitic stainless steel, phosphor bronze or silicon bronze and staples should be of austenitic stainless steel.

Marking stud positions

It is essential that the positions of studs are marked to enable wall tie fixing.

Lowest timbers

It is essential that the lowest timbers in the wall are protected by the breather membrane

Manufacturer

Du Pont (U.K.) Limited, Wedgwood Way, Stevenage, Herts SG1 4QN
Tel: +44 (0) 1438 73 4000 Fax : +44 (0) 1438 73 4836

Page last updated Tuesday, June 1, 2010