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Building Science by Norman Aceron Garcia


by Norman Aceron Garcia

nachi.16015Housewrap is a protective covering installed on exterior walls before the stucco, siding or other cladding is placed. It is usually made from spun-fibre polyethylene or plastic used to shield the building envelope against water entry. Housewrap prevents liquid water while letting water vapour to pass through. This allows humid or moist air to dissipate from the interior and at the same time restrains water outside.

Housewrap is very beneficial in humid climates or in areas that experience heavy rainfall because it prevents water penetration that could damage the house framing. In wet climates that normally have high levels of moisture content, housewraps ensure that mould growth problems are kept under control. It also has insulating value because it minimizes air movement within wall cavities.

Despite of these remarkable characteristics, it can be detrimental or cause more damage than good to the building envelope if it is installed improperly. The most common mistake contractors commit in housewrap installation is handling it as if it were a vapour retarder, thereby installing it accordingly with improper overlapping. It can cause serious damage over time if housewrap is installed in a manner that actually blocks water from dispersing in the wall system.

During transport and construction, careless handling that could cause tears and holes can damage housewrap. When this happens, water will go through the wrap if damage goes unnoticed, which will further negate the benefits that housewrap is designed to provide. If the housewrap is left unprotected to the elements for a long duration, this could lead to debris and wind damage, which can be overlooked once the siding is attached and the wrap is covered.

To install housewrap properly:

  • Contractors must comply with the manufacturer’s installation instructions to prevent water to flow into the area behind it;
  • Both the sill plate and foundation joint must be covered by the housewrap;
  • Windows and doors should be installed after the installation of the housewrap;
  • Upper layers must be lapped over lower layers. Horizontal joints must be lapped at least 150 millimetres;
  • Vertical joints must be lapped 150 to 300 millimetres, depending on the probability of wind-driven rain occurrences;
  • Proper nailing roofs or staples with minimum length of 25 millimetres must be used. They must be spaced 300 to 450 millimetres centre-to-centre throughout;
  • Joints must be covered with the tape recommended by the manufacturer; and
  • There should be provision for drainage at the bottom of the external cladding material.

Housewrap is an effective building material that helps shield the home from moisture build-up and water intrusion problems. However, proper installation must be observed to achieve the full benefit of this material.

Norman Aceron Garcia is a Professional Engineer of Mr. Peg Property Inspections Inc. Please email for free technical consultation.

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