Remedies: moisture

Houses built during the 1970s generally have few weathertightness issues. With renovation, attention will be needed to ventilation to ensure that internal moisture does not become a problem.


Weathertightness and external moisture

Houses built during the 1970s and early 1980s generally had few significant weathertightness issues (Figure 1), although some of the 'modern' style houses, particularly those without eaves or with new, untried cladding materials or glazing systems, have experienced occasional leaks.

The use of boric treated radiata pine framing is likely to have allowed the framing to deal with an occasional wetting without significant deterioration.

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Where the external skin of the building is repaired, modified or extended, the performance requirements of Building Code clause E2 External Moisture must be met. Issues to address may include:

  • detailing windows where an existing window requires replacement or a new window is to be inserted into an existing wall
  • dealing with minimum roof pitches if they are below the current minimum slope requirements for the roofing material
  • the need for a cavity behind the cladding when matching into an existing building (see Regulation and compliance).

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Areas of highest risk

Areas of higher risk of possible water entry with 1970s buildings are:

  • through the gap between the top of a brick veneer cladding and a soffit lining
  • at the top of windows finished up to the underside of the soffit where no head flashing was installed (see below)
  • at the sides of aluminium windows where rusticated weatherboard plugs fitted behind the window jamb flange may become loose or fall out 
  • where there may be insufficient flange cover to the cladding
  • where sealant has been used instead of a flashing
  • where asbestos-cement claddings have suffered impact damage
  • where lapped joints in timber weatherboards, particularly rusticated profile, which have opened over time
  • basement walls.

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Window flashings

Traditional window and other head flashings were usually inserted into the lap or joint of the weatherboard immediately above the opening. As long as the flashing remains in good condition, the detail appears to have generally worked well at protecting the top of the window.

In a number of 1970s buildings, the aluminium window finished hard against the soffit lining without the use of a flashing. On exposed sites there is a risk, depending on the wind zone and eaves width, for water entry above the head flange.

E2/AS1 3rd edition amendment 10 details that require the flashing to be lapped under the wall underlay cannot be applied to an existing wall unless the cladding is being removed. However, where a window is being removed and a new window fitted to the existing opening, it is usually possible to incorporate air seals and flashing tapes.

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1970s houses, because they had aluminium joinery, particleboard or concrete floors, sheet internal wall linings and often no open fireplaces, were much less draughty than houses of earlier periods.

Draughts around windows may occur as the seals age, and this can be addressed by having the seals replaced (which will also assist in keeping out water).

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Internal moisture

The greater airtightness of houses of the 1970s means that there is a greater risk of trapped internal moisture generated from cooking, washing, unflued gas heaters and unvented clothes dryers.

Once insulation is installed and other renovation work has been carried out, the house will generally become more airtight, so consideration must be given to how the principles of Building Code clause E3 Internal Moisture - such as preventing an accumulation of internal moisture and avoiding the possibility of fungal growth - can be incorporated into the renovation work.

Systems to remove moisture must be included in the design solutions. Options include:

  • install extract fans that are ducted to the outside in kitchens and bathrooms. G4/AS1 has been updated to include mechanical extract fans in rooms with cooktops, showers and baths as a means of demonstrating compliance
  • install security catches to windows to allow them to remain open to provide ventilation without a security risk 
  • install proprietary trickle ventilators within window joinery to provide continuous ventilation
  • increase the amount of heating provided.

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Musty smells

Musty indoor smells may be the result of:

  • a leak through the roof or wall cladding or a roof deck
  • a plumbing leak (Figure 2) or moisture accumulation in concealed spaces such as under a built- in bath
  • deterioration of particleboard flooring from a damp subfloor
  • poor ventilation, unflued gas heater use and clothes driers not vented to the outside which result in high internal moisture levels
  • basement wall leak.