Sarking: What is it and When is it Needed?
Sarking-type material means a material such as a reflective foil or other flexible membrane of a type normally used for a purpose such as waterproofing, vapour proofing or thermal reflectance.
Reflective insulation means a building membrane with a reflective surface such as a reflective foil laminate, reflective barrier, foil batt or the like capable of reducing radiant heat flow. Some types of reflective insulation may also serve the purposes of waterproofing or vapour proofing.
Performance Requirements P2.1.1 and P2.2.2 (NCC 2016) are satisfied for roof cladding if it complies with one of the following:
- Roofing tiles: AS 2049 and AS 2050.
- Metal roofing: AS 1562.1.
- Plastic sheet roofing: AS/NZS 4256 Parts 1, 2, 3 and 5; and AS/NZS 1562.3.
- Corrugate fibre-reinforced cemenet sheet roofint: AS/NZA 1562.2.
- Asphalt shingles: ASTM D3018-90.
- Pliable membrane and underlay: AS/NZS 4200 Parts 1 and 2.
The Objective is to –
- Safeguard occupants from illness or injury and protect the building from damage caused by –
- Surface water; and
- External moisture entering a building; and
- The accumulation of internal moisture in a building; and
- Discharge of swimming pool waste water; and
- Protect other property from damage caused by –
- Redirected surface water; and
- The discharge of swimming pool waste water.
A roof and external wall (including openings around windows and doors) must prevent the penetration of water that could cause –
- Unhealthy or dangerous conditions, or loss of amenity for occupants; and
- Undue dampness or deterioration of building elements.
‘Sarking’ installation does prevent all of this.
Has the building been designed to meet the requirements shown below?
- Does the cavity drain?
- The damp course flashing is installed level in the brickwork. Where is the fall that creates the discharge path?
- The surface tension of the water in the camp course flashing and any debris blocking its path will cause moisture retention and a lack of discharge. (Weepholes actually allow cool moist air and hot humid air into the cavity).
- This retained water becomes moisture, creating vapour, humidity and a thermal gradient between it and other exposed elements in that cavity.
Condensation will form on any surface which is below the dewpoint temperature of the air in immediate contact with it. The extent of condensation depends on the moisture content of the air space in contact with the surface and the duration of this contact. Hence, in roofs and walls, factors such as ventilation and air conditioning, moisture content of roof and wall timbers, and water vapour due to cooling, and industrial processes, all these can contribute to the potential problem. Condensation can lead to black mould. The type of pliable building membrane material and its intended function in conjunction with the analysis of the data regarding condensation will determine the placement of the material.
Condensation is a very complex problem and can occur under a variety of conditions not just cold conditions. Literature on this subject is available from CSIRO/BRANZ/ASHRAE and should be consulted when building in areas where condensation is likely to occur.
When condensation is likely to occur, the appropriate use of a pliable building membrane as a vapour barrier or as thermal insulation, or both, can be effective as a preventative measure.
Pages 30-31 of AS 4200-2017 clearly identify timber or metal framed walls having a pliable and or breathable membrane over it to stop external moisture from degrading the structural framework and moisture (Figures 4.7 (a-c)). This installation was the standard practise by builders and carpenters back in 1996, prior and onwards.
40% of new houses have moisture and mould problems and 70% of built houses have moisture and mould problems.
Project home builders, ignorant builders and those with a lack of TAFE awareness have seen this mandatory installation overlooked and have caused these percentages.
Understanding what the best insulation for different Australian climates can be very difficult. The public are mostly indoctrinated that bulk is better, and thicker is better still. It is common to find fiberglass company advertising mentioning only batts and vague detail (or none at all) about their range of foil products.
The selection of the right material or combination of materials will depend on location and climate. In hot climates, reflective foil laminates are clearly the correct choice as bulk insulations are not radiant heat barriers but rather radiant heat Page 28 absorbers, which slow down the transfer of heat (relatively low level at 33 degree C), store it, and then slowly release the heat when cooler periods arrive, and bulk insulation in ceilings causes yet other problems – it traps summer heat within rooms from escaping, as revealed in a 1981 federally funded insulation research project undertaken across Queensland.