Healthy home construction does away with the sarking foil and instead introduces two new types of wrap.
Fig. 18.104.22.168 Healthy Wall Construction
- A vapour permeable building wrap – This plastic wrap is located on the outside of the wall and replaces the sarking. Like sarking it maintains external waterproofing by being unbreachable to liquid water, but unlike sarking it allows “gas-water” or water vapour through.
- An airproof wrap – This new plastic membrane is put on the internal side of the wall studs. It is installed by specialists and taped at all joints. Once installed, a vacuum is used to suck out all the air from the house and measurements are taken to ensure there is no leakage. This wrap, like sarking, is non-vapour permeable, but unlike sarking is airtight.A vapour permeable building wrap – This plastic wrap is located on the outside of the wall and replaces the sarking. Like sarking it maintains external waterproofing by being unbreachable to liquid water, but unlike sarking it allows “gas-water” or water vapour through.
From the outside: Any moisture trapped within the insulation cavity is able to dry and evaporate to the outdoors. However, there will be far less condensation than a traditional wall because this time cold air is passing through the insulation and warming (i.e. evaporating) rather than warm air passing through the insulation and cooling (i.e. condensing). The outside air cannot breach the interior thanks to the airproof wrap.
From the inside: Because of the airproof wrap, interior humidity does not have access to your insulation and the opportunity to condense. This means that warm humid air is instead trapped within the house unable to escape.
Fig. 22.214.171.124 shows an internal cavity between the airproof wrap and the plasterboard for plumbing and electrical services. Because the plasterboard alone does not create an airtight seal between the cavity and the interior, they will both be the same temperature and pressure meaning a dewpoint will not exist here.
The cavity serves to ensure that airtightness is not lost when the electrician starts to cut holes for power points, lights and switches, and when plumbers do the same for water services. Instead wiring and plumbing run through the cavity and come into the house at a single sealed point.
Air tightness makes homes 25% more efficient and cheaper to run than a traditional house.