The traditional method of constructing a low slope membrane roof is to install insulation between the rafters leaving an air space between the insulation and the roof deck above see figure 1.
Roof space ventilation nz.
For this method to be most effective approximately equal amounts of ventilation should be placed at the soffits or eave level and at or near the top of the attic space.
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Positive pressure or roof cavity ventilation systems.
Ventilation of the ceiling space is required as there is a risk of condensation forming on the underside of the roof deck.
The roof space is generally inaccessible with little natural ventilation and the small roof space can accelerate problems with moisture.
They bring filtered air from the roof space or outside into the living spaces through a single or multiple ceiling vents.
Essentially the system works by taking air from the attic or roof space and pumping it into the main living areas though ducts or vents.
In skillion roofs the roof cladding and ceiling run parallel typically within 300 mm of each other.
A 20mm space is needed between the roof cladding or the purlin to provide ventilation between the soffit and the ridge or gable vents.
Achieving calculated continuous and unimpeded airflow through the roof cavity is relatively straight forward.
Whilst it is possible to retrofit passive ventilation solutions to existing buildings it is highly recommended to incorporate passive ventilation during the design phase of any new building project.
Positive pressure ventilation systemsthese are very common in nz in existing homes but do not comply with current ventilation standards for new builds.
This forces the stale air to leak out through gaps windows and.
While there are proprietary products made for this purpose safety mesh stapled to the bottom or top chord is equally effective although this is not required if a cavity batten is used.
Passive roof ventilation products that provided continuous calculated unimpeded airflow that mitigates of internal moisture issues in roof cavities.
This roof construction called a cold roof does have some disadvantages.
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There are a wide array of filter types usually designated by a letter and a number for example g4.
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Positive pressure or roof cavity ventilation systems are the most common type available in new zealand.
Outside air enters the attic space through soffit or eave vents rises through the attic space as it warms and exits through vents that are positioned at or near the top.
