Understanding the science behind buildings and the use of the right pre-cladding products and systems will ensure a more energy-efficient building envelope and a dry building.
NZ has been focusing on heating, insulating, double glazing, roofing underlays and energy efficiency. Ventilation of non-habitable spaces has largely been ignored which has resulted in internal moisture and condensation issues. DriSpace vented roof and wall systems apply the basic principle of “If you heat and insulate, but don't ventilate, you will condensate.”
To get ventilation of metal roofs right, a minimum two out of three key factors below must be considered:
- High vapour permeable underlay (preferably with drainage and ventilation above the underlay)
- Adequate passive ventilation
- Vapour tight ceilings
DriSpace Residential Literature provides solutions to different roofs, including longrun trussed roofs, longrun skillion roofs and tiled roofs. It is an easy-to-follow guidance for architects, designers and contractors and is available for free download on the DriSpace website.
Let’s have a look at one of the DriSpace systems for residential buildings: a trussed roof design with roof pitch less than 30°C.
- Roof: Over fascia vents, G1200N or G2500N are installed at the eaves to introduce airflows into the roof cavity, and G502 Roll Rafter Tray is installed to ensure airpath is created and not blocked by the ceiling insulation. DriStud synthetic roof underlays with vapour resistance of less than 0.5MNs/g are installed to provide sufficient vapour permeability. 10mm vented battens are installed between the longrun roof and underlay to provide ventilation and drainage of moisture from dew point condensation.
- Wall: DriStud Wall Wrap with high vapour permeability and water resistance is installed with the DriStud Cool Window Flashing Tape. Then vented battens, VB20, are used as non-structural cavity battens. There are a number of sealants independently tested with Cool Window Flashing Tape and the list is available on the DriSpace website and Masterspec.
There is a specification code for each system and design in the DriSpace Residential Literature. Just use the specification code and all the system components are automatically specified together. It is a simple and easy way to specify systems which eliminates any unnecessary mistakes of missing out some products.
DriSpace also offer system solutions to cold roof ventilation and walls for schools for both new builds and re-roofs in accordance with updated MOE design requirements. MOE design recommends warm roofs for schools and DriSpace supports the recommendations. In fact, they have been working with warm roof manufacturers, and there are a number of DriSpace products used, including DriStud Roof Underlays and Cool Window Flashing Tape.
For cold roofs, the MOE design requirements include a vapour control layer to make the ceiling vapour tight. Install Proctor SmartVap 100 above the ceiling plasterboard and DriStud FRU38 roof underlay draped over rafters and under a counter batten. Or alternatively you can install DriStud FRU38 on the purlins, then install 10mm vented battens VB10 between the steel longrun and underlay to provide ventilation and drainage above the underlay.