Our Avonhead high-performance house being built by John Garlick Builders has above sheathing ventilation (ASV) to the roof.
AVS is a good option for all roofs but especially necessary for SIP roof structures.
The build up is as follows:
1 - roof structure.
Formance 215mm SIP roof panels generally with insulated splines
Structural splines were only necessary for some of the larger spans.
Thanks to Eliot Sinclair for their SED which minimised the need for structural splines.
2 - roof underlay.
Pro Clima NZ Ltd Solitex Mento 3000.
3 - counter battens
These are 45x20mm @ 600mm crs. They are H3.2 treated as they sit above the underlay. The counter battens are screw fixed structurally to provide fixing for the purlins.
4 - fixing sealing tape
Between The counter batten and the roof underlay is Pro Clima NZ Ltd Tescon Naidek. This seals both the counter batten and purlin fixings so the SIP stays dry.
5 - purlins
These are 90x45mm @ 600mm crs. Again H3.2 treated. The purlins are fixed with a single screw through the counter batten and 11mm OSB skin to the SIP.
Note both the counter batten and purlin spacings are determined by the wind load requirements.
6 - separation strip
As the metal roofing is in contact with treated timber Kingspan Thermakraft Super course 500 is fixed over the purlins.
The roof space is ventilated at the eave with behind fascia ventilation and at the ridge with a ridge vent. This allows free flow of air up the 35 degree roof to dry out condensation forming under the metal roofing. The ventilation space also provides a drainage path.
