R-value contribution of membranes versus reflective sarking
Like most sarking membranes, the Enviroseal™ membranes are thin materials that do not contribute any material R-value to the construction. Reflective foil laminate materials that promote an R-Value, rely upon a still air cavity (an air void in the structural building frame) to create an 'R-Value' that relates to the specific thickness of the air gap as part of the total wall or ceiling system.
Where the frame is filled with bulk insulation and there is no air gap between the sarking and the insulation it should be noted that there is no opportunity for either reflective sarking or vapour permeable membrane to contribute a reflective space R-Value.
In walls where light weight cladding is directly fixed to the frame or where a single sided reflective foil laminate is used there is no difference in R-Value whether using a reflective sarking or non-reflective membrane such as Enviroseal®. The same applies when the frame is filled with bulk insulation, as there is no loss in R-Value in comparison with an assembly using a reflective foil sarking in the same location.
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Interior Ventilation
Occupant comfort is a key consideration for interior ventilation and the level of interior ventilation can influence the relative humidity of the interior environment.
Without specific ventilation to manage this humidity inside the building, the water vapour generated as a result is then likely to enter the building envelope through the various gaps and leaks in the building structure.
