Can anyone explain why two kinds of sarking are used on my house please?
Our brickies have used red & white branded sarking under the bricks. On the front there's a tiny bit of green. The whole unbricked quarter front will have cladding.
On two other builds of the same design, we've noticed they used green sarking under all the Hardieplank cladding.
Does anyone know the difference know the difference between these two types of sarking?
http://i1292.photobucket.com/albums/b572/MandyBarlow/Avalon/Now%20building/2-24-July-2015-sidejpg_zpsgr3htfso.jpg
Different kinds of sarking?
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My guess is the difference is because they finished off the roll of the white stuff, and had the green one left... There are differences in the application though. The differences in sarking include:
The permeability is important in terms of condensation and vapour control in the house structure. Generally they use vapour non-permeable on the hot side of framing, and permeable on the cool side. Because our climate has heating and cooling, the general approach is to put a permeable membrane on the outside of the framing. This allows the moisture vapour to still get out of the building in winter. Some of the permeable membranes are more or less suited for direct application under weatherboards.
The reflectivity is whether there is a reflective foil coating to one or two sides. If on the outside, the reflective coating is usually dulled to prevent glare in construction. The foil provides insulation from radiated heat, but it only useful if there's around 25mm air gap in front of the foil. So the foil is useful on the outside of the sarking when under brick veneer, but not useful when under weatherboards, unless they are battened out. It doesn't necessarily hurt to have the foil under weatherboards, but doesn't help either. Similarly, foil on the inside isn't helpful when the frame cavity is filled with insulation.
So, the white sarking may be heat reflective, but they figure that wasn't needed under the weatherboards. In the end though, it probably comes down to the lengths of what was in the rolls they had on hand.
- Strength
- Permeability
- Reflectivity
The permeability is important in terms of condensation and vapour control in the house structure. Generally they use vapour non-permeable on the hot side of framing, and permeable on the cool side. Because our climate has heating and cooling, the general approach is to put a permeable membrane on the outside of the framing. This allows the moisture vapour to still get out of the building in winter. Some of the permeable membranes are more or less suited for direct application under weatherboards.
The reflectivity is whether there is a reflective foil coating to one or two sides. If on the outside, the reflective coating is usually dulled to prevent glare in construction. The foil provides insulation from radiated heat, but it only useful if there's around 25mm air gap in front of the foil. So the foil is useful on the outside of the sarking when under brick veneer, but not useful when under weatherboards, unless they are battened out. It doesn't necessarily hurt to have the foil under weatherboards, but doesn't help either. Similarly, foil on the inside isn't helpful when the frame cavity is filled with insulation.
So, the white sarking may be heat reflective, but they figure that wasn't needed under the weatherboards. In the end though, it probably comes down to the lengths of what was in the rolls they had on hand.
Thanks OJ!
So, the white sarking may be heat reflective, but they figure that wasn't needed under the weatherboards. In the end though, it probably comes down to the lengths of what was in the rolls they had on hand.
The OP did say that he has seen two other identical builds where they have done the same. So must be some specific difference that has nescictated different products rather than just using what is on hand.
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