Suppose a house has radiant barrier housewrap, then 1 x 2 furring
strips on the outside and topped with 4 x 8 hardie concrete siding.
Would there be any problem if I installed foil backed fiberglass in
the wall cavity with the foil facing the interior?
New construction. Goal is:
Repelling max amount of heat in summer before entry into the interior.
Repelling max amount of heat back into the interior in winter.
The wall studs are 2x6 with R19 fiberglass to impede movement of heat
in any direction. R19 is the greatest R value I've found so far for
5.5 inch wall cavities. Do you know of better insulation materials
that will fit into that cavity?
Ceiling will be ~R50 with perforated radiant barrier laid over top.
2x6 floor joists will be insulated but haven't addressed that yet.
Any info or critique would be greatly appreciated.
Radiant barriers can't be used facing up, as they will collect dust.
They must also face an air space, otherwise they are defeated by
conduction. For new roof construction, I think a radiant barrier on
the underside of the roof sheathing works best.
Research has shown that a white or light colored roof works best as it
The best form of roof is one covered with sprayed polyurethane foam
five inches thick, covered with two inches of reinforced concrete.
The downside is the weight.
As heat always moves to cold and you suffer from radiation, conduction
You really must ensure that there are no gaps of any size through the
walls and ceilings gaps round all pipes and wires must be sealed.
Fibre glass is not a good insulator as it is impossible to fit without
leaving gaps for the heat to find its way through, also it sags over
time leaving space at the top for convection. Any gap over 16mm will
allow convection currents to start and transfer heat from outside to
inside and vice versa.
Sprayed poly foam between the studding will completely fill the spaces
You need to ensure that all of the internal fabric of the building is
isolated from the main structure.
Placing two inch thick polystyrene over the main frame and walls on
the inside of the rooms will solve this.
Final point sprayed poly foam between the joists means that you can
use the loft for storage without the worry of compressing fibre glass
that loses if effectiveness (all be it small.) As mentioned elsewhere
a radiant barrier is a waste of money.
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