radiant barrier in new construction


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?
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It should work, but what house wrap is a radiant barrier, unless its foil.
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On Fri, 5 Sep 2008 15:22:47 -0700 (PDT), ransley

The one I'm looking at is here: http://www.radiantguard.com/ Looks like there are several speciality providers.
My main concern was the possibility of trapping moisture between the two barriers....
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Normal house wraps let moisture through but not rain so it likely will trap moisture. Why not use it under drywall inside.
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Just what exactly is your target? What are you trying to achieve?
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On Sat, 6 Sep 2008 09:40:52 -0700 (PDT), PerryOne

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.
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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.
Cheers, Wayne
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Research has shown that a white or light colored roof works best as it reflects heat.
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 and convection.
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 for ever.
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. Perry
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Spray foam or foamboard at 5.5" can be R 40 with a radiant barrier on the foamboard
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