Before I finish out a room I have upstairs, it's just studs at this point, I want to add a layer of foam board like THIS along the joists for extra insulation.
But do I lay it with radiant barrier towards the roof line or towards the room? It says it needs an air space to be effective, well both ways gives me an air space.
No idea if we did it right, but we put silver towards the inside of the house, when we installed inside. I think the biggest reasoning was that when screwing it in, the silver surface held the screw better. We did studs. Then the foam board, then sheet rock.
How do you get airspace if you face it towards the drywall? Are you using hat channels or furring over the insulation board?
AFAIK, the silver side goes out, and the joist space is your air space. I have never actually installed the stuff, however.
In my metal shop I clad the inside with OSB that had a radiant barrier side facing the outside. The metal studs had the airspace between the OSB and exterior walls. This let me paint the wood side white to make it bright inside and can more easily be touched up when I mess it up.
In the house I will be following the roofline so there will be an airspace between the decking and foam boards. I can put the silver side in or out and have an airspace. My brain says the silver will reflect the heat out and stop it from getting into the house if I put it towards the roof decking, but radiant barrier decking has the silver towards the inside of the house.
On the walls I am putting a 1/2" thick soft foam board with no radiant barrier between the studs (filled with insulation) and the sheetrock. But my purpose is mostly to dampen sound transference. This is to be a media room with the potential for LOUD music & TV. The soft foam is supposed to dampen the vibrations, but is not good for roof type installations since it can hold moisture and cause wood to rot whereas the hard foam doesn't do that.
I don't know, but Google does:
http://energy.gov/energysaver/articles/radiant-barriers
http://www.youtube.com/watch?v=QoF1XtZpZeI&feature=related
I belive the silver side needs to face upwards towards the heat source. The airspace needs to be between the heat souce and the radiant barrier.
Example: If you were installing this in an attic there needs to be a slight gap between the roof and the radiant barrier, with the silver side facing the sky.
http://www.youtube.com/watch?v=OROTrjn1j9E - Isulating a garage door.
A claimed R value of 5 from only 3/4" foam seems a little optomistic.
We put one inch board up on one side of our house as it was an easy project...no windows on that side. Lots of variables, but the IR pyrometer indicated a definite improvement in wall temperature. This on a house with 2x4 construction on that wall, with normal fiberglass insulation.
stuart in mn wrote: A claimed R value of 5 from only 3/4" foam seems a little optomistic.
It depends upon the type of foam. 3/4" of soft foam won't get that much R-value, but the hard foam has a greater R value.
I'm trying to decide between 1/2" foam @ 3.2 R value or 3/4" foam @ 5. Both have the radiant barrier and I just don't know how much value the radiant barrier adds. If the radiant barrier had a large intrinsic value then I'd go with the 1/2" and save myself $4 a sheet.
But this is one of those things you get one shot at. It's easy to get to now, but once I enclose the room I'll never have a chance to change my mind.
Here's my answer. According to: http://www.ornl.gov/sci/ees/etsd/btric/RadiantBarrier/rb_calc.shtml
The radiant barrier alone will reduce by cooling costs by .02¢ per square foot of attic space.
The link 914 Driver gave me says that the radiant barrier needs to be facing the heat source which means the silver side goes up. BUT dust reduces it's effectiveness.
Now that I know what the radiant barrier adds I can say that long term I'd be better off with the 3/4" foam, but if I'm going to live there only another 5-7 years and I were a selfish bastard that didn't care for anyone but myself then I'd go with the 1/2"
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