"Robert Gammon" wrote in message
m...
News wrote:

snip

I always thought the shiny side reflects, so needs to be facing where
heat needs to be reflected back and there needs to be a 1" gap between
that and any other surface. Having it under floors facing down should
not be effective. Yet I have read that some makers say it does not matter
which way it goes, I find that hard to believe.


We're talking about the FOIL side. Its going to be shiny regardless.

With a crawl space underneath, IT MAKES LOADS of sense. But the
direction it faces is CLIMATE dependent. Cold climates, foil side faces
towards the house to radiate heat back to the floors. Hot climates, it
faces down to reflect back heat from the crawl space.

Foil, insulation, paper, or foil insulation foil are available

In new construction, you can get foam boards for sheathing that have the
radiant barrier foil attached, in some cases to BOTH sides.
www.atlasroofing.com for an example of such. A 2" board will add about
$1.15 sq ft to materials cost of the house and adds R12 to the walls.
Similar boards are available for roofs, in areas that will see water
freeze on the roof.

I think you're confusing the placement of the "vapor barrier" with the
placement of a "radiant barrier".

In construction, it is best to place the *vapor* barrier on the 'warm side'.
So in heating climates, the vapor barrier is place on the inside and in
cooling climates on the outside. The logic behind this is you want to block
the moisture that seeps through the wall *before* it cools down and has a
chance to condense.

But the foil of a *radiant* barrier can be on either the hot or cold surface
and the difference is not very much. The most important part about radiant
barriers is that a) they be positioned/installed so the foil remains clean,
b) the have an air gap facing the foil (direct contact with the next layer
makes the foil useless), c) they are only effective if air convection
against their surface is not an issue.

A 2" thick foam board with *no* radiant foil will add about R12 to the
walls. If the foamboard has a closed-cell surface coating, it can double as
a vapor/draft barrier as well. Sandwiching a foil layer between other
materials with no air gap is a complete waste of money.

daestrom