daestrom wrote:

"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.


A 2" thick foam board with a radiant barrier applied to the board with
the board sitting behind a brick or concrete block wall has the required
airspace in front of the radiant barrier. If HardiPlank or HardiPanel
siding products or stucco are applied over the foam board, then paying
for a radiant barrier is nonsense.

You assume that the cladding is applied directly to the foam board. Not
always true.