I'll assume you're asking about a radiant barrier.

The right product properly installed is marginally worth the cost in the walls. However, in the attic, combined with proper venting and insulation it can be very effective, according to the Florida Solar Energy Center

See the link for a good overview of radiant barriers.

Here is a link that might be useful: Reflections How to determine if radiant barriers can help you reach your energy performance goals.

I'm talking about osb roof decking that already has the radiant bairier applied to it.

radiant barrier plywood or osb is same as in link.
techshield & solarply are name brands of decking
with rb attached. works in new construction or
roof decking replacement just like in existing homes
where rb is attached to undersides of roof rafters
with foil facing into attic space.

read info with this in mind.

where is the ductwork in the house...attic?

best of luck.

Yes attic

Any body else?

I guess you mean that the ductwork is in the attic?

rb will reflect heat out of attic, but attic will still
be hot. hot vented attics lessen the thermal properties
of ductwork.

better choices are to put ductwork inside conditioned
living space, or to turn attic into semi conditioned
unvented foam sealed attic.

we have done both rb & foam unvented attics
here in La., also hot humid area. making the
attic semi conditioned works better, less tons
of hvac & makes thermal bypasses like IC recessed
lights, openings for supply boxes & bath vent fans
in ceiling less of an issue.
without careful attention to air sealing of ceiling of
house, there will be air exchanged from hot attic
into living space below.
the foam is the tradeoff that makes not paying
attention & sealing these penetrations popluar.

big thermal bypasses, like fireplaces open from
attic into house, shower/tub areas with dropped ceilings
are often left unsealed. insulation is placed over these
openings, but no air sealing is done.

this hot air from attic in these areas leads to need
for more tons of a/c, and cost you every month.

weigh the benefits of both before making your
decision.

best of luck

$975 - are we talking a really big house?

I have a pretty complex roof line on a 2300 per floor house and it was less than $400. But of course this was only the roof decking and that is all you should be doing.

The quick answer is best practice keeps ductwork out of the attic. But if ductwork is in attic, the radiant barrier is worth it in hot climates. But I am not sure it is worth grossly overpaying for it.

In FL, it would seem that foaming the roofline would be more common.

As pointed out above, the link I posted discusses radiant barrier OSB (TechShield Radiant Barrier OSB sheathing). A spokesman for the manufacturer says using the product as roof and gable end sheathing adds $300-$400 in cost for the typical home. The article quotes the Florida Solar Energy Center and builders as saying annual electrical savings of 3-6% are possible. You'll have to figure out how long it will take to payback the initial added costs.

I've often wondered if diy for the gable ends
with rolls of rb wouldn't be more cost effective.
of course it depends on how difficult it is to
reach these areas too. 18 on 12 roof would
make for some really tall gables.

back when products like tech shield offered
a $3.00 per sheet rebate costs to use this
produce on gable end walls was more reasonable.
of course there were the on the job issues..of
crew putting foil to outside of house rather
than facing into attic space.

really good link Worthy...one for me to save!
I like that it compares products..although not
prices..of radiant barrier materials.
easy to see that performance is very close
in all products while costs vary greatly itrw.

best of luck OP

I suspect it would be more cost effective to insulate the rafters bays. Foil facing on the bottom of the roof sheathing would then be modestly effective if ventilation baffles were used to provide an air space below the foil facing. In general, a radiant barrier is not an an effective substitute for insulation.

double post

This post was edited by Renovator8 on Mon, Mar 25, 13 at 11:27

Has anyone had a problem with shingles deteriorating due to increased heat reflected back on them once you install radiant barrier osb?

no one that I know of. back around 2002
Techshield offered a discount on RB plywood/osb
lots of people in my area used it on their
builds.To this day...I've not heard one bad
thing about these homes.

for contractors & roofers who had never used
RB decking..the whole void shingle warranty thing
was their mantra.
rather than taking the time to learn..they just
bad mouth new products.

but there is no proof that raising the temp of
the roof deck by 2-3 degrees has any impact
on shingle life.
studies have proven this.

some people just don't like new products
and rather than take the time to learn about
them...they insist there is something bad
associated with them
too bad there isn't a snopes.com for building
urban legends.

best of luck.