Radiant Barrier

[gasser65]

Anybody, pros or homeowners have experience good or bad with having spray-on radiant barrier installed?

[DanW13]

Might want to read up on it over at a site called Building science website, there's alot of good information to read on with respect to radiant barriers, and other home building science. But I am sure some will chime in with there experience.

[jerryd_2008]

Don't know much about radiant barrier, but an energy consultant here always says that it needs an air space to be effective. He is referring to the material that you apply to the roof trusses. As recommended in previous post, do your research. Here is a web site that might cover the sheet material that is applied to trusses: www.dougrye.com

He will usually take calls for free at 501-653-7931 8:00-4:30 M-F (CST). He also does a weekly radio show on Saturday mornings in 17 states.

[energy_rater_La]

I used a foil backed paper with a nylon scrim for strength, the least expensive
rb product on the market. foil faces into attic space, attached to rafters with
buttoncap nails.

there are lots of rb products on the market, some like foil bubble foil rb promote
outrageous R-values. in reality r-value is around 10. not R-19 or higher.

spray on rb can be less effective due to absorbtion rate of wood that they are applied to
which is why foil faced sheets have continuous R-values and sprays don't achieve this same continuous value.
(that just facts...however...)
rb installs like I did are very time consuming and labor intensive...took me 2 mornings and I lost 10 lbs...
sprays go on easier, but the reflective quality is less. its that trade off thing again...
search these sites for rb info
florida solar energy center
building science
southface inst.

btw...didn't someone here from texas do a spray on rb???

best of luck

[drk]

I agree with all the above post. Let me add that the spray on does not lose any of the reflective properties as it ages. The foil once it gets a skim of dust on it it will hot the heat and not reflect it. I think I have read that it will lose half in two years.

[DanW13]

I agree with all the above post. Let me add that the spray on does not lose any of the reflective properties as it ages. The foil once it gets a skim of dust on it it will hot the heat and not reflect it. I think I have read that it will lose half in two years.

I think that assessment you made would be Dependant on other variables such as how well ventilated the attic space is, and how well sealed the rest of the attic is from the living space. I would think it would take longer than 2yrs before dust would play a vital role in obstructing the RB IMO.

[catmanacman]

im not impressed with the spray on radiant barrier the attics that i have been in that have it do not seem to be any cooler and every thing in the attic is silver including the furnace and coil on the other hand i believe the cool ply is a good product

[Shophound]

btw...didn't someone here from texas do a spray on rb???



I did. Only wish I had a thermometer sensor up in the attic prior to spraying like I do now. On days over 100 degrees outside I'm still seeing 135 degree temps cooking the sensor on the attic floor. If that's down from 150 I'd call it a gain, but I consider the blizzard of fiberglass insulation the company that blew both the barrier and the insulation into my attic the true workhorse. The spray on isn't ineffective in my observation, it is just not as effective as either a foil based RB product at the roof deck. If I had the funds and the ability to do it all over again, the roof deck would be foamed and the attic sealed, end of story.

[mark beiser]

Don't know much about radiant barrier, but an energy consultant here always says that it needs an air space to be effective.

The air space can be on either side, it doesn't have to be between the RB and roof deck.

[jerryd_2008]

I think that assessment you made would be Dependant on other variables such as how well ventilated the attic space is, and how well sealed the rest of the attic is from the living space. I would think it would take longer than 2yrs before dust would play a vital role in obstructing the RB IMO.

Heard of dust being an issue if the RB is laid on insulation. Kind of wonder how much dust will cling to it if it is nailed to the roof trusses.:rolleyes:


The air space can be on either side, it doesn't have to be between the RB and roof deck.

Believe that is true since some new roof decking has it already. Here is one manufacturer's Energy Star recommendations: http://www.radiantbarrier.com/attic.htm. This is a good site to ramble around in for ideas and information.

Note they do suggest one possibility being over insulation, but remember dust accumulation. Also heard using over insulation depends on whether ducts are in attic.

[energy_rater_La]

if the foil faces the roof deck dust build up will still occur.. not as quickly
as if laid atop the insulation of attic flooring.

studies show that in 5 years dust build up reduces rb's reflective quality by 50%

for me.. it was hard enough work that it isn't something I would want to do again,
in five years or longer.

gravity has a lot to do with dust, which is why installing foil facing down is the
proper install. dust doesn't gravitate up...this is why rb osb and cdx work so well.

there are other ways to achieve this..ice house roof with foil faced sheating on top
of roof decking, furring strips and roofing. Then edges of roof have to be sealed.
lots of work, most retrofit houses don't go this route..but this was a roof (slate)
replacement.

and shophound..I thought it was you who did the spray!

I thought you would find what I learned this weekend of interest.
(getting a bit off topic OP..sorry)
anyhow house on piers 1680 sq ft. 3.5 tons of a/c.
the only upgrade they are consitering is foam (open cell) on roofline
and under floors. open cell is 3.9 per inch..install will be approx 4"
for R-15.6 they already have R-30 blown insulation (FG) in attic,
floors were never insulated.
my first concern was would they achieve a 30 point reduction with this upgrade.
our program mandates a 30% reduction from as is to improved house.
this one upgrade improved the house 33%.
their last utility bill was $200. with the foam install it should be around $120
a month. payback....13 years.
this house had 2600 cfm of leakage..the vinyl flooring actually picked up off the floor
when the blower door was running. home owner's mouth dropped open!
now load calc shows that house could be heated and cooled with 2 tons of a/c.
I'll test once foam is installed...I'm excited to see the results..and thinking about
make up air options..home owner bought a stand alone dehumidifier the day after
my testing and RH is down from 65% to 55% in just a few days..even with the
afternoon showers we are having.

[Shophound]

and shophound..I thought it was you who did the spray!

I thought you would find what I learned this weekend of interest.
(getting a bit off topic OP..sorry)
anyhow house on piers 1680 sq ft. 3.5 tons of a/c.
the only upgrade they are consitering is foam (open cell) on roofline
and under floors. open cell is 3.9 per inch..install will be approx 4"
for R-15.6 they already have R-30 blown insulation (FG) in attic,
floors were never insulated.
my first concern was would they achieve a 30 point reduction with this upgrade.
our program mandates a 30% reduction from as is to improved house.
this one upgrade improved the house 33%.
their last utility bill was $200. with the foam install it should be around $120
a month. payback....13 years.
this house had 2600 cfm of leakage..the vinyl flooring actually picked up off the floor
when the blower door was running. home owner's mouth dropped open!
now load calc shows that house could be heated and cooled with 2 tons of a/c.
I'll test once foam is installed...I'm excited to see the results..and thinking about
make up air options..home owner bought a stand alone dehumidifier the day after
my testing and RH is down from 65% to 55% in just a few days..even with the
afternoon showers we are having.

Vinyl flooring lifting up off the floor during a blower door test...what a trip! So much for that floor acting as a vapor barrier. :D

Open cell foam at roof deck at 4" = about 15.6 R value? Will the R30 on the attic floor stay? If so it seems biggest gain by foaming the roof deck is massive heat gain reduction to ducts in attic and much less cooking of of the R30 FB than prior to foaming.

Amazing how often pier and beam floors are left uninsulated. I once took care of an apt. complex in the Sacramento Valley...known for mild winters and hot summers...winters can have days on end of chilly, damp fog, making one feel colder than the actual temperature. Apt. units were pier and beam with no underfloor insulation. My own unit was split level and was NEVER warm on those chilly nights in spite of electric heat spinning meter off wall. Management got tired of paying high bills on my unit (and hearing everyone else complain as well) so they let me start insulating select units. What a difference post insulation made to interior comfort.

[EDGtx99]

It's been a year since I had the "75%" spray-on RB installed. At the time, I hadn't yet had ridge vents cut into the roof. I measured the attic temp a few times and saw it did drop a few degrees compared to similar other days. It dropped about another 10 once the roof could breathe better after the ridge vents were installed.

Right now, it's 94 outside and only 107 in the attic. On near 100 degree days, my attic will hover between 110 and 115 at this time of day.

[energy_rater_La]

Yes R-30 will stay, I have to meet with foam company to make
sure that they understand that the blown insulation will have to be
moved back at rafter and attic floor (soffit area) to make a good foam
seal. foam co owner wants to come for blower door test of house when
foam install is complete. I'm thinking I'll test the house with the attic closed
first (see if vinyl picks up then!! LOL!) and then open attic to see make sure
there is no ambient leakage into attic.
I'll let you know...homeowner leaving for vacation, work will start when
he returns.