Energy saving radient barriers for your home?

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goes211's picture
goes211
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Energy saving radient barriers for your home?

Does anyone have any experience with this using this type of product in the attic to supplement your homes insulation?  Do they really help lower your heating and A/C costs and if so by what margin?  Are they best to be installed on the inside of the roof or directly over open flooring?  Are they worth having them professionally installed or are they a do it yourself sort of project? 

I was trying to figure out if something like this might be worth the cost.  Thx

http://www.google.com/search?q=Radiant+Barriers

DrKrbyLuv's picture
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Re: Energy saving radient barriers for your home?

Generally, those products do not carry an "R" value because the listing would be embarrassing.  They claim that the traditional "R" measurement is not adequate to gauge the performance of their "reflective" product.

Studies have been done though I haven't looked for awhile.  Basically, the reflective products seem to do better reflecting heat during hot months and as a result, I think the product does better in hot climates.  Also, an air gap is required to help the insulation value.  This may not be possible depending on where and how you plan on installing the product.

Often times these reflective products are used as a vapor shield around relatively cold duct work to prevent condensation.

Larry

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Re: Energy saving radient barriers for your home?

I have some experience with it being put directly under a roof, specifically a metal roof.  I used to install metal roofing years ago and I know one customer with a very small house said that after we installed a green metal roof(which gets quite hot) with low-e(I've also seen it go by the name double bubble) it lowered his cooling bill by around $500 that year.  I have also just finished putting it under my metal roof on a cabin I am building. The difference between the low-e and without is amazing.  The metal without will literally burn you in the summer if you left your hand against it, while the low-e temperature seemed to be the same as ambient air. As far as other roofs I don't know the effectiveness, but for metal I would highley recommend it.  

 

http://www.radiantbarrier.com/double-white-insulation.htm

This is the stuff that I put on my cabin.

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Re: Energy saving radient barriers for your home?

 

Goes211,

When I built my home in '03, the idea of radiant barrier plywood roof sheathing kinda fell through the cracks and standard plywood was installed. I considered retrofitting,  but after much inquiry I achieved a better understanding of the heat issues involved and I concluded that it was more effective to provide adequate attic ventilation than to retrofit with a radiant barrier material. In new construction radiant barrier plywood is definitely a good idea, but retrofitting was far more labor intensive. The material cost was higher also because it is cheaper to buy radiant barrier backed plywood than to apply an aftermarket material after having already paid the cost of the (non-radiant barrier) plywood roof sheathing. However, I've learned through experience and inquiry that probably 95% of houses in Southern California have inadequate attic ventilation and I would presume that to be true for the rest of the country. The Uniform Building Code (UBC)  requirements reflect a very minimum of eave vents and gable vent size and specify no ridge vents. By providing copious attic ventilation, a 'chimney' effect is created, providing a much cooler attic space and less heat entering the living space. Once the sun sets, a 'whole house fan' for evening use will quickly cool the house down to outside temperatures. I found this to be a much more effective solution.

As a side benefit, the lifespan of your roof will be lengthened, as attic heat will dry out the oils in the asphalt felt underlayment of your shingles much quicker.

 

 

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Re: Energy saving radient barriers for your home?

This might not be the kind of barrier you are thinking of but it's easy to paint on: Hytechsales.com for hy-tech ceramic paintg additive which I have used to paint the inside and outside of your remodel job. I like this because it creates a fire-retardent (not a complete stop but slows it down), sounds proof, creates a hard shell on wood siding and hides some wall faults. I've used 3 coats before the final color but 2 is recommended.

EGP

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Re: Energy saving radient barriers for your home?

I have used it for my attic and made window coverings for windows that face the sun in summer.

We have a concrete roof and the difference is noticeable. I have two fans that are thermostatically controlled in the attic and they run less now during hot weather, than before I installed the reflective barrier.

The most noticeable difference is when it is used in the windows. This lowered the temerature in my daughters room, which faces southwest. We have custom wooden blinds and low E glass, but when I put this stuff over the window, the temperature dropped 20 degrees inside. Its not pretty, but it saves a bundle on the A/C in summer.

My 2 cents worth. Your mileage may vary.

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Re: Energy saving radient barriers for your home?

What others have stated or implied about best impacts in warm/hot months is correct.  It's solar gain collected and conducted by the shingles or what have you, to the sheathing and rafters that you isolate from attic air (which would pick it up via convection) with a radiant barrier.  The book Residential Energy by John Krigger and Chris Dorsi says you can expect 2% to 10% savings, for cooling, depending on climate and insulation level.

If you're willing to change your roof color to (near) white, you can get similar results.  There are paints for the purpose.  Some utilities have had Cool Roofs programs, so you might want to inquire about that.

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Re: Energy saving radient barriers for your home?

deggleton - agreed, that's pretty much my take on it.  As far as insulating against the cold, some companies will show an "R" value that includes an air gap that may or may not be applied.

If radon is a concern, the reflective products claim that they provide a vapor barrier if applied under the concrete slab and around the perimiter foundation.  It makes sense but I am not sure how well and how long it works.

Larry

 

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Re: Energy saving radient barriers for your home?
DrKrbyLuv wrote:

deggleton - agreed, that's pretty much my take on it.  As far as insulating against the cold, some companies will show an "R" value that includes an air gap that may or may not be applied.

I believe there is next-to-no insulating value when there is no air gap, but with an air gap of some inches and a very careful installation there is some.  When there is no air gap, there can still be a benefit because the energy that's radiated goes nowhere.

DrKrbyLuv wrote:

If radon is a concern, the reflective products claim that they provide a vapor barrier if applied under the concrete slab and around the perimiter foundation.  It makes sense but I am not sure how well and how long it works. 

I don't see a good reason to use a reflective product where there is no light and almost no temperature variation.  Heavy poly, when the sheets are sealed where they overlap, can be a vapor and radon barrier, probably at lower cost.

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Re: Energy saving radient barriers for your home?

deggleton wrote:

I believe there is next-to-no insulating value when there is no air gap, but with an air gap of some inches and a very careful installation there is some.

Yup, I think the thermal resistance is overstated (Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux) by the fact that manufacturers refuse to publish "R" values of their stand-alone product.  Air is a decent insulator so to add that to your product's effectiveness can be misleading.  That said, there seems to be some value in reflecting radiant heat especially with high temperature surface installations like steel roofs.   

Another problem with reflective insulation is that the effectiveness values do not comply with ASHRAE Energy Standards which are adopted by most states and jurisdictions.  If it is not code compliant, the value to the property may not be effected. 

BTW, are you an HVAC mechanical engineer?

Larry

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Re: Energy saving radient barriers for your home?
DrKrbyLuv wrote:

BTW, are you an HVAC mechanical engineer?

Nope, not that.  Just one who came of age when energy became everyone's concern (more or less) and is nearly a BPI certified Building Analyst (waiting for my field exam to be scheduled, having succeeded in the written portion).

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Re: Energy saving radient barriers for your home?

Goes211,

Hello, my brother and I recently insulated his attic radiant barrier insulation.  He has not been through the summer yet to compare his AC bills but he has completed a winter cycle and notices an improvement in his utility bills.  Radiant barrier insulation is more prevalent in the south due to the extreme summer heat but is also effective in northern climates as well.  The only thing that changes is the application method.  In southern climates, you insulate under the roof joists, in northern climates on the floor.  For areas in the middle like my brother in the Midwest you should insulate the roof joists and if you want to maximize your winter savings, insulate the attic floor similar to a blanket.  His house style is a ranch and the home is approximately 30 years old so the attic was open and fairly easy.  If you are capable of doing it, I certainly wood, the quotes he received for installation seemed to be very high.  He spent approximately $400 dollars and we were finished in about 8 hours. 

He purchased from this company.   http://www.insulationstop.com.  This is the info he read the got him interested.  http://www.insulationstop.com/radiant-barrier-blog/2010/02/27-energy-cost-savings-using-attic-radiant-barrier/ .

Additionally, he is going to receive a tax credit from his purchase for a federal program to weatherize homes. 

Hope this helps.

 

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Re: Energy saving radient barriers for your home?

If I have it professionally installed it looks like it would cost > $1 sf which means the total cost would be over a couple of thousand.  For that cost I doubt it would give a good return on the investment.  I am still considering doing something myself but it also might be more cost effective to just add an additional attic fan.

Thank you all for the input.

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Re: Energy saving radient barriers for your home?
goes211 wrote:

If I have it professionally installed it looks like it would cost > $1 sf

The way this thread developed, it's not clear what it is.  Hopefully, you are/everyone is clear that a radiant barrier is a thin reflective material with virtually no insulation value of its own.  Its main function is to bounce back warmth radiated by building materials, not to slow movement of warmer air from one volume to another.

Unless you have what's called a hot roof, with insulation between rafters, by all means insulate the floor of your attic, which is beneficial in all seasons.  Make sure to first seal all penetrations of that plane, to greatly reduce what's called the stack effect.  A fan, unless a solar-powered one, will add to your bill, in two ways (both more kWh and higher cost electricity).  In any case, a fan is another penetration of the building envelope that can contribute to heating/cooling/moisture problems.

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Re: Energy saving radient barriers for your home?

    I installed radiant barrier on our home.  Just in the attic under the rafters.  It was a true radiant barrier- not an insulating type.  In NorCal, our two story home would get to about mid 80's on the upper level without A/C.  After installing, the temp dropped by a couple of degrees.  The biggest improvement was in how much faster the home would cool down after turning on the A/C or the whole house fan in the evening.  The radiant barrier effectively reduced the huge thermal mass of hot air in the attic that the A/C would have to fight.  I also noticed that our attic fan ran much less frequently.  

    I installed it myself.  Its a pain in the a** to hang in an attic with a truss roof, blown insulation and a/c ducts everywhere.  Would I do it again, maybe.  If I built a house from the start, I would inlcude it- would use the roof sheething with the radiant barrier pre-applied.  My brother recently finished his home and he used the raidant barrier sheething and wrapped the whole exterior with it as well.  He doesnt need a/c and its a large house in an area where 100 degrees in common in CA.  The funny part was watching his siding contractor crew install all the hardi-plank over the radiant barrier siding- they all hade to wear sunglasses and shirts over there heads to keep from getting sunburnt!

     I see radiant barrier as just part of the overall equation.  Ceiling Fans, Whole House fans, Attic fans, Eave& ridge vents, CFLs, are all great ways to get the electric costs down and then Solar PV to eliminate it!

Kman

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Re: Energy saving radient barriers for your home?
deggleton wrote:
goes211 wrote:

If I have it professionally installed it looks like it would cost > $1 sf

The way this thread developed, it's not clear what it is.  Hopefully, you are/everyone is clear that a radiant barrier is a thin reflective material with virtually no insulation value of its own.  Its main function is to bounce back warmth radiated by building materials, not to slow movement of warmer air from one volume to another.

Unless you have what's called a hot roof, with insulation between rafters, by all means insulate the floor of your attic, which is beneficial in all seasons.  Make sure to first seal all penetrations of that plane, to greatly reduce what's called the stack effect.  A fan, unless a solar-powered one, will add to your bill, in two ways (both more kWh and higher cost electricity).  In any case, a fan is another penetration of the building envelope that can contribute to heating/cooling/moisture problems.

Sorry if I was not clear.  Because I started this thread I assumed that everyone would understand that I was referring to a radiant barrier which I recently saw at a local homeshow.  I live in the Carolinas and my understanding was that radiant barriers seem to work best at reflecting summer heat away from the living space.  My thoughts about an additional attic fan was that it may also work at lowering the summer attic temperature but at a lower cost.

What I really wanted to know is if a radiant barrier is worth the cost?  To have it professionally installed would cost > $1 per square foot and based upon my home size it would end up costing quite a bit of money.  My assuption is this is probably not a great investment so I am leaning towards not doing anything.

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Re: Energy saving radient barriers for your home?

Goes,

I live in Texas and the radiant barrier does work if properly installed, but to see a return on your money any time in the next decade you have to install it yourself. The installation process can be tricky because of the need to create an airspace to minimize the conduction of heat from the roof surface. The additional radiated heat can also shorten the lifespan of your shingles, however.

A more cost effective approach in hot climates is to paint your roof white, if its possible to do so. There are special paints specifically made for this these days.

Don't waste your money on radiant barrier paints for the attic or interior. My father had this done and a subsequent energy audit showed no benefit.

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Re: Energy saving radient barriers for your home?

JAG wrote:

The additional radiated heat can also shorten the lifespan of your shingles, however.

Interesting point that I had not considered.  Did you install the radiant barrier over the traditional fiberglass insulation or tucked under the roof?  Did he have a ridge vent to ventilate the surface temperature of the roof?

Larry

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Radiant Heat and Roof Sprinklers
DrKrbyLuv wrote:

Did you install the radiant barrier over the traditional fiberglass insulation or tucked under the roof?  Did he have a ridge vent to ventilate the surface temperature of the roof?

The radiant barrier is installed onto the rafters that support the roof decking, creating an airspace of several inches between the roof decking and the radiant barrier. The roof deck is not insulated. Ridge vents are necessary, but have no effect on reducing shingle temperature.

Radiant heat is generated by the solar gain exciting the molecules in the shingles, which in turn radiate heat in all directions, some of this is directed into the building. The barrier redirects this radiant heat back towards the shingles, which increase their temperature even further and causes them to age more quickly. 

A great strategy to reduce unwanted heat gain from asphalt shingles is to use a roof sprinkler. On a hot day, the heat removed by the surface evaporation of water can be very significant. Attic temperatures can drop by more than 40 degrees with the use of a roof sprinkler system. Roof discoloration can be minimized by using rainwater. Its a viable alternative to painting your roof white.

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Re: Energy saving radient barriers for your home?

Radiant Barriers are very effective.  They can lower attic time by up to 30 degrees F.  Radiant bariers do require at least 3/4" airspace to work.  In new construction or if the entire roof is to be replaced the foil laminated to the OSB is the best route.  in an existing home there are radiant barriers that can be attached to the underside of the rafters that will work well.  Having said that be very sure there is sufficient ventilation from the soffits all the way to the ridge.  Radiant barriers do not raise the shingle temps more than 3 or 4 degrees which is well within most manufactures specs.  The hotter the temperatures the more effective radiant barriers are. 

Radiant barriers can be spread over the attic floor but over time any dust build up will decrease the effectiveness.  Also keep in mind that the foil reflects abut 97% of the suns radiant energy back out through the roof but if anything comes in contact with the foil the foil becomes a conductor and the heat passes through the foil to the material touching it so keep any material away from the foil surface.  Do not spray foam insulation on the foil surface because it completely negates the effect of the foil and make the investment in the radiant barrier a complete waste.

Radiant Barriers do not have an R value because the R measures the resistance to heat passing through it and that is not the purpose of a radiant barrier.  Energy savings will depend on the size, shape, location, exposure, window sizes, the occupants and their life style.     

Doug M

 

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