Comments on: Oooh, Shiny Stuff! – Radiant Barrier Fundamentals

By: David Butler

David Butler — Mon, 07 Jul 2014 06:58:44 +0000

@Stephanie, when re-roofing,
@Stephanie, when re-roofing, there's one more important thing to consider. Attic heat gain largely depends on the roofing materials. For example, dark roofs obviously absorb more heat than white roofs.

White and light color metal and tile roofs offer the best performance on pitched roofs (other than 'flat' roofs), but cost much more than shingles. And white shingles aren't very practical since they get dirty very quickly.

Research has led to a new class of shingles that reflect heat better than than conventional shingles without having to be white. Check out the Cool Roofs Rating Council website for more information and a rated products directory. Certainteed currently offers the highest rated "cool roof" shingle -- the Landmark Solaris Platinum (comes in three medium colors).

Energy Star has a Certified Roof program (products with initial reflectance > 0.25 and aged reflectance > 0.15), but its product search page isn't very useful since it doesn't have a filter for roofing type.

Finally, here's a calculator for the Department of Energy for estimating the benefit of cool roofing products: Roof Savings Calculator.

By: David Butler

David Butler — Mon, 07 Jul 2014 00:35:11 +0000

@Stephanie, I agree with
@Stephanie, I agree with Allison's advice (re: radiant barrier not making sense in Detroit) with the following caveat... IF your roof sheathing must be replaced anyway during re-roofing, TechShield or similar (OSB with radiant barrier factory bonded to the wood) costs less than $0.10 per square foot extra. Field-installed radiant barriers cost many times that due to labor and rarely if ever worth the cost. In any case, a radiant barrier might help reduce your attic heat load, but you'd be better off spending your money to fix the underlying problem(s).

In addition to what Allison recommended (be sure to read those articles), improperly designed HVAC is often a major contributor to upstairs cooling issues. In most cases, comfort issues are the result of poor duct design and/or installation quality, not inadequate capacity.

The most common problems include leaky ducts and undersized returns. Also, a single zone AC/heat system (e.g., one heat/cool thermostat for both floors) cannot maintain comfort on two levels without some way of redirecting some of the supply air between seasons.

It may be possible to add a balancing damper to direct more air upstairs in summer, and less in the winter (requires an adjustment every spring and fall). Installing a balancing damper to an existing system usually requires significant ducts mods, especially if duct system is already undersized (another common problem).

You mentioned roof/attic venting... when you added insulation, the installer may not have installed baffles to keep insulation from spilling into the soffits, thus blocking ventilation air flow.

When solving problems like this, it's important to look at the house as a system. Unfortunately, most contractors focus on a single component -- if I only have a hammer, then every problem looks like a nail. In reality, most comfort issues are the result of multiple contributing factors.

By: Allison Bailes

Allison Bailes — Sun, 06 Jul 2014 15:57:57 +0000

Stephanie:
Stephanie: A radiant barrier doesn't make sense in Detroit. You're better off spending your money on air sealing and insulating the ceiling. Have you had a blower door test done? Here are some articles that might help:

How to Choose a Company to Do a Home Energy Audit

Hidden Air Leakage Sites in Your Attic

Mind the Gap - Air Leakage at the Top Plates

How to Sheathe an Attic Kneewall — And How Not to

By: Stephanie

Stephanie — Sat, 05 Jul 2014 04:04:14 +0000

I am a homeowner getting roof
I am a homeowner getting roof estimates. I live in the Detroit, MI area. I live in a two story and we have a problem with a hot upstairs. We need a solution to cool the upstairs. The roofers are talking about checking the soffits, eaves, and baffles for the best ventilation in. They say our roof vents are not placed correctly on our hip roof. About 9 yrs ago we had insulation blown into our attic, but not 100 percent sure it is R38. I hope it is. After reading multiple posts I believe the radiant barrier or more insulation would be the answer in addition to proper ventilation. What do you think? None of the roofing companies have mentioned it.

By: Greg Pruitt

Greg Pruitt — Sun, 11 Mar 2012 01:45:52 +0000

recnetly had a customer say
recnetly had a customer say that he was quoted $3500.00 for radiant barrier and two fans with a guaranantee to drop temps in attic by 10 degrees. we foamed it for $500.00 more and he is already cold in his two story home. Foam is the only soulution for a two story hot upstairs.

By: Greg Pruitt

Greg Pruitt — Sun, 11 Mar 2012 01:43:07 +0000

Enjoyed everyones comments,
Enjoyed everyones comments, we often spray foam over radiant barrier in the Houston Market. Temp go down from 155-125 on a 100 degree day to 77-85. when we are quoting against radiant barrier in the after market. we are often about the same price, some times $500.00 less or $500.00 more. We alsway reduce the attic temp down two between 77-85 dgrees on a 100 degree day. Radian barreir is a good band aid. Foam insualtion does what people hoped the radiant barrier would do. It does work, just not near as good, and the paint is a joke!

By: David Butler

David Butler — Wed, 03 Aug 2011 20:54:53 +0000

Right on queue for this
Right on queue for this thread, RESNET signs MOU with RIMA, the shiny stuff trade association…
http://bit.ly/mTex5S 

RIMA membership includes makers of foil faced bubble wrap. I visited the Relflectix website prepared for bear and was pleasantly surprised to see an extensive section “About Reflective Technology” that seems to go out of its way to provide factual information and dispel some of the myths about reflective insulation. Too bad the distributors aren’t always on the same page.

By: Michael Blasnik

Michael Blasnik — Mon, 25 Jul 2011 23:11:34 +0000

John: if I change the attic
John: if I change the attic from R-30 to R-38 I see savings of about 40 kWh/yr in cooling and 16 therms/yr in heating -- about $20. Again, these estimates are all based on my taking a generic Energy Star home from Houston (slab, SEER14, low SHGC windows. tight well insulated ducts, etc) and moving it to Atlanta.

I did the calculations using my own simple spreadsheet algorithms (which aren't really so simple) and they include some assumption that the insulation isn't perfect in any scenario.

By: John Brooks

John Brooks — Mon, 25 Jul 2011 22:30:01 +0000

Thanks Michael...your
Thanks Michael...your estimate of benefit for Atlanta is not-so-different from REM/Design

So instead of spending $200+/- for Radiant Barrier = +/- $5/year benefit

What if you upgrade the insulation to R-38 instead ... what is the benefit/yr?

Can I trouble you for another estimate?

Are you using your own spreadsheet or a certain software?

By: Michael Blasnik

Michael Blasnik — Mon, 25 Jul 2011 20:56:47 +0000

John:

John:

When I run the same model using Atlanta I find cooling savings of about 90 kWh/yr and heating use increase of about 4 therms. So that's maybe a $5/yr net benefit. Again this is for a new Energy Star level home. ymmv