You can easily tell it has been a hot summer by the amount of talk about white roofs, cool roofs, and radiant barriers going on in different blogs, forums, etc... So I am curious on what you're thoughts are on the options & best practices. As this varies by climate make sure you put down what climate zone(s) your best practices are for.

 

To start off, I just replied to one for a house in Florida, where they want to paint the shingles to help cut the heat & extend the life of a 10 year old roof in good shape 

...we used to do it in Tucson. The same products used for flat roofs can generally be used for shingles or rolled roofing. It generally takes 2 or 3 people, one rolling out the base coat while another rolls out a layer of fiberglass mesh and embeds it into the base coat (or second coat depending on instructions). The final coat or two is then applied over that.

The cost though is pretty close to simply redoing the roof with ENERGY STAR or similar shingles, though I would say the system will perform better at reflecting radiant heat. As XXXXX states, it still requires maintenance & should not be done if the roof is wet.

As for interior radiant barriers, while they do work (somewhat) - having it inside the structure is not as good on the outside and it will loose effectiveness over time.

Ah the famous paybacks was brought up by another - in this case the why bother it won't do any good

maybe, maybe not - a lot depends on the house, issues they are trying to address, etc... In some cases the payback maybe within a year or five, while in other cases they might not see any benefits as there are no air handlers up there, the attic was done right & it has enough insulation in it to handle the normal attic temps

So folks, thoughts, opinions, what is the best practice in your area?

Views: 1147

Replies to This Discussion

Richmond, Virginia is mixed humid. Here is some interesting data I collected from a new home on a sunny 96 degree day in the afternoon.This house has HVAC equipment in the attic, I beg builders not to do that! It appears that radiant roof sheathing works in significantly reducing attic temps when used with proper passive venting. However during the winter, in this climate zone, more energy is used during the heating season. I have heard the claims from radiant barrier manufacturers that this product prevents heat from escaping the attic in the winter. Air heated inside the house shouldn't be in a vented attic!! Proper air sealing and insulation at the upper conditioned boundary should be in place.
Attachments:

Very good points & nice documentation - as for the manufacturer's claims, I would hazard a guess that is only if you install the radiant barrier like it is recommended up north - directly on top of the insulation.

 

By the way, nice way of showing the temperature, I just might have to steal that idea

 

Well I do not live in a Florida like climate.  I live in western Montana, but I'll give it a shot.  We sometimes use what's called a cold roof here to vent the roof better, The idea is to prevent ice daming on the eves in the winter, which is actually from poor insulation in the roof.  So I would think about putting down an aluminum foil faced foam board with the foil up, like fan fold eps.  I would then place 2x4s verticle on top of the existing rafters above the roof sheathing.  then I would place 2x4s on top of this screwed down with RSS structural screws horizontally.  This will lift the roofing up by three inches and also give a one and a half inch air space for the air to vent out the ridge from the soffits.  I would then use galvanized steel roofing with a roofing underlayment under it.  I would have an engineer look at it for wind speed, like in a hurricane.  I did my cottage this way and I need no air conditioning, but I live in Montana at 3400 ft.   

   

I have worked with an Energy Star Cool Roof coating for 25 years, since way before there WAS an Energy Star. Our coating is one of the most versatile products there is because ours can also be used as an interior or exterior paint.

 

I have read a lot of posts on this board and I cannot recall anyone discussing The Solar Reflectivity and Thermal Emissivity levels of whatever material they are looking at on the outside of the building.

 

As an example, lets say we are looking at a home with a gray asphalt shingle roof and stucco walls painted a light beige. Whatever the outside surface is, that is the proprietary surface, in this case, the gray shingles and that light beige coat of paint.

 

The shingles and the paint have their own measurable levels of solar reflectivity. In warm climates if you can do anything to raise the level of solar reflectivity, you will keep that structure cooler and save energy.

 

I used to have a list of different materials and their levels, going by memory here so please forgive me if I am off a point or two..

 

Gray asphalt shingles - 20% Reflectivity (according to the roofing industry but I have my doubts there.)

 

Light beige standard exterior paint – usually around 12% when new, drops to around 5% once oxidation occurs in a few years. That thin layer of oxidation then becomes the proprietary surface.

 

Our coating, applied to that roof and those walls, will put a new proprietary surface that will have a Solar Reflectivity level of 83% and a Thermal Emissivity level of 90%. In doing that, you have also created that 'Building envelope' everyone wants to achieve.

 

Creating a 'Building envelope', everyone on this board surely understands what that means when it comes to the standard insulations with the R-values. With our Energy Star Cool Roof coating applied to the roof and the exterior walls, the R-rated insulation inside can now perform their function on a greatly reduced temperature scale.

 

Our coating is NOT labor intensive as someone has described another coating being to apply. Very seldom do we require a primer except on new bare wood or when rust is present.

 

Once our coating is on the outside surfaces, the surface temperature will be within 5 degrees of whatever the ambient air temperature is at the time. Example; gray asphalt shingle roof on a 90 degree day can reach 160 degrees. With our coating, 95 degrees.

We can also apply our coating to any AC unit and exposed metal ducts on the roof as that application has dropped the air temperature coming into the building by 5 to 25 degrees. I have done that more times than I can remember. There are several statements on our website

 

We can also go into the attic and coat the AC with, plenum and the duct work, metal or flex ducts. Doing that alone normally drops the homeowners entire electric bill by around 25%.

 

You can also create that building envelope by coating the interior walls and ceilings in a building.

 

When considering ANY coating you also want to determine if it will retain heat in the cold months. Here are a few things ours has done when it comes to retaining heat; On boilers and steam pipes, a thick coat of our coating dropped the skin surface temperature from 267F down to 155F, a 35% reduction in heat loss. There are other statements on our website. These temps are much higher than what you would keep your home but the reductions in heat loss will still be the same.

 

At any rate, if you currently DO NOT consider the reflectivity levels on the exterior of a home, you might be doing them and yourself a dis-service.

 

Hal Skinner

www.ct-texas.com

Prior Experience: R30 2x4 Vaulted Roof System Example #105:

  • Light Color Shingles on Exterior
  • 1 in roof decking
  • 2x4 Rafters 16" Space
  • R13 Batt Insulation
  • Double Sided Radiant Barier
    • Also Acts as Vapor Barrier
  • Adequate Ventilation Provided by
    • Automatic Power Attic Fan Peak of Roof
    • Proper Vents in Soffits and Gable Ends

ENERGY SAVINGS:

  • Reduced the Need for 1 window AC unit in Typical Two Story Stick Built Home-
  • This translates to a Savings of $30 / Month during Cooling Months or $120-$160 / Year.
    • This Application Payed for itself in the 1st Summer 06. At the time of writing this article the estimated savings for 5 yrs is $600. This Pays for 100% of the Materials used in the Green Roof System for the Upstairs Bedroom Remodel.
  • The Only drawback reported by owner (which wasn't really a drawback since it was his teen-age sons room) was the decrease in cell phone reception,
    • This is caused by the Reflective Nature of the Reflective Foil Radiant Barrier.

 

All blogs get fantastic stories about how product "X" is saving them lots of money.  Problem is that they are not based on science.  Your listing of work done makes no sense from an energy efficiency standpoint.  You insulated at the roof line, with a "double sided radient barrier" toward the attic.  You have "proper soffit and gable vents" and "power attic fan".

If you move the building envelope from the ceiling to the roof line, you are going toward a conditioned attic.   Conditioned attics are not vented.    The reason for conditioned attics is to bring HVAC equipment, ducting or storage space in the attic into the conditioned space, away from the extreme heat and cold. Venting this space brings the heat/cold inside.  The insullation at the roof does nothing for you.

If the attic is vented you should have the insulation between the attic and conditioned space, not at the roof line.  The insulation should have the vapor barrier touching the heated ceiling below and have all ceiling penetrations air sealed.

Installing a radient barrier above a vented attic may help reduce the temp in the attic some in heating dominated climates, but the insulation between the attic and the conditioned space below is responsible for keeping the high/low temps from passing to the conditioned space.   Better results from  air sealing and adding insulation at ceiling.

Most  radient barriers I see in home show booths, pitched by remodelers and advertised are "miracle products", "same as used by NASA", products way over sold for the minimal benefts they provide in most installs.  The three most common types are rolls of smooth or preforated mylar like films or a double layer, bubble wrap product.  The common thread is the bright reflective surface.  Everybody likes shinny stuff!

In the case above I must guess the preforated material was not used as a vapor barrier should not allow air passage and must be fully sealed at all seams.  This means you have a solid moisture proof surface exposed to the cold air in the attic.  Should this surface be at a temperature below dew point, it will condense moisture that can drip on to the insulation above the ceiling below.  (That is why the insulation vapor barrier is in contact with the warm ceiling below)  If you elected to use the buble wrap type, you have the same possible problem plus you fell for the exagerated Rvalue claims used to sell this stuff at high prices.

If you have insulation above the ceiling, the best thing you can do to improve is the energy efficiency in this area is to (1) air seal all penetrations of the ceiling plane, (2) install proper soffit vents that prevent air washing of the insulation and (3) add more insulation to meet or exceed the code requirements for your zone.  Always intall insullation per manufacturers instructions: fully lofted and completely filling the space.

 2x4 Vaulted Roof System Example #105 taken from post at: http://stlouisrenewableenergy.blogspot.com/p/weatherization-tips.html

Mr A Hyde: you commented: "All blogs get fantastic stories about how product "X" is saving them lots of money.  Problem is that they are not based on science."  

 

Mr A Hyde: I based the snippet of one of my experiences using the Double Sided Radiant Barrier.  I based this snippet on:

 Real Time Energy Savings from the Owner of the Property.  

Specifically:

"The Owner removed one of the two AC window units that were needed to cool the 2nd floor of the Bedroom Remodel." 

This translates to a Savings of $30 / Month during
Cooling Months or $120-$160 / Year.
  • This Application Payed for itself in the 1st Summer
    06. At the time of writing this article the estimated savings for 5
    yrs is $600.  This Pays for 100% of the Materials used in the
    Green Roof System for the Upstairs Bedroom Remodel.
If you would like to email the owner of the property to verify what I wrote let me know and I'll send you the property owners email address.  Scotty
I think that radiant barriors really work.  I wonder what the real amount of energy that is reflected really is.  If you look at a piece of foil faced foam with an infrared camera it lights up.  I also know that the latest rage in jackets is now using this reflection of energy.  I shake my head at all of the black asphalt ( metal too ) roofs I see around here.  Black is for solar collectors, white for roofs.  I think we need to not reject the foil bubble wrap totally, but understand where to use it in combination with high insulating materials.  Is anybody on this continent producing the vacume panels like what is coming out of Germany?

Scotty

I took the time to look at your preceeding post.  I like to see companies post information about how they do their work.  The first section about insulating the rim joist area was pretty informative for a possible client.

Then you got on to attic insulation and "takes a whole house approach"  and "air infiltration areas to be resolved before adding insulation" and I thought you were on a real energy efficiency roll. But a few lines later you jumped into "Reflective Radient Barriers have R-Values that range from R-3.7 to R-17" .  Where do you get these numbers?  Is the R-17 a double layer radient barrier product with three inches of closed cell foam as filling between the two reflective surfaces? 

I see claims on a regular basis from companies pushing these products as a cure all miracle product.  They even provide test lab results with claims of high R-Value.  When you read the test results the claimed R-Value is usually from a complicated assembly with sealed dead air spaces , an assembly that is almost impossible to assemble and maintain in the normal home building industry.  An example is the 1/4 inch thick "bubble wrap insulation with very visible printed labeling of R-6.  However, the data sheets from the test lab state that to achive the R-6 you must install as a sealed wrap around the ducting with minimum 3/4 inch sealed dead air space all around the duct.  The spacers must not allow sagging of the bubble wrap - there must be a full 3/4 inch minimum sealed air space for the life of the installed ducting.  If just taped around the duct (the way I see it installed) it is rated as R-1.

You follow this with "Prior Experience: R-30 2x4 Vaulted Roof System Example #105" - the item that caused me to make my original post.  Following this is a list of installed componets: "shingles, 1"decking, 2x4 rafters @ 16", R13 batts, double sided radiant barrier- noted as vapor barrier".  Assuming you install 1/2 inch sheetrock as the ceiling, I would rate this assembly at less than half the claimed R-30.  The radient barrier is in direct contact with the batts and the sheetrock and has no dead air space to assist in improving its stated "reflective barrier" properties. 

If the client ended up with better energy efficiency it was because you did a good job of air sealing, not because you built an "R-30" roof/ceiling.    From your site it appears you are trying to do a good job for your customers and you are trying to provide information to guide possible clients.  Just be carefull about advertized products that claim to do so much more than their compeditors.  Advertizing is to sell products - not to provide factual information.  " Truth in advertizing" is whatever the salesman can get away with today.  Read all the actual MDS and test reports.  Check out the "experts" - if (s)he is from RIMA remember this is the Reflective Insulation Manufacturers Institute, established by and run by the people selling the product.

Claims like this tend to elicit comments from me.   We are true third party energy auditors and energy efficiency consultants.  We do not sell or install any products so we do not need to slant our inspection/testing results to aid in making a sale.  We try to act as an advocate for the homeowner (or future home owner) in a quest for a more energy efficient home.  We provide plan reviews, and even on site training, to assist architects, builders, sub contractors and remodlers with making their projects more energy efficient  and qualify their projects in the various energy programs.  We are in SE PA and you can contact me direct at ahyde@SavingGreenEnergyAudits.com

 

RSS

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Christopher Morin's blog post was featured

5 Things New Energy Efficiency HVAC Contractors Need to Know

1. Do not sell on Price! Use 'Simple Payback'The price of High-efficient equipment will undoubtedly…See More
36 minutes ago
Jim Gunshinan's blog post was featured
36 minutes ago
Profile IconDan Liska and Rob Moreno joined Home Energy Pros
37 minutes ago
Jim Gunshinan posted a blog post
3 hours ago
Kim Tanner commented on Diane Chojnowski's group Home Energy Pros on Twitter
"Follow The Energy Conservatory on Twitter! We'll follow…"
6 hours ago
Kim Tanner joined Diane Chojnowski's group
Thumbnail

Home Energy Pros on Twitter

We've created a twitter list of members of Home Energy Pros who tweet!See More
6 hours ago
Bud Poll replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"Hi Kaushal, First step is to understand where you are in terms of energy costs.  If current…"
8 hours ago
Kaushal Bharath Raju posted a discussion

Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.

We have a small 1940s single level house (1005sqf) in Berkeley, California that is in need of a…See More
16 hours ago
Christopher Morin posted a blog post

5 Things New Energy Efficiency HVAC Contractors Need to Know

1. Do not sell on Price! Use 'Simple Payback'The price of High-efficient equipment will undoubtedly…See More
21 hours ago
David Eggleton commented on David Eggleton's group Considering Permaculture &/or Transition
"In August 2014, in Minnesota, there's another unprecedented opportunity to meet and mix with a…"
yesterday
Glen Gallo commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"Nate, RE: Duct test On my own home and a rental I have tested more than once over the last many…"
yesterday
Profile Iconangela hines and Charles Goldman joined Home Energy Pros
yesterday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service