Opinions on Radiant Barriers

[HowardH]

We are getting a bid to have a RB sprayed in our attic under the roofing to help out on our electric bill.  Are they worth the cost?  What kind of savings can we realistically expect?  We live in the Dallas area where it is hotter than HE double toothpicks itself for 4 months out of the year.  

 

[Holzhacker]

In terms of RB, I'm guessing you are talking about insulation. Maybe RB is a regional term. You mentioned 'spray in', so I am going to guess you are talking about expanding foam insulation. The expanding foam spray in stuff comes in various chemical compositions depending on brand, type, etc. The two big category differences are open cell type and closed cell type. Each has it's own characteristics and needs for successful long term use without creating conditions that can over time cause damage to your home.
I would suggest:
- contract specify brand, type, and expanded thickness of material
- contract specify any related work that may be required under product Manuf Specs installation requirements
- Copy of Manuf Spec and install guidelines prior to start of job
- contract to specify if they are spraying the rafters, ceiling joist cavities or both
- access to electrical boxes or other mechanicals must be maintained
- do your research on the product to be used
Depending on the product used, your existing, attic space, soffit, roof or ridge venting may need to be closed off, left as is or changed to some extent. Additionally if you have any type of chimney going through the insulated space that chimney may also need to be dealt with in a specific way. Moisture control is a key issue with expanding foam insulation. Moisture issues and leaks tend to be more difficult to find and take longer to detect. Consider verifying the condition of your roof, flashings and penetrations in conjunction with this work.
Sorry for being so vague but it really varies depending on the product and install.
Be careful of the lowest bid or a vague contract. Often times such contracts do not contain additional work or information that may be part of the Manuf install requirements. If such requirements aren't followed and you have a problem, your recourse may be limited.
If you google open cell closed cell insulation you'll get a wealth of info.
You can also try a couple places like
jlconline,com, inspectorsjournal.com and
http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11600
Good luck

 

[WarnerConstCo.]

We are getting a bid to have a RB sprayed in our attic under the roofing to help out on our electric bill.  Are they worth the cost?  What kind of savings can we realistically expect?  We live in the Dallas area where it is hotter than HE double toothpicks itself for 4 months out of the year.  

Basically the RB is reflecting the heat at the underside of the roof decking?

See them all the time in your climate, in my climate it would cause all sorts of issues.

 

[HowardH]

Yes, I'm talking about the barrier applied under the roof decking.  It supposedly reflects most of the heat back out rather than heating up the attic to 130 deg.  If it works, it would significantly help keep our house cool and elec bill down.

 

[GPowers]

I installed radiant barriers in our pool house. The rolls of AFS-Foil were stapled to the rafters after the roof was built.

 
In the following photos you can see the radiant barrier stapled up to the raffters and the end gable.

I purchased it from a company called AFS-Foil her in So. Ca. The stuff works. But remember what keeps out the heat in the summer also keeps out the heat in the winter. The pool house stays significantly colder, then the main house, in the WINTER and the summer.

 

[HowardH]

we don't have much of a winter down here usually so any relief from the heat is very welcome!!

 

[GPowers]

we don't have much of a winter down here usually so any relief from the heat is very welcome!!

I live in Southern California and still noticed how much chiller the pool house was in the winter, vs the main house. Just pointing it out as I was focused on the A/C savings in the summer and never though that the same heat through the roof was warming the house in the winter.

 

[MarkF]

Howard I would be concerned about ventilation first before you do any thing with a Radiant Barrier.  The heat needs to get out of your attic no matter what you do.  Inadequate ventilation will cook the sheathing/roofing and will reduce the lifespan of the roof.  We considered adding a radiant barrier last year when we replaced a hail damaged roof.  The original roof ventilation was built to the code on our house.  The addition of 3 passive turbine vents and 6 extra feet of ridge vent added to the original ridge vent has made a big difference in our attic temperature and utility bill so far this summer.  No need right now for the radiant barrier. 

 

[tbellemare]

My house was built in the '70s with only gable end ventilation. It didn't even have any soffit vents. For ridge vents to work (or gable end vents), you need significant ventilation from the soffit. I have added soffit and ridge vents and it seems to help considerably.

Tom

 

[WarnerConstCo.]

My house was built in the '70s with only gable end ventilation. It didn't even have any soffit vents. For ridge vents to work (or gable end vents), you need significant ventilation from the soffit. I have added soffit and ridge vents and it seems to help considerably.

Tom

That is normally a big no-no.

In your climate it may be ok.
If you put a ridge vent on with gable vents around here, you will cook your roof in as little as 8 years and end up with 2 feet of snow in your attic during the winter.

 

[tbellemare]

How does it cook the roof? Are you saying it isn't drawing from the soffit?

Should I consider closing the gable ends? I have thought about it.

Tom

 

[WarnerConstCo.]

How does it cook the roof? Are you saying it isn't drawing from the soffit?

Should I consider closing the gable ends? I have thought about it.

Tom

Most Jack-Leg roofers around here just throw on a ridge vent no matter what the ventilation is at the time.

Houses with gable vents normally have no kind of soffet vents and you can not easily add them.

With just gables and ridge vent, the heat will rise out of the gable vents and get sucked back into the ridge vent.  This causes an attic to be 40-50 degrees hotter then it should be.
Works the opposite way with snow.

I would cut some foam and tape it or whatever over the gable vents.

With proper soffet vents and proper ridge vent you should move even more air.

 

[tbellemare]

That's exactly what I was thinking - that I was short-circuiting my soffit-to-ridge ventilation by leaving gable vents open.

I still don't understand why no soffit vents with gable vents? It seems like the idea is to wash the air from the soffit up across the underside of the roof and out the top.

Thanks,

Tom

 

[WarnerConstCo.]

That's exactly what I was thinking - that I was short-circuiting my soffit-to-ridge ventilation by leaving gable vents open.

I still don't understand why no soffit vents with gable vents? It seems like the idea is to wash the air from the soffit up across the underside of the roof and out the top.

Thanks,

Tom

Gable vents take advantage of the natural wind direction to push the heat out.

I still think that gable vents are the simplest and easiest form of attic ventilation.

With soffet vents you have to make sure the insulation is not covering up the ends of the rafter bays and around here we have to run R-38 in attics for code.  That is a lot of insulation along the eaves of a house.

 

[GreenGA]

When my house was built, for ventilation,  the builder installed gable vents and nothing else!   He even installed Styrofoam baffles to move the air from the, nonexistent, soffit vents.  [mad]

The plan this year is to, finally, install soffit vents.  Perhaps next summer we'll see an improvement in inside air temperature. (i.e. lower electricity bills)  [crying]

That's exactly what I was thinking - that I was short-circuiting my soffit-to-ridge ventilation by leaving gable vents open.

I still don't understand why no soffit vents with gable vents? It seems like the idea is to wash the air from the soffit up across the underside of the roof and out the top.

Thanks,

Tom

 

[GPowers]

I thought the OP was asking about Radiant Barriers, not attic ventilation?

 

[tbellemare]

I see what you're saying now, Warner.

When I vented the soffits, I made sure there was an opening between the bottom of the roof deck and the top plate. I had to make some minor adjustments to the insulation in places.

In this climate, cooling is FAR more important than heating. I normally don't need either for about 6 months but I need cooling for a solid 4 months.

I've seen demo's of the reflective radiant barrier of the type that Howard is talking about and the demo made it look like it would be quite effective. My first thought was that it would really bake the shingles by hitting them twice with the infrared but then I thought that maybe they are only going to get so hot, and they reach that heat pretty quickly basking in the Texas sun.

Tom

 

[WarnerConstCo.]

There is nothing wrong with just gable vents.

They work quite well.

I have used a product by DCI, called smart vents.  They allow me to cut in an intake vent a few feet up from the eaves to get around all the insulation that is out by the eaves of some houses.  Way easier then climbing in there and moving insulation back and installing baffles.

 

[Dave Ronyak]

My portions of my ranch style home in NE Ohio have hydronic radiant heat pipes installed in the ceiling of the main level.  The attic is immediately above that ceiling.  To help reduce heat losses, immediately adjacent the upper side of that ceiling are two spaced layers of aluminum foil and over that is fiberglass insulation.  Installation of the radiant heat barriers made a significant reduction in my winter heating bill.  During sunny summer days there is no discernible heat radiation down through the roof or those ceilings.  This is in marked contrast to my former home in the same community which had no radiant heat barriers and an even greater depth (in inches) of blown in cellulose insulation.  Both houses have asphalt shingled roofs with a 4/12 pitch, undereave and ridge vents, and the former house also had end gable vents and an attic exhaust fan.

Another product I have used is radiant heat reflecting (insulating) paints, primarily from a company which makes and markets them under the brand name Nansulate.  See www.nansulate.com which also contains testimonials and data.  I have used these special paints on outside walls under the finish color coat and on ceiling areas that do not have heat piping and on some aluminum window trim (which did stop sweating in winter due to condensation of humidity in the house).  As Warner Construction has stated, in our northern climate, underside of roof radiant barriers are not recommended.  The opposite is common practice in your area. 

Dave R.

 

[jmbfestool]

I find it very stange living in the UK we try and insulate are houses as much as possible to reduce heating bill but you have to try and keep your house as cold as possible to reduce you cooling bill.    Funny really

JMB