Radiant barrier, insulation for attic

[masraum]

My house is a 1950sqft 2 story built in '67. It's got blown in insulation in the attic as well as some roll type insulation over the top of the blown in. It looks like it was installed by a 6 year old. --> The previous owner put up curtain rods with whatever was laying around (6 holes would mean 6 different fasteners including nails, regular and phillips style screws). We've got a new roof with ridge vents and new vented soffits. When we had the roof installed, we were poor and I was uninformed so we didn't splurge on any of the fancy insulation stuff (hind sight...).

I'd like to do 2 things in the attic, but I think the first will be to add some sort of radiant barrier to the underside of the roof. I've read that you can either install it between the rafters/top cord to the bottom of the decking (requiring a minimum of 3/4" air space between the decking and barrier) or attach it directly to the bottom edges of the rafters/top cord which gives a pretty healthy air space. Eventually, I'd also like to reinsulate, but that will probably come second.

So, I've read on the internet about radiant barrier, I've read a previous thread here about it, Radiant barriers - Bunk or real?

Does anyone here have more info or experience. Are there any brands/types to avoid or that are best? Are there any gotchas or specific advice for an install.

Tell me what ya got!

The weather right now is gorgeous (California weather) 45-55° at night and 70-75° during the day. Consequently, neither my heat nor AC has been kicking on. I've got temp sensors in a room upstairs, in the attic, and outside (in a shield to keep it out of direct sunlight). What I've noticed, is that in this weather the attic still gets to 100°+. The temp inside the house, gradually rises and continues to rise even after the outside temp has dropped considerably until the temp in the attic gets lower than the inside temp.

In the graph below, at the peak of the daytime temp, the attic is 104°, outside it's 76° ±1° (my shield isn't perfect) and inside it's 70°. At 8pm the attic temp is 72°, the inside temp peaks at 72°, and the outside temp has already dropped to 59°. So it's obvious to me that the hot air in the attic continues to heat my house well after the outside temp has dropped. I think that part of the problem is that my roof is angled front to back and side to side, so the ridge vent is very short (I think it's about 4-6' long (haven't measured). I assume that some radiant barrier and new insulation would help a lot.

This time of year, it's not a problem. It probably keeps the house warm enough to keep our heat from having to kick on at night, but during the summer, I think it's probably very bad. This past summer, I saw the attic temps go to 125-130°.

[RWebb]

won't your utility do an evaluation and tell you the most cost-effective things to do?

PS - radiant barriers can definitely have an effect.

[daepp]

My family in the suburbs of NOLA and Houston are all paying to have the underside of their roofs sprayed with some type of expansion foam. In fact, my cousin recently completed a new house and he did no insulating of the ceiling - just the underside of the roof and all exterior walls with this spray on stuff. His highest electric bill this summer was $240 for a 4000 sq ft house. And, his attic is cool....

[masraum]

Originally Posted by DAEpperson

My family in the suburbs of NOLA and Houston are all paying to have the underside of their roofs sprayed with some type of expansion foam. In fact, my cousin recently completed a new house and he did no insulating of the ceiling - just the underside of the roof and all exterior walls with this spray on stuff. His highest electric bill this summer was $240 for a 4000 sq ft house. And, his attic is cool....

Yeah, I'd love to go with the spray on foam. I've heard that it's fairly pricey. I'm not sure that I could sell the wifey on the expenditure since we don't plan to be in this house forever. Maybe, I'll have to look into it.

[daepp]

From what I understand it can be done a few different ways.

- sprayed on and just left to expand on its own
- sprayed on and then screeded (?) off even with the rafters to give a smooth look
- they even told me it can be palce over existing - hard for me to believe

I have looked for someone to do it out here on the left coast to no avail. My electric bill avgs $550 per month!!!

[masraum]

Originally Posted by DAEpperson

From what I understand it can be done a few different ways.

- sprayed on and just left to expand on its own
- sprayed on and then screeded (?) off even with the rafters to give a smooth look
- they even told me it can be palce over existing - hard for me to believe

I have looked for someone to do it out here on the left coast to no avail. My electric bill avgs $550 per month!!!

Yowza. Makes my 3 peak months of $250-330 look pretty good.

I'd think that as efficient an insulator, that there would be folks all over the left coast doing it. I think it also provides extra structural support which should be good for the left coast.

[Nathans_Dad]

I had radiant barrier put in about 3 months ago. It's tough to say if it is really having any effect yet, we will need to wait until next season and compare month to month. Right now it is beautiful in Texas and we aren't running the AC or the heat very much at all.

One thing I will say is make SURE you cover anything that is in the attic yourself. Don't trust the radiant barrier guys to do it. Don't ask how I know lol.

[masraum]

Originally Posted by Nathans_Dad

I had radiant barrier put in about 3 months ago. It's tough to say if it is really having any effect yet, we will need to wait until next season and compare month to month. Right now it is beautiful in Texas and we aren't running the AC or the heat very much at all.

One thing I will say is make SURE you cover anything that is in the attic yourself. Don't trust the radiant barrier guys to do it. Don't ask how I know lol.

What do you mean by "cover anything that is in the attic"? Cover it with the barrier? Like what?

[red-beard]

Check out this place

http://atticfoil.com/radiant-barrier-pricing.htm

[TimT]

What do you mean by "cover anything that is in the attic"? Cover it with the barrier? Like what?

He means cover anything of value.. protect it from overspray

cheap 99 cent plastic drop cloths work well

[masraum]

Originally Posted by TimT

He means cover anything of value.. protect it from overspray

cheap 99 cent plastic drop cloths work well

OK, for the spray stuff as opposed to the rolls of foil on thin foil covered matting.

[stomachmonkey]

Originally Posted by DAEpperson

...my cousin recently completed a new house and he did no insulating of the ceiling - just the underside of the roof and all exterior walls with this spray on stuff....

His name Sean?

[Nathans_Dad]

Yeah, the guy that came out to my house said the spray on is superior to the foil. We went with the spray on stuff, just make sure you use drop cloths!!!

[red-beard]

Rick, take a read through this

Radiant Barrier Spray Paint, Foil Insulation & Attic Ventilation

What Is a difference between Radiant Barrier Spray and Radiant Barrier Foil?
Both the spray and the foil "Reflect" radiant heat. The spray can reflect up to 75% and the Foil will reflect about 97%. Foil is actually the "Best" radiant barrier. You can do-it-yourself by ordering Radiant Barrier Foil here. Foil is the best and most cost effective way to go whether you staple it to the rafters or lay out radiant barrier over the existing insulation. For complete information comparing the benefits of radiant barier foil insulation to radiant barrier spray paint visit Radiant Barrier Foil Insulation Do-It-Yourself Radiant Barrier Tips

What Is a Spray-On Radiant Barrier?

Spray-On Radiant Heat Barrier is essentially a "liquid foil". We all know that foil is a heat barrier. Thre are many brands of paint and have different performance characteristics. The best are water-based low-e paint called HeatBloc-75 made by STS Coatings or Radiance e.25. made by BASF. It CAN be a good product if installed correctly. However, foil is indisputable for out performing radiant barrier spray paint. Read this report from RIMA for complete comparisons of rdiant barrier paint.

Do-It-Yourself Radiant Barrier Foil
If you like Do-It-Yourself projects, consider installing a Radiant Barrier Foil. The radiant barrier foil actually blocks over 95% of the radiant heat (better than the spray type) and is fairly easy to install. Click here to learn more or purchase Radiant Barrier Foil.

How does a Radiant Barrier work?
Whether you chose to have the Radiant Barrier Paint sprayed or you choose to do-it-yourself or hire a professional to install Radiant Barrier Foil insulation, your home will be more comfortable and energy efficient. Radiant barrier paint has up to an "e" value of 0.25. This means it reflects or "blocks" 75% of the Radiant Heat transfer from the roof into the attic and then the home. The Radiant Barrier Foil has and "e" value of about .03 meaning it will reflect or block nearly 97% OF THE HEAT GAIN!! This is similar to having a Giant Shade Tree instantly land in your yard! By reducing the radiant heat gain, the attic temperature is cooler by as much as 20-30 degrees. More important than the attic temperature is the reduction in radiant heat transfer into the attic and home. The best way to demonstrate this is to ask - Would you feel "cooler" sitting in the SHADE on a 100 degree day or sitting in the SUN on an 80 degree day? Most would agree they would rather be in the shade even though the air is hotter. The bottom line...A radiant barrier will act like shade for you home. This means less heat gain into your living space and a cooler, more energy efficient and comfortable home with lower electric bills.

A radiant barrier will help stop the heat at the source. Think about this. Where does most of the heat come from on a hot summer day? The sun of course. The heat from the sun drives right through your roof, your attic and into your home. A radiant barrier acts like a mirror or the reflective sunscreen you put up in your car. A radiant barrier saves you money on your summer electric bill and can usually pay for itself in between 2-5 years.


How is Radiant Barrier Applied?
Radiant Barrier Spray Paints are sprayed on the underside of the roof deck and Radiant Barrier Foil Insulation is either stapled across the rafters or layed out over the existing blown-in insulation.

Why is it Applied to the UNDERSIDE of the roof?
At first it does not make sense, but think about this. If you hold a mirror up to the sun and reflect the light on your arm you would SEE the light, but you would FEEL the heat. The sun emits both visible light and invisible infrared energy. It is the infrared energy that is being reflected that you feel, NOT the light. Radiant barrier has two qualites that make it work: Reflectivity and Emissivity. Reflectivity is the ability to "reflect" radiant heat while Emissivity is the abiltiy NOT ro "Release" heat in the form or radiant energy. Want more info? Polar-Ply (a radiant barrier roof deck material designed for new construction has a good website) So, even thought radiant barrier is installed underneath the roof it will still reflect the radiant heat flow.

What about A "Radiant Barrier Rebate"?
Some companies use a "Rebate" as a sales gimmick. If they raise their price and then give a "rebate" do you really get a "deal"?

[masraum]

I just checked, my ridgevent is 6' long. THere's a central board running the length of the top of my roof, so there's about 1" on either side of that board. So, I've got 2 strips that are 1" wide and 72" long for the air to escape. By my math that's 144 sqin or 1sqft of vent at the top. I'm not sure how much surface area my soffit vents make, but a sqft at the top sounds inadequate for a 2000 sqft roof.

[Heel n Toe]

Call about three insulation contractors and have them come out and give estimates. Ask a lot of questions like the one about the 6 ft. long ridge vent. By the time you've gotten your three estimates, you'll know which way you want to go.

If you're still not sure after talking to 3... keep calling... go for 5 or more... you'll get there.

You mentioned reinsulating the ceiling area in your attic... it would probably be a good idea to just blow in a lot of cellulose on top of what's already there. You do need it insulated, because even with the radiant barrier, on a hot day, it will still be hotter up there than it is in your house... you want to insulate against that heat radiating downward through your ceiling into your house.

[Nathans_Dad]

red-beard, thanks for the info, all I can say is what the guy selling me the product told me.

They used the 3M spray which he said was the best on the market. We talked about foil and he said the spray was better. Obviously he was trying to sell me the spray.

The site you linked is trying to sell foil, so their data will be skewed that way as well.

From the Efficient Attic Systems website (which sells the spray):

A spray-on radiant barrier is an innovative application of a high-tech material that reflects radiant heat. It has great advantages over previous types of radiant barriers (like foil) including better coverage and a longer effective life-span. It is sprayed over all nail punctures in a uniform manner, so there are no holes or gaps, it is not a vapor barrier so it will not contribute to mold, and it does not block antenna and mobile phone reception.

As in most cases, there are pluses and minuses to each.

In any case, I'm happy with my barrier so far.

[red-beard]

Rick, either will work. And the site directs you to both spray and foil type barriers. The link to the data shows the emissivity information from foil vs. spray on. In my roof, I expect to use a combination of spray on and foil, because some parts are so hard to access.

I also expect that It will have a dramtic effect on my house, since the upstairs is about 1/2 the sq footage of the downstairs, and there is a lot of extra square footage of roof.

I also will be installing some serious electrically driven ventilation fans. The ridge vents are just not enough.

Finally, I expect to be installing solar water heaters on a portion of my roof, for my pool. The water temp has dropped to 70 deg F...getting a bit cold to swim. I expect i can extend the season by at least 2 months with solar water heaters.

[Scuba Steve]

I've retrofit radiant barrier under most of my southern attic exposure over the last year. Here's my experience.

First off, the structure. 3,000 square feet. Peak utility bills of close to $300 in summer 2008 with a programmable thermostat and me going easy on the a/c. Two story, majority of the roof facing due south at the rear of the house (it is both 1 and 2 floors high in that direction), built in 1992.

I bought rolls of radiant barrier from a place called Radiant Guard(?) online. 1,000 square feet for about $140 shipped. Rolls are 4 feet wide. I stapled it to the underside of the rafters, so it's a little more than 3 inches under the decking. Did most of the southern exposure - all of it but about 50 square feet at the southwest end. I won't say it's easy, but really it has more to do with accessibility of the area you're installing it in. If you have something to stand on life is a whole lot easier.

Before attic temperatures were normally in the 140s in the afternoon. After I did this project the temperature would rise into the low 110s, so it was a pretty significant difference. But I realized one thing - where is all the hot air supposed to escape? All it could do is rise to the peak of the roof...

Next I installed ridge venting and that also made a pretty big difference. On the hottest days the attic would barely top 100 - more or less ambient temperature outside! Anyway utilities overall have dropped by 40% on average year over year. My peak bill this summer which was a really hot one in San Antonio was just over $200 - after I turned the a/c down so that it's cooler this year than last.

Other small projects I did were to seal around everything penetrating the sheetrock (outlets, faceplates, plumbing, wires, ...) and tint the windows in the main bedroom which also faces due south and used to heat up 5 degrees warmer than the rest of the 1st floor. It's been a huge improvement in terms of quality of life and everything that I've done has already paid for itself this year.

[masraum]

Originally Posted by red-beard

In my roof, I expect to use a combination of spray on and foil, because some parts are so hard to access.

Good thinking. My roof is also a nightmare. You'd have to be a ninja or a contortionist to crawl through the whole thing. The combination of the two might be the way to go.

Originally Posted by red-beard

Finally, I expect to be installing solar water heaters on a portion of my roof, for my pool. The water temp has dropped to 70 deg F...getting a bit cold to swim. I expect i can extend the season by at least 2 months with solar water heaters.

My mom has a solar water heater on her pool. She's on the north side of the pan handle of Florida. Her temps are usually 5-20° cooler than mine. The solar heater makes a huge difference to her pool. Not only that, but I'd think that it helps shield the roof a bunch.