I'm getting ready to put a new metal roof on my home which will consist of putting firring strips above the existing roof then attaching the metal roof to the firring strips this will leave approximately a 1" dead air space between the old roof and the new roof. Everything I've read says that the dead air space is needed to accomplish any gains from the radiant barrier. My idea is to put the radiant barrier over the existing roof, nail the firring stips down to hold the radiant barrier in place then go over it with the metal roof. I know that radiant barrier is usually recommended to go in the attic space, but I live in a modular home and don't have access to the attic, therefore I am wanting to know if anyone on the forum has ever tried using the barrier on the exterior of the roof. I know it would benefit in the summer by reflecting the heat back away from the house, but since some of the warm air from heat in the winter naturally gets into the attic space is it going to have any benefit in the winter or will it make the house cooler in the winter because of not getting the radiant heat? I used Prodex insulation/radiant barrier in my garage at the home where I lived in NC and saw a noticeable gain in how cool the garage was in the summer and also how warm it was in the winter without a/c or heat, but I used the insulation/radiant barrier on the inside of the stud walls and ceiling instead of the exterior of the building. If anyone has tried the application I am considering please post what your results were or send me a PM.
I don't have any experience but it seems like a good plan- with the air space and reflective insulation, you will definitely decrease your summer cooling bills- technically it would also slow the flow of heat from the attic in winter.
Oddly, in all the residential and government roof jobs I've figured bids for or worked on, I don't think I've ever heard of a radiant barrier.
From your description it sounded to me like it needs air space below it, not above, and google results imply that too. Really, though, I think it needs air space above AND below.
I would guess from your non-access that the roof is built with trusses and the attic has no entry at all? Well, since you're going to put on a new roof, why not just cut an access hole through the old roof so you can get in and install the radiant barrier before you put on the new roof? Depending on the truss design it can be difficult to move around in there but certainly not impossible.
Even better, now's a good time to install some kind of access hatch. It's not good to have a large hollow space inaccessible. Being able to get into your attic allows you to add insulation, control pest infestations, run wires, and fall through the ceiling like Clark Griswold.
What kind of metal roofing are you going to use? Standing seam aluminum?
I've spoke with several companies that sell and install the barrier and all have told me that as long as you have an air space either side of the material you will get the same results.
I've already given some thought to an access panel, but I think I'll still put the barrier under the roof since even at the highest point in the attic there would only be about 3' of room for moving and would make it very hard to get the material all the way back the the eaves of the house. I've also already talked with the person who is doing my roof (old time friend) and he said if I'd get the material he didn't have any problem with putting it on during the roof application. It might add a little expense to the roofing job, but will only be a small amount of labor and he works really cheap anyway. He's going to build me a 4' covered walkway between the house and garage, the 16'X28' garage and put a 1400 sf metal roof on the existing house all for $7700.
I'm not sure what type metal the roof is, I know it's not aluminum and is just standard grade residential material with either a 30 or 40 year warranty I forgot which he said. He put the same roof on my parents house approximately 20 years ago and still looks almost as good as it did the day he put it on. Since he done the work and supplied the materials for them and my dad was very pleased with it I decided to go with the very same material and color they got. He still gets his materials from the same supplier so everything should be just like theirs. I'm sure you've seen some roof colors that discolor after only a few years, the one on my parents house has hardly faded at all.
If I was still able I'd have bought the materials and done the work myself, but being disabled with a bad back that's just no longer possible so now I have to find people I know do good work at a good price and that's getting harder to do all the time.
I just wanted to give a little bit of update on this thread. I contacted some companies that sell radiant barrier and had them send me samples. One of the companies sent me a sample about 8" X 12". I ran an experiment of my own with the sample and a portable kerosene heater. I placed the barrier directly on the metal grill on the outside of the heater and left it there for a few minutes then put my hand close to the barrier and could feel very little if any heat on the outside of the barrier, so then I touched the barrier on the outside very quickly and could tell there was very little if any heat about the barrier so I then placed my hand flat on the barrier whch is against the metal grill of the heater and held my hand there for several minutes with the heater running and my hand never felt much if any heat at all from the heater. I also removed the barrier from the heater and the side which was clsest to the heater wasn't even hot. After running this little experiment I placed an order for 3000 sf for my roof of my house and garage and interior walls of my garage. I checked several distributors of the radiant barrier and all of them had the same weight material, but there was lots of difference in price from one company to the other so if anyone else is interested in buying any the best price I found was $116. per 1000 sf roll including shipping at http://store.texasheatmanagement.com/ I'm just posting this in case anyone else is interested in buying any of the barrier. Most other places places were about $130-$150 per roll plus shipping.
Ford Man ,
The radiant barrier is also known as a "fly roof" and sometimes also "stand off roof" and is quite common here in Australia in the hotter areas.
Basically the house is built and then a second roof panel (pressed steel sheeting with a zinc or galvanised surface coating sold under the trade names of either Zincalume or Colourbond) is then added on "stilts" (small thermally isolating structures shaped like a small pyramid with the top cut off).
This second roof fits parallel to the first with an air gap about 200 mm (8 inches or so) between the two. The angle of the roof - typically 30 / 45 degrees - means there is a flow of air between the two roof panels as the fly roof is heated by the sun.
The main roof sits in the shade produced by the fly which also helps moderate temperatures.
The best arrangement for the roof style is a single plane design shed roof.
Hope this helps somewhat.
Have a Google search for Fly roof for more details.
I finally got the new metal roof on the house with the radiant barrier placed between the existing roof and the new metal roof with approximately a 1" air space. I heat with a Monitor 422 kerosene heater which is a 22,000 BTU vented unit and am currently using the capsule tank that came with the heater, because I haven't had the chance to hook it up to an outside tank since I just moved to the new home in Oct. and have been very busy since. I filled the capsule tank up which is 1.33 gallons Wednesday night about midnight and had to refill it tonight (Friday) around 8:00 PM so 1 1/3 gallons of kerosene lasted about 44 hours with the heaters thermostat set at 68* from 10 AM till 10 PM and set at 60* from 10 PM till 10 AM. This was heating about 1100 square feet (got a couple seldom used rooms closed off to save energy). Wednesday night and Thursday were cloudy/raining with outdoor temperatures from the upper 30's to upper 40's and Thursday night and Friday morning were in the lower 30's with highs Friday in the mid 50's. The current outdoor temperature is 42* at 12:10 AM so the heaters thermostat went back to 60* over 2 hours ago and the indoor temperature is 65* so I've had a 3* decrease in indoor temperature in just over2 hours so I think the barrier is doing it's job and not allowing as much heat to escape through the roof. My real concern wasn't heat loss in the winter, but hoping to cut cooling costs in the summer so the heat savings is just an added bonus. The only bad thing is since we haven't lived here during a previous summer I won't have anything to compare to, to see how much it's actually saving, but I'll be cooling about 450 more square feet than I was at my previous home so maybe I can make some comparison using the utility costs of the old house, since both houses had about the same insulation and were close to equally air tight and near the same climate.
Thought I'd post an update on the radiant barrier. As I said in a previous post I can't compare cooling costs to a previous year because we just moved here in Oct. 2010, but our last electric bill was about $82. which I think is pretty good for a 1400 sf. home with outdoor temperatures running in the 90's to low 100's. We've been keeping the house at about 75* inside. I think the radiant barrier is well worth the money I spent. Where I was living in NC last year I was only cooling about 1000 sf. and the electric bill was running about $100.-$120. per month and the house wasn't as cool as where we are living now. I've also noticed that the a/c doesn't usually run for extended lengths of time. Since the 1st day of this month we have used about 400kwh and there have been a couple days where the heat index was between 110*-120*. I think our power bill for May when we didn't use the a/c at all was about $45. so the actual cost of cooling the house was less than $40. last month. I'd definitely recommend radiant barrier to anyone who's considering building a new home or just wants to make improvements to help on heating and cooling costs.
Our highest electric bill this summer was just under $112. for an all electric home with the a/c keeping the indoor temperature about 75*. For about the last month even with daytime outdoor temperatures in the low to mid 80's the radiant barrier has kept the house comfortable without using the a/c.
Thought it was time for another update on the radiant barrier. The heat I use in our home (1400 SF) is a Monitor Vented Kerosene unit. These are very efficient heaters and I've been using them for about 16 years. I used one in my home in the Charlotte, NC area without radiant barrier before moving to KY. The heated area was about 1000 SF and I usually averaged 125-150 gallons of kerosene use per winter. This winter in a 1400 SF home with colder KY temperatures with the radiant barrier installed on the roof we used 85 gallons of kerosene to heat all winter. I enjoy heating all winter for what my neighbors were paying each month for electric heat. So using an average of 137.5 gallons normally used in our NC home apposed to 85 gallons and heating an extra 400 SF of space at a price of $4. per gallon for kerosene the savings was $210. on heating for the winter. I also suspect the electrical savings for the a/c last summer was $30-$40 per month. We usually use the a/c about 4 months of the year so using an average savings of $35. a month in a/c the cooling savings would be $140. per summer. Last summer our highest electric bill was $112. and that was with several days that month being around 100* with a heat index of 110-120*. Using those figures I figure the payback for the material $348. and an additional $100. in labor added to my metal roof installation for rolling it out and fastening it down the payback is going to be less than 1.5 years. At current heating and cooling cost figuring the material will last at least 20 years installed underneath the metal roof the savings after payback will be $6552., not bad for a $448. investment, much better than putting it in a certificate of deposit at the current rate of about 1% return. I wish I had a way of putting radiant barrier on all the walls underneath the exterior siding for even more savings, but that won't be done unless I eventually have to have the house re-sided. The cost of radiant barrier material at current prices to do the exterior walls would only be about $250. and I'm pretty sure the payback would be a year or less. After seeing the energy savings with radiant barrier on the roof alone if I were building a new house I'd have it on the roof, floor joist, and walls.
In the all metal exterior garage I used R-13 insulation in the walls covered with radiant barrier on the inside and radiant barrier alone on the bottom of the trusses, in the winter it's warm enough to work in the garage without heat and in the summer the temperature is cool enough you can stand to work in it without having a heat stroke. I had the radiant barrier alone in my garage in NC and could work in it late night (1:00-2:00 AM) in the middle of the winter without heat. A few times when I'd first start working in it I'd start a portable 10K BTU kerosene heater to knock off the chill, but would have to turn it off in about 5-10 minutes, because I'd be sweating and would work for several hours without ever starting the heater back up.
In case anyone is interested in buying any radiant barrier here's a link to the cheapest price I could find when I bought mine. Texas Heat Management Online Store The price has increased since I bought mine, but is still cheaper than most other suppliers were selling it for at the time of my purchase. I had several different companies send me samples and all the materials were the same weight and strength just different brands. When I bought mine the price also included free shipping, I'm not sure whether they still offer that or not.