Airspace for solar barrier
I am adding a solar barrier between layers of an alluminum roof. The existing roof is over a covered florida room. The roof system has a lower layer that is also the ceiling. The lower layer is connected to the top layer by 3 inch alumuinum I beams. The roof is insulated with porous styromfoam which is noisy when it rains and does not stop any heat penetration at all. Impossible to aircondition! I purchased a solar barrier to place between the layers of room. When installed draped over the I beams after removal of the styrofoam, it gives the 2 inch airspace that is required for the new solar barrier to reach it’s dsigned isulation rating of R16. The new product has the reflective material sanwiched over a thin layer of foam insualtion. The total product thickness is 5/16 inch thick.
My question is if I add back the old styrofoam over the draped solar barrier, will it suffice as the 2 inch airspace since it is porous? Or should I just throw it away?
Thank you,
Phil Ragan
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Replies
I'm highly sceptical as to this "solar barrier" providing R16 or anything close. Could you provide some more information about it?
Phil,
You've been snookered. You are describing a radiant barrier; at best, it might make your air spaces have an R-value of R-2 or R-3. However, the thermal bridges of the aluminum roof joists are conducting so much heat that the R-value of the assembly is far less.
You need a continuous layer of rigid foam or mineral wool under the rafters, not a radiant barrier, if you want to reduce heat flow through your roof assembly.
For more information, see Radiant Barriers: A Solution in Search of a Problem.
The radiant barrier rolls over the ibeams and then drops down to cover the top of the ceiling layer. There will be a layer of the insulated solar barrier over the I beam and then the top layer is screwed back down to the I beam.
I just know I used radiant barrier in a home I built in North Florida and it worked wonders! It was draped over the trusses before the plywood was nalled down. Even before the ceiling insulation was installed it was super cool below. The plumbers and carpentars couldn't believe the difference. This was in July.
I will give a try and post back. It will take about a day to remove the screws from the roof and then install the barrier and screw the panels back on!
The product I am using is called Prodex Total. You can find it on the web.
Thanks,
Phil
There's no doubt that it will keep the attic cooler, but you don't live in the attic, so this is of dubious value. If your attic is well air sealed and insulated, then it doesn't matter much how hot it gets. The money is generally better spent thermally separating the attic from the living space, rather than trying to improve conditions in the attic itself. Read the article Martin posted -- it goes over all this in detail.
I appreciate your answer. I am working on my florida room that only has three inches between roof and ceiling so I am limited to options..
Thank you,
Phil Ragan
Phil,
I didn't know what a "Florida room" is, but I Googled it, and it looks like what is usually called an enclosed porch, or a three-season room. Is that right?
A radiant barrier works. It transforms an R-1 air space into an R-2 or R-3 air space, and this transformation can lower the temperature of your attic or your porch. If you want to install the radiant barrier, go ahead. Just remember that you don't have an R-16 ceiling.
Real insulation would be better, especially if you are using an air conditioner to cool the room. Real insulation is a material like rigid foam, cellulose, mineral wool, or fiberglass. The minimum code requirement for ceilings in the warmer parts of Florida is R-30, which would be about 4 or 5 inches of rigid foam, or at least 9 inches of fluffy insulation.
Thank you Martin. Yes sir, when I take the remove the aluminum roofing panels, there is only three inches to play with. The I beams are manufactured upward from the ceiling panels so I don't have many options. I am hoping rolling the radiant barrier across the beams and draping it between the beams will give me some relief. The beams will be covered with the 5/16 inch material and then I plan on using longer screws to screw the roofing panels back in position using the same holes from the previous screws. The screws have neoprene washers to better seal he panels. I am definitely researching the mineral wool material having not heard of it before.
One last question, should I re install the styrofoam panels back over the radiant barrier between the I beams or toss it? The system has 2 inch thick styrofoam panels that are laid longways between the beams.. I have added photos and yes I need to pressure wash the the panels. The oak trees are already blooming in midwest florida. You can see the foam between the layers in the second picture. You are right in that it is an enclosed porch. The windows are thermopane.
Thank you for your advise. Phil
Phil,
If you take off the roofing panels, you have an opportunity to install a continuous layer of rigid insulation above the metal rafters if you want to. Perhaps you could install OSB sheathing, followed by a continuous layer of 2-inch-thick rigid foam insulation (not thin strips) above the sheathing. Then you could reinstall the roofing panels with longer screws.
Thank you. Phil
Phil
Read up on thermal bridging. With metal it is much worse than wood. What you have is like a car radiator. When the sun beats down on the roof it travels through the metal and is dissipated into the room. I think that is the reason the existing insulation is not working.
You need to keep the heat from the reaching the metal. A cool roof approach over a layer of rigid insulation would be the may to go.