Insulation

[muncybob]

Getting ready to add on a 1 story addition to our 2 story home in central PA. I've been reading about a reflective wrap and insulation. The reflective wrap appears to take the place of the conventional house wrap and the interior reflective rolls are some sort of foam that is coated on both sides by a reflective layer....this is then installed with a small air pocket and you can add fiberglass insulation for greater R value. My question is does anybody have knowledge about some of the claims I've seen where as much as 50% of heat loss is radiated loss as compared to air leakage? If this is true would it not make sense to use the reflective approach? I did insulate some homes years ago when in college and remember some firberglass batts that had a reflective layer rather than the kraft faced I've seen lately but nobody seems to know anything about the reflective batts now. [img]/forums/images/icons/confused.gif[/img] We also will be installing a metal roof(the main house has this also) and I've read that a reflective layer below the metal roof will help...but hwat does this relected heat do to the metal roof?

[Pat]

Not much is what reflected heat will do to a metal roof.

For the reflective material to work the shiny side has to be in air not jammed up against anything, even F/G fibers. There are "bubble wrap" type blankets with an aluminum layer on both sides. Heat transiting the air space (bubbles) is reflected.

I installed an inch of rigid foam with foil on one side under the roof of my mom's sun room with an inch gap from the OSB deck. The foil rejects 97% of the radiant load back toward the deck but the air gap and the convective flow sweep out the heat so the deck and the shingles aren't cooked but are in fact cooled.

The reflective layer is there to reject radiant heat (remember heat is transferd by conduction, convection, and radiation) You need a gap with no path for conduction for the foil to work. If the foil is in contact with solid material it is a good conductor.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[muncybob]

OK....I undertsand what you are saying.What about reflecting heat back towards the living space than reflecting it away and up to the roof since we live in a cooler climate and the roof will get direct sunlight only part of the day. I was thinking of installing the rigid reflective board with an air space above our suspended ceiling and then fiberglass batts above the boards???

[Pat]

Oh, sorry Bob... I didn't note your location. If you are in a heating dominated climate then you got it right: ceiling then air space, then foil side of rigid foam, and then batts or blown in or whatever on top. You don't want any sort of vapor retarding effect on any of the insulation added above the rigid. This would tend to trap moisture between the rigid and the other barrier and seriously reduce the insulation's performance as well as cause other problems. Just check the specs on any kraft paper backing or whatever or better yet use unbacked or blown-in.

Most of the rigid foam I've seen has foil only on one side with something else on the other side because it is cheaper and works as well as double sided if one side has no air space. In some cases that something else looks like foil but isn't. If there is writing on one side then that is the NON-FOIL side which in your case gets oriented up toward the roof.

The rigid will still help cool your ceiling in summer as it adds R-value AND if I recall correctly the emissivity of the foil side is not too high. (Emissivity is the ease with which the surface emits radiation.)

Those % figures that get strewn about regarding radiative losses versus infiltration and so on can be true in certain circumstances but in general the rule of thumb is to tighten up the envelope to reduce infiltration and then insulate to increase the R-value. This is the "world view" of the Energy Star folks backed by research and experience. If you are contemplating an expensive retrofit, you might want to hire an energy conservation consultant, someone to take a look at your envelope with an IR sensor/camera and see where your heat losses actualy are or you might want a general energy audit.

As far as the infiltration (air leaks) go, if you can get around in your attic(and other spaces), go there with some incense sticks (this is not an exorcism or other religious rite) and use the smoke trails to track drafts to/from their source so you can seal them up. This can have a terrific payback if your house wasn't built really tight. This would be a smart thing to do before adding insulation as the extra insulation could get in the way. Another indicator of air infiltration is often a dirty area on the insulation where the insulation is filtering out the dust in the leaking air so keep an eye out for that too.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]