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I am having a problem with condensation on my radiant barrier in the attic..

Mark Renfrow | Posted in General Questions on

I replaced my shake roof and used decking with the radiant barrier on the attic side. I installed standing seam metal roofing. The contractor installed a ridge vent on the main section of the house and I have plenty of soffit vents.

I am wondering if I need more outflow venting? Is this a common problem with radiant barrier since its a great conductor?

I live in Dallas, 3e W/H.


  1. GBA Editor
    Martin Holladay | | #1

    Condensation on cold attic surfaces is usually a sign that there are air leaks in your ceiling. Warm, humid indoor air is escaping through these ceiling leaks -- and then the humidity is accumulating on the coldest surfaces in your attic.

    The radiant barrier is not the problem -- the problem is your leaky ceiling. You need to hire a weatherization contractor or home-performance contractor to perform air-sealing work. Ideally, the work should be directed by a blower-door.

  2. Mark Renfrow | | #2

    Martin, I have had a blower door and learned a lot. At first we couldn't get the house up to pressure because it leaked so bad. Turns out much was in the duct work. (The attic has return air, the crawl space has supply). I do have lots of can lights (non IC rated) and had many of them sealed with insulation board boxes sealed to the ceiling, however there are still some that weren't fixed due to accessibility.

    Given that, can I skin this cat another way?

  3. GBA Editor
    Martin Holladay | | #3

    I doubt if the condensation will cause any harm, unless it's so bad that it's dripping onto the attic floor and soaking your insulation. Once warm weather comes in the spring, the condensation will stop.

    However, if it were my house, I'd be up in the attic tracking down those leaks. If you have can lights you can't seal, then remove the can lights from the interior, patch the drywall, and replace the can lights with surface-mounted fixtures.

    Did you caulk or foam the long cracks between partition top plates and the partition drywall?

    Is your attic access hatch weatherstripped?

    Have you looked for wiring penetrations, pipe penetrations, duct penetrations, and poorly sealed chases?

  4. Mark Renfrow | | #4

    It does drip some but not continuously.. As you said it stops in the warm weather.

    I have one of those contemporary (1965) low angle roofs and attic access is pretty tough on the edges. I blew in lots of loose fill insulation before I was really energy conscious. Caulking the partitions would be very difficult in the 15 inches of insulation up there. But how does that help? Doesn't the sheet rock essentially seal from air leaks? I have foamed all the exterior wall outlets and switches.

    I have a few ceiling j-boxes that have fixtures...can I seal those from inside?

    The attic access in is unconditioned space (garage).

  5. GBA Editor
    Martin Holladay | | #5

    The next time you are up in your attic, push the insulation away from a partition top plate. You'll see a long crack between the partition top plate and the drywall. Unless your drywall crew was unusually conscientious, this crack is almost undoubtedly not caulked.

    Here's the usual air leakage mechanism: air enters the partitions through electrical boxes. (Although you mentioned doing air sealing work in the electrical boxes in your exterior walls, you didn't mention the interior partitions.) The air then escapes into the attic through the crack between the partition drywall and the partition top plate.

    Weatherization contractors are very familiar with the problem. They usually use spray polyurethane foam (applied from the attic) to seal these partition top plate leaks.

  6. Mark Renfrow | | #6

    Thanks Martin. I see. That makes sense. If I cant get to the top plate I can try to seal the interior wall boxes and the junction between the baseboard and floor?

    Related to the j-box question above...can I foam the wire penetrations into electrical boxes? So far I have sealed around them, added foam under the plate and put clear safety plugs in the outlets to stop the air leaks there.

    It might be worth noting that all the walls have 2x4 firebreaks in the wall cavities. (Fun for wiring).

    Is it possible that the condensation areas reflect where the warm air is entering? Any chance I could find problem areas just by visually inspecting the underside of the roof?

  7. GBA Editor
    Martin Holladay | | #7

    I doubt if you'll have much success stopping air leakage through partitions by attempting to seal electrical boxes in partitions or caulking the baseboard -- although these measures can't hurt, as long as you don't fill the electrical boxes with foam.

    When weatherization contractors can't access partition top plates, they often find that the easiest remedy is simply to install dense-packed cellulose in the partition stud bays. If I were you, I'd start by crawling around in my attic, or hiring a contractor who was willing to do so.

  8. Mark Renfrow | | #8

    Well here in Dallas, finding good contractors for this sort of thing is tough. My energy audit didn't mention the top plates nor did the contractor I hired. Then of course there's the issue of what they step on (ducts, wires etc) when they are up there and finally the unlikely fact you cant inspect their work with all the insulation up there.

    Lastly, not knowing how much leakage is coming from that source you cant really do a cost benefit analysis. The blower door tells you how much overall leakage and the smoke stick defines the sources but with all those can lights no-one looks any further.

    I think I need a can-lightectomy. As you mentioned early on. Thanks for your help.

  9. GBA Editor
    Martin Holladay | | #9

    Here in the Northeast, we're lucky. Lots of weatherization workers (many originally trained by the low-income weatherization program, but now working independently) have been air-sealing attics and blowing dense-packed cellulose for 20 years. There may be fewer competent weatherization workers in Texas.

    I have to smile, though, when you worry about "the issue of what they step on (ducts, wires etc) when they are up there."

    Texas contractors may be worse than Vermont contractors -- I'm not saying they are, but they may be -- but surely anyone who performs work in an attic should know where to step, or they are really in the wrong line of business.

  10. Mark Inman | | #10

    Hey Mark. I live in Houston, so not far Zone wise from you. For addressing leaky recessed cans, I bought Commercial Electric 6 in. White Airtight Baffle Trim (12-Pack) (T49) from Home Depot. I'm sure it's not "air tight", but it probably reduces leakage by 90%. There's also another option, more expensive, but brings both air tightening and energy efficiency into a single product: EcoSmart E26 10.5-Watt (65W) LED Down light Light Bulb (E). I have this over our cooktop. Works great.

    As for getting to the top plates from the attic end, that sounds tough. One solution might be to try to foam the stud cavities near the ceiling. Great Stuff's black can is for larger gaps. You could cut small slits with a sheetrock saw and insert a ledge into the wall, then drill a small hole above the ledge to spray through the straw. A third hole could be for a camera to monitor thatyou've hit the gap completely. Seems like a lot of work, but you could just tackle it in stages, and it would keep you out of the attic. And I agree, the 'qualified weatherization contractor' is not an easy animal to find in Texas.

  11. Mark Renfrow | | #11


    Its probably a combination of weatherization AND energy efficiency sensitivity. They are going to have to drag Texans kicking and screaming into energy efficiency consciousness. Add to that a "heat" bias in their work (radiant barrier first, all else second) and you get the picture.

    My home is 3400 sq ft (Texas sized) and I have around 40 can lights which the contractor said they sealed but when the roof came off all was revealed. They got maybe half. I didn't have the time to fix the problem before the new decking went back on.

    I spent $1978 to heat and cool the house last year which is a big improvement, but as always, more work to do....

  12. Mark Renfrow | | #12

    Thanks for the tips Mark. I am having a little trouble understanding how the baffle trims work. My leakage is mostly around the bulb. The cans are non IC, rectangular boxes with the round standard openings and trim. (Lightolier product).

    I did but one of those LED lights but light quality and dimmability were still an issue. They also don't fit my cans. But that does bring me to a general question...has anyone foam sealed the inside of one of these cans and used low heat producing bulbs to solve the problem?

    I honestly don't think this top plate leakage is a big issue, but your foaming idea makes some sense especially right before I paint again.

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