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35×40 garage. Old leaky metal roof was replaced. Condensation spots in the same spots.

Speedwaytaco160 | Posted in General Questions on

I just had my old leaking metal roof replaced last week. I had them install a bubble foil under my metal roof.

I currently have batt insulation under my radiant barrier. It’s stapled in between my purlins. I have noticed in a few spots my insulation is wet. I did have a leaky old metal roof so I thought replacing the roof would help which is did. I have some old damp spots in the exact same spots as before I pulled down the insulation and checked behind it and it’s dry. Just the paper is damp.

My building did have old existing skylights which I had covered up with the new roof. I am missing batt insulation in those 6 places. I had a few pieces also fall down when they installed the new roof.

For heating I have a Vented infrared propane heater currently in the garage which is empty currently.

Would you recommend :
1.Replacing old damp insulation and filling it the empty spots…then
2. installing a vapor barrier…then
3. filling my 325 gal propane vented heater and turning on my heater?

looking for any help at this point, I just spent a decent amount of money on my new roof and I am disappointed to see some wet spots still. In order for me to replace the insulation batts I need to rent a scissor lift to get that high and replace them. I currently have a drum fan running to keep the air moving. I am having them come over tomorrow and make some repairs to the roof and I am going to ask them to inspect the roof just in case the new roof is leaking which I dont think it is, but doesnt hurt to check. 

I appreciate the help.

Located in Clarksville TN

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Speedwaytaco160.

    It looks like there are some horizontal venting baffles above the fiberglass and between purlins. Is that what I am seeing?

    If the problem is in fact condensation, a vapor retarder may help (the kraft facing on your existing batts is a vapor retarder), but air sealing is even more important. You may need to find a way to air seal beneath the insulation. You might consider installing drywall or detailing a vapor retarder as an air barrier.

  2. Speedwaytaco160 | | #2


    Yes I do have baffles under all of my kraft faced insulation. Ive read on garage journal and also here that if I install an air barrier over my kraft faced insulation I may caught mold. I was looking at a few products for air barriers.

    Some people cut slices into the kraft faced insulation and installed a vapor barrier over it. They mentioned that slices would let the moisture travel through the insulation as if it were not faced with paper. I know I need to fill in the places that are missing insulation. Just looking for the right steps to take in order so I dont go backwards.

    Thanks for the reply Brian.

  3. Expert Member
    Akos | | #3

    Your first problem is that you have a cold side vapor barrier with the bubble wrap. This means that any moisture that makes it past the insulation will condense on the plastic, which is exactly what you see.

    Since it is a shop which I assume doesn't have a huge interior moisture source, it doesn't need to be detailed as a house roof, but you still need to take care.

    The best would be to add some continuous soffit to ridge venting above the insulation. This would allow any moisture that accumulates there to be carried out.

    Since your purlins go the wrong way, I don't think this would possible without major roof work. Your best bet is as Brian suggested a decent warm side air barrier/smart vapor retarder.

    Probably the cheapest is a layer of OSB with the seams taped. OSB is a reasonable smart vapor barrier and will allow drying towards the inside. As long the OSB is air tight and you keep the interior humidity in check, the sweating should stop.

    It will take a while to dry out the ceiling, you would have to keep an eye on interior humidity and make sure it stays bellow outside dew point (NOT RH, there are tables for converting RH and temperature to dew point.). This might mean running a dehumidifier in the winter time.

  4. Speedwaytaco160 | | #4

    So I have a dehumidifier in my garage currently. I think it may not be working maybe someone can help me out. My ThermoPro TP50 Digital Hygrometer Indoor Thermometer is reading 54% RH right now, it has been raining all day. I set my dehumidifier to 30 it is only showing 38. Does this mean that my dehumidifier is broken? This unit is 3 yrs old and I have read on many forums that the new Dehumidifies only last a few years. Thanks for any input.

  5. gusfhb | | #5

    Depending on how tight your garage is you might be trying to dehumidify the great outdoors, so if you are getting a bunch of liquid out, it is probably doing its best

  6. Speedwaytaco160 | | #6

    Looking for opinions on this product at lowes VS OSB for the interior of my building on the ceiling. Thanks for any reply.

  7. Speedwaytaco160 | | #7

    Bump, still looking for answers

  8. Speedwaytaco160 | | #8

    ok, I am in some serious need of some help here. I plan on renting some equipment and installing insulation and replacing the old wet stuff but what do I do after that? Since it is detached and I live in the county can I just install 1/2 OSB? or 1/2 drywall.

  9. Expert Member
    Akos | | #9

    Couple of questions first. Did the dehumidifier reduce the interior humidity? Did the batts dry up?

    If you are still getting moisture buildup in the roof, you need to find the source of it before installing any additional insulation. You might have to find a way to get proper vent channel running from the eaves to the ridge in there, which will not be easy with your purlins. The existing baffles are not doing anything.

    If the roof did dry up, the new air control layer should be something permeable. You don't want to use the foil faced product you show above as the roof will have no way of drying.

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