I have several rolls of black 30 weight black felt paper left over. Can I use this as an underlayment on the roof purlins to prevent roof sweating? This would be cheaper compared to maybe the single bubble vapor barrier. For the first two years, the garage wont be insulated.
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roof condensation
- Thread starter noel4747
- Start date
Falcon67
Well-known member
FWIW - I have used 15 and 30 lb as exterior "vapor barrier" under siding and never noted a problem. When my dad and grand dad build outbuildings or added on to houses they did the same thing. This was way before Tyvek. I don't think it will "prevent" roof sweats caused by certain weather conditions but it can control where that moisture goes.
myredracer
Well-known member
What type of roofing material - metal? What type of framing/rafters? Low pitch roof with no attic space or gable style with attic space? Location?
I hired a roofing contractor to install a standing seam metal roof on our house. He specializes in metal roofing only and does it for all types of buildings - residential, institutional & commercial. I had the roof built with 2x4 purlins and not plywood or OSB. The contractor put down a layer of heavy roof felt everywhere as a thermal break to prevent/minimize condensation. We live in the PNW with high humidity levels for extended periods and condensation has never been an issue.
Need to be careful not to tear it when putting on the roof. Because of the tar in it, you can't fix it with any sort of tape because it just won't stick.
It's every important to have the roof assembly properly vented to code for the specific location where the structure is. Must be a vented air space between insulation and roof deck (except for spray foam).
I hired a roofing contractor to install a standing seam metal roof on our house. He specializes in metal roofing only and does it for all types of buildings - residential, institutional & commercial. I had the roof built with 2x4 purlins and not plywood or OSB. The contractor put down a layer of heavy roof felt everywhere as a thermal break to prevent/minimize condensation. We live in the PNW with high humidity levels for extended periods and condensation has never been an issue.
Need to be careful not to tear it when putting on the roof. Because of the tar in it, you can't fix it with any sort of tape because it just won't stick.
It's every important to have the roof assembly properly vented to code for the specific location where the structure is. Must be a vented air space between insulation and roof deck (except for spray foam).
trusses will be four feet span, using 2*4 purlins and followed up with metal roofing. The issue I come across is the purlins will be seperated by two feet so 3ft wide felt paper wouldnt staple down good. I think I may just spend the extra money for the single bubble barrier. Any other suggestions?
Depending on where you are Noel you can use sarking to do the job. That's what we use around where i live. Relatively inexpensive from the hardware store and it doesn't absorb any water. (not sure if your felt paper will)
but if you want to deal with the moisture problem directly then maybe some ventilation is the key
Here is some general info on ventilating a shed for your convenience
but if you want to deal with the moisture problem directly then maybe some ventilation is the key
Here is some general info on ventilating a shed for your convenience
matt_i
Well-known member
If you do use it, be really careful where you step. The center of the span is a poor choice.