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METAL roof enclosed porch open rafter insulation (condensation)

METAL roof enclosed porch open rafter insulation (condensation)


  #1  
Old 01-12-16, 07:30 PM
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METAL roof enclosed porch open rafter insulation (condensation)

I enclosed my 12x20 porch . I installed metal roof on 2x4 16" C purlins and purlins screwed to the 24"C rafters . After completing enclosure and adding heat source I quickly saw the terrible condensation inside the metal ! I am asking for any opinions or ideas on the 2 ways I believe the condensation could be solved . #1 Spray at least 3" of closed cell foam up on inside of metal between and probably over the purlins . I was told by a foam company that 3" should resolve the moisure . #2 Use ADO Durovent http://adoproducts.com/as_durovent up inside the rafters and against the purlins . As you can see with #2 the Durovent would run inside the rafters from the house facia upper end down to and into the soffit area . Note there is a 2x6 where the roof originally ended but I added the overhang later . Thus where the Durovents go trhu that rafter I will need to cut out for the baffles to pass into the soffit area . Then at the upper end house facia end I would need to cut out or drill holes in areas between rafters into what would be the house attic . This should allow moisture drainage into soffit area and ventilation . Under the Durovent I would install fiberglass insulation and later probably plaster board . Name:  sunporch insul 2.jpg
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  #2  
Old 01-12-16, 07:42 PM
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I would not want to vent all the moisture into the attic. And with such a low slope you are just not going to get much air movement in that direction anyway.

The foam will prevent the condensation on the ceiling, but if there's that much moisture in the air, it will find somewhere else to condense.

What is the heat source? Unvented gas heaters are notorious for generating lots of moisture. If that's what your using, changing to something that is vented may be all you need to do.
 
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Old 01-12-16, 07:56 PM
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It is a ventless ! What if i didn't vent at top using the Durovents and just allow moisture to drain at soffit ?
 
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Old 01-12-16, 08:05 PM
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I have gallons of moisture , almost a rainstorm up on the metal . I did have a small electric heater for a while and I had 6" fiberglass in rafters , I did not see the condensation until the ventless was installed and water dripped down thru fiberglass badly . So you are saying the ventless causes lots and lots of inside moisture ? So if I vented a heater and went with some kind of moisture barrier like the foam or durovent the moisture would be less and controllable ?
 
  #5  
Old 01-13-16, 06:40 AM
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When gas is burned one of the products of combustion is water vapor, lots of it. A gas furnace or a vented gas heater exhausts the water vapor to the outside, so it doesn't add to interior humidity. Ventless heater exhaust the water vapor into the room. When you combine that with cold outside temps and little insulation, the vapor condenses on colder surfaces and that's what you are seeing.

If you insulate the ceiling, but keep the ventless heater, it's likely the water will condense on the windows or walls, whatever colder surfaces there are.

The electric heater didn't generate any water vapor so that's why you didn't see the problem with that.

I see you are in PA, so have a lot of cold weather. Insulating the ceiling will certainly make it easier to keep the space comfortable so is a good idea in any case. You may find that good insulation will let you run the heater much less and reduce the problem, but most likely replacing the heater with a vented model is the best solution. Alternately, you could look a different form of heat, like electric baseboards. They cost more to run, but won't have the moisture problem.
 
 

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