insullation and ventilation of metal roofing

Guest User
2/6/2004
I'm looking for additional help on my new metal roof's condensation problem. I have a 200 year old house that we just replaced the metal roof. We have horizontal purlins, then 30 lb felt paper with metal roofing over that. We also placed a full length venting ridge cap. I have tried using proper vents (or rafter mates) attached to the purlins on the underside, then r-19 insullation followed by a vapor barrier but still have condenstation dripping. Unfortunately we don't have soffit vents since the house was built without enough roof over-hang to allow installation of them. If I were to build a knee wall, insulate that wall, and place large gable vents at each end behind the wall would that improve air flow up the rafter mates to the ridge vent or just be wasting time? Any suggestions?
Guest User
2/7/2004
Your idea of a knee wall is interesting. However, I suspect the gable vents would only feed the rafter mates nearby them and would not supply eneough intake air to feed all of them. Is there any way to just install several opposing gable vents, putting power fans behind them in one end? If you did this, you might even eliminate the ridge vent? Out of curiosity, have other things been done which have resulted in the house being more airtight than in the past? New windows, doors -- siding and housewrap or insulation? Can you do anything to minimize moisture in the house? Make sure all exhaust fans and dryer vents go to the outside. Also, things like plants, cooking (hey, there's a suggestion your wife might like -- go out to eat more often!), and ventless gas stoves put a huge amount of moisture into a home as well. Other than this, I'd really suggest looking at whether there is some way to get soffit overhangs and soffit vents added to the house.
Guest User
2/7/2004
Oops -- your name is Judy! Enjoy additional meals out Judy! (just kidding)
Guest User
2/9/2004
Unfortunately the improvements I have made so far are probably not enough to cause the moisture problem. I have put in new exterior doors and replaced 14 of the 39 windows. During these projects I found there is no insulation, fiberglass or otherwise, just empty wall cavities. Can you provide the formula I should use for ventilation air flow per sq ft of roof? I think I'll try gable vents at each peak plus I hope to take up the attic flooring in order to put in a vapor barrier plus fiberglass. I'm willing to entertain any ideas to stop the 'rain' from entering the living spaces. thanks.
Guest User
2/9/2004
Judy, Here's a link to a page which provides pretty good information on this subject. It does a better job than I could do by writing things here. I hope it helps. http://www.airvent.com/homeowner/whyVent/evaluate.shtml
Guest User
2/19/2004
I am in the process of evaluating roofing selection materials as we will shortly be replacing our 16-20 year composite roof. As we have little circulation in the attic, it is imperative we use a ridge vent system. Is this possible wirth meatl roof sungles??
Guest User
2/19/2004
Check with the roofing manufacturer for details but, yes, I am certain that all quality metal roof shingle manufacturers will have some sort of detail for ridge ventilation. To be effective, you need eave soffit ventilation as well for intake, with the ridge acting as exhaust.
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