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I have a barn shake cedar roof in Tofino BC that I would like to replace with metal because of all the tree needles and heavy rain here. The roof is a problem one as there are two roof slabs with a vertical wall connecting them at almost the peak. Venting the lower slab will require the removal and replacement of the vertical board and batten cedar siding which connects the lower to the upper roof in order to properly install flashing and venting. The plan is to strap vertically and then horizontally the existing roofs' shiplap decking in order to provide the ventilation space needed.
The problem is that the vapour barrier in the house has to be presumed to be defective as I have seen it slashed in other parts of the house. The cathedral ceilings are a non replaceable cedar strip filled with fiberglass insulation. The house has survived all these years because the barn shakes breathe.
The Questions: How do I stop moisture escaping the house through the defective vapour barrier from condensing on the underside of the metal roof and raining on me? What do you suggest I do? add a vapour barrier and foam board insulation between the strapping? Foam in place? Fortunately, the climate here is mild year round but more insulation might save on the heating bills.
Should I just use 30 lb felt, no extra insulation and let the roof breathe and hope the felt works for 30 or more years?
Suggestions Please!
Kevin
8/24/2004
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