Guest User
11/3/2010
Present roof is asphalt shingles,planning on installed medal roof, can I nail down 2x4s and install the medal roof directly ontop of the shingles...the 2/4s will leave a air space and the present shingles will act as a moisture barrier that will allow any condensation to drain off....is this a good idea or a bad one and why? thx in advance.
Nate Libbey
11/5/2010
JC, Should work fine. Some people put vertical 2x4s down first, then horizontal 2x4s. This prevents the slight possibility of moisture getting trapped above a 1x4. Either way should work fine. Another advantage of this air gap is that it will provide insulation value as well.
Eric Novotny
An informed customer is the Best Customer!
11/5/2010
Posted in other thread: Yes, that is all I need to know. There is no concern with your roof sweating in this application because the attic is already ventilated in some capacity with soffit vents or some sort of gable vent. The benefit to installing the metal roof on purlins in this case would be to allow for some over deck venting that will keep that roof more consistent with exterior temperatures, either cold or hot. Your insulation and envelope layer is the floor of your attic. If you are loosing or gaining heat, that is the area that needs to be addressed. While you can quite easily install the metal over the existing asphalt, I have never been a huge fan of it as it does at to the weight of the roof assembly and you cannot properly inspect or replace the plywood as necessary. Again, the insulation layer is your attic floor and if you have inadequate insulation, that is where it needs to be addressed. Putting the roof on purlins is okay, but a direct to deck application will make the roof more walkable.
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