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.
Info @windowsonwashington.net
An informed customer is our best customer.
11/4/2010
What kind of attic or roof line do you have now?
Guest User
11/4/2010
roughly a 4-12 pitch and a closed in unfinished attic with insulation on the attic floor joist(not the rafters). Is that what you need to know?
Info @windowsonwashington.net
An informed customer is our best customer.
11/5/2010
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.
Guest User
11/5/2010
would you be more comfortable with just medal roof directly to the asphalt shingles..am I reading this right? without purlins Or are you saying it is better to remove the shingles and go directly to the decking.without purlins or am I better off to use the purlins. plz tell me what you think would be the best choice givin my situation..thank you
Info @windowsonwashington.net
An informed customer is our best customer.
11/5/2010
I am not a huge fan of leaving the asphalt shingles on the roof because I prefer to inspect the plywood and add fasteners where necessary and replace where necessary. You will need a minimum of a slip layer between the asphalt and the metal if you go that route. The point of over deck venting (i.e. purlins) is to keep the roof consistent with exterior temperatures and keep it from taking on heat from the home or transmitting heat into the home. That is much more important if you have an insulated/hot roof deck where you do not have an attic. That is not the case here. Putting the roof on purlins is unnecessary the time spent creating that system could be used to remove the existing asphalt shingles. A roof that is on purlins is also much less walkalbe.
Guest User
11/7/2010
oh I got it, one question though..what kinda slip sheet do you prefer..would tyvek work? or just tar paper?
Info @windowsonwashington.net
An informed customer is our best customer.
11/7/2010
Tyvek is a building wrap. I would look for a synthetic roofing underlayment. Check with the manufacturer of the roofing on what to use.
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