Guest User
I am considering an "R panel" roof in a galvalume (unpainted) finish for my modified A-frame lake cabin. The present roof is asphalt shingles mounted to 1x6 tongue and groove roof decking. The roof decking also is the interior ceiling. The crest of the roofline juts out about 3 feet, sweeping back to the corners of the home to form an "awning" (albeit a very high one) over the front and back of the house. Thus, the front and back roof edges, while straight, are not square. My questions are these: 1. What is the appropriate edge treatment for the front and rear of the house. There are presently no gutters. One installer has said that the vertical panel will just be cut on a diagonal line. This will leave rainwater to channel off in intervals as the roof edge sweeps back. He says putting an edge trim on will have some guttering effect but will cause "leaks" at the seams of the edging. He thinks it better to do nothing. I'm also concerned about the look of a ragged / unfininshed edge. 2. Because the roof decking is thin and cannot be pierced (the screws would show on the interior), he suggests using either 3/4 or 7/8" screws and "double screwing"; i.e., 2 screws between each rib (which are on 12" centers). He also proposes to leave existing single layer of asphalt shingles on. Is the size of the screws and leaving the roof on (separately or in combination) appropriate? We get a fair amount of wind being on the lake. Thus, we need solid attachment. 3. Does galvalume provide a decent reflectivity component compared to high-reflective paint (such as kynar)? The silver / gray color works aesthetically and I'd prefer not to pay for paint unless I need it. As you might expect, the house (which is in the southeast) is tough to cool on 90+ degree summer days, though I was hoping a metal roof vs. current black shingles would help. 4. I considered putting furring strips and foam board insulation but given the intermittent use (as a lake cabin) the cost - benefit didn't seem to be there (is there anything tax credit-wise in new federal energy legislation that might change that analysis)
Allan Reid
Dura-Loc Roofing Systems, Inc.
The first choice should be to contact the manufacturer of the panel and get their recommendations. Also ask to see the prtoduct approval report on the panel which will show tested flashing and attachment details. Having said that here are my comments; 1) You have a splayed or chinese gable on your cottage where the ridge is longer than the eave. The building coide requires a drip edge at the eave and this type of gable is considered an eave. Install drip edge aalong the eave and up the gables. Seal the roof sheets to the drip edge with butyl tape and fasten securely. The second option is to fold the metal sheet over and under the drip (180 degrees. This provides a secure wind detail. 2,3) They are somewhat related. The building code calls for a 1" vented air space under the roof covering. This is the most important thing you can do to elliminate heat transfer. I suggest strapping the roof vertically with 1 1/2" thick lumber over the rafters and fasten down through into the rafters. Then strap the roof horizontally to accept the metal roof sheets. Use profiled vented closure strips at the ave and ridge. It is the ideal time to insulate and certainly even a little will go a long way. You also are required to put a moisture barrier down. There are some reflective thin foil faced barriers that act as both underlay and help reflect heat. Galvalume is reflective although it is poor on the emissive side but with the vented air space it will perform great. A PVDF white painted would certainly help. 4) the new energy bill does have some tax credits in it but the are currently unclear and we are waiting for the tax department to interpret. Think about the retirement years when you spend more time there so insulation is beneficial.
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