Guest User
7/21/2008
I am going to be putting a new metal roof over an old raised seam metal roof that is directly over the original cedar shingles. We have developed a significant leak and on close inspection need a roof immediately. I have installed asphalt shingles and new install metal roofing so I have a very basic understanding of the installation, not an expert. Also of note I am in a very northern climate that experiences several feet of snow a year. I have spent hours here researching different installation techniques but am still not 100% on the process. I have both a 6/12 and 7/12 pitch joined with a hip, four foot difference in height, both are second floor and there are two simple first floor roofs on each side, no big deal there. There is some sag and without totally rebuilding the entire roof structure there is no way to eliminate it. I have also found some soft spots in the eves; these will be replaced with new siding next year but will remain for now, no option there unless I find some that are completely rotten.. I plan on using an economical 29ga material (probably Fabral) installed over strapping. My biggest concern is what to use for strapping, orientation and the spacing. As well as hammering down the old seams so they do not cause problems with the installation of the strapping. Does strapping have to be notched for the flattened seams or does it span the gap without noticing it on the final roof? This is what I have been told. Several have suggested simply hammering down the seams installing 1x3 strapping and the new roof directly over that, if I went this route I would install 1x4 in the perimeter for added strength. One person suggested using 2x4s for strength and to allow shims between the seams once flattened. Then there is spacing some say 24” and others 16”. It was also recommended that I not hammer down the seams, install 2x4s vertically and then horizontally, and install a layer of rigid insulation. Now you see why I am confused. I am on a limited budget but want a quality installation that will last, not show strapping locations after a heavy snow load, walked on or being spaced to far apart. The difference in cost of the 1x3 strapping and the 2x4 are significant though the 2x4 strapping sounds like it would have its merits. Any advice, references or suggestions WOULD BE GREATLY appreciated as this project is an immediate MUST do. Thanks in advance for any help on this one!!!
Guest User
7/21/2008
You stated that you have some sagging. That is a sign that you do not have enough support for the weight of the existing roof. Now, you are going to add even more weight. If you are going to get by as economically as you can, but still have a decent roof, I would beat down the seams and use 2x4's and a 26 gauge metal, not 29 gauge.
Todd Miller
Classic Products, Inc.
7/21/2008
Thanks Wade. Good advice. I would follow up and say that you definitely need to work with an engineer at Fabral and get their input and ideas based upon how they have designed and tested their product. The person to contact is Bill Croucher, [email protected]
Guest User
7/22/2008
I will be calling Fabral prior to finalizing plans for sure, thanks for the contact name. As far as the concern over the roof sag. The house is over 150 years old and I think this contributes significantly to the sag that is seen. The ridge does not sag and overall everything is square with no idications of deformation beyond the sag seen along the length of field. With this type of construction there is no way of knowing the real load bearing weight capacity. I feel that even adding the weight of the new roof the overall potential load should be reduced since there will be less ice forming and a the new surface will more readily shed the snow. I was calculating the additional weight added with 2x4s and 29ga at aprx .95 sq ft and a total area of 1975 sq ft; it does not take alot of snow to add up to 2000 pounds. I could be wrong here so feel free to jump in. Even if I stripped the old roof I would need to add a layer of plywood/OSB and felt and my calculations show this option to weigh more then just going over the existing roof. Again I could be wrong.
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