underlayment for corrugated metal roofing

Lee Josselyn
8/9/2016
I'm replacing a roof (probably 50-60 years old) on a historic log cabin. It has vertical logs covered with horizontal 3/4" thick 6" x 10' wood planks (1/4" gaps between planks) covered with a fairly think asphalt underlayment (looks 1/8" thick), covered with 1/2" corrugated bare steel sheets (very rusted). The roof is fairly flat with sloped sides of 1.5" in 12" and 2.75" in 12". The ridge cap was formed by hammering the top 4 inches of the corrugated sheets on one side over the ridge line. I'm trying to replace with materials as authentic looking as I can. I'm planning to use 22 gage bare steel 1/2" corrugated roof sheets. I'm not sure how I'm going to hammer over the ridge cap yet but my first plan was to have a metal shop break the (20 degree) angle for me first. [Other ideas would be welcome]. My real question is what I should use for underlayment. The old roof never leaked so I'm thinking of using a 30# Asphalt Saturated Felt (I think is kind of like the old one). If the old underlayment was still OK (after 50+ years) I was also thinking of leaving it in place and just going over it with new. I'd like the new roof to last 50+ year w/o leaks.... Any advise on my plan? Underlayment? Ridge cap formed by hammering a break in corrugated metal?
Info @windowsonwashington.net
An informed customer is our best customer.
8/9/2016
I would bend the legs up and have a cap fabricated that can be installed on the ridge. It should give it a nice detail.
Lee Josselyn
8/10/2016
What would your underlayment advise be? Do I possible keep the old and put new on top?
Info @windowsonwashington.net
An informed customer is our best customer.
8/10/2016
I would just use one of the synthetic underlayments in the case I would remove the old roof.

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