Re-roofing advice needed

Marc Albertson
Hello, I am replacing a metal roof (5v) on a workshop on a new piece of property we just purchased. This is my first time attempting a roofing job, so I have read as much as I can find and think I can do a good job. The existing roof is probably 30 years old. It was put up without a substrate, attached directly to the joist and purlins. The roof is a flat roof with a shallow 2.5:12 pitch, so installation will be relatively easy. The roof is 15' x 30'. My plan is to remove the existing roof and build a substrate in order to provide better protection and enable me to walk safely on the roof. I am building the substrate from 7/16" OSB and then covering the OSB with #30 roofing felt to provide a water barrier. I have purchased weather striping to seal the overlaps in the 5v. The installation seems pretty straight forward made even easier as I found a local company that is able to sell me the 5v cut to my specification, so I can use a single sheet for the 15' length. The only things that I need advice on are: 1) Should I attach the 5v directly to the felt covered OSB or should I run 1x4's every 24" to provide a means of ventilation? I have read so much conflicting advice on this. Most manufacturers websites I have gone to show the 5v installed directly to the substrate. It would be easier and cost less this way, but if the 1x4's are necessary, then I need to head back to the lumber yard soon. 2: I live in Florida and we are getting rain almost everyday. I can no longer wait out for a dry spell and need to proceed. I can get the substrate and felt completed in a single day, however it might take me 3 or 4 days to complete the installation of the 5v. If it rains prior to the 5v being installed will the felt paper be enough to protect the substrate or do I need to cover the roof everyday with plastic? If the felt alone is enough, do I have to wait until it is completely dry prior to installing the 5v? 3) The top of the roof will butt up against a 2' high wall that for some unknown reason extends up the back side of the building (design feature, wind protection?) and I will use 4" angle flashing where the two join. I have read conflicting information about joining two dissimilar metals together. Should I glue roofing felt to the underside of the flashing where it contacts the 5v? Also, the flashing will attach vertically to the wall, I plan on running a bead of calk along the top flashing joint to seal it. Does this sound correct? 4) Lastly, the long eave opposite the above wall extends one foot past the side wall of the structure. What is the best way to seal the 5v at this point since there is nothing to mount flashing to? I apologize for the long post, but I want to do this job right. My beautiful wife, while supportive, is skeptical. I would like to drive the last nail, confidently step from the ladder while the sun glistens of the newly installed roof leaving her tingling from the awesome job I have done. However, if I step off the ladder and hear a creaking sound followed by a mushroom cloud where my workshop once stood, I will never live it down!
Todd Miller
Isaiah Industries, Inc.
Thanks so much for your questions. I will try to answer them. Direct to deck or on battens is acceptable. All things considered, I would probably go direct to deck (with underlayment of course) in your application. Properly installed, the 30 pound should provide enough protection. You do not need to wait for it to dry out before proceeding. I am not sure if you really have dissimilar metals but separating the two somehow is wise. I would suggest some sort of termination bar (wood or metal) plus sealant to hold the flashing against that vertical wall. Can you add a fascia to your rafter tails and use a drip edge on the eave? I am sure you will have a successful project. You're doing your homework well. Good luck.
Eric Novotny
An informed customer is the Best Customer!
1. Direct to deck is fine and over deck ventilation is more often used in climate where the issue is keeping the roof closer to ambient because of ice damning issues. An overdeck vent would help keep some of the heat out of your space as well but if that is not an issue of significance, go direct to deck. 2. Wet, not soaked, is okay. If you are worried about it, spend the extra cash on some synthetic underlayment and it is even more of a non issue. 3. +1 to Todd's observations. What metals are you talking about? The big offenders are joining copper with galvanized or aluminum. You just need some sort of slip layer and whatever works will be fine. 4. +1 again. Fascia board across the rafter tails is ideal with a drip edge.

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