DIY Roof Replacement -- Metal over Ashphalt

[dougstash]

I can’t say I’ve ever installed metal roofs but I have installed 10 sloped shingle roofs. In every case I had to replace at least some sheathing before I put the new roof on. Additionally without stripping the roof there’s no way to put a proper roof vapor barrier on as well as ice and rain membrane around the eves.  Even DIY roofing is always expensive and it’s worth it to do it right to ensure your roof will last as long as possible. 

Here’s what I’d do
Day 1: strip the roof. Bring help and hire some friends. Have some tarps on hand to cover the roof should it rain
Day day 2: replace anything that needs replaced. Drip edge, sheathing etc. roll out ice and water membrane at the bottom of the roof and in any valleys, chimneys etc. roll out a new synthetic felt paper (definitely worth it to go synthetic.  It is way stronger, a better leak barrier and very grippy on the feet. It’s worth it for the safety factor alone.) Now your roof is dried in. Now you can take your time with the rest of the replacement.

It’s not worth it to cut corners in my professional opinion.

[uniwelder]

I mean, if ANY rain at all falls in Australia, the roofs either leak or they don't. Right? This isn't Elbonia we're talking about from the Dilbert cartoons.

I would think baking in the sun is harder on the washers than being damp.

Yes it is.  Older washers didn't age well.  Those from before the 1970's would last 15 years roughly.  Those from the the 80's onwards are still reasonable, and can be 40 years old and still functioning.  But they are sealing at the TOP of the corrugations, so the actual seals do not have to do much.  That is one of the fundamental reasons this roofing is so successful at keeping the water out.

I'm replying here with my own previous comment---

I put on my own metal roofs (screwed down ag panel type) on a new construction garage, as well as replacing a 65 year old 5V metal roof on my previous house.  The old 5V panels were put on with lead capped nails, which about 1/4 were missing or uncapped by the time it was replaced, and the roof didn't leak by any amount that was noticeable.  The nails went through the ridges.

@lthenderson in a previous comment you said you'd have leaks whether the screw went through the ridge or the flat.  I wonder if they were actually leaks or condensation from under the metal panel?  You're so adamant that a screwed down metal roof is going to leak, but there are plenty of people that don't have that issue.  In particular, my own case where I didn't even have secure fasteners (or any at all) over 1/4 of my roof, but since it was through the ridge, it didn't seem to matter.  I had no evidence of leaking within my house--- no wet spots or staining on the ceiling, no rotten boards in the attic, damp insulation, etc. 

[lthenderson]

@lthenderson in a previous comment you said you'd have leaks whether the screw went through the ridge or the flat.  I wonder if they were actually leaks or condensation from under the metal panel?  You're so adamant that a screwed down metal roof is going to leak, but there are plenty of people that don't have that issue.  In particular, my own case where I didn't even have secure fasteners (or any at all) over 1/4 of my roof, but since it was through the ridge, it didn't seem to matter.  I had no evidence of leaking within my house--- no wet spots or staining on the ceiling, no rotten boards in the attic, damp insulation, etc.

I'm not adamant that a metal roof is going to leak. I'm just saying there is a lot higher chance than many people let onto for a variety of reasons. The biggest reason is that these leaks don't happen from day one and may take 20 to 30 years to develop as washers break down and temperature shifts heave screws. How many people here who claim the opposite have lived in the same house with the same metal roof for that long? I would wager few if any. But on the farm that I have lived or been on for the last 50 years, nearly every metal roof has leaked at some point. We have dozens of building with probably acres of metal roofing so more experience around them than most. That is primarily what drives my belief, experience.

I also say that it depends a great deal on whomever does the installation. On my previous house, the metal roof leaked in less than a few years. The previous owner had newly installed the metal roof, on top of shingles, right before I bought it. Three years later we had soft spots all over the house in the ceiling drywall from leaks and like I have mentioned before, for the rest of my tenure in that house, I spent lots of time on the roof every year tightening fasteners, adding silicon, etc. to keep the leaks from doing even more damage. Again, this probably wouldn't have happened had someone did a bang up good job at installation, such as not installing them on top of shingles which is what sparked this thread.

I'm not trying to stop anyone from installing metal roofing. In fact, I think a hidden fastener standing seam metal roof would be the way to go. I'm just offering my experience over 50 years of being around metal roofing as something to think about especially if you plan on living there for the rest of your life. If you are only going to be living in that house for the next 10 years, it likely won't affect you at all regardless of the quality of the job that was done.  If people pay a premium to get a roof that has the potential to last 50 years but replace it every 30 years due to inevitable leaks, I just think one would be money ahead to just put on shingles that also last 30 years. Again, it is my personal experience and my opinion and like anything on this forum, your mileage may vary.