?'s for the resident roofers

Ok guys that deal with roofing on a more regular basis than I, I'd like your thoughts and real life opinion.
Let me lead up to my questions..
Within the last couple of years, my shop desperately needed rre-roofing. The original shingles from 1977 finally deteriorated and started breaking. I repaired all damage and stripped the roof with aged 5/4 boards before covering with metal roofing. I'm happy with the finished product and all seems well with no leaks or issues.
Now, the roof on my home is nearing it's life's end and I will need to do something soon. I have been leaning toward metal for this also, but am getting mixed opinions that now have me a bit confused. Some claim that leaks are sure to occur, with the most common culprit being the gaskets on the screws. I could see that as plausible if the screw did not have solid material to attach to, which brings up the next question/concern. I'm not confident the base plywood would maintain enough integrity to hold the screws tight. Many claim success just laying the roofing over existing shingles, screw it down and you're good to go. Others swear by stripping, then roofing... My original shingles are stapled, so removal and replacement would be a pain, and I'm not big at all on stacking an additional layer over old.
I feel the life expectancy of metal is better than shingle but at this point am just a but unsure of the best procedure to use that will hold up the best.
What say ye?

Remove shingles, allows you to check for any possible wood damage and as the metal expands and contracts with temp changes the grit of the shingles can wear the metal. Use purlins, will give an additional air gap and hold the screws.
I’ll be doing mine sometime in the next few years and that’s what I’ve read.
I’m not a roofer.
Only thing I’ve heard mixed reviews on is where to place the screws. Manufacturer says in the flats, but seems like if there were a gasket failure it’d be better in a peak.
I know we have some professionals here. I’m sure they’ll have some advice.

nchunter, if I were to remove the shingles, I would probably go back with architectural shingles. These are stapled down, and are a pain to remove. Almost every staple has to be pulled or driven in after shingle is broken off. I currently have no damage, just wanting to be proactive and re-roof before getting to that point. IF I were to put metal over the existing shingles, they would be covered with felt prior, to lessen the abrasiveness between the two. My big concern to doing that would be the screws losing their integrity by being run through the existing material and into plywood; not confident they will remain snug enough over time.

If your confident there’s no damage to existing wood go over the shingles with purlins then metal. Eliminate wear and screw integrity issues using the purlins.

nchunter said:

If your confident there’s no damage to existing wood go over the shingles with purlins then metal. Eliminate wear and screw integrity issues using the purlins.

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That is what I'm thinking, but with quite a few claiming leaks with metal are inevitable, it gives me pause. I sorta look at the existing roofing being a backup, but not sure how leak proof even that would be after striping runs are screwed down, especially horizontal with the roof. Also, what to use, 1X's or 2X's, pine or another type wood?

Go with "commercial" metal no exposed fasteners. But remove the old roof.

nccatfisher said:

Go with "commercial" metal no exposed fasteners. But remove the old roof.

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I assume you are referring to what I have always called "standing seam" roofing? Edges are crimped.

bigten said:

I assume you are referring to what I have always called "standing seam" roofing? Edges are crimped.

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Yep..................

I went with metal on my house a few years ago. Went through a lot of the though processes that you are going through. My old roof had 2 layers of shingles and there was no way I was going to leave them on to be a heat sink under the tin so that part was easy. I did not have any known leaks but did find some damaged sheating at a couple of places near the eaves. My house is older and is not sheated with plywood.

I priced screw down and standing seam. IIRC, the standing seam was around 4K higher than the screw down. I went with the screw down, figuring it would last as long as I do. If I was younger, I probably would have spent the money to go standing seam.

So I have screw down over black paper screwed directly to the 1" x 6" sheating. No complaints so far.

Thanks...

Moisture barrier is critical!! Whether the shingles are on or off.....and roofing felt is not the appropriate moisture barrier

ScottyB said:

Moisture barrier is critical!! Whether the shingles are on or off.....and roofing felt is not the appropriate moisture barrier

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And what would that be? The white construction wrap? Never seen that put on a roof that I can think of.

I can get the name of it on Monday it is similar to Tyvek but it is made to keep the sweat of the roof from running in every nail hole up there... or at least that is what they put on my lakehouse ( old shingles still on roof) i will get you a name

The moisture barrier is called titanium roof underlayment. Definately not the same as house wrap.

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Titanium is what is used around here.

So, this "titanium" is to be used over existing roofing, under metal to eliminate any leakage? Interesting, especially since I am not looking forward to removing my existing shingles. More info please..

All I can add is don't screw it down to your plywood sheeting....that is a mistake for sure. I have seen them done that way...screws striped out later on and leaking. Once it leaks that plywood around that hole is history...you not going to fix it with a bigger screw. Also if you strip it with 1xs or 2 xs...that first one on the edge where the gutter is.....I would tamper that edge with the facer board and put it even with the facer. If you don't and you decide to put gutter on later...you end up with a gap up top. Nothing to screw your gutter too. The bad part about a tin roof and gutter is when it snows...that snow comes off a tin roof in one big sheet...if the gutter isn't screwed up good....that snow will take it off. You can get some snow birds to hold the snow back too but they aren't cheap.

I'm in the gutter business and we do a lot of metal roofs. Biggest compliant we hear when changing to a tin roof is the water is running over the existing gutter. This is because once you strip it with boards, it raises the roof line up 1-2". The gutter needs to raise up with it..thus what I was already talking about. Most of the time you cant and only option is go with a larger gutter like a 6" gutter.

One more thing ..I would leave at least a 1.5 over hang on that tin past my facer board. Bet way to keep that bottom edge straight that I have seen is run you a string down there and hold your tin to it.

Metal screws nowadays have a cupped metal washer between the head and the neoprene washer. They also have a lifetime warranty screw available if you'd like but you'd better throw your shoulders back, they're over twice the price and IMO, not worth the money. The screw itself is not the culprit in a leak, it's 100 times more likely that the screw was improperly installed, ie, driven too deep, distorting the washer and effectively breaking the seal the washer provides. In 20 years of metal roofing I've never had to go back because of a failed fastener that was properly installed. And screws go in the flats next to the rib on the lap side of each plane. Hides and holds the laps down better and eliminates the need for butyl tape on each lap. The only time I put a screw in the high rib is where each panel overlaps the previous one at the eave for extra protection from storm winds. Run double screws in each flat adjacent to the ribs at both the top and bottom of each panel.

If I was a young man I might bite the bullet and install a standing seam roof because of the cleaner look more than anything but it is extremely labor-intensive to install, the materials are 2-3 times more expensive, and truth be told, a screw-down metal roof, properly installed and flashed, will probably last until you die....

I'm also a big fan running of #2 pine purlings from eave to peak on 2' centers to screw the metal down on, I won't put one down without them and for a couple of reasons. First, I can take a screw gun and spin metal roofing screws into sheathing until they'll smoke. You won't do that on a #2 pine purling. Also that 3/4" of dead air space provides an R value of about 6 and the purlings give a much more secure surface to screw to. I always nailed purlings down every 12" with two 2-8D ringshanks, one above the other, leaving the middle of the purling open for the screw. If you can hit trusses so much the better but I've never really worried about it and I've had literally dozens of homes take direct hits from hurricanes from here to Florida and I never got a phone call except to thank me...

The most worry-free screw down roof to me is done by adding a synthetic underlayment under the purlings. On most homes it only adds a couple of hundred bucks to the cost and prevents the possibility of hot air from the attic leaking up underneath a cold panel and causing condensation/moisture on the underside of the panels. That's the culprit on most leak complaints, water has a way of finding a place to penetrate and it may be 20' from where it started. You can chase your tail for days.....

One more tip: Make sure the installer blows the surface off with a leaf blower at the end of each day. Installing the screw generates metal shavings that will lay on the surface and rust, eventually damaging the finish. Even if they pre-drill all the holes for the fasteners there will be shavings from the screw installation.

Well I think that sums it up. Very good information.

Thanks longrifle. Chances are high that whatever I do, I'll do the job. Not a carpenter or roofer by trade, but have done enough to be confident doing them. You answered my questions well and have somewhat relieved my concern of the "inevitable" leaks some speak of. I have no issues now but am seeing chipped shingles, so I know time is running out on my existing cover and I want to redo before it does become a problem. I also want to add an inch or so more overhang than I currently have which would be doable but a little more work and material if re-shingled. More simple if I go metal. And no, no gutters. (Not actually directed to you). I'd rather have the drip line than the issues that come with gutters and downspouts.

bigten said:

I'd rather have the drip line than the issues that come with gutters and downspouts.

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And what issues are those?
I prefer to get all that water away from my foundation if possible and, therefore, prefer gutters.

Triggernosis said:

And what issues are those?
I prefer to get all that water away from my foundation if possible and, therefore, prefer gutters.

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I would have to agree here.....

I just used a 2" panel reveal at the eave and raise the gutters up 3/4", the thickness of a 1 X. I've done that on every house that has existing gutters.

Bear in mind too that bulk of the water running off of a metal roof is traveling much faster and hits quite a bit farther away from the foundation than it does from a shingle roof...

Triggernosis said:

And what issues are those?
I prefer to get all that water away from my foundation if possible and, therefore, prefer gutters.

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Trees for one thing. I've seen many gutters sag and cause problems. I graded my property to run water away from my foundation and just prefer to not have them.