Putting a metal roof over asphalt shingles

[Magicman]

Yup, my snow load is a mite less.   :D

[thecfarm]

I just put some on my building. The guy at the lumber place said put the screws at 16 inches. He figured out the screw amount 16 inches on center.I put boards on the roof,no strips. I was undecided about steel or shingles.

[ET]

I put metal on my 1000 sq/ft workshop over rolled roofing 8 years ago. I removed as much of the old R/R as i could but alot was stuck on really bad and time was of the essence (rainy season). I followed manufacturers directions and screwed next to ribs on the flat and using a 3/4 screw threw the ribs. I also used that rubber string and placed under each rib from top to bottom. All screws lined up and it came out great. With that many screws installed over good decking i cannot see that metal moving much at all. I used white to reduce heat in the shop.

[Al_Smith]

As I type my son is having a metal roof installed over shingles .They layed down a layer of some type barrier to prevent deteriation from the shingles .

Kind of odd as I have something like 12,000 sq feet of new hidden seam 22 gauge lock seamed standing seam roofing material .He couldn't find anyone locally who knew how to install it .

[Bill Gaiche]

As I have stated above, haven't had one problem with our roof as of today. It was installed over shingles in 2001. Thats about 12 years ago. bg

[Randy88]

Which version of tin are you guys putting on, ridge and valley or free standing with hidden fasteners?    I've been looking at tin on my house too, every time I ask I get a different answer and none are even close to being the same. 

[thecfarm]

Ridge and valley with exposed screws. That free standing,standing seam is nice stuff. I would have it,but kinda pricey but 4 times as good as what I just used.

[WDH]

On the metal roofing with the exposed screws, you can get a pan head screw where the pan head completely covers over the little neoprene washer and compresses it just the right amount.  The normal screws do not have a head that covers all the way over the washer, they just compresses it.  The pan head type screws are a lot more expensive, but they are worth it because you will not have leaks in the future.

[thecfarm]

WDH,That's what I've been using,pan head screws.One inch,9 cents each,2 inch ones,14 each. The place that I brought the steel from calls them painted wood grip screws.

[1woodguy]

   Anyone notice on some roof overs some of the screws back out after a few years?
  I usually just screw it right over shingles unless roof is spongy feeling
Then I just use any one or two bys I have around
  I did an old mobile home for someone ( it had the rounded roof ) I just made trusses from junk 2x4s
   used old salvaged treated 2x6s from a deck I removed for something to hook trusses to
nailed old wood siding to  them for something to screw the metal to that was over ten years back and it's ok
They still live in it

[Randy88]

Ok guys, questions, on the free standing roofs, do they actually stay put and not leak with the hidden fasteners, everyone claims they do and one guy who actually makes the tin, rolls it onsite told them they will leak and will actually float and are not as nice, strong or durable as a ridge and valley tin, he's the only one to ever mention this to me, everyone else claims they are just as good as ridge and valley.     On the ridge and valley tin, do you screw then on the ridge or in the valley, we used to nail on the ridge and have been having problems over time with them leaking, when we go to check it out, the tin has been moving enough to wear the hole larger and the nails are loose, so we've been screwing the tin on lately, seems to stay put better, but now we're considering screwing in the valley for new tin installation.   

Next question, my house has an old slate roof on it now, any suggestions as to how to put a new tin roof on it?  I figured we'd have to take all of the old slate shingles off and start completely over again, some say do nothing to the old base roof, just tin over it, and others claim I should put a membrane down, after taking off the old roof, and one guy told me he'd take off the old and just put tin on with nothing under it, seeing how we now have all options covered what's the right way to do it?  I can't imagine leaving the old roof on, we'd break it up badly trying to tin over it and I thought it would be a disaster myself, but I don't want it to leak anywhere either and every tin roof on every shed I have has some leaks in it somewhere over time.   

Onto the third question, the tin itself, we've torn down some old buildings that had the old style corrugated tin on it, both the 2.5 inch and also the one inch or inch and a half corrugation on it, we used it inside to line my shop so we just flipped it over and screwed it on upside down, it looks like new underneath and most think its new tin, but its heavy galvanized tin, about three or four times heavier than the new tin you can buy today, galvanized rusts over time and colored metal wears off over time, I have now two sheds that have no white color on at all left, my dad built the sheds back in the 80's and he's been having the galvanized shed roofs painted every few years for decades now, as of yet we've done nothing to the worn off white colored steel.    Sorry this is getting long winded but does it make sense to just put a new galvanized roof on or go with a colored steel and let the color wear off over the years first, some tell me its the same tin, colored is just painted over the galvanizing and others say its completely different and galvanized is heavier on galvanized tin verses the painted style, any ideas as who's right, basically which will last longer before it starts to rust out and need painting??

[pineywoods]

I have re-roofed my house and a couple of barns. My experience may differ from others. I ripped off the old asphalt shingles because the were extremely old and brittle, plus the house had 2 layers of shingles. Put a layer of roofing felt down on the decking. Otherwise warm moist air against the bottom side of the cold metal will condense and eventually rot the decking. If you leave the old shingles in place, no problem. I used the ridge and valley type, ridges every 6 inches. Watch the way the edges of the sheets lap. The edges are different for a reason, and they lap right backwards from what you would think. The short edge goes on top. Never use nails to fasten any sheet metal roofing. Decades of experience shows the nails will eventually back out. Screws won't. The neoprene washers under the screw head are critical. Water tight seal, yes, but more important...The metal will expand with heat and shrink with cold. The soft washer will compress and expand as the temperature changes, rather than trying to pull the screws out. Don't over tighten the screws and flatten the washers. Do not pre-drill the holes for the screws. Use self drilling screws.  About where to put the screws, I differ with most folks. The suppliers say use 1 inch screws and put them on the flat right beside the ridge. I think they say that because it does make the installation a good bit easier. My thinking is this. When, not if, the washers eventually come apart from age, you are definitely going to have leaks. By then, I'll be too old and decrepit to get up on the roof and fix the problems. I use 2 inch screws and put them through the top of the peaks, drilling through both layers of the laps. Here, over tightening   will cause another problem. It will flatten the peaks and mess up the alignment between sheets.
Another observation.. I have an old broiler house/shed that I use for lumber storage. Roofed with used corrugated metal. there's LOTS of extra holes. Stand inside and look up and you can see sunlight in dozens of places. the holes are all on the top of the peaks. Don't leak a drop...

[Farmerjw]

Here in Indiana, I can literally hear my lean to roofs on the barn expand and contract as the sun comes out in the morning and goes behind clouds.  With this, I believe them when they say put something over the shingles.  It isn't so much that the metal expands and contracts enough to wear through, it is it does it enough to scratch and cause rust then it is like a chevy pickup in the '70's, rust through quickly!  I also was taught on roofs to put the screws on top of the ridge, on walls on the flats.   But to each their own.

[1woodguy]

I always put the screws on the ridges also.

  Put up a quick screened porch once dew collected inside and dripped
Ended up removing metal and used osb and layer of felt under metal

[Randy88]

Where do you get pan head screws from, I've never seem them anywhere, nor heard of them.   

[thecfarm]

I got mine from a small lumber yard in town. I know the big box stores has them too.

This should do it for ya

http://www.metalsales.us.com/files/installation-guides/Application%20Manual-West%20Coast.pdf

Page 25,Fasteners
This where the steel that I just brought came from.

[loghorse]

i have put tin 29gauge on my cabin up north and on the house i live in.on this house some pieces are 24 feet long ,one piece.i put the screws on the ridge which  the tin supplier and i disagree about each time i see him.one thing of note ,tear off the old dripcap and put new drip on  on top off shingles.do not be in a hurry and slap the tin on without fixing the drip cap.right now galv is 1.60 alineal foot,wite is 1.90 a lineal foot.both 36 inches wide,29 gauge.brand new no. 1 tin .around here we call this pole barn tin.

[WDH]

Here is an example of what I called a "pan head" screw.  Probably not the right term, but the picture shows you how the screw head will cover over the washer, not just compress it.

http://www.levisnailsandscrews.com/proZ.php

[Magicman]

I don't know the name of the roofing screw, but it is not a "pan head" screw.  Pan head screws have a rather large flat head.  LINK  They can be either slotted or Phillips.

[Randy88]

We've been using the screws from either menards or home depot, does anyone know what those are considered, good or bad?   Or have a comparison of those to what your referring.   

[Magicman]

I doubt that there is any appreciable difference between manufacturers of the roofing screws that WDH posted.  They are actually designed to be used on the flats rather than the ridges of the roofing.

[thecfarm]

I brought some steel from Home depot years ago and than some from that link I posted.I had some screws left over from Home Depot, I looked at the link that WDH and thay all look just about the same. The link that WDH put in,the part below the head does look more like a pan. If you go to the left of his link where it says to browse screws,those are more like the ones that I have been using.

[thecfarm]

Here's what I have been using.



 

The 2 on the left are from Home Depot, years ago. The washers can be easily removed from the screw.
The 2 greens ones on the right are from the steel place. The washers are thinner,but are not easily removed from the screw.
And I brought the steel from a local lumber yard,delivered free, and I was in one of the big box stores  and checked out thier prices. I have no idea about the steel panels,but the ridge caps was about $12 more and the edge trim for the trimboards was about $8 and the so called flashing pieces was about $8 more too. The stuff looked exactly the same thing as what I have.

[pineywoods]

Go with the hex head screws, a phillips head will collect water in the recess. Use a socket in a drill that has adjustable torque. Most suppliers will stock a 1/4 inch socket with a short shaft that fits in the drill chuck.

[thecfarm]

Make sure it's magnetic too.