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Forum topic by JCamp posted 04-19-2018 10:16 PM 635 views 0 times favorited 14 replies Add to Favorites Watch
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JCamp

819 posts in 699 days


04-19-2018 10:16 PM

In the next few months I am going to be redoing my old garage. This will involve building on a lean to. The garage has shingles that’ll need replaces in a few years anyway so I thought instead of trying to match the new rood shingles to the old roof shingles Id suck it up and put on a full new roof. My plan is to do it all pretty much my self and go over it all with metal.
My question is does it need to put down 1×4 or 1×6 runners along the roof to put the metal on or just put right on the shingles? My thoughts is that I need runners. Am I wrong?

-- Whatsoever thy hand findeth to do, do it with all thy might


14 replies so far

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John Smith

1379 posts in 311 days


#1 posted 04-19-2018 10:33 PM

you must have runners to help in keeping the metal level plus air circulation.
(this is what the roofing just told me last week about my home).
but – for a lean to or barn roof – I doubt it would matter to go directly on the shingles.
other than you may have leaks around the screws or nails that fasten the metal to the shingled roof.
at least put down 30 pound felt first.

-- I started out with nothing in life ~ and still have most of it left.

View Kelster58's profile

Kelster58

670 posts in 689 days


#2 posted 04-20-2018 12:03 AM

I use Fabral Roofing.. Installation guides/manuals/videos can be found on their website. I think if you read the installation guide for “Grand Rib” they recommend purlins. I have seen metal roofing installed directly over shingles. I am with John Smith. I would use purlins.(“runners”)

http://fabral.com/

http://fabral.com/supporttech/specs-and-documents/

http://http://fabral.com/media/1965/storage-install-guide.pdf

-- K. Stone “Tell me and I forget, teach me and I may remember, involve me and I learn.” ― Benjamin Franklin

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ocean

107 posts in 982 days


#3 posted 04-20-2018 12:20 AM

I agree with John and mount metal roof to runners. I don’t think it is a good idea to leave the shingle on. My roofer removed the shingle from my house and then installed what is called a slip sheet then the metal roofing. The slip sheet can be roofing felt or even heavy construction paper. The reason for the slip sheet is due to the difference in expansion between the roofing (metal in this case) and the layer below. That is where removing shingles is important as they can wear a hole in metal in a few short years of expansion and contraction. You may fine this hard to believe but a friends house had exactly that problem only six years after the addition of a metal roof.

-- Bob, FL Keys

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JCamp

819 posts in 699 days


#4 posted 04-20-2018 01:28 AM

Thanks guys. I figured that was the case I just wanted to make sure. I don’t intend to remove the old shingles so I was afraid that they’d wear through like ocean had mentioned.
Thanks again

-- Whatsoever thy hand findeth to do, do it with all thy might

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msinc

535 posts in 652 days


#5 posted 04-20-2018 01:46 AM

I have seen it done where they leave the shingles, but I would never do it that way. Why leave all that extra weight on the roof and trusses? The boards you put down that run across are called “purlings” and you don’t necessarily need them IF the roof has sheathing {plywood}. I built a hunting cabin a few years back and I used purlings. I used 2X4’s across the roof trusses and it worked perfect. If you use boards that are less than 2X4’s you probably wont be able to walk on it and you need to to screw the metal down. If the roof has sheathing and you still want to use purlings you can pretty much use just about anything, e.g., 1X4’s would work fine because you can walk on the sheathing.
Every time I have seen metal put down right over the sheathing they always applied a layer of either felt or most of the time this synthetic rubber covering. You don’t need any of that with purlings. It goes without saying that a standing seam metal roof is the better design, but anything metal is way better than shingles.

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tealetm

97 posts in 1006 days


#6 posted 04-20-2018 02:35 AM

Purlins the correct term.

If you are going to leave the shingles on- which is fine if there’s currently only one layer). Yes you should use purlins to mount the metal panels to.

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msinc

535 posts in 652 days


#7 posted 04-20-2018 11:25 AM


.........Purlins the correct term….......
- tealetm

Yes, you are correct. Purlins is the correct term. Thank you.

View LesB's profile

LesB

1818 posts in 3592 days


#8 posted 04-20-2018 05:20 PM

Good advice here but I see one small potential problem. Will you ever have to walk on this roof? If so all those unsupported areas between the purlins will be flexible and can bend and kink under your weight.
If it were mine (and I have done this) I would strip off the shingles, put down a layer of 3/8 to 1/2” plywood or oriented strand board, cover with felt paper, and then the metal roof. Metal roof chill faster in cold weather and condense moisture on the under side so the felt paper or similar water proof barrier is needed…..even if you decide to put the metal over the existing shingles.
Be careful, metal roofs are very slippery.

-- Les B, Oregon

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squazo

109 posts in 1794 days


#9 posted 04-20-2018 08:37 PM

I am actually doing this exact same thing right now. I decided on union corrugated brand. I am using there product Advantage Lok 2. It goes directly over shingles, after you put down a special menbrane. It is also a standing seam roof which means it had no exposed screws. Which means no screw holes to leak. You still use screws but they are overlapped with the next piece of metal. They have excellent 3D videos explaining installation. It was easy to measure. Approximately 2,000 square ft cost me 5 grand. They have a 40 or 50 yr warranty when installed this way even when DIY. I got that in writing. They have allot of different styles to choose from but I chose Ad Lok 2. Good luck.

Once the roof is on my house and out of my shop I will be spray foaming my shop.

Good luck.

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msinc

535 posts in 652 days


#10 posted 04-21-2018 12:59 AM



Good advice here but I see one small potential problem. Will you ever have to walk on this roof? If so all those unsupported areas between the purlins will be flexible and can bend and kink under your weight.
If it were mine (and I have done this) I would strip off the shingles, put down a layer of 3/8 to 1/2” plywood or oriented strand board, cover with felt paper, and then the metal roof. Metal roof chill faster in cold weather and condense moisture on the under side so the felt paper or similar water proof barrier is needed…..even if you decide to put the metal over the existing shingles.
Be careful, metal roofs are very slippery.

- LesB

I agree, the metal roof/temperature difference causing condensation is the real reason for the moisture barrier. If shingle material could wear thru a steel panel you wouldn’t have to worry about no rubber or felt stopping it. Standing seam metal roofing is thicker and it is stronger because of the seams so it can be easily walked on, especially the Union Roofing brand. My roof is a 6/12 in the front and 8/12 in the back and I walk on it without any signs of problems. Now, the so called “five vee crimp” or the ones that require exposed screws…just about all of those are thinner material, I wouldn’t try it. But, then again, you can easily see where the purlins are because of the screws and safely walk if you are careful. Steel roofs are definitely slippery and not for the faint of heart. Wear a life line…it could be the thing that means the difference between seeing another birthday and pushin’ up daisies!!!!

View d38's profile

d38

108 posts in 411 days


#11 posted 04-21-2018 03:00 PM

Do you live in snow country? I do, and had steel put on a new garage about 5 years ago. Snow slides off and piles up on the driveway. I could add snow dams, but don’t want to screw more holes into the roof. Wish I had shingles instead.
Just something to consider.

View WyattCo's profile

WyattCo

93 posts in 253 days


#12 posted 04-21-2018 06:13 PM

Up until recently, I was a general contractor. The only time I used purlins was to level out a roof with miner sags. All others, I put felt paper down over the existing shingles and screwed the metal roofing on top of it all.

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MrRon

5089 posts in 3392 days


#13 posted 04-22-2018 05:11 PM

https://www.tricountymetals.com/documents/5V-Manual5-WEB.pdf. This is a good guide to metal roofing.

View laterthanuthink's profile

laterthanuthink

23 posts in 278 days


#14 posted 04-22-2018 05:23 PM

Thanks for the excellent PDF MrRon. I too have a metal roofing project this summer, if it summer ever gets here.

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