tin roof over shingle question.....

glennster

Well-known Member
looking at getting a tin roof put on an old tool shed at the other farm. roof has a planked deck, not plywood, and old shingles on it. one of the roofers wants to just install nailers on the old shingles and screw the tin to it. i am kind of leaning to getting the 30 yr old shingles torn off and installing the tin over that, using the nailer boads on top of the old roof deck. any thoughts?? btw shed is about 25 x 50. not a pole building.
 
I would remove the shingles if there is more than one layer. If just one I think either way would be fine. I prefer to remove them anyway, but that's just personal preference. On the house here there were 4 or 5 layers of shingles on some roofs and the top layer didn't hold well because the nails were not penetrating to the wood. It cost a lot at the dump to get rid of all of that and start over but it's better now.
Zach
 
I"ve always torn them off. It allows for a smoother appearance of the new tin. On an older building, extra weight of the old shingles may be a factor in the future.
 

Good point about it bending the tin roof. If there is only one layer of shingles, snap chalk lines 2" apart running from the ridge to the eaves and use a Skilsaw with the blade exposed just enough to cut the shingles. Pull out the 2" bit of shingles and nail your stringers there. If there is only one layer, no reason to pull them off, they'll add a bit of insulation from summer heat on the roof.
 
Had a tornado tear up my roof on house about ten years ago. to tear it off and put new shingles was more than putting tin over the old roof. wanted a metal roof anyways, they put 1x4 s down and screwed the tin on. The house is now cooler and warmer in the winter. as long as the nailers are straight the roof will be also.
 
I just had the house done with metal. It cost more than shingles, not the fancy metal just the same as on pole buildings. But I'm not dealing with shingles blowing off ever again ! I had 4 estimates and ALL of them agreed in that they tear off the old shingles. Only 1 layer. ,use screws and put vapor barrier down first. You can also then repair any bad spots. The one I went with also in addition to tearing off the old installed furring strips to get good screw holding.
 
We have done a lot of roofs with steel over and we have not always removed the shingles. We remove them around the perimeter and then we screwnail 1x4 every two feet and close in all ends withthem. We then screw our steel sheeting to the 1x4's. If there is more than two layers of asphalt shingle we would remove them,as long asthe shingles are flat we go right over..there is some insulation value and sound deadening by leaving the old ones on..it is usally up to the customer if they want the cost of removal or just going over. A steel roof over shingles won't fail.
 
Faulty installation is the only reason for shingles to blow off. And the only guarantee with metal roofs is that they ALL leak.
 
I had my barn re-roofed. East side was asphalt 3 in 1 and the west had corrugated galvanized over old wood shingles. They stripped it all and ran felt paper then the new metal.
 
I re-roofed my riding arena, barns and lounge with painted steel (about 23,000 sq ft). The roofer put 1 x 3 (rough cut) nailing strips over the shingles and installed the metal. That was a couple of years ago, so far NO problems. I wish I'd gone with steel when I built the complex but my wife didn't want the noise of rain on metal. The shingles do a pretty good job of dampening the rain noise on the new roof.
 
Over top is cheaper, don't have to pay or take time to remove old shingles and you don't have the mess from shingles everywhere. Just had the house done a couple years back. Contractor crew ran 2x's across the roof like a ladder over the shingles then screwed the steel right on that.

Here are some pictures, lower porch section was done a year or two before rest
a224518.jpg

a224519.jpg

a224520.jpg
 
Make sure they nail the boards to the rafters not just to the plywood. The whole tin roof can peel off of it isn't fastened down properly.
 
Don't even think about the R value you will get from the old shingles It's 0.44. Do some research and see how many steel manufacturers will guarantee their steel roofs over shingles. I would never even consider putting steel over old shingles. That's the way the house I live in was done just before I bought the place, I pray every time the wind blows. One good thing about leaving the shingles on you will never know how bad the roof boards are. The old roof boards will be pretty bad after 30 years with shingle on them. Take the shingles off, then you will probably have to put 5/8" plywood over the roof boards. Then if you read the manufacturers instructions for the steel, you will find he recommends a shorter fatter screw that will hold better in the 5/8" plywood. I would take the old shingles off,probably have to put plywood on, then the steel. Don't let those Amish just bend the steel over the ends of the building, there's a piece of metal made for those ends.
R values.ABC supply

Fabral

abcmetalroofing

another one
 
My thought is fire. Any firefighters out there with experence trying to put out a fire with tin over shingles? I would think a shed would be different than a home in that reguard. joe
 
I have some pics of a house with the metal over the shingles and a fire in between them from a wood burner chimney fire.

I will post them Saturday.
 
I'd want 2x4 Nailers screwed into the rafters.1x Nailers would tend to check and split over time being under that hot steel in the summer.I also prefer to strip off old roofing and not keep adding more weight,plus it makes for a better looking job.
 
More than anything I would remove the old shingles because of the weight. With the shingles there if you ever had a leak you could never find it because it would drain to another spot.
 
I was looking at a steel roof for house. The roof I was looking at had the hidden fasteners and they would only grantee the roof if you striped old shingles off.
 
I've heard all the 'stories'. I have always put metal right on top of the shingles and screwed it down.
 
How much do the old shingles weigh, and how much more weight are you adding with the steel?

I will never put a second layer of shingles over an existing layer, and I would never put steel over shingles. Old shingles are just unnecessary weight that add no strength. Sure, the roofer will give you a much cheaper quote if he can skip the tearoff, but do you want it done cheap or right?
 
Neighbor decided to put steel over shingles using nailing strips on his house. He didn't have any leaks before he started but he had two leaks when he finished. It took him 2 years to find the leaks.

A contractor told me that he won't put steel over shingles. Applying steel directly over shingles is a no-no according to him. The expansion and contraction of the steel will cause movement so the grit on the shingles will wear right through the steel. Putting steel over nailing strip introduces a whole different set of problems. He removes the shingles, puts down a waterproof membrane and then puts down the steel sheeting.
 
My concern about not removing the old roof is how to get air circulation to the nailers between the two roofs. I'm not sure how much value a 75 year steel roof will have if the nailers holding it down rot out after only 15 to 20 years. However, if you don't intend to stay there that long, it won't be your problem to fix it.

Our local building inspector now requires all old shingles to be removed when installing any new roof. It costs more, but the next owner has a better idea of what he's actually buying.
 

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