Metal roof over shingles roof.

clemsonfor · Aug 4, 2019

I'm sure this has been discussed but this is my go around for it.

So let me hear your suggestions, things to avoid, how you did yours. What trim did you use on sides, is it a mistake to not use trim on your sides. Metal directly over overlay, use perlins over felt, did you run two layers one horizontal and one vertical for air movement, single layer of perlins vertical for air movement, just horizontal. Did you do a two part chimney flashing, the lower lever then a cap layer or just a single layer and silicone to chimney.

I am contemplating this and probably going to redo my roof at my farm house (second home). Want to see what others have done, I don't want to spend a ton on all the fancy trim if not needed , and what pitfalls to avoid.

So let's hear what you have done, DIYer's guys @EddieWalker and other builders.

Granthol · Aug 4, 2019

I wouldn’t lay right over shingles. If your decking is good you could lay down felt, I’d use 30 lb not 15, and attach to the decking. I’d at least use a bird stop on the ends to keep out birds, and other things that could get in there. If you don’t care about the trim it’s not necessary, it’s for show. Seal up the rake and eaves no matter what you do to keep squirrels, birds, bugs etc from building a new condo.

BoylermanCT · Aug 4, 2019

I'm doing metal roof on two shed right now. One is an existing shed and the other is new construction. I am stripping off the old shingles and putting down new felt and the metal goes on that. On the new I am putting down 5/8" OSB for the decking, then felt and metal roof. For trim I am using drip edging at the bottom and up the sides, and will caulk where the roofing meets the drip edge. I am also using the foam filler strips to fill in the gaps of the roof ribs so bees and such can't get in. They have denver style trim for the roof edges. If this were my house I would use it. But on sheds there is no need.

TractorGuy · Aug 4, 2019

I contemplated the same but couldn't bring myself to do it. I ended up having my shingle roof stripped and went back with high end shingles. Glad I did too. We have a big live oak hanging over the house. Acorn would have driven me crazy.

I got estimates and two out of three contractors wanted to go over my existing roof. One estimate for metal and the other for shingles. The metal roof estimate was a couple grand higher than the contractor that stripped the roof and did a proper reroof.

Not sure about your state but FL doesn't consider it a reroof unless it's stripped and renailed to current code. They allow you to roof over existing shingles one time but it isn't considered a new roof.

Some insurance companies require houses to have a new up to current code roof every 25 years.

clemsonfor · Aug 5, 2019

This is a very rural area. And there is one OLD layer of three tab shingles on this roof.

I am going to do the work myself. I know screws are expensive and the trim will add up depending on how much you go with. But just one side of the roof I ran some quick numbers and not considering fasters for either style. Architectural shingles cost 20-25% more than me buying galvalume 5 rib steel roofing panels to do the same area. For me it's hard to see useing shingles to do it when metal is very similar priced. They will be closer to the same price once trim for the given area is purchased.

EddieWalker · Aug 5, 2019

The 5 rib metal is usually quite a bit thinner then the 4 rib metal R panels. You need to know how thick the metal is before deciding if it's cheaper then shingles. Here, I can go to a metal building company called Mueller's that has 26 gauge R panels that cost less then the thinner stuff at Home Depot and they will cut it to the exact measurement that I want it. They also sell all the trim, flashing and valleys that you need, along with screws. I show the sales guy my plan and we work out what I need. If he suggests something that is new to me, or that I don't understand, he explains it to me so it makes sense. I don't do a lot of metal roofs, or any roofs, but when I do, this is where I go. I would look for a company like this in your area.

R Panel - Mueller, Inc

Installing purlins over a single layer of 3 tab shingles shouldn't be a problem unless there are other issues. The purlins should be 4 feet or less a part from each other and they need to be perfectly flat. The longer the purlin, the easier it's going to be to keep it all flat. The purlins need to be attached directly to the rafters or trusses. You could probably get away with 1x4's for this, but I would use 2x4's and 4 inch screws if I was doing it.

I would also cut open the ridge so there is air flow out of the attic at the ridge. This is going to be a pain to do, but it's really important to have the best air flow possible under the metal and over the shingles. Then install a ridge vent over the metal.

Metal roofs are not hard to install, but like everything else, you need a solid plan and you have to take you time to make sure it's all done right. Measure from the edge of the first panel to the edge of where you will end, top and bottom, to make sure that you are are staying parallel while installing the metal. Put the screws where the manufacturer says to put them. Mueller wants them in the flat of the panel, but enough people on here have commented that where they bought their metal, installing the screws into the top of the rib is how their supplier says to do it. Either way, never over tighten the screws. Snug so the rubber bulges just a bit, and then stop.

Buy all new vents and be sure to get the proper vent sealer for the vents.

Is there a brick chimney to deal with? They are where a lot of issues happen!!!

Diggin It · Aug 5, 2019

I did 5 rib over shingles that were leaking. I had tried to repair/patch the shingles a few times with no luck. Not about to do a full tear off, no money for that. One by fours were nailed down through the shingles into the old plank decking. Panels screwed to them. 'Mini corner' trim along the sides with eave drip edge along the eaves. Valleys, transition trim and Ridge Caps for those areas. Chimney was flashed and caulked.

No leaks in 4-5 years so far, who knows over the long term.

No change in noise during rains.

Don't want to think about large hail, though I'd imagine it would only be dimpled as opposed to shingles being penetrated.

Side benefit is no shingle grit plugging up the gutters.

For those who have the big bucks and the need for appearance, there are metal panels that look like shingles. Not sure what the installation methods are.

atsah · Aug 5, 2019

Ice and water shield rolled on the roof over the shingles first, then the metal roofing.. I only do out buildings with screw down metal, my house is standing seam, it's the only way to go on a house IMO..

clemsonfor · Aug 5, 2019

EddieWalker said:
The 5 rib metal is usually quite a bit thinner then the 4 rib metal R panels. You need to know how thick the metal is before deciding if it's cheaper then shingles. Here, I can go to a metal building company called Mueller's that has 26 gauge R panels that cost less then the thinner stuff at Home Depot and they will cut it to the exact measurement that I want it. They also sell all the trim, flashing and valleys that you need, along with screws. I show the sales guy my plan and we work out what I need. If he suggests something that is new to me, or that I don't understand, he explains it to me so it makes sense. I don't do a lot of metal roofs, or any roofs, but when I do, this is where I go. I would look for a company like this in your area.

R Panel - Mueller, Inc

Installing purlins over a single layer of 3 tab shingles shouldn't be a problem unless there are other issues. The purlins should be 4 feet or less a part from each other and they need to be perfectly flat. The longer the purlin, the easier it's going to be to keep it all flat. The purlins need to be attached directly to the rafters or trusses. You could probably get away with 1x4's for this, but I would use 2x4's and 4 inch screws if I was doing it.

I would also cut open the ridge so there is air flow out of the attic at the ridge. This is going to be a pain to do, but it's really important to have the best air flow possible under the metal and over the shingles. Then install a ridge vent over the metal.

Metal roofs are not hard to install, but like everything else, you need a solid plan and you have to take you time to make sure it's all done right. Measure from the edge of the first panel to the edge of where you will end, top and bottom, to make sure that you are are staying parallel while installing the metal. Put the screws where the manufacturer says to put them. Mueller wants them in the flat of the panel, but enough people on here have commented that where they bought their metal, installing the screws into the top of the rib is how their supplier says to do it. Either way, never over tighten the screws. Snug so the rubber bulges just a bit, and then stop.

Buy all new vents and be sure to get the proper vent sealer for the vents.

Is there a brick chimney to deal with? They are where a lot of issues happen!!!

I am not sure if this is four or five rib metal. This is from a company that custom cuts and is cheaper than Lowe's just like you said. I have their flyer with prices beside me. It doesn't have a pic or diagram on it but the trim profiles and panel colors. It does say 29 and 26 gauge. Not sure what thickness I was quoted. But the galvanized was $1.70/ft.

As for chimneys yes there is two brick chimneys. A larger one that's maybe 18x 24" or so and one that's about 12" square

As for cutting the ridge. I understand why and how air moves etc. But if I do perlins horizontal from left side of roof to the right of the roof unless you leave gaps where the bits of the boards meet you will get no air flow from the bottom of the roof to the top of the roof since there would be blocks from the 2x4 every four foot. Do you leave say a six inch gap at each but of perlins to allow this air flow?