Shed roofing - metal vs shingle?

[brass89]

Hi all, was hoping for some input or tips regarding roofing. It's a shed but will also be used for a workshop. Will likely be heated as needed (not permanently heated). This will be for an 8x12 with a 7-8/12 pitch which I understand can be a little steep on a smaller roof.

So far general info says metal is more expensive than shingles but it seems around the same to me. Bundles of shingles (3 to a sq - just under 33sq ft a bundle) are around $25. I can get imperial rib steel sheets 3ft wide x 12ft for just under $25. To account for a slight overhang on a gable roof at the eaves and projection past the front and rear, 5 sheets of steel is $125. 6 bundles of shingles is $150 (3-tab, not architectural or anything fancy). Maybe a 7th bundle for starter row and ridge cap.

I'm thinking steel will be easier to put up but can't seem to find any consensus on what method provides a leak free roof. That's my biggest concern. I've done rough steel roofs on pole barns and stuff and they usually leak due to using second hand sheets or whatever fasteners were on hand. (aka, not the 'right' way).

Was planning on 6ft long rafters of 2x6, held with osb plates at the peak and no ridge board spaced 24" oc. Should I put down osb sheathing on the rafters, cover with roofing paper, add purlins and attaching steel panels to this? Should I put the purlins down first, then the osb, covered with roofing paper and the steel sheets directly on top? Should I forego the osb and just put bare purlins and steel (like a polebarn) and roll the dice with condensation issues? Or just scratch the steel all together and go with shingles?

My other issue is this - the steel is very limited in my area. I have choices of plain corrugated which I'm concerned will rust prematurely. Or galvalume type imperial rib painted (preferred). I don't seem to have access to all the nifty pieces that help complete a steel roof, like ridge caps and fascia trim pieces I've seen that cover the edges of the steel and direct any water/snow back onto the roof and down to the eaves. The only ridge cap they seem to have is a rounded top with a 1.5" radius which looks to me like a pain in the **** to seal at the ends of the ridge. I have a local farm type store with some steel, or I have the orange or blue big box stores which have very little options in stock. Most everything is mail order from metal sales or some place and it's like a month out. I want this thing up and done in the next week, not be trying to roof on halloween.

How have you guys done your roofs? For those who have done steel panel, how did you do it so it doesn't leak or drip condensation? Out buildings it's acceptable to stop 'most' of the water and a few drips aren't a big deal but I'd prefer a place for my tools to be water tight. Thanks.

 

[redrunner]

A lot faster to put up did about 60 foot of the house in 1 1/2 screwed top and bottom then went back and screwed the middle sections. That took another 45 minutes to do that. No were near as fast with shingles. Plus you save time if you have to replace it by not having to strip the place. We had the new tar paper down and just had to place the panels. One on top walking the ridge, one on planks at the bottom and two bringing the panels.

 

[Woody610nb]

I just did my 30 x 34 shop with steel, screwed to purlins. No osb, but insulation under the steel. Where are you located? I paid $.66 a sq. ft. for the steel. painted black. You really do need ridge cap to seal the cap.

 

[brass89]

Thanks redrunner. I've also put up shingles but it's been awhile. As I recall around 4 roofing nails per shingle, which adds up. Especially since I'm using a framing hammer (no air nailer).

Woody610nb, I'm in the midwest a little south of st louis. A fair amount of rain, moderate snow in winter. I think the imperial rib panels I was looking at run around the same as you paid, 3ft coverage wide by 12ft long. (figured I'd cut each panel in half for the 6ft long halves of the roof). They're 24.60/panel so.. $.68-$.69 sq ft. The local ones are white, they said they had other colors if I wanted to special order. I'm good with whatever lol. Yea I know I need a ridge cap, my choices are limited though. Here's a pic of what's avail. It's either this (and try to figure out how to seal the round radius at the end of the peak) or jerry rig a cap by cutting down a regular panel and bending it over the ridge.

 

[brass89]

I've also never bothered with seal tape at the seams when screwing panels down, maybe that will make a difference as well. Hadn't planned on insulating the shed roof, and it won't stay heated like a nice shop or garage. Might run a heater out there if I have to work in there during colder months. Just trying to avoid it turning into an indoor shower.

 

[Cyberbear]

For an 8 x 12 shed, 2 x 4 rafters are adequate, but 2 x 6 is better if you wish. With something that small I'd just sheath over the rafters and not bother with purlins at all, and it gives better support and is the best for nailing or screws.
Metal or shingles: both are good depending on the various factors such as cost, longevity, wind, pitch, etc. Personally, I'd go with the metal using a standing seam and screw it down.
Metal also provides a superior fire resistance and usually holds up well in the weather. If screwed down properly and a high pitch, the wind should be no problem.

 

[arz71]

Where I live they have sheet metal (metal building roof) materials like left over or over stock.

The sheet metal itself is not that bad expensive the sheet metal screws are expensive like $40-$50 a bag.

I bought a 30x50 shop building (metal building/insulated with dual doors), but have an old chicken coup building. They put a concrete floor in it and it is about 22x20 or so.

All of the metal for the roof was like $300 or so I would see if you can find a place that has left over or over stock.

 

[readhead]

Sheet the roof and put shingles on it. Even hand nailing you should be done by lunch.
If it is not heated condensation should not be a problem.

 

[volleyball]

I did my 12 X 14 shed with a 2/12 pitch shed roof. 1/2" foam board underneath mostly for sound deadening. Ran the joists across the roof to eliminate purlins and less notching as it follows the pitch. 2x6 for rafters. I did put one perpendicular across the center underneath as insurance. I have had over 18" of wet snow up there over the years.
I used the 3' wide panels. They were scraps from a roofing company so they were over 13'.
Be sure to used the neoprene washers in the top of the ridges, not the valley. You use the valleys on walls only.
You can overlap panels and not worry about water if you overlap at least 6". I have a temp situation with the same low pitch and it has not gotten wet under there in 4 years and the panels are just sitting there with some boards on top, not one screw or nail.
A roll of flashing and you can make your own trim.
If you need a ridge cap, any one is fine, they should have some for vented roofs in stock.

 

[rieferman]

Many will tell you how it's done, but I would urge you to just pick up the application guide. Google Everlast Roofing to find an industry leading example. This will teach you proper techniques for today's materials. For example, fasteners now have EPDM rubber washers (rather than neoprene which is prone to UV failure) and fastening on the flat (not rib) is often the manufacturer recommendation for residential gauge projects.

 

[SARG]

And with metal roofing screws are definitely preferred over nails.

The nails will become loose over time .... I have a 40 x 60 garage with a leaky roof to prove it.

When I built the technique was nails on top of the ridges ...... which creates a real PIA when trying to remove snow ........ today they state screws on the flats.

 

[brass89]

I wish they still had discount metal around here. They used to, either miscuts or cover pieces from bundles. No place locally (within around 50mi) has those anymore. Everything is full price and when I asked they said it's just the way of things. Cutting machines are getting more efficient and less damaged pieces etc.

I appreciate the idea of going by industry code, but I'm not all that impressed. Seems like the industry keeps changing, but I'm not seeing the upsides. Back in the day, when things were simple they just had 'paint'. Or 'wood'. Now everything has a specific application - well this is floor rated sheathing and this is super duper weather seal and this is maintenance free all weather siding or whatever. Everything is guaranteed for 25, 50yrs or a lifetime. The only stuff I see actually lasting 50yrs + is the old stuff that wasn't 'rated' for anything. Not trying to be cynical, just what I've noticed. If I knew how to build like they did in the 20's (and had access to materials from then) I'd opt for that. Can't tell you how many roofs I've seen leak with 50yr 120mph hurricane rated shingles, this protective layer and that protective layer..and within 3-4yrs, it leaks. Far more often than they should, whether it's the materials or cruddy work.

On another note, I had this idea but not sure I've really seen it referenced. If using sheathing (like osb) under the metal panels, people warn against relying on the sheathing to screw the metal to. Obviously screws sink better in purlins. If the order of things is rafter, sheathing, roof felt, purlins, steel - then the purlins ride on top and any condensation dripping to the covered sheathing becomes trapped by the horizontal purlins. Some have cut a bunch of little grooves to give that moisture someplace to drain.

What about something like the diagram (yes, it's rough and not to scale). 2x6 rafters, purlins inset into 1.5" deep notches in the rafters making them flush with the rafters. Sheathing over this, covered with roofing felt, then the metal sheeting. Screws would go down through the metal into the osb, but would grab the purlins beneath the sheathing (no pull out problems like screwing to sheathing alone). This way the purlins aren't creating a horizontal dam along the roof to trap moisture.

I know there's better ways of roofing with insulation, solid foam panels etc but I'm still trying to keep it a shed build. It'd be different if it was a house. Just don't want a shed dripping all over a workbench and tools is all. Metal would require the purlins anyway, sheathing the roof in 7/16" osb only adds around $40 to the project - the roofing paper I'll already have since I plan to use it around the walls instead of tyvek. The only real hassle would be notching out the rafters and that shouldn't be too bad. Understandably this takes away from the 'meat' of the 2x6, but would drop the height of the 2x6 to 4" (from 5.5") wherever it's notched. Still taller than a 2x4. Thoughts?

 

[brass89]

I've seen rec's for both screws on ridges and screws on flats.. Thought screws on flats was for some sort of standing seam with interlocking ridges. Why are screws on ridges a pain in the snow? Anymore than screws on flats? I'd think the screw heads would pose as drag for snow either way. Maybe using a roof rake to knock snow off?

 

[volleyball]

You don't need to rake it and the screws are not enough to hold snow. The washers are the weak point whether they erode or the screws loosen up over the decades. The screws in the ridges also help with eliminating wicking if your panels overlap.
OSB is a waste of time and money in a shed. Won't add needed strength as the metal is enough to walk on, or hold a lot of snow.
You will want a sound deadener if you have it anywhere near a bedroom window. Mine is about 25' away and its makes a world of difference.

 

[brass89]

Originally I was going to skip the sheathing but I couldn't find any way to successfully put down roofing felt under the metal without it. Not relying on it for strength or snow load, that's why I thought 7/16" would be ok. Basically just a backer for the roofing felt as an additional protection from condensation forming on the metal inside. The only other osb might be shelves, looking at 3/4 treated ply for the floor and smartside 4x8 panels for the walls/siding. I guess that's a sort of osb.

 

[volleyball]

As I said, I put Dow blue foam under mine. I have no condensation that I have ever found. Either the foam is enough or it runs off on top of the foam to the outside.
I have another area that is a temp situation that has 3/4" plywood subfloor with the metal laying on top. The walls are block and it is just dead storage. Been in there when very humid but zero on the ceiling.

 

[brass89]

Hard to tell because there's different foam boards. You said blue, the only blue one I could find was 1/2" thick 4x8 sheets with an r value of 5. Not much info on it, might have to dig deeper. Looks like it has some sort of facing/foil for reflective? There's also another blue-ish looking one by dow but more of a green, says it's r3.3 i think. The greenish blue is almost $12 a sheet here, the blue is almost $15 a sheet. Wish it was closer in price to the sheathing/roofing felt, it's almost twice the price.

Not that I have a need to be or intend to be on the roof much, but how does it hold up? The foam I mean. Just using purlins, metal tends to flex some when you're on top of it. Does the foam board flex or break with nothing behind it? I'm guessing you tacked the foam panels to the rafters/purlins then screwed the metal sheets over it.

 

[volleyball]

It is a shed and any R was good enough. It does make a difference. Been in sheds with dark roof and boards. It was mostly for the sound though.
I have no purlins. I built it with the 2x6's going from side to side. I had the boards long enough from an old roof. Plus no notching. Laid foam on top. Taped seams before it went up so it was 1 piece. Put panels on top and screwed through both. I have 16" spacing so no droop.
Going with foam and metal because the metal is structural, meant that I have less static load which allow me more live load.

 

[brass89]

That's cool, still been trying to picture how you did your 2x6 horizontally without rafters. Is it a single angle roof? Forget the proper name, where one wall is higher than the opposing, no peak.

I'm less concerned with sound, more with moisture/condensation. The doors will be home made so they won't seal like a prehung. Any vents are going to let humidity in and will probably match outside humidity (often 50-60%, maybe a little higher in peak summer). Just need to keep the snow and rain out and would've gone with bare metal inside other than if I'm out there in the colder months and run a heater I don't want to create a rainstorm inside.

 

[volleyball]

Yes it is a shed roof. It was originally against the building and I moved it. It was low because it was to have a deck above it.
To picture it, build a shed floor and box it in. Lay it on top of a half a normal pitched roof framed that is twice as deep.
Porches were built this way. They framed them the opposite of they way you would frame a deck. That way the boards run straight out from the house with a pitch for run off.
If that doesn't make sense, let me know and I'll take a picture on the next sunny day.

 

[brass89]

Gotcha..Makes sense if it came off the side of the house. Not sure I could get away with that for a gabled roof. Purlins aren't too bad, just planning on using some 2x4's. Wish everything was as cheap as the 2x4's lol.

 

[volleyball]

You don't need a double pitched roof for a shed. The only reason is appearance.
If you want gable, rip 2x4 into 2x2 for your purlins and run 24" spacing. You will need wider facia boards because of the extra height. Or build it the way I did. Cut a triangle out of the center point. Add a ridge beam board. It does make the side walls the bearing walls which can make the doors in the front easier to build.