Shed Roof

[Berner]

Getting my materials in order for a wood shed and I'm going back and forth about the roof. The shed is going to be 16x8 with a 2ft overhang on all sides. I will be running 2x8 rafters 16" on ctr. The slope fill be 1.5/12. The two roof options are:

1) Sheathing with 1/2 inch plywood, tar paper and asphalt shingles. Total cost will be roughly $380.

2) Metal roof on top of rafters. Total cost around $500.

I love the looks of the metal roof and for a few more bucks I think it will last much longer. What would you guys do? Is it ok to place a metal roof directly on top of the rafters without sheathing or waterproof underlayment?

Can't wait to stop dealing with the blue tarps.

 

[barnuba]

Getting my materials in order for a wood shed and I'm going back and forth about the roof. The shed is going to be 16x8 with a 2ft overhang on all sides. I will be running 2x8 rafters 16" on ctr. The slope fill be 1.5/12. The two roof options are:

1) Sheathing with 1/2 inch plywood, tar paper and asphalt shingles. Total cost will be roughly $380.

2) Metal roof on top of rafters. Total cost around $500.

I love the looks of the metal roof and for a few more bucks I think it will last much longer. What would you guys do? Is it ok to place a metal roof directly on top of the rafters without sheathing or waterproof underlayment?

Can't wait to stop dealing with the blue tarps.

You just need to add purlins that run perpendicular to the rafters - you fasten the metal roof directly to the purlins - no sheathing or underlayment needed.

 

[MJFlores]

I ran pressure treated strapping across the rafters every 2 feet down, and screwed the metal roofing to that. Metal is the way to go...lasts forever and snow slides right off. When building a wood shed remember, a wood shed doesn't have to be air tight...you want plenty of air flow to help dry wood. Mine is open in front, with rough cut hemlock board from top down spaced about a half inch for air flow...wood dries nicely in there yet it's enough to keep the rain out.

 

[Berner]

I ran pressure treated strapping across the rafters every 2 feet down, and screwed the metal roofing to that. Metal is the way to go...lasts forever and snow slides right off. When building a wood shed remember, a wood shed doesn't have to be air tight...you want plenty of air flow to help dry wood. Mine is open in front, with rough cut hemlock board from top down spaced about a half inch for air flow...wood dries nicely in there yet it's enough to keep the rain out.

Sounds good. Do I need to run strapping ontop of the rafters or is blocking good enough? Inbetween the 2x8 rafters I was going to cut another 2x8 16" long block that will run perpendicular to the rafters flush on the top and bottom. I was going to fasten the metal roof to the rafters and blocking. What do you think?

 

[Boiler74]

First, if using PT wood make sure your fasteners for the metal roof are rated for it. This new PT wood eats fasteners not properly treated for it.

Second, I would just run 2x4 purlins on top of the rafters. A heck of a lot faster than blocking between the rafters. And you'll have to do a lot of toe-nailing if you want your blocking to be in a straight line. You want that straight line so you know where to screw down the metal. Also, a 2x4 flat purlin gives you a better screwing surface and is more forgiving if you wander a bit with the screws off your line. You'd have 3.5" rather than 1.5" to hit.

Finally, if you are out in the open metal makes sense. Under trees that can drop limbs a conventional roof will hold up to that a bit better.

 

[Michael Golden]

You can span your rafters farther apart than 16" with metal. I went 3' with mine and 2x4 purlins every 16", I'm sure this depends on snow load though. At work they built a lean to off our 40 x 60 pole barn, it is a 4/12 pitch and 12'. I found this part about the lean to different, they spread the 2x8 rafters 6' apart and put 2x4 12" on center on edge! This lean to was built 20 years ago and doesn't show any sag.

 

[Hogwildz]

1.5 in 12 is not much of a pitch. You may want to consider a steeper pitch.

 

[Lumber-Jack]

For metal roofing rafters 24" on center with 1x4 strapping (purlins) is pretty standard around here, with the strapping 16" on center. I can't see any advantage to using 2x4s for strapping unless your rafters are further apart then 24". You'll save some $$$ using 1x4s over 2x4s.
One trick you can use for helping the metal roofing go on way faster and easier is to pre-drill the screw holes while the metal roofing is still in a stack. Just make sure the metal roofing is all stacked exactly on top of each other figure out exactly where the screw holes need to be to line up with the strapping and drill the holes through all the sheets at once. It makes it a lot easier to put the screws in once you get the sheets up on the roof. This is how the pros do it. ,

EDIT; For anything but a woodshed I would still put felt paper or some membrane on the strapping directly under the metal. Under the right moist and cool weather conditions I have seen water condensate on the bottom of bare metal roofing and watched it rain under the roof as it warmed up and the sun hit the metal roof. If this ever happen under a woodshed it wouldn't be a big deal.

 

[Bushfire]

As everybody has said - metal roof with strapping perpendicular to the rafters. Only problem I had was having to wait for delivery on the metal roof. My local HD and Lowes don't stock it, so I had to special order it at HD and took about 2 weeks. It also arrived a little damaged, but it's barely noticeable (it's a woodshed) and I got about 50% off for my troubles.

 

[BurnIt13]

I just rebuilt my own garage with a 1.5/12 pitched roof. Aside from the fact that it had 5 layers of roofing on it, the main reason it failed was because the top layer was shingles. The slope isn't steep enough and water got under the shingles.

Even though it is just a shed you are building, the roofing system will fail if you shingle it. To do it right to protect the sheathing you would need to use Ice & Water which would just be ridiculous for a shed roof. Overbuilding it just to put shingles on will cost as much as metal.

Other options:

1. Rolled Roofing. Same ideas as shingles but 3or4' wide rolls of asphalt roof that overlap each other. The seams are glued together. Not much better than shingles.
2. Rubber Roofing. This is the best idea....but probably too expensive and overkill for a shed.
3. Corregated Plastic. Installed the same way as metal...use purlins instead of sheathing. Probably a bit cheaper than metal though.

 

[Rock Crusher]

Late to the party, but Ondura roofing could be considered as well. It's a corrugated asphaltic fiberglass sheet that comes in a variety of colors. Easy to install, long lasting, snow slides off easily and cuts with a circular saw. I believe it to be cheaper than metal, but not certain.

 

[Longstreet]

For residential construction, I believe 4/12 is the flattest slope you can use asphalt shingles on. You could probably get away with less on a shed, but never 1.5/12, that just isn't enough slope.

 

[phishman]

another crazy idea -- use some clear polycarbonate panels and make a solar wood kiln:

http://www.builditsolar.com/Projects/WoodDrying/wood_kiln.htm

i second the advice against using shingles. have some old structures here with flat(ish) asphalt roofs and every single one of them needs a new roof. shingles suck.

 

[Berner]

Lots of good info here. Looks like I will be trying to increase my pitch and running some purlins across the top of the rafters. Pics to come after Turkey Day.

 

[Rebelduckman]

As mentioned earlier, 2×4 pearlings are overkill. I've roofed several houses and all we used was 1×4 strapping

 

[peakbagger]

My shed roof is close to 1/2"/12. I had left over shingles, plywood and tarpaper when I built it so I did shingles. Its been 15 years and no leaks. Its a wood shed, even if it does leak in heavy rain who cares.

 

[Lumber-Jack]

My shed roof is close to 1/2"/12. I had left over shingles, plywood and tarpaper when I built it so I did shingles. Its been 15 years and no leaks. Its a wood shed, even if it does leak in heavy rain who cares.

I would care. A leaky roof will eventually rot your plywood.
It's true that a 1.5/12 pitch isn't enough for shingles on a plywood roof, but it would be fine for a woodshed with a metal roof with open purlins (strapping).

 

[peakbagger]

Free plywood, no trace of leaks in 15 years, it makes sense to me. I keep an eye out for metal roofing and currently have some for temporary pile covers, if the plywood rots out before the shingles wear out, I will install the metal.

 

[shoot-straight]

down here, pole buildings have rafters 4' oc and 2x4 purlins 2' for metal roofs. if your going with 16" rafter spacing, 1x's would be fine for the purlins. my pitch is pretty flat too, i have no issues with snow or rain.

 

[bob95065]

I'm building a similar shed. My shed will have a covered area that is 24'x8' with a 2' overhang for a 28'x12' roof. If I stack 6' high I'll have 9 cords under cover. We burned about 3 1/2 last year (first year in house) so I'll have 2 years stored with a little margin.

I put the joists 4' OC with perpendicular blocking spaced 2' OC. I priced materials and I am going with a combination from Lowes and Home Depot.

I am using 2'x12' galvanized metal corrugated roofing panels from Home Depot. They are $22.46 each: http://www.homedepot.com/p/Gibralta...vanized-Corrugated-Roof-Panel-13474/202344563

I bought wiggle wood and bolts at Lowes. Their picture is terrible so this is a picture from Home Depot :http://www.homedepot.com/p/Kelleher-3-4-in-x-1-1-2-in-Redwood-Wiggle-Moulding-R632/202071725
The Lowes prt # is 12564. An 8' length is $2.55. The advantage of wiggle wood is you can put the screw at the top of the wave on the corrugation which will reduce leaks.

Lowes had the best price for galvanized roofing screws with a rubber washer: http://www.lowes.com/pd_579015-2890...5&UserSearch=579015&productId=50209965&rpp=32
$12 for a bag of 100.

I'm putting the roof on today. I'll get some pictures to you later.

I hope this helps,

Bob

 

[billb3]

I'm building a similar shed. My shed will have a covered area that is 24'x8' with a 2' overhang for a 28'x12' roof. If I stack 6' high I'll have 9 cords under cover. We burned about 3 1/2 last year (first year in house) so I'll have 2 years stored with a little margin.

I put the joists 4' OC with perpendicular blocking spaced 2' OC. I priced materials and I am going with a combination from Lowes and Home Depot.

I am using 2'x12' galvanized metal corrugated roofing panels from Home Depot. They are $22.46 each: http://www.homedepot.com/p/Gibralta...vanized-Corrugated-Roof-Panel-13474/202344563

I bought wiggle wood and bolts at Lowes. Their picture is terrible so this is a picture from Home Depot :http://www.homedepot.com/p/Kelleher-3-4-in-x-1-1-2-in-Redwood-Wiggle-Moulding-R632/202071725
The Lowes prt # is 12564. An 8' length is $2.55. The advantage of wiggle wood is you can put the screw at the top of the wave on the corrugation which will reduce leaks.

Lowes had the best price for galvanized roofing screws with a rubber washer: http://www.lowes.com/pd_579015-2890...5&UserSearch=579015&productId=50209965&rpp=32
$12 for a bag of 100.

I'm putting the roof on today. I'll get some pictures to you later.

I hope this helps,

Bob

That's what I replaced my father's shed roof with when it rotted but I didn't bother with the wiggle boards
the original roof was plywood and three tabs. 12/12 pitch (or pretty close to it).
I figured the panels would rust but they haven't.
The panels weren't $22 each ten years ago either.