Diy shed...flat top acceptable in our climate?

[kevj1085]

Basic question, making a 5x20 wooden shed with 6 ft height. New to this but feel confident. Only issue is lean to roofs intimidate me by the looks of it. I live in desert climate where it rains maybe 8-10 times a year if that. We barely get any. I would feel so much better if the roof could be 100% flat. That way all I would need are side walls flush, rafters straight across (trying to keep rafters from any overhang), then just put the roofing sheet and shingles on and move on. Is this acceptable? I understand rain drainage wouldn't be great with flat, but seeing as how it barely rains and reaches extremely hot temps, I feel the water would dry up in a matter of minutes anyway, or I could always put my mover blower on top of it for an hour until it dried. Is this acceptable practice?

[gooki]

I wouldn’t do it. At the minimum I’d go for a mono pitch roof on the shed.

[Dave1442397]

I've seen the pitch created on the roof by using a special insulation called tapered insulation. This has a preset pitch to slope the water to the drains and is layered above the roof framing. This has the added benefit of further insulating the roof.

[former player]

On a small building you only need a very slight slope to stop water from pooling.  An inch or two would be enough without being intimidating.

[BDWW]

Honestly, sounds like a terrible idea for a couple reasons. Water will pool on any "flat" roof. Shingles are not meant to be flat, they will allow water through if laid flat. They're meant to shed water down on to the next shingle, and off the roof.

Second, you want overhang on your roof. There are ways to build with no overhang, but it needs to be done perfectly to not have any issues. The overhang allows water to drip off away from the wall. With no overhang, water will just run down the wall, and inevitably get in the wall.

[nereo]

Honestly, sounds like a terrible idea for a couple reasons. Water will pool on any "flat" roof. Shingles are not meant to be flat, they will allow water through if laid flat. They're meant to shed water down on to the next shingle, and off the roof.

Second, you want overhang on your roof. There are ways to build with no overhang, but it needs to be done perfectly to not have any issues. The overhang allows water to drip off away from the wall. With no overhang, water will just run down the wall, and inevitably get in the wall.

Agree.  A perfectly flat roof is a bad idea, but you can build something very close (e.g. a 1/12 pitch) that appears flat and eliminates the issues without causing you any additional problems.  If your roof is 6' wide just make one side 6" higher than the other before running the joists across.  Easy peasy.  You don't even need to cut angles for something that low pitched.

For DIYers, always have an overhang of at least 4" on every side with a drip edge.  It's WAY EASIER to build a roof with an overhang than to build one flush with the wall, and as BDWW said you are inviting trouble in.  Even if done perfectly at the time of construction buildings warp nad flex, and a zero-pitch, no-overhang roof is bound to be problematic.

Regarding "how often it rains & how fast it might dry"... a few minutes of standing water is MORE than enough time for it to infiltrate.  If water isn't moving downslope, it will find every pinhole and hairline fracture and wick through it.  Just avoid this entirely and build a slight slope into your roof.

[trollwithamustache]

yeah, there is  no roof out there that is  actually flat. even the flat warehouse or house roofs all slope here and there (engineered) just a little for rain management.

at 5 x 20, I am guessing you want to take a corrugated roof material along the 5" dimension and have it stick out a little on each side? At a minimum you can build the frame square and flat and add a small piece on one side to raise it up an inch and give you a tickle of slope.

It will rain on you at some point, and a truly flat roof will pool at the roofing material seams and leak into your shed. Thus un-shedding it in a philosophical kind of way.

[Cadman]

5'x20'? Interesting dimensions. If that's exterior, and you're using 2x4 wall framing, you technically could get away with 2x4's on edge as your roof members (4.5' span). I'd personally go 2x6 for the structural benefit, but also because it will look a little more pleasing.

I'll be the dissenter and say that you absolutely can go 100% flat in this scenario...IF you use a continuous roof membrane, like rolled rubber which is available at most big box stores. Give yourself a 6" overhang all around, bring the rubber over the sides and use termination strips around the perimeter. Peel and stick roofing may even work here given what you're going for.

I'd also recommend optimizing your dimensions to take advantage of stock material sizes and availability. For example, 6' lumber is cheap and plentiful, and would give you the 6" overhang on each side, but you may have to do more sorting to get good pieces compared to 8' or ~92" pre-cut stuff.

Same goes for the roof. You could increase spacing to 24" OC with 2x6's if you went with 5/8 or 3/4 substrate. Etc.

[Papa bear]

5x20 sounds like a terrible size for a shed.  Walk in closets usually are minimum 6’ wide, so basically you’re building a large hallway.   You really don’t get much usable space here. Is this going to be next to an existing structure? That would make sense if it is and would be accessible like a “reach in” closet.

As for the roof, putting a pitch on it isn’t rocket surgery.  This isn’t hard to do. Look up a few things online for cutting rafters for the angles and birds mouth cut.  If you’re building the rest, build it right and spend the extra hour doing some more research.


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[nereo]

... I had similar question about the 6' height.  Since i'm 6'5" I can't imagine wanting to build a shed I couldn't stand up in.
::shrug::

[former player]

 A shed that's only 5' wide may fit the space available.  And can be very useful: if it's the long side that opens the shed  doesn't need to be high because no-one needs to step into it.  Everything in the shed is on view rather than getting hidden behind other things.  It could be great for bikes and garden tools, for instance.

[affordablehousing]

this meets my three strikes rule - three questionable ideas in one little project, and I'd start over-

-6' high, that's awful, you want some head clearance, and with most framing materials coming 8' tall, that's just wasteful.
-5x20, just bad dimensions, you won't be able to put stuff too deep to have access if you're moving down one side or the middle, unless this is a lean-to for firewood, in which case the dimensions are still bad which leads to-
-flat roof, ridiculous! Unless you want to think of this as a very temporary structure, like 1-2 years, this will rot out quickly.

There's a million very simple shed videos on youtube, pick any and use it as a guide. overhangs and pitch can cure a lot of sins in building.

[Steeze]

I'll echo others - you will want some overhang and a pitched roof. Can be almost flat - but should have a couple inches of pitch at a minimum. If it is nearly flat then you will not want to use shingles, but a continuous membrane as others have stated - rubber or corrugated poly carbonate (plastic) would be OK.

Dimensions are a bit odd too - I would go 7' high at a minimum and 6' wide at a minimum. If you have the room I would do a full 8'x8'x20' since most lumber is 8' anyhow. 5' might be OK if you will only put stuff on 1 wall.

[trollwithamustache]

I'm imagining a series of bay doors along the 20' side, and that seems maybe nice for a "big closet" style shed. So not so crazy?

[GuitarStv]

If you're thinking of something that's 5x20 . . . why not get a shipping container?  20 ft general sized containers are almost exactly those dimensions, and (although they've got a flat roof) they're also waterproof.

[ender]

You'll be happier if this is 8 foot walls.

Makes it easy to get presized studs and you can just use 4x8 sheets of plywood without cutting them and even the precut siding sheets.

And 6 foot walls with a flat ceiling will suck for anyone who is close to 5' foot 8" or taller.

[nereo]

Maybe the OP will come back with more information. 
Plenty of good advice here, plus a lot of quesitons that could help the OP decide what makes the most sense in his/her situation.

[kevj1085]

Apparently I'm late to my own party! I live in a hoa community and rules state your shed should be 20 feet back from the perimeter wall gate, should be against your house, and can't go more than 7 feet high. I have built my shed about 10 feet away from the gate, it is against the perimeter wall not house (way more convenient there), and since my wall isn't more than 6 ft high where the shed is, I can't allow it to go any higher. Also, the width of the walk way leading from my gate to the back yard is only 10 feet wide. I changed the dimensions to 4x20 exterior, and since I have kept the shed about 6 inches away from the wall, this leaves about 5 feet of walking space or less between the shed doors and the house wall. It's a fairly narrow walk way. This shed was not made to house wheelbarrows and serious tools etc. It was merely to clear up our garage from the holiday boxes so we could free it up to split the garage half for our gym equipment, the other half as a work space/hang out with a couch, tv, etc. The size, even as 4x20 with about a 5 foot entry, is more than enough for me to just put boxes in.

[former player]

That explains a lot about your proposed dimensions.

With a proposed length of 20 feet I would strongly suggest two different 5 foot entries: future self will thank you for ease of access and cleaning.

[kevj1085]

That explains a lot about your proposed dimensions.

With a proposed length of 20 feet I would strongly suggest two different 5 foot entries: future self will thank you for ease of access and cleaning.
I made 2 48 inch doors, with 48 to the left and right of both.

[Fishindude]

I'd do a real low slope roof on it and cover with white EPDM rubber membrane roofing material.