I’m building a shed, and want a large single door on the end. It’s 47" wide by 74" high (roughly 4’x6’ or 120cm x 180cm), framed like a regular house door would be (header of two 2x boards with plywood sandwiched; joist and trimmer on each side). I’d like the door to avoid sagging, and also be strong enough so when kids inevitably climb on it that’s fine too.
I see lots of patterns for shed doors, for example (from secrets-of-shed-building) the zig zag, with a pair of triangles bearing weight down to the hinge edge:
Or (from artofit but are they the new pinterest or something?) the high single diagonal:
Or rectangles, or exes on the lower or both halves. Does the variety mean it doesn’t really matter?
The shed has plywood sheathing, and I’m planning to have a single panel of plywood sheathing on the door, does that provide enough shear stiffness?
And I’ll probably use 2x4 framing on the back/inside of the door, maybe lap joints for fun though most people seem to just do butt joints, probbly flat against the door though I see some folks putting the 2x4s edge against the door like they’re just framing more wall.
Any experience with sagging or successful doors very welcome, or structural theory to apply here! Thanks in advance.
You’ll notice that those two examples have a different number of hinges. The two hinge door uses a single big z to get the load down to that bottom hinge. The three hinge door uses two zs, one to get the top’s half of the door’s load to the center hinge and the bottom z for the bottom half’s load. That’s really the secret, such as it is.
For a shed door, it’ll probably be fairly heavy and exposed to weather and humidity. So it’ll swell and the weight will fluctuate through the year. I’d go with three medium to heavy duty hinges if it were me and design the door based on that. Then when one hinge inevitably fails, your door doesn’t fall off, it just squeaks for a while until you replace the faulty hinge. With the two hinge design, it could be a lot of load on that bottom hinge.
But then, I over engineer everything I build…
Ah nice, I didn’t notice the two v three hinge thing. Nice!
But then, I over engineer everything I build…
Appropriately engineer.
Too much is always enough.
The cross support is not needed if you use plywood. Houses are often built like that too - a stick frame made rigid by the contruction boards.
If you do use the support then make sure you put it the right way around. It’s supposed to span from the bottom hinge to the opposite top corner so that when the door tries to sag is starts compressing the wood. The other way around it doesn’t work so good and that’s a really common mistake that people make.
Yeah, and the opposite is true if you ever need to combat sagging in a gate or something like that: put a cable going from top hinge to bottom corner, and tension it until things square up.
Can you give more info on this? I have a sagging gate that someone must have “rebuilt” at some point. The cross brace runs from the top hinge to the bottom corner in a sagging Z shape with about 14 nails trying to keep it together at the joints) but somehow the fence pickets are all level. Its gotten so bad that one of the hinges keeps popping out.
I was planning on trying to fix it but the fact that there is no rectangular frame breaks my brain on the rebuild process. I suppose the fence pickets are ‘structural’ here. I’m not sure how to rebuild it on the ground with the support and pickets all properly located in relation to the hinges without a lot of precise measuring that I don’t trust my abilities to meet.
Basically, if a door/gate is sagging, it’s turning a rectangle into a parallelogram. If you draw a line from corner-corner of a rectangle, you will get the same measurement on both diagonals. In a parallelogram, you’ll get a long one and a short one.
The long one will go from the top hinge to the outside corner, the short one will go from the bottom hinge. If you put a support in the long diagonal, it will be in tension (good for cable), and if you put one in the short diagonal it will be in compression (good for wood).
If you are building a new one, you can just put a wood support where it will get compressed. If you already have a sagged one, you need to fix the sag first. Easiest way to do that is with a cable and turnbuckle. Just tighten the turnbuckle until you have a rectangle. Then you can either leave it, or stick a wooden support in where it will be under compression and remove the cable.
Edit: and for your case, you unfortunately probably need to take out the diagonal element first cause otherwise it will probably combat the tension from a cable.
Those images in your post show doors made of multiple vertical planks. The planks can shift relative to each other, which is largely prevented by a diagonal compression brace.
Look at how a stick framed house is built. The plywood is typically all that is necessary to provide shear strength, as required by code. The plywood will not be the failure point of your door unless the wood becomes so compromised that it has no structural integrity. Keep it painted and you shouldn’t have anything to worry about.