Framing for Sheet Roofing over Alley (small)

itakitez

Hi guys

I have a quick roofing question.

I live in a terrace house with a 3m or so concrete alley separating the houses, half is mine, half the opposing neighbor, who has already extended his house to the line and up (3 floors). Therefore, the measurements I'm working with are approximately 5' deep by 13' long

Now there is too little light in there for a small garden potted yard (original plan) so I want to convert it to an outdoor laundry area - just washing machine and maybe store bicycles or the like.

My current plan is to use a wooden frame with PC roof. I live in the subtropics, so no snowload and there is little to no wind since other people have already built in the alley (our houses stand over 30ft) so lift isn't a problem. Also, due to the narrowness, rain isn't too much of an issue either (even during hurricanes), but we do get quakes.

This brings me to my two questions,

1. I plan to tether 4x4 posts to the wall and top them in pairs with 4x4 rafters to make 3 rough stands of decreasing height according to the drop I need (5 degree), then 2x2 purlins running the length to support and tie the roofing plastic to (see picture).

Is this strong enough?


(whoops, this should read 13x5)


2. Do I need to tie the roof to the concrete structure (house) or would the tethering be sufficient?


I am out in Taiwan so I can't just ask at the local depot and the current building estimate is $5000 (when the materials will cost about $300) and the build quality is not above my own skills. Oh, and there aren't building regs... Also, this is a temporary measure (3-5years) since I am saving to add a real strong roof in there and install a small toilet/dog wash/laundry area, but this will have to wait (for both the cash and until I find a decent builder here).

itakitez

Lucky I looked into this a little more - gotta make a slight correction - realised my original plan to make the A-frames of decreasing size was a major no-no!

So found out that for structural integrety I have to make that level as possible (shown the purple still with the level dark green 2x4 sitting on stop), then rip more 2x4s to form an angle (shown in light green)



So now that I am away from dangerously unstable - any opinions on whether this will hold for 3-5 years?

xxPaulCPxx

You dont need to use two different pieces at the top there, just use on 13' long 2x4, but cut a small birdsmouth so that it will sit flat on slightly lower verticals. Imagine the vertical on the far left is a ridge beam, the middle one is another ridge beam, and so is the for right.

So what is going to keep your whole assembly from racking to one side or the other? Are you going to bury those 4x4, or are you going to put angled supports at the top?

itakitez

@Paul - the bird's mouths seems like a better idea, I was unsure of the stability

I am cannot bury the posts since there is already a concrete slab there so can only tether to the walls on either side so I was concerned that in a quake the top would shift and damage the walls. Thanks for the tip, I will add some angled supports to the stanchion/crossbars that also brings down material costs.

I will start trying to source the materials, seems like 4x4s have to be ordered in advance so may have to drop to 2x2 then I would be more concerned with structural integrety

Made more accurate measurements, the size is 400cm x 170cm or 13'2" x 5'6"