90 degree joint for lean-to roof joist

[Chris152]

Excuse the rather rudimentary artwork but I need to join a joist to the one (temporarily) in situ. It'll have to support further 5 smaller joists (2"x3") that will in turn support a plastic corrugated roof. It'll be joined to another 6x2 at the other end (it's 3m long).

What joint should I use for this?

Thanks, Chris

EDIT - On reflection, I think the easiest and strongest thing is to add another vertical post at the junction of the two joists, so both can attach securely to it and it's further supported onto the ground.

Problem solved, I think!

 

[Chris152]

OK, Mostly in place now. But what is the correct screw spacing for miniature corrugated plastic sheet? I've searched the net but can't find the answer.

 

[MikeJhn]

Look up the manufacturers details should recommend fixing details, but I would say every third corrugation on the high point with rubber washer fixings, have a look at Unduline roofing sheets for the idea: https://www.eroofs.co.uk/uploads/manuals/Onduline Fixing Guide.pdf

 

[MikeJhn]

EDIT - On reflection, I think the easiest and strongest thing is to add another vertical post at the junction of the two joists, so both can attach securely to it and it's further supported onto the ground.

Problem solved, I think!

Or let a corbel into the existing post to support the new Rafter.

 

[Chris152]

Look up the manufacturers details should recommend fixing details, but I would say every third corrugation on the high point with rubber washer fixings, have a look at Unduline roofing sheets for the idea: https://www.eroofs.co.uk/uploads/manuals/Onduline Fixing Guide.pdf

Thanks Mike.

Should 60cm spacing of battens be ok?

edit - Sorry, that looks fine according to the link you shared, Mike.

 

[MikeJhn]

It all accords where you live and the loading you expect on the roof, high winds and snow then closer spacing, it's up to you, personally I would only want to do this once so would go with 450mm spacing.

 

[Fergie 307]

If you use the onduline bitumen sheets on any pitch less than about 30°, I have found you need to space the battens at about 300mm, otherwise they will tend to sag between them over time. Steeper pitch and 450 is fine.

 

[Chris152]

These are the ones we bought today. Went to Trago Mills in Merthyr, a mind-blowing place on account of the size of it, like Heathrow airport but with stuff. Also somewhat like a vastly extended Middle-of-Lidl.

https://www.trago.co.uk/3050mm-10-m...QjtmrLLo5lfGcCaqkw_aem_mVi9mavdFzMcGLGF38m6eA

Much cheaper than anywhere else, and exactly what I wanted. (Well, I really wanted a clear glass roof, but £££).

 

[Jacob]

Excuse the rather rudimentary artwork but I need to join a joist to the one (temporarily) in situ. It'll have to support further 5 smaller joists (2"x3") that will in turn support a plastic corrugated roof. It'll be joined to another 6x2 at the other end (it's 3m long).

What joint should I use for this?

Thanks, Chris

EDIT - On reflection, I think the easiest and strongest thing is to add another vertical post at the junction of the two joists, so both can attach securely to it and it's further supported onto the ground.

Problem solved, I think!

View attachment 191873

Joist hangers? Lots of shapes and sizes
https://www.speedyfixings.com/builders-metalwork/joist-hangers/

 

[Fergie 307]

These are the ones we bought today. Went to Trago Mills in Merthyr, a mind-blowing place on account of the size of it, like Heathrow airport but with stuff. Also somewhat like a vastly extended Middle-of-Lidl.

https://www.trago.co.uk/3050mm-10-m...QjtmrLLo5lfGcCaqkw_aem_mVi9mavdFzMcGLGF38m6eA

Much cheaper than anywhere else, and exactly what I wanted. (Well, I really wanted a clear glass roof, but £££).

If they are like the ones I have used before they are surprisingly strong. I would think 450 is probably ok. Problem with the bitumen type ones is that in the summer when they get hot they become a bit softer, so apt to sag. Certainly I found that on a roof with the ridge orientated broadly east west it was the south facing ones that suffered this problem more.
Only problem I have found with the clear ones is that if they are not firmly held down they can vibrate in strong winds and then you can find cracks developing round the fasteners. You need to use soft plastic fastening cups. I would say probably one fastener for each 200mm of width, further apart if it's in a sheltered spot.