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.

 

[MikeJhn]

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

OK inside a building with a ceiling, but very ugly on an external pagoda or lean too.

 

[Chris152]

Thanks all.

I'm struggling with the final step - I can't figure out the fixings to use for mini profile corrugated sheets. These are the ones made by the manufacturer (Corolux):

https://www.trago.co.uk/corolux-miniature-profile-fixings-pack-of-10.html

It seems a bit odd to try hammering them into position on such a fragile sheet, especially as there will be about 45 per sheet and 5 sheets - plenty of room to make a mistake!
I'd much prefer the usual screws with caps, but wonder if they'll leak - any thoughts or experience with this?

 

[MikeJhn]

It's a bit like using a powered screwdriver you become an expert of knowing when to stop just after you have finished.

 

[Chris152]

It's a bit like using a powered screwdriver you become an expert of knowing when to stop just after you have finished.

Surrounded by shattered fragments of plastic! Ha

 

[Beau]

Thanks all.

I'm struggling with the final step - I can't figure out the fixings to use for mini profile corrugated sheets. These are the ones made by the manufacturer (Corolux):

https://www.trago.co.uk/corolux-miniature-profile-fixings-pack-of-10.html

It seems a bit odd to try hammering them into position on such a fragile sheet, especially as there will be about 45 per sheet and 5 sheets - plenty of room to make a mistake!
I'd much prefer the usual screws with caps, but wonder if they'll leak - any thoughts or experience with this?

The spacers look good but the nails!

Not installed a lot of clear corrugated but fixed acres of the regular sort down and generally use screws like this https://www.screwfix.com/p/easydrive-flange-self-drilling-roofing-screws-6-3mm-x-80mm-100-pack/5672p

 

[Chris152]

The spacers look good but the nails!

Not installed a lot of clear corrugated but fixed acres of the regular sort down and generally use screws like this https://www.screwfix.com/p/easydrive-flange-self-drilling-roofing-screws-6-3mm-x-80mm-100-pack/5672p

Yes, I was looking at that sort but wondered if they would actually seal the small profile ones. They seem to recommend them for corrugated metal and again, I wonder why not plastic?
I may try to get a small quantity of those, and of the regular profile pvc sheet sort, and try them out to see how they go. Another option is to get the Corolux ones and swap the nails for screws, but I think we'll need about 200 of them, which could drive me nuts.

 

[XTiffy]

I have used this type of sheet for many applications, (I absolutely agree with the previous advice about support) I substituted the nails for screws with the clip down covers, I used the green outdoor screws (Toolstation et al). No problem with leaking. The single sheet type do however suffer from condensation when it is cold overnight (ask our horses!) and that is worse than leaking. In my barn I put a single strip of glass fibre corrugated sheet to give light and the rest of the metal barn roof has a fabric wicking layer. There is a huge amount of condensation dripping from the clear section but none elsewhere.

 

[Chris152]

I have used this type of sheet for many applications, (I absolutely agree with the previous advice about support) I substituted the nails for screws with the clip down covers, I used the green outdoor screws (Toolstation et al). No problem with leaking. The single sheet type do however suffer from condensation when it is cold overnight (ask our horses!) and that is worse than leaking. In my barn I put a single strip of glass fibre corrugated sheet to give light and the rest of the metal barn roof has a fabric wicking layer. There is a huge amount of condensation dripping from the clear section but none elsewhere.

Thanks XT - To be clear, did you use this sort alone:
https://www.screwfix.com/p/essentia...Vv6ODBx0ZqzL6EAQYASABEgL1cPD_BwE&gclsrc=aw.ds

or those in combination with the seal from these:
https://www.wickes.co.uk/Wickes-Min...MI6M_jqcTIiQMVTZRQBh2PcA-pEAQYASABEgL6e_D_BwE