Building with "prefabricated timber joists" - ideas please!

[agulesin]

Hello there,

I've managed to scrounge some "prefabricated timber joists" from a local jobsite where they were surplus for the job. I'm thinking to use them to replace/renew our outhouse/lean-to which has seen better days.

I am thinking to use some of the as verticals, and others (as designed!) to support a simple polycarbonate or whatever transparent roof. At the moment the roof is only just high enough to stand up straight so I'll raise a foot or so.

Any ideas/tips regarding the design of the thing or how to join them at the corners would be appreciated. At the moment the beams are 4 meters or so long but I think I can cut and insert a piece of 2x4 between the existing ones to shorten them.

Here's a photo of the type of beams in question: prefabricated timber joists

Dimensions are about 8' by 5'. See illustration:



Thanks for all your support!

 

[OvertonPlumber]

Grab a copy of the easy joist design guide will provide you with all information you need. I also had same idea I have 2 large 6mtrs trusses in my garage. However I also picked up all the dedicated metalwork that allows you to join them at right angles etc.

https://www.wolfsystem.co.uk/products/easi-joist.aspx

 

[agulesin]

Thank you for that MrBenchmark, it's very useful information.

One thing which I need to confirm: The brochures say "Do not cut, drill, notch" etc. but as I'm only going to use them to a) fix one to the house wall to support the roof and b) use the others as a "wall" between the existing half-height block wall and the roof on the low side, I suppose that won't be a problem.

In other words, they are not becoming part of a weight-supporting structure, so it should be OK to chop them up as required... (I'm not expecting the Building Inspector to visit at any time!).

If not, they'll be available as firewood for anyone willing to collect!

 

[endecotp]

You should have no need to drill or notch because they have huge gaps in them!
Presumably you will need to cut them to length though; apply common sense and make the new end look as much like the existing end detail as you can.

 

[agulesin]

"Drill" as in to screw to the wall! Haven't got any washers THAT big I'm afraid!

I'm planning to fix one flat against the house wall if that helps. It will rest on the retaining wall at the other end.

(Other wall with door is part of an existing structure.)

Why use these rather than normal 2x4? because they were F R E E !!

 

[gonch69]

your fine to screw through them as we use structural coach screws to make doubles and triples with some joists having fixings every 400mm top and bottom just dont drill big hole in them we just done a job with these that were plyed then had 100mm of screen layed on top they take a lot of weight less flexing than jji tji joists