Garden outbuilding joists

[Andrew1981]

Hi after a bit of help iam building out garden garage/shed it’s 4.5m x 8m iam finding it hard to work out that joist I need iam going to but them 400mm apart any advice would be grateful 

[SteamyTea]

I think you will find it is a bit more complicated than just asking the question.

A lot more details is needed.

 

But here is some light reading

 

https://www.structuralbasics.com/flat-roof-beam-design/

 

https://www.structuralbasics.com/timber-truss-roof/

 

https://www.structuralbasics.com/rafter-roof-design/

 

https://www.structuralbasics.com/purlin-roof-design/

 

 

 

Edited February 24, 2024 by SteamyTea

[saveasteading]

33 minutes ago, Andrew1981 said:

any advice would be grateful 

Building regulations document A.

[Galileo]

There's also "Eurocode 5:Design of Timber Buildings" from back in the day when we had influence.

 

https://www.icevirtuallibrary.com/doi/book/10.1680/dtb.31623

[saveasteading]

That's going to be rather from first principles isn't it?

Ie not easy-to -use tables.

Somewhere I've got a book full of tables that takes all the science out of it.  Such must be findable online I'd think.

 

[ETC]

Try this: http://www.buildingcontrol-ni.com/assets/pdf/TechnicalBookletD2012.pdf

[Nick Thomas]

I used https://www.timberbeamcalculator.co.uk/en-gb/span-tables/flat-roof-joists - and I've been walking around on top of it since with no issues (although it said 2x6 C24 was fine, I bumped to 2x8 for availability reasons, so not the best test, I guess)

[SteamyTea]

39 minutes ago, saveasteading said:

Somewhere I've got a book full of tables that takes all the science out of it.

What is it called, most book are available online these days.

[saveasteading]

26 minutes ago, SteamyTea said:

What is it called,

If I could find it I would be able to tell you.

Section tables for timber joists?  Searching for that I found this table...probably the same as the NI one. https://www.timberbeamcalculator.co.uk/en-gb/span-table/floor-joists?load=1.5&class=C24

 

and in nhbc https://nhbc-standards.co.uk/2018/6-superstructure-excluding-roofs/6-4-timber-and-concrete-upper-floors/6-4-8-timber-joist-spans/

[Onoff]

They'll have to be deeper if you want to span 8m than they will at 4.5m!

[saveasteading]

56 minutes ago, Onoff said:

to span 8m than

Just about possible with engineered joists, deep and no spaces. Not to be discounted.

[Iceverge]

 

47*220mm C16 @400cc will be fine. 

 

Use 3x layers of 75mm mineral wool as insulation then. 

 

And 18mm OSB glued and screwed as decking. 

[ETC]

Christ on a bike - just use the tables from NI in TBD.