Andrew1981 Posted February 24 Share Posted February 24 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 Link to comment Share on other sites More sharing options...
SteamyTea Posted February 24 Share Posted February 24 (edited) 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 by SteamyTea 1 Link to comment Share on other sites More sharing options...
saveasteading Posted February 24 Share Posted February 24 33 minutes ago, Andrew1981 said: any advice would be grateful Building regulations document A. Link to comment Share on other sites More sharing options...
Galileo Posted February 25 Share Posted February 25 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 Link to comment Share on other sites More sharing options...
saveasteading Posted February 25 Share Posted February 25 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. Link to comment Share on other sites More sharing options...
ETC Posted February 25 Share Posted February 25 Try this: http://www.buildingcontrol-ni.com/assets/pdf/TechnicalBookletD2012.pdf 1 Link to comment Share on other sites More sharing options...
Nick Thomas Posted February 25 Share Posted February 25 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) Link to comment Share on other sites More sharing options...
SteamyTea Posted February 25 Share Posted February 25 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. Link to comment Share on other sites More sharing options...
saveasteading Posted February 25 Share Posted February 25 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/ Link to comment Share on other sites More sharing options...
Onoff Posted February 26 Share Posted February 26 They'll have to be deeper if you want to span 8m than they will at 4.5m! Link to comment Share on other sites More sharing options...
saveasteading Posted February 26 Share Posted February 26 56 minutes ago, Onoff said: to span 8m than Just about possible with engineered joists, deep and no spaces. Not to be discounted. Link to comment Share on other sites More sharing options...
Iceverge Posted February 26 Share Posted February 26 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. Link to comment Share on other sites More sharing options...
ETC Posted February 26 Share Posted February 26 Christ on a bike - just use the tables from NI in TBD. 1 Link to comment Share on other sites More sharing options...
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