Sat, 02 May 2026 12:03:25 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268956#Comment_268956 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268956#Comment_268956 Thu, 14 Jun 2018 07:58:15 +0100 tony
eg twelve foot span 12/2= 6 + 1 >> use 7x2 joists — ie 47x175 Most houses are built this way sometimes I have seen the mass market builders using half inch sizes to save a bit of Monet]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268958#Comment_268958 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268958#Comment_268958 Thu, 14 Jun 2018 08:54:37 +0100 adam_w
Is this based on the assumption that joist spacing is 400mm?

Thanks,

Adam]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268959#Comment_268959 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268959#Comment_268959 Thu, 14 Jun 2018 09:29:36 +0100 owlman
That's in order to give the "IMPRESSION" of a better job, tony. ]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268963#Comment_268963 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268963#Comment_268963 Thu, 14 Jun 2018 10:44:39 +0100 skyewright Posted By: owlmanThat's in order to give the "IMPRESSION" of a better job, tony.
Could being more precise be considered needless "POINTILLISM"? ]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268968#Comment_268968 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268968#Comment_268968 Thu, 14 Jun 2018 12:38:36 +0100 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268971#Comment_268971 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268971#Comment_268971 Thu, 14 Jun 2018 13:29:35 +0100 Paul in Montreal
http://www.johnbridge.com/vbulletin/deflecto.pl

Paul in Montreal.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268974#Comment_268974 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268974#Comment_268974 Thu, 14 Jun 2018 14:18:01 +0100 CWatters https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268978#Comment_268978 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268978#Comment_268978 Thu, 14 Jun 2018 14:45:45 +0100 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268983#Comment_268983 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268983#Comment_268983 Thu, 14 Jun 2018 19:53:17 +0100 WillInAberdeen Posted By: tony
eg twelve foot span 12/2= 6 + 1 >> use 7x2 joists — ie 47x175

Maybe I misunderstood but for a twelve foot span, building regs table A1 requires 8x2 or 47*195 ?

Edit: just been searching and can't find the reference anymore. NHBC's table allows 47*170 for up to 3.55m span which is very nearly 12 feet.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268984#Comment_268984 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268984#Comment_268984 Thu, 14 Jun 2018 21:03:33 +0100 djh http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_A_1992.pdf]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268989#Comment_268989 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268989#Comment_268989 Thu, 14 Jun 2018 23:19:12 +0100 Peter_in_Hungary
But if you want 406 spacing and 3.51 span then 51x178 works at 48kg/m2 or 51x203 at 97kg/m2 and then again for 3.66m span a 51x178 for 24kg/m2 works.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268991#Comment_268991 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268991#Comment_268991 Fri, 15 Jun 2018 10:20:29 +0100 WillInAberdeen
Thanks DJH, the table has been moved out of the old Approved Doc (free to download) which now refers you to TRADA (paywall) - grrr!

Here's a handy 'on site' guide http://www.haringey.gov.uk/sites/haringeygovuk/files/note07_-_domestic_timber_floors.pdf]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268993#Comment_268993 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268993#Comment_268993 Fri, 15 Jun 2018 11:39:47 +0100 Peter_in_Hungary Posted By: WillInAberdeenThanks Peter, that's dating back a while! from before we went 'metric' - joists now come in 47 or 45mm thickness.
Err - why is 47mm more metric than 51mm?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268996#Comment_268996 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=268996#Comment_268996 Fri, 15 Jun 2018 19:49:04 +0100 jamesingram https://www.rightsurvey.co.uk/rafters-span-tables/
gone
so
http://www.home-extension.co.uk/roof-rafters-span-tables.html

also for those only able to think in new money the (span/2)+2 works in decimetres

3m span =30 dm/2 = 15 +2 =17 =170mm =170/50 joist = 7"/2" old money
]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=269003#Comment_269003 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=269003#Comment_269003 Sat, 16 Jun 2018 19:51:10 +0100 Peter_in_Hungary Posted By: jamesingram3m span =30 dm/2 = 15 +2 =17 =170mm =170/50 joist = 5"/2" old money
https:///newforum/extensions/Vanillacons/smilies/standard/bigsmile.gif" alt="" title="" >
Except that 170mm is 6.7"]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=269006#Comment_269006 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=269006#Comment_269006 Sat, 16 Jun 2018 23:51:27 +0100 WillInAberdeen
Peter, I dunno why the standard 47mm thickness is considered 'metric' either...! Makes no sense.
Something to do with adopting the European standard thicknesses perhaps? EN336 standard.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=269007#Comment_269007 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=269007#Comment_269007 Sun, 17 Jun 2018 02:42:45 +0100 djh Posted By: Peter_in_HungaryErr - why is 47mm more metric than 51mm?
51 mm is imperial, not metric (50.8 mm = 2").
47 mm is 50 mm timber (i.e. metric) that has been regularised.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=269021#Comment_269021 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=269021#Comment_269021 Mon, 18 Jun 2018 18:06:55 +0100 jamesingram actually i should have put 7"/2" (175mm)
edited]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=269024#Comment_269024 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15763&Focus=269024#Comment_269024 Tue, 19 Jun 2018 07:13:08 +0100 tony