Green Building Forum - How to make 18mm T+G OSB/3 Airtight? Sat, 02 May 2026 11:52:46 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=153643#Comment_153643 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=153643#Comment_153643 Thu, 09 Aug 2012 22:04:17 +0100 fostertom
Tho, how closely BuildDesk agrees with reality is another matter, which only closer study in WUFI wd answer.]]> How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=153644#Comment_153644 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=153644#Comment_153644 Thu, 09 Aug 2012 22:06:31 +0100 fostertom How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=153648#Comment_153648 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=153648#Comment_153648 Thu, 09 Aug 2012 22:27:47 +0100 borpin Posted By: fostertomThen BCO shd be satisfied - why not? Just because it is not something he is familiar with. At the very least it will go back and forth at least 5 times! I agree with you FT, I just did not have the stomach for the fight. Add to that the fact they will want a breathable membrane outside the OSB (why? where is it breathing to? Oh because you always have a membrane outside a TF wall rather than considering why it is required....) etc etc.]]> How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=153651#Comment_153651 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=153651#Comment_153651 Thu, 09 Aug 2012 22:32:35 +0100 fostertom How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=153698#Comment_153698 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=153698#Comment_153698 Fri, 10 Aug 2012 13:49:39 +0100 an02ew
Posted By: fostertoman02ew, why 11mm nor 9mm OSB? Why not 6mm in fact, at least for walls, which aren't walk-on? Just asking.


i am using 11 mm for 2 reasons, firstly for added stiffness to the walls which are much larger than our previous work Tom, i am concerned about the pack of cards effect. Secondly having read all of this discussion, i am convinced that OSB would have a better chance of maintaining its airtightness on a thicker sheet. it will be impossible to keep the sheets dry during construction especially with the bad weather. Apparently the sheets have a much better chance of air tightness if they are keep dry.]]> How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154882#Comment_154882 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154882#Comment_154882 Sat, 25 Aug 2012 16:19:23 +0100 Cav8andrew possibly a further 50mm layer of insulation (type to be decided but in which services could be buried), Fermacell boards.
Any thoughts on any aspect of this.]]> How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154890#Comment_154890 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154890#Comment_154890 Sat, 25 Aug 2012 19:44:28 +0100 fostertom How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154891#Comment_154891 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154891#Comment_154891 Sat, 25 Aug 2012 20:01:39 +0100 Cav8andrew How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154893#Comment_154893 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154893#Comment_154893 Sat, 25 Aug 2012 20:43:51 +0100 fostertom http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=6890 - it's about where in the sandwich the vapour resistance has to go (inner layer(s) 5x as resistant as outer), in a 'breathing' construction that requires no internal VCL. Your 18 OSB, without holes, places most of the resistance outboard. With holes in the 18 OSB, all the resistance is inboard in the 12 OSB, as it should be, for breathing construction. If not breathibng construction, then yes you need a strong inboard VCL.]]> How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154895#Comment_154895 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154895#Comment_154895 Sat, 25 Aug 2012 21:03:49 +0100 Cav8andrew How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154904#Comment_154904 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154904#Comment_154904 Sun, 26 Aug 2012 07:59:32 +0100 an02ew Posted By: Cav8andrewVAPOUR & AIR BARRIER (liquid or taped sheet),

i assume taped sheets as just light weight polythene would be alot cheaper that liquid? what sort of liquid and where in your build would it be applied? back of plasterboard sheet? would VC plaster be cheaper?]]> How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154913#Comment_154913 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154913#Comment_154913 Sun, 26 Aug 2012 10:06:07 +0100 Cav8andrew The products I have info. on are from Sto and Prosoco and would be applied to the 12mm OSB before the 50mm layer of insulation and Fermacell is installed, as in the sequence described above. I have yet to fully research these products as to their total or partial permiability. If using Fermacell plastering would not be an option but I guess if plasterboard is used VC plaster could be explored, however I am keen to avoid wet trades and Fermacell is a product I have some experience of in respect of getting an acceptable final finish.]]> How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154952#Comment_154952 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154952#Comment_154952 Sun, 26 Aug 2012 22:21:35 +0100 Viking House The house in some of these photos http://www.viking-house.ie/timber-frame-house.html cost €10k extra to build, so I'm not sure it was necessary to spend so much on Fermacell and Gutex.

Here's 2 studies from the US and Canada where the wall build-ups are the wrong way around, being 5 times more breathable on the inside than the outside.
http://www.viking-house.ie/downloads/Tsong79.pdf
http://www.viking-house.ie/downloads/Spokane.pdf
No evidence of fungus, mould or decay were discovered when the walls of close to 250 houses were opened, leading me to conclude that the 5:1 breathability rule is a bit of a red herring!

So don't worry about using OSB for airtightness, it works fine and don't worry about the breathability of the wall just get it airtight!]]> How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154961#Comment_154961 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=154961#Comment_154961 Mon, 27 Aug 2012 08:37:29 +0100 Cav8andrew How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=155571#Comment_155571 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=155571#Comment_155571 Tue, 04 Sep 2012 12:31:01 +0100 davidfreeborough
David]]> How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=170027#Comment_170027 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=170027#Comment_170027 Tue, 12 Mar 2013 14:22:06 +0000 fostertom Expanding foam gapfilling glue for glueing the OSB to studs/rafters: you may have to order it but in his branch of T-P, Sabrefix D4, used for fixing Norboard housebuilder’s chipboard flooring, £5 for 1 litre, or boxes of 12 (you’ll be using a lot), which is under half price he was paying before.]]> How to make 18mm T+G OSB/3 Airtight? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=178594#Comment_178594 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361&Focus=178594#Comment_178594 Tue, 25 Jun 2013 11:05:12 +0100 TimSmall