Sun, 03 May 2026 09:57:10 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310435#Comment_310435 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310435#Comment_310435 Tue, 31 Mar 2026 18:59:32 +0100 Peter_in_Hungary
The question is - Is a VCL above the plasterboard (i.e. on the warm side of the insulation) required?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310436#Comment_310436 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310436#Comment_310436 Wed, 01 Apr 2026 12:49:44 +0100 Nick Parsons https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310438#Comment_310438 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310438#Comment_310438 Wed, 01 Apr 2026 23:30:47 +0100 Peter_in_Hungary https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310439#Comment_310439 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310439#Comment_310439 Thu, 02 Apr 2026 10:35:57 +0100 djh https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310440#Comment_310440 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310440#Comment_310440 Thu, 02 Apr 2026 15:20:17 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310467#Comment_310467 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310467#Comment_310467 Sun, 12 Apr 2026 22:09:19 +0100 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310490#Comment_310490 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310490#Comment_310490 Tue, 14 Apr 2026 10:23:57 +0100 WillInAberdeen
Classic explanation and photos of this by Lstiburek:
https://buildingscience.com/documents/insights/bsi-049-confusion-about-diffusion]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310494#Comment_310494 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310494#Comment_310494 Tue, 14 Apr 2026 12:05:34 +0100 djh https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310495#Comment_310495 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310495#Comment_310495 Tue, 14 Apr 2026 12:28:31 +0100 fostertom
I'm dubious about billiard-ball whizzing-around molecules of water remain free to keep whizzing, once coagulated into liquid droplets (i.e. condensing faster than they're evaporating). So what, other than capillarity, drives their "'rather' keep on moving towards the outside"? NB water molecules are not themselves individually either 'gas' or 'condensed to liquid' - they're either free-whizzing, or coagulated.

What defines a 'surface', in water molecules' terms? something that's more or less transparent to individual whizzing-around molecules, but impervious to coagulated droplets?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310499#Comment_310499 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310499#Comment_310499 Tue, 14 Apr 2026 15:52:07 +0100 WillInAberdeen
Lstiburek will explain why water likes to do that better than me, because I'd like to talk about Gibbs free energy and stuff like that! But think of the Great Cold Outdoors as being a big dehumidifier that keeps the outside of your insulation nice and dry.

If you have more hair than me then try this experiment - walk around outdoors on a cold day with no hat on. Does the outside of your hair-do get damp with condensation? No! Could try this with a cat or dog instead. :-)]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310504#Comment_310504 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310504#Comment_310504 Tue, 14 Apr 2026 22:04:51 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310509#Comment_310509 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418&Focus=310509#Comment_310509 Wed, 15 Apr 2026 10:27:59 +0100 djh