Green Building Forum - Durability of air tightness Sat, 02 May 2026 11:01:37 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264183#Comment_264183 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264183#Comment_264183 Mon, 25 Dec 2017 21:07:50 +0000 nick1c Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264184#Comment_264184 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264184#Comment_264184 Mon, 25 Dec 2017 21:15:23 +0000 Nick Parsons Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264185#Comment_264185 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264185#Comment_264185 Mon, 25 Dec 2017 21:40:38 +0000 tony
The problem I have with tapes and membranes are the longevity of the tapes, possible perforation of the membranes and something I call the bellows effect which will more problematic where there are gales.

I would go masonry, good detailing, air tightness better than PH, wet plaster, mitigation of thermal bridges, etc

In Canada they regularly achieve very good levels of air tightness less than 0.1, here we barely understand what its or the importance of having it. Scottish islanders have a better understanding of it and I often help them with suggestions, specifications and detailing, want do you consider to be a good spec in terms of the numbers, in other words how low do want to go?]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264195#Comment_264195 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264195#Comment_264195 Wed, 27 Dec 2017 10:10:24 +0000 fostertom
On timber framed construction, rather than membranes/tapes, airtight but breatheable board glued and screwed at all joints with gapfilling adhesive. OSB is the obvious candidate but there's disagreement as to whether OSB is airtight, not quality-controlled from manufacturer's batch to batch. I've put my faith in the words I heard from Peter Warm, one of UKs three (?) PH Assessors - 'I've never yet found a building that failed PH airtightness because of OSB'.

Glued and screwed OSB is very hard to install wrong, is within the skill range of everyday chippies, is robust in use - all the opposite of the dreaded tapes and membranes.]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264200#Comment_264200 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264200#Comment_264200 Wed, 27 Dec 2017 12:47:32 +0000 Rex
I am also concerned about the durability of the tapes, so used the self-adhesive, aluminium duct tape on everything. It is inexpensive but somewhat fragile. My thought was, if the adhesive fails (which I suspect it will in time) the aluminium tape will not.

For example, around all window frames, I lined the inner joint with tape, knowing that when the drylining was installed, the tape will be sandwiched in place. Likewise, the timber sole plate; the screed sandwiches the tape in place. Also the inside of the timber frames wherever there was a panel joint, the Warmcell insulation will hold the tape in place.

Seven years down the line, it would be interesting to have the house re-tested but I have better things to do with my time and money!]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264202#Comment_264202 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264202#Comment_264202 Wed, 27 Dec 2017 13:16:49 +0000 djh Posted By: nick1cDoes anyone know if the longevity of different methods of achieving good air tightness has been investigated and if so what the results were? It looks as if we may be in a position to build a house in a wet and windy site. I would love to construct it to achieve at least passivehaus levels of efficiency, but am concerned about the toll Atlantic gales will take over the years.
There have been investigations, yes, although I don't remember the names of the authors or papers unfortunately. The Pro Clima and the Siga products are good and have both good theoretical/tested results of up to 100 years and practical results exceeding 30 years or so to date. There may be other good products but there are also horror stories about some products so caveat emptor.

Plaster is good - it's my main airtightness barrier - but you need to think about where it is likely to crack and have a backup plan. Cracking depends on the substrate and the geometry. It's very likely at corners and junctions and having membranes and tapes behind the plaster (and keyed into it) at such locations is pretty much essential. Slab to wall, wall to roof, doors and windows, corners of the building etc. Some cracks can be seen and repaired but other locations will be hidden. Also think about penetrations etc. I just made a rule that there are no services in my external walls and nothing connected to it, except by glueing. Most people will want to find a different solution, I expect. Cracks form because of differential movement as the building dries out, no matter how solidly built, as well as movement due to wind.

Medite make OSB products that are guaranteed airtight; I don't know about other manufacturers. The guarantee applies when the panels are taped together. I don't know whether anybody has done any testing of glued panel structures, nor how they deal with the omission of expansion joints. I've no reason to suppose that the system Tom describes doesn't work though.]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264205#Comment_264205 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264205#Comment_264205 Wed, 27 Dec 2017 14:58:48 +0000 PeterStarck Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264208#Comment_264208 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264208#Comment_264208 Wed, 27 Dec 2017 18:36:06 +0000 tony Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264210#Comment_264210 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264210#Comment_264210 Wed, 27 Dec 2017 22:49:42 +0000 fostertom Posted By: djhMedite make OSB products that are guaranteed airtightAnd other manufacturers. But these are by coating the board, not by quality-controlling the through-and-through composition of the board. Consequently they may be airtight until surface-damaged (just like membranes) or the taping fails (just like 'tapes'!) but they also become vapour-impermeable. That fallacious durability and that non-breatheability rule them out as far as I'm concerned.]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264219#Comment_264219 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264219#Comment_264219 Thu, 28 Dec 2017 16:25:03 +0000 delprado
I dont understand why people dont like foams - around a floor joist in a retrofit, and not exposed to uv, its airtight and can take quite a bit of movement (apparently).]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264225#Comment_264225 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264225#Comment_264225 Thu, 28 Dec 2017 17:26:18 +0000 gravelld
Icynene has quite remarkable sponginess. It is actually like a bath sponge.

I'd put up my head and question this reliance on plaster or render, unless something is added to guarantee elasticity. My own walls are not a pretty sight. Membranes are made for this purpose.

djh any references I can read to on regarding the use of tapes with plaster?]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264226#Comment_264226 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264226#Comment_264226 Thu, 28 Dec 2017 17:33:09 +0000 tony
I plastered the membranes and the “tony tray” into the walls by trapping them being expanded metal.]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264229#Comment_264229 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264229#Comment_264229 Thu, 28 Dec 2017 19:52:49 +0000 WillInAberdeen
The best survival seems to have been where the bead of sealant was at least 5mm wide.

I think the airtight layer needs to be on the inside where you will see it and maintain it. Where there are eg kitchen units in front of it, the draughts can go on for years before I happen to be doing something under there and notice the crack.]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264237#Comment_264237 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264237#Comment_264237 Fri, 29 Dec 2017 09:39:18 +0000 Simon Still Posted By: fostertomOn timber framed construction, rather than membranes/tapes, airtight but breatheable board glued and screwed at all joints with gapfilling adhesive.

We build with SIPs, additional internal insualtion, internal airtight barrier and tapes. Our neighbour did timber frame with external OSB and gapfill adhesive. Having seen/done both I'd go for OSB/Adhesive if I was building again. A lot less faff and the external shape of a house is a lot easier to work with than the internal. Also seems much less chance of damage to the airtight layer from internal works in future]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264239#Comment_264239 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264239#Comment_264239 Fri, 29 Dec 2017 13:43:38 +0000 djh Posted By: gravellddjh any references I can read to on regarding the use of tapes with plaster?
Both the Pro Clima and the Siga product literature describe their use quite well.]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264310#Comment_264310 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264310#Comment_264310 Tue, 02 Jan 2018 11:36:03 +0000 fostertom Posted By: Simon StillA lot less faff and the external shape of a house is a lot easier to work with than the internal. Also seems much less chance of damage to the airtight layer from internal works in futureExactly, Simon.

Also, if the studwork voids are filled with blown-in cellulose rather than insulation roll or cut boards, the cellulose itself is pretty airtight (tho not ideally enough on its own) so any accidents/later punctures of the (well shielded) OSB is backed up by in-depth supplementary airtightness - so the overall spec is very robust longterm.

That's in addition to the great virtues of blown-in cellulose - first, being organic material, it's hygrocopic (a separate topic) and second, because it fully fills all gaps without joints and remains under slight elastic compression, the actual in-use insulation value it delivers is far beyond its modest nominal lamda, compared with the alternatives mentioned above.]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264314#Comment_264314 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264314#Comment_264314 Tue, 02 Jan 2018 12:12:38 +0000 tony Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264319#Comment_264319 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264319#Comment_264319 Tue, 02 Jan 2018 13:32:22 +0000 Nick Parsons
Poetry!

Insulation across the nation]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264337#Comment_264337 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264337#Comment_264337 Tue, 02 Jan 2018 20:53:27 +0000 fostertom
Posted By: tonyAre we talking wet or dry blown in? I thought settlement was a significant issue, certainly it has been in the past.
Def dry - good practice shd rule - will look out the video.]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264345#Comment_264345 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264345#Comment_264345 Wed, 03 Jan 2018 09:32:24 +0000 Simon Still Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264429#Comment_264429 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264429#Comment_264429 Fri, 05 Jan 2018 07:48:22 +0000 borpin Posted By: PeterStarckOur house has the airtightness built into the fabric of the walls and roof in the form of Icynene and OSB. We didn't use airtightness membranes or tapes at all. +1]]> Durability of air tightness https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264464#Comment_264464 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15470&Focus=264464#Comment_264464 Sat, 06 Jan 2018 13:01:21 +0000 fostertom Posted By: Simon StillIs there any reason the same approach (external/sealant adhesive joints) wouldn't work on a SIP or CLT construction?How would that work, when the outer skin stops at the edge of ea panel i.e. doesn't bridge unbroken across joints or between elements? In other words it's full of joints to be sealed by some method, vs eliminating such joints by making the outer skin continuous. The challenge is not the general surface of the panels, but the joints between them.]]>