Airtight construction and wellbeing

[Anonymous]

I am interested to get some reactions to my thinking on airtightness. I will state my thoughts rather straightforwardly, looking to get some thoughtful and critical answers.
It is a purely energy use driven issue. Once energy use has come down through high insulation levels, losses due to air leakage are the next target. I understand this fully. My concern is that the 'zero energy' targets are losing the plot slightly.
Environmental awareness is not a technical issue. At bottom, the issues concerned are to do with a love of and respect for life (implying acceptance of death), as opposed to a neurotic fear of personal death, leading to an out of balance approach to the rest of the ecosphere.
Life is the most complex phenomenon known to man. Therefore, any reductionist approach to living systems will fail. This is where we are now.
The 'zero energy' approach risks being just another set of blinkers.
Truly sustainable buildings do not set zero energy or any other technical standard as their goal. Truly sustainable buildings aim to be supportive of life in the widest possible way. Obviously technical standards can and will provide important tests in some areas, energy use being one.
But the logical outcome of the airtight building approach is to get rid of all openable windows, as users opening windows rapidly becomes the single largest cause of loss of heat energy. Pesky humans! Fancy wanting a breath of (not pre-warmed or ducted) fresh air! Fancy wanting to feel the same beeze that rustles the leaves of the oak tree!
We must aim for buildings that do not use energy needlessly, but which support the best possible models of human life. That is, humans must be encouraged to feel connected with life, with nature.
Living in totally controlled internal environments has been shown time and time again to make people physically and mentally stressed, and often actually unwell. It has a subtle psychological and cultural effect as well, as increasing isolation from nature breeds contempt and uncaring attitudes. A simple example is the common practice in air conditioned buildings of users setting thermostats to lower temperatures in summer, than they do in winter. The low energy designer may tut and say 'stupid people'; the true environmentalist looks at the situation holistically, and says, 'there is something going on here – why do these people feel the need to do this? How can I make a positive move to change the behaviour?'
In sum, I am not saying – design leaky buildings. I am saying – take a life friendly, holistic approach to aim for true sustainability.

[Nick Grant]

Seems we have some common ground!!!

I'd add a third approach which is trying to be air and even vapour tight but keeping the cold (out) side vapour permeable (carefully avoiding use of word 'breathing' as it implies air movement). So I personnaly wouldnt feel bad about a non breathing layer in my walls provided it is in the warm part. I know others prefer the idea of the whole wall being vapour permeable but I am unconfident about that approach mixed with plenty of insulation as opposed to say cob.

I see huge problems with poor ventilation in any building (made worse by poor insulation and cold bridging leading to condensation and mould) but really do want to separate out the issues of ventilation and leaky construction. I really don't see any danger of houses being built too airtight (constructiuon not ventilation). Aim for tight and scrape 10 AC/h is more likely with typical designs I see on site. Hence my strong concern with any meme that spreads the idea of a bit of leakage being a good thing. I was infected with the same and it resulted in the mistake of running the 'Tyvec' horizontally round the outside rather than vertically (and so trapped between battens for better airtightness). I thought a bit of air would be a good thing but thought it on a hot still day rather than mid winter with howling gale which now blows through the wall insulation.

I share your concern about Zero energy but perhaps for different reasons but disagree about your sums for embodied versus running energy – see other post re refurb or demolish. However I am a fan of refurb in many situations for other reasons.

To pick up on Tahir's post, a lot of talk about low energy houses is based on zero experience beyond perhaps visiting the Waites House at CAT at some point! There are so few genuine low energy homes in the UK that ideas that they are like living in a plastic bag or concrete bunker take hold all too easily. The first low energy house I visited was Sue Roaf's in Oxford and I was struck by how lovely and even the temperature was despite snow outside. So Tahir, I'm sat in my office at a comfortable 20C and 44% relative humidity but then it's almost summer so no great achievement. . . .

[Anonymous]

a lot of talk about low energy houses is based on zero experience beyond perhaps visiting the Waites House at CAT at some point! There are so few genuine low energy homes in the UK that ideas that they are like living in a plastic bag or concrete bunker take hold all too easily. The first low energy house I visited was Sue Roaf's in Oxford and I was struck by how lovely and even the temperature was despite snow outside. So Tahir, I'm sat in my office at a comfortable 20C and 44% relative humidity but then it's almost summer so no great achievement. . . .

Well that helps me, not! 🙂

Any good books for simpletons on the subject?

[Nick Grant]

Hi Paul

Just spent a couple of days visiting eco-buildings and it reinforced my belief that airtightness has to be designed in rather than achieved though advanced origami skills with membranes around numerous penertrations and oodles of silicon. Sealants may not be completely avoidable but can be largely designed out.

Defininitely agree re membranes mechanically trapped, eg under battens, at joints rather than tapes.

[Mark Siddall]

Another thread deserving another lease of life:

With regard to airtightness I have a number of questions ranging from the strategic level to that of the detail.

1) Most of the documents that I have read suggest that a strategy based upon a 'single line of defense' is the best one. This may be acceptable in the grander scheme of things but does this apply to the fiddly details around openings and penetrations?

2) In terms of creating an airtight seal mechanical clamping/pressure plates seem to get the thumbs up. I can see the logic and have to say its my preferred solution. Are there any best practice techniques that can be recommended when using this approach i.e. lengths of laps between one element and the next, the number/location of pressure plates (note earlier query in 1), bonding to surrounding materials (particularly when a membrane is interfacing with masonry)?

3) What other methods are considered to achieve a good, long term standard of airtightness? Paul mentions the use of self-adhesive EPDM/Bitumen membranes for addressing airtightness at windows/door details. Does anybody know any manufactures of such products? Which ones are the best, which are more prone to degradation.

Mark

[SimmondsMills]

I think the Canadians have some useful site manuals for air tightness membrane work as part of their recent low energy housing programmes. You could google 'Canadian R2000' .

Also David Olivier, will know..!

I agree, it would be worth finding this sort of guidance in an electronic format.

[Mark Siddall]

Andy,
I've been looking into the R2000 scheme. There are no construction details available on the net (at least non that I have found). R2000 does have a catalog of standard details in book form. The IRC-NRC have some reasonably useful stuff but nothing that can be confidently stated to comply with Silver or push towards the boundaries of Gold standards. I've not got my hands on a hard copy of the R2000 standards yet…..hopefully when my bank balance is feeling a bit healthier I'll get my hands one.

Finally, R2000 is a standard for timber frame and I am more interested in masonry: for its thermal mass. Though the some of broader airtightness techniques can be gleaned from R2000 I expect there will be some subtle differences. So in the mean time thoughts and experiences to the questions above would be useful.

Mark

[David Olivier]

A huge topic. A scientific study of R-2000 homes in mid-80s? found that they were healthier in several respects than leakier homes (leakier in Canada means maybe 4 air changes/hr at 50 Pa) with less thorough ventilation.

The advice to clamp membranes at the joint and not rely on sealant alone was first issued in Canada about 25 years ago I think since when I've been advising UK clients to do this in their buildings! There is some poor advice prevalent in the UK which is now almost a generation behind Canada and Sweden and suffers from the absence of public sector-funded research &/or leadership. I have a whole bookshelf of various volumes on superinsulated airtight buildings – all foreign – and it should go in a bibilography as soon as AECB issues some more detailed design guidance.

If a building needs advanced origami skills, it's unlikely to be very airtight. At the most, in my opinion, designers should only assume that builders need to know how to fold a membrane around a corner. This is not understood in the UK because there's been no industry training on the scale of the R-2000 Program (£30 million, 20 years, said to have reached about 70% of registered builders).

Masonry doesn't need a membrane; plaster is very airtight. Concrete can be airtight by itself. 85% of the 6000+ Passive Houses probably use these two materials as the air barrier on their walls. There's less literature on making masonry and concrete buildings airtight – largely because there's less to do and the procedures are less complicated.

David.

[Mark Siddall]

Paul,
Thanks some excellent points there many confirming the direction that my thoughts have been headed in. Earlier in the thread, many months ago in reality, you mentioned an adhesive EPDM membrane….any tips about a manufacturer? (I admit not the ideal solution given the pressure plate strategy but when I am placed in a spot with a contractor I would like to have a fall back position.)

Mark

[Mark Siddall]

A related subject is the cost benefits of airtightness i.e. the cost/kWk saved. See https://aecb.net/forum/index.php?topic=749.0

Any help with providing the information requested on that thread would be appreciated.

Mark

[Mark Siddall]

An interesting articles on airtightness and testing in the UK on Mark Brinkley's blog.

http://www.housebuildersupdate.co.uk/2006/09/whod-be-pressure-tester.html
http://www.housebuildersupdate.co.uk/2006/10/timber-frame-wins-on-airtightness.html

Mark

[Mark Siddall]

Just tying a couple of relevant threads together.

What is the minimum permissible ach/hr?
https://aecb.net/forum/index.php?topic=763.0

Gas Cookers
https://aecb.net/forum/index.php?topic=761.0

Stamford Brook
https://aecb.net/forum/index.php?topic=783.0

[Mark Siddall]

I am currently considering the issue of airtightness in large framed structures. There are two frame types concrete and steel.

CONCRETE
A concrete frame is useful if you have suceed to introduce masonry infill as the expansion and contraction issues are less problematic, thus helping to ensure greater long term airtightness. Also concrete frames are easier to detail and the abutment details can be simplified, thus helping to ensure airtightness is easily achieved.
The problem arises where: –
1) the ground conditions can not take the load and the cost of remediation is prohibative
2) you have a project manager/D+B contractor that is perhaps a little short sighted and believes steelframe to be cheaper and can delvier an equally robust design without additional effort.

STEEL
So we are left with a steel frame structure. Complications arise due to the increased complextity of details i.e. steel to steel junctions and bracing etc.
For airtightness the sensible thing to do is separate the external leaf from the frame, thus allowing continuity of the air barrier, however this results in reduced internal area (impact of internal columns/bracing), reduced flexibility (columns get in the way of moving partitions) and for comercial client loss of revenue. As a consequence in reality setting the primary structure internal of the external leaf is not a very viable option despite its energy benefits.

So finally I get to the question, what are the 'best' strategies to over come airtightness the issues that arise from setting a steelframe (bracing, junctions and all) within the plane of the external leaf?

Mark

[Anonymous]

Mark

Some observations based on parallel experience (Wellcome extension to Science Museum). We were required to provide a 30m tall firefighting shaft – with 2 hour fire integrity. This was originally, and sensibly, proposed as in-situ concrete, but was then altered to steelwork on cost grounds.
The fire protection detailing package became an epic of special conditions, movement joint issues etc. etc. – leading to my first observation – there may be a saving on material, but the design and installation work will be massively increased. So 'without additional effort' will not be true.
Second observation – fire protection is dealt with on paper and by visual inspection – submission of details and a few walks round a busy site. Airtightness is dealt with by testing. I would doubt very much whether our carefully thought through fire protection details were successfully installed at all points – let's hope they are never reality-tested! But your D&B contractor may have plenty of time to repent at leaisure if the building fails its tests due to many small failures of workmanship throughout the envelope.

[David Olivier]

Mark

Tell your contractor / manager firmly that they're not comparing like with like!

Concrete-frame buildings are OK as regards airtightness – as easy (or hard, depending on one's point of view) as load-bearing masonry with concrete floors.

Steel-frame offices / schools are a nightmare as regards airtightness, unless the air barrier can be routed completely outside the frame.

Bill Bordass has lots of horror stories of where they leak like sieves. I've managed to avoid steel-frame except occasionally for steel posts in houses to support the corner where the window wraps around two sides of the building (the steel is well inside the glazing at this point). I was involved in one job which was a steel frame (by order of the QS) but it was never built so we don't know how much it would have leaked despite efforts to make it airtight.

It's like concrete versus timber-frame houses; I was talking to a developer yesterday and we both suspect that the design costs must be higher for the timber-frame house, other factors being equal. In particular, to reach a very high standard of airtightness, the junctions are more complex than they are with solid-walled masonry or concrete-walled buildings. I haven't discussed this point with any architects, what do you think?

David.

[Mark Siddall]

David,
I’m not surprised by the catalogue of horrors.

Lucky you for avoiding steel frame you’ve obviously had pretty understanding contractors and clients. :- )
I can only dream…..

It's far from ideal burying the air barrier that deep into the building fabric. There is little or no oportunity to undertake remedial work post air test or at some later date. This said wrapping the building in a poly bag will minimise the compexity as you'd avoid awkward junctions and interfaces. The biggest problem then in how to apply a weathering finish to the building and not undo all the good work.

Not having done timber frame I can’t pass any real judgement on its complexity in design…though I hope to be able to in the near future….all in all I think Andy would have for more to add on this subject. I think that making a timber frame airtight is far easier than a steel frame, as the assembly process is easier to coordinate at floor, wall and roof interfaces (membranes can be detailed to lap far more readily).

I think that during construction concrete and masonry with plaster are more robust and less vulnerable to mechanical damage. Insitu concrete is the ultimate wet trade could offer excellent airtightness and a very architectural internal finish if the formwork and concrete spec is good enough. Also there’s no point passing the air tests on completion of construction project only to have the building unavoidably degrade later in its life; so ease of repair/maintain in the long term is critical. Concrete and plastered masonry tick this box also.
NOTE: This only works if full wet plaster is used rather than parge coat (with parge you technically end up with a very similar, i.e. inaccessible, set up to timber frame).

Mark

[SimmondsMills]

loads more design time in timber frame detailing!

[Mark Siddall]

A link to another thread, on this forum, touching on Canadian Airtightness services outlets and there availability (or lack thereof) in the UK. https://aecb.net/forum/index.php?topic=870.0

Mark

[Mark Siddall]

One thing that has not been raised on this thread, perhaps because the obvious stuff is the easiest to miss, is that improved airtightness can be achieved by minimising the number of interfaces and trades to manage (not just by simplifying the geometry). Changes in material or construction technology will always pose a threat to the airtightness of a project, as closer management will be required (and this is not always around when you need it).

A further quote from Kerstin “To get an n50 of 0.6 (that's 1m3/m2@50pa to you and me) you need good design and skilled workmanship, working hand in hand. The benefit of timber frame is that you don't have to change the principled approach or system as often as you normally have to in a massive building. More details = more devils!”

The question arising from all this is; thought timber frame may have more details (lapping each sheet of membrane), but in having fewer trades/technology interfaces to manage than traditional masonry (bricky, joiner/membrane installer/s for the roof, plasterer), is it more likely to provide a reliable result?

Mark

[Mark Siddall]

I have been studying the airtightness requirements of a notional Gold standard house of 84sqm and have calculated the Air Permeability in accordance with TM23/ EN 13829:2000.
Given that the Passive House requirement is for an n50 <=0.6ach/hr the result of the calculation was surprising. It would seem that a house of this size with minimal surface area (rectangular on plan with pitched roof and no oddities) would require an Air Permeability of 0.569m3/hr/m2@50pa. This is some 25% lower than the <=0.75m3/hr/m2@50pa noted in the AECB guidance notes.
Two matters arise from this: –
1) Ensure that you calculate the Air Permeability requirements for each Gold standard project.
2) Should the AECB Standards make more recognition of the Passive House n50 <=0.6ach/hr requirement?

[Mark Siddall]

Thanks David, opening out the discussion to cover the Gold standards airtightness requirements is, for clarities sake, an important matter.
Whilst I am under no illusion that the achieving high standards of airtightness is difficult, especially in Blighty. Given your comments I have had cause to reflect upon the Passive Houses in Lindas, Sweden. These had an air leakage of 1.1m3/hr/m2@50pa (0.3 l/s@50pa), though they were 120sqm each….
The sensitivity analysis that was undertaken on this project helped to highlight the importance of airtightness and the limits to which it could be stretched (rather, I should say compromised). In this case the estimated as-built background air change rate was 0.05/hr. Using the rule of thumb (x20) this means that you can “get away with” 1ach/hr@50pa; in the case of Lindas this equates to 1.1m3/hr/m2@50pa. (It is worth noting that at Lindas they had left some bunce in the design; more insulation, slightly over egged MVHR).

I take you point that the timber frame must be concieved from the start with airtightness in ones mind and traditional UK detailing may not always prove successful and that of sequencing the works in the appropriate manner.

Mark

[David Olivier]

Paul

As a matter of interest, can you suggest any airtight dampers? On one building which I'm involved in, it's been decided to use a separate air extract from the kitchen rather than link it to the main MVHR system (which needs good filters to keep all grease out of the ductworks).

Also, can you suggest what the wind speed should be limited to, in order to improve the precision of air permeability tests, both for low-rise and tall buildings?

This 1.1 m3/m2hr @ 50 Pa in Sweden is unremarkable. They were achieving about this rate (well, 0.7-1 ac/h @ 50 Pa) on very carefully-built wooden houses 30 years ago.

The PHPP worksheet from Germany uses a factor of 0.07 to convert volumetric air leakage to design air leakage, for the purposes of heat loss calculation.

David.

[Mark Siddall]

David,
The 1.1m3/hr/m2@50pa was not meant to be remarkable. What it was meant to demonstrate/confirm is that Passive House/Gold can be achieved in agreement with your earlier statement on n50 vs. air permeability, though some trade offs have also to be accomodated.

To clarify certain aspects of airtightness detailing, here's what could turn out to be a little heresy…..

I am reading “Airtightness and Thermal Insulation” by Carlson et al (1980). I'm only a third of the way through but a preferred solution around windows seems is a one part polyurethane foam. In constructed case studies it was proven to bear up quite well, and further tests one year later showed little or no deterioration in performance.

At the time the book was written one part (rather than the more common two part!) polyurethane foams were a relatively new addition to armoury of airtightness detailing. All in all the materials future looked promising, other more recent documentation suggests is has good durability. There was/is a concern about air pockets forming in the foam which would then lead to limited weaknesses its performance. The impression gleaned from the book is that it is a promising solution. One advantage is that the foam can bed easily around the fixings used to secure the window where membranes could be torn or penetrated. The greatest problem with polyurethane is that, though it bonds well to most materials, it does not bond well to polythene. Some other documentation that I've read *implies* that polyurethane, when used to achieve airtightness details, is not a VOC concern. (The reason I say 'implies' is that the section on IAQ discusses a range of sealants, and highlights those that may be of concern to people that are chemically hypersensitive, polyurethane though discussed is not highlighted as a concern.)

It seems that polyurethane is relatively problem free to install and offers reasonable longevity to boot. Why all the talk of fiddly membranes around windows, doors, sole plates etc?

Mark

[Mark Siddall]

I suppose it depends upon whether the plastic element of Thermabate is made from polythene or UPVC and whether the forces from the expanded foam will cause twisting/distortion in the Thermabate. (Some info that I have read suggests that some expanded foams can distort windows/door frames!)

Though I have never tried to bend Thermabate to my mind it is bound to be a less robust material than a good doorframe. Also how well the Thermabate is fixed will also have a major impact. Given that Thermabate is not designed to take structural loads I believe that it is unlikely that the fixings will be sufficiently robust. As a consequence if such distortion does occur, and even if airtightness is not compromised, then thermal bridging and/or thermal looping could also become an issue. I would think that such a defect is likely to go undetected, even on a well-managed site. As a consequence for masonry build I’m minded to stick with the membrane approach.

As for timber frame, though it is technically suitable, as you say, the key thing is ensuring that the appropriate cultural shift towards airtightness also takes place. If the constructor is using a familiar material (i.e. polyurethane foam) they are more likely not to read the spec and default to using the material in familiar (and rather unsuccessful) techniques. So, even if it is just because it is an unfamiliar technique, by having to install a membrane they are more likely to pay more attention to the detail (and read the spec?). Okay, I’m convinced. Stick with the membranes ;- )

(By the way it is also worth noting that the book Airtightness and Thermal Insulation is of Swedish origin and predominantly deals with timber frame construction rather than masonry.)

Mark

[Author]

Posts