K78

Health risks associated with passive houses

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4 minutes ago, gravelld said:

But that ain't evidence.

 

 

I agree completely.  

 

I treat PH certification as being something like very modern design.  It may well put off a lot of people, but it's just as likely to spark greater interest in at least some of those who aren't put off.  Whether that impacts the final price is probably very situation dependent. 

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1 hour ago, jack said:

I don't believe the word Passivhaus by itself is a trademark.  From memory they only have a trademark on the logo.  There may be a question over whether the word "Passivhaus" is confusingly similar to the logo.

 

 

Wolfgang Feist would appear to own a number of EU related marks for both "passivhaus" and "passive house".

Figurative marks with letters provide protection against the use of the words too. [insert blurb about the technicalities of trade mark law]

Of course registrations are class specific but he has registered class 37,41 and 42 which is a pretty good catch all for what they do.

 

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While my house ain't at pH standard its close enough for me. In my last pad, a 1960 council townhouse, the air quality was terrible. It was stuffy and generally in winter had damp patches due to the high amount of condensation. The change to what my new house is like now is night and day. No condensation and no stuffy air. My wife always opens the windows to let fresh air in even though I explained that is what the mhrv is doing. Now I just let her work away. People get too wrapped up in trying to make sure your house has no cold bridges and has thick insulation everywhere and airtightness tape on everything. Me I have a large wrap around window that is as big a cold bridge as you could get. Does it bother me, not a bit. It lets an unreal amount of light in and is nice to look out at. I even have two stoves, one pellet and one wbs. I love sitting in front of them on a cold day looking out the big window watching the world go by. 

 

Remember that at the end of the day you have to live in the house when it's done so have nice big windows and even let the wife open them. Enjoy the time you spend in the house instead of obsessing over the minute details that pH requires. 

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11 minutes ago, Declan52 said:

Me I have a large wrap around window that is as big a cold bridge as you could get. Does it bother me, not a bit.

 

As long as you're comfortable with going to hell  :P

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@jack I'm pretty sure the reason for Jeremys property being downvalued by a surveyor, would have been because it's timberframe with timber cladding. 

 

I managed a Halifax agency for 10 years. I was constantly dealing with survey retentions and problems. 

 

Many surveyors want to pass responsibility of any risk to another party. Hence the reason 99% of surveys recommend damp and timber inspections in houses with no evidence of damp. 

 

If they come across a house without a block skin many of the "old school" surveyors just don't like them. They can be quite derogatory with their opinions in my experience.  

 

They also base their valuations on comparable evidence (recently sold local houses). So "non standard" builds cause them a headache. 

 

Their lives are easier if everyone just sticks to building cavity walled houses, hence they don't encourage anything else :) 

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51 minutes ago, Barney12 said:

With the amount of stuff I am guilty of it was never in any doubt.

 

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Looks like I spent £4k on a 4.5m wide, 2.2m high passive cat flap without even realising. Cat has chosen the living room slider as her chosen means of entry and exit.

 

Agree with Jack  - when its very cold or hot out then the windows and doors can stay closed and the house is nice and comfortable, rest of the year I don't really care.

 

Our trades noticed this during the summer - they slowly realised that if they shut the front door & windows early on on a warm day the house stayed cool, if they left them all open, it got too hot. They admitted that it was counter intuitive but obviously worked!

 

We never bothered to get passive certification, seemed like a lot of money for no real benefit.

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22 hours ago, K78 said:

I've read a lot about the benefits of passive house design over the past few years on ebuild and other forums, but not much on any negatives.

 

My biggest concerns with passive house design have always been around air quality and internal temperature. I really struggle in stuffy environments. I even open windows in winter.

 

The honest answer is that we simply don't have sufficient data yet.

 

There certainly is evidence that any form of 'managed' ventilation system, particularly those that operate at fairly low ACH, is a major contributor to 'sick building syndrome', and there are technical reasons that you can't make the very simplistic MVHR systems that are currently available work at the sort of ACH we'd like them to be able to work at for human health and wellbeing.

 

It won't be popular for me to say so on these forums, I know, but PassivHaus is at the extreme end of the design spectrum and it is invariably promoted by people who (whether they see themselves as such or not) are extremist 'fanatics' in building technology terms.

 

I don't mean that in quite the negative way it perhaps appears, and I do support exploration of these construction strategies - it's the only way we'll gain the necessary experience - but I do think we need to be careful not to dismiss such concerns, as they're certainly not unproven or without basis.

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9 minutes ago, Sensus said:

 

The honest answer is that we simply don't have sufficient data yet.

 

There certainly is evidence that any form of 'managed' ventilation system, particularly those that operate at fairly low ACH, is a major contributor to 'sick building syndrome', and there are technical reasons that you can't make the very simplistic MVHR systems that are currently available work at the sort of ACH we'd like them to be able to work at for human health and wellbeing.

 

It won't be popular for me to say so on these forums, I know, but PassivHaus is at the extreme end of the design spectrum and it is invariably promoted by people who (whether they see themselves as such or not) are extremist 'fanatics' in building technology terms.

 

I don't mean that in quite the negative way it perhaps appears, and I do support exploration of these construction strategies - it's the only way we'll gain the necessary experience - but I do think we need to be careful not to dismiss such concerns, as they're certainly not unproven or without basis.

 

An interesting reply. I guess the question is; where should the design sit between the fairly poor standard of current regs churned out by the major developers and the fanatical (I think that's a fair description) passive house? 

 

It it seems the low volume market (and especially timber frame manufacturers) want to trade off the ph band wagon. Many do it so they can command premium prices. 

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33 minutes ago, Sensus said:

There certainly is evidence that any form of 'managed' ventilation system, particularly those that operate at fairly low ACH, is a major contributor to 'sick building syndrome', and there are technical reasons that you can't make the very simplistic MVHR systems that are currently available work at the sort of ACH we'd like them to be able to work at for human health and wellbeing.

 

I'd love to hear more about this.  What little I've been able to find in the past suggested that UK regs ventilation rates actually resulted in too much air exchange, leading to unduly low levels of moisture during dry winter months.  

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1 minute ago, Barney12 said:

 I guess the question is; where should the design sit between the fairly poor standard of current regs churned out by the major developers and the fanatical (I think that's a fair description) passive house?

 

Well, for a start, I think you need to recognise that the current Regs in no way represent a 'fairly poor standard'.

 

Even the minimum standards being built to these days are a massive leap forward over the stuff that was being built when my career started, which in turn were a big step forward from the stuff that had gone before.

 

For comparison, when I first started,

Walls and roof (IIRC) - U=0.6

Windows - U = 6.0

Doors: No requirement

Floors: No requirement

Thermal bridging: No requirement

Airtightness: No requirement

 

Contrast that with where we're at today...

 

It could be argued that the industry and the Regulations are being forced forward at a pace that represent an Olympic hundred-metre sprint, just after they've learned to walk. The numbers of houses that have been built to the current B.Regs standards, much less PassivHaus, represent a tiny proportion of the nation's overall housing stock, yet are already exhibiting obvious and typical characteristic deficiencies that major developers are well aware of.

 

The truth is that a lot of very experienced people, with access to a lot more research than you and I, have decided that the current Regs are as far as it is reasonable to go (and further, if the mutterings of many senior members of the BRE and Building Control Alliance are to be believed), with our current level of technology, knowledge and understanding, and despite the political imperative to reduce carbon emissions.

 

Current Building Regulations new-build  minima are already very strict, compared to the majority of the UK's housing stock, and anyone who pushes beyond them should recognise that they are entering territory into which the leading experts have decided, on balance, that it is unwise to push mainstream development any further just at present.

 

I know that I will be sounding extremely negative, but my concern - being aware of the characteristic deficiencies that are beginning to show themselves - is that if we fail to proceed with sufficient caution, we will see a sudden backlash (as we did with system building in the '60's and timber frame in the '70's) which will set back development by decades. :(


 

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2 hours ago, K78 said:

@jack I'm pretty sure the reason for Jeremys property being downvalued by a surveyor, would have been because it's timberframe with timber cladding. 

 

 

That may well be the case, but the story Jeremy relayed was that the surveyor specifically told him that "eco" houses, such as Passivhaus standard houses, were worth 10% less because the eco angle put people off.  Nothing about the construction method (although that may have framed - pardon the pun - the surveyor's thinking).


I tried to find the thread over on ebuild, but it's tough given he had nearly 11,500 posts!

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3 minutes ago, Sensus said:

Current Building Regulations new-build  minima are already very strict, compared to the majority of the UK's housing stock, and anyone who pushes beyond them should recognise that they are entering territory into which the leading experts have decided, on balance, that it is unwise to push mainstream development any further just at present.

 

 

Genuine questions: are these "leading experts" all unbiased researchers without links to large builders?  Do you believe that the sole or dominant reason for stopping here is that independent experts have concerns?

 

And while the rules may in theory be strict, do you believe that when a developer builds 10 or 100 or 1000 houses, all of them are built to fully meet the regs?

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9 minutes ago, jack said:

 

I'd love to hear more about this.  What little I've been able to find in the past suggested that UK regs ventilation rates actually resulted in too much air exchange, leading to unduly low levels of moisture during dry winter months.  

 

I'm not sure that's possible, with the UK's maritime climate! Which is where, incidentally, a number of European techniques and strategies fall over - our winters are comparatively very warm and wet compared to mainland Europe.

 

Certainly, one of the characteristic defects that has started to exhibit itself with houses build to current regs is internal mould growth, which isn't something that happens if your atmosphere is too dry.

 

Of course, moisture levels are only one part of the problem with low ventilation rates; the other biggie is build up of pathogens and contaminants that are harmful to human health.

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1 minute ago, Sensus said:

Certainly, one of the characteristic defects that has started to exhibit itself with houses build to current regs is internal mould growth, which isn't something that happens if your atmosphere is too dry.

 

This is in houses to current regs without MVHR though.  When most of us talk about "beyond regs" levels of airtightness, we're generally talking about implementing MVHR at the same time.  

 

I assume the main concerns with moisture are the interstitial kind, rather than the "black patch in the corner" that you sometimes get on external walls of poorly insulated houses?

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1 hour ago, jack said:

 

Genuine questions: are these "leading experts" all unbiased researchers without links to large builders?  Do you believe that the sole or dominant reason for stopping here is that independent experts have concerns?

 

And while the rules may in theory be strict, do you believe that when a developer builds 10 or 100 or 1000 houses, all of them are built to fully meet the regs?

 

Fair question!

 

The 'leading experts', I would say, are the guys who work in Building Control and in the BRE. People who get to see data from thousands of houses, not just the occasional self-build, and who have access to expensive research facilities.

 

It's difficult to be truly independent of any association with large builders, because large builders are the ones who are building houses in more than penny numbers, and yes, they do also contribute to BRE research.

 

But having worked within several of those large builders, in positions where I was directly dealing with the BRE and Building Control at a national and strategic level, yes, I genuinely believe that the 'experts' are unbiased to a sufficient degree. I'll never convince the conspiracy theorists, I know, but even those of us who worked within the developers genuinely wanted to understand and overcome the issues (if only for entirely cynical reasons: if we could overcome the current problems and/or learn to build to a higher standard than our competitors for reasonable cost, it would give us a substantial commercial advantage!).

 

I do believe that the dominant (though no, not the sole) reason for stopping here is independent concern. I've said previously on this forum, already, that I know from first hand conversation with them that some of the most senior guys responsible for formulating Building Regulations standards are gravely concerned that Part L has far outstripped Parts C and Part F, and that a root-and-branch overhaul of the latter, demanding much further research, will be necessary before we can go much further.

 

When a developer builds 10 or 100 or 1000 houses, the basic design and specifications will be fully compliant, by and large. The two areas where there will be some variability is with air tightness and sound transmission, both of which are extremely sensitive to workmanship, and neither of which is currently tested on a 100% plot-by-plot basis.

Edited by Sensus

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43 minutes ago, jack said:

 

That may well be the case, but the story Jeremy relayed was that the surveyor specifically told him that "eco" houses, such as Passivhaus standard houses, were worth 10% less because the eco angle put people off.  Nothing about the construction method (although that may have framed - pardon the pun - the surveyor's thinking).


I tried to find the thread over on ebuild, but it's tough given he had nearly 11,500 posts!

 

I remember the thread. It sounds like a typical surveyors excuse to a home owner. And a bad one at that. It's crazy to say that the "Eco" angle puts anyone off these days. If anything "Eco" carries a huge premium. 

 

What puts many brits off is the thought of a timber frame with timber cladding. I'm considering it and my parents and many friends think it's odd at best. 

 

Even though its the buyer or builder who usually pays for the survey, the valuation is usually to satisfy the mortgage lender.

Edited by K78

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1 hour ago, jack said:

 

This is in houses to current regs without MVHR though.  When most of us talk about "beyond regs" levels of airtightness, we're generally talking about implementing MVHR at the same time.  

 

I assume the main concerns with moisture are the interstitial kind, rather than the "black patch in the corner" that you sometimes get on external walls of poorly insulated houses?

 

Yes, I've experienced it (personally) in houses fitted with MVHR - of which, I should say, I've been responsible for the construction of several hundred (mainly on sites to Code Level 4). Only a small percentage of them suffer problems, but that, of course, is why the knowledge gained from numbers becomes important: it's no good saying ''Well I built my own house, and I never suffered a problem".

 

And no, it does tend to be the 'black patch in the corner' kind; not associated with cold spots any longer, but more that you get 'dead spots' in the air circulation which in combination with high levels of relative humidity (moisture from respiration, cooking, washing that isn't sufficiently dispersed by the low ACH ventilation) can facilitate mould growth. We spent a fair while trying to blame thermal bridging before we worked out the true culprit though.

 

Ironically, we also spent several years chasing the red herring of interstitial condensation with regard to one of the other characteristic defects of housing to the current regs - loft condensation - before realising that several entirely different and unrelated mechanisms have now taken over as the root cause of the problem!

 

Edited by Sensus

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1 hour ago, Sensus said:

And no, it does tend to be the 'black patch in the corner' kind; not associated with cold spots any longer, but more that you get 'dead spots' in the air circulation which in combination with high levels of relative humidity (moisture from respiration, cooking, washing that isn't sufficiently dispersed by the low ACH ventilation) can facilitate mould growth. We spent a fair while trying to blame thermal bridging before we worked out the true culprit though.

 

In a way, this sounds to be less an air exchange rate problem, and more an issue of internal air paths.  I guess the paths are too difficult to model (especially given the different ways in which people use houses) so the simplest solution is to increase ventilation rates.

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1 hour ago, tonyshouse said:

What are these please?

 

What, the causes of loft condensation in modern cold roofs?

 

Well, in the 'old days' it was caused by warm, moist air leaking out through the structure or poorly sealed loft hatches and condensing as it cooled within the insulation - classic 'interstitial condensation'. You'd also occasionally get localised condensation happening on improperly lagged pipework or water tanks. You can still get these with build defects, so you need to rule them out first.

 

These days, the problem has shifted, though: the big cause of the problem is that ceilings are now so well insulated and sealed that the air temperature within the loft space drops below dewpoint (where previously it would have been kept warm enough by heat leaking from the house), so you actually get a dewfall on top of the insulation each night. It soaks into the insulation, and the insulation is so thick that it stands no chance of drying out when temperatures rise the following day, no matter how much ventilation you pass over its upper surface. The effect is cumulative, and the next thing you know, your insulation is saturated. The worst time of year for it is between about now and Christmas - we used to wait with despondency for the glut of complaints when people when up into their lofts to recover their Christmas decorations each year! The NHBC is still trying to fob people off on recent new build by saying that it's just moisture from the drying-out process, but we know that this isn't true (I've experienced it on timber frame, for a start, which is essentially 'dry build' - and also experienced it year after year on properties that have had plenty of time to dry out).

 

Next factor is aerodynamic: a ventilated pitched cold roof acts like a very crude aerofoil (aeroplane wing) and the air flowing over it forms a low-pressure 'bubble' on the leeward side. The reduction in pressure causes cooling, and you end up with the upper roof structure cooling below ambient temperature. Condensation forms on the underside of the roofing membrane and drips onto the insulation below (and is continually replenished, because you're continually flowing cold, damp air over it... increasing the loft ventilation actually worsens the problem: ask me how I know!).

 

Finally, and this is beyond my own understanding of physics, so don't shoot the messenger - I'm only relaying what I was told by the eggheads at the BRE - they tell me that dense solids like roof tiles will continue to radiate heat energy in a way that gases like air don't, so their surface temperature will actually drop below ambient air temperature at night, even when there is no aerodynamic effect, exacerbating the aforementioned surface condensation problem.

 

All the above problems are very sensitive to site microclimate, so you will frequently get them on some clusters or orientations of plots on a site, and not others.

 

The fixes can be relatively straightforward:

  • Use a warm roof construction (developers are reluctant to do this on cost ground).
  • Use an essentially impervious form of roof insulation (ie. polyisocyanurate foam; Kingspan or Celotex) instead of mineral wool, so that any condensation sits on the surface and has a chance to evaporate off the following morning, instead of soaking in or accumulating.
  • As a 'bodge' fix, it sometimes works to lay a loose visqueen 'vapour barrier' across the top of the mineral wool insulation, again to prevent the condensation from soaking in to the insulation, but if you do this you need to be damned sure that the problem is dewfall condensation rather than interstitial condensation, otherwise you'll worsen the problem instead of curing it.
Edited by Sensus

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40 minutes ago, jack said:

In a way, this sounds to be less an air exchange rate problem, and more an issue of internal air paths. 

 

It is, but the two are inter-related and inseparable.

 

With the very limited and localised vents provided with MVHR, it's impossible to guarantee decent and reliable levels of air circulation to all parts of all rooms without increasing ACH rates to the point that sets up drafts that make people feel uncomfortable, and without the air velocities in the MVHR ductwork rising to the point that they become an audible nuisance.

 

Ironically, having an old fashioned, leaky, low-airtighness envelope inadvertently distributes air circulation much better than our current, crude MVHR systems stand any chance of achieving, and so does the job much better! Of course, they manage heat loss a little less well, so you have to decide whether you prefer low heating bills or a healthier internal environment. :)

 

 

Edited by Sensus

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Sensus, I am a bit confused. Or rather quite confused.

 

I lived in 4 houses in the last 7 years. 2 old, c. 1900 solid walls, 2 mid century. Apart from the current bungalow (1950), which is detached and on the slope and for these or some other reason is significantly better, all other houses were a nightmare. Built-in wardrobe to external wall in 1950 semi (that is on the first floor) was full of mould. We had mould on the wall behind a sofa - not even sitting too close to this wall. We still find clothes that we did not use (hence did not need to wash) after moving here 2 years ago and those smell musty. So what I am trying to say is all these badly insulated houses with "healthy internal environment" did not in fact feel healthy at all. At the same time I am pretty certain those who have UFH will not get mould on their properly insulated walls. When we compare leaky vs airtight shouldn't we look at the share of each type suffering from such problems? 

Edited by oldkettle

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You're making the assumption, I think, that there is only a single mechanism at work causing the problem.

 

That's why I mentioned loft condensation, which is a parallel in many ways: yes, you get loft condensation as a result of interstitial condensation from air leakage in older houses, but you also get it as a result of dewpoint and surface condensation in new ones. There's a happy medium between the two where it's not a problem.

 

Yes, you get mould growth as a result of surface condensation in poorly insulated older houses, but you also get it as a result of moisture build up and poor air circulation in very airtight new ones. Again, there's a happy medium to be had where it's not a problem.

 

Simples. :)

 

I'm a big fan of happy mediums: you'll usually find that there's a good reason that extreme design solutions lie at the extremes. ;)

 

 

As an aside, the design of older properties (whilst undoubtedly not being as scientifically sound or efficient as new ones) was formulated to work with the very high ventilation rates that you got with open fires, which were pretty much the only heating technology available unitil the middle of the last century.

 

The most comfortable house I have ever lived in was a Grade II listed, Cotswold limestone thatched cottage. No DPC or cavity walls and lime mortar that sucks up moisture like a sponge (as did the thatch). There were gaps under the doors that the local mice could (and did) march under wearing top hat and tails. It cost a fortune to heat, and you had to keep the structure warm the whole time in winter, to drive the moisture back into the walls - so it didn't suit our modern 9-5 lifestyle where people resent leaving the central heating running all day while they're out - but it was fabulously snug in winter, lovely and cool in summer, and the air always felt noticeably fresh (unless one of the mice had died somewhere unexpected after being 'winged' in a trap).

Edited by Sensus

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Interesting discussion. Scary, but very interesting!

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