Treated Floor Area query

[Anonymous]

Can anyone give me a definitive answer on how to measure these areas in terms of the TFA required in PHPP?
1. Dogleg stair with storage cupboard underneath.
2. Storage cupboard at 0.73m2, full height.
3. Same sized cupboard at first floor but enclosing MVHR plant.

My assumptions:
1. As storage cupboard is within stair 'area', it does not count towards TFA.
2. Include at 60% of floor area, as a 'secondary room'.
3. Treat as a duct ie does not count towards TFA?

Interested in anyone thoughts/experience. Thanks

[Anonymous]

Thanks for the advice, Pete. Your response aligns with Alan C's.

I had assumed for now that the cupboard under the stairs is not included, even at 50%, because it is within the stair footprint – maybe it should be though. I understand that even Wolfgang may be on the case now!

[Nick Grant]

Thanks Pete

Interesting discussion on reference areas on iPHA site:

http://bit.ly/dfFiam

I like your approach for larger plant rooms.

Still some anomalies to wrestle with such as how many coat hooks and shoe racks in the MVHR cupboard for it to count as a cupboard?

Mark, stairs not counted (unless 3 or less as part of circulation where levels change) but cupboards/circulation under does as long as there is enough height.

[Anonymous]

Interesting. iPHA site insists on unfinished wall dimensions ie omit plaster finish. What about internal stud walls?

[Mark Siddall]

Hadn't picked up on that. Seems like a bizzare state of affairs. Doesn't really seem to make much sense.

Mark

[Mark Siddall]

I agree with the pragmatism.

[Anonymous]

OK. So the updated PHPP guidance note is now clear on this “The floor area is determined by the clear width between building elements (eg plaster to plaster).”

However, there was still some different interpretations today at CEPHD course as to the meaning of some of the definitions. For example, “Not part of the floor area are: . . . , door and window niches (an exception are windows down to the floor with a depth of more than 0.13m).” I took this to mean that entrance door recesses are never included but glazed French doors with deep internal reveals would be. And having learnt PHPP at one of Pete's courses, I have always included internal door openings as part of the subtracted partition area. So far so good I thought until I found out today that the BRE include internal door 'threshold' in the TFA and always include entrance door recesses, regardless of depth. They have even omitted cupboards from TFA. I know these might seem small quibbles but when PHPP is so precise about everything else it seems strangely loose when it comes to measuring TFA, despite the warning that care must be taken to calculate the area correctly!

I suggested to Rob McCleod today that it might be because the measurement protocol is actually defined in the German Floor Area Ordinance, in the same way that we have the RICS Code of Measuring Practice here in the UK, and therefore PHPP guidance does not feel the need to go into great depth in the Manual. This seemed plausible to Rob and had not occurred to him before so he will check with his German partner.

Interested in anyone's thoughts on the above.

[Nick Grant]

You are right, I think this is standard in Germany for working out rental etc as well. It doesn't matter too much what convention used as long as comparing like with like so all need to use same with PH.

[Mark Siddall]

I agree that consistancy is key. I think this is the German doc in question: http://www.gesetze-im-internet.de/bundesrecht/woflv/gesamt.pdf Offers little more info than PHPP though! (If Google translate does enough.) An important one for PT to address!

Mark

[Mark Siddall]

Mark
I interpret it that both Windows and open wall recesses that extend to the floor (in excess of 130mm) are included in the TFA. You do not include entrance doors according to the German doc. Pete's logic would suggest that IF any recess is over 130mm it is usable. Thus Pete's approach would avoid confusion when French door arrangements are used.

Mark

[Anonymous]

The BRE Passivhaus team provided us with this translation of the Wohnflachenverordnung which may be of interest?

[Mark Siddall]

Great! With no penalty for built-in storage this new BRE interpretation I have an extra 1m2 per house. Which saves me 0.3 kWh/m2.yr. Now begining to feel a little more comfortable about whether or not this particular project will get certified.

Thanks!
Mark

[Nick Grant]

Really good to know that there is a problem and to flag it up, I'm sure this will get resolved and that this grit will lead to a clear pearl!

Meanwhile I'm really enjoying learning some new German language gems such as Putzabzug although I expect I'll struggle to use it in conversation.

Really great to have your input here Kara, thanks.

Nick

[Anonymous]

Your welcome!
You should try Donaudampfschifffahrtsgesellschaft once you've mastered Putzabzug. Some of the queries above were sorted with a “please clarify” request (60% of auxiliary rooms, and clear width of finished surfaces count), and I was told that an English language document defining all possible things TFA is about to be released by PHI any time now. This is where we all should knock on wood …

[Nick Grant]

Kara, you broke Google with that one! It suggests 'Danube Steam Navigation Company' or is that correct? I'm always pleased to be able to ask where the tram stop is in Germany, even if I can't follow the directions!

So yes, touch wood and I'm sure this will be sorted very soon.

Nick

[Anonymous]

Nick, if you type Donaudampfschifffahrtsgesellschaft into google itself, it tells you that it does indeed mean Danube Steam Navigation Company (see http://www.ddsg-blue-danube.at/deutsch/html/d_geschichte1.asp).

The one that has always annoyed me is its translation of 'speicher' as 'memory', whereas 'storage' is a much more useful translation if you're talking about your solar pufferspeicher. I've tried several times to suggest the alternative without success. I guess it's because the translator is written by modern computer geeks and nowadays the world is run on flash memory instead of core store. But today google translation isn't offering me any translation at all for the word…. ?

Putzabzug is interesting because it doesn't help to use the usual technique of splitting words that google doesn't understand into smaller ones. 'putz abzug' doesn't help and 'putz ab zug' is even worse.

I had trouble in that BRE document with their use of 'corridor'. I suspect that sometimes they mean corridor and other times they mean lobby. I couldn't make sense of the document without assuming that, anyway.

[Mark Siddall]

If a corridor is treated at 60%, as BRE doc suggests, then I'm packing my bags. The area calculations would be so mean that it's stoopidly hard to achieve PH in the UK for domestic buildings (which are small, thus lossy, and in located in an often grim overcast climate). Having a hard enought time on Racecourse as it is!

Pete's interpretation is far more reasonable.

Mark

[Anonymous]

Well, if you believe Passipedia, then everything above ground, no matter what, is living area, ergo 100%, as long as it has the minimum height, and is not stairs. Makes sense to me, for a single family dwelling. Things get more complicated with apartments. How to go about staircases and corridors externally of the apartments in this case (assuming they are within the thermal envelope)? I suggest to cut the ties to Wohnflaechenberechnung entirely, as it really only makes sense when looking at single family dwellings or units in isolation, and come up with something sensible and universally applicable instead. Frankly, I don't see a good reason why any area within the thermal envelope should be discounted, unless it is excessive. There should be a height element (after all, we are heating volumes), but that's it in my view. There might be some people exploiting this be including large utility spaces in the thermal envelope, so this might require a maximum ratio of living spaces (with a good definition for them) to utility spaces, say 90:10. Utility space above this ratio (the exact numbers here are certainly debatable), is disregarded entirely, everything within this ratio is regarded fully. This would also give an incentive to locate activities that do not require conditioned air (like most storage for example) external of the thermal envelope. How about that?

[Nick Grant]

Claire

This raises a different issue. If a building is struggling to hit PH due to say less than compact form, too much glazing etc, then yes making it bigger (assuming the basement is heated) can help to reduce the kWh/m2.a but it will of course increase the total kWh/a. Unless this extra space means you will take in lodgers this goes against the whole point which is to reduce energy consumption rather than to achieve a PH logo.

Or have I misunderstood you?

Nick

[Claire Jenkins]

Nick
Yes, that's what I meant by 'morally dubious'. I'm just trying to think around any options that don't compromise the things we particularly like about the design (which you've probably recognised as you're PHPP consulting on it!) We're not too bothered about certification, but do want very low energy use.
I was interested in this thread for the question about how storage/utility basement space should be counted, at 60% or 100% – sounds as if it would be difficult to know, but as you say, that may be beside the point.
In real life, rather than PHPP, does it make a difference if rooms are kept shut most of the time? If they don't have a heat source, then they would only be warmed by the recovered heat in the MVHR air input. So perhaps closed storage rooms or unoccupied guest rooms would naturally stay a bit cooler and contribute less to the heating demand?
Claire

[Anonymous]

It makes a difference -but only a small one, unless you insulate interior partitions, and use tight interior doors (it is rather difficult to maintain a temperature gradient within a well insulated building). If you'd only condition them with the unheated supply air, you'd need to somehow bypass the resistance heater, plus – as the ventilation system is usually cascading – rooms further down the chain will also be supplied with unheated air; and of course the amount of recovered energy from air you use to condition storage rooms would be lost for conditioning the spaces you actually live in.

Back to PHPP: the idea behind PH is to use the supply air you need anyway as the sole means of heating. The supply air that is needed anyway would be around 30cbm per hour and person (as persons need air – not floors); with an occupancy of say 4, that gives you 120cbm air per hour. Spread over a lot more than the anticipated 30sqm per person, your air layer will get quite thin, and the amount of heat you can distribute per sqm will be rather slim, probably not enough to be comfortable. So, for many reasons (environmental, economical, technical), it is advisable to minimise spaces within the thermal envelope that are not meant for human occupancy.

Kara

[Claire Jenkins]

Thanks, Kara. That makes it very clear. We're still undecided about what kind if heating we would use – I like the idea of the electric air heating, but judging by one of the other threads I was reading, it seems rather controversial here!

[Nick Grant]

Whoops, sorry Claire, should have recognised your name! Too much on and we have not met yet so only the building is in my mind.

Kara, hate to disagree with you but I'm a bit of an air heating sceptic and certainly anti electric heating.

Claire, As Kara says (I agree with everything else I have ever heard her say!) the rooms will be at similar temperatures and it could be a problem if a closed off room got too cold as when you open the door to it you could get condensation as the warm air (holding more moisture) rushes in.

Ventilation wise storage rooms tend to have (a little) extract rather than supply. Without ventilation odours could build up from stored smelly stuff.

Nick

[Anonymous]

Nick

No worries re disagreeing – yet am not hugely partial to air heating anyway. It's an option, and in a PH usually the option with the smallest price tag attached (and it felt as though cost were an issue with the original query). Agreed, if they are available, there are certainly better energy sources than electricity for heating (gotten quite used to there not being anything else available, as this is certainly so for the bulk of areas, here). I have to say, though, that I like the simplicity of air heating, and sometimes feel that people are overdoing the technical aspect of PH. A friend in Germany has an incandescent light bulb in the air duct of his rather small house. If it gets really cold outside, he switches it on … Now, from a primary energy point of view, this might not be the best thing to do, but budget wise and for the element of surprise (when he tells people about his heating system), I quite like it.

Kara

[Nick Grant]

Shame to waste the light by putting it in a duct!!

[Claire Jenkins]

Don't worry, Nick, I'm not offended. I thought from your mention of non-compact form and too much glazing that you might have already made the connection. I guess I'm not alone in having those issues!
Claire

[Anonymous]

Nick

He's using CFL for actual lighting, of course, if he hasn't switched to LED by now. But the 75W heat he gets out of the inefficient 100W bulb, evenly distributed by the ventilation system, suffice to keep him happy (it is a small house). Cost of heating system: about 10 Euro – hard to beat. I am not suggesting to use more bulbs for a larger house, though, or designing this for clients…

[Anonymous]

Just going back to the original gist of this thread for a moment, I have received this from the BRE:

Some of you may be aware that BRE has been in discussion with PHI with regard to the ‘Treated Floor Area’ in Passivhaus for design and certification, with the objective of having a document that we as certifiers and the designers can all reference. With this in mind BRE has translated the German Floor Area Ordinance – BauGB Wohnflächenverordnung – WoFlV for Domestic Dwellings. I understand that the original German document is very much left to readers interpretation, for this reason we have included a grandfather clause stating that ‘the document has been created as a guide and further clarification may need to be discussed and agreed with your certifying body’.

The Passivhaus Institut has agreed the content of the document and has acknowledged the value requesting that they include in Passipedia and may form part of future editions of PHPP. This document is intended to be a guide and BRE will be referencing it in our future training courses and certification criteria. I must add that the information in the document should not supersede the information in your current projects but is there for future reference. The document will be available to download from our website in due course, in the mean time I have attached a copy for your reference.

[Anonymous]

Is it just me or is this a very confusing and surprising document?

It's confusing in part because it's the combination of a German standard and some PHI proscriptions that differ. It's very surprising to me that for something so fundamental and so important as the floor area measurement, the PHI hasn't produced its own clear and unambiguous specification.

This version has been tidied up from the previous draft that we saw and at least the colours match now, though not providing numbers for the figures makes it a little more difficult to discuss them and the lack of page numbers makes it even worse. For instance, on the second page there are two figures that appear to be identical. Is that a mistake or are they supposed to be the same and if so why repat the figure?

Most of my confusion stems from trying to interpret the actual meaning. I suspect some of it may make sense in whatever context the German standard is normally used but not when it's used in conjunction with PHPP.

On the third page, for example, why would the energy demand of the whole floor of a building depend on whether one room is 'inhabited'?

And why is the basement corridor, which is closed off by doors from all the rooms not excluded from the TFA as it says it should be on the second page?

On the fourth page, it says “living area is thermally separated by a door between corridor and living room”, but what does that mean? Normally an internal door in a house would not be thermally insulated and in a passivhaus it might well have a gap underneath to ensure the MVHR works properly. Are they just saying that there's a door and adding the bit about thermal separation to confuse the reader, or are they saying that the requirement is for an insulated door and if so, what U-value is required?

Similarly, looking back at the left hand figure on the first page, where is the thermal envelope? Is the triple glazing in the main building wall, with a lean to single-glazed greenhouse, or is it perhaps triple glazed all round the outside with a decorative divider? And are the two cases treated the same? How are solar gains allocated? Is the greenhouse assumed to be maintained at 20 C?

Back on the second and fourth page, it says that [full width] steps are included in the TFA, but a [part width] flat opening is not. Presumably a full width flat opening is included but exactly how big a stub wall is needed before it is excluded?

Why is the bifold door on the fourth page treated differently? Is it a step and if so what difference does that make?

???

[Mark Siddall]

Similarly bemused Dave.

On the basis of a project that I'm working on I find it worrying that that the TFA the corridor/living room relationship is so sensative to whether or not a door is present and whether or not it is insulated – depends upon the page you read. If this was so fundamental why is has it not been mentioned in the PHPP manual?

I agree, you'd think that for the European/Global market PHI would be stearing a away from referance to German standards and developing there own where appropriate – even it the heritage relates to some German standards. …..But there again it was not PHI that wrote the document. Its a confusing mess.

[Anonymous]

under current definition only certain basement areas can be counted towards the TFA, eg the window area of basement rooms must be a minimum of 10% of the floor area, and of course these rooms have to be within the thermal envelope.

Kara, is the window proportion absolutely mandatory for a basement to be habitable?

We are planning a large basement which will be within the thermal envelope, have a ceiling height above 2m, but will not have very much in the way of glazing, certainly less than 10% of the internal basement floor area. The lack of natural light isn't a big issue for the intended use of the rooms, and less glazing helps reduce the thermal losses as well as suiting the plot better.

In this scenario, would it have to be excluded from the TFA, or could it be included?

[Claire Jenkins]

According to the BRE document above, there doesn't actually need to be a habitable room; if it's at last 2m high, and inside the thermal envelope, and then it's counted at 60%.

[Anonymous]

According to the BRE document above, there doesn't actually need to be a habitable room; if it's at last 2m high, and inside the thermal envelope, and then it's counted at 60%.

I agree with this interpretation for the basement 1 example int he BRE document.

Similarly, the basement 2 example states and clearly shows that just one room in the basement needs to be habitable to count the full basement as habitable.

Fortunately one of our basement rooms will (just) have more than 10% glazing, which according to the notes allows it to be considered 100% as TFA. Again, according to the basement 2 example, this should allow the whole basement to be treated as habitable and presumably at 100% for TFA, even though the majority of the basement has no glazing at all.

However, this is different to Kara's interpretation of the rules.

In my opinion, the PassivHaus standard cannot afford to have this kind of vague interpretation. There has to be clear rules that make sense and minimise subjective interpretation.

[Anonymous]

Mark,

If you can make the case that the basement rooms are indeed habitable, I would discuss this with your certifier. Would be very difficult making the case in NZ, as those rooms are non-compliant with Building Code requirements for habitable rooms here, but that might well be different in your part of the world.
I agree with your point that there should be an open and thorough debate about how exactly the TFA is composed. Ambiguity is currently aplenty, and this cannot be afforded, as the TFA undoubtedly is the most important figure in the energy balance of a Passive House. There needs to be something based on reason, rather than a German ordinance that originated from the funding of social housing. Not that I think there is anything wrong with funding social housing, only the purpose with regard to PH is certainly different. It made sense to refer to existing regulation as long as PH was pretty much confined to Germany, but I believe now would be a good time to reconsider.

Kara

[Anonymous]

I agree with Mark B that there needs to be clarity. Areas that are apparently open to subjective interpretation such as this are a gift for anyone who dislikes passivhaus and a pain for everybody trying to use it. And even apparently pathological examples like an above-ground basement shouldn't lead to contradictory answers.

To add one more twist, I don't think the New Zealand Building Code is relevant to you Kara, because the definition of habitable that must be used is the German definition. At least that's according to the PHPP manual, which the certification guide says is the authority on the subject.

Can anybody offer clarity on a related subject? What is the procedure for resolving questions such as those that have arisen here? Is it just a question of individuals or organizations asking specific questions or is there some more formal procedure? And if questions are asked and resolved, how are the answers published and incorporated into the body of generally available knowledge about passivhaus?

[Anonymous]

Mark,

Glazed/floor area ratios are a PHI requirement – as such, if you want to go with PHI rule – your case is clear: basement rooms with less than 10% of the floor area glazing cannot be counted 100% towards TFA. I was talking about reasoning with your certifier about an exemption from that rule, and I felt that if PH rules say: not habitable, AND building regulations say: not habitable, this was a hard sell. Again, in this instance, PH rules make sense to me, generally; I accept, though, that you might feel that your basement spaces are perfectly suited as habitable rooms (and not having seen any plans, sections or elevations, you are certainly a better judge than I am). My advise was, that in this case you should take the issue to you certifier for a discussion.

What is needed amongst other things, in my view, is a clear definition what constitutes habitable rooms with reference to TFA in Passive Houses. Just listing bedroom, living room, kitchen and so forth is simply not enough identification. There is a need for additional signifiers. PHI chose to use the glazed area ratio as a signifier (oddly enough for basement rooms, only), and maybe this is not the most suitable determinant. On the other hand: you can't leave this to simple declaration by the applicant, as otherwise some people might count their insulated garages towards the TFA. And maybe this is the place, where PHI rules could refer to local building regulations for a definition of what is considered “habitable”. I would prefer this over a rigid definition of habitability, as what is considered habitable in NZ for example, differs slightly – and for a reason – from what's considered habitable in Germany. The “spirit” of energy balancing in PHPP is to minimise energy consumption per habitable area. I would have no problems if what is considered habitable allowed for local variations within reason. You might not be able to directly compare a PH in Aberdeen with one in Auckland then, but as climate is markedly different anyway, this wouldn't matter much.

Kara

[Anonymous]

Hi Kara – thanks very much for your help on this, I'm starting to see the “light”, even if it doesn't make much sense to me.

Glazed/floor area ratios are a PHI requirement – as such, if you want to go with PHI rule – your case is clear: basement rooms with less than 10% of the floor area glazing cannot be counted 100% towards TFA.

I've looked through the (English) PHPP manual and it only says that basement and secondary rooms that are *not* living space (according to Wohnflaechenberechnung) are counted at 60%, leaving the implication that basement rooms that *are* habitable count as 100% as would any other habitable room inside the thermal envelope.

You stated that Wohnflaechenberechnung had no requirement for glazed/floor area ratios regarding the definition of habitable vs non-habitable, so this has no bearing.

However, looking at (the Google translation of) the PassivHaus web page referenced from the BRE document, it does appear to specifically say that rooms below ground that do not have 10% glazing cannot be counted as TFA at 100%, but only 60%. If this is a binding rule for certification then I reluctantly have to agree with you.

The BRE document seems at best unclear on this, and should be revised to avoid uncertainty.

It does make me wonder if there are any other mandatory rules which only exist buried in German language web pages on the PassivHaus site that you only get to find about if you pay for the training.

I was talking about reasoning with your certifier about an exemption from that rule, and I felt that if PH rules say: not habitable, AND building regulations say: not habitable, this was a hard sell. Again, in this instance, PH rules make sense to me, generally; I accept, though, that you might feel that your basement spaces are perfectly suited as habitable rooms (and not having seen any plans, sections or elevations, you are certainly a better judge than I am). My advise was, that in this case you should take the issue to you certifier for a discussion.

Understood, I agree with your approach of trying to secure an exemption if the design is clearly such that the room is habitable even if strictly not compliant with the rules.

The house design won't change now, even if it prevents certification on what I see as arbitrary rules on what counts as habitable space below vs above ground. Adding glazing to the basement would increase the cost and heat loss of the building, make the garden less usable and provide insignificant benefit to the basement. We're also too far down the road to make such radical changes and I'm happy with the heating requirements as is.

At least it looks like it will avoid me having to make the decision over whether certification would be worth the cost or not.

What is needed amongst other things, in my view, is a clear definition what constitutes habitable rooms with reference to TFA in Passive Houses. Just listing bedroom, living room, kitchen and so forth is simply not enough identification.

Couldn't agree more on the desire for clarity, but a list such as you describe could never cater for every circumstance. The current written PHPP approach seems to be that everything (other than stairs, areas with low ceilings, or strangely certain rooms below ground etc.) is habitable, unless Wohnflaechenberechnung says it isn't. This seems to be a safer approach than attemping to put together a list of “allowable” uses for habitable spaces.

If you want to limit the floor space per occupant then enforce a strict limit, but don't proscribe how an occupant may choose to use their space allocation – people's lifestyles and activities vary widely, especially between countries.

There is a need for additional signifiers. PHI chose to use the glazed area ratio as a signifier (oddly enough for basement rooms, only), and maybe this is not the most suitable determinant.

This specific rule for basements is inconsistent – I can see no reason why rooms below ground should be treated any differently to those above ground. Has anyone attempted to justify this? Is it possible that it is really just a wording or translation issue due to differing expectations of how a basement is likely to be used between Germany and elsewhere?

On the other hand: you can't leave this to simple declaration by the applicant, as otherwise some people might count their insulated garages towards the TFA.

I tend to agree, and I'm necessarily not arguing for this, although as Devil's advocate who's to say that an insulated, airtight and adequately ventilated garage/workshop isn't as appropriate a use of space as any other “hobby” room. (No PassivHaus compliant garage doors exist as far as I know, so we're probably safe.)

And maybe this is the place, where PHI rules could refer to local building regulations for a definition of what is considered “habitable”. I would prefer this over a rigid definition of habitability, as what is considered habitable in NZ for example, differs slightly – and for a reason – from what's considered habitable in Germany. The “spirit” of energy balancing in PHPP is to minimise energy consumption per habitable area. I would have no problems if what is considered habitable allowed for local variations within reason. You might not be able to directly compare a PH in Aberdeen with one in Auckland then, but as climate is markedly different anyway, this wouldn't matter much.

This is one approach. However, I don't think that UK building regulations currently have any meaningful concept of habitable vs non-habitable rooms, especially regarding natural light, or ceiling height etc. If a room is inside the thermal boundary then it is theoretically habitable. So the UK interpretation, at present any way, would potentially be much laxer than other countries, and as such I think it potentially weakens the PassivHaus brand.

The Code for Sustainable Homes does credit additional points for “rooms with a view of the sky”, but it is not a mandatory requirement, and even then CfSH is effectively optional at the moment.

[Anonymous]

Just to let you know that since we haven't found an answer to the question of how clarification comes about, I have asked the Passivhaus Institut whether they can clarify the situation.

[Anonymous]

I received a reply. It raises as many questions in my mind as it answers, so I thought I'd just post it as is whilst I sort out my thoughts.

Cheers, Dave

In answer to your question on, “What is the procedure for resolving
questions such as those that have arisen here?”, Passive House Institute
has given much thought to this and for this reason, created the
Interntional Passive House Association (iPHA) and it's tool, Passipedia
(www.passipedia.org).

Passipedia, the Passive House resource, constitutes a vast array of
cutting edge, scientifically sound, Passive House relevant articles. It
is here where the Passive House Institute hopes to gather all in depth
information on Passive Houses, as well as Passive House findings from
around the world are being presented. Indeed, the highlights of almost
20 years of PHI research on Passive Houses are being posted here, often
for the first time ever in English and iPHA is constantly working to add
more information. On Passipedia, basic Passive House information and
insights are available for all to see, whereas members of the
International Passive House Association (iPHA) receive special access to
the more in depth sections (to become a member, visit
http://www.passivehouse-interntional; or inquire with our British Affilate, the
Passivhaus Trust). In all cases and unlike Wikipedia, users can be sure
that whatever is posted there has gone through a quality control process.

Of course, definitive information can also be found on the Passive House
Institute website, which we are currently working to improve, as well as
on the iPHA website (www.passivehouse-international), where there is
also an FAQ section that will increasingly be linked to Passipedia articles.

The above, in short, is an outline of how we are working to make sure
all are on the same page.

With regard to your specific TFA questions, if you don't find what you
are looking for in Passipedia yet, then please ask and we will do our
best to get the answer out.

All the best,

Sarah Mekjian

International Communications

International Passive House Association (iPHA)
Passive House Institute
Rheinstraße 44 | 46
64283 Darmstadt
Germany

Tel: +49 (0)6151 | 826 99 55
Fax: +49 (0)6151 | 826 99 34

info@passivehouse-international.org
http://www.passivehouse-international.org

[Anonymous]

OK, here's my attempt at a “march for sanity” with regard to the TFA (my suggestions for how it should be dealt with):

No spaces outside of the thermal envelop count towards the TFA neither fully nor partially.
All floor spaces within the thermal envelop form part the TFA, if the room receives either direct natural light, or is directly connected (door, through-way, stairs) to a room that does receive natural light.
All dimensions used for the assessment are clear width dimensions.
Stairs count towards the TFA with their projection to the upper floor (=opening in the slab).
Steps that do not bridge to the next full storey (raised or split level) count with their projected area to the respective higher level.
Lifts are counted with their projected base area for the lowest level only.
Floor space with a clear height below 1m is deducted from the TFA. A 50% deduction applies to floor space with a clear height between 1 and 2m.
Note: the height provisions remain in place, as in the end, we are conditioning volumes.
There are no special provisions otherwise for reveals etc.

Circulation spaces in multi-occupancy buildings:
circulation spaces within thermal envelope=even attribution to connected units;
circulation spaces outside of thermal envelop do not count towards the TFA;
circulation spaces within intermediate spaces (half insulation to the outside, half insulation to the inside)=individual attribution based on heat flow analysis.

Note: for this definition it does not matter whether rooms are labelled “bedroom, hobby, office or laundry”; no differentiation of habitability, frequency of use, or nature of auxiliarity is needed.

Maybe we can discuss here how things should be, and then present a well debated proposal for adoption? Seems the best way forward to me.

Comments, please!
Kara

[Alan Clarke]

Thank you Kara, very helpful. However I am confused by your wording about stairs – I thought stairs didn't count towards TFA?
Alan

[Anonymous]

Mark,

thanks for sharing your thoughts!
In my proposal there would be no differentiation for above/below ground rooms, and no minimum natural light requirement for rooms that count as rooms with natural light. What I was after here is a way of preventing that the TFA is wilfully extended to include large areas that are not intended for dwelling, and thus reward the waste of energy for conditioning those. It is debatable whether the lighting requirement serves that purpose. I have issues with the list of rooms, though, as there are variations in meaning in the cultural context. I would not be able to tell what internationally constitutes a living room, kitchen or bedroom, but can tell you that Germans and Kiwis would not agree on some features.
Maybe the light requirement is not the best signifier, and maybe I am overly cautious in this regard anyway. How would: “all rooms within the thermal envelope that are intended for human occupation form the TFA” sound to you? It may then indeed be up to a negotiation with the certifier to establish fitness for human occupation in the context of the concrete project. If all decisions in this regard (and all other substantiated deviations from the general rules) were put into a database, a set of precedences was formed to guide further decision making. Does that make more sense?

Kara

[Nick Grant]

Kara

I like where this is going as I have a small brain.

Game playing is more likely with more complex definitions as are genuine mistakes. If someone adds a big room with no windows off a small room with big window just to score TFA then they are not fit to be designing buildings.

I like the stairs simplification for pragmatic reasons as it is a pain to work out how much TFA can be claimed back under them and we have spent time fiddling with winder designs to scrape a few extra cm2 on a small dwelling. Then the stair construction changes and some headroom under is lost so TFA reduces. Also Alan has pointed out that including stairs helps smaller dwellings achieve PH target as the stairs are a larger % of TFA than for bigger building.

The only caution would be that excessive stair footprints that waste useful heated TFA would not be penalised but I think there are bigger fish to fry, especially when considering buildings that are large enough to accommodate such luxuries (or religious requirements) as his and hers stair cases.

So much time is spent arguing TFA interpretations so I would think this should be welcome all round.

Schools TFA gets interesting as there is the circulation space treated as 60% rule combined with UK practice of putting teaching space in the circulation where it is wider. Then throw in creative architect's tapered and curvy corridors and start negotiating. My experience with the schools is that we learn a new rule, spend 2 hours re-measuring and end up with the same TFA as some areas go up and some go down.

Lets KISS

Hey when this is sussed we can look at shading in PHPP!

Nick

[Nick Grant]

Wasn't fishing for compliments Kara, I'm happy with my limited brain power 🙂

What seems inconsistent is that you propose including the stair hole but not the more useful (but tricky to determine until built) area under stairs. How about an arbitrary (number to be decided) 'subtract 50% of projected stair plan stair area from total TFA. Saves spending hours designing thinner steeper stairs to get that last m2 in a small dwelling but does penalise adding extra stairs which waste space. Otherwise I'm happy for stairs to be included fully as TFA because:

1. open plan stairs can be part of the living area (see Alexander's Pattern language!), great play area for kids (now I remember why I have limited brain power).
2. helps small dwellings get enough floor area to hit 15 target.
3. not optional.
4. can be a fiddle to calculate and then can change when built.

Lift should arguably be included as TFA on all floors as are not usually added on a whim. Could be seen an penalising disabled access if left out.

Double height spaces and mezzanines should not, I believe, be included (the double height space in our house is part of what would make it impossible to hit 15kWh/m2, nice but inefficient). Would also get into complexities of the imaginary upstairs under sloping ceilings not counting fully if under 2m!! Lets not go there.

[Anonymous]

I like the “subtract 50% of projected stair plan area”. Great simplification! Lifts: yes should be included on all levels. Agreed on not including imaginary floor area.
I feel we have created something simple, logical and practicable here. How do we get this debated wider?

To summarise:
All floor areas within the thermal envelope form the TFA. Stairs are counted in the following way: with 50% of their projected area to the lower level, and 100% of the projected area to the upper level. Lifts count with their projected floor area on all floors they connect.
Floor space (apart from floor space underneath stairs) with a clear height below 1m is deducted from the TFA. A 50% deduction applies to floor space with a clear height between 1 and 2m. No special provisions for anything else within a unit apply. The certifier has the right to deduct excessive areas that are not intended for human occupation (like overly large storage rooms). A database lists decisions in this regard (and all other instances where decisions deviating from the rule were made) for transparency and guidance.

Circulation spaces in multi-occupancy buildings:
circulation spaces within thermal envelope=even attribution to connected units;
circulation spaces outside of thermal envelop do not count towards the TFA;
circulation spaces within intermediate spaces (half insulation to the outside, half insulation to the inside)=individual attribution based on heat flow analysis, negotiated with the certifier.

[Nick Grant]

How about starting a discussion on Passipedia based around this simplified proposal with link to this discussion to avoid repetition??

In terms of debating wider we can start by pointing certifiers and the like at this discussion.

Nick

[Anonymous]

It's great how this forum (or this thread in particular) has gone from me asking a dumb question to providing a simplified TFA solution. Lets hope it gets taken up as a cause by the somewhat-bemused, non-German Passivhaus community as you suggest. Great work Nick and Kara.

[Anonymous]

Hi Mark,

I share the concern of this becoming arbitrary, individual decision making (to a degree). Hence I propose to have a database with “precedences”, and to continuously add all decisions deviating from the general rules in there. We had similar for a retrofit incentive programme I was administering, and it worked well in that instance. Adds transparency and gives good guidance. Can easily be accessible worldwide. All certifiers would have a password for posting, and everyone else can read.

Kara

[Nick Grant]

I think we need to try and anticipate game playing but it would be a bit mad to add a basement on the basis that the improvement is heat loss area to TFA made it easier to hit 15kWh. The basement would need to be fully insulated, heated and ventilated so would be silly to then use it as a junk store. Whilst I'd be wanting all but plant and store rooms to have a window if it was my house, there are dwellings such as Hockerton underground houses where this is not the case.

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