Treated Floor Area query

[Mark Bennett]

Dave,

Yes and No.
Wohnflaechenberechnung gives examples of what habitable rooms are (living rooms, bedrooms, kitchen ...) but puts no requirements on them with regard to light, location etc.  Again: vagueness.

Ah, this doesn't sound vague to me, at least the light aspect of it. If a room is clearly a bedroom (for example), with appropriate ceiling height then it is habitable, whether it has windows or not.

As an aside, if Wohnflaechenberechnung makes no requirement on glazed/floor area ratios, where does the requirement in the BRE document come from?

What I was referring to was: if you want to make the case that rooms in a basement with very little natural light may be viewed as habitable spaces, it will be difficult to argue the case, if local building regs were in direct opposition to this.

This is a very different point. The point here is whether local definitions of what is a habitable room trump the PassivHaus rules, which are currently, in effect, Wohnflaechenberechnung.

I don't think there is any regulation in PassivHaus that states local rules take precedence, so I would argue that from a global PassivHaus perspective the local rules are irrelevant.

Of course, any building also needs to take into account the local building regulations/codes, whether PassivHaus or not, and this will put additional constraints on the design. This will be true globally, with different rules being applicable in different countries.

PassivHaus can't possibly adopt the superset of all nationalities local building codes, otherwise we'd never be able to build anything. In this respect PassivHaus needs to restrict itself to the important points and leave the rest to local variation, which it pretty much does for everything other than apparently TFA calculation.

[Kara_Rosemeier]

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

[Mark Bennett]

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.

[Dave Howorth]

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.

[Dave Howorth]

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
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
www.passivehouse-international.org

[Kara_Rosemeier]

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

[Kara_Rosemeier]

Alan,

Erase all memory of previous TFA incarnations, and see the world with new eyes ... Seriously, I am attempting to free ourselves from the phantom of Wohnflaechenverordnung here. I suggest the projected area of stairs to count, as in the end, we are conditioning air volumes (with area just being a more figurative proxy), and there certainly are air volumes associated with stairs. They are not contained in Wohnflaechenverordnung, as this was intended to calculate areas eligible for social housing incentives. Different ballgame. Please punch holes in my logic; I am hoping we can together create something far more fitting to our purpose than legacy instructions, and  I do not claim that the proposal I posted is already the perfect piece. Don't get me wrong: I have no desire of re-inventing the wheel, but current TFA  procedure feels more like a rugby ball to me, in the context of energy efficient housing.

Kara

[Mark Bennett]

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.

I'm not yet fully convinced on the natural light aspect, perhaps because I don't fully understand what this is trying to achieve. I think we need to clearly understand the higher level objective before we can seek to put a sensible system in place.

For now, I'll assume that there is an assumption that a room can't be "useful" unless it has access to some natural light. Hence you are trying to enforce frequently used rooms to have a natural light source. (An alternative would be to minimise the requirement for artificial lighting and therefore the energy usage. There may be others.)

In this case, I see some flaws in your suggestion.

First, how much counts as natural light? Is it still the 10% of floor area, or would a tiny window in a big room be enough? Without some clear definition, the rule is subject to abuse or willful misinterpretation and we would not be driving the kind of building design that was intended.

I'm also concerned about the suggestion that it would be OK to include a room with no direct natural light if it was attached to a room with natural light. So would a small hallway with a window be enough to allow a massive room without windows to be included? I don't see the reasoning behind this suggestion and think that it will also be subject to abuse.

If my assumption about the purpose of this rule is correct, then I'd probably be inclined to go with the rule as it stands, even if it means my particular design fails the criteria and therefore fails certification.

Rooms with the required natural light count as 100%, rooms with less natural light count at a reduced percentage for TFA. (See below.)

My main argument was that having a different rule for basements than for rooms above ground is unfair and unjustified. If you're proposing to remove any differentiation of treatment for above/below ground, then I fully agree.

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.

I think we need to be a little bit careful here.

There are some room types, that will only be used intermittently - bathrooms, laundries and utility/plant rooms are the most obvious examples, but there will be others. These probably don't need much natural light, and I would argue that enforcing a high degree of natural light would be a mistake. I am against a proscribed list of usages that are allowable, some will be obvious, but others won't be anticipated and we should provide some mechanism for gray areas (no pun intended)  to be considered. For the borderline cases we should put the onus on the designer to provide a compelling argument why the lack of natural light doesn't affect the usefulness of the space, and to leave it within the hands of the certifying body to make the definitive decision.

There will be other rooms where lots of natural light could be a disadvantage, a media/cinema room is one example, as is the probably now mostly defunct photographic darkroom. Possibly walk-in larders could be included. Again there will be others and it should be up to the designer to justify why the room is still useful with no/reduced natural light.

Both of these "classes" need to take into account the use of all potential occupiers. Not just those raising the certification, but also considering the likely use that future occupiers would make of the space. (I think this just shoots down my darkroom example, since very few future occupiers are likely to want a darkroom, even if the initial clients did.)

Of course, then there's the rest of the rooms, where good degrees of natural light should be required.

My argument was about having a proscriptive and absolute list of rooms that are acceptable without natural light. By all means have a list of usages that don't need natural light by default, but allow a mechanism to have exceptions fairly considered on a design by design basis.

I think that removing the differentiation between usages, while simplifying the process, is probably the wrong way to go.

Better to have a defined set of room types that fit into reduced/no light classes and a mechanism for arbitrating borderline cases.

I hope I'm not being inconsistent with my previous posts, and that this helps.

[Kara_Rosemeier]

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

 

[Kara_Rosemeier]

Nick,

you fit an awful lot of thinking into that small brain of yours 
Sorry, I have to disappoint re simplicity with stairs: areas underneath the stairs would still count if of appropriate height in my proposal. In addition, the projected area of the stairs (the hole in the ceiling) would count towards TFA as well. The reasoning is again the volume of air.

I gave the room definition more thought: currently, my proposal of including all rooms that are habitable could be construed as not including storage, laundries and other utility spaces at all, as arguably, those do not invite to dwell.
As long as those are within the thermal envelope, they should however be counted, in my view, in just the same way as the other spaces within the thermal envelope. I cannot come up with a good reason of why they would only count as a percentage of the other areas. We know that there is no marked temperature gradient in Passive Houses unless it is purposefully designed in, thus these rooms will be conditioned to the same degree as all other rooms. So, currently: where ever I have a slab/ceiling within the thermal envelope, and at least 2m clear height above, I have 100% TFA; in addition, I have TFA for the opening in a ceiling, where a stair is landing. Only thing I am not quite clear about: how to deal with double height rooms or mezzanines? I am reluctant to count these areas double, but this was inconsistent with the previous air volume argument, unless air volume was defined as the air volume surrounding people (and arguably, there are very few 5m tall people around).

Any better ideas?

Kara

[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.

[Kara_Rosemeier]

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