Treated Floor Area query

[Kara_Rosemeier]

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!!

[Y 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

[Kara_Rosemeier]

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...

[Mark Elton]

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.

[Dave Howorth]

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.

[Mark Bennett]

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?

[Kara_Rosemeier]

Mark,

according to PHI instructions, 10% of floor area as window area is the minimum for any underground areas to be considered living space, and thus 100% TFA. And while I am critiquing TFA procedures, and in particular the BRE interpretation of them, in other regards, in this instance I fully agree. The reference area for an energy efficiency standard should reflect the area people are actually living in. Only this way can we get to optimise energy demand. It is my opinion that areas that do not require conditioning out of necessity should strictly be placed outside of the thermal envelope. In my view the question of where to put the thermal envelope, and which spaces to in- and exclude is one of the most far reaching design decisions for energy efficiency. Every space within the thermal envelope will cost you energy. If conditioning is not strictly necessary (and as there are no windows intended, a assume no one is going to live in your basement), the basement ceiling should be insulated - huge energy savings, huge building cost savings. All it takes is a smart way to access the basement (in Kranichstein eg, basements are accessed via unheated, covered porches), as otherwise dealing with the stairs gets a bit complicated. The basic surface area to volume ratio is the most powerful tool in bringing down energy consumption of buildings. The first thing to consider for this is reducing the conditioned volume to the minimum, then determining an enclosure of this with a very tight fit, and thermally separate it well. Sprawling geometries and uses will be expensive in more than one regard. Passive House was born out of the concern to deliver energy efficient houses cost efficiently. Compactness of the conditioned core is a precondition for achieving this.

Sorry if you only wanted a quick answer, but being a lecturer, I sometimes cannot help myself 

Kara

[Mark Bennett]

Mark,

according to PHI instructions, 10% of floor area as window area is the minimum for any underground areas to be considered living space, and thus 100% TFA. And while I am critiquing TFA procedures, and in particular the BRE interpretation of them, in other regards, in this instance I fully agree. The reference area for an energy efficiency standard should reflect the area people are actually living in. Only this way can we get to optimise energy demand. It is my opinion that areas that do not require conditioning out of necessity should strictly be placed outside of the thermal envelope. In my view the question of where to put the thermal envelope, and which spaces to in- and exclude is one of the most far reaching design decisions for energy efficiency. Every space within the thermal envelope will cost you energy. If conditioning is not strictly necessary (and as there are no windows intended, a assume no one is going to live in your basement), the basement ceiling should be insulated - huge energy savings, huge building cost savings. All it takes is a smart way to access the basement (in Kranichstein eg, basements are accessed via unheated, covered porches), as otherwise dealing with the stairs gets a bit complicated. The basic surface area to volume ratio is the most powerful tool in bringing down energy consumption of buildings. The first thing to consider for this is reducing the conditioned volume to the minimum, then determining an enclosure of this with a very tight fit, and thermally separate it well. Sprawling geometries and uses will be expensive in more than one regard. Passive House was born out of the concern to deliver energy efficient houses cost efficiently. Compactness of the conditioned core is a precondition for achieving this.

Sorry if you only wanted a quick answer, but being a lecturer, I sometimes cannot help myself 

Kara

Thanks Kara. Very bad news if this is the case since the rooms on the lowest floor are truly intended to be used as habitable, even with limited glazing. Your assumption that they are "unconditioned rooms" used for plant etc. is not the case. Furthermore, the inclusion of the basement in the thermal envelope in my design results in an envelope that is roughly cuboid, essentially minimising the ratio of surface area to habitable floor space.

Does the same rule and assumption about usage apply above ground? Are rooms above ground with less than 10% of the TFA as glazing also excluded from the TFA? I can see that this could be the case for rooms on the north side of a building. In fact my bathroom is only just above the 10% limit and I have visited a PassivHaus where at least two (I assume) habitable rooms had no external glazing at all.

If not then I think there is a significant inconsistency. If I built my design completely above ground, including the lack of glazing, then it would be allowable as TFA, but the fact that the lowest floor is below ground in my case means it isn't.

While I sympathise with the desire to minimise the living space allocated to individuals in order to reduce the energy load a rule like this doesn't sound right to me.

If this is the desire, then better to enforce a strict limit of the TFA per occupant rather than some arbitrary rule about glazing in basements. (I don't believe that the current guide is a necessary part of certification, since the aforementioned PassivHaus would not have received its certification if it was.)

[Y 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%.

[Mark Bennett]

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.

[Kara_Rosemeier]

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

[Dave Howorth]

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?

[Kara_Rosemeier]

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. 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.
Yet, this is only a side issue, arising from the interpretational wiggle room. The real issue is getting clarity, and once again, I second the call for more clarity.

Kara