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Green Building Bible, Fourth Edition
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    • CommentAuthorBargeman
    • CommentTimeFeb 3rd 2008 edited

    I have recently installed a solar / thermal store system in a newly built Passivhaus. The builders have achieved an air permeability test score of 0.47 m3/m2h @ 50 Pa. To me this seems outstanding and shows what can be done with attention to detail. For example, we were required to ensure that all penetrations of the outer membrane are air tight. The testers said that previously their best result was 1.5 m3/m2h @ 50 Pa.

    From asking around I have not heard of a lower test result anywhere in the UK to date. Is anybody aware of a new build property in the UK achieving a lower air permeability score ?

    • CommentTimeFeb 3rd 2008
    The lowest we have tested hasd been aroun q50 = 1.5 for a wet plastered, solid fllor and mid ceiling flat and also for Carol Atkinson's straw bale mobile home.

    Using q50 (permeability) is the WRONG value.

    Do you know the n50 (air changes per hour, ach) value as this is the true measurement of the ventilation rate?

    The test value is not the only input needed to estimate the actual air change rate:

    The building regulations use an estimate of n50 / 20 to calculate the actual ventilation rate.
    In reality this should vary from 1/10 (exposed) to 1/30 (sheltered)

    So, for the same test value an sheltered site building will have 1/3 the infiltration rate of an exposed site.

    This is also the reason why many bungalows have inadequate ventilation and poor air quality.

    Also what ventilation system did you install ? - Current building regulations are allowing trickle ventilation in air tight houses that will (statistically) almost certain lead to ill health and premature deaths; Hence, my concern whenever I test air tight houses with no adequate ventilation provision....
    • CommentAuthorBargeman
    • CommentTimeFeb 3rd 2008
    Thanks Paul,

    The house is a large detached timber framed build over 3 storeys. A full MVHR system has been installed in accordance with Passivhaus design principles.

    I'm aware that the air changes per hour value is used on the continent, but have not come across a way of converting from that to the m3/m2h @ 50 Pa value used in SAP and to which buildings are tested under Part L1A. Clearly agree that this does not represent the actual infiltration, but is does give an objective way of comparing build quality.


    • CommentTimeFeb 3rd 2008

    your air tightness test certificate must have the ach value on it (this is a requirement ffrom building regulations).

    If they have not provided this then it is not a valid test... To calculate the n50 value yourself multiply q50 by the surfaace area and then divive by the internal volume of your home.

    The q50 measurement is not a an objective way of comparing building performance - it is a false indicator.
    - for example it includes the surface area of the floor, if for example this is a solid floor I have never seen air leakage on a solid, imperveous surface, the only air leakage is around the edges. This means the q50 value is meaningless. Air leakage rates are intednded for use in designing thermal performance and ventilation; for this purpose n50 (ach) is the objective and comparitive measurement.

    Interestingly Brain Anderson (BRE) and some members of the Part L committee, who I have contacted agree that the q50 value should not be used. However they are not bothered enough to do anything about it.

    The consequence of this is that typical new build (60m2 floor area) the infiltration rate is out by (typically) 40%! A huge problem that those in power ignore because they can (I am planning on being a complete pain if they do not correct this and other errors in SAP by the 2010 revision of building regs).

    Good to hear about Passive building going on!
    • CommentAuthorsipman
    • CommentTimeFeb 3rd 2008

    What kind heating system was installed

    Provided a decent u-value was achived i can't imagine much space heating would be required
    • CommentAuthorBargeman
    • CommentTimeFeb 3rd 2008
    Paul - Just to be clear, this is not my house. I am not the owner or the builder and I have not seen the test certificate, However I have no reason to question the veracity of the figures. My company's role has been to install the solar collectors and the thermal store. My question is purely out of interest to find whether a better airtightness result has been achieved in a UK new build.

    Thanks for the formula. By surface area do you mean total usable floor area and does this include open spaces that span multiple floors ?

    I appreciate that you and others may have issues with the methodology employed by BRE to measure heat losses due to ventilation and I wish you well in your efforts to persuade the powers that be to amend their procedures. However in the meanwhile I would still like to know whether anybody is aware of a lower air tightness test score.

    Sipman - apart from a couple of towel rails the main heat distribution system is the MVHR. This has a duct heater with a water to air heat exchanger connected to a thermal store. The duct heater is used to 'top up' the air inflow temperature after the heat recovery by the MVHR. Heat is supplied to the thermal store by a 60 tube solar collector and a small gas boiler. Because of the passivhaus construction it is anticipated that the additional heat requirement from the boiler will be minimal.

    I think that this discussion is about an AECB members house: http://www.aecb.net/forum/index.php?topic=1369.msg5637#msg5637
    See, Elmdale on this link http://www.touchwoodhomes.co.uk/content/view/26/46/

    It's the tightest build that I've heard of to date. Anyone else heard of better?

    • CommentAuthortony
    • CommentTimeFeb 3rd 2008
    There was once a test done in the wast country on a solid stone wall cottage, rendered inside and out and a solid floor; it was owned by a man who hated cracks so went round everywhere with a caulking gun. From memory, this was in the 1970's and done by BRE, it was less than 0.2. The best ever in the UK still as far as I know none the less.

    If you want to see low results go to Canada or Europe. We are relative newcomers to this subject. What we call tight they consider a colander.
    • CommentAuthorsipman
    • CommentTimeFeb 3rd 2008
    The best test result we have achieved is 1.7m3/m2h at 50pa - this was on a new school block that we built, although we had no control of the follow on trades

    The maority of the selfbuild houses we construct are not tested

    0.47 is an excellent result
    We will be testing a certified passiv build over the coming weeks. hope to achieve similar figures.
    Our tester thinks we should be fine with our detailing but fingers are definately crossed. 0.6 is a pass for us anything better is a bonus.

    We have used 15mm OSB internally then taped the joints.
    Could you airtightness advocates please start quoting figures in air changes per hour (ACH) at 50 pascals, rather than the somewhat meaningless m3/m2. Large buildings give much better m3/m2 figures as their volumes are much larger, proportionately, than their surface areas. Over here in Canada, air tightness figures are always ACH@50Pa. Just for the record, R2000-level construction here requires less than 1.5ACH@50Pa.

    Paul in Montreal.
    Hi Bargeman, Do you have more info on the water to air duct heater?
    • CommentAuthorEd Davies
    • CommentTimeFeb 4th 2008
    For m³/m², is the m² the total surface area (floor, walls, ceiling) or just the floor area?
    Posted By: Ed DaviesFor m³/m², is the m² the total surface area (floor, walls, ceiling) or just the floor area?

    I believe it is the surface area of the building envelope. Inter floor leakage is irrelevant - it's leakage to/from the outside that loses/gains energy (winter/summer).

    Paul in Montreal.
    • CommentAuthortony
    • CommentTimeFeb 4th 2008
    This m³/m² stuff often means m³ of air lost per m² of total envelope area and they often include the solid floor area ( which wont loose any anyway) to help the figures along.

    The bigger the building the better these losses sound and I m not sure that I like this method.
    • CommentAuthorEd Davies
    • CommentTimeFeb 4th 2008
    Thanks, that's what I thought but something I read ages ago seemed to indicate it was m² of floor area. So m³/m² is a measure of the quality of the envelope whereas ACH is a measure of the overall performance of the building?

    Something which puzzled me was this page:


    which says:

    "Air leakage through unsealed joints must be less than 0.6 times the house volume per hour (this is the equivalent of an air permeability value of less than 1 m3/hr/m2 @ 50 Pa)."

    I guess that they are making this equivalence for a typical size of house.

    I'm thinking that if you double all of the dimensions of a building but keep the same envelope techniques/care then the m³/m² number should stay the same but the ACH value should halve. If that's right then ACH gives a bit of an unfair advantage to larger buildings. For actual heating requirements it's m³/hour which is of interest, of course.

    By the way, Biosphere 2 was reasonably well sealed. Its air change rate was 10% per year; I make that 11.5µACH :-) That's not at 50 Pa, of course; I don't know how the internal pressure evolved relative to outside.
    • CommentAuthorBargeman
    • CommentTimeFeb 8th 2008

    Brian Anderson at BRE confirms that they have not tested anything below 0.47 m3/m2h in the UK to date and will be making enquiries of other testers.

    • CommentAuthorMike George
    • CommentTimeFeb 8th 2008 edited
    <blockquote><cite>Posted By: Ed Davies</cite>For m³/m², is the m² the total surface area (floor, walls, ceiling) or just the floor area?</blockquote>

    Hi Ed, this is the document referred to in Part L1. http://www.attma.org/ATTMA_TS1_Issue_1_March_06.pdf

    Page 4 defines how the m³/[h.m²] is quantified. It is indeed the whole envelope as others suggest. Lots of examples follow.

    <blockquote><cite>Posted By: Paul in Montreal</cite>Could you airtightness advocates please start quoting figures in air changes per hour (ACH) at 50 pascals, rather than the somewhat meaningless m3/m2. </blockquote>

    The trouble is this is what has to be adopted by regulation here.
    • CommentAuthortony
    • CommentTimeFeb 8th 2008
    You are not allowed to laugh at that Paul! ------------------------------ just have a little smile at us back here still in the stone age. :smile:
    • CommentTimeFeb 9th 2008 edited
    Interestingly Brain Anderson and BRE used to use ach in SAP untill some morons (don't know who, but have suspicions) started using permeability. Unfortunately BRE simply amended SAP!

    I agree completely with Paul in M that permeability has absolutely no place in any serious discussion as all serious work on ventilation and infiltration considers ach.

    The regulations are completely and uterly wrong - we should not follow their misguided path.

    The building regulations in the form of the ATTMA document (Which I have issues with but have had to sit and pass an exam on) requires air tightness test results to be cetrified with both permeability and ach. This means that ALL air tightness test results in the UK should have the correct ach value.

    The UK passive house adjustment is not correct - a 1:0.6 ratio only applies to a specific size of building and should not be used.

    On the sample range of domestic buildings we are testing the range of discrepency (q50 to n50, permeability to ach) has varied from -60% to + 50%.

    This means infiltration heat loss (typically 40% of all heat loss) is so far out as to be worthless.

    The affect on the total new build stock is, I have (roughly) estimated, in the region of 20,000 average homes of additional CO2 per annum.

    BRE have also messed up the effect of wind exposure buy not assessing overal site exposure. In 'SAP world' building on a windy hill does not increase air leakage....

    They have also messed up the HRV calculations so that they do not even agree with Part F... (Briefly PArt F assumes that HRV is used to top up ventilation to 0.5 ach, SAP assumes it is supplying a full 0.5 ach. (So in a home that is EST best practice, n50=4, the HRV would supply 0.3 ach, not 0.5)

    And so on...

    Using SAP to design low heat loss buildings is, therefore, meaningless.
    At Code Level 4 / Passiv Haus levels, especialy, please do not believe the output from SAP.
    • CommentAuthortony
    • CommentTimeFeb 9th 2008
    OK Paul, now you can laugh out loud as much as you like!!!
    • CommentAuthortony
    • CommentTimeFeb 9th 2008
    I m going to go off and cry down the sink.
    • CommentAuthorRobinB
    • CommentTimeAug 31st 2010
    Has anything changed?
    • CommentAuthorsinnerboy
    • CommentTimeSep 1st 2010
    The July/August edition of http://constructireland.ie/Back-Issues/ carries an article about a new timber framed house in Co Cork which achieved n50 0.11 and Q50 0.29 . ( Reminder PHI requires n50 0.6 )

    If interested the magazines contents are posted on the CI site about 2 months after the hard copy - so check the site around late October .
    The direct link to the article is here: http://constructireland.ie/Vol-5-Issue-1/Articles/Passive-Housing/Athenry-eco-house-built-to-passive-standard.html

    The actual figures for air tightness measurements I'll quote from the article:

    "“The preliminary test in November 2009 achieved a result of 0.405 ACH/hr – translating to an air permeability of 0.61 m3/hr/m2 at 50Pa. The dwelling was under construction at the time but most of the air permeability measures had just been installed. The final test was conducted in February 2010, when the dwelling was fully constructed. This was both a pressurization and a depressurization test, achieving an average result of 0.30 Ach/hr – a permeability of 0.38 m3/hr/m2 at 50Pa. This is an exceptional result and far in excess of any dwelling I have tested previously.”"

    Paul in Montreal.
    • CommentAuthorsinnerboy
    • CommentTimeSep 1st 2010
    Thats not the one Paul . The house I refer to is in Cork not Athenry . The only way to read the article I refer to is to buy the current CI issue or await the weblink
    Ooops, anyway, the Athenry one is also interesting in its own right :thumbup:

    Paul in Montreal.
    I have a bit of history on the Athenry project that may interest you because I was involved at the start. I was initially contacted by Scott Cook about the Athenry house because I had the house plans on my website. I forwarded the contact to Cyril Mannion because he lives near Athenry and I was a bit swamped with work at the time.
    Cyril spent a year working on the project before he started on site, doing PHPP courses, becoming a Certified Passive House Designer etc,.

    When Cyril was doing the PHPP he couldn't get the heating load below 14.5kWh/m2.annum, it seems there wasn't enough room on the Excel sheet to take all the windows in the house so he extended the sheet, when he sent the PHPP to Germany they checked it and said that the Solar Gain from the south facing windows wasn't being registered so after corrections the heating demand dropped to 11kWh/m2.annum. One of the reasons he had to get such a good airtightness test was to give himself some leeway and to keep the house under 15kWh/m2.annum, he thought, but 0.6 would have been more than enough.

    The awarding of the Passive House cert now depends on whether or not the client has funds to install a balcony which will protect the house from overheating, because the Passive House institute have said everything else is in order.

    Against the advise of Cyril Mannion, Scott Cook installed a wood burning stove last November because his wife insisted, Cyril brought a different client to view the house last March and noticed the stove which hadn't been there before, it seems they lit it only once last winter, they had to open all the windows and doors because it was like a sauna and they threw glasses of water into the stove to quench it!
    • CommentTimeSep 4th 2010
    Posted By: Viking Houselike a sauna and they threw glasses of water into the stove to quench it!

    Just like a real sauna then:bigsmile:
    Hi how does this compare

    Ive seen this value quoated around for a while - basic story is on building dot co dot uk

    The British Library’s £26m Additional Storage Building at Boston Spa, West Yorkshire, boasts an air leakage rate of 0.5m3/m2/h, one twentieth of that required by Builidng Regulations, and is also the first of its kind in the world to incorporate automated storage and retrieval systems, optimum environmental controls, and pioneering low-oxygen fire prevention technology in a single building.

    Mike up North
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