Passivhaus-Airtightness-Guide

www.passivhaus.org.ukPassivhaus primer: Airtightness GuideAirtightness and air pressure testing inaccordance with the Passivhaus standard- A guide for the design team and contractorsThe Swimming House, floating Passivhaus, Lake Weissensee, Austria (Source: R. McLeod)BRE is registered with the Passivhaus Institutas an official Certifier for Passivhaus Buildings

2 Passivhaus Primer – Airtightness guideBackgroundThis primer is an aid to understanding the key principlesinvolved in achieving the airtightness performance requiredto meet the Passivhaus standard.The primer also describes how to ensure that the building is correctly air pressure tested forcompliance with Passivhaus certification (n 50 ) pressure test requirements.Unwanted air leakage significantly increases the space heating demand of a building, as wellas causing occupant discomfort from cold draughts. Air leakage can also lead to long termproblems in the building fabric where it is repeatedly damaged by the transmittance of watervapour which results in interstitial condensation. In areas affected by atmospheric pollutionunwanted air leakage can contribute to reduced levels of Indoor Air Quality (IAQ). Achievingthe advanced Passivhaus standard of airtightness (in conjunction with the use of appropriatelydesigned ventilation systems) will help to eliminate these problems.The ‘Larch Passivhaus’, under construction at Ebbw Vale, Wales. Source: R. McLeod

Passivhaus Primer – Airtightness guide 3Air leakage – causes and affectsAir leakage through gaps in a building’senvelope can be caused by either thebuoyancy effect of air or by the pressuredifferential created by wind blowing on abuilding. Typically both of these factors willinfluence the total rate of air leakage at a givenpoint in time.Buoyancy: As air warms up within thebuilding it expands and becomes less dense,causing it to rise upwards and leak out throughgaps in the fabric at a higher level. The airthat is lost from the building is then replacedby colder external air, which is drawn intothe dwelling through gaps in the fabric at alower level. This uncontrolled air leakage isexperienced by the building occupants as colddraughts.Wind: As wind blows against the buildingcolder outside air will be forced under pressurethrough any gaps in the envelope. On theleeward side of the building the external airpressure is lower and will draw warmer airfrom inside the building out through any gapsin the envelope. The stronger the wind thegreater this pressure differential is and thehigher the resultant background air leakagerate will be (Figure 2).Figure 1+ve pressure+ve -ve pressureBuoyancy effectAs the air in abuilding warms upit expands andbecomes less dense– causing it to riseWindward(+ve pressure)Leeward(-ve pressure)Figure 2Wind driven air leakage (source: LTM GmbH)

4 Passivhaus Primer – Airtightness guideMoisture ingress and interstitial condensationWhen warm moist air flows out through agap in the building fabric the air cools downand as the air cools its capacity to hold watervapour is reduced. When the warm air comesin to contact with a sufficiently cold surfacethe water vapour condenses to a liquid state(Figure 3). When condensation occurs withinthe build-up of the building fabric it is knownas interstitial condensation. Over time, if theinterstitial condensate remains trapped in thebuilding fabric, it will lead to a deteriorationin the fabric U-values and possibly structuraldamage and mould growth.Beware of gaps and where humid aircan flow through the building fabricOutside: 0ºC;80% relative humidity360g of water /m.dayInside: 20ºC;50% relative humidityFor comparison:Vapour diffusion only 1g water/m 2 /day1mm wide crackFigure 3Implications of moisture vapour ingress through a 1mm crack (Source PHI/ Sariri)

Passivhaus Primer – Airtightness guide 5Airtightness Requirement for PassivhausCertificationVery low air leakage rates are requiredby the Passivhaus standard and must bedemonstrated for each certified building bymeans of a “blower door” air tightness test.The air change rate must be less than orequal to 0.6 air changes per hour, under testconditions.Passivhaus airtightness (n 50 ) ≤ 0.6 h -1 @ 50 PaNote: The limiting value of 0.6 h -1 @ 50 Pashould be used as the default design airtightness value in all preliminary Passive HousePlanning Package (PHPP) calculations until averified pressure test reading is available.It is important to note that achieving a heatingdemand of 15kWh/m 2 yr or a peak loadof ≤10 W/m 2 often requires the elementalspecifications to be far better than therecommended Passivhaus limiting values.This is particularly the case for buildings thatdo not have an optimum form. Thereforethe limiting value of n 50 being 0.6 h -1 @50 Pa should be seen as the maximum airleakage permissible. Attaining the Passivhausstandard of airtightness is challenging, butachievable when a clear and well thought outstrategy is arrived at during the design stage.This strategy must be maintained and fullyimplemented during the construction phases.It is therefore imperative that the contractorsclearly understand the airtightness strategyand are able to easily implement the sequenceof work on site.It is worth noting that in practice anairtightness level of n 50 = 0.6 h -1 @ 50 Pa isroughly equivalent to having a hole in theenvelope area of the building less than the sizeof a 5 pence piece for every 5 m 2 of buildingenvelope (see Figure 4). In comparison abuilding that achieves the limiting figurefor airtightness to comply with the BuildingRegulations Part L (2013) (Section 6 of theBuilding Standards, Scotland and BuildingRegulations Part F, Northern Ireland) will havean equivalent hole the size of a 20 pence piecefor every 1 m 2 of envelope.UK Building Regulations Compliant1mPassivhausCompliant5mFigure 4Building Regulations vs Passivhaus indicative maximum air permeability areas

6 Passivhaus Primer – Airtightness guideUK Building Regulationsand the Passivhaus StandardDifference betweenAP 50 , q 50 and n 50To comply with UK non-domestic BuildingRegulations (Part L2) it is necessary to carryout an air permeability pressure testing on allbuildings with a usable floor area > 500m 2 .Whilst for the domestic regulations (PartL1) arepresentative sample of dwellings on eachnew build site must be tested. The result ofthis test is expressed as the AP 50 value. This isthe measure of a volume of air (m 3 ) that flowsthrough the building fabric (m 2 ) every hour ata reference pressure of 50 Pascals (Pa) – hencethe AP 50 units are m 3 /(h.m 2 ).In order to calculate the air permeabilitythe ATTMA (Air Tightness Testing andMeasurement Association) TS1 standarddefines the envelope air barrier line as being‘along the line of the component to be reliedupon for air sealing’. In practice this couldbe anywhere within the building envelopebut typically measurements are taken up tothe internal wall surface. The ATTMA AP 50test result is commonly referred to as the ‘airpermeability’ however technically it is definedas the rate of air flow (m 3 /h) at a pressuredifference of 50Pa (which is analogous to thev 50 referred to in Passivhaus terminology). The2010 Building Regulations state that the airlineand the thermal line of a building should becontiguous. It is worth noting that a buildingregulations test can be either a pressurisationor depressurisation test, but for Passivhaus bothtests with the final result being the averageof the two. The actual testing procedure islargely identical however and both the BuildingRegulations and Passivhaus compliance testsmay be carried out at the same time.For Passivhaus certification the airtightnesstarget is expressed differently as n 50 , whichis defined as the number of air changes perhour in the building at a reference pressuredifferential of 50 Pascals. Since the result iscalculated using the building’s internal airvolume (m 3 ), rather than using its envelopearea (m 2 ) the n 50 units are expressed asm 3 /m 3 .h which may be simplified to h -1 orac/h.Note: a standardised conversion betweenAir Permeability (AP 50 ) and Air Change Rate(n 50 ) values is not possible as they do nothave a direct relationship with one another.Furthermore each test uses differentmeasurement and testing protocols.Taping of ‘intelligent’ airtightness membranes, Larch Passivhaus (Source R. McLeod)

Passivhaus Primer – Airtightness guide 7Achieving the Passivhausairtightness standard in practice1 Design stage – identifying the air barrierstrategyThe key principle for achieving airtightness is to create a single,continuous and robust airtight layer (or air barrier). This layer surroundsthe heated volume of the building and in general it should be located onthe warm side of the insulation, therefore also fulfilling the requirementsof the vapour control layer (VCL). It is important to define a singlecontinuous air tight barrier – either it’s a complete barrier or it’s not!Having a secondary layer is often confusing and is unnecessary.It is helpful to identify the location of the air barrier in the building’sfabric by using the ‘red line’ method. To do this, simply mark the line ofthe air barrier using a red pencil onto a section through the building. Itshould be possible to trace the air barrier around the whole buildingenvelope without any breaks in the line. If you need to lift your pencilfrom the paper then you must mark this area as a break in the air barrier,and provide a clear detail showing how the gap is to be connected andsealed. For example a gap in the barrier caused by a penetrating servicespipe or window unit will need a robust detail to ensure an effective sealis achieved. For this reason it is recommended that multiple sectionsthrough the building fabric as well as each floor plan are assessed(including all service penetrations) during the initial design stages.At the detailed design stage all complex junctions and air tightnessdetails should be documented by large scale drawings (1:10) highlightingairtight barriers in a bright colour. At this level of detail it is common toshow both the line of the internal air-tight barrier or VCL (red line) and alsothe line of the external wind barrier layer (WBL) (blue line), these barriersserve separate functions and should be clearly labelled to avoid confusion(Figure 7). It is important to note that the air-tight barrier may not alwaysbe a specialist membrane; at times it will be a rubber seal or a pane ofglass or possibly a laminated timber board. When drawing connectingdetails it is important to understand precisely where the air-tight line isand how the various connecting elements will be joined together.Figure 5‘Red line’ technique used to define the air barrier12InternalExternalFigure 6 Detailed design – cross section through window head detailshowing continuity of internal air tight barrier (No.1) and external windbarrier (No. 2) (image courtesy bere: architects)

8 Passivhaus Primer – Airtightness guide2 Detailed Design/Productionstage – installationsequenceFinal production drawings should also containsequenced illustrations of the key stagesinvolved in installing the airtight barrier atcomplex junctions. Any careful sequencingneeded to install a membrane or create anair-tight seal should be annotated on thesedrawings (right).Stage 1Lay airtightnessbarrier over rooftruss and RHS.Fix in place usingdouble sidedtape. Leavehanging downStage 2Fix 18mm OSB toSW purlin. Foldback membraneand tape to insideface of OSB. Fillvoids withinsulation fromaboveStage 3Lay a continuoussheet ofmembrane acrosswhole face ofOSB. Tape overmembraneencasing rooftrussessStage 4Fix 12mmplasterboard soffitFigure 7 Staged sequence drawings, showing steps to achieving final airtight detail(courtesy bere: architects)

Passivhaus Primer – Airtightness guide 9Types of air barrierIt is crucial to specify the appropriate materialsthat will be used to form the air barrier. Anair barrier must be impermeable or virtuallyimpermeable (i.e. not allow air to pass throughthem at 50 Pascals). Typical air barrier materialsinclude:––Vapour control layer membranes (used intimber frame construction)––Concrete (but not unparged concreteblocks)––Orientated Strand Board (used for SIPSpanels and sheathing in timber frame)––Cross laminated timber plate (used asstructural panels)––Parging coat (applied directly to masonry)Do not use materials that are permeablesuch as fibrous insulation material. It doesnot matter how hard a permeable material ispacked into a gap, air will still be able to passthrough it.Oriented Strand Board (OSB) class 3(external grade) has been successfullyused as an air barrier on a large numberof Passivhaus projects however researchshows that there is substantial variance(

10 Passivhaus Primer – Airtightness guideDetails and drawings must be clearlypresented to ensure they can be understoodand are able to be achieved on site. It isrecommended that critical airtight details areprepared in large scale (1:10) and colour codedfor clear reference. Consideration needs tobe given to the sequencing and buildabilityof air tight junction details particularly aroundwindows and doors and this should be clearlyindicated on production drawings.Try, where possible, to keep penetrationsthrough the airtight envelope to a minimum.Take care when grouping services together(electrical cables, pipes and ventilation ducts)to ensure adequate space is left to seal aroundindividual penetrations using proprietaryseals (top hats and gaskets). Avoid servicespenetrations, MVHR units, boilers etc. beinglocated too close to a corner or a wall as itmay be impractical to access the gap forsealing. Ideally all penetrations are made as thebuilding element is installed to ensure the sealis to the correct element of the wall. This mayinvolve installing pipes or spigots to seal intothe air line and then allowing the actual pipeor cable connections to be sealed to whensubsequently installedSelect and specify materials that are robustand durable to form the air barrier. Theobjective is to achieve an airtight structure forthe life of the building, not one which will beadequate for the air pressure test, but thendegrade in a short space of time. Never try tomake savings by specifying cheaper alternativematerials (for example cheap buildingtapes), as these will not offer the robustnessrequired to achieve a Passivhaus standardof airtightness. A review of the comparativeperformance of common Europeanairtightness tapes can be found in the German‘Test’ magazine (Stiftung Warentest, 2012).Figure 9 A proprietary seal for a servicespenetration through a membraneTaping of window junction to airtightnessmembrane, Larch Passivhaus(Source R. McLeod)

Passivhaus Primer – Airtightness guide 113 Delivering airtightnesson- siteIt is essential that the construction team isfully briefed on the airtightness requirementsof Passivhaus and receives clear, well laid outdetails in good time. It is advised that a clearcommunications plan and project deliveryprogramme should be developed accordingto the RIBA Plan of Work 2013. The RIBA Planof Work stages include sustainability checks/audits that ensure that quality assurance anddue diligence are carried out at each stage.Effective project management is essential toensure a high standard of construction. It isessential for site management to have sometraining on airtightness and for the site tradespersonnel to receive ‘toolbox talk’ trainingsessions prior to installing the airtight barrier.Airtightness ChampionAppointing an ‘airtightness champion’ is agood way of ensuring that site operativesremain aware of the importance of the airtightbarrier throughout the build. The ‘airtightnesschampion’ is responsible for maintaining theintegrity of the air tight barrier throughoutthe build and reporting any issues back tothe design team and project manager. Thisairtightness champion should be someonewho will be on site throughout the build, butnot the Project Manager or Clerk of Works astheir time is often taken up with administrativetasks. The airtightness champion roles mustbe a good communicator and someone whotakes pride in their work and has the authorityto halt and change work if required. Theairtightness champion must be thoroughlybriefed by the design team and must be ableto pass on that information to all of the subcontractorsand trades visiting the site.Airtightness Champion – responsibility checklist1 The role of air tightness champion must be separate from the foreman’s role withinthe construction team. He/ she is likely to be a member of the builders team with aparticular trade role throughout the construction but their main project responsibilitymust be that of air tightness champion, reporting regularly to the design team, siteforeman and main contractor.2 Understand & communicate the airtight/vapour control layer (VCL) and wind barrierlayer (WBL) strategy. Ensure its adoption by all trades on-site (including scaffoldersand sub-contractors).3 Know where the VCL and WBL planes are and which materials form them. Superviseand inspect all relevant works affecting these internal and external planes.4 Ensure that Site Inductions emphasise Air Leakage and the necessity to avoid damageto both barrier planes.5 Manage relevant variations, which can often compromise the Air Barrier.6 Operate an inspection checklist for key elements, interfaces and penetrations. Keep acamera on hand to take photographic evidence of any damage to the VCL and WBL.7 Take regular temperature and humidity readings: some tapes seals and membraneswill not cure or seal effectively if the atmospheric relative humidity is above 80%.Specialist briefing with the airtight membrane suppliers is advised, so that theairtightness champion knows the correct application conditions for each product.8 Ensure all materials that form part of the VCL and WBL are correctly prepared andused and that proprietary products (including cleaning and priming materials) areavailable on site well before they are required.9 Liaise with pressure testing specialists to organise visits for audits and tests, ensuringall necessary preparatory works are complete in time.10 Verify that weather conditions are satisfactory for testing in advance of issuing a finaltest confirmation (using advanced Met Office and MetCheck advanced forecastssupported by any site anemometer readings on the day).11 Determine how many dwellings need to be tested and prepared for testing prior toeach audit or test.12 Ensure that envelope area and volume for each dwelling unit is traceably calculatedand confirmed with the ATTMA tester. Vn 50 reference volume to be determined inaccordance with guidance issued in this document.13 Ensure that recommendations from post-testing air leakage audits are acted upon.14 Airtightness compliance logs for trades and domestic contractors: ensure records areup to date and any variations recorded/remediated (see Figure 10).15 Use a leakage check kit to check the effectiveness of any remedial sealing works.

12 Passivhaus Primer – Airtightness guideAchieving airtightness in practice comesdown to attention to detail and commonsense, for example making sure that surfacesare dry and dust free (and primed wherenecessary) prior to using adhesive tapes.Having extra rolls of tape, a vacuum cleanerand primer on hand is essential to ensuringthe job is carried out thoroughly; as is a smallheavy roller to ensure even pressure andadhesion over the entire length of tape.Sites that have achieved very high standardsof airtightness and satisfied PassivhausCertification have found specific airtightnesschecklists and regular inspections of detailshelpful. The airtightness champion shouldkeep a detailed logbook of the airtightnessprogression of each unit being tested. Thislog (or logs) should be stored on a clip boardand kept in an easily accessible locationwithin the site office or unit concerned.Ideally each trade would keep a separatelog sheet (Figure 10) which should list thedate, time and nature of any works carriedout affecting the airtight layer as well as thecontractor responsible for that element ofthe work. Interim pressure test results shouldalso be recorded in the airtightness log.Careful planning and sequential working areessential to achieving airtightness. A structuredplan of work will ensure that the air barrier issealed as the work progresses. Areas shouldbe inspected before follow-on trades coverand hide crucial details to ensure the air barrieris continuous. For example, it will be necessaryto check that any gaps left around a servicepipe have been sealed prior to installing abath, as once the bath has been put in place itmay be very difficult to gain access to seal anyremaining holes left in the air barrier.Sequencing of airpressure testsIt is recommended that at least three airpressure tests are carried out during theconstruction phase. All tests should becomparable in terms of results i.e. the (Vn 50 )volume used should be the same for all testsand is effectively the final volume of thefinished building.1 The first test should ideally be done as soonas the air barrier is complete, but before anyservices and/or appliances have been fitted.This allows the robustness of the air barrierto be assessed. Any defects (air leakagepaths) can be easily identified and remediedat this point. This test can be carried outbefore all of the windows are installed bytemporarily shuttering (and taping) anyopenings.2 The second air pressure test should becarried out after services have beeninstalled, but before fixtures and fittings(baths, shower trays, kitchen units etc.) havebeen installed. It is crucial to achieve anairtight seal around all services penetrationsbefore they are hidden from view by followon trades, and a test at this stage will ensurethis has been achieved.3 The third air pressure test must be carriedout at practical completion for certificationpurposes. By checking the performanceof the building through prior testing andremediation the result of this test should beconfirmation of a well-sealed project. Thefinal test result is the test result recorded forPassivhaus certification purposes.Air pressure tests should always beaccompanied by a thorough air leakage audit;so that any air leakage paths can be identifiedand remedied whilst the tester is on-site. Thisprocedure may take some time and requiresgood diagnostic skills of the tester as wellas trained operatives on hand - where forexample poorly adjusted window gearing is aculprit. This time audit and remediation timemust be factored into the programme from theoutset as it is an essential requisite of achievingthe Passivhaus standard.It is worth noting that the additional expenseto the project from a few extra air pressuretests is negligible in comparison to thepotential extra costs that may be incurred bynot achieving the air tightness standard oncompletion - resulting in extensive remedialsealing work. Because of the importance ofrepeated pressure testing many Passivhauscontractors own a small (‘Wincon’ type blowerunit) and thermal anemometer that can beused for interim diagnostic testing.Figure 10 Airtightness quality control- logbooks for each trade(Image courtesy: Passive House Builders)

Passivhaus Primer – Airtightness guide 13Calculating the pressure testreference volume (Vn 50 )Airtightness performance of a Passivhausis measured in air changes per hour at a50 Pascal pressure difference between theinside and outside of the building. This isreferred to as the n 50 value, and is determinedby calculating the volumetric flow of air (m 3 /h)required to maintain a pressure difference of50 Pascals (v 50 ) divided by the internal (heated)air volume (m 3 ) (Vn 50 ). It should be noted thatthe v 50 (volumetric flow rate at 50Pa) value isthe same as the ATTMA q 50 value.n 50 =v 50Vn 50The Vn 50 volume is the conditioned volumeof the building in normal operation withmeasurements taken from the visible wall,floor and ceiling finishes.This is not the same as the air permeabilityenvelope area (A E permeability ) approachgenerally used in the UK, which ignoresinternal walls and floors and is measured tothe air barrier element. This means that voidsbetween the ceilings and floors, internalwall voids are not included in the Passivhausvolume calculation (room by room volumecalculation will naturally exclude these). Beamsand visible rafters are not typically deductedfrom the volume of the building however.The loft space is generally excluded (in coldroof constructions) as it is not conditioned andin such cases the loft door has been designedto be airtight. The opening for stairs shouldbe calculated and included, while the solidelement of the actual stairs should be ignoredsuch that the entire stair volume is included inthe Vn 50 . Internal wall voids, floor voids andceiling voids are excluded from the Vn 50 . Inpractice this may require detailed plans of thefinal construction to be issued to the personcarrying out the calculations, since someof these volumes may not be enclosed orformed at the time of the initial pressure test.Measurements should therefore be takenoff drawings to allow direct comparisonsbetween different people’s calculations in away that is not affected by different individualsmeasuring different lengths etc. Dimensionsused should be checked on site to ensure thatthe calculation of volume is reliable, and thatthe built form complies with the plans. Windowreveals are not normally included but externaldoor revels (which are 13cm deep or deeperare included). Hidden risers, wall and floor voidsare not included in the volume but any largestore cupboards inside the finished surface (e.g.containing MVHR etc.) are included.The calculated Vn 50 volume is critical to thefinal test result. Should the calculated volumebe overestimated at any time, it will resultin an under estimate of the airtightnessresult, so it is imperative that it is agreedupon as early as possible in the build anddesign process. Having to downward revisethe calculated volume at a late stage ofthe design could jeopardise compliancewith Passivhaus certification criteria. It istherefore imperative that the Vn 50 volumeused to calculate the airtightness result ischecked by a competent third party and thiscalculation must be documented within thePassivhaus certification folder. Where thereis any uncertainty/ discrepancy over theinterpretation of the Vn 50 dimensions thelower figure should be used (until furtherclarification has been provided by thePassivhaus certifying body).Figure 10 and Figures 11a-b provide anillustration of the volumes which are to beincluded (blue) and excluded (yellow) fromthe Vn 50 calculation. In general the Vn 50should be calculated on a room by room basisby measuring the room volume from thefinished floor/wall/ceiling surface. In generalall conditioned air spaces within the thermalenvelope are included in the Vn 50 howeverenclosed air spaces behind partitions orabove suspended ceilings are excluded, as arewindow reveals and door reveals (if less than13cm deep). Full height reveals greater than13cm deep should be included in the Vn 50 . Asummary table of volumes to be included andexcluded from the is provided in Table 1.Table 1Air volumes and solid elements to be included and excluded from the calculationTest methodObjectVolume included / excluded fromStairsInclude the volume of air displaced by the stairs (unless the stairs are of monolithic stone or concrete construction without anyair void or cupboard beneath them)Stair void in floor plateInclude the air volume of the stair void in the floor plateWindow revealsExclude (unless full height window with reveal depth ≥ 13cm)Door revealsExclude (unless door reveal depth ≥ 13cm)Columns Include the volume of air displaced by any columns (unless the cross sectional area of an individual column is greater than 0.1m 2 )Beams Include the volume of air displaced by any beams (unless the cross sectional area of an individual beam is greater than 0.1m 2 )Attic/ loft spaceInclude if warm roof construction with openable loft hatch. Exclude if cold roof construction or not accessible via loft hatch/internal opening.Ductwork and fluesInclude the volume of air displaced by ductwork and flues (unless the duct or flue is room sealed and the cross sectional area isgreater than 0.1m 2 )CupboardsInclude the air volume displaced by all wall mounted cupboards and shelving units. For walk in wardrobes sand large servicescupboards measure internal volumes as per a room.Storage cylinders and appliances Include the air volume displaced by all hotwater storage cylinders, header tanks and building services (unless the total airvolume displaced by an individual appliance is greater than 1% of the net internal air volume)Skirting boards, architrave etc. Include the air volume displaced by skirting board, architrave etc

14 Passivhaus Primer – Airtightness guideFigure 10 3D view of Passivhaus air pressure test volume (Vn 50 )a) Front – cross section b) Side – cross sectionFigure 11

Passivhaus Primer – Airtightness guide 15The airtightness performance of a buildingis measured by an ‘air pressure test’ (oftenreferred to as an ‘airtightness test’ or‘blower door test’). To achieve a result thatis compliant for Passivhaus Certificationthe test must conform to BS EN 13829(2009) ‘Thermal Performance of Buildings– Determination of air permeability ofbuildings – Fan pressurisation method’. Bothpressurisation and depressurisation tests mustbe undertaken for Passivhaus certificationpurposes, with the combined result of bothdemonstrating that an air change rate ofless than or equal to 0.6h -1 @50Pa beingachieved. For final testing the building shouldbe prepared in accordance with BS EN 13829Test Method A (test of a building in use), withall external doors and windows closed (exceptthe one being tested from) and water intraps. The only temporary seals to be appliedshould be to designed ventilation which inmost cases will just mean sealing the inletand exhaust of the MVHR for the test. Othertemporary seals to non-designed ventilation(i.e. around door frames, any holes in thefabric) will lead to the test result being invalid.Note that this only applies to the final test,for pre-tests sealing incomplete or missingelements is acceptable to gain a benchmarkfor that which has been completed. Table 3(below) provides a Passivhaus n 50 pressuretest openings protocol checklist.To demonstrate competency for airtightnesstesting in the UK the air pressure tester shouldeither be accredited by the British Instituteof Non-Destructive Testing (BINDT) for ‘airpressure testing dwellings’ or be a member ofthe Air Tightness Testing and MeasurementAssociation (ATTMA) for testing dwellings andnon-dwellings and be fully versant with thePassivhaus n 50 test procedure, as described inthis document.Preparation for the testMaximum acceptable wind speedIn preparation for the air pressure test thelocal weather conditions must be observed;in particular the mean wind speed and anygusting. Testing should not be undertakenwhen wind speeds are above 6m/s (i.e.above Beaufort Force 3). Even wind speedsabove a light breeze (Beaufort Force 2) willbegin to introduce an element of error intothe test results (Table 2). When wind speedsexceed 3 m/s caution is needed since therisk of error rises significantly, particularly forexposed buildings (Table 2). This error can bereduced by using four reference tapping pointsaround each side of the building, to moreaccurately gauge the mean internal/ externalpressure differential (Table 2).The effect of wind is effectively measured bythe fan off pressures taken at the start of thetest – they must be within +/- 5Pa. Higherbuilding differential pressures (above 50 Pa)should also be achieved – up to 80-90 Pa (with10 measurement points taken as a minimum).Care must be taken to ensure these higherpressures do not affect the seals and/or fan inthe doorway.Table 2. Influence of wind speed and number of pressure tapping points on max error margin(source Dr.-Ing. Achim Geißler)

16 Passivhaus Primer – Airtightness guidePreparing the buildingIn preparation for the pressure test thebuilding’s ventilation system must be closedand sealed. In residential buildings this willinvolve sealing the MVHR inlet and extractducts from the external air. The inlet andexhaust ducts should be sealed at theirexternal ends to avoid testing the MVHRunit or internal ductwork. Note that innon-residential buildings using intermittentventilation strategies (e.g. schools) where theventilation system is turned off during eveningand weekend periods (to save energy), theinlet and exhaust must have tightly shuttingflaps to ensure that additional heat is notlost from the building (as air leakage) whenthe ventilation system is turned off. Whentesting Passivhaus buildings with intermittentventilation systems the sealing flaps must beclosed during the pressure test but must notbe sealed over.All water traps must be filled, or if no wateris present in the building these traps mustbe temporarily sealed. Other openings in theexternal envelope like doors, windows andloft hatches must be closed for the durationof the test, and must not be temporarilysealed. All sealed openings must be notedand recorded in the test report. Internal doorsmust be wedged open for the duration of theairtightness test to ensure an even distributionof air pressure throughout the building.Figure 11 Air pressure testing fan installed in the entrancedoorway of a building

Passivhaus Primer – Airtightness guide 17Testing protocolPassivhaus guidance recommends that theair pressure testing fan equipment shouldbe fitted into a window opening rather thanan external door opening; this is because anexternal door may have a letter box, key holesand potential air leakage issues, particularlywhere there is a level access threshold.However, as most testing bodies in the UK usefan testing equipment that is designed to fitinto a door frame it is usually more practicalto adopt this more conventional method oftesting. If there are doubts about a doors airtightness separate tests should be conductedusing front and rear doors, or a window testmay be commissioned.For Passivhaus Certification it is compulsoryto carry out both a pressurisation test anda depressurisation test on the building.The depressurisation test can be particularlyrevealing of leakage paths around windowcasement seals, where inadequate or poorlytuned gearing mechanisms fail to hold thewindow casement tightly in the frame.A series of pressures between 10 to 60Pascals are used for the test, this correspondsto the pressure generated by wind speedsof 4-10 m/s on a building. The results of thepressurisation and depressurisation tests areaveraged and the resultant figure is valid fordemonstrating compliance with Passivhausrequirements. This is different to compliancetesting for UK Building Regulations, whereeither a pressurisation or depressurisation testis required (but not both) - so it is importantthat the person undertaking the test is awareof this additional requirement.BS EN 13829 ‘Thermal Performance ofBuildings – Determination of air permeabilityof buildings – Fan pressurisation method’provides the overarching testing protocolwhich needs to be followed to ensure avalid test result is achieved. This testingmethodology is also provided in the UKvia ATTMA Technical Standards TSL1 (fordwellings) and TSL2 (for non-dwellings). It isimportant to note that the existing procedurefor measuring the volume of a building inthe ATTMA guidance documents does notcomply with the requirements of Passivhauscertification, see ‘Calculating the Vn 50 volumeof a Passivhaus’ (above).It should be noted that with respect to thesealing of openings in preparation for the testthat neither BS EN 13829 Method A or MethodB can be directly followed. A summary tablebelow has therefore been provided (below)for the purposes of carrying out a Passivhauscompliant n 50 test. The air pressure testreport must document the condition of everyopening. Furthermore, in accordance with thestandard, the person carrying out the test mustcomprehensibly document the net interiorvolume and the net floor area, either basedon the production drawings (final plans) oron-site measurements. If the net volume andnet area are provided by another consultant,the pressure tester must independently verifythese values.V n50Negativepressure50 PaCellarDoorTest fanwith volumetricflow anddifferentialpressuremeasurementAirtightcoverFigure 12Air flow paths during under-pressurisation test - 50Pa negative pressure

18 Passivhaus Primer – Airtightness guideTable 3Checklist for preparing the building openings for the n 50 Passivhaus testBuilding component/opening/ fittingGuidance notes1 External door Close doors; may be locked2 Internal door All doors open3 Closet doors No action4 Hatch/trap door to unheated attic Close door and latch; do not seal.Leave open if attic is within airtight envelope5 Basement door leading to unheated cellar/cellar corridor (within envelope) Close door6 Open fire place - NOT ADVISED FOR PASSIVHAUS Decommission; remove ashes; close inlet air7 Built in (tiled) or free standing solid fuel stove (or boiler) with independent external supply air* Decommission; remove ashes; close air inlet8 Room air dependent (gas) fire within heated building space - NOT ADVISED FOR PASSIVHAUS Decommission; no action9 Solid fuel stove etc. which is dependent on room air - NOT ADVISED FOR PASSIVHAUS Decommission; no action10 Gas fired boilers (non- room air dependent) in heated building space (e.g. condensing boiler Turn off no actionwith balanced flue)11 Hatches/doors/ access to unheated building spaces ( garages, storage rooms) combine with 5 Close door; may be locked12 Key hole No action; do not seal13 Air release valve duct in unheated building space Seal14 Kitchen hood * Decommission; no action15 Ground source heat exchanger (inlet air duct/ plenum from EAHE) Seal16 Fixed vents in window/ skylights (trickle vents) - NOT ADVISED FOR PASSIVHAUS Close; no action.17 Additional vents or supply air openings No action.18 Air inlet and exhaust valves (external air supply/exhaust ducts to MVHR). Seal**19 Letter box door flap (Not advised for Passivhaus doors unless airtight!) Close; do not seal20 Cat door flap Close; do not seal21 Opening “inlet air or vents” in boiler room/oil storage room - NOT ADVISED FOR PASSIVHAUS No action22 Laundry dryer in heated building area with exhaust air to the outside*- NOT ADVISED FOR Close; no actionPASSIVHAUS23 Laundry chute to unheated building area - NOT ADVISED FOR PASSIVHAUS Close; no action24 Central vacuum cleaner facility Close; no action25 External roller shutter (shutter belt conduit) No action; do not seal26 Top cover of (access) shafts with pumps/ installations in unheated building area Close; no action27 Side access hatches to the attic eaves combine with loft hatch – same thing Close; no action (leave open only if attic eaves are withinair tight envelope)28 Missing window/door handle Seal; (add note in testing protocol log sheet)29 Empty conduit (or ducting) to unheated building area (e.g. due to posterior installed solar panels) No action; do not seal (add note in testing protocol logsheet)30 Air grilles/air bricks (existing openings for background ventilation of an existing chimney void) No action31 Suspended ceiling No action32 Windows in unheated spaces Close* If equipment is missing (not yet installed) then these items should be temporarily sealed and the sealing procedure should be noted in the air pressure testingprotocol log sheet** in non-res buildings with intermittent ventilation systems - sealing flaps must be closed during the pressure test but must not be sealed over.Note: The above guidance has been translated and compiled from Appendix 3 ‘Checklist for approved measurement Method A’ as presented inFachverband Luftdichtheitim Bauwesene. V.(FLIB, April 2008)

Passivhaus Primer – Airtightness guide 19Testing different building formats in accordancewith the Passivhaus standardDetached buildingsThese are tested as a whole unit. Every part ofthe internal volume that is surrounded by theair barrier and within the thermal envelope willbe subject to the test, therefore it is essential tomake sure internal doors are wedged open toensure the free flow of air around the building.Loft hatches should be closed (but not sealed)if the insulation and VCL are located at joistlevel (cold roof), but left open if the insulationand VCL are located at the rafters (warm roof).Note, if there is no loft hatch the volume of theair in the loft is not included in the Vn 50 even ifit is a warm roof construction.For large buildings it will be necessary to makesure that fan equipment used to pressurise anddepressurise the internal volume is adequatelysized to achieve the pressure differentialsrequired for the test (i.e. > 50 Pa). Converselyfor small units (dwellings) it is important tomake sure that fans are not oversized as overpressurisation (> 100 Pa) may cause damageto the building’s fabric. Competent air pressuretesters will have experience in calculating thefan capacity requirements for different sizes ofbuildings.Terraced / semi-detachedhousesPartitioning walls between individual terracedand semi-detached houses need to be airtight,and therefore terraced and semi-detachedhouses must be tested separately. Thewindows in the adjoining houses should beopen during the airtightness test to make surethe air pressure in these adjacent dwellingsequalises with the outside. If this is not possible(e.g. if the adjoining dwellings are occupied)then the tester should note this in the testreport. A terrace of five houses is illustratedin figure 13, each of these houses would betested individually.Figure 13Testing terraced houses

20 Passivhaus Primer – Airtightness guideFlatsIf the communal and circulation areas (foyer,corridors and staircases) in a block of flatsare all within the thermal envelope (builtto Passivhaus standard) then the block willbe tested as a whole building (all doors toindividual flats and all internal doors must bewedged open); the fan testing equipmentwill be installed into the main entrance doorand must be appropriately sized to ensurepressure differentials are maintained equallythroughout the whole building. For UKBuilding Regulations compliance it will thenbe necessary to carry out further air pressuretests on a sample of individual flats (in thiscase the flats to be individually tested will bedetermined by the Building Control Body).When communal circulation areas (foyers,staircases and corridors) are outside thethermal envelope and therefore not heated, itwill be necessary to test each flat individually;however it is important to note that PassivhausCertification requires the tester to balance thepressures (i.e. co-pressurise) between the flatbeing tested and adjacent dwellings (i.e. flatsthat adjoin the flat being tested - including flatsthat are directly below, to each side and directlyabove). This method of testing is often complexand can be costly. An alternative to thisapproach may be to test an entire group of flatsat the same time by ducting air flow into eachflat, but again this method of testing is complexand should only be attempted by a competentair pressure tester.Co pressurisation – general note:If one overall thermal element is split intoseparate units which are not linked via apassivhaus standard common area then copressurisation tests should be carried out toeach unit with each unit separately achievingthe required standard.Flat 3 Flat 4CorridorFlat 1 Flat 2Four flats inside a single thermalenvelope, all linked by a commonstair can be tested using a singleairtightness test.The test volume is shown in grey.Figure 14Flat 3Flat 2Flat 13 flats inside 1 thermal element but allaccessed independently externally.No loft access so volumes in greydefine the Vn 50 .Note V n50 much smallerthan the thermal shell volume.Testing regime:Flat 1 with flat 2 co pressurisedFlat 2 with 1 and 3 co pressurisedFlat 3 with flat 2 co pressurisedMulti residential units withcommercial unitsIf the commercial unit is separated from thedomestic units by a thermal break and an airbarrier then it will be necessary to air pressuretest these areas separately. Where there is nothermal separation, such as in a single liveworkunit, then the block would be tested andcertified as one unit.Figure 15

Passivhaus Primer – Airtightness guide 21Air leakage audits – leak detectionAn air leakage audit is helpful when carryingout an air pressure test to identify any airleakage paths that may need to be sealed toimprove airtightness performance, and also toprovide helpful guidance on areas to tightenup in future projects.Smoke pencils, thermo-anemometers andinfrared thermographic cameras and even theback of a hand can all be helpful to identify airleakage paths in the building’s fabric.While the building is being pressurised smokepencils can be used to release small controlledquantities of dense white smoke that allowsair to be visualised as it leaves the buildingthrough gaps in the envelope. Not all gaps willnecessarily result in an air leakage path; the airbarrier may be robust inside the fabric evenif there is a large gap visible in the finish layerinside the building. If smoke moves quicklythrough a gap it indicates that the opening isconnected with a lower pressure zone (i.e. it isconnected to the outside).For very leaky buildings, or a preliminaryair leakage audit prior to an EnerPHitrefurbishment project it can sometimes behelpful to use larger scale smoke machinesthat can fill large voids with smoke. Standingoutside of the building it will be possible tosee smoke emanating from the fabric throughgaps, which can then pinpoint where remedialsealing is necessary.Thermo-anemometers are able to detectlocalised air movement by inserting anelectrically heated probe element into anairstream. The air speed is then inferred fromthe increase in heating power necessary tomaintain the probe at a given temperature.These devices can pinpoint fine air leakagepaths, and can be used over and over again,which is an advantage over smoke pencils -which can only be used once.Infrared thermographic cameras can also beused to identify internal cold patches in thefabric caused by air leakage paths and heatbeing lost externally by warm air escapingthrough an air leakage path. Care must betaken when using infrared thermographiccameras to ensure the inside of the buildinghas been heated to a temperature that is atleast 10 0 C above the external temperature.If taking external images it is necessaryto avoid sunshine on the fabric and rain/dampness which will show as hot and coolpatches respectively, and do not necessarilycorrespond to heat loss paths or air leakage.Some high quality infra-red cameras arecapable of photographing laminar air flowthrough door and window seals. Thesecameras are expensive and must be used bya competent person, their use is not typicallyrequired if the building has been pressuretested and thoroughly audited at the first fixstage.Figure 17 Thermo-anemometer usedto detect air leakage pathsFigure 16Smoke pencil used to identify air leakage pathFigure 18 Infra-red thermographic imageof air leakage between window casementand frame

22 Passivhaus Primer – Airtightness guideRecommendations and Further informationFurther practical training is highlyrecommended for contractors and designerswho need to achieve Passivhaus airtightnessstandards for the first time. Professionaltraining such as the Passivhaus Tradesman’scourse and Certified Passivhaus Designercourse are available through the BREAcademy. Product specific day courses onair tightness membranes and tapes areoften freely available from specialist productmanufacturers and provide essential practicaladvice on the correct specification and usageof these products.For more information on Passivhauscertification and airtightness diagnosticservices please contact BRE onPassivhaus@bre.co.ukor 0845 873 5552.AuthorsDr. Rob McLeod(BRE Associate)Mike Jaggs(Associate Director, BRE Academy)Ben Cheeseman(Technical Chair ATTMA)Adam Tilford(Head of Passivhaus UK)Kym Mead(Director Passivhaus Trust)AcknowledgementsDr. C. Hopfe (Loughborough University) fortranslation from German of lt FachverbandLuftdichtheitim Bauwesene. V (2008)Dr.-Ing. Achim Geißler for Influence of windspeed and number of pressure tapping pointson max error margin (Table 1)Toby Rollason (Eco Design Partnership) for 3Dillustrationsbere architects for 2D illustrationsReferences1 ATTMA, 2007. The Air Tightness Testingand Measurement Association TechnicalStandard 1: Measuring air permeability ofbuilding envelopes. July 20072 BS EN 13829, 2001. Thermal Performanceof Buildings – Determination ofair permeability of buildings – Fanpressurisation method3 Checklist for approved measurementMethod A, 2008. Presented in Fachverband Luftdichtheitim Bauwesene.V. April2008.4 FLIB, 2002. in Fachverb and LuftdichtheitimBauwesene (FLIB) Trade Association forairtightness in construction engineering:FLIB supplementary sheet for DIN EN13829, FLiB e.V. c/o Technology andFounder Centre Kassel, 20025 Langmans, J. et al., 2010: Air permeabilityrequirements for air barrier materialsin passive houses. 5 th InternationalSymposium on Building and DuctworkAirtightness. October 21-22, 2010,Copenhagen/Lyngby, Denmark6 Ó Sé, G., 2011. Passive House Blower DoorTesting Guidelines. Document version:1.0. GreenBuild, Inch, Gorey, Co. Wexford,Ireland, 10 Aug 20117 Peper, S., Feist, W., and Sariri, V., 2008.Airtight project planning of Passive Houses– guidance. Technical information PHI1999/6, Passive House Institute, Darmstadt1999/ 9. edition 2008 (in German only)8 Peper, S., Bangert, A., and Bastian, Z., 2014.Integrating Wood Beams into a PassiveHouse. Technical paper, PHI DarmstadtJanuary 2014. Available: www.passive.de9 Stiftung Warentest, 2012.Dachdämmsysteme: Bloß keineWärmebrücke. Haushalt und Garten sectionp68, 4/2012.

BRE TrustThe BRE Trust uses profits made by BREGroup to fund new research and educationprogrammes, that will help it meet its goal of‘building a better world’.The BRE Trust is a registered charity in England & Wales:No. 1092193, and Scotland: No. SC039320.Other Primers in this series:Passivhaus Primer: IntroductionPassivhaus Primer: Contractor’s GuidePassivhaus Primer: Designers’ GuidePassivhausBREBucknalls LaneWatfordHertfordshireWD25 9XXE passivhaus@bre.co.ukW www.passivhaus.org.ukR +44 (0) 845 873 5552