BRE Passivhaus Contractors Guide

8/3/2019 BRE Passivhaus Contractors Guide

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Passivhaus primer: Contractors guide

So youve been asked to build a

Passivhaus?

BRE is registered with the Passivhaus Institutas an ofcial Certifer or Passivhaus Buildings

www.passivhaus.org.uk

Photo courtesy of BRE


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2 Passivhaus Primer Contractors guide

Passivhaus Primer: Contractors guide

This contractors guide toPassivhaus is aimed as a practicalintroduction and is therefore

the right place to start. Itaddresses the issues that buildingcontractors face when taskedwith a Passivhaus project andgives simple advice and tipson how to deliver a successfuloutcome a certified Passivhaus

whilst minimising cost and risk.

This guide complements theBRE Passivhaus Primer suitewhich provides furtherbackground to specific aspects of

the Passivhaus standard.

What is Passivhaus?

Passivhaus is an advanced energyperformance and thermal comfort standardfor both residential and non residentialbuildings. The concept was inspired by along history of vernacular buildings aroundthe world which do not require activeheating or cooling yet achieve remarkablestandards of thermal comfort. Developedand refined by building physicists during theearly 1990s in Germany, it is now the fastestgrowing energy performance standard inworld and can be adapted to almost all typesof climates.

A Passivhaus may be defined as a buildingin which a comfortable internal temperatureis achieved solely by heating or cooling thefresh air that is introduced in order to meetthe occupants ventilation requirements.

Since it is not possible to introduce a lot ofheat to a building via the ventilation systemalone Passivhaus buildings need to have avery low heating demand.

To operate with only minimal supplementary

heating Passivhaus buildings require thefollowing characteristics:

Unbroken super insulation

Virtually thermal bridge freeconstruction

High quality triple glazed windows

These address the first path via whichheat is lost from buildings: conduction ofheat through the building fabric.

Very airtight building envelopeThis addresses the second path via whichheat is lost from buildings: infiltration

and exfiltration of air though gaps in thebuilding envelope, otherwise known asdraughts.

Mechanical Ventilation with HeatRecoveryWhich addresses the third way heat islost from buildings: via the deliberateintroduction of fresh air and extraction ofstale air for the purpose of ventilation.

Most of the issues faced by contractorscommissioned to deliver Passivhaus buildingscome down to being able to accuratelycost and reliably implement these five keycharacteristics of Passivhaus design, shown

in Figure 1.

Figure 1 Passivhaus schematic

Solar thermal

collector (optional)

Triple pane

double low-eglazing

Super insulation

Supply air

Supply air

Extract air

Extract air

Ventilation system with heat recovery ground

heat exchanger (the heat exchanger is optional)


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Passivhaus Primer Contractors guide 3

Certification requirements

In order to have a building certified as aPassivhaus the following performance criteriamust be met:

Building energy performance

Specific heatingdemand

or Specific peak load

15kWh/m2.yr

10 W/m2

Specific coolingdemand

15kWh/m2.yr

Primary energydemand

120kWh/m2.yr

Elemental performance requirementsAirtightness 0.6 ACH (n50)

Window U value 0.80 W/m2K

Services performance

MVHR heat recoveryefficiency

75% *

MVHR electricalefficiency

0.45 Wh/m3

*Note: MVHR efficiency must becalculated according to PHI standards notmanufacturers rating

Passivhaus certification is awarded on thebasis of as built rather than as designedperformance, therefore pressure test results,commissioning certificates and a recordof the build must be submitted before acertificate can be issued by the BRE, or othercertifying body.

Construction methods

and materialsThe Passivhaus standard defines the buildingperformance and thermal comfort ofoccupants. It is not prescriptive with regardto the construction method. The architectof a Passivhaus may therefore producedesigns based on typical UK constructions,such as timber frame or masonry cavity wall.Alternative constructions more typicallyfound in continental Passivhaus designs suchas solid masonry with external insulationmay also be specified along with modernmethods of construction (MMC) such asstructural insulated panels (SIPs) or insulated

concrete formwork (ICF) as illustrated inFigure 2.

As a dedicated energy performance standard,Passivhaus does not directly address the widersustainability issues facing the constructionindustry. It does not, for example, involvedetailed assessment of the environmentalimpacts of specified materials, or site wastemanagement concerns.

Passivhaus complements, and can be used

alongside, more holistic sustainabilityassessment standards such as theCode for Sustainable Homes (CSH) andBREEAM (Building Research EstablishmentEnvironmental Assessment Method) to deliverbuildings which are both extremely energyefficient, comfortable and address a broadrange of sustainability issues.

Passivhaus building have been deliveredusing standard building materials suchas concrete blocks, expanded polystyrene(EPS) and polyisocyanurate (PIR) insulants.Other developments have used lowerenvironmental impact materials such as

responsibly sourced timber, cellulose orwood fibre insulation and extruded clayZeigel blocks. Whilst the later approachwill typically result in a lower carbon andenvironmental footprint both approaches arevalid for the construction and certification ofPassivhaus buildings.

Figure 2 Passivhaus construction possibilities

Masonry with EIFS Polystyrol rigid foam ICF Lightweight elementwooden structural insulatedpanel or fully insulated I-beam

ICF based on expandedconcrete

Prefabricated lightweightconcrete element

Block plank wall

Prefabricated polyurethanesandwich elements

High-tech vacuuminsulation panel

Lightweight concrete masonrywith mineral wool insulation


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Renewable energy technology

Passivhaus aims to achieve a very highlevel of inherent energy efficiency. Thecertification requirements are based onannual energy consumption in kWh perm2 treated floor area. This differs from theUK Building Regulations which uses annualcarbon dioxide emission per m2 floor area asthe compliance metric. Therefore, unlike theUK Building Regulations, Passivhaus does notallow energy use and the resultant emissionsfrom a building to be offset using on sitegeneration of zero carbon electricity. Anysuch generation is specifically excluded fromPassivhaus certification.

The use of solar thermal systems to meet

part of the domestic hot water heatingdemand is however allowed and expected.Any PV panels added to a Passivhauscannot be used to offset reduced standardsof energy efficiency. Therefore a PV orrenewable energy equipped Passivhaus is themost robust starting point in the drive to zerocarbon buildings.

Figure 3 shows the Larch house in Ebbw Vale,a certified Passivhaus that also meets therequirement of Level 6 of the Code forSustainable Homes.

Figure 3 The Larch house, Ebbw Vale


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Delivering Passivhaus

Ensuring completion of the design

Delivering a Passivhaus requires an integrateddesign approach; therefore it is unlikely tobe possible to commence the constructionphase of a project before the vast majorityof the design work is complete. Startingbefore detailed design work and Passivhausplanning has been completed may result incompromises to the building performancethat threatens its certification. For exampleit is hard to rectify the level of insulation inthe ground floor or the design of the floorto wall junction detail, after this has beenconstructed. Therefore before commencingsite work it is important to check that thedesign work is complete and that all therequired drawings are in place; includingplans, sections and clearly annotated detailsfor all junctions between building elements(e.g. floor to wall), components (e.g. windowto wall) as well as building services layouts.Figure 4 shows a good example of a wall tofloor junction developed by Bere Architectsfor the Ebbw Vale project, showing the levelof detail Passivhaus design requires.

Construction materials

High quality buildings require high qualitymaterials that are delivered and installed ingood condition. Therefore the handling ofmaterials and their protection on site mattersto the performance of the completedPassivhaus. Substituting materials duringconstruction is not advisable as the use ofinferior or non-certified products couldjeopardize Passivhaus certification.

Insulation for example must conformprecisely to the specification and can only

be accepted if the packaging is undamaged,correctly labelled and stamped with a CEkitemark. During installation it must be laidin a continuous manner, leaving no gapsbetween panels or rolls. Even a 5mm gapbetween insulation panels will result inthermal bypass as warm air moves throughthe gap significantly increasing the effectiveU value of a completed wall. Insulationpanels must therefore have square edgesto ensure that there are no gaps and thismeans protecting the insulation duringtransportation, storage and handling on site.

The extremely low energy consumption of

Passivhaus buildings means that drying outof materials can consume a considerableproportion of the heating energy usedduring the first year of occupation. Materialsshould therefore be kept dry on site.

Figure 4 Wall to floor junction developed by Bere Architects for the Ebbw Vale projec t


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Building services components

Indoor air quality, which should beexceptionally good in Passivhausbuildings, will be spoilt if ductwork,MVHR and control systems are notadequately protected during their storageand installation. It is essential that allductwork, MVHR units, attenuators,filters and control systems are stored ina dry, dust free environment. For thisreason it is advisable to ensure that openends of ductwork and MVHR spigots arekept completely sealed until they are fullyinstalled. Any dust or dirt entering theductwork or MVHR systems will need to

be removed before commissioning andit is far easier and less costly to avoid thissituation altogether.

Sequencing

As with any construction programme,implementing the Passivhaus standardon-site requires that jobs are sequencedcorrectly. Passivhaus however has somespecific requirements in order to achievethe required level of air tightness andthermal bridge free junctions. Ensuringan airtightness of 0.6 ac/h @n50 requiresa continuous air barrier. An airtightconstruction of this standard cannot beachieved through last minute attention todetail and expanding foam alone!

Sequencing is about forward planning sothat complex and interdependent tasks arescheduled in the most efficient manner andmaterials are delivered to site when needed.The sequencing of a Passivhaus build requiresa detailed understanding of the assemblyprocess as well as critical stages in the build.A series of briefing meetings between thedesigners and contractors will be needed toensure that the correct sequencing of keystages is clearly understood at the outset.The clerk of works and site manager shouldbe present during these briefings. Projectmanagement Gantt charts should highlightcritical stages in the project sequencing,including any special ordering or preparatoryrequirements.

Tool box talks and site briefings should bescheduled prior to critical stages in the buildprogramme. Detailed production drawingsannotating any special sequencing and fixingprocedures should be displayed on-site sothat site operatives are able to verify detailedinstallation procedures.

Building services, Racecourse, Gentoo Homes

Insulated DHW pipes


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1 Super insulation

The first aspect of implementing a Passivhausdesign that differs from standard UKconstruction is the amount of insulationthat must be incorporated into the buildingenvelope. Up to 300mm, and sometimesmore, is common in Passivhaus buildings.This will require familiarisation withpotentially new forms of construction suchas externally insulated solid masonry walls,or with new details such as the installation ofwindows into 300mm cavities.

Construction of junctions will also differ fromthe current generation of buildings in orderto accommodate this thickness of insulation.For example, trussed rafters are likely tohave up stands to ensure the full thickness ofinsulation can be carried right into the eaves.These details and the method of fixing theinsulation must be determined before thecommencement of work on site. Theseprocedures will be unfamiliar to the majorityof the UK industry and additional trainingand site management is likely to be requiredto ensure their proper implementationon site. Sufficient time for familiarisation,training and site briefings should beincorporated into the build schedule.

2 Thermal bridge free construction

Minimising thermal bridging is an issuefor both designers and constructors andcan result in very simple details for certainmethods of construction: for example aninsulated raft foundation combined withan externally insulated solid masonry wallprovides a very simple floor-wall junction.Other details will be inherently morecomplex, for example the installations ofweather tight and thermally bridge freeroof lights (which may be best avoided inPassivhaus building for this very reason).

Implementation of thermal bridge freedetails requires forward planning andthe availability of the correct materialsat the right time during the constructionprocess. If for example a single courseof aircrete block work is required at thebase of a wall constructed from aggregateblocks, the materials must be on hand to beincorporated at the appropriate time.

The design must be implemented accordingto the designers drawings, so the additionof timber studs or noggins where none areshown on drawings is not acceptable whenconstructing Passivhaus buildings as it will

result in additional thermal bridging.

3 Triple glazing

This is possibly the single most expensiveadditional investment needed to achievethe Passivhaus standard. Fine tuning thewindow specification is an important part ofachieving the Passivhaus standard and thewindow specification may not be finaliseduntil late in the design process. Becauselead times for manufacture and delivery ofglazing and doors can be long it is advisableto place orders as early as possible to avoiddelays on site.

Ensuring that the correct glazingspecification has been delivered to site is thefirst step in ensuring proper installation inaccordance with the design. This involvescomprehensively checking the order. Notonly should the window dimensions andreference codes be checked off but so shouldthe product specification to ensure a mistakehas not been made at the factory.

Each window and door should be uniquelycoded with the following information:

Frame type and UF value (EN 10077)

Glazing type and UG value (EN 673)

Solar energy transmission g-value(EN 410)

Daylight transmission (EN 9050) Glazing and gap dimensions

Spacer type used

Special low emissivity coatings

Inert gas fill type

It is likely that the designer has specifieda unique g-value for the glazing of eachfaade, and possibly for each opening asthis is a way of fine tuning the useful solargains that enter the building. It is thereforepossible that two windows which appearto be identical with respect to frame type

and dimensions are actually intended fordifferent openings. It is essential that thewindows are correctly coded for eachopening in line with the designers windowspecification.

Correctly installing Passivhaus glazing

and doors is a specialist job and technicalsupport and training from the manufactureris needed. Triple glazed systems areparticularly heavy and special liftingequipment may be needed to lift largerwindows and doors in to place. Prior toinstallation the window openings should beinspected and cleaned of any dust or debris.Priming of the reveal surfaces may also berequired if proprietary air tight tapes arebeing fixed to masonry.

To achieve a thermal bridge free windowconnection windows may be designed tofloat in the opening which is subsequently

back filled with foam insulation once thewindow is in place. Air cushions and otherpositioning devices will allow the installer toworks closely to the designers drawings atthis stage where millimetre tolerances maymake the difference between a bridged anda bridge free connection, which can be seenbeneath the window frame shown beinginstalled in Figure 5

The final critical aspect of glazinginstallation is the air tightness of the unitsonce installed, and this can only be checkedon site during the air pressure test. It istherefore important that an experiencedinstaller is on site during the pressure testto make any additional adjustments tothe window and door gearing necessary.Sufficient time should be allocated in thepressure testing and air leakage detectionschedule for this procedure.

Figure 5 Window frame installation

Five steps to achieving Passivhaus on-site


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4 Airtight building envelope

Airtightness is central to the Passivhausconcept and the standards required gofar beyond Part L (2010) requirements. Adetailed air tightness strategy should bespecified by the designers and indicatedon all production drawings. The airtightlayer is normally located on the warm sideof the insulation layer and should not beconfused with a wind barrier (vapour diffuse)membrane on the outside of a timber framebuilding.

In order to ensure that compliance withthe designers intentions are maintainedthroughout the build an airtightnesschampion should be appointed. Ideally thisperson would be a site operative who willbe present throughout the build; someonewho thoroughly understands and cancommunicate the designers air tight strategy.

In some cases the airtight barrier will haveto be installed or partially installed duringearly stages of the build when it would notnormally be necessary to address theseissues. For example, to ensure continuityof an internal air tight barrier across theintermediate floor to wall junction in a timberframe, a section of the air barrier will needto be laid over the top of the ground floor

wall construction before the first floor joists

(or cassettes) are added. The air barrier will

then need to be returned around the outerends of the joists or floor cassettes so it cancontinue up the inner side of the first floorwall. Failure to install the air barrier at thisstage would jeopardise the final air tightnessas the alternative solutions are far less robust.

In masonry construction air tightness islikely to be achieved using wet plaster,it is necessary to carefully parge wallsbefore intermediate floors and partitionwalls are installed, and before any serviceruns hinder access to walls and preventthe installation of a continuous barrier.Junctions between masonry and joinery

require special attention as proprietaryair tight tapes will be needed to ensure acontinuous air tight seal at these locations.Plastering lathes and mesh should be usedto mechanically fix and seal any tapes backto the parge coat.

Ideally the air tight layer should be locatedbehind the services void, as shown inFigure 6, and on no accounts shouldplasterboard be used as the air tight layer.Any departures from or changes to the airtightness strategy shown on the drawingsneeds to be communicated to thePassivhaus consultant or designer beforethey are made.

Figure 6

Photo courtesy bere:architects


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A minimum of two pressure tests will be

needed, and three are advisable in somecases. The first should be conducted atthe end of first fix when the glazing anddoors have been installed, but the airtightbarrier is still open to inspection. It isrecommended that the key contractor,clerk of works and site operatives arepresent during the pressure test in order toidentify and remedy any defects in the airtightness layer.

A second pressure may be carried out oncethe services have been installed. This isgood practice particularly in timber frameconstruction where service run fixings and

cabling may have damaged the air tightmembrane.

A final test must be carried out at thecompletion of works. This test is neededto verify the airtightness after all of thebuilding services have been installed andcommissioned. In England this test must becarried out by a competent person registeredwith the British Institute of Non DestructiveTesting (BINDT) and carried out in accordancewith BS EN 13829 test conditions.

Once the n50 test has been passed thetest certificate should be forwarded to thePassivhaus certifying body (BRE Passivhaus

UK) as evidence of compliance with theair pressure testing requirement. Furtherinformation on preparing for the airpressure can be found in the PassivhausPrimer Air pressure testing.

5 Ventilation system

Passivhaus buildings are dependent on theirMVHR system to ensure good indoor airquality. The correct design, installation andfunctioning of the MVHR system mean it willsave around five times more energy than itconsumes. Inappropriate installation or thespecification of low quality components willcause noise intrusion to occupied areas ofthe building, irritating occupants.

The following checks should be made:

The system is complete and installedcorrectly, with sound attenuatorsbetween the MVHR unit and distribution

ductwork and between rooms. Forcertification purposes maintain aphotographic record during theinstallation, particularly at penetrationsof the intake and exhaust ducts throughthe building envelope. Check that vapourtight insulation and top-hat seals havebeen used on the intake and exhaustducts.

All installed ductwork and the MVHRunit must be clean inside and free fromsite dust. Filters should be clean and dryand in place to protect the unit at startup. These checks should be made beforestating the system for the first time, ordust may be distributed throughout theentire ductwork.

All components that require maintenancesuch as post heater, filters, duct cleaningaccess points, fire dampers if fitted, andbalancing valves are accessible.

UK fire regulations have been adheredto, for example air movement betweenrooms is via door under cuts, and thatthere are not vents at the top of firedoors.

The system has been properlycommissioned by the Building Services

engineer and commissioning certificateshave been completed for Passivhauscertification. O&M manuals or acomprehensive user guide should beavailable to occupants at handover.

MVHR unit, Racecourse, Gentoo Homes


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Summary and conclusion

Delivering a Passivhaus building on budget

and on time for the first time can seem likea daunting prospect. But as the scientistLouis Pasteur once said chance favours theprepared mind. By taking the time to readthis primer you are hopefully better informedabout the key issues that set a Passivhausapart from a conventional build

Passivhaus is not a passing whim but rathera logical step change as we progress to azero carbon low energy future. By workingcollaboratively with the design team,defining clear roles of responsibility andusing an experienced supply chain, up-skilling to meet the Passivhaus standard can

be a rewarding and fruitful process.If this Primer has whet your appetite to learnmore about Passivhaus check out the otherPassivhaus primers and training courses onoffer from the BRE Passivhaus UK websitewww.passivhaus.co.uk

Passivhaus glossary

Specific heating demand

This is the annual space heating requirementof the building, over the course of the year,normalised to the treated floor area of thebuilding in m2. It is a measure of energy andis therefore measured in kWh. The limitingvalue for a building to comply with thePassivhaus standard is 15 kWh/m2.yr

Specific cooling demand

This is the annual space cooling requirementof the building, over the course of the year,normalised to the treated floor area of thebuilding in m2. It is a measure of energy andis therefore measured in kWh. The limitingvalue for a building to comply with thePassivhaus standard is 15 kWh/m2.yr

Specific heat load

This is the heat output in Watts ( i.e. it is ameasure of power) required of the heatingsystem on the coldest day of the year,normalised to the treated floor area ofthe building in m2. The limiting value fora building to comply with the Passivhaus

standard is 10 W/ m2.Primary energy

Primary energy is the energy that must beextracted from the environment in orderto deliver energy at the point of use. Forexample around 3 units of energy must beextracted from the earth in the form of fuel(gas or coal) in order to deliver a single unitof electricity to a building. The limiting valuefor a building to comply with the Passivhausstandard is 120 kWh/m2.yr

n50

n50 refers to the German standard for

measuring airtightness of building in airchanges per hour when the building ispressurised and then depressurised. Thisdiffers from the UK method known asq50, which specifies the air tightness ofbuilding specific to the envelop area in m3of air leakage through each m2 of buildingenvelope when the building is depressurised.The limiting airtightness value for a buildingto comply with the Passivhaus standard is 0.6 ac/h @ 50 Pascals.

Photo courtesy bere:architects


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Our services

Consultancy

All members of BREs Passivhaus teamhave completed the Certified PassivhausDesigner training and are able toprovide expert advice at all stages of thedevelopment, including:

Design Concept and Strategy

Low energy design advice

Construction techniques

Toolbox talks for on-site inductions andmanagement

Generating Passivhaus informationpacks for specific buildings

Thermal modelling of constructiondetails

Certiication

BRE is registered with the Passivhaus Institutas an official Certifier for Passivhaus buildings

Pre assessments

Full Building Certification

Reduced rate certification via BREsPassivhaus Certification Scheme (PCS) forqualified CEPH Designers

Testing

Airtightness detailing and testing to n50and q50 testing methods

Airtightness compliance reportsfor Passivhaus Certification and UKcompliance

IR Thermography

Co-heating testing

Monitoring and testing for as builtperformance

Post occupancy surveys

Training

BRE is registered with the Passivhaus Institutas an official training centre for Passivhaustraining courses

Certified Passivhaus(CEPH) Designer

A fast track training programme leadingto the examination required to become afully Certified European Passivhaus (CEPH)Designer. This qualification is recognised asthe industry standard for those intendingto work professionally as a Passivhausdesigner in the UK and abroad. BREs CEPHDesigner training course has one of thehighest pass rates in Europe which has beenacknowledged by Dr. Wolfgang Feist.

One-day PassivhausIntroduction and Workshop

An introductory course and workshopis aimed at all those with an interest inlow-energy design, construction and thePassivhaus standard. It introduces thedelegates to the Passivhaus principles,walking them through best practiceconstruction techniques whilst highlightingthe outline specification and certificationcriteria. The course also introduces thedelegates to the Passivhaus Planning Package(PHPP).

For further informationPassivhaus

BREBucknalls LaneWatfordHertfordshireWD25 9XX

E [email protected] www.passivhaus.org.ukR +44 (0) 845 873 5552T www.twitter.com/PassivhausUK

Denby Dale Green Building Store

BRE are registered with the Passivhaus Institut

as certifers and designers or the Passivhausand EnerPHit Standards.

Passive House

Passive House Institute accredited

Certifier

DESIGNER

CERTIFIED

PASSIVE HOUSE

DESIGNER


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PassivhausBREBucknalls LaneWatford

HertfordshireWD25 9XX

E [email protected] www.passivhaus.org.ukR +44 (0) 845 873 5552

BRE TrustThe BRE Trust uses profts made by BREGroup to und new research and educationprogrammes, that will help it meet its goal obuilding a better world.

The BRE Trust is a registered charity in England & Wales:No. 1092193, and Scotland: No. SC039320.

Acknowledgements

Authors: Rob McLeodAdam TilordKym Mead

With thanks to: bere:architects

Other Primers in this series:Passivhaus Primer: IntroductionPassivhaus Primer: Designers GuidePassivhaus Primer: Airtightness Guide

BRE are registered with the Passivhaus Institutin Germany as certifers and designers or thePassivhaus and EnerPHit Standards.

Documents

BRE Passivhaus Contractors Guide