How to build a  

Passivhaus: 

 

Rules of thumb

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About the Passivhaus Trust

The Passivhaus Trust is an independent, non-profit organisation that 
provides leadership in the UK for the adoption of the Passivhaus 
standard and methodology. Its aim is to promote the principles of 
Passivhaus as a highly effective way of reducing energy use and 
carbon emissions from buildings in the UK, as well as providing high 
standards of comfort and building health.

The Passivhaus Trust aims to:

preserve the integrity of Passivhaus standards and 
methodology
promote Passivhaus principles to the industry and 
government
undertake research and development on Passivhaus  
standards in the UK.

Authors

Jonathan Hines, Director, Architype
Sally Godber, Partner, WARM: Low Energy Building Practice
Bill Butcher, Director, Green Building Store
Mark Siddall, Director, LEAP
Paul Jennings, Director, ALDAS
Nick Grant, Director, Elemental Solutions
Alan Clarke, Director, Alan Clarke Engineering
Kym Mead, Associate Director, Passivhaus Trust
Chris Parsons, Director, Parsons + Whittley Architects

The Passivhaus Trust would like to thank the following people for 
taking the time to collectively review the information within this guide.

Nick Grant, Kym Mead, Mark Siddall, Peter Warm, Marion Baeli,  
Lynne Sullivan 

Cover image: Burnham Overy Staithe 
Architect: Parsons + Whittley Architects 
Client: Hastoe HA 
Photo Credit: Debbie Harris, 2up Photography

For more information: 

www.passivhaustrust.org.uk 

 

 

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How to build a Passivhaus:  

Rules of thumb

 

1 

 

Design approach and system choices 

4

2 

 

PHPP and quality assurance 

8

3 

 

Building fabric: 

12

   

  Walls 

14

        Ground floors 

18

        Roofs 

19

        Junctions and thermal bridges 

20

        Windows and doors 

21

4 

 

Airtightness 

24

 

Building services: 

28

        Mechanical ventilation heat  

 

  recovery (MVHR) 

30

        Heating and hot water 

34

        Solar thermal and photovoltaics 

37

       Fenestration and shading 

38

6

  

Whole-building systems 

40

7 

 

Construction and quality assurance 

42

8 

 

Certification and quality assurance 

46

9

  

Handover and maintenance 

48

Contents

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Design approach 

There are many factors infl uencing your approach 
to designing a building, including: location and site; 
your client’s brief, budget, and programme; funding 
requirements and regulatory standards; and your own 
design philosophy. 

Passivhaus should be seen as one of the fundamental 
factors infl uencing design as it cannot be achieved 
simply by meeting each separate technical standard such 
as airtightness or window U-values. Passivhaus should 
become an integrated part of your design approach, 
underpinning, and even inspiring, all the other factors 
infl uencing your design.  

Choosing the design approach 

To ensure that Passivhaus is integrated into the design of 
the very earliest ideas, its principles and standards must 
be understood by all members of the design team.

Key early decisions that may be diffi cult or impossible to 
change later – including siting, orientation, building form, 
and fenestration – have a major impact on the viability 
and economy of achieving Passivhaus.

It is recommended that the design is modelled using 
the Passivhaus Planning Package (PHPP) at the earliest 

opportunity, in order to test and shape these key early 
design decisions. PHPP should be seen and used as 
a powerful design tool, helping you to develop your 
design approach, rather than as a procedure for proving 
compliance later, when it might be too late.

Explore the impact of the building’s form-factor ratio, the 
area of external envelope through which heat will escape 
compared to the area of usable internal building area, 
and you will quickly discover that whilst almost anything 
can be made to work, the better this ratio is then the 
more economic the solution. Aim for a ratio of 0.3 or less.

Test the infl uence of altering the building’s siting and 
orientation, or the total and relative quantity of glazing 
on each elevation, and you will be able to understand the 
way in which simple environmental principles infl uence 
the energy effi ciency of a building’s performance. 
Achieving good design requires not only the solving of a 
multitude of design challenges, but in the development of 
creative synergy between them. 

Good Passivhaus design requires a fully integrated design 
approach, out of which an even greater creative synergy 
can be developed. This will produce buildings that not 
only meet the client’s brief, and look and feel good, 
but do actually work with proven energy effi ciency and 
excellent comfort.

1

Passivhaus Planning 
Package (PHPP) 
Manual cover

Design approach 

and system choices 

Jonathan Hines

Summary 

Passivhaus should inform and infl uence every aspect of your design approach and choice of 
construction system. This need not be seen as limiting creativity of design nor as restricting 
what construction system to adopt. To achieve an economic solution, Passivhaus must be 
understood and integrated into the design approach and system choice from the outset.

4

 

Rules of thumb  

Design approach and system choices

  

 Form-Factor Ratio

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System choices

Passivhaus does not dictate any particular construction 
system. Indeed, practically any construction system can 
be used and adapted to achieve Passivhaus, though each 
will have its own advantages and challenges for your 
particular project.

The important issue to consider is which construction 
system is best suited to achieve the stringent 
requirements of Passivhaus – such as airtightness, 
elimination of thermal bridging and appropriate U-values 
– given the particular building type you are designing, its 
function and the form you are developing.

As a general rule avoid mixing different systems within 
one building, as this introduces interfaces that will make 
achieving Passivhaus challenging and more expensive 
than it needs to be.

System choices for Passivhaus developments

Construction systems can generally be classifi ed as 
lightweight with less thermal mass (such as timber or 
steel frame) or as heavyweight with more thermal mass 
(such as masonry or concrete frame), although elements 
of thermal mass can be introduced to timber or steel.

The high levels of fabric performance and carefully 
controlled solar gain lead to internal environmental 
conditions remaining very stable. Passivhaus does not 
generally require either light or heavy thermal mass, and 
other considerations such as function, occupancy and 
climate will infl uence this choice.

An important factor in choice of system, is the likely 
procurement route, and the availability of an appropriate 
contractor. Thus if you are working on a domestic project 
and local builders are experienced in traditional masonry, 
choose masonry as you are more likely to achieve 
Passivhaus by working with the available skill base.

On larger projects there may be pressure to use steel 
frame due to its familiarity to large contractors and 
consequent cost advantages, so you may need to choose 
steel frame and adapt it to suit Passivhaus.

Similarly, key aspects of construction detailing should 
inform system choice. Details and junctions need to be 
designed with construction and assembly on site under 
realistic conditions (eg weather!) in mind. This is to avoid 
site compromises or later changes under pressures such as 
time, cost and materials availability during construction 
that can easily compromise design and cost.

Key Passivhaus issues with each of the main construction 
systems are summarised below.

Steel frame: 

• Address potential thermal bridge with connection of 

columns to foundations.

• Ensure steel structure does not pass through the 

thermal envelope at fl oors, roofs or for ancillary 
elements of the building.

• Achieving airtightness on the inner side of the wall 

will be challenging, if not impossible, due to the 
number of structural penetrations. Ideally locate the 
airtightness line within the wall and on the outside 
of the structure where it can be continuous and 
unbroken by the structure.

• Avoid heavy external cladding hung off the 

structure, or excessive cantilevered structures, as 
this will create unnecessary thermal bridging.

ABOVE: Standard masonry construction. Photo: Architype. 
LEFT: Standard concrete frame construction. Photo: Architype.

Rules of thumb  

Design approach and system choices  

  

 

5

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Timber frame: 

• Generally easy to build on a concrete raft ‘floating’ 

on EPS insulation, to eliminate thermal bridging.

• Consider the wall build up carefully, to avoid 

thermal bridging caused by solid studs, and use 
I-beams or a two layer wall with an inner structure 
and outer insulation wrap.

• Airtightness can generally be achieved with a 

membrane or racking board with tape over joints; 
racking boards are more robust. If a membrane is 
used on the internal face of the wall it is beneficial 
to have a service void to protect the membrane.

• Avoid elements of structure crossing the thermal 

envelope, for example, avoid roof overhangs with 
projecting joists that act as thermal bridges and 
make airtightness tricky.

• Avoid heavy cladding that might require a separate 

foundation.

Traditional masonry:

• Achieving Passivhaus with traditional masonry 

requires very wide insulated cavities between inner 
and outer masonry and thermal bridge free ties.

• This can create tricky detailing at window and 

door openings, and structural instability over large 
openings.

• It also creates voids under cavity barriers that are 

difficult to insulate on site.

• Airtightness can generally be achieved with parge 

or plaster.

• A wide cavity building on a concrete raft floating 

on insulation can be tricky, as the external skin 
requires support, so a thermal break will generally 
be required.

• integrate Passivhaus into your design

approach from the earliest possible point

• use PHPP as a design tool to understand,

influence and improve design

• make the building itself do all the hard work

in achieving Passivhaus economically

• ensure that orientation, form and

fenestration are optimised

• select a construction system that is

appropriate for your building type, form and
function, procurement and contractor.

do

Concrete frame:

• Address potential thermal bridges at the connection 

of columns to foundations.

• Ensure concrete structure does not pass through 

the thermal envelope at floors, roofs or for ancillary 
elements of the building.

• Airtightness can be achieved with parge or plaster 

where external walls are infilled with masonry, or 
with membranes or board and tape, where infilled 
with lightweight construction such as timber or 
steel stud.

• Avoid heavy external cladding hung off the 

structure, or excessive cantilevered structures such 
as balconies, as this will create unnecessary thermal 
bridging.

• leave Passivhaus until late in the design

process or treat PHPP as a compliance
check late in the design

• assume that Passivhaus dictates any

particular construction system

• combine unnecessarily different

construction systems within one building

• create design problems such as thermal

bridges or challenging air tightness
details by using unnecessary cantilevered
structures or structural penetrations.

don’t

6

 

Rules of thumb  

Design approach and system choices

  

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Case Study Enterprise Centre

The Enterprise Centre, a new development by the 
Adapt Low Carbon Group at the University of East 
Anglia (UEA) in Norwich, is aiming to achieve both 
Passivhaus certification and BREEAM outstanding 
ratings, as well as having one of the lowest 
embodied carbon footprints of any building of its 
size in the UK.

The development hopes to be the first to offer 
both Passivhaus performance alongside natural 
and  bio-renewable materials sourced through 
local supply chains. The design team hosted a 
number of workshops with local suppliers to 
determine which locally sourced products could be 
used in the construction of the building.

Shading analysis was undertaken to calculate the 
optimal level of shading for comfortable internal 
conditions.

Future climate data was generated by the UEA 
Climate Team, and used to simulate a range of 
design scenarios in PHPP to identify the most 
robust solution over an 87-year period. The 
lifecycle carbon study, including embodied carbon, 
allowed optimisation of the building mass, glazing 
ratios, shading and natural ventilation design. 

Rules of thumb  

Design approach and system choices  

  

 

7

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8 

Rules of thumb  

PHPP and quality assurance  

Introduction

Training in the use of PHPP is strongly recommended, 
in order to be fully competent with the software. This 
section is aimed at those who have undertaken training 
and are embarking on one of their fi rst Passivhaus 
projects.

Climate and altitude

Check carefully that you have identifi ed the right weather 
data set. The map on page 11 is very useful. The 22 data 
sets follow county boundaries, use additional county 
maps if you’re unsure which set to use. 

Entering the altitude of your site is just as important. 
Most of the data sets are from locations less than 50 
metres above sea level, and if your site is signifi cantly 
higher than the weather station this could easily add 
1 kWh or more to the heating demand. Conversely 
some sets are at quite high altitude – the Severn set for 
instance uses data from RAF Lynham, which is at 150 
metres.

Heat loss areas

Heat loss areas in Passivhaus are measured to the outside 
of the thermal envelope. This can be less straightforward 
than the SAP internal measurement methodology, as 
what constitutes the outside of the thermal envelope 
may not be immediately clear. Put simply, the thermal 
envelope ends at the last element used in your U-value 
calculation. So for a masonry wall with fully fi lled cavity 
the last element is the exterior brick or block; for a timber 
frame wall with a ventilated cavity and rain-screen, the 
thermal envelope will end on the outside of the timber 
frame wall, because the thermal performance of the 
rain-screen and cavity are unpredictable and are therefore 
ignored. Using dimensions which match the element 
build-ups you use for U-value calculations will help ensure 
an accurate PHPP model. 

A critical eye

Passivhaus certifi ers will be keeping a watchful eye out 
for things that will affect the building performance in 
practice, for example:

• manufacturer/supplier claims for material 

conductivities – if you are unsure use standard 
values from the PHPP handbook 

• correct inclusion of repeating thermal bridges (refer 

to BS 6946 for guidance)

• can the insulation be easily constructed without air 

gaps between or behind the material?

• areas that are likely to be damp (eg, in contact with 

ground), as conductivity of porous elements such as 
open-cell insulation or lightweight blocks can vary 
signifi cantly with moisture content

• is there a risk of thermal bypass?

So, be critical about the information you’re given. For 
example, are insulation conductivities stated using the 

Heat loss areas must join up!

Summary 

The Passivhaus Planning Package (PHPP) is a very useful and powerful design tool, but it 
is easy to misinterpret the conventions, giving erroneous results. Avoiding these simple 
mistakes can reduce the need to fi nd additional energy savings late on in a project. In a 
worst-case scenario, such mistakes might mean that a project cannot achieve certifi cation.
Be conservative with values, as the thermal performance of elements very rarely gets better 
during design development. Optimistic inputs will be a problem later!

2

Use of PHPP and quality 

assurance

Sally Godber

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correct conventions? (Eg, 90/90 values, see 
www.bbacerts.co.uk for further information)

Window entries

Unlike the UK’s National Calculation Methods (NCMs), 
such as SAP and SBEM, where each rough opening can be 
considered as one window, PHPP needs accurate window 
entries, which count each casement separately. Entering 
two adjacent window casements as one means that the 
frame losses are underestimated, and the solar gains 
overestimated. Also, opening windows nearly always have 
thicker frames than fi xed, so it is good practice to assume 
that all windows are opening ones early on in a design; 
this should avoid underestimating frame heat losses.

Using an installation psi-value of 0.04W/m

2

K is a good 

conservative estimate for early design, and can easily 
be improved upon. This typically represents a window 
installed into a standard timber frame.

Primary energy 

For most Passivhaus dwellings in the UK the primary 
energy target is easily met. The exceptions are when 
providing heating and/or hot water by direct electric or 
when using a district heating system/central plant. For 
this reason in most cases the primary energy does not 
need to be modelled early in design.

 

Ventilation rates

PHPP generally assumes a ventilation rate of around 0.3 
air changes per hour (ACH), which is based on German 
property sizes and occupancy rates. For most UK homes, 
which are smaller and more densely occupied, higher 
ventilation rates are required. 

MVHR duct data

The fresh air and exhaust ducts from the MVHR to the 
outside environment are essentially outdoor spaces 
within the thermal envelope and can add signifi cantly 
to the heat loss of your design. Be realistic about the 
duct lengths, diameters and the amount of insulation 
which will be fi tted. Where the MVHR is located right 
against an external wall, duct lengths of >1.5m are still 
likely. 160mm diameter ducts and 25mm insulation are 
typical values for a domestic installation and closed 
cell insulation should be used to avoid condensation 
problems.

Multiple MVHRs 

If your design includes more than one ventilation unit, 
for example, in a terrace of houses or block of fl ats, you 
must use the Additional Vent sheet which is included in 
the more recent versions of PHPP. Although this sheet is 
challenging to use, it is vital to do so, as without it you 
will underestimate duct losses signifi cantly.

A test to see if you’re using the ‘Additional Vent’ sheet 
correctly is to fi ll in the ‘Ventilation’ sheet for a single 
ventilation unit, with associated duct lengths. Change the 
fl owrate to represent the area served by that ventilation 
unit. The effi ciency should be similar to the overall value 
in the ‘Additional Vent’ sheet.

Shading

The shading sheet is probably the trickiest within PHPP 
to get right, and it’s worth reading the PHPP manual 
carefully so you understand the instructions, especially 
about averaging reveal fi gures. It’s not sensible to be 
overly conservative and assume more shading than there 
is, because this can hide overheating problems. Be clear 
and reasonable in your assumptions and a Certifi er is 
unlikely to disagree with you. If you are at all uncertain, 
get a Certifi er appointed and agree the shading strategy 
early on.

For very complex shading it is possible to use separate 
software to calculate the shading such as IES, TAS or 
Ecotect. See page 94 of the PHPP manual for more 
information. 

Whilst it is possible to get carried away worrying about 
shading accuracy, a good design should not be too 
sensitive to exact shading values as this suggests there 
is probably too much glazing. It is better to be more 
conservative in your assumptions.

Rules of thumb  

PHPP and quality assurance  

  

 

9

Input into PHPP of two casement windows

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Overheating

The overheating check in PHPP is basic, and as such 
shouldn’t be used for non-residential or complex 
residential buildings. PHPP considers the building as one 
zone, distributing the gains evenly and as a result won’t 
identify high solar gains concentrated in one room. Be 
cautious about using high ventilation rates to solve an 
overheating issue, as this may not be realistic due to 
security or noise issues. A useful stress test is:

• Use the IHG sheet to accurately represent the 

actual internal gains – and consider modelling 
various scenarios to demonstrate differences in user 
behaviour. Note this will require several additional 
sheets to be fi lled in such as the hot water and 
electricity sheets. To represent small buildings with 
high occupancy, a value of 7W/m

2

 is reasonable if 

no other data is available. 

• Input minimum user-operated summer shading. If 

you are building the house for yourself then you may 
be willing to open and shut blinds 10 times a day 
but the next residents may have a different view!

• In our experience the effectiveness of MVHR 

‘summer bypass’ mode is overstated in PHPP so set 
at half normal vent rate (0.2ACH, for example).

• Assume no natural ventilation during the day.

• Assume half the achievable night time ventilation – 

again in most cases this is user determined, and be 
careful about assuming internal doors are open.

The upper limit for certifi cation is to keep the building 
below 25°C for <10% of the year, and best practice 
is <5% of the year. It is likely the latter will become a 
certifi cation criteria in future.

• engage with a building designer at the

earliest opportunity

• model your design in PHPP at the early design

stages

• make sure you are using the correct climate

data within PHPP.

do

• assume that a building specifi cation from

a previous development will suit all future
Passivhaus buildings

• be over-reliant on glazing.

don’t

Typical TFA markup where inclusions/exclusions 
can easily be identifi ed 

Solar gains

Whilst it is possible to build almost anything to the 
Passivhaus standard, be cautious about projects with 
large expanses of glass. These will have a strong reliance 
on high performance glazing but the structure that 
surrounds glass is more complex and therefore probably 
won’t perform as well. In addition, the building is highly 
reliant on the weather for both internal comfort and 
energy consumption – this does not make it easy to 
achieve the comfort and energy requirements!

QA process

It is easy to make mistakes with any modelling software, 
so having a robust QA procedure within your organisation 
is key. Ideally there will be someone who can look over 
your PHPP on a regular basis. Clear mark-ups of treated 
fl oor area, heat loss areas, windows and shading make for 
easy checking, as does keeping previous versions of your 
PHPP.

 If your experience is limited employ a Certifi er early on in 
a project to check what you’re doing, agree any points of 
contention and provide any hand-holding you may need. 
Whilst certifi cation usually starts pre-construction, having 
some experienced input (especially before planning) will 
ensure you’re on the right track.

10  Rules of thumb  PHPP and quality assurance  

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