Andrew Lundberg of Passivate gave a great presentation on Thermal Bridging for our QualiBuild briefings "Getting Practical about Quality on Site."

1. THERMAL BRIDGING IN
LOW ENERGY BUILDING
ANDREW LUNDBERG
PASSIVATE – BUILDING FABRIC & ENERGY CONSULTANCY

2. Presented at the QualiBuild
briefing Getting Practical
about Quality on Site
20 Jan 2016

3. CONTENT
 Low-energy building – the FUTURE….
 What is thermal bridging and where does it occur?
 The knowledge gap
 Thermal bridging | air-tightness | wind-tightness – an
important relationship
 Examples of poor workmanship (design & construction)
 Examples of the right approach

4. Low energy building – the FUTURE
 Low energy building has arrived!
 (actually we’ve had it since 2011…but we still don’t realise it…)
 We now consume 60% less energy in dwellings than in 2005.
 By 2020, we will consume almost 70% less than in 2005. This is nZEB
(nearly zero energy building).
 Passive House is a voluntary low-energy building standard.
 What’s the difference between Part L (2011), nZEB, and Passive
House??
 What do they have in common?

5. What is thermal bridging?
 Heat loss across walls/floors/roof etc. is generally uniform. Heat wants to get
from inside to outside as fast as possible, i.e. straight through the
component!
 Where two parts of the building meet at junctions, e.g. window reveals,
eaves, flat roof/gable wall junctions etc. heat flow can be increased due
to structural components penetrating insulation, poor detailing by designers
and poor installation by trades.
 This leads to increased heat flows, and can create a risk of mould growth
due to low surface temperatures.
 Every surface in the dwelling should be above 15oC, when it’s 20oC inside
and 0oC outside. If it’s not, it fails!

9. Psi values
 We can count heat loss through walls, floors, roofs, windows etc. using U-
values. The lower the U-value the better, as less heat is being lost across
that component.
 We count heat loss at junctions using psi values.
 The good news….there is no limit as to what psi value you achieve at any
junction for Part L compliance.
 The bad news…poorly designed junctions have low surface temperatures,
and can fail Part L requirements due to that. The fRsi value describes the
mould growth risk
 Only the fRsi value must be of a certain value for Part L compliance.
 Psi-values in general are counted in the BER for a dwelling, and have a
significant effect. So even though there is no limit on what you have to
achieve, you might not pass the BER without good psi values.

10. Avoiding thermal bridging issues

11. Indigenous resources
 ACCEPTABLE CONSTRUCTION DETAILS
 Published first in 2008, then revised in 2011 (released in
2014)
 A catalogue of ‘how to build junctions’ to demonstrate
Part L compliance
 Available for free download on www.environ.ie under
the Building Standards link and Technical Guidance
Documents
 More and more manufacturers have detailed drawings
available which have been designed and assessed to
avoid thermal bridging!

12. The knowledge gap
Designers not
adequately
educated on
principles of good
building fabric
design
Poor quality of
information
delivered to site
Site trades not
adequately
educated on
principles of good
building fabric
design (ask WHY
not WHAT)
Value
engineering on
site not supported
by informed
decisions or
analysis
Sub-standard
building quality

13. Air-tightness | thermal bridging | wind-
tightness
 All three go hand-in-hand
 Air-tightness prevents energy loss from
heated air escaping through the
building fabric. It also prevents moist
air moving through cold parts of the
fabric, risking interstitial condensation.
 Good design for thermal bridging
reduces energy loss across junctions,
and can be used to keep some
materials warm and reduce risk of
interstitial condensation, as well as
eliminate mould growth risk.
 Wind tightness prevent wind ingress
into the structure from outside, which
can cool the structure down and
prevent insulation from doing its job!

14. Examples or poor design or
construction

15. Steel beams

16. Eaves detail – cavity closer

17. Eaves detail – cavity closer
 Compliant with Part L
(temperature is above 15
deg. C)
 Heat flow is 500% higher
than if no cavity closer
block had been used (Psi
value of 0.269W/mK as
opposed to 0.053W/mK
for the standard detail)

18. Window jamb

19. Window jamb
 No continuity between
insulation in cavity,
jamb insulation and
window frame.
 Mould & condensation
occurring at some
window reveals and
front door.

20. Warm attic (dormer)

21. Warm attic (dormer)

22. Warm attic (dormer)

23. Wall penetrating roof insulation

24. Example of good design process

25. Example of good design process

26. Example of good design process

27. Example of good design process

28. Examples of good build process

29. Start as you mean to go on…

30. Completed radon

31. Roof battens complete

32. Wind-tightness blocking installed

33. Meeting on site to discuss detailing

34. Continuity of insulation…

35. In an ideal world…
Designers
understand
principles of good
fabric design & use
specialist
consultants where
needs
High quality of
information
delivered to site
Site trades
adequately
educated on
principles of good
building fabric
design…they know
WHAT to do and
WHY to do it
Value engineering
on site supported
by informed
decisions or
analysis
High-standard
building quality
delivered to clients

36. Thanks for your
attention!