The document summarizes a presentation on building envelopes. It discusses the physics of heat, air, and moisture transfer and how they relate. It covers various risks of inadequate envelopes like moisture problems. It also reviews concepts like vapor diffusion, vapor retarders, rain penetration strategies, and drying. The goal is to understand building science principles to design better, more durable building envelopes.

1. 2013-02-09
Building Envelopes
Building Science
Physics – Risks -
Strategies
Rick Roos M.A.Sc.
Free Powerpoint Templates
Rick Roos
• Professor
of
Building
Science
George
Brown
College
• Principal
of
Integral
Building
Science
– Savings
By
Design
–
Enbridge
Gas/SBC
– QA/QC
Evaluations
– Energy
Analyses
– Utilities/Governments
– Architects/Builders
Building Science
1

2. 2013-02-09
Overview of presentation
• Purpose
of
the
envelope
• Physics
of
Heat,
Air
and
Moisture
• Control
Layers
• Risks
of
Inadequate
Envelope
• Design
Considerations
• Envelope
Assemblies
New Solutions, New Problems
• Advent of insulation led to moisture
problems
• Tighter envelope led to health issues
• Building Science born from the need to
KNOW how to build better
Roos Building Science 5
Building Envelope Requirements
• Control
heat
Klow
• Control
air
Klow
• Control
water
vapour
Klow
• Control
rain
penetration
• Control
light,
solar
• Control
noise
• Control
Kire
• Provide
strength
and
rigidity
• Be
durable
• Be
aesthetically
pleasing
• Be
economical
2

3. 2013-02-09
Physics of the Building Envelope
Preparing for the Future
• Increasing demands for energy performance
• Where are we headed?
• What are the influences?
Policy to Powerpipe
Interna'onal
• Kyoto,
Rio
Conference,
Agreements
Earth
Summit
Internal
• Demand
Side
Management;
Policy
Building
Code
Ini'a'ves
Changes
BeCer
• SB-­‐12;
Energy
Performing
Star;
R-­‐2000;
Passive
House
Buildings
3

4. 2013-02-09
Path to Net Zero (Energuide)
Divide and Conquer
• Convenient to discuss building science in
it’s component parts separately
– Heat Transfer
• Conduction
• Convection
• Radiation
– Moisture
• Bulk Water
• Capillary Transport
• Vapour Diffusion
– Air Leakage
Heat
Transfer
4

5. 2013-02-09
Heat transfer
• Conduction
• Convection
• Radiation
-20˚C +20˚C
Conduction
Radiation
Convection
Movement from warmer to colder
Fourier’s Law - Conduction
q= A/R x ΔT
5

6. 2013-02-09
There are R-values…then there
are R-values
• Nominal R-value (OBC)
• Effective Ra-value
– Thermal bridging
• Structural elements that bypass insulation
• ‘Highway’ for heat transfer
Accounting For Thermal Bridging
2-dimensional heat Finite Element Analysis
transfer
• Realistic modeling of heat
flow paths
• Previous accounts did not
reflect the actual
importance of 2-D heat
transfer
17
Effects of Thermal Bridging
10
9
8
7
R-27
R-24
R-22
6
RSI (M2K/W)
5
4
3
2
1
0
1a
6b
1b
2a
6a
4d
2b
5b
7
5a
4a
4c
4b
3
8b
8a
ii
1a
e
e
e
e
e
e
e
e
e
e
e
as
e
e
e
as
e
e
e
as
as
as
as
as
as
as
as
as
as
as
as
as
as
as
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
Whole-Wall RSI
6

7. 2013-02-09
Heat & Moisture Inter-
relationship
• Heat and moisture act together
• Difficult to consider one without the other
the other
Roos Building Science 19
Moisture Transport
• Capillary
Transport
• Bulk
Water
Transport
• Vapour
Diffusion
– Adsorption
• Air
Leakage
1:10:100
7

8. 2013-02-09
Vapour Diffusion
• Vapour
moves
from
areas
of
high
concentration
to
low
• Vapour
pressure
drives
vapour
movement
• Primary
inKluence:
Temperature
How Does Vapour Move?
• Vapour
moves
from
high
to
low
concentrations
of
vapour
pressure
• InKluences
relative
humidity
• Relative
humidity
determines
moisture
content
Permeance Testing
Dry Cup Wet Cup Inverted Cup
8

9. 2013-02-09
Which Permeance
Value?...When?
• Dry Cup (between 0% and 50% RH)
• When RH levels are expected to be in this region
• E.g. vapour retarder in cold climates
• Wet Cup (between 50% and 100% RH)
• When RH levels are expected to be in this region
• E.g. exterior sheathings in cold climates
• Inverted Wet Cup
• When the material is expected to experience bulk
water exposure
• Drainage Plane materials e.g. Housewrap
Permeance Data Tables
Adsorption
15% Relative Humidity 30% Relative Humidity 100% Relative Humidity
9

10. 2013-02-09
Sorption Isotherms
Risks of High Levels of R.H.
• Elevated
R.H.
levels
– For
extended
periods
of
time
• Increased
Moisture
Content
(building
materials)
• Risk
of
Biological
Growth
Rule: Each Layer Weaker Than
The Last
Option A: Option B:
• From interior to exterior • From interior to exterior
during heating season during heating season
– Fibreboard, untreated – Foamed polystyrene
– Perforated asphalt-coated insulation 25mm (29 kg/m3)
sheathing paper – Cellulose Acetate Film
– Nylon film 0.025mm – Fibreboard, sheathing
grade
10

11. 2013-02-09
Vapour Trap
• Only ONE vapour retarder is allowed in an
assembly!
• This must be placed on the warm side of
the assembly
• If two are installed, this traps moisture
between the two materials creating
potential for moisture related damage
OBC Vapour Retarder
Requirements
• The building code requires vapour
retarders on every exterior building
envelope component
• The maximum permeance for a vapour
retarder in our climatic region is 60 ng/
PaSm2
Example: Is This Assembly Acceptable
During the Heating Season?
Vapour Retarder
11

12. 2013-02-09
Vapour Retarder
• Why
retarder
not
barrier
• Warm
side
of
the
assembly
• Need
not
be
continuous
Vapour Retarder
• OBC
–
60
ng/PaŸSŸm2
• Drying
potential
to
the
interior?
• Materials:
– Vapour
retarder
paint
– “Smart”
vapour
retarders
– Oriented
Strand
Board
• Only
ONE
vapour
control
layer
per
assembly!
Sun-­‐Driven
Moisture
36
Roos Building Science
12

13. 2013-02-09
Rela've
Humidity
at
Condensa'on
Plane
100
Risk of
Mold
75
#REF!
#REF!
#REF!
#REF!
50
#REF!
#REF!
25
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Roos Building Science 37
Capillary
Transport
Capillary Rise (?)
wood cells
13

14. 2013-02-09
Capillary transport-Forces
on
water
molecules
Wetting
Hydrophilic
Vs.
Hydrophobic
• Hydrophilic
natural state
• Hydrophobic
coating applied
14

15. 2013-02-09
Capillary Rise
What Effects Capillary
Transport?
• Water rises most in thinnest tube and least
in widest tube
• Fluid rises because the adhesive forces of
water against capillary material is greater
than the cohesive energy between the
water molecules
Capillary Moisture Transport
• Capillary
breaks
• Damp-­‐prooKing
• Gap
size
• Sponge
video
15

16. 2013-02-09
Rising
Damp
Efflorescence
Subflorescence
16

17. 2013-02-09
Subflorescence
Bulk
Water
(Rain
Leakage)
Roos Building Science 50
Wall
Classifica*on
System
By
Rain
Penetra*on
Control
Strategy
17

18. 2013-02-09
Storage or Mass Construction
52
Perfect
Barriers
• Joints between
elements also
designed as perfect
barrier: single bead
of sealant
• Poor record of
performance
• Examples: metal
panels, some
window frames,
EIFS
Screened-­‐Drained
Walls
18

19. 2013-02-09
Pressure
Moderated
Air
Space
Drainage
and
Flashing
Concepts
Drying
• Drying:
– Evapora*on
from
inside
or
outside
surfaces
– Vapour
transport
by
diffusion
– Drainage,
driven
by
gravity
– Ven*la*on,
if
provided
19

20. 2013-02-09
Drying Potential
• Wall, ceiling and floor systems can
experience interstitial condensation
– Air leakage
– Bulk water intrusion (rain water)
– Excessive relative humidity
• It’s acceptable, if it is allowed to dry!
• The mechanism for drying is vapour
diffusion
Drying
(Drainage)
• Drainage is the most effective means of
removing water from wall systems
– Very important mechanism for moisture
control
• Even if well drained, there will be water in
adsorbed, absorbed states and adhering
to surfaces
Drying
(Diffusive
Drying)
• Diffusive drying can occur towards the
exterior AND the interior
– Depending on assembly
• Due to solar radiation in cold climates,
drying toward the interior can be very
important
20

21. 2013-02-09
Drying (Air Movement)
• Air movement can move large amounts of
moisture
• While moisture-laden interior air (in cold
climates) can cause significant problems
– Dry inward moving exterior air can contribute
to drying
• Reliance on uncontrolled air movement is
not a reliable or responsible approach
Drying
(Ven*la*on)
• Ventilation of exterior air
behind cladding
– Due to wind pressure
– Solar heated rising air
• This can be useful in
accelerating drying
• Ventilation bypasses vapour
resistant cladding materials
thereby allowing drying
• A clear space of 19mm is
recommended
Air Movement – 3
Requirements
• A Fluid
• A Pressure Difference
• An Opening
21

22. 2013-02-09
Air Flow
64
Buoyancy of Air – Stack Effect
Saturation
Cold Air Warm Air
22

23. 2013-02-09
Psychrometric Chart
Air Leakage - Condensation Plane
68
Air
Air
Pressure
Pressure
Dewpoint Temperature against
Condensation Plane Temperature
69
35
30
25
20
15
Temperature
(°C)
10
5
0
-­‐5
-­‐10
-­‐15
40087
40118
40148
40179
40210
40238
40269
40299
40330
40360
40391
40422
Roos Building Science
#REF!
#REF!
23

24. 2013-02-09
Condensing Plane Temperatures
Air Leakage – Vapour Diffusion
71
Air
Air
Pressure
Pressure
Vapour
Pressure Vapour
Pressure
Roos Building Science
Mold
24

25. 2013-02-09
Substrate
Classes
• Substrate
class
0:
Op'mal
culture
medium
(e.g.
full
medium).
This
isopleth
system
represents
the
maximum
growth
possible
for
any
mold
found
in
buildings.
• Substrate
class
I:
Bio-­‐u'lizable
substrates,
such
as
wall
paper,
plaster
board,
building
products
made
of
biologically
degradable
materials,
materials
for
permanently
elas'c
joints,
strongly
contaminated
surfaces.
• Substrate
class
II:
Less
bio-­‐u'lizable
substrates
with
porous
structure,
such
as
plasters,
mineral
building
materials,
certain
woods,
insula'ng
materials
not
belonging
to
group
I.
Mold
Germina'on
&
Growth
Isopleths
Spore Germination
Mold
Spore Spore contents
(moisture storage
Exterior consideration)
Wall
Spore wall (vapour
diffusion resistance)
25

26. 2013-02-09
Moisture
Isopleths
(With
VR)
Moisture
Isopleths
(No
VR)
Control Layers
26

27. 2013-02-09
Control layers
• What
do
we
need
to
control?
– Heat
transfer
–
Thermal
Control
Layer
– Bulk
water
intrusion
–
Rain
Control
Layer
– Air
leakage
–
Air
Control
Layer
– Vapour
diffusion
–
Vapour
Control
Layer
• Some*mes
Control
layers
are
combined
into
a
single
material
or
membrane
Thermal Control Layer
• Continuity
• Thermal
bridging
Strategies to Address Thermal
Bridging
• Exterior Insulation
– Increase ratio of outboard to inboard
insulation
– Towards 100% exterior insulation
• Reduce area occupied by structural
components
27

28. 2013-02-09
Thermal Bridging
Effects
of
Thermal
Bridging
Roos Building Science 84
28

29. 2013-02-09
Strategy #1
Strategy #2
• Exterior Insulation
• Blunts the effects of
thermal bridging
Strategies to Address Thermal Bridging
• Exterior Insulation (‘Outsulation’)
– Increase ratio of outboard to inboard
insulation
– Towards 100% exterior insulation
• Reduce area occupied by structural
components
29

30. 2013-02-09
Calculating Effective R-Values
Parallel Planes In Series
Effective Thermal Resistance
• RSIeff = RSIseries + RSIparallel
Exterior Insulation
• Building
code
• Thermal
bridging
• Convenient
balance
30

31. 2013-02-09
Rain Control Layer - Drainage Plane
• Resists
liquid
water
penetration
• Vapour
permeable
• Eliminate
capillary
transport
predominantly
Drainage Plane
92
Roos Building Science
Bulk water leakage
• Drainage Plane
– Assume water will get past 1st line of defence
• Contiguous overlapping system
31

32. 2013-02-09
Water Damage - Mold
Flashing
Sealing
32

33. 2013-02-09
Window Sill Pan
Air Control Layer
• Must be continuous
• Detailing in drawings
• Detailing on site
• Specify responsible on-site person
Location of Air Barrier
33

34. 2013-02-09
Common
Air
Leakage
Locations
Attics & Roofs
• Main
areas
of
roof
and
attic
air
leakage:
– Plumbing
stacks
– ASc
hatch
– Recessed
fixtures
– Par**on
walls
– Chimneys
• Stack
Effect
34

35. 2013-02-09
Ceiling & Attic Air Leaks
Air Leakage Related Mold Growth
Air Leakage – Plumbing Stack
35

36. 2013-02-09
Air Leakage - Building Envelope
• Common
areas
of
air
leakage
in
new
homes
– Rooms
over
garages
– Behind
tubs
and
stairs
– Behind
back
framing
– Recessed
fixtures
– Exhaust
fans
– Headers
and
sills
– Electrical
and
cable
boxes
– Window
framing
Rooms
over
garages
Exposed
Kloors
and
cantilevers
36

37. 2013-02-09
Back
Framing
Pot
lights
Headers
and
cantilevers
37

38. 2013-02-09
Sill Plates
Electrical
and
cable
boxes
Windows
38

39. 2013-02-09
Air Barrier Strategies
Exterior Air Barrier Systems
Air Leakage Control Summary
• Key
areas
on
which
to
focus:
– Know
the
main
air
leakage
loca*ons
– Provide
adequate
training
to
subtrades
– Perform
air
barrier
inspec*on
– Perform
air
leakage
tests
early
in
the
construc*on
phase
– Facilitate
explora*on
of
new
air
barrier
techniques
39

40. 2013-02-09
Air leakage of building envelopes
 Blower-­‐door
test
(fan
pressuriza'on
test)
–
measures
enclosure
integrity
Roos Building Science 119
Wall Assemblies
40

41. 2013-02-09
Standard 2006 OBC (R20)
2006 OBC Wall Typical Approach to R27
Double Stud Framing
Exterior Insulated Finish System
Next Generation Reason for Improvement
41

42. 2013-02-09
Insulated Concrete Form
Insulated Concrete Form
Structural Insulated Panels
42

43. 2013-02-09
Cross-Laminated Timber
The Perfect Wall
• All control layers on
the exterior of the
structure
– Thermal
– Rain
– Vapour
– Air
• Protect the structure
• Eliminate thermal
bridging
• Eliminate risks of
moisture damage!
Risks of inadequate building
envelope
• Moisture
Related
Risks
• Air
Leakage
• Bulk
water
leakage
• EfKlorescence
• SubKlorescence
• Vapour
– Outward
– Inward
• Thermal
losses
• Architectural
detailing
– Old
EIFS
system
– Window
flashing
• WorkKlow
management
– Who’s
job
is
it
to
detail
the
air
barrier?
43

44. 2013-02-09
Design Considerations
• Increased
ratio
of
‘out’sulation
to
insulation
– Blunt
or
eliminate
thermal
bridging
– Reduce
moisture
related
problems
• Flashing,
Klashing,
Klashing!
• Air
barrier
continuity!
• Capillary
breaks
• Vapour
retarders
bi-­‐directional
drying
potential
• Toward
the
perfect
wall
Build better buildings
44