Thermal bridges in concrete construction solutions to address energy code compliance, thermal comfort, and energy savings

Thermal
Bridges
in
Concrete
Construc4on
Solu%ons
to
Address
Energy
Code
Compliance,
Thermal
Comfort,
and
Energy
Savings
! Graham
Finch,
MASc,
P.Eng
RDH
Building
Engineering
Ltd.
Vancouver,
BC
Passive
House
North
2013:
September
27-‐28,
Vancouver,
BC

A
usual
Saturday
Morning
in
Vancouver…

Today’s
Presenta4on
Outline
! Why
care
about
concrete
balconies
and
exposed
slab
edges?
! True
impact
of
uninsulated
slab
edges
and
balconies
on
R-‐values,
energy
code
compliance,
energy
costs,
&
thermal
comfort.
! Comparison
of
alternate
solu%ons
to
improve
thermal
performance
of
slab
edges
and
balconies.
! How
can
balcony
thermal
breaks
improve
effec%ve
R-‐values,
energy
code
compliance,
energy
costs,
and
thermal
comfort?

Introduc4on
! Lots
of
effort
underway
to
improve
energy
efficiency
of
the
building
enclosure
&
whole
buildings
! Energy
Code
Changes,
ASHRAE
90.1,
NECB,
&
IECC
awareness
! Passive
House
! LEED
&
other
Green
Building
programs
! Lots
of
industry
a[en%on
to
thermal
bridging
of
poor
performing
aluminum
frame
windows
in
high-‐rises
! But..
S%ll
missing
one
of
the
most
significant
thermal
bridges

What
Do
Most
People
See
with
Balconies?
! Outdoor
space
! Fresh
air
! Sunshine
! Views
! More
floor
space
! Plants/garden
! BBQ/ea%ng
area
! Architecturally
appealing
! Arguably
a
requirement
in
our
housing
market
! Storage
(Bikes)

What
Do
Engineers
and
PH
Designers
See
with
Balconies?
! Uninsulated
concrete
slab
! Degrades
wall
thermal
performance
(increased
heat
loss)
! Lowers
effec%ve
R-‐value
of
wall
! Increased
space-‐hea%ng
&
cooling
requirements
(More
kWh
+
$$)
! Colder
interior
surfaces
(risk
of
condensa%on/mould,
thermal
discomfort)
! Finish,
waterproofing,
railings,
and
other
interface
detail
considera%ons
&
maintenance
! Structural
design
considera%ons
! Exhaust
vent
loca%ons

What
Thermal
Impact
Can
Balconies
Possibly
Have?
! Walls
have
effec%ve
R-‐value
greater
than
R-‐15
(hopefully!)
! Exposed
slab
edges,
balconies,
eyebrows
have
an
R-‐value
of
~R-‐1
! 8”
slab
in
a
104”
(8’-‐8”)
high
wall
! Individual
balconies
occupy
1
to
2%
of
gross
wall
area
in
typical
high-‐rise
! Con%nuous
exposed
concrete
slab
edge
or
eyebrow
occupy
~8%
of
gross
wall
area
! How
can
something
small
ma[er
that
much?
Can’t
I
just
ignore
it?

Concrete
Balcony
and
Slab
Edge
Impact
Research
Study
! RDH
performed
a
study
to
look
at
the
impact
of
exposed
slab
edges
and
balconies
in
Mul%-‐
Unit
Residen%al
Buildings
(MURBs):
! Thermal
performance
(effec%ve
R-‐values),
! Energy
code
compliance,
! Thermal
comfort
&
condensa%on
poten%al,
! Whole
building
energy
consump%on
&
costs
! Assess
solu%ons
available
in
the
market
! Impact
on
effec%ve
R-‐value
! Thermal
comfort
improvement
! Costs
&
poten%al
payback
! Energy
savings

Thermal
Impact
of
Exposed
Slab
Edges
on
Wall
R-‐values
! Thermal
bridging
(at
slab
edges)
results
in
heat
bypassing
wall
insula%on
–
reducing
effec%ve
R-‐
value
of
en%re
wall
! Effec%ve
R-‐values
ma[er
for:
! Building
code
! Energy
code
compliance
(prescrip%ve,
BE
trade-‐off,
or
energy
modeling)
! Building
space
condi%oning
loads
(hea%ng
&
cooling)
! Whole
building
energy
consump%on

Impact
of
Exposed
Slabs
&
Balconies
–
Exterior
Insulated
Results
from
thermal
modeling
using
calibrated
finite
element
3-‐dimensional
so_ware
R-‐values
for
8’8”
High
Wall
-‐
No
Balcony
or
Eyebrow
(Center
of
Wall)
Insula4on
Strategy
Effec4ve
R-‐value
3”
EPS
(R-‐12),
Exterior
Insula%on
R-‐13.9
4”
EPS
(R-‐16),
Exterior
Insula%on
R-‐18.0
6”
EPS
(R-‐24),
Exterior
Insula%on
R-‐25.8
R-‐values
for
8’8”
High
Wall
with
Balcony
or
Eyebrow
(Overall)
Insula4on
Strategy
Effec4ve
R-‐value
3”
EPS
(R-‐12),
Exterior
Insula%on
R-‐7.4
(-‐47%)
4”
EPS
(R-‐16),
Exterior
Insula%on
R-‐8.6
(-‐52%)
6”
EPS
(R-‐24),
Exterior
Insula%on
R-‐10.6
(-‐59%)
Exterior
insula%on
over
concrete
wall

Impact
of
Exposed
Slabs
&
Balconies
–
Interior
Insulated
R-‐values
for
8’8”
High
Wall
-‐
No
Balcony
or
Eyebrow
(Center
of
Wall)
Insula4on
Strategy
Effec4ve
R-‐value
R-‐values
for
8’8”
High
Wall
with
Balcony
or
Eyebrow
(Overall)
-‐
Similar
for
Exposed
Slab
Edge
Insula4on
Strategy
Effec4ve
R-‐value
1”
XPS
(R-‐5)
+
R-‐12
ba[s/steel
studs
R-‐7.5
(-‐48%)
2”
XPS
(R-‐10)
+
R-‐12
ba[s/steel
studs
R-‐8.9
(-‐55%)
3”
XPS
(R-‐15)
+
R-‐12
ba[s/steel
studs
R-‐10.0
(-‐60%)
1”
XPS
(R-‐5)
+
R-‐12
ba[s/steel
studs
R-‐14.3
2”
XPS
(R-‐10)
+
R-‐12
ba[s/steel
studs
R-‐19.7
3”
XPS
(R-‐15)
+
R-‐12
ba[s/steel
studs
R-‐24.7
XPS/ba[
insula%on
to
interior
of
exposed
concrete
wall

Energy
Code
Impact
of
Uninsulated
Balconies
! Energy
efficiency
requirements
within
City
of
Vancouver
VBBL
and
BCBC
! Both
currently
being
revised
with
more
stringent
energy
provisions
! Both
have
prescrip%ve
requirements
for
minimum
building
enclosure
R-‐
values
(effec%ve)
or
may
use
trade-‐off
paths
(B.E.
or
Whole
Building)
! ASHRAE
Standard
90.1-‐2004/2007
(current)
&
2010
(upcoming)
! Wall
R-‐value
minimum
of
R-‐15.6
(steel
framed),
R-‐11.1
to
12.5
(mass)
! Na%onal
Energy
Code
for
Buildings
NECB
2011
! Wall
R-‐value
minimum
of
R-‐18
to
R-‐20.4
Lower
Mainland
(all
wall
types)
! Walls
have
limited
trade-‐off
ability
due
to
maximized
window
area
and
low
window
thermal
performance
! Some
Examples…
Exposed
Slab
Edge
Percentage
for
Different
WWR
100%
wall:
0%
windows
60%
wall:
40%
windows
50%
wall:
50%
windows
40%
wall:
60%
windows
20%
wall:
80%
windows
8”
slab,
8’
floor
to
ceiling
7.7%
12.8%
15.4%
19.2%
38.5%

Band-‐Aid
Solu4ons?
Just
Add
More
Wall
Insula4on?
12” thick
insulation
boards,
~R-50
Exposed
Slab
Edge
Percentage
for
Different
WWR
100%
wall:
0%
windows
60%
wall:
40%
windows
50%
wall:
50%
windows
40%
wall:
60%
windows
20%
wall:
80%
windows
8”
slab,
8’
floor
to
ceiling
7.7%
12.8%
15.4%
19.2%
38.5%

Thermal
Comfort
and
Moisture
Issues
Increased
heat
loss
at
slab
results
in
colder
indoor
floor
and
ceiling
temperatures
–
increasing
risk
for
mould/condensa%on

Ceiling
and
Flooring
Moisture
Issues

Addressing
Exposed
Slab
Edge
and
Balcony
Thermal
Bridging
! Impossible
to
ignore
in
Passive
House
designs,
comfort
&
energy
! Minimum
prescrip%ve
and
trade-‐off
energy
code
compliance
“difficult”
! Wall
R-‐value
reduc%ons
in
order
of
~40-‐60%
! Space
heat
energy
and
cost
increases
in
order
of
10%
! Very
hard
to
trade-‐off
with
more
insula%on
due
to
deprecia%ng
returns
! Designers
usually
trade
off
the
wall
R-‐value
to
allow
for
more/larger
windows
–
so
a
lower
baseline
wall
R-‐value
is
not
advantageous
! Mechanical
and
other
energy
modeling
trade-‐offs
also
difficult
! There
is
a
cost
jus%fica%on
for
thermal
break
balcony/slab
edge
products
! Cost
premiums
offset
by
the
savings
from
adding
insula%on
into
the
walls
or
windows
! Allows
for
larger
floor
areas
(less
insula%on,
thinner
walls)

Insula4ng
Can4levered
Concrete
Balconies
-‐
Op4ons
Concentrated
reinforcement
with
insula4on
Structural
cut-‐outs
with
beam
reinforcement
Balcony
Insula4on
wrap
(varying
depth
of
coverage)
Manufactured
slab
edge
/
balcony
thermal
break
60%
length
structural
cut-‐out
(w/
and
w/o
exterior
insula%on.
Extra
reinforcing
steel
in
remainder
to
support
slab.
Approx.
Cost
$50//
Concentrated
reinforcement
within
40%
of
length
(remainder
insula%on).
Approx.
Cost
$
25//
2”
(R-‐10)
extruded
polystyrene
(XPS)
insula%on
wrap
(coverage
2’,
4’
6’
and
full
edge
wrap).
Approx.
Cost
$200-‐$250//
Manufactured
balcony
thermal
break
within
slab
separa%ng
interior
from
exterior.
Approx.
Cost
$50-‐$80//

R-‐value
Improvement
from
Balcony
Insula4on
Solu4ons
! R-‐20
exterior
insulated
concrete
wall
(R-‐21.4
with
backup
construc%on)
! Compare
alternate
insulated
balcony
insula%on
solu%ons
! Structural
cut-‐out
! Concentrated
rebar
! Insula%on
wraps
! Balcony
slab
thermal
breaks

Linear
Transmijance
–
ψ
(Psi)
Values
U-wall = 0.266 – simple math for 2.7m tall wall , ψ
of
0.72
doubles
heat
loss
! Linear
Transmi[ance
values
for
alternate
solu%ons
! Uoverall = Uwall + (Ψbalcony · Lbalcony)/ Aoverall
! For an example case: wall with exterior insulation, R-20
(RSI-3.5, U-0.284)
! Overall wall – U=0.266 accounting for backup and air-films

Cast-‐in
Place
Concrete
Balcony
Slab
Thermal
Breaks
! Thermally
decouples
the
concrete
slab
connec%on
from
inside
to
outside
! Stainless
steel
tension
reinforcing
! Polymer
concrete
compression
blocks
! Gypsum/concrete
fire
plates
! Expanded
polystyrene
insula%on
filler
! Tested
and
proven
solu%on
in
Europe

R-‐value
Improvement
from
Balcony
Thermal
Breaks
Wall
Insula4on
Strategy
Effec4ve
R-‐value
1”
XPS
(R-‐5)
+
R-‐12
ba[/studs
=
(R-‐14.3
c.o.w.)
R-‐7.5
2”
XPS
(R-‐10)
+
R-‐12
ba[/studs
=
(R-‐19.7
c.o.w.)
R-‐8.9
3”
XPS
(R-‐15)
+
R-‐12
ba[/studs
=
(R-‐24.7
c.o.w.)
R-‐10.0
R-‐values
for
8’8”
High
Wall
with
6’
Balcony
R-‐values
for
8’8”
High
Wall
with
6’
Balcony
&
Thermal
Break
Wall
Insula4on
Strategy
&
Thermal
Break
R-‐value
Effec4ve
R-‐values
R-‐2.5
R-‐5
thermal
thermal
break
break
1”
XPS
(R-‐5)
+
R-‐12
ba[/studs
(R-‐14.3)
R-‐11.0
R-‐12.1
2”
XPS
(R-‐10)
+
R-‐12
ba[/studs
(R-‐19.7)
R-‐14.4
R-‐16.6
3”
XPS
(R-‐15)
+
R-‐12
ba[/studs
(R-‐24.7)
R-‐17.0
R-‐19.5

R-‐value
Improvement
from
Balcony
Thermal
Breaks
25
20
15
10
Impact
of
Thermal
Breaks
on
the
Effective
R-‐value
of
an
Exterior
Insulated
Concrete
Wall
Effective
5
0
0 5 10 15 20 25 R-‐value
of
Wall
(Inc.
Balcony)
Nominal
R-‐value
of
Wall
Exterior
Insulation
Clear
Wall
(No
Balcony)
Wall
with
Balcony
(No
Thermal
Break)
Wall
with
Balcony
-‐
R-‐2.5
Thermal
Break
Wall
with
Balcony
-‐
R-‐5
Thermal
Break

Exposed
Concrete
Slab
Edge
Thermal
Breaks
! Exposed
slab
edge
is
just
as
bad
thermally
as
a
protruding
eyebrow
or
balcony
! Solu%on:
Exterior
insulate
or
slab
edge
to
wall
thermal
break

R-‐value
Improvement
from
Exposed
Slab
Thermal
Breaks
Wall
Insula4on
Strategy
Effec4ve
R-‐value
1”
XPS
(R-‐5)
+
R-‐12
ba[/studs
(R-‐14.3)
R-‐7.4
2”
XPS
(R-‐10)
+
R-‐12
ba[/studs
(R-‐19.7)
R-‐8.7
3”
XPS
(R-‐15)
+
R-‐12
ba[/studs
(R-‐24.7)
R-‐9.8
R-‐values
for
8’8”
High
Wall
with
Exposed
Slabs
R-‐values
for
8’8”
High
Wall
with
Internal
Slab
Edge
Thermal
Break
Wall
Insula4on
Strategy
&
Thermal
Break
R-‐value
Effec4ve
R-‐values
R-‐2.5
thermal
break
1”
XPS
(R-‐5)
+
R-‐12
ba[/studs
(R-‐14.3)
R-‐10.8
2”
XPS
(R-‐10)
+
R-‐12
ba[/studs
(R-‐19.7)
R-‐14.2
3”
XPS
(R-‐15)
+
R-‐12
ba[/studs
(R-‐24.7)
R-‐16.9

Impact
of
Balcony
Thermal
Breaks
on
Code
Compliance
! When
slab
thermal
breaks
are
used,
it
is
possible
to
a[ain
prescrip%ve
minimum
wall
R-‐value
requirements
! Be[er
R-‐values
to
trade-‐off
other
components
! Lower
energy
consump%on
! Easier
energy
code
compliance
(i.e.
ASHRAE
90.1/NECB)
! Some
examples..
Exposed
Slab
Edge
Percentage
for
Different
WWR
100%
wall:
0%
windows
60%
wall:
40%
windows
50%
wall:
50%
windows
40%
wall:
60%
windows
20%
wall:
80%
windows
8”
slab,
8’
floor
to
ceiling
7.7%
12.8%
15.4%
19.2%
38.5%

Thermal
Comfort
Improvements
from
Thermal
Breaks
thermal
break
Thermal
break No
13.9oC
13.9oC
8.2oC
OUTDOORS INDOORS
-‐10oC 20oC
18.6oC
18.6oC
8.2oC
15.6oC
15.6oC
Exterior
Insula4on Interior
Insula4on Window
Wall
3.8oC
3.7oC
9.0oC
5.4oC

Whole
Building
Energy
Savings
! Whole
building
energy
model
(EnergyPlus)
used
to
assess
impact
of
slab
edge
&
balcony
thermal
breaks
! Archetypical
high-‐rise
concrete
frame
MURB,
40%
window
area,
SHGC
0.3
! Space
heat
40-‐60%
of
total
energy
load
! Exposed
slab
edges/balconies
around
perimeter
of
building
! Zoning,
thermal
mass,
shading
effects
! Modeled
within
8
North
American
climate
zones
to
specifically
assess
hea%ng/cooling
loads
in
each
! Assess
local
energy
use
&
costs

Whole
Building
Energy
Savings
–
Climate
Zones
4-‐7
! Assessed
impact
of
R-‐3.4
and
R-‐5.7
slab
thermal
breaks
around
perimeter
! Space
heat
energy
savings
are
equal
to
4
to
10
kWh/m2/yr
or
7-‐8%
of
total
! Minimal
cooling
energy
savings
(due
to
low
Canadian
cooling
loads)
! $
savings
dependant
on
local
hea%ng
fuel
costs
! Payback
depends
on
fuel
cost,
and
climate
–
15
to
30
year
range

Summary
&
Key
Points
! Exposed
slab
edges
and
balconies
have
a
significant
reduc%on
on
R-‐value
of
surrounding
walls
! Prescrip%ve
and
BE
trade-‐off
energy
code
compliance
is
difficult
–
can’t
add
more
insula%on
to
walls
to
trade-‐off
! Thermal
comfort
implica%ons
–
mould
&
condensa%on
poten%al
! Solu%ons
available
to
address
slab
edge/balcony
thermal
bridge
–
manufactured
balcony
thermal
break
most
cost
&
thermally
effec%ve
! A
must
for
Passive
House
Projects
! Simpler
energy
code
compliance
–
large
R-‐value
improvement
! Thermal
comfort
improvements,
less
mould/condensa%on
risk
! Space
heat
energy
&
cost
savings
in
the
range
of
7-‐8%
for
MURBs
in
climate
zones
4-‐7,
less
in
zones
1-‐3

Ques4ons
gfinch@rdhbe.com
604-‐873-‐1181
4
reports
available
at
www.rdhbe.com

Thermal bridges in concrete construction solutions to address energy code compliance, thermal comfort, and energy savings

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