Passive House North 2013 Presentation on Thermal Bridges in Concrete Construction. Solutions to Address Energy Code Compliance, Thermal Comfort and Energy Savings

1. Solutions to Address Energy Code Compliance,
Thermal Comfort, and Energy Savings
Thermal Bridges in Concrete Construction
Graham Finch, MASc, P.Eng
RDH Building Engineering Ltd.
Vancouver, BC
Passive House North 2013:
September 27-28, Vancouver, BC

2. A usual Saturday Morning in Vancouver…

3. Today’s Presentation 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 solutions to
improve thermal performance of slab
edges and balconies.
How can balcony thermal breaks improve
effective R-values, energy code
compliance, energy costs, and thermal
comfort?

4. 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 attention to
thermal bridging of poor
performing aluminum frame
windows in high-rises
But.. Still missing one of the most
significant thermal bridges
Introduction

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

6. Uninsulated concrete slab
Degrades wall thermal
performance (increased heat loss)
Lowers effective R-value of wall
Increased space-heating & cooling
requirements (More kWh + $$)
Colder interior surfaces (risk of
condensation/mould, thermal
discomfort)
Finish, waterproofing, railings, and
other interface detail
considerations & maintenance
Structural design considerations
Exhaust vent locations
What Do Engineers and PH Designers See with Balconies?

7. Walls have effective 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
Continuous exposed concrete slab
edge or eyebrow occupy ~8% of gross
wall area
How can something small matter that
much? Can’t I just ignore it?
What Thermal Impact Can Balconies Possibly Have?

8. RDH performed a study to look at the impact
of exposed slab edges and balconies in Multi-
Unit Residential Buildings (MURBs):
Thermal performance (effective R-values),
Energy code compliance,
Thermal comfort & condensation potential,
Whole building energy consumption & costs
Assess solutions available in the market
Impact on effective R-value
Thermal comfort improvement
Costs & potential payback
Energy savings
Concrete Balcony and Slab Edge Impact Research Study

9. Thermal bridging (at slab edges)
results in heat bypassing wall
insulation – reducing effective R-
value of entire wall
Effective R-values matter for:
Building code
Energy code compliance
(prescriptive, BE trade-off, or
energy modeling)
Building space conditioning loads
(heating & cooling)
Whole building energy
consumption
Thermal Impact of Exposed Slab Edges on Wall R-values

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

11. Impact of Exposed Slabs & Balconies – Interior Insulated
Insulation Strategy Effective
R-value
1” XPS (R-5) + R-12 batts/steel studs R-7.5 (-48%)
2” XPS (R-10) + R-12 batts/steel studs R-8.9 (-55%)
3” XPS (R-15) + R-12 batts/steel studs R-10.0 (-60%)
R-values for 8’8” High Wall with Balcony or Eyebrow
(Overall) - Similar for Exposed Slab Edge
Insulation Strategy Effective
R-value
1” XPS (R-5) + R-12 batts/steel studs R-14.3
2” XPS (R-10) + R-12 batts/steel studs R-19.7
3” XPS (R-15) + R-12 batts/steel studs R-24.7
R-values for 8’8” High Wall - No Balcony or Eyebrow
(Center of Wall)
XPS/batt insulation to interior of
exposed concrete wall

12. Energy efficiency requirements within City of Vancouver VBBL and BCBC
Both currently being revised with more stringent energy provisions
Both have prescriptive requirements for minimum building enclosure R-
values (effective) 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)
National 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…
Energy Code Impact of Uninsulated Balconies
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%

13. Band-Aid Solutions? Just Add More Wall Insulation?
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%

14. Thermal Comfort and Moisture Issues
Increased heat loss at slab results
in colder indoor floor and ceiling
temperatures – increasing risk for
mould/condensation

15. Ceiling and Flooring Moisture Issues

16. Impossible to ignore in Passive House designs, comfort & energy
Minimum prescriptive and trade-off energy code compliance “difficult”
Wall R-value reductions in order of ~40-60%
Space heat energy and cost increases in order of 10%
Very hard to trade-off with more insulation due to depreciating
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 justification for thermal break balcony/slab edge products
Cost premiums offset by the savings from adding insulation into the
walls or windows
Allows for larger floor areas (less insulation, thinner walls)
Addressing Exposed Slab Edge and Balcony Thermal Bridging

17. Insulating Cantilevered Concrete Balconies - Options
Concentrated reinforcement
with insulation
Balcony Insulation wrap
(varying depth of coverage)
Structural cut-outs with
beam reinforcement
Manufactured slab edge /
balcony thermal break
60% length structural
cut-out (w/ and w/o
exterior insulation.
Extra reinforcing steel
in remainder to
support slab.
Approx. Cost
$50/ft
Concentrated
reinforcement
within 40% of
length (remainder
insulation).
Approx. Cost
$ 25/ft
2” (R-10) extruded
polystyrene (XPS)
insulation wrap
(coverage 2’, 4’ 6’
and full edge wrap).
Approx. Cost
$200-$250/ft
Manufactured
balcony thermal
break within slab
separating interior
from exterior.
Approx. Cost
$50-$80/ft

18. R-20 exterior insulated
concrete wall (R-21.4 with
backup construction)
Compare alternate insulated
balcony insulation solutions
Structural cut-out
Concentrated rebar
Insulation wraps
Balcony slab thermal breaks
R-value Improvement from Balcony Insulation Solutions

19. Linear Transmittance values for alternate solutions
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
Linear Transmittance – ψ (Psi) Values
U-wall = 0.266 – simple math for 2.7m tall wall , ψ of 0.72 doubles heat loss

20. Thermally decouples the concrete slab
connection from inside to outside
Stainless steel tension reinforcing
Polymer concrete compression blocks
Gypsum/concrete fire plates
Expanded polystyrene insulation filler
Tested and proven solution in Europe
Cast-in Place Concrete Balcony Slab Thermal Breaks

21. R-value Improvement from Balcony Thermal Breaks
Wall Insulation Strategy Effective
R-value
1” XPS (R-5) + R-12 batt/studs = (R-14.3 c.o.w.) R-7.5
2” XPS (R-10) + R-12 batt/studs = (R-19.7 c.o.w.) R-8.9
3” XPS (R-15) + R-12 batt/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 Insulation Strategy &
Thermal Break R-value
Effective R-values
R-2.5
thermal
break
R-5
thermal
break
1” XPS (R-5) + R-12 batt/studs (R-14.3) R-11.0 R-12.1
2” XPS (R-10) + R-12 batt/studs (R-19.7) R-14.4 R-16.6
3” XPS (R-15) + R-12 batt/studs (R-24.7) R-17.0 R-19.5

22. R-value Improvement from Balcony Thermal Breaks
0
5
10
15
20
25
0 5 10 15 20 25
EffectiveR-valueofWall(Inc.Balcony)
Nominal R-value of Wall Exterior Insulation
Impact of Thermal Breaks on the Effective R-value
of an Exterior Insulated Concrete Wall
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

23. Exposed slab edge is just as
bad thermally as a protruding
eyebrow or balcony
Solution: Exterior insulate or
slab edge to wall thermal
break
Exposed Concrete Slab Edge Thermal Breaks

24. R-value Improvement from Exposed Slab Thermal Breaks
Wall Insulation Strategy Effective
R-value
1” XPS (R-5) + R-12 batt/studs (R-14.3) R-7.4
2” XPS (R-10) + R-12 batt/studs (R-19.7) R-8.7
3” XPS (R-15) + R-12 batt/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 Insulation Strategy &
Thermal Break R-value
Effective R-values
R-2.5 thermal break
1” XPS (R-5) + R-12 batt/studs (R-14.3) R-10.8
2” XPS (R-10) + R-12 batt/studs (R-19.7) R-14.2
3” XPS (R-15) + R-12 batt/studs (R-24.7) R-16.9

25. When slab thermal breaks are used, it is possible to attain
prescriptive minimum wall R-value requirements
Better R-values to trade-off other components
Lower energy consumption
Easier energy code compliance (i.e. ASHRAE 90.1/NECB)
Some examples..
Impact of Balcony Thermal Breaks on Code Compliance
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%

26. Thermal Comfort Improvements from Thermal Breaks
-10oC 20oC
NothermalbreakThermalbreak
OUTDOORS INDOORS
13.9oC
18.6oC
13.9oC
18.6oC
8.2oC
15.6oC
8.2oC
15.6oC
Exterior Insulation Interior Insulation Window Wall
3.8oC
3.7oC
9.0oC
5.4oC

27. 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
heating/cooling loads in each
Assess local energy use & costs
Whole Building Energy Savings

28. 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
heating fuel costs
Payback depends on fuel cost,
and climate – 15 to 30 year
range
Whole Building Energy Savings – Climate Zones 4-7

29. Exposed slab edges and balconies have a significant
reduction on R-value of surrounding walls
Prescriptive and BE trade-off energy code compliance is difficult –
can’t add more insulation to walls to trade-off
Thermal comfort implications – mould & condensation potential
Solutions available to address slab edge/balcony thermal
bridge – manufactured balcony thermal break most cost &
thermally effective
A must for Passive House Projects
Simpler energy code compliance – large R-value improvement
Thermal comfort improvements, less mould/condensation risk
Space heat energy & cost savings in the range of 7-8% for MURBs
in climate zones 4-7, less in zones 1-3
Summary & Key Points

30. Questions
gfinch@rdhbe.com
604-873-1181
4 reports available at www.rdhbe.com