NBEC 2014 - Balcony Thermal Bridging
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Transcript of NBEC 2014 - Balcony Thermal Bridging
The Importance of Balcony and Slab Edge Thermal Bridges in Concrete Construction
GRAHAM FINCH, MASC, P.ENG, PRINCIPAL,
RDH BUILDING ENGINEERING LTD. VANCOUVER, BC
COAUTHORS: BRITTANY HANAM & JAMES HIGGINS
Outline
à Why care about concrete
balconies and exposed slab
edges?
à Impacts of uninsulated slab
edges and balconies
à Comparison of alternate
solutions
à Benefit of balcony thermal
breaks
à Plenty of efforts underway to improve
energy efficiency of the building
enclosure & whole buildings
à Energy Code Changes, ASHRAE 90.1,
NECB, & IECC
à LEED, Passive House & other Green
Building programs
à Lots of attention to thermal bridging of
poor performing aluminum frame
windows in high-rises
à But.. Still missing one of the most
significant thermal bridges
Introduction
à Outdoor space
à Fresh air, smoking?
à Sunshine
à Views
à More floor space
à Plants/garden
à BBQ/eating area
à Architecturally
appealing
à Requirement in our
housing market?
à Storage (Bikes)
What Do Most People See with Balconies?
à Uninsulated concrete slab
à Degrades wall thermal performance
(increased heat loss)
à Lowers effective R-value of wall
à Increased space-heating & cooling
requirements (More kWh + $$)
à Colder interior surfaces (risk of
condensation/mould, thermal
discomfort)
à Finish, waterproofing, railings, and
other interface details & maintenance
à Structural design considerations
à Exhaust vents
What Do Engineers See with Balconies?
à Walls have effective R-value greater
than R-15 (hopefully!)
à Exposed slab edges, balconies,
eyebrows have an R-value of ~R-1
à 8” slab in a 104” (8’-8”) high wall
à Individual balconies occupy 1 to 2% of
gross wall area in typical high-rise
à Continuous exposed concrete slab
edge or eyebrow occupy ~8% of gross
wall area
à How can something small matter
that much? Can’t I just ignore it?
What Thermal Impact Can Balconies Possibly Have?
à Study to assess impact of exposed slab
edges and balconies in Multi-Unit
Residential Buildings (MURBs): à Thermal performance (effective R-values),
à Energy code compliance,
à Thermal comfort & condensation potential,
à Whole building energy consumption & costs
à Assess designed or proprietary solutions
available & used in the market to improve
performance
Concrete Balcony and Slab Edge Impact Research Study
à Thermal bridging (at slab edges)
results in heat bypassing wall
insulation – reduces effective R-value
of entire wall
à Effective R-values matter for:
à Building code
à Energy code compliance
(prescriptive, BE trade-off, or energy
modeling)
à Building space conditioning loads
(heating & cooling)
à Whole building energy consumption
Thermal Impact of Exposed Slab Edges on Wall R-values
Impact of Exposed Slabs & Balconies – Exterior Insulated
R-‐values for 8’8” High Wall -‐ No Balcony or Eyebrow (Center of Wall) InsulaBon Strategy EffecBve
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) InsulaBon Strategy EffecBve
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
Results from thermal modeling using calibrated finite element 3-‐dimensional soSware
Impact of Exposed Slabs & Balconies – Interior Insulated
InsulaBon Strategy EffecBve R-‐value
1” XPS (R-‐5) + R-‐12 baDs/steel studs R-‐7.5 (-‐48%)
2” XPS (R-‐10) + R-‐12 baDs/steel studs R-‐8.9 (-‐55%)
3” XPS (R-‐15) + R-‐12 baDs/steel studs R-‐10.0 (-‐60%)
R-‐values for 8’8” High Wall with Balcony or Eyebrow (Overall) -‐ Similar for Exposed Slab Edge
InsulaBon Strategy EffecBve R-‐value
1” XPS (R-‐5) + R-‐12 baDs/steel studs R-‐14.3
2” XPS (R-‐10) + R-‐12 baDs/steel studs R-‐19.7
3” XPS (R-‐15) + R-‐12 baDs/steel studs R-‐24.7
R-‐values for 8’8” High Wall -‐ No Balcony or Eyebrow (Center of Wall)
XPS/baD insula:on to interior of exposed concrete wall
Energy Codes & Minimum Effective Wall R-values
à Energy Codes drive minimum thermal performance
& insulation/glazing levels
à Within Canada, Provincial/National Building Codes
à ASHRAE 90.1-2010 & NECB 2011
à In the US, varies by state though similar targets
Climate Zone Wall Any ConstrucBon Type – ResidenBal or Commercial : Min. R-‐value
8 31.0
7A/7B 27.0
6 23.0
5 20.4
4 18.6
NEC
B 2
01
1
ASH
RA
E 9
0.1
-20
10
Climate Zone Wall – Steel Framing -‐ ResidenBal/Commercial Min. R-‐value
Wall – Mass ConstrucBon -‐ ResidenBal/Commercial Min. R-‐value
8 27.0 Res, 15.6 Comm 19.2 Res, 14.1 Comm
7A/7B 23.8 Res, 15.6 Comm 14.1 Res, 14.1 Comm
6 15.6 Res, 15.6 Comm 14.1 Res, 12.5 Comm
5 15.6 Res, 15.6 Comm 12.5 Res, 11.1 Comm
4 15.6 Res, 15.6 Comm 11.1 Res, 9.6 Comm Clim
ate
Zone
à Typical Wall R-values for Most of Canada
à ASHRAE 90.1-2007/2010
• Wall R-value minimum of ~R-15.6 (steel framed), ~R-11.1 to R-14.1 (mass)
à National Energy Code for Buildings NECB 2011
• Wall R-value minimum of R-18 to R-23 (all wall types)
à Walls have limited trade-off ability due to maximized window
area and low window thermal performance
à 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%
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%
Thermal Comfort and Moisture Issues
Increased heat loss at slab results in colder indoor floor and ceiling temperatures – increasing risk for mould/condensation
à Impossible to ignore in energy efficient designs, comfort & energy
à Minimum prescriptive and trade-off energy code compliance “difficult”
à Wall R-value reductions from slab in order of ~40-60%
à Space heat energy and cost increases in order of 10%
à Very hard to trade-off with more insulation due to depreciating returns
à Designers usually trade off the wall R-value to allow for more/larger
windows – so a lower baseline wall R-value is not advantageous
à Mechanical and other energy modeling trade-offs also difficult
à There is a cost justification for thermal break balcony/slab edge solutions
à Cost premiums from the product can be offset by the savings from adding
insulation into the walls or windows
à Allows for larger floor areas (less insulation, thinner walls)
Addressing Exposed Slab Edge and Balcony Thermal Bridging
Insulating Cantilevered Concrete Balconies - Options
Concentrated reinforcement with insulaBon
Balcony InsulaBon 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 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//
à R-20 exterior insulated
concrete wall (R-21.4 with
backup construction)
à Compare alternate insulated
balcony insulation solutions à Structural cut-out
à Concentrated rebar
à Insulation wraps
à Balcony slab thermal breaks
R-value Improvement from Balcony Insulation Solutions
à Linear Transmittance values for alternate solutions
à Uoverall = Uwall + (Ψbalcony ⋅ Lbalcony)/ Aoverall
à For an example case: wall with exterior insulation, R-20
(RSI-3.5, U-0.284)
à 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
à Thermally decouples the concrete slab
connection from inside to outside
à Stainless steel tension reinforcing
à Polymer concrete compression blocks
à Gypsum/concrete fire plates
à Expanded polystyrene insulation filler
à Tested and proven solution
Cast-in Place Concrete Balcony Slab Thermal Breaks
R-value Improvement from Balcony Thermal Breaks
Wall InsulaBon Strategy EffecBve R-‐value
1” XPS (R-‐5) + R-‐12 baD/studs = (R-‐14.3 c.o.w.) R-‐7.5
2” XPS (R-‐10) + R-‐12 baD/studs = (R-‐19.7 c.o.w.)
R-‐8.9
3” XPS (R-‐15) + R-‐12 baD/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 InsulaBon Strategy &
Thermal Break R-‐value
EffecBve R-‐values
R-‐2.5 thermal break
R-‐5 thermal break
1” XPS (R-‐5) + R-‐12 baD/studs (R-‐14.3) R-‐11.0 R-‐12.1
2” XPS (R-‐10) + R-‐12 baD/studs (R-‐19.7) R-‐14.4 R-‐16.6
3” XPS (R-‐15) + R-‐12 baD/studs (R-‐24.7) R-‐17.0 R-‐19.5
R-value Improvement from Balcony Thermal Breaks
0
5
10
15
20
25
0 5 10 15 20 25
Effective R-‐value of W
all (In
c. 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 (NoBalcony)
Wall with Balcony(No Thermal Break)
Wall with Balcony -‐R-‐2.5 Thermal Break
Wall with Balcony -‐R-‐5 Thermal Break
à Exposed slab edge is just as
bad thermally as a protruding
eyebrow or balcony
à Solution: Exterior insulate or
slab edge to wall thermal
break
Exposed Concrete Slab Edge Thermal Breaks
R-value Improvement from Exposed Slab Thermal Breaks
Wall InsulaBon Strategy EffecBve R-‐value
1” XPS (R-‐5) + R-‐12 baD/studs (R-‐14.3) R-‐7.4
2” XPS (R-‐10) + R-‐12 baD/studs (R-‐19.7) R-‐8.7
3” XPS (R-‐15) + R-‐12 baD/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 InsulaBon Strategy &
Thermal Break R-‐value
EffecBve R-‐values
R-‐2.5 thermal break
1” XPS (R-‐5) + R-‐12 baD/studs (R-‐14.3) R-‐10.8
2” XPS (R-‐10) + R-‐12 baD/studs (R-‐19.7) R-‐14.2
3” XPS (R-‐15) + R-‐12 baD/studs (R-‐24.7) R-‐16.9
à When slab thermal breaks are used, it is possible to attain
prescriptive minimum wall R-value requirements
à Better R-values to trade-off other components
à Lower energy consumption
à Easier energy code compliance (i.e. ASHRAE 90.1/NECB)
à 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%
Thermal Comfort Improvements from Thermal Breaks
-‐10oC 20oC
No thermal break
Thermal break
OUTDOORS INDOORS
13.9oC
18.6oC
13.9oC
18.6oC
8.2oC
15.6oC
8.2oC
15.6oC
Exterior Insula;on Interior Insula;on Window Wall 3.8oC
3.7oC
9.0oC
5.4oC
à Whole building energy model
(EnergyPlus) used to assess impact of
slab edge & balcony thermal breaks
à Archetypical high-rise concrete frame
MURB, 40% window area, SHGC 0.3
à Space heat 40-60% of total energy load
à Exposed slab edges/balconies around
perimeter of building
à Zoning, thermal mass, shading effects
à Modeled within 8 North American
climate zones to specifically assess
heating/cooling loads in each
à Assess local energy use & costs
Whole Building Energy Savings
à Assessed impact of R-3.4 and
R-5.7 slab thermal breaks
à Space heat energy savings are
equal to 4 to 10 kWh/m2/yr or
7-8% of total heating
à Minimal cooling energy savings
(due to low Canadian cooling
loads)
à $ savings dependant on local
heating fuel costs
à Payback depends on fuel cost,
and climate – 15 to 30 year range
Whole Building Energy Savings – Climate Zones 4-7
à Exposed slab edges and balconies have a significant reduction on R-
value of surrounding walls
à Prescriptive and BE trade-off energy code compliance is difficult –
can’t add more insulation to walls to trade-off
à Thermal comfort implications – mould & condensation potential
à Solutions available to address slab edge/balcony thermal bridge –
manufactured balcony thermal break most cost & thermally effective
à A must for energy efficient projects
à Simpler energy code compliance – large R-value improvement
à Thermal comfort improvements, less mould/condensation risk
à 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