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



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%)



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



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





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








Thermal Comfort and Moisture Issues

Increased heat loss at slab results in colder indoor floor and ceiling temperatures – increasing risk for mould/condensation

Ceiling and Flooring Moisture Issues

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

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



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



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




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








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

Questions

Graham Finch [email protected] - 604.873.1181

Engineering

NBEC 2014 - Balcony Thermal Bridging