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

Solu%ons to Address Energy Code Compliance, Thermal Comfort, and Energy Savings

Thermal Bridges in Concrete Construc4on

!   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?

!   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

Introduc4on

!   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 Most People 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 Do Engineers and PH Designers See with Balconies?

!   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?

What Thermal Impact Can Balconies Possibly Have?

!   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

Concrete Balcony and Slab Edge Impact Research Study

!   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

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) Insula4on Strategy Effec4ve

R-‐value

3” EPS (R-‐12), Exterior Insula%on R-‐13.9



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

Results from thermal modeling using calibrated finite element 3-‐dimensional so_ware

Impact of Exposed Slabs & Balconies – Interior Insulated

Insula4on Strategy Effec4ve R-‐value

1” XPS (R-‐5) + R-‐12 ba[s/steel studs R-‐7.5 (-‐48%)



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-‐14.3



R-‐values for 8’8” High Wall -‐ No Balcony or Eyebrow (Center of Wall)

XPS/ba[ insula%on to interior of exposed concrete wall

!   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…

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 Solu4ons? Just Add More Wall Insula4on?

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/condensa%on

Ceiling and Flooring Moisture Issues

!   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)

Addressing Exposed Slab Edge and Balcony Thermal Bridging

Insula4ng Can4levered Concrete Balconies -‐ Op4ons

Concentrated reinforcement with insula4on

Balcony Insula4on 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//

!   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

R-‐value Improvement from Balcony Insula4on Solu4ons

!   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

Linear Transmijance – ψ (Psi) Values U-wall = 0.266 – simple math for 2.7m tall wall , ψ of 0.72 doubles heat loss

!   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

Cast-‐in Place Concrete Balcony Slab Thermal Breaks

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 thermal break

R-‐5 thermal break

1” XPS (R-‐5) + R-‐12 ba[/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

!   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

Exposed Concrete Slab Edge Thermal Breaks

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

!  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..

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 Insula4on Interior Insula4on Window Wall 3.8oC

3.7oC

9.0oC

5.4oC

!   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

!   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

Whole Building Energy Savings – Climate Zones 4-‐7

!   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

Summary & Key Points

Ques4ons [email protected] 604-‐873-‐1181

4 reports available at www.rdhbe.com