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
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
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%)
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%)
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
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
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
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
! 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
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
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
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 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