Optimizing Concrete Thermal Bridges - Balcony and Slab Edge Thermal Breaks
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The document discusses the thermal performance issues associated with uninsulated concrete balconies and slab edges in multi-unit residential buildings, highlighting the negative impact on effective R-values, energy costs, thermal comfort, and condensation risks. It details various insulation strategies, the necessity for thermal breaks, and their potential to improve energy code compliance and overall building efficiency. Additionally, recommendations for balcony thermal breaks suggest significant energy savings and enhanced comfort within the context of current energy codes.
Optimizing Concrete Thermal Bridges - Balcony and Slab Edge Thermal Breaks
- 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