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An Analysis of Retrofit Strategies
Net Zero/Passive/Deep Building Enclosure Retrofits for Houses
! Graham Finch, MASc, P.Eng
! Brittany Hanam, MASc, P.Eng, BEMP
Buildings XII Conference – Clearwater Beach, Dec 1-5, 2013
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Overview
! Background
! Net Zero Building Enclosure Targets & Potential Savings
! Interior and Exterior Building Enclosure Retrofit Strategies
! Hygrothermal Considerations & Risk Assessment Evaluation Methodology
! Economics of Net Zero Building Enclosure Retrofits
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Why Existing Buildings
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! In 2010, Total US building stock = 275Billion sq.ft. ! Build 5 Billion sq.ft/yr
! Renovate 5 Billion sq.ft/yr
! Tear down 1.75 Billion sq.ft/yr
! Therefore by 2035, ~75% of the built environment will be new or re-built (Architecture 2030)
! Existing buildings pose a very large but unique challenge to renovate to low energy use
The Energy Savings Potential of Existing Buildings
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! Easier “Low-hanging fruit” retrofits shown to have reasonable energy payback and therefore moderate incentive for owners – but not huge savings ! Mechanical equipment upgrades
! Lighting upgrades
! Air-sealing & easy insulation upgrades (attics)
! Extensive “Deep retrofits” of building enclosure have potential for large savings but are expensive and have a difficult time paying for the work with the energy savings – low incentive for owners
! Incremental Retrofits have greatest potential for uptake when work already being performed
Retrofitting Existing Buildings for Energy Savings
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! Extensive retrofit of the building enclosure to improve energy efficiency (either stand-alone or part of other work/renovation) ! New cladding & added wall insulation, New roof & added
insulation, New high-performance windows, air sealing etc.
What is a Net Zero/Passive/Deep Building Enclosure Retrofit?
Photos: Chris Mattock, Super Insulation Retrofit 1980s, Nanaimo, BC
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0
10000
20000
30000
40000
50000
60000
Baseline Insulate Walls & Air Seal
Double Glazed Windows
Insulate Attic & Basement
Best Net Zero Enclosure Retrofit
Annu
al Heatin
g Energy Con
sumption,
kWh pe
r year
EGH-41 EGH-54 EGH-63 EGH-70 EGH-85
The Potential for Net Zero Building Enclosure Retrofits
! Home with no energy upgrades
! R12 attic insulation ! No wall insulation
! Single glazed windows
! No basement insulation
! Air-leaky enclosure
! Example: Two storey house in Vancouver
! Super-insulated walls, basement and attic
! Triple glazed windows
! Air tight construction
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! Objective: Identify and evaluate building enclosure retrofit strategies to bring existing homes to “net-zero ready” energy use so that mechanical and renewable energy could bring energy consumption to net zero level
! Target: 4 of Canada’s most popular housing Archetypes built from 1950’s to 1980’s
! Assessed each retrofit measure in terms of: ! Effective thermal performance
! Hygrothermal performance and moisture risk
! Construction cost & energy savings payback
! Practical implementation & constructability
! Environmental considerations of materials
! Mechanicals/ventilation – not covered here
Net Zero Building Enclosure Retrofit Study
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Building Enclosure Retrofits - Housing Archetypes
2 Storey with attached Garage
1 Storey Raised Bungalow 2 Storey Row House (end unit)
1.5 Storey “Victory House”
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Building Enclosure Retrofits – Climate Zones
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Net Zero Building Enclosure Retrofit Measures
Roof or Attic
Above Grade Walls
Windows and Doors
Below Grade Walls
Basement slab
Interior Retrofits
+Air-sealing
Exterior Retrofits
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! Exterior retrofits typically preferred for best thermal and hygrothermal performance
! Exterior retrofits most practical when other issues are being addressed (moisture damage) or if replacing cladding/ windows
! Interior retrofits don’t change the look of the house (historic nature)
! Interior retrofits necessary if there are property setback requirements
! Interior retrofits result in loss of usable floor space & re-work of electrical, services etc.
! Best strategy is likely a combination of exterior and interior strategies
Interior vs. Exterior Retrofits for Wood-frame Houses
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! What level of enclosure thermal performance is required to achieve net zero ready/passive levels in Canada?
! General guidelines developed from energy simulations & literature – Effective R-values ! Ceiling or Roof: R-50 to R-60+
! Above Grade Walls: R-30 to R-40
! Windows: R-6 or higher (triple pane, SHGC=0.4-0.5+)
! Below Grade Walls: R-20
! Foundation Slab: R-10 to R-20
! Air tightness: <1 ACH @ 50 Pa
! BUT - be aware of diminishing returns to over insulating
! Biggest impacts from windows, airtightness & details
Net Zero Building Enclosure Targets
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Roof or Ceiling Retrofits: Interior
Top up or replace existing attic insulation
Flash and fill attic insulation
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Roof or Ceiling Retrofits: Exterior
Exterior roof insulation
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Above Grade Wall Retrofits: Interior
Interior Double Stud Wall Vacuum Insulation Panels
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Above Grade Wall Retrofits: Exterior
Exterior Insulation Larsen (exterior site-built) Truss
Exterior Vacuum Insulation Panels
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Below Grade Wall Retrofits: Interior
Interior XPS Insulation
Closed-cell Sprayfoam insulation
Vacuum Insulated Panels
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Below Grade Walls: Exterior
XPS or rigid mineral fiber insulation
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Basement or Slab On Grade
XPS insulation
Vacuum Insulated Panels
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Window Details
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! Not a lot of field studies of highly insulated wood-frame assemblies to compare to ! Some anecdotes of issues with some types of assemblies
! Some recent studies (last 2 years) which support the findings
! Retrofitting existing assemblies so no control over some materials (not touched during work) ! Interior details (Air tightness? vapour control?)
! Exterior details (Rainwater leaks, window details, vapour barrier materials?)
! Use calibrated hygrothermal modeling as a tool to help assess risk (not necessarily predict actual performance)
How to Assess Risk of Retrofit Strategies?
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1. Model baseline assembly (i.e. 2x4 wall w/ batts), calibrate to reflect reality 2. Model proposed assembly & compare to baseline
• Unfortunately this result (where most people will stop) doesn’t tell us about the risk of this assembly under possible real-world scenarios
3. Add air-leakage to baseline, calibrate load manually to a point which brings assembly to a point just before failure BUT dries out safely (i.e. survivable air-leak)
• Model proposed assembly with same quantity of leak
• Look at impact of indoor RH assumption
• Look at details, can you engineer this risk out? How? 4. Add rain-water leak to baseline, calibrate load manually to a point which
brings assembly to point just before failure BUT dries out safely (i.e. survivable water leak)
• Model proposed assembly with same quantity of leak (i.e. % driving rain) • Assess driving rain load, can you change by design? How good are
window details and other penetrations? Can you engineer out risk?
Relative Performance Hygrothermal Assessment Process
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Interior Double Stud and Moisture Risk Assessment
What to do? Engineer the risk out, tight control of interior air control – test it
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Split Insulation and Moisture Risk Assessment
Insulation Ratio Here is over 2/3 to the exterior of the sheathing Careful with lower ratios with foam & high indoor RH
What to do? Engineer the risk out, allow some drying/drainage behind foam
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! Exterior insulation retrofits generally safer than interior retrofits because of potential for rain/air leaks to wet existing structure ! Risk higher where new or existing impermeable materials and
dual vapour barrier situation entrapping moisture
! Vapour permeable exterior insulation approaches with ventilated claddings work well (not difficult since vertical strapping installed for cladding attachment)
! Interior insulation retrofits can be successfully done but airtightness and rainwater control is critical (so outside work needed) ! Most realistic for basement walls and slabs, use of air-tight
and impermeable insulation products work better
! Details are as important as the assemblies
General Findings from Risk Assessment
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! Costing performed for each building enclosure retrofit measure & detailing
! Separate incremental costs for adding insulation or increasing insulation levels if replacing cladding, renovating, re-roofing, replacing doors, etc.
! Calculated a value index for each measure (cost of retrofit vs annual energy savings) to compare between measures and renewables
! Costing of interior and exterior retrofit options for each archetype in Canadian cities (local construction costs) to bring to a net zero ready level
! Incremental cost of energy efficient component compared to full upgrade cost
! Energy modeling of each archetype and city with local utility rates
! Energy savings payback, and return on investment considered
Financial Assessments of Retrofit Measures
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Example Payback Analysis – Bungalow
City Total vs Incremental
Retrofit
Cost Annual Savings
Value Index
Simple Payback (years)
Discounted Payback (years)
Return on Investment
Vancouver Total $73,900 $1,400 $1.82 55 33 1.8% Incremental $37,400 $1,400 $0.92 28 20 3.6%
Edmonton Total $75,800 $1,300 $0.94 56 33 1.8% Incremental $38,500 $1,300 $0.48 29 21 3.5%
Winnipeg Total $68,700 $3,700 $0.82 18 14 5.4% Incremental $34,800 $3,700 $0.42 9 8 10.7%
Toronto Total $74,800 $1,300 $1.32 56 33 1.8% Incremental $37,900 $1,300 $0.67 29 21 3.5%
Montreal Total $72,100 $2,100 $1.13 34 23 2.9% Incremental $36,600 $2,100 $0.57 17 14 5.8%
Halifax Total $67,200 $6,300 $1.07 11 9 9.4% Incremental $34,000 $6,300 $0.54 5 5 18.5%
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! Retrofits of existing buildings pose good opportunity for significant energy savings to point where net zero energy use (with mechanical and renewables) is possible
! Risk of retrofit options can be evaluated by using relative hygrothermal risk assessment procedure ! Many retrofits can be performed with little risk provided care is
take to control water, air, and vapour in details
! Don’t expect a deep building enclosure retrofit to pay for itself unless you already pay a lot for heating energy
! Consider opportunities for incremental energy efficiency improvements at time of any building enclosure work – paybacks can be reasonable
Study Conclusions
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! Deep energy retrofit of 1980s vintage concrete frame multi-unit residential building – owners decision to renew aesthetic (old concrete, leaky windows)
! Original overall effective R-value R-2.8
! Exterior insulate and over-clad existing exposed concrete walls (R-18 eff.)
! Install new triple glazed fiberglass frame windows (R-6 eff.) – triple glazing incremental upgrade <5 year payback
! Retrofitted effective R-9.1 (super-insulated for a building of this type)
! 55% reduction in air leakage measured
! Enclosure improvements 20% overall savings (87% space-heating)
! Actual savings being monitored – and seeing predicted savings
Final Thoughts – Deep Retrofits of Larger Buildings
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Questions
! [email protected] 604-873-1181
Full Report& 8 Fact-Sheets available from CMHC or email me