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

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

Why Existing Buildings

!   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

!   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

!   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

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

!   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

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”

Building Enclosure Retrofits – Climate Zones

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

!   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

!  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

Roof or Ceiling Retrofits: Interior

Top up or replace existing attic insulation

Flash and fill attic insulation

Roof or Ceiling Retrofits: Exterior

Exterior roof insulation

Above Grade Wall Retrofits: Interior

Interior Double Stud Wall Vacuum Insulation Panels

Above Grade Wall Retrofits: Exterior

Exterior Insulation Larsen (exterior site-built) Truss

Exterior Vacuum Insulation Panels

Below Grade Wall Retrofits: Interior

Interior XPS Insulation

Closed-cell Sprayfoam insulation

Vacuum Insulated Panels

Below Grade Walls: Exterior

XPS or rigid mineral fiber insulation

Basement or Slab On Grade

XPS insulation

Vacuum Insulated Panels

Window Details

!   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?

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

Interior Double Stud and Moisture Risk Assessment

What to do? Engineer the risk out, tight control of interior air control – test it

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

!   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

!   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

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%  

!   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

!   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

Questions

! gfinch@rdhbe.com 604-873-1181

Full Report& 8 Fact-Sheets available from CMHC or email me