Existing Housing Stock
Four Square Revisited
Toward Zero Energy Renovation
Age of US Housing Stock (all unit types)
Number of Housing Units (thousands)
25000
In Need of Energy Retrofit
New
Homes
20000
15000
10000
Betsy Pettit, FAIA
Building Science Corporation
www.buildingscience.com
5000
0
before 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s
1919
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Source: US Census Bureau, Annual Housing Survey: http://www.census.gov/hhes/www/housing/ahs/ahs.html
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How Old and New Houses Use Energy
Getting Bigger as Time Goes On
• Average House Size in 1940: ~1100 sq ft1
Total Btu Consumption per Household, 2001
• Average House Size in 1973: 1660 sq ft2
120
Average Single Family Home Size, 1973-2005
3,000
2,500
Space Heating
80
House Size (sq ft)
million Btu per household
100
Electric Air Conditioning
60
Water Heating
Refrigerators
40
Other Appliances and
Lighting
2,000
1,500
1,000
500
20
0
1973
1983
1993
2003
0
Total
1990s
1980s
1970s
1960s
1950s
• Average House Size in 2005: 2434 sq ft
before
1950
Source: US Census Bureau, Annual Housing Survey: http://www.census.gov/hhes/www/housing/ahs/ahs.html
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1. Wilson, Alex and Jessica Boehland “Small is Beautiful” Journal of Industrial Ecology, Vol 9, No 1-2. 2005
2. EIA, Annual Energy Review, 2001 data: www.eia.doe.gov/emeu/aer
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How a 100 year old house is renewed
to last an additional 100 years
How a 100 year old house is renewed
to last an additional 100 years
cost $100/sq. ft.
Building Enclosure
Air Leakage
Wall Insulation
Attic Insulation
Windows
BEFORE
CONDITIONED SQ. FT. = 2,000
10 sq. in. of leakage area per 100 sq. ft. of surface area
Little to none
R-19
Single pane glass with storm window
Building Enclosure
AFTER
BEFORE
Heating
Cooling
DHW
60% AFUE for the old boiler -gas -delivered by radiators
9 EER for the window units
0.4 EF for hot water efficiency- AVERAGE
summer efficiency is much worse
winter efficiency would be about at 60% (since the boiler is heating the house already)
Mechanical Systems
CONDITIONED SQ. FT. = 3,600
Conditioned Attic
Mechanical Systems
AFTER
Heat
R-39 High Density Spray Foam on sheathing
Sealed combustion 92% AFUE gas boiler
boiler in conditioned basement
R-21 roof deck insulation – Total Roof R-60
Walls
R-13 cellulose blown into existing 2x4 walls
Cooling
Wall Sheathing
14 SEER split system in conditioned space
4” Polyiso R-28 sheathing – Total Wall R-41
DHW
0.80 EF side-arm storage tank
Basement Floor
Under-slab 2” XPS, R-10
Ducts
R-4.2 flex runouts in dropped ceiling or in floor joists
Basement Walls
4” R-28 HD SPF on perimeter walls
Windows
Andersen Woodwright Replacement Windows
Infiltration
2.0 sq in leakage area per 100 sf of envelope
Leakage
none to outside (5% or less)
Ventilation
Fan Cycler Supply-only system integrated with AHU
33% Duty Cycle: 10 minutes on; 20 minutes off
Weighted Average U=~0.33, SHGC=~0.33
60-80 CFM continuous average flow
Return Pathways
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Transfer grilles/jump ducts at bedrooms
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Load Reduction by Conservation - 360 > 120 kBtu’s
6
Remaining Loads
Then add Site Generated Energy
6520 kWh and 566 Therms Predicted
Annual Loads Comparison
Boston Area Super-Insulated 4 BR House
Energy Consumption with Average US Usage
400
350
10^6 Btu/year
300
Plug, 2950 kWh
22%
250
Cooling, 752 kWh
6%
200
150
Heating, 394 Therms
36%
Appliances, 1768 kWh
13%
100
50
Lighting, 1050 kWh
8%
0
Original
Condition,
156%
usage
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Benchmark
Airseal
(baseline) Benchmark,
12.4
savings
Heating
Cooling
Prototype,
45.8%
savings
Hot Water
68F/78F,
49.4%
savings
Lighting
3.5 kW PV,
68.0%
savings
Appliances
7.0 kW PV,
78.7%
savings
Plug
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Hot Water, 172 Therms
15%
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Actual First Year
Actual First Year
3200 kWh and 570 Therms
3200 kWh and 570 Therms
Electric @ $.15 /kWh Gas @ $1.50/therm
Electric $471 Gas $858
Electric/mth - $39 Gas/mth = $71
Electric @ $.15 /kWh Gas @ $1.50/therm
Electric $471 Gas $858
Electric/mth - $39 Gas/mth = $71
Adding Solar Hot Water
Adding Photovoltaic
• A 64 sq. ft. glycol SHW installed with storage = $6,000
•This would create about 180 therms
•At $1.50 per therm the savings would be $270 per year
•Over 22 years at this rate savings would = $6,000
•$6,000 at 5.6% would cost $35 per month
•The electric use was about 300 kWh per month
•A 4kW PV system will create about 300 kWh per month
•At $4 per kW the system would cost $16,000
•The electric bill over 32 year at this rate would be $16,000
•$16,000 at 5.6% will cost $92 per month
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Four Square Renovation
Four Square Renovation
34’-0”
34’-0”
30’-0”
30’-0”
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First floor plan
Second floor plan
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Four Square Renovation
Four Square Renovation
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30’-0”
34’-0”
30’-0”
34’-0”
Second floor plan
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Second floor plan
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Four Square Renovation
Four Square Renovation
34’-0”
34’-0”
30’-0”
30’-0”
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Second floor plan
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Second floor plan
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Four Square
Renovation
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Four Square
Renovation
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Cross section through house
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Air barrier continuity
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Four Square
Renovation
Four Square
Renovation
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Air barrier continuity
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Air barrier continuity
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Four Square
Renovation
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Four Square
Renovation
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Air barrier continuity
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Drainage plane
continuity
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Four Square
Renovation
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Drainage plane
continuity
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Four Square
Renovation
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Drainage plane
continuity
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Four Square
Renovation
Four Square
Renovation
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Drainage plane
continuity
Thermal continuity
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Four Square
Renovation
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Four Square
Renovation
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Thermal continuity
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Thermal continuity
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Four Square
Renovation
Four Square
Renovation
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Thermal continuity
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Four Square
Renovation
Vapor barrier
continuity
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Four Square
Renovation
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Vapor barrier
continuity
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Vapor barrier
continuity
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Four Square
Renovation
New Windows
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Vapor barrier
continuity
Photos courtesy of Dan Morrison, Fine Homebuilding Magazine
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New Windows
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Four Square
Renovation
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Mechanical schematic
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Old Boiler to New Boiler plus air handlers,
outside air intake, filtration, and exhaust at
baths and kitchen
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