Upload
others
View
0
Download
0
Embed Size (px)
Citation preview
Residential Exterior Wall Superinsulation Retrofit Details and Analysis
Kohta Ueno
Thermal Performance of the Exterior Envelopesof Whole Buildings XI International ConferenceDecember 8, 2010
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 20
5
10
15
20
25
30
35
40
45
Northeast Midwest South West
Mill
ions
US
Hou
sing
Uni
ts 2000 to 20051990 to 19991980 to 19891970 to 19791960 to 19691950 to 19591940 to 1949Before 1940
Background/Building Energy Use• Residential and commercial energy use
• 120 million housing units (current existing stock); 70% built before energy codes
• Greatest concentration of oldest housing stock in Northeast/Midwest (heating‐dominated)
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 3
Exterior Insulation Retrofits• Residential wood‐frame walls• Going beyond nominal R‐13/R‐19 walls(R‐8/R‐13 whole‐wall R values)
• Exterior retrofit advantages– Insulation outboard of vulnerable structure– Interior is habitable during retrofit– Retain interior finishes (lose exterior finishes)– No loss in interior square footage– Can inspect condition of enclosure (during cladding removal)
– Exterior stairwells (code minimum widths)
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 4
Previous Work (Exterior Retrofits)• Insulation exterior to structure well‐established technique (Hutcheon, Baker and Makepeace, Lstiburek, CCHRC)
• Dumont & Orr “Chainsaw Retrofit” 1987 (R‐40+ enclosure; 3.0 ACH 50→0.3 ACH 50)
• ORNL 2007 hot box & airtightness measurements of exterior insulation; included foam up to 1” thick (10‐15% energy savings)
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 5
Overview of Case Study Houses
Bedford, MA“Farmhouse”
Single family house1500 + 1060 sf
circa 1850
Habitat for Humanity (volunteers & technical
high school)
All new mechanicals
Arlington, MA“Duplex”
Duplex (over/under)1280 + 1800 + 1280 sf
circa 1930
Local energy-conscious general contractor
Retained steam system
Concord, MA“Four Square”
Single family house2800 + 800 sf
circa 1915
Local energy-conscious general contractor
All new mechanicals
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 6
4” Polyisocyanurate Foam
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 7
Arlington Duplex Retrofit
REDACTED
REDACTED
REDACTED
REDACTED
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 8
Foam Sheathing Cladding Attachment
250 lbs/113 kg load (7.8 psf): <0.003” deflection
Wood siding ~2 psfFiber cement 2-3 psfStucco 8-10 psf
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 9
“Innie” and “Outie” Windows
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 10
“Outie” Window
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 11
“Innie” Window
Recommend placing drainage plane at window location (whichever method used—innieor outie)!
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 12
“Innie” vs. “Outie” Windows• “Outie” Advantages
– Simpler drainage plane connections/geometry
– Lower cost (extension trim is interior material)
– Similar appearance to conventional construction
– Simpler window replacement
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 13
“Innie” vs. “Outie” Windows• “Innie” Advantages
– Window supported by lumber frame (foam install)
– Greater protection from wind‐driven rain (inset)
– Less condensation risk (?)
– Thermal performance (?)
– Can use existing window trim
– Solar shading (advantage or disadvantage)
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 14
Retrofitting Exterior Air Barriers
Bedford, MA“Farmhouse”
6.2 ACH 50
No secondary air barrier (housewrap w.
connections); mediocre roof-wall connections
Arlington, MA“Duplex”
5.0 ACH 50
Basement compartmentalized?
(1000 CFM 50 vs. 2129 CFM 50 total)
Concord, MA“Four Square”
3.1 ACH 50
Mechanical penetrations, porch attachments, replacement sash
windows
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 15
Retrofitting Exterior Air Barriers
St. Agatha, ON
~1 ACH 50
Spray foam on exterior; all windows well air sealed; casement/
awning typical
Belmont, MA
0.9 ACH 50
Rigid foam as air barrier, “chainsaw” retrofit of roof
overhangs/eaves, meticulous air barrier, blower door tests in
progress
Utica, NY (NYSERDA)
2.3 ACH 50
Rigid air barrier layer under foam/over board sheathing; spray foam
roof-wall & bsmt rim joist (non-”chainsaw”)
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 16
Retrofitting Exterior Air Barriers• Roof‐wall connections
• Wall‐foundation connections
• Wall‐window connections
• Windows (actual units)—installation flaws?
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 17
Retrofitting Exterior Air Barriers• Structural attachments
• Mechanical system penetrations
• Trades knowledge?
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 18
Retrofits and Water Intrusion• Generally improves wall durability
– Rebuilt drainage plane; redundant layers– Ventilated drainage gap (3/4” cavity)– Reduced risk of interstitial condensation
• Reduced vapor permeability due to foam– Reduced drying to exterior of bulk water events– Reduced airflow → reduced drying?
• Hygrothermal simulations of “survivable” leak in pre‐ & post‐retrofit walls– Limited applicability—”bounding exercise”
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 19
0%
5%
10%
15%
20%
25%
30%
35%
9-2008 4-2009 11-2009 5-2010 12-2010 6-2011
Woo
d M
oist
ure
Con
tent
(%)
-20
-15
-10
-5
0
5
10
15
20
25
30
Exte
rior T
(C)
Case 1 North Existing Case 2 South Existing Boston Temperature
S S S
“Survivable” leak (Existing Wall)
0%
5%
10%
15%
20%
25%
30%
35%
9-2008 4-2009 11-2009 5-2010 12-2010 6-2011
Woo
d M
oist
ure
Con
tent
(%)
-20
-15
-10
-5
0
5
10
15
20
25
30
Exte
rior T
(C)
Case 1 North Existing Case 2 South Existing Boston Temperature
N
S
N
S
N
S
0.5% incident rain penetration ≈ 20-25% peak north MCs1% incident rain penetration ≈ 35-40% peak north MCs →“unsurvivable” leak
0%
5%
10%
15%
20%
25%
30%
35%
9-2008 4-2009 11-2009 5-2010 12-2010 6-2011
Woo
d M
oist
ure
Con
tent
(%)
-20
-15
-10
-5
0
5
10
15
20
25
30
Exte
rior T
(C)
Case 1b North Existing Case 2b South Existing Boston Temperature
N
S
N
S
N
S
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 20
0.5% Leak in Retrofit Wall
0%
5%
10%
15%
20%
25%
30%
35%
9-2008 4-2009 11-2009 5-2010 12-2010 6-2011
Woo
d M
oist
ure
Con
tent
(%)
-20
-15
-10
-5
0
5
10
15
20
25
30
Exte
rior T
(C)
Case 3 North Retrofit Case 4 South Retrofit Boston Temperature
S S S
0%
5%
10%
15%
20%
25%
30%
35%
9-2008 4-2009 11-2009 5-2010 12-2010 6-2011
Woo
d M
oist
ure
Con
tent
(%)
-20
-15
-10
-5
0
5
10
15
20
25
30
Exte
rior T
(C)
Case 3 North Retrofit Case 4 South Retrofit Boston Temperature
N
S
N
S
N
S
0.5% incident rain penetration → upwards “ratcheting” wood MCsPreviously survivable leak becomes “unsurvivable”
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 21
0.25% Leak in Retrofit Wall
0%
5%
10%
15%
20%
25%
30%
35%
9-2008 4-2009 11-2009 5-2010 12-2010 6-2011
Woo
d M
oist
ure
Con
tent
(%)
-20
-15
-10
-5
0
5
10
15
20
25
30
Exte
rior T
(C)
Case 3a North Retrofit Case 4a South Retrofit Boston Temperature
N
S
N
S
N
S
Reducing rain leakage to half (0.5% → 0.25%) keeps wood MCs stable; same range as existing wall. Rain control critical for retrofits.More permeable exterior rigid insulation? XPS→ minimal. EPS → Improvement
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 22
Oil $ Install costAnnual
SavingsSimple
PaybackPayback w/o
airtight$2.50 Inner 2" $8,200 $510 16 25$2.50 Outer 2" $4,100 $118 35 59
$4.00 Inner 2" $8,200 $816 10 15$4.00 Outer 2" $4,100 $188 22 37
Economic Analysis• Diminishing returns at greater insulation levels
• Original analysis $4/gallon → $2.50‐$3.50/gal
• $4/sf incremental cost of opaque wall upgrade not including recladding costs
• Airtightness as part of calculated energy benefit
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 23
Conclusions• Excellent opportunity for retrofit during periodic exterior cladding replacement
• Air barrier detailing and technology can use improvement; examine more options– Fully adhered membrane
– Exterior spray foam
• Impermeable exterior insulation reduces available drying
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 24
Questions?
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 25
4‐½” High Density Spray Foam
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 26
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 27
Cladding Support over Foam
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 28
Cladding Support over Foam
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 29
Nominal vs. Actual R Value
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 30
Taped Sheathing Air Barrier
New England Region Modular PassiveHaus: 0.7 ACH 50
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 31
Arlington Duplex Retrofit
Residential Exterior Wall Superinsulation Retrofit Details and Analysis 32
Exterior Retrofit Complications