1
Roofs
Roofs, Attics, and Cathedrals
John Straube, Ph.D., P.Eng
www.buildingscience.com
Building Science Corp
© 2008!
Building Science
Corporation!
Building Science.com
Building Science.com Building Science.com
© buildingscience.com
2
Building Science.com
Joseph Lstiburek – Roofs 5
Building Science.com
– Roofs 7
Building Science.com Building Science.com \8
© buildingscience.com
3
Vented Attics
•! Air leakage thru ceiling is a problem in colder
climates
–!Ducts are a disaster
•! Condensation and heat gain on ducts in
warm climates
•! Modern roofs often hard to vent
Building Science.com
How do I leak?
•! Let me count the ways …
Building Science.com
Big Air Leakage
Points AHU
Sheet metal and high-temperature
caulk
Caulk electrical
fixtures to
drywall
Seal HVAC
penetrations
Seal
bottom plate
Seal electricalpenetrations
Seal plumbing
penetrations
Seal and
insulate dropped
soffit
Seal chases
•!Ductwork
•!Partitions •!Dropped soffits
•!Cabinetry
•!Ceiling lights
•!Rimjoists •!Plumbing stacks
•!Attic hatch
Airflow Control No. 11/79 Building Science.com Building Science.com
© buildingscience.com
4
Building Science.com
Paritition leaks (1/8”x 100 ft)
Building Science.com
Building Science.com
Air sealing
Building Science.com – Roofs 16
© buildingscience.com
5
Building Science.com 17
Building Science.com 18
Building Science.com 19
Air Leaks – cathedral ceilings
Building Science.com
© buildingscience.com
6
Building Science.com Building Science.com 22
Building Science.com 23
Building Science.com 24
© buildingscience.com
7
Building Science.com –Roofs 25
Building Science.com 26
Hard to Vent
Building Science.com – Roofs 27
Building Science.com Joseph Lstiburek – Roofs 28
© buildingscience.com
8
Unvented Cathedral Ceilings
•! Not absolutely necessary to vent if airtight and
vapour tight material,
–! e.g. spray foam.
–! Or insulated sheathing
•! May be most practical in retrofit
•! If no wetting, little drying required
–! Demands very high performance
–! >R40, no penetrations
–! spray foam is a practical solution
–! beware thermal bridges
Building Science.com
Hybrid: Air, thermal, fire
Building Scienc.com Insulation and Thermal Bridges No. 30/65
R6+R30
R6+R16
Warm Climate Zone!
Hybrid: Air, thermal
Building Science.com Insulation and Thermal Bridges No. 31/65
R6+R30
R6+R16
Cold Climate
Zone
2” HD spray foam
3.5” spray cellulose/fiberglass
2x6 wood frame
4” (R30) or 6” (R38) HD spray foam
Note: rafters insulated on the inside
R40+ roof, fire protection
Building Science 2008 Insulation and Thermal Bridges No. 32/65
Cold Climate (Zone 5/6) Solution
© buildingscience.com
9
Calculation
Building Science.com
Hybrid Roofs with code levels of insulation
•! IRC 2007 Supplement
Building Science.com – Roofs 34
… or air impermeable insulation
Building Science.com
35
Building Science.com
Simple Vented roof Air leaks! Ventilation path?
Unvented roof for more complex roof lines
© buildingscience.com
10
Low Slope Roofs
Building Science.com
– Roofs 37
Building Science.com
Low Slope Commercial
Building Science.com
Best Practise Exposed Membrane
Building Science.com
40
© buildingscience.com
11
Building Science.com
– Roofs 41
BuildingScience.com
Unvented Sloped Roofs
Building Science.com
– Roofs 43
Building Science.com
– Roofs 44
© buildingscience.com
12
Building Science.com
Roofs 45
Building Science.com
Roofs 46
Building Science.com
– Roofs 47
Zone 4 or lower
Building Science.com
© buildingscience.com
13
Building Science.com
– Roofs 49
Building Science.com
– Roofs 50
Building Science.com Building Science.com
Joseph Lstiburek – Roofs 52
© buildingscience.com
14
Vented vs. unvented shingle temperatures
Building Science.com
– Roofs 53
South-facing shingle temperatures
Jacksonville, FL 16-Sep to 18-Nov 2000
0
50
100
150
200
250
300
350
30
40
50
60
70
80
90
10
0
11
0
12
0
13
0
14
0
15
0
16
0
17
0
18
0
Temperature (F)
Nu
mb
er
of
ho
url
y
ob
se
rva
tio
ns
unvented S shingle vented S shingle
Building Science.com
Ventilation & Roof Temperature
Cathedral 5C/9F hotter than attic
Vented cathedral is same as Unvented
Building Science.com
Roof ventilation could provide cooling Ice Dams
•! Cold Climate problem
•! Need snow and temperatures around freezing
Building Science.com
© buildingscience.com
15
Building Science.com – Roofs 57 Building Science.com
– Roofs 58
Building Science.com Building Science.com
Joseph Lstiburek – Roofs 60
© buildingscience.com
16
Building Science.com
Joseph Lstiburek – Roofs 61
Building Science.com
Building Science.com \63
Building Science.com \64
© buildingscience.com
17
Building Science.com Roofs 65 Building Science.com
Joseph Lstiburek – Roofs 66
Conclusions
•! Highly ventilated open attic is with R60+ of low
cost fibrous insulation is best
–! Requires exceptional air sealing of ceiling
–! No duct work!
•! Unvented roofs provide more options
–!Airtightness is critical to success
–!Requires spray foam or full adhered
membrane
Building Science.com Building Science.com \68
© buildingscience.com
18
Building Science 2008 Joseph Lstiburek – Roofs 69
Building Science 2008 Joseph Lstiburek – Roofs 70
Building Science 2008 Joseph Lstiburek – Roofs 71
Building Science 2008 Joseph Lstiburek – Roofs 72
© buildingscience.com
19
Building Science 2008 Joseph Lstiburek – Roofs 73
Building Science 2008 Joseph Lstiburek – Roofs 74
Building Science 2008 Joseph Lstiburek – Roofs 75
Building Science 2008 Joseph Lstiburek – Roofs 76
© buildingscience.com
20
Building Science 2008 Joseph Lstiburek – Roofs 77
Building Science 2008 Joseph Lstiburek – Roofs 78
Building Science 2008 Joseph Lstiburek – Roofs 79
Building Science 2008 Joseph Lstiburek – Roofs 80
© buildingscience.com
21
Building Science 2008 Joseph Lstiburek – Roofs 81
Building Science 2008 Joseph Lstiburek – Roofs 82
Building Science 2008 Joseph Lstiburek – Roofs 83
Building Science 2008 Joseph Lstiburek – Roofs 84
© buildingscience.com
22
Building Science 2008 Joseph Lstiburek – Roofs 85
Building Science 2008 Joseph Lstiburek – Roofs 86
Building Science 2008 Joseph Lstiburek – Roofs 87
Building Science 2008 Joseph Lstiburek – Roofs 88
© buildingscience.com
23
Building Science 2008 Joseph Lstiburek – Roofs 89
Building Science 2008 Joseph Lstiburek – Roofs 90
Building Science 2008 Joseph Lstiburek – Roofs 91
Building Science 2008 Joseph Lstiburek – Roofs 92
© buildingscience.com
24
Building Science 2008 Joseph Lstiburek – Roofs 93
Building Science.com
Joseph Lstiburek – Roofs 94
Building Science.com
Joseph Lstiburek – Roofs 95
Building Science.com
Joseph Lstiburek – Roofs 96
© buildingscience.com
25
Building Science.com
Joseph Lstiburek – Roofs 97
Building Science.com
Joseph Lstiburek – Roofs 98
Building Science.com
Joseph Lstiburek – Roofs 99
Building Science.com
Joseph Lstiburek – Roofs 100
© buildingscience.com
26
Building Science.com
Joseph Lstiburek – Roofs 101
Building Science.com
Joseph Lstiburek – Roofs 102
Building Science.com
Joseph Lstiburek – Roofs 103
© buildingscience.com