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10/26/2016
1
Property Services, Inc.
Attic & Crawlspace Ventilation
Property Services, Inc.
Joe Konopacki
• Multifamily Property Management & Rehab
• Home InspectionsIL Licensed Home Inspector
• Building ScienceBPI Building Analyst RESNet Energy RaterBPI Trainer
Property Services, Inc.
What results from poor ventilation?
Property Services, Inc.
Attic & Crawlspace Ventilation
Overview
Why ventilate?
Symptom, Source, Solution
How to ventilate (in most cases).
Purpose of space, Driving force, Openings, Distribution
Ventilating crawlspaces.
Special cases.
10/26/2016
2
Property Services, Inc.
Attic & Crawlspace Ventilation
Purpose of Attic Ventilation
Manage Heat
Manage Moisture
Image credit Michael Meininger
www.mmeininger.com
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
• Material Failure
• Discomfort
• Ice-Dam Damage
• Poor Efficiency
- Keep the entire roof
as cool as possible, in
summer and winter.-
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
10/26/2016
3
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
Property Services, Inc.
Attic & Crawlspace Ventilation
• Convection
Heat Management
• Conduction
• Radiation
Property Services, Inc.
Attic & Crawlspace Ventilation
Convection vs. Radiation
(ventilation)
Heat Management
10/26/2016
4
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
William Rose PhD
University of Illinois
Shingle Research Lab
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
William Rose PhD
University of Illinois
Shingle Research Lab
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
Important Factors
129 132
196
204
White
Vented
White
Unvented
Black
Vented
Black
Unvented
Max Temperatures
Rudd, A., 1996. “Vented and Sealed Attics in Hot Climates”
Carl G. Cash, PE, and Edward G. Lyon, PE, 2002.
“What's the value of ventilation?”
1. Geography
2. Orientation
3. Roof Color
4. VentilationHigh Solar
Reflectance
High Solar
Absorption
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
William Rose PhD
University of Illinois
Shingle Research Lab
Expected Shingle Life
• Cheap, Dark shingles - shorter service life
• High quality, Light shingles - longer service life
• Organic shingles (1980’s) - end of service life
• Vented vs Unvented - not a factor
10/26/2016
5
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
Icicles & Ice Dams
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
Icicles & Ice Dams
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
Icicles & Ice Dams
Heat Loss
• Missing/thin insulation
• Air leaks from home
• Heat source (furnace)
• “Vagrant heat loss”
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
Icicles & Ice Dams
Vagrant Heat Loss
10/26/2016
6
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
Icicles & Ice Dams
No Heat Loss
• No melting
• No problems
• Except maybe
large snow load
Property Services, Inc.
Attic & Crawlspace Ventilation
Heat Management
• Ventilate
• Air seal
• Insulate
Before
After
Property Services, Inc.
Attic & Crawlspace Ventilation
• Convection
Heat Management
• Conduction
• Radiation
• Maintain air flow
• Cool the sheathing
• Shading
• Reflective Roof Covering
• Interior radiant barriers
• (Air Seal first)
• Insulation
Property Services, Inc.
Attic & Crawlspace Ventilation
Moisture Management
Condensation / Drips
Mildew / Mold
Rot
-like substance
10/26/2016
7
Property Services, Inc.
Attic & Crawlspace Ventilation
Moisture Management
Moisture comes up from the home.
Seal all air leaks from the home!
Property Services, Inc.
Attic & Crawlspace Ventilation
Moisture Management
JK1
Property Services, Inc.
Attic & Crawlspace Ventilation
Moisture Management
JK1
Property Services, Inc.
Attic & Crawlspace Ventilation
Moisture Management
JK1
Slide 27
JK1 Joe Konopacki, 10/5/2014
Slide 28
JK1 Joe Konopacki, 10/5/2014
Slide 29
JK1 Joe Konopacki, 10/5/2014
10/26/2016
8
Property Services, Inc.
Attic & Crawlspace Ventilation
Moisture Management
JK1
Property Services, Inc.
Attic & Crawlspace Ventilation
Moisture Management
JK1
Property Services, Inc.
Attic & Crawlspace Ventilation
Moisture Management
Property Services, Inc.
Attic & Crawlspace Ventilation
Moisture Management
• Condensing surfaces
Hot Attic Cold Attic
Condensation on outside of duct Condensation on inside of duct
Slide 30
JK1 Joe Konopacki, 10/5/2014
Slide 31
JK1 Joe Konopacki, 10/5/2014
10/26/2016
9
Property Services, Inc.
Attic & Crawlspace Ventilation
Moisture Management
• Permeability of Assembly Layers
Shingles have the
lowest permeance
Property Services, Inc.
Attic & Crawlspace Ventilation
Moisture Management
Exhaust spot
ventilation to
outside
Halt escaping air-borne
moisture
• Seal Duct
Leaks
• Air
Seal
Even Ventilation Distribution
• Keep air moving
• Limit dead air
spots
Intake
low
Exhaust High
Intake
low
Property Services, Inc.
Attic & Crawlspace Ventilation
– Passive Gable/End Vents
• Possible in attics
– Needs cross-wind
• Not so in crawlspaces
– Mostly upward vapor diffusion
– Adds to building leakage
– Needs cross-wind
Ventilation Types
Property Services, Inc.
Attic & Crawlspace Ventilation
Ventilation Types– Active Exhaust (Fan$)
• Is It Necessary ?
– Attics - Not typically
– Hip Roofs - Maybe
– Crawlspaces - w/Humidistat
• Sizing & Position
– Volume – Rate of Exchange (cfm)
– Attic – exhaust to hot side
– Crawlspace – exhaust to cool/damp side
• Interactions to Monitor
– Combustion Safety
– Energy loss
10/26/2016
10
Property Services, Inc.
Attic & Crawlspace Ventilation
Position of vents
– Gable vents
– Powered Exhaust fans
Property Services, Inc.
Attic & Crawlspace Ventilation
Position of vents
– Exhaust
• Roof vents
• Ridge-vents
– Intake
• Continuous or…
• Individual openings
• Away from the home
Property Services, Inc.
Attic & Crawlspace Ventilation
Position of vents
Vent Chutes
Up & Over Insulation
Every Rafter Cavity
Wind BafflesSoffit
Vent
Property Services, Inc.
Attic Ventilation
Chutes & Baffles
• Minimum 1” air space below sheathing.
• Extend beyond installed insulation.
10/26/2016
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Property Services, Inc.
Attic & Crawlspace Ventilation
Continuous
Roof Ventilation
Property Services, Inc.
Attic & Crawlspace Ventilation
How much Ventilation?
– Total Capacity
• 1/300 ratio for attic with vapor barrier to cond. space
• 1/150 w/o vapor barrier
– Ex: 1500 sqft attic ÷ 300 = 5 sqft
720 sqin• 5 sqft =
• Correct for NFVA
Property Services, Inc.
Attic & Crawlspace Ventilation
How much ventilation?
– Typical Distribution
• Typical 50% Intake, 50% Exhaust
• 25% along each eave x2
– Ex: 2.5sqft (360sqin) Exhaust
• 1.25sqft(180sqin)
Intake x2 (per Eave)
Property Services, Inc.
Attic & Crawlspace Ventilation
How much ventilation?
– Recommended Distribution
• 60% Intake 40% Exhaust
• Creates a slightly pressurized attic
– Attic pressure pushes back
against stack effect.
“It's nearly impossible to have
too much [intake ventilation].”
- Paul Scelsi, 2003.
“Balancing Ventilation”
10/26/2016
12
Property Services, Inc.
Attic & Crawlspace Ventilation
Attic Size (ft2) Eave 1 (in2
) Eave 2 (in2) Ridge (in
2)
1500 180 180 360
Total Net Free Area (in2) 25% 25% 50%
720
Attic Size (ft2) Eave 1 (in2
) Eave 2 (in2) Ridge (in
2)
1500 216 216 288
Total Net Free Area (in2) 30% 30% 40%
720
Typical
Recommended
Property Services, Inc.
Attic & Crawlspace Ventilation
Net Free Vent Area
Actual open space available for air flow
per sq-ft of area
Soffit Vent
Edge Vent
Ridge Vent Roof Vent
Gable Vent
Property Services, Inc.
Attic & Crawlspace Ventilation
Net Free Vent Area
Consider eave depth and vented panel frequency
Property Services, Inc.
Attic Ventilation
How much Ventilation?
– 1500 sqft attic
Suppose 30’ x 50’ with 50 linear ft of eave on each side
Choose material with enough Net Free Vent Area
Overhang Depth Matters
10/26/2016
13
Property Services, Inc.
Attic Ventilation
Net Free Vent Area
Consider eave depth and vented panel frequency
3” 5” 9”6” Overhang
144’ 87’ 48’
12” Overhang72’ 44’ 24’
24” Overhang36’ 22’ 12’
Linear ft of vented material needed
Property Services, Inc.
Attic & Crawlspace Ventilation
Net Free Vent Area
The NRCA Roofing and Waterproofing Manual, Fifth Edition
Property Services, Inc.
Attic & Crawlspace Ventilation
Unvented Attic
• Hot roofs
– Unvented assembly
• Vented roof deck
– Air space below
deck & shingles
Property Services, Inc.
When Unvented Attics makes Sense
• Finished attic space
• Wildfire regions
• Windy rainy/hurricane regions
• Windy winter regions
– Vented roof deck in High Snow-Load Area
10/26/2016
14
Property Services, Inc.
Attic & Crawlspace Ventilation
Knee-wall/Cathedraled Attic Variations
Property Services, Inc.
Attic & Crawlspace Ventilation
Typical Compact/Flat Attic
The Good
, no ventilation and warm roof
Property Services, Inc.
Attic & Crawlspace Ventilation
Typical Compact/Flat Attic
The Bad
, some ventilation and warm roof
Property Services, Inc.
Attic & Crawlspace Ventilation
Typical Compact/Flat Attic
Moisture is Trapped
In Lower Cavities
The Ugly
, poor ventilation and a colder roof
10/26/2016
15
Property Services, Inc.
Attic & Crawlspace Ventilation
Climate Strategies
• Heating Climate
– Keep moisture inside the home
– Insulate to create warm surfaces
– Allow for drying to the outside
– Ventilate cold surfaces
• Cooling Climate
– Keep moisture outside
– Allow for drying to the inside
Property Services, Inc.
Attic & Crawlspace Ventilation
Purpose of Crawlspace Ventilation
– Manage Moisture
• Reality does not match intent
– Problems
• Only works when air outside is drier – Not so, in warm/humid climates
• Needs cross-wind
• Moisture moves up to drier home (Vapor diffusion)
• Increases building leakage
• Major source of attic moisture!
Property Services, Inc.
Attic & Crawlspace Ventilation
Crawlspace Ventilation
Vapor Diffusion Building Leakage
Needs
Drier AirNeeds
Cross-Wind
Moisture Allowed to Enter
What if this flooring is vapor tight?
Property Services, Inc.
Attic & Crawlspace Ventilation
Crawlspace Ventilation
10/26/2016
16
Property Services, Inc.
Attic & Crawlspace Ventilation
Crawlspace Ventilation
Property Services, Inc.
Attic & Crawlspace Ventilation
Crawlspace Ventilation
Property Services, Inc.
Attic & Crawlspace Ventilation
Crawlspace Ventilation
Property Services, Inc.
Attic & Crawlspace Ventilation
Encapsulated
or
10/26/2016
17
Property Services, Inc.
Attic & Crawlspace Ventilation
Ideal Crawlspace Moisture Control
• Control moisture at the soil… and the walls• Vapor Barrier – 6+mil Poly sheathing
• Sub-slab Ventilation – (radon system)
• Unvented assembly, so seal existing wall vents
• Options:
– Add HVAC supply air into the crawl space -needs transfer grille to home
– Exhaust moist air from the crawl space to outside -needs transfer grille to home
– Install a dehumidifier -no transfer grille
Property Services, Inc.
Attic & Crawlspace Ventilation
Ideal Crawlspace Moisture Control
• Control moisture at the soil… and the walls
• Options:
– Add HVAC supply air to crawl space
– Exhaust crawl space to outside
• Both require 1cfm/50sqft
– Install a dehumidifier -no transfer grille
Property Services, Inc.
Attic & Crawlspace Ventilation
Crawlspace Ventilation
Bringing it full circle
Property Services, Inc.
Attic & Crawlspace Ventilation
Crawlspace Ventilation
Bringing it full circle
10/26/2016
18
Property Services, Inc.
Attic & Crawlspace Ventilation
Questions?