Joe Konopacki 10/26/2016. Attic & Crawlspace Ventilation. What results from poor ventilation? Attic & Crawlspace Ventilation. Overview Why ventilate?

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1 Joe Konopacki Multifamily Property Management & Rehab Home Inspections IL Licensed Home Inspector Building Science BPI Building Analyst RESNet Energy Rater BPI Trainer What results from poor ventilation? Overview Why ventilate? Symptom, Source, Solution How to ventilate (in most cases). Purpose of space, Driving force, Openings, Distribution Ventilating crawlspaces. Special cases. 1

2 Purpose of Attic Ventilation Manage Heat Manage Moisture Material Failure Discomfort Ice-Dam Damage Poor Efficiency Image credit Michael Meininger - Keep the entire roof as cool as possible, in summer and winter.- 2

3 Convection Radiation Convection vs. Radiation (ventilation) Conduction 3

4 William Rose PhD University of Illinois Shingle Research Lab William Rose PhD University of Illinois Shingle Research Lab Important Factors 1. Geography 2. Orientation 3. Roof Color 4. Ventilation Carl G. Cash, PE, and Edward G. Lyon, PE, What's the value of ventilation? White Vented Max Temperatures High Solar Reflectance White Unvented 196 Black Vented 204 High Solar Absorption Black Unvented Rudd, A., Vented and Sealed Attics in Hot Climates Cheap, Dark shingles Expected Shingle Life - shorter service life High quality, Light shingles - longer service life Organic shingles (1980 s) - end of service life Vented vs Unvented - not a factor William Rose PhD University of Illinois Shingle Research Lab 4

5 Icicles & Ice Dams Icicles & Ice Dams Icicles & Ice Dams Heat Loss Missing/thin insulation Air leaks from home Heat source (furnace) Vagrant heat loss Icicles & Ice Dams Vagrant Heat Loss 5

6 Icicles & Ice Dams No Heat Loss No melting No problems Except maybe large snow load Before Ventilate Air seal Insulate After Convection Maintain air flow Cool the sheathing Radiation Shading Reflective Roof Covering Interior radiant barriers Conduction (Air Seal first) Insulation Condensation / Drips Mildew / Mold -like substance Rot 6

7 10/26/2016 JK1 PropertyServices, Inc. PropertyServices, Inc. Moisture comes up from the home. Seal all air leaks from the home! JK1 PropertyServices, Inc. JK1 PropertyServices, Inc. 7

8 Slide 27 JK1 Joe Konopacki, 10/5/2014 Slide 28 JK1 Joe Konopacki, 10/5/2014 Slide 29 JK1 Joe Konopacki, 10/5/2014

9 JK1 JK1 Condensing surfaces Hot Attic Cold Attic Condensation on outside of duct Condensation on inside of duct 8

10 Slide 30 JK1 Joe Konopacki, 10/5/2014 Slide 31 JK1 Joe Konopacki, 10/5/2014

11 Permeability of Assembly Layers Shingles have the lowest permeance Even Ventilation Distribution Keep air moving Limit dead air spots Exhaust High Halt escaping air-borne moisture Air Seal Duct Seal Leaks Intake low Exhaust spot ventilation to outside Intake low Ventilation Types 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 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 9

12 Gable vents Powered Exhaust fans Position of vents Exhaust Roof vents Ridge-vents Intake Continuous or Individual openings Away from the home Position of vents Attic Ventilation Position of vents Chutes & Baffles Soffit Vent Wind Baffles Vent Chutes Up & Over Insulation Every Rafter Cavity Minimum 1 air space below sheathing. Extend beyond installed insulation. 10

13 How much Ventilation? Total Capacity 1/300 ratio for attic with vapor barrier to cond. space 1/150 w/o vapor barrier Continuous Roof Ventilation Ex: 1500 sqft attic 300 = 5 sqft 5 sqft= 720 sqin Correct for NFVA 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) 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, Balancing Ventilation 11

14 Attic Size (ft 2 ) Eave 1 (in 2 ) Eave 2 (in 2 ) Ridge (in 2 ) Total Net Free Area (in 2 ) 25% 25% 50% 720 Typical Net Free Vent Area Actual open space available for air flow per sq-ft of area Recommended Attic Size (ft 2 ) Eave 1 (in 2 ) Eave 2 (in 2 ) Ridge (in 2 ) Total Net Free Area (in 2 ) 30% 30% 40% Ridge Vent Soffit Vent Roof Vent 720 Edge Vent Gable Vent Net Free Vent Area Attic Ventilation How much Ventilation? 1500 sqft attic Suppose 30 x 50 with 50 linear ftof eave on each side Choose material with enough Net Free Vent Area Overhang Depth Matters Consider eave depth and vented panel frequency 12

15 10/26/2016 Attic Ventilation PropertyServices, Inc. PropertyServices, Inc. Net Free Vent Area Net Free Vent Area 6 Overhang 12 Overhang 24 Overhang Linear ft of vented material needed Consider eave depth and vented panel frequency The NRCA Roofing and Waterproofing Manual, Fifth Edition PropertyServices, Inc. Unvented Attic Hot roofs PropertyServices, Inc. When Unvented Attics makes Sense Finished attic space Unvented assembly Vented roof deck Air space below deck & shingles Wildfire regions Windy rainy/hurricane regions Windy winter regions Vented roof deck in High Snow-Load Area 13

16 Knee-wall/Cathedraled Attic Variations Typical Compact/Flat Attic The Good, no ventilation and warm roof Typical Compact/Flat Attic Typical Compact/Flat Attic The Bad The Ugly Moisture is Trapped In Lower Cavities, some ventilation and warm roof, poor ventilation and a colder roof 14

17 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 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! Crawlspace Ventilation Crawlspace Ventilation Vapor Diffusion Building Leakage What if this flooring is vapor tight? Needs Cross-Wind Moisture Allowed to Enter Needs Drier Air 15

18 Crawlspace Ventilation Crawlspace Ventilation Crawlspace Ventilation Encapsulated or 16

19 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 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 Crawlspace Ventilation Crawlspace Ventilation Bringing it full circle Bringing it full circle 17

20 Questions? 18