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Basics & Theory

Building Science: Understanding Attic Ventilation
Building Science digest describes how attics or roofs can be designed and constructed to be either vented or unvented in any hygro-thermal zone, and that the choice of venting or not venting is a design and construction choice not a requirement determined by the physics or by the building code.
Issues & Performance

Advanced Energy: Impacts On Houses By Powered Attic Ventilators
Advanced Energy offers a research report showing for a sample of houses it was determined that on average, powered attic ventilators draw 231 cfm of conditioned air out of the house and cause by themselves .72 air changes per hour.

Energy Vanguard: #1 Reason Power Attic Ventilators Don't Help
Energy Vanguard says power attic ventilators don't help because using a fan to blow hot air out of the attic doesn't address the radiant heat flow from the roof to the attic floor.

Energy Vanguard: Power Attic Ventilators Are Bad Idea
Energy Vanguard says in order for the powered attic fan to work the air needs to come from the outside and not be pulled from the house so this means that the attic ceiling needs to be airtight. If the attic ceiling is airtight you don’t need the fan. Your money is better spent on something else.

Energy Vanguard: The Best Way To Cool Your Attic
Energy Vanguard says some people swear powered attic ventilators are the best way to keep their attic cool and reduce air conditioning costs. Apparently they haven't seen the research about what works better, without the drawbacks.

Fine Homebuilding: Roof Venting Doesnt Affect Cooling Loads
Fine Homebuilding says you cannot measure cooling energy savings that might be attributed to the existence of a ventilation channel.
Procedures

ASHRAE: Attic Ventilation Not Always Best Solution
ASHRAE article says while attic ventilation can be beneficial under some circumstances and climates, it should not be seen as the principal strategy to eliminate moisture and other problems in attics and rooms.

BC Housing: Attic Ventilation & Moisture Research Study
BC Housing online Attic Ventilation and Moisture Research Study report presents the findings of a two-phase research project that looked at the presence of moisture and mold growth on the roof sheathing of ventilated attics constructed in coastal climates. Phase 1 examined and confirmed through field testing and monitoring that in some maritime climates mold growth may occur even in well ventilated attics. Phase 2 of the study focused on evaluating the factors that lead to moisture collection and mold growth in order to identify design solutions and treatments that would minimize the potential for mold growth. (PDF)

BOABC: Controlling Mold Growth In Ventilated Wood-Frame Attics In BC
Building Officials Association of BC online slide show presentation describes issues and considerations for controlling mold growth in ventilated wood-frame attics in BCs cool marine climate. (PDF)

BSC: Overview Of Unvented Roof Systems
Building Science Corporation article was written to tie together and summarize their various papers on unvented conditioned cathedralized attics. 2003 (PDF)

BSC: Unvented Roof Assemblies For All Climates
Building Science Corporation digest on Unvented Roof Assemblies for All Climates provides a brief description of different types of unvented roof assemblies, benefits of unvented roof construction, and how closed-cell spray polyurethane foam can be used to create an unvented roof assembly that works in all climate zones.

Buiding Science: Guide To Attic Air Sealing & Roof Ventilation
Building Science says attics should be air sealed prior to adding insulation. Adding insulation alone does not save much energy and can lead to durability problems. This guide provides information for the air sealing and roof ventilation prep work necessary prior to adding attic insulation. (PDF)

Builder Magazine: Soffit Venting Solutions When No Roof Overhang
Builder magazine describes some simple roof venting solutions if the roof doesn't have a projecting eave and soffit.

Building Science Seminars: Cathedral Ceilings & Conditioned Attics
Building Science Seminars online slide presentation describes design and insulation considerations for cathedral ceilings and conditioned attics. (PDF)

Building Science: Eliminating Attic Vents
Building Science articles says that it's better to seal and insulate the attic, making it part of the home's conditioned space. This will reduce mold and mildew problems and save energy by keeping conditioned air leaking from the ducts inside the house. (PDF)

Building Science: Moisture-Safe Unvented Wood Roof Systems
Building Science online slide show describes background, considerations and procedures for building moisture-safe unvented wood roof systems. (PDF)

Building Science: Research Paper On Moisture-Safe Unvented Wood Roof Systems
Building Science research paper describes a hygrothermal modeling study, including all of the US climate zones, for a range of interior humidity levels and numerous arrangements and types of insulation. The results showed that so long as airtightness is provided, and wintertime humidity is controlled, numerous unvented solutions using either or both spray foam (open and closed cell) and fibrous insulation (cellulose and mineral fiber) can be successful. Climate, the solar properties and exposure of the roofing, the air and vapor permeance of the insulation (s) and interior humidity are the most important factors to be considered in the design of moisture-safe unvented roof systems. (PDF)

Building Science: Unvented Roof Summary Article
Building Science article was written to tie together and summarize various papers on unvented conditioned cathedralized attics found on their website. It is meant to summarize the main arguments, and provide pointers to where detailed information and measured data can be found. (PDF)

Building Science: Vented & Unvented Roofs
Building Science online slide show describes issues and solutions for vented and unvented roofs. (PDF)

Building Science: Venting Vapor
Building Science describes issues, considerations and best practices for venting roof and attic spaces.

CMHC: Study Of Attic Ventilation & Moisture
CMHC research found that too much or too little attic ventilation will increase moisture levels in attic wood members. The field work showed that stack effects usually determined the rate of infiltration of moist house air into the attic but that the attic ventilation rates were more dependent upon wind conditions. (PDF)

Fine Homebuilding: Crash Course In Roof Venting
Fine Homebuilding article by Joe Lstiburek describes when to vent your roof, when not to, and how to execute each approach successfully.

Fine Homebuilding: Roof Venting Done Right
Fine Homebuilding describes issues and considerations for proper roof venting.

Fine Homebuilding: Venting A Roof Without Eaves
Fine Homebuilding Q & A says the easiest to add venting to a roof without eaves is installing a venting drip edge.

GBA: All About Attic Venting
Green Building Advisor says we vent attics for four reasons, and all four goals can be better achieved by adopting measures other than attic venting.

GBA: Attic Ventilation May Not Solve All Moisture Problems
Green Building Advisor discusses whether mold on plywood in this attic is the result of inadequate attic ventilation or air leakage. More attic ventilation would not have solved this mold and moisture problem; extensive air sealing will (and reduce the energy bills as well), however.

GBA: Lstiburek's Rules For Venting Roofs
Green Building Advisor online video by Dr. Joe Lstiburek describes proper roof venting as needing an airtight ceiling, lots of air flow, plenty of soffit vents, and deep insulation at the attic perimeter.

GBA: Vented Or Unvented Attic?
Green Building Advisor says deciding on vented or unvented attic depends on whether it's going to be a living space.

JLC: Can Wind Short-Circuit a Ridge Vent?
Journal of Light Construction Q & A says without an external baffle, either a single- or a double-sided roof vent can allow outside air to come in and short-circuit the venting process. (PDF) Free site registration required.

JLC: Installing Rigid Soffit Venting
Journal of Light Construction online video series shows how to use using wire screen for installing rigid soffit venting.

JLC: Roof Ventilation Update
Journal of Light Construction article by the one of the construction industry's leading researchers explains roof ventilation and why what we think is true often isn't, and how some of our best hunches, based on observation of field performance, have paid off with problem-free attic assemblies. (PDF) Free Registration Required

JLC: Roof Venting In A Wet Climate
Journal of Light Construction provides some considerations for roof venting in a wet climate.

RDH: Re-Thinking Ventilated Attics, How to Stop Mold Growth
RDH Building Engineering describes issues and solutions for mold growth on the underside of sheathing in the Pacific Northwest.

Saturn: Attic Vents & Venting
Saturn Resource Management describes how attic vents and roof venting serve a variety of purposes, depending on roof design and climate.

Southface: Insulation & Ventilation Of Ceilings & Attics
Southface fact sheet describes benefits and procedures for insulating and ventilating attic spaces.

US DOE: Calculating Attic Passive Ventilation
US Department of Energy describes how to calculate the amount of attic passive ventilation needed.

US DOE: Unvented Roof Assemblies Using Cellulose Or Fibreglass Insulation
US Department of Energy online slide show presentation by Joe Lstiburek discusses several advances in unvented roof technology to condition attics, including the use of diffusion venting and dehumidification. These approaches will allow the use of cellulose and fiberglass insulation systems rather than the current approaches that rely on rigid insulation or spray polyurethane foams. (PDF)

US DOE: Unvented Roof Systems & Advanced Framing Strategies
US Department of Energy allows access to the online video of their High-Performance Enclosure Strategies, Part I: Unvented Roof Systems and Innovative Advanced Framing Strategies webinar. It focuses on methods to design and build roof and wall systems for high performance homes that optimize energy and moisture performance. Presenters are Joe Lstiburek and Vladimir Kochkin.

US FPL: Issues Related To Venting of Attics
US Forest Products Laboratory report Issues Related to Venting of Attics and Cathedral Ceilings supports current recommendations for attic ventilation in cold and mixed climate but recommends that attic ventilation be treated as a design option in warm, humid climates. (PDF)
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