Roof venting details save on energy cost (C) Daniel FriedmanRoof Ventilation Details for Energy Conservation

  • ROOF VENTILATION ENERGY SAVING DETAILS - CONTENTS: Roof framing options and construction details that permit optimum roof ventilation to also conserve energy, reducing cooling & heating costs. Roof ice dam leaks can be cured or avoided by these roof and attic venting details. Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices
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This article discusses saving energy by roof framing options and construction details that permit optimum roof ventilation to also conserve energy, reducing cooling & heating costs.

Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

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Article on Roof Structural Details to Prevent Ice Dams while Saving Energy Costs

Roof ventilation design details (C) Daniel FriedmanProvide Adequate Roof Cavity Space for Lots of Ventilation and Lots of Insulation

This roof ventilation design details article from Steven Bliss's "Building it Right" column in Solar Age Magazine and available in the three links just above, describes a few adjustments for insulated roofs that will assure good ventilation without wasting building heating or cooling energy.

The author explains the basics of ice dams and ice dam leaks on buildings, the need for a 1- to 2-inch air space over the outer wall top plate, and the importance of continuing the air ventilation pathway up under the roof to the ridge outlet. At the same time, good roof ventilation design prevents leaks from wind, rain, insects, and rodents.

Good attic or under-roof ventilation and insulation design is described for truss roofs as well as framing tips to save time and construction costs. The "raised-heel" or Arkansas truss design is explained - a method for obtaining additional insulation over the top plate for buildings constructed in cold climates.

For cathedral ceilings the author recommends flat trusses to provide adequate ceiling depth to permit both good insulation and good air ventilation in the structure.

Use Roof Vents and Roof Eaves Baffles to Assure Air Inflow for Roof Ventilation

The writer explains the use of vertical blocking or baffles to provide airflow passage between each pair of rafters or roof trusses. Where blown-in insulation is to be installed, the baffles need to continue all of the way up to the ridge outlet vent. Baffles may be site constructed using hardboard or manufactured rigid roof baffle products. Raised heel or flat truss design roofs include a vertical baffle flush with the side wall sheathing, or building wall sheathing can be continued vertically to form the baffle.

Additional Roof Venting & Gutter Details to Prevent Leaks and Rot at Roof Eaves

The writer, an advocate of the fully-vented cold-roof building design (to prevent ice dams, attic or roof condensation, and related rot or mold problems as well as providing a cooler building in hot weather) reviews gutter hanging details to assure that leaks do not occur at the vented roof eaves such as using strap hangers to keep gutters away from the fascia board, and placing the gutters low enough in snow-regions that the gutters won't be knocked off of the building by sliding snow and ice.

Options to provide intake venting at the overhang or soffit at the roof eaves include locating a continuous vent strip at the outermost edge of the overhang to minimize wind-blown rain entering the soffit from below.

The author cites model building codes on the amount of net free roof vent area in the attic: 1/300 of the ceiling area if the ceiling has a vapor barrier, and 1/150 of the ceiling area if no vapor barrier is installed.

We agree with the article's conclusion that these code specifications were written long ago when houses were more drafty, and when the prime concern was winter condensation risks.

Because of the increased use of air conditioning in buildings even in northern climates, summer energy costs have become a concern also suggesting that more ventilation than these minimums is recommended today.

Finally, if a whole house fan is to be installed blowing into the roof space or attic, still larger ventilation areas will be needed for the fan to work effectively (and to avoid a fire risk).

Original article

"Detailing for Roof Ventilation, the insulated roof requires a few adjustments in detailing - all the changes for the better" - links to the original article in PDF form immediately below are preceded by an expanded/updated online version of this article.

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.


Continue reading at ROOF VENTILATION SPECIFICATIONS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see ROOF FRAMING TIES & BEAMS for a discussion of proper framing of a cathedral ceiling

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