Architecture/cold roof

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Expert: - 8/27/2007


Question
Does a "cold roof" require a 1:300 ratio of ventilation in order to be effective?

Answer
Mike: Thanks for your question!

A classic "cold" roof design doesn't require the same kind of ventilation as a warm roof, since you're not trying to remove hot, humid air from the interior of the roof structure.  1:300 is a very basic "building code" rule-of-thumb and doesn't always work for every attic in every climate anyway.

In fact, the basic 1:300 requires 50% to 80% of the clear vent area to 3' or more above the eave vents to meet code...it gets a little complicated even in the very rough "code compliance" format.

A cold roof's ventilation system is designed to allow heat that escapes the insulation below to be carried away by convection without melting the snow on the outer roof surface above.  The proper amount of ventilation depends on a lot of factors; the specific climate is probably the most important.

Generally, a couple of inches of ventilation space in a cold roof is enough to get the convection currents going, and generally, the steeper the pitch the better.  But if you need to be sure it will work, you'll need to do a more thorough analysis of the whole system including the pitch of the roof, the amount of insulation, the length of the overhangs, etc.

I do wish I had a simple answer for you, but cold/warm roof design is a highly-debated and technically-oriented subject.  Each situation is unique!

Hope this helps,

Richard Taylor, AIA
www.rtastudio.com
www.rtaplans.com

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Richard Taylor, AIA

Expertise

Ask me about all aspects of house, remodeling. , and room addition design and construction. Ask me about historic homes, renovation, and restoration. Ask me about materials and techniques, and about how you can get the best value for your design and construction dollar. Ask me how you can make your home a very special place. I can't, however, answer specific structural engineering questions in this forum - that's something you'll need on-site observation for.

Experience

I own a full-service residential architectural firm, and have been designing custom homes, remodelings, and room additions across the country since 1983. Check us out at Richard Taylor Architects and RTA Plans. I have written and been published extensively on the subject of residential architecture.

Organizations
American Institute of Architects, City of Dublin Architectural Review Board, Vice Chair of City of Dublin Planning and Zoning Commission, American Planning Association, Board Member Historic Dublin Business Association, Past Editor of SPLASH (a software forum), Past Editor of Open Directory Project, Assistant Scoutmaster, Boy Scouts of America

Publications
Business First of Columbus, Suburban New Publications, About.com, Cleveland Plain Dealer, Columbus Dispatch Residential Architect Custom Home Architect Remodeling Architect

Education/Credentials
Bachelor of Environmental Design (Architecture) Miami University 1983
For more about home design, check out my blog at Sense Of Place and join the conversation on our Facebook Page.

Awards and Honors
2010 Dublin Chamber of Commerce Business Person of the Year

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