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Roofing/Whethger our house needs a ridge vent and eve vents

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Question
Our house stands on a hill just south of S.F. within 1/4 mile from the ocean. Built in 1979 with the top story having cathedral ceilings and with a two story window between the first and second floors which creates a large open area between the two floors of the house. When our "spec" house was built, the builders didn't provide a ridge or eve vents for ventilation.  there are plywood areas on our roof which have failed as evidenced by concave areas which have appeared on the roof's surface. A roofing contractor has told us that we need to have a ridge vent due to the cathedral ceilings in this house.  Another roofing contractor told us when I asked them to add a ridge and eve vents to their bid, that they in turn talked to other roofer's in our area (we do get driving rain and high winds so close to the ocean here) and said the other roofers advised them that due to our location on the hillside with wind driven rain; eyebrow vents would be a better venting system than ridge and eve vents- What do you think? The first roofing contractor plans in their bid to use a Lomanco ridge vent and Lomanco deck eave vents-- The contractor who advised eyebrow vents has included in their bid four (4)O'Hagen eyebrow vents.  Our roof area is 969 Sq. ft. and the CA State building code requires one (1) Sq. ft. of venting for every 150 sq. ft. of roof area. Which venting system, if either, do you think is best for the situation I've described to you?  The concave areas of plywood under the roof shingles are on the western side of the pitched roof facing towards the ocean.  What do you think?

Answer
Pamela,

Your question is a bit complicated and extensive to answer, likely I will give you an answer that will reuslt in additional questions. You state the ceilings are cathedral, so they are high flat ceilings with no attic, only a space as thick as the main joist, usually filed with batt insulation. Now with a cathedral ceiling you would have a low-slope type roof, so a "ridge vent" is impossible as it is unlikely a low-sloped roof would have a definable ridge.

By the vents you are stating, these are used for steep-sloped roof systems, such as tile, shingles and similar.  Lomanco 700 or 800 and O'Hagin Weathermaster are made for use with steep-roofing systems, common with asphalt shingles. The O'Hagin Weathermaster is designed in a way to work effectively in more severe weather conditions.

I suspect what you have is a steep-sloped roof and vaulted ceilings, similar in overall function to cathederal, but is the same or similar slope to that of the roof and not flat. Any further comments will focus on the roof being a steep-sloped roof with vaulted ceilings.

The requirements for ventilation for California are taken diretcly from the International Residential Code (IRC) therefore be it your home in San Francisco, CA or Boston, MA the ventilation is the same. The criticla point with ventilation is balancing the home's need intake and exhaust. If you add exhaust ventilation without sufficient intake, it will do little to function at all. I suspect the "concave" deflection of the plywood is simply a function of living in a continuously moist environment as much as a ventilation issue. Thinner plywood in coastal exposures do tend to disort plywood sheathing over time. For maximum ventilation with the home design as I beleive it is, would be to ensure the space between every joist to  have intake ventilation at the soffit (see Lomanco SV Vent or similar) and ventilation at the ridge (see Lomanco standard or solar vents)  Cheap continuous ridge vents are not a good solution in areas with higher winds and heavy rain.

Let's start with this information and you can do some research to better understand these products. Review this and we can chat more to help you understand all you desire. I want to reiterate that the plywood sheathing deflection is liklely as much a function of age in a coastal environment.

Steven C. Wadding RRC,RRO,CDT  

Roofing

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Steven C. Wadding RRC,RRO,CDT

Expertise

General questions in regards to most roof types and situations. As the Technical Services Manager for Polyglass USA, Inc. this would not be a forum to address any issues directly related to a product my employer manufacturers.

Experience

I have been active in the roofing and waterproofing industries for more than 30 years with extensive experience from product installation, product development and consulting. I have been active in the Construction Specifications Institute and Roof Consultants Institute for approximately 20 years. I am a member of ASTM and am a voting member of various subcommittees. I have many years of consulting experience in the fields of Roofing, Waterproofing and Exterior Building Envelope disciplines.

Organizations
Roof Consultants Institute Construction Specifications Institute ASTM

Publications
Division 7 Technical Binders for Malarkey Roofing Products and Polyglass USA, Inc. CSI Phoenix Chapter Cactus Comments

Education/Credentials
Registered Roof Consultant - Roof Consultants Institute Registered Roof Observer - Roof Consultants Institute Certifified Document Technologist - Construction Specifications Institute Spray Fireproofing Special Inspector - International Code Council

Awards and Honors
Registered Roof Consultant - Roof Consultants Institute Registered Roof Observer - Roof Consultants Institute Certifified Document Technologist - Construction Specifications Institute Spray Fireproofing Special Inspector - International Code Council

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