Guest guest Posted October 10, 2010 Report Share Posted October 10, 2010 Connie, I would agree that in climates with cold winters, keeping warm house air out of the attic is the way to prevent ice dams (and mold too!). And that ventilation is a way to reduce warmth and ice damming. But I believe that the primary result of adding soffit vents is to cool the soffit area and stop ice damming. The ridge vent has far less impact. (This might be worth an experiment; cover a ridge or soffit vent in a home with ice damming and see what happens!) Charlie Headrick, an engineer came up with a great ridge vent (that was sold through Headrick Products) but the company and web site were bought by GAF (as I recall) and then promptly shut down. Charlie set up some great experiments to prove how useless some ridge vents are. He built a model, shingle-roofed attic in a lab, cut out a 2-inch hole in the ridge and experimented with 24 different brands of ridge vents. He measured the temperature increase in the attic when the roof shingles were heated with heat lamps. The comparison controls for the experiment were having the slot completely open (for maximum ventilation) and having it completely closed (with duct tape) for no ventilation. The temperature increases for some of the ridge vents were comparable to having the ridge opening taped shut, in which the temperature increase was 65.8F. The temperature increase for the Shingle Vent II was 51.5F compared to the open slot tempearture increase which was 30.9F. By comparison, for the best ridge vents, the temperature increase was only 33.9F. I can send anyone interested the report if you like. In my own experience, I have smoke tested several ridge vents in homes in the winter. Virtually no air went out the vents. So, soffit vents with a ridge vent (if it functions properly) or gable-end vents, or roof vents are a fine idea but most importantly, heat and air losses to the attic (by convection, not diffusion) must be stopped. May May Indoor Air Investigations LLC Tyngsborough, MA www.mayindoorair.com 978-649-1055 > RE: ROOF VENTILATION > > POSTED BY: \ " CONNIE\ " CONNIE@... > CONNIEMORBACH > > Fri Oct 8, 2010 10:45 am (PDT) > > Hi Jeff > I agree that many ridge vents are installed incorrecly, with some not > being cut and when cut not cut wide enough in accordance with > manufacturer's specs. Also, most attic ventilation is not designed > properly. > > In mixed climates, proper roof top and soffit ventilation is > essential to prevent ice damming will occur in the winter months. > > If installed correcly, we do not find that ridge vents are useless in > the winter in the midwest. There is still heat diffusion from the > living space, and it must have somewhere to go. The insulation and > craft paper vapor barriers do retard vapor and heat diffusion, but > there is still vapor and heat diffusion at other areas, such as whole > house fans, recessed lights, wire and pipe penetrations, top of stud > plates, etc. Ridge vents should be baffled to deflect wind at the > exit. > > In MI, we have had success with Shingle Vent II ridge vent in > combination with soffit vents designed to achieve 1 sq. ft of free > vent space per 150 sq. ft of attic floor space, with 50% of > ventilation at the ridge and 25%at each soffit. To make the > soffit-ridge connection effective, recessed lights, wire penetrations, > and other pathways to the attic must also be properly insulated. This > can best be achieved with two-part closed cell foam. Sottit vents are > kept open with baffles that completely span the truss spaces. WEe > also install a template styrofoam block at the tops of the exterior > walls. > > The Shingle Vent II has a baffle that deflects the wind from the > exit, maintaining a low pressure zone so that the high pressure air in > the attic will exit. There are are probably other roof top vents that > can achieve the same effect if properly installed. This is the one > that has resulted in the best results for our clients. > > Without proper ventilation that includes ridge or roof top and soffit > vents, ice damming will occur in the winter months. > > What do you recommend for roof top ventilation. > > Connie Morbach, M.S., CHMM, CIE > Sanit-Air, Inc. > sanit-air.wordpress.com > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted October 10, 2010 Report Share Posted October 10, 2010 Thanks for the information Jeff. I agree that migration of heat must be stropped. However, with new construction (multiple roof lines, recessed lights, etc) this seems to be a detail that does not receive enough attention. In my experiences, poor installation, as opposed to the product, causes the problems. In many constructions, the soffit and ridge vents are partially or completed obstructed. When the problematic attics are remediated and properly ventilated, the problems do not return. Attic ventilation can not follow cookie-cutter templates because houses with multiple roof lines, hip constructions, and other details must be designed individually. Also, in some cases, an attic without a problem can develop condensation due to changes in life style. For example, I inspected an attic with dense mold growth and condensation that did not exist the year before for the same family. They reported that the only change was the birth of a baby. A humidifer was operated in the baby's room throughout the winter months. The existing ventilation, insulation, vapor barrier combination could not handle the added moisture. Interestingly, we don't usually find the same issues in older homes. I really appreciate the information on the test results you sent. Connie Morbach, M.S., CHMM, CIE Sanit-Air, Inc. > > > > > > > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted October 10, 2010 Report Share Posted October 10, 2010 Jeffry, I would appreciate more info on this as we plan on building a new (safe) home next year (also repairing the crummy cabin on our property. Thanks, * * On Sun, Oct 10, 2010 at 6:35 AM, <jeff@...> wrote: > > > Connie, > > I would agree that in climates with cold winters, keeping warm house > air out of the attic is the way to prevent ice dams (and mold too!). > > And that ventilation is a way to reduce warmth and ice damming. > > But I believe that the primary result of adding soffit vents is to > cool the soffit area and stop ice damming. The ridge vent has far less > impact. (This might be worth an experiment; cover a ridge or soffit > vent in a home with ice damming and see what happens!) > > Charlie Headrick, an engineer came up with a great ridge vent (that > was sold through Headrick Products) but the company and web site were > bought by GAF (as I recall) and then promptly shut down. > > Charlie set up some great experiments to prove how useless some ridge > vents are. He built a model, shingle-roofed attic in a lab, cut out a > 2-inch hole in the ridge and experimented with 24 different brands of > ridge vents. He measured the temperature increase in the attic when > the roof shingles were heated with heat lamps. The comparison controls > for the experiment were having the slot completely open (for maximum > ventilation) and having it completely closed (with duct tape) for no > ventilation. > > The temperature increases for some of the ridge vents were comparable > to having the ridge opening taped shut, in which the temperature > increase was 65.8F. The temperature increase for the Shingle Vent II > was 51.5F compared to the open slot tempearture increase which was > 30.9F. By comparison, for the best ridge vents, the temperature > increase was only 33.9F. I can send anyone interested the report if > you like. > > In my own experience, I have smoke tested several ridge vents in homes > in the winter. Virtually no air went out the vents. > > So, soffit vents with a ridge vent (if it functions properly) or > gable-end vents, or roof vents are a fine idea but most importantly, > heat and air losses to the attic (by convection, not diffusion) must > be stopped. > > May > May Indoor Air Investigations LLC > Tyngsborough, MA > www.mayindoorair.com > 978-649-1055 > > Quote Link to comment Share on other sites More sharing options...
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