Ventilation: Breathe In…Breathe Out
August 10, 2016
Proper Venting for a Lifetime
Proper attic ventilation is critical to a healthy and efficient home. Attic ventilation plays a great role in reducing your summer air conditioning costs by venting heat out of the attic. It also vents out the moisture which migrates from inside the home to the attic. In winter, good ventilation helps to avoid ice dams on your roof.
Breathe In…Breathe Out
Effective ventilation requires intake and exhaust air. Usually intake air is achieved through eave soffit vents. Exhaust venting is done through vents higher on the roof such as ridge vents, turbine vents, or various types of “can” vents. A good way of thinking about ventilation is to understand that your desire is to continually and consistently “bathe” the underside of the roof deck with fresh air. This prevents condensation, keeping your decking dry and preventing the growth of mold.
Always think of air-flow when thinking of ventilation. Air flows over the shortest distance possible. Think, for example, if your home had soffit vents, gable vents, and a ridge vent. The intention is to bring air in the soffit and out the gable and ridge. What will really happen, though, is the gable vents will bring in air to feed the ridge vent, reducing or eliminating the draw through the soffit vents. That drastically minimizes the effectiveness of the venting in your attic. Well balanced attic ventilation will often consist
of ridge vents and soffit vents with the net free air flow being equal between the two types of vents. If they are not equally balanced, you would want to have the soffit vents slightly exceed the net free air-flow through the ridge vent.
Avoid Moisture Build-Up
If you choose a metal roofing product that needs to be installed over battens or “strapping” and you do not have solid decking in place, you will need to pay exceptionally close attention to proper ventilation in order to avoid condensation problems. In fact, because of this, you will often find that the most credible manufacturers of metal roofing products that can technically be installed over battens will advise always having solid decking in place for residential applications. That is always our advice.
If your home’s construction does not allow for ventilation, then you need to check whether a vapor barrier is in place in the roof assembly to prevent moisture from migrating to the decking or roofing. This vapor barrier can be a sealed sheet of polyethylene (usually directly behind the ceiling drywall) or certain types of insulation such as sprayed-on polyurethane. If these things are not in place, then having a vented “cold roof” constructed on top of your current roof may be wise.