Attic Ventilation – Protect Your Home
Ice on your roof or shingles curling, look no further, your attic needs proper ventilation. As a home inspector, one of the most common problems I find is improper or inadequate attic ventilation.
According to building code requirements, your attic should have one square foot of venting for every three hundred square feet of roof area. Twenty-five percent of this ventilation must be at soffits and twenty-five percent at top of roof. The remaining fifty percent can be located anywhere in the roof.
Your attic is ventilated by convection; air enters at your soffits and exits at the top of your roof, allowing any warm air and moisture to leave your attic space. Remember, water or moisture is one of the worst enemies of your home, and every effort should be made to ensure that it is kept away or removed immediately.
Soffit vents are located along the bottom of your roof. Modern soffits are covered with aluminium panels which have holes for the purpose of ventilation. Where most problems are encountered is where your rafters meet your walls in the attic space. Insulation is frequently allowed to completely fill the void between rafters and the ceiling joists. This prevents any air movement from the aluminium soffit to the top vents. The building code requires that plywood be nailed across the rafters to ensure air channel that reaches down to soffit area and allows free movement of air. Styrofoam vents called Mor-vents or Sur-vents can be stapled into place also. Cardboard vents are also being used although in my experience this tend to fall down or sag as a result of moisture.
Turbines are a popular addition to newer homes and will remove more air and moisture than a passive vent system, but only when the wind is blowing. The better turbines also use plastic bearings, preventing that annoying squeaking that metal bearing can produce. There are some negative comments that have been made against using roof turbines, which are; they can create a negative pressure in your roof, allowing more heat and moisture to enter attic from home, which could increase your heating requirements. Also, the design of the turbine may allow rain and snow into your attic when not turning. I can verify this fact as I have personally seen the moisture imprint on small areas of insulation below roof turbines.
Ridge vents are installed along the top of your roof and provide an excellent means of ensuring air from soffit vents can escape your attic. Ensure your ridge vent has baffles to ensure proper suction of air from attic or else the wind may just blow from one side of ridge vent to the other. Net Free Area (NFA) is stamped on the vent and indicates the resistance; the higher the number means the less resistance.
Moisture can enter you attic from many sources, penetrations through your building envelope are major contributors. Plumbing, electrical wires, bath and kitchen exhaust holes provide easy access for moisture to enter your attic.
When buying a new home a professional home inspection will identify if any of this items are present. If moisture is allowed to gather in your attic, mould will start forming on sheathing and even on your insulation. These materials may then be required to removed and replaced at a huge financial cost to the homeowner. Another common fault found in attics is areas of little or no insulation where somebody has gone into attic to do renovation or installation of wires etc. This creates an area where heat is escaping from your home, which can cause frost and moisture where your warm air meets the cold. Although unusual, some people have actually vented their bathrooms or kitchens directly into the attic, providing a supply of moisture, warm air and contaminates directly into your attic.
Roger Frost, The Barrie Home Inspector, has over 26 years of experience in building, inspections and code compliance. As the owner of Napoleon Home Inspections he has inspected every type of residential home and is qualified for commercial and industrial inspections. Visit his web site at http://www.napoleon.cc to view other informative articles on residential homes.