Are your shingles curling and your roof looks like a series of bumps and lumps? Chances are you have an attic ventilation problem. Your house is surrounded by its building envelope, which is a combination of insulation and water and air barriers. This envelope is designed to keep heat or cold in your house with minimal leakage to the exterior. Unfortunately this is not always the case. The attic is especially vulnerable to leakage, as hot air rises and if the attic is under negative pressure, will draw air from the rooms below.

The purpose of your attic ventilation system is to maintain attic temperature close to air temperature outside your home. This then prevents heat and moisture buildup in the attic. This venting is accomplished by soffit vents along your eaves and passive or turbines near the ridge of your roof. Some homes utilized a ridge vent system that runs along the ridge or you roof. Building codes require one square foot of vents for every 300 square feet of roof area, and twenty-five percent must come from eaves and twenty-five from the top of your roof. The remaining fifty percent can be space wherever. The purpose of these vents is to remove any unwanted temperature build up in the attic by convection. That is why it is so important not to block any of these vents with insulation etc.

Checking the eaves of your home for available vents is the most important part of inspecting your attic. When insulation is installed over your outside walls it meets your roof as it comes down to meet exterior wall. This is where your insulation will block ventilation for eaves. Building code requires that material be installed across the rafters to create a ventilation channel from eaves to attic space. Another popular method is to install the Styrofoam vents which are stapled against the roof sheathing, again allowing free ventilation of eaves past the insulation.

Ice dams on the edge of your roof are a good indication that your attic is ventilated poorly, or it might be that you have insufficient insulation. At the first sign of ice dams on your house, don’t hesitate to call in a local insulation professional to inspect your attic. The combination of ice build-ups in the winter and excessive heat build-up in the summer will reduce the life expectancy of you roof dramatically.

This is a brief overview of some of the aspects of attic ventilation; contact a local professional whenever you suspect problems with any of the major systems of your home. A local building supply store can supply names of reputable contractors if required.

Barrie Home Inspector