Last month, I wrote about the attic as a system of components and mentioned that the article could actually be written into a book with chapters expounding on each area in greater detail. 2017 was a DIY (“Do-It-Yourself”) year of articles, and I enjoy running into people who tell me they enjoy the articles or call me with a question. That’s rewarding! So for 2018, let’s break down the attic into a series of articles. I hope you find them helpful and will enjoy them as much as I enjoy writing them.
One of the most important components in the attic is something you can’t see, but you can certainly see and feel the results (or consequences) of it! On a recent inspection, the prospective buyer followed me up into the attic with a concern he had seen. He asked me what were all those holes “over there” around the edges of the attic space. Those holes are actually part of the all-important system of the air flow in the attic called ventilation, i.e., the action of moving air. Ventilation is a system of components, all sized and positioned to provide constant and balanced intake and exhaust of air. The lack of proper air flow or ventilation can produce short-term and long-term consequences.
There is a mathematical calculation for the amount of ventilation there should be flowing through the attic space. Different entities such as the International Residential Code (“IRC”), U.S. Housing Authority (“USHA”), International Building Code “(IBC”), and roofing materials manufacturer’s installation instructions have codes or required installation guidelines for the proper amount of attic ventilation. Proper attic ventilation consists of a balance between the air intake (in the eaves, soffits, and/or fascia of the structure) and the air exhaust (at or near the ridge of the roof). In no case, should the amount of exhaust ventilation exceed that of the amount of intake ventilation. Think about the air flow … air flow in at the lower part of the attic and then air flow out at the higher part of the attic. It’s that simple, and it needs to work right.
The IRC best calculation for optimal attic ventilation performance is to have 1 sq. ft. of ventilation for every 150 sq. ft. of attic floor space for a ratio of 1:150. You will also see acceptable calculations per the IRC up to 1:300 depending on different climate zones. For our area, you should have 1:150 ventilation in your attic.
Older homes in the Greater Houston area that were built with cedar shingles now usually have composition shingles installed. The original cedar shingles had a natural ventilation to them, and now those attics should be revised with additional vents to achieve an acceptable air flow. The most common mistake homeowners make when installing additional insulation is to block the holes at the soffit, thus starving the attic for air intake. There are many different kinds of vents for ventilation – ridge vents, static vents, turbine vents (“whirlybirds”), power vents, solar vents, gable vents, continuous soffit vents, whole house fans, and more.
In the summer, the natural air flow in a well-vented attic moves extremely hot air out of the attic. This protects the roof shingles from underneath from blistering and deteriorating more rapidly and removes moistures from the attic. By lowering the attic temperature, you can actually extend the life of the roof and save money on the expense of repairs, maintenance, and replacement. The insulation installed in the attic resists heat transfer into the interior of the home, thus the attic floor and interior ceilings will be cooler.
There is a free phone app called “Air Vent” you can use to calculate the ventilation in your own home. Shingles, HVAC equipment, water heaters and other items will last longer in a well-ventilated attic. A home with a properly ventilated attic will be healthier and more energy efficient. Be well ventilated my friends!
