Q: Could you help me decide how to relieve oppressive heat in my rental house, a 1912 Southern California bungalow? In July, August and September, the second-floor bedrooms are uninhabitable until long after sundown.
The house was apparently built with no air vents into or out of the attic adjoining those rooms. The following suggestions have been made:
- Install a wind- and heat-driven turbine on the roof;
- Install an electric exhaust fan;
- Build vents into the roof near the ridge, and drill holes for incoming air into the boards between the rafters at the front of the house under the eaves.
I want to provide some relief for my tenants without huge expense.
A: Both of us having been landlords, we applaud your desire to provide a comfortable living space for your tenants, and we have several suggestions to reduce the second-floor oven temperature. Here are the improvements we would make, in the order in which we would make them:
Insulate the attic: This is the first line of defense. Indoor temperatures seek the temperature outside. In winter, warm house air migrates outside. In summer the opposite happens. Insulation retards this migration.
Insulation is usually figured in R-value, a measurement of the resistance to heat flow. The greater the R-value, the greater the heat resistance. Heat from the roof radiates into the attic space and in turn radiates through your ceilings into the living space.
If the attic isn’t insulated, do it. If it is insulated, and the insulation is less than 12 inches thick, beef it up. Twelve inches of batt or loose insulation provides a resistance factor of R-38. This is probably more than your building code requires, but in this case more is better. The material is inexpensive, and if you do the labor yourself, you’ll get a huge return on your investment.
Provide adequate attic ventilation: Hot air rises. The trick is to move the air up from the eaves to the ridge vents and out of the attic.
Holes in the lower portion of the roof, called soffit vents, allow the relatively cooler outside air to enter the attic and force the warmer attic air out of the top, or ridge. When you insulate, make sure you do not block the soffit vents. Nail pieces of plywood across the rafters to make an air channel from the soffit vent into the attic.
Ridge vents are an integral part of this system. But rather than go with common "eyebrow" vents, have the roofer install a ridge vent along the entire length of the ridgeline.
Ridge vents are installed by cutting the roof sheeting back a few inches on each side, nailing a long plastic vent over the opening and covering the vent with composition roofing material. One architect told us he prefers instead to drill multiple holes in the sheeting to maintain structural integrity.
Either way the result is a watertight continuous vent system that exhausts hot attic air that is replaced with cooler outside air drawn in through the soffit vents.
Install a fan: There are three choices: a passive fan, a temperature-controlled fan and an electric whole-house fan. All work in concert with insulation and ventilation.
The passive fan is the turbine. It depends solely on convection. We don’t like it. Frankly, with insulation and adequate ventilation, the turbine won’t bring much to the party.
Temperature-controlled fans are electrically powered or solar-powered. We prefer the electric version.
Solar-powered attic fans rely on a small solar panel (typically 10- or 20-watt) to power a DC motor. Intake vents provide high-capacity powered ventilation without electricity operating costs. Most vents are mounted high on the roof near the ridge and are combined with soffit vents at the roof overhang or gable vents located on the building walls near the roof peak for balanced intake and exhaust airstreams.
The plus is that they work for free, using the sun’s rays. The minus is they work only when the sun shines. If a cloud drifts by, blocking the sun, the fan stops. Worse, as the sun moves through the sky, contact with the solar panel is lost and the fan stops. At best you’ll get part-time cooling.
The hardwired version is thermostatically controlled to kick on when the attic reaches a certain temperature. True, they do use electricity from the grid, but usage is minimal. The bottom line is that you’ll exhaust hot air when you need to regardless of the vagaries of sun and cloud movement.
Beefed-up insulation, vents and an attic fan could well be all you need. But if you want to go for the whole megillah, consider a whole-house fan.
Attic fans move hot air from the attic only. They do nothing to promote air exchange inside the house. A whole-house fan pushes hot air from inside while drawing in cooler air inside through open doors and windows. Placing a whole-house fan at or near the high point of the house will accelerate the removal of hot air to the attic while replacing it with cooler air from outside.
But a whole-house fan will not make the temperature lower than that of the outside air. Run a whole-house fan only when the temperature outside is lower than the house’s inside temperature. Nights and early morning are the best times.
Some planning is required to choose a whole-house fan. You’ll need to size the fan to work efficiently. Unless you’re an accomplished carpenter, you may need help with installation. Also count on using an electrician to properly wire the fan. If a permit is required, get one.
Once more, though, your first line of defense against the heat is insulation and proper venting. Start from there, see how it works and if it’s not good enough, check into the fans.