Daylighting is the centuries old practice of lighting the interior of a building with openings in the structure. As this is about roofing we ignore windows and discuss skylights here. Using skylights to light an interior space can directly reduce the electricity costs. Skylights can also reduce the need to replace lights as they wear out, which for some building owners is a considerable expense. Other possible reasons to install skylights include studies that have shown natural daylight makes employees more productive and shoppers more prone to purchase. The Federal government offers a $.60 per square foot tax deduction for the current year (up to the installation cost) provided the skylights are partnered with sensors and controls on the interior electric lights. To obtain the deduction an engineer must certify the installation. Sensor and control costs may be partially offset by refunds from the electric companies.
Skylights come in different shapes, sizes and types. There are skylights with two domes (we recommend) and some with one dome (not recommended). The domes can be clear, glazed or prismatic. The clear domes let the light through unfiltered. The glazed domes dim the light slightly. The prismatic domes are made of little prisms that offer two advantages. The first prismatic advantage over regular skylights is that sunlight can be caught and utilized when the sun is lower in the sky. The second prismatic advantage is the light coming through all the prisms is diffused and distributed evenly throughout the interior space, without any traveling bright spots that normal skylights may have.
Skylights come in many different sizes. Solar tubes are approximately 6″ in diameter. Other sizes vary from 4′ x 4′ to 4′ x 6′ and can ramp up to about 50′ x 100′ or even larger. Setting up skylights to maximize light isn’t simply a matter of just buying and installing the largest skylight possible. The layout of the interior needs to be taken into account. Skylights over storage rooms don’t make sense. The position of the interior rooms, high storage racks or other types of partitions should be taken into account when placing the skylights. Skylights can also be utilized as smoke vents – which open automatically should the heat in the building reach a certain temperature in case of fire to let the smoke out. Some smoke vents work with a fusable link and springs that cause the smoke vent domes to pop open. A newer version smoke vent supposedly has the domes melt when they reach a certain temperature.
Installing the skylights is not a trivial expense. The skylights are typically craned to the roof, a hole is cut in the roofing material and then the roof deck itself. The hole in the deck typically needs some type of reinforcement. Making a hole in the roof over an office area can be messy and disruptive (imagine cutting a hole in a concrete deck over someone’s desk). Once the skylight curb and domes are installed on the hole the roofing needs to be re-flashed or made water-tight around the new skylight curb. If a skylight is installed into a finished area the interior must be repaired around the skylight and probably re-painted.
There are some skylight calculations being done that attempt to determine the payback period of the skylight investment based on reduced electrical usage. If a calculation is done for you, make sure all installation costs are included, not just the cost of the skylights themselves.