Acrylic or polycarbonate dome skylights come is several sizes today. The traditional ones, however, are square to rectangular in shape, and run about 5″ in height. Their width and length can be anywhere from 12″ to 36″, and are 1/8″ thick.
These domes can be mounted onto wooden curbs (2×2″ to 2×6″), around which the roof shingles are caulked or thin-metal flashed to prevent any rain leakage around them. These domes can also be surface mounted directly onto the tar paper and wooden sheeting directly beneath the shingles transparent colored acrylic sheet.
In the latter case, the dome’s surrounding shingles themselves are directly laid over its flat outside flanges similar to the way the shingles are commonly laid over the flat metal of roof vents, furnace stacks, sewer vents and so forth. This installation minimizes the dome’s height.
Problem. Either way, or no matter how the domes are mounted, they can and will produce unwanted condensation and similar leaks even if they have an inner plastic shield within them. These domes are also vulnerable to being cracked from large hail, fallen tree branches, earthquakes, or careless roofers. When these events happen, the skylights will leak rain water as well in addition to forming moisture.
Solution. Build and install a shallow-box-like 5-1/2″-high hard transparent cover over the dome on the roof. This cover will act like a storm window does by taking the brunt of temperature change and the formation of most condensation. For this article, a 20″ square dome (which includes a 1″ flange on each side of the 18″-square dome itself), 5″ high, and surface mounted directly to the roof sheeting will be used as the example to be covered with the box-like storm cover. Similar covers can be built proportionally for other dome sizes.