Mar 8, 2010

Skylights: Good or Bad for the Home

Skylights and clerestories can brighten interiors with natural light, especially in spaces where it would not be possible to put enough windows. They can enhance almost any interior and are becoming increasingly popular. We hear about all sorts of exotic and futuristic ways to save energy. But we hear very little about some simple, proven and cost effective methods: operable skylights. Operable skylights can help reduce cooling costs in most climates. Once installed they require very little energy and almost no maintenance. Skylights are especially great for small spaces. They're a great way to let in light and make a tiny room feel significantly larger. In the bathroom, they provide a sense of privacy (no one but the birds can peek inside), while in the kitchen, they create a sense of connection to the outdoors.

(image from Apartment Therapy) However, in order to gain the maximum benefit from a skylight, it's important to understand the usage, designs, materials, positioning, and proper installation.

FABRICATION & MATERIAL CHOICE The material used in skylights can impact energy savings, occupant safety, and unit reliability. Consider the choice of glazing carefully. The two types commonly used are plastic and glass. Plastic glazing are usually inexpensive and less liable to break, their surfaces scratch easily and they may become brittle and discolored over time. Glass is usually found on more expensive skylights. It is much harder and durable than plastics and do not discolor. They are often made with a tempered glass on the exterior side and a laminated pane on the interior side.

WHERE TO PLACE SKYLIGHTS Skylights have several benefits if placed cleverly depending on the local sun paths. The location is important, if you want to maximize natural lighting and passive solar heating potential. Skylights on roofs that face north proved fairly constant but cool illumination. Skylights on the east provide maximum light and solar heat gain in the morning. On the west they provide afternoon sunlight and heat gain. You can prevent unwanted solar heat gain by installing the skylight in the shade of deciduous (leaf-shedding) trees, or add a movable shading device. In a city like Bangalore do not place your skylights where the Sun shines the longest and strongest in summer on south & west facing sides here, unless shaded by trees. Also for easy access and cleaning place your skylights where they are accessible from a terrace as you could end up having dusty, sorry looking skylights. Do not place them in bedrooms as there would be too much light in morning to sleep in and darkening shades are ridiculously expensive and difficult to operate. Skylights should be placed in those spaces that require the extra light, like an indoor green space, Work spaces which do not receive sufficient natural light through windows thereby avoiding artificial task lights. Passages/Corridors which do not have external walls to puncture a regular window for natural lighting. Skylights in passages can especially bring in a lovely accent to your building. Another good use of skylights would be in bath areas especially over your towel racks thus helping your towels to dry quickly in an otherwise moist and damp environment. Skylights are a great blessing especially for spaces that cannot have punctures in the wall because you share the wall with your neighbors building. Beautiful example of this home in Bangalore, where the architect strategically used a long strip of skylight to bring in natural light to the room which otherwise would have had to be artificially lit as the neighboring property shares the same wall.

HOW TO INSTALL SKYLIGHTS When choosing a skylight, one option you may want to consider is whether or not your skylight will be operable. Operable skylights can be opened to vent heat buildup and let in fresh air. The slope, or tilt, of the skylight also has a great effect on solar heat gain. A low-slope will admit relatively less solar heat in the summer and more in the winter, exactly what is desirable. A rule of thumb is to achieve a slope equal to geographical latitude plus 5 to 15 degrees.

PREVENTING LEAKS Leaks are very common with skylights. To avoid them, you should mount the skylight above the roof surface, install a curb (a raised, watertight lip that helps to deflect water away from the skylight) and flashing, thoroughly seal joints, and follow the manufacturer's guidelines. It's also prudent to apply a layer of sheet waterproofing over the flanges/flashing of the skylight. A skylight that is set in a roof-line with about a 60 degree angle should have a metal edging installed a few inches up the slope from the skylight that directs water runoff away from the skylight during storms. This would help keep the skylight trouble-free.

USING SKYLIGHTS TO COOL YOUR HOME: As any good cooling or heating system, the use of operable skylights to cool a home does require some design and planning. But when properly designed and installed, operable skylights can help keep your home cooler and save you a substantial amount of energy. Here are a few tips:

-The best location for operable skylights is on the side of the house opposite of the prevailing winds. This helps draw air out of the house. For example, in Bangalore the best location would be on the east or north sides of the house. If the house has two floors and an open staircase then a centrally located skylight in the 2nd floor hallway will work very well.

-A single story house may require more than one operable skylight because it may not have the vertical space (height) to create a good convection current.

-An operable skylight in a bathroom can double as a moisture venting system.

-The size of the skylight is not as important as its location.

-The best time to add an operable a skylight is when new roofing is installed or when the roofing material is relatively new and flexible.

-Some manufacturers of operable skylights provide optional shading and screening systems.

-Some skylight models open and close with small motors and can be programmed with thermostats, rain detectors and all sorts of fancy equipment. Motorized and automatically controlled units can make a lot of sense, for example in hard to reach locations. Some models can be operated via manual hand cranks, while more sophisticated, electronic models can be operated by a wall switch or remote control. The highest-end models operate automatically via temperature sensors and rain-triggered closing mechanisms. Basic manual operable skylight models are an economical option for providing fresh air and natural light. They are operated via an extended rod and are designed to be used in ceilings less than 15 feet high. For within-reach applications, a simple hand-crank is often preferred.

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