If you have sky-high energy goals, don’t let the roof cap your potential.
Typically dismissed as out of sight and out of mind, your roofing system is likely underutilized.
“The roof is a platform for energy conservation,” explains Matt Barmore, product manager of sustainable systems for manufacturer Firestone Building Products. “Many of us don’t think about the roof until it leaks, but it can do a lot more than keep out water. It can save you money.”
Skylights are an increasingly popular way that your roof can work for you. Let the following factors guide your next new construction or retrofit project.
Types and Tools
First determine your options, which are dictated by building type, size, and orientation.
“There are a number of choices, and your decision depends on the space and how to configure it based on the designer’s vision,” Barmore explains. “Clerestory windows are growing in popularity, and there are a growing number of solutions with prismatic lenses.”
Domes and tubes with prismatic systems capture and diffuse light to reach the right effective skylight to floor area ratio (eSFR).
“These advanced lenses can provide almost three times the light as a conventional flat, translucent panel,” says Randy Ahland, business development manager of building products for manufacturer Varco Pruden Buildings. “The coverage difference is almost literally night and day.”
In overcast climates, light scoops – tilted south-facing skylights – are ideal. They can be customized to provide less direct sunlight in the summer and more in the winter, and for other considerations.
“Daylight availability is a curve around noon. You want to flatten it by collecting at low angles and rejecting at high angles,” explains Lisa Heschong, principal at energy efficiency consultant Heschong Mahone Group. “General advice for choosing skylights is the highest transmission, best diffusion, and double glazing.”
To make the right selection, use the free tool SkyCalc from research group Energy Design Resources.
“SkyCalc will give you an eight-page engineering document with a lot of helpful information. I suggest flipping to the executive summary on the last page,” Barmore says. “It tells you the number and size of skylights needed as well as your upfront cost, estimated savings, and ROI.”
Automation can take your skylight project to the next level.
“Photocontrols in conjunction with daylighting produce the best bang for your buck,” Ahland says. “Skylights will certainly benefit buildings without controls, but most owners want to see impact on the bottom line. Controls ensure the lights get turned off.”
The human eye has difficulty detecting when light levels are acceptable. But controls can, in addition to making life easier for FMs.
“I’ve been in a building with skylights on a nice sunny day, and all the interior lights were on. With so many things going on, the building manager forgot, and I had to tell him to shut them off,” says Barmore. “An automated system takes the guesswork out.”
Controls can incorporate manual override, but you likely won’t be using that switch to turn lights on.
“In a study, we found users that thought the system was less aggressive than they wanted, so they shut fixtures off themselves,” Heschong says.
To push your project over the top, find the sweet spot at the intersection of these three areas: reductions, rebates, and reroofing.
Lighting is one of the biggest pieces of the energy pie, so your first motivation is reduced energy costs. See sidebar for a case study with typical savings.
“Generally a skylighting solution pays for itself within four to seven years,” says Barmore. “Afterwards, when you start saving on energy every month, that’s probably the biggest incentive.”
But if the cuts aren’t compelling on their own, look for rebates and tax credits.
Some regional utilities will cover part of the upfront cost for upgrades, and the Energy Policy Act of 2005 provides up to 60 cents per square foot for cutting lighting consumption.
However, a skylighting project may be most feasible when roofing is already in the budget plan.
“Reroofing is the best time for a retrofit because you can determine the best use of your capital,” Barmore says. “Ask yourself what you can get out of your roof.”
Don’t miss the big picture and reroof without reasoning.
“Think about holistic solutions. Don’t just focus on the roof or the lighting, because all systems interact and have an impact,” explains Ahland. “It’s not about one or the other. It’s about the entire pie.”
Chris Curtland firstname.lastname@example.org is assistant editor of BUILDINGS.