These days, it’s hot enough up here in Vermont that a person could forget what the winters are like. But make no mistake: winter will come, and when it does, the energy efficiency of your home will once again be a major concern.
Building a house? Moving into a new place? If you’re thinking about whether a one- or two-story house will be the best fit for your family, you’ll probably want to know which setup will use your heat energy more effectively. Based on that criteria, your best bet will actually be the two-story job.
Rob Roy explains. (With numbers!)
The following is an excerpt from Mortgage Free! Innovative Strategies for Debt-free Home Ownership, Second Edition by Rob Roy. It has been adapted for the Web.
Heat Loss Comparison of One- and Two-Story Design
For the sake of easy figuring, we’ll compare a simple 32-foot-square one-story design with a 32-foot-square two-story design, each built on a floating slab. Each story has 9-foot-high walls, and the stairwell space eats up 48 square feet on each floor, so 96 SF of useful floor area is lost to the need of accessing the second story.
|Skin area, single-story home||Skin area, two-story home|
|Slab||32′ × 32′ = 1,024 SF||Slab||32′ × 32′ = 1,024 SF|
|Walls||128 PF × 9′ = 1,152 SF||1st story walls||128 PF × 9′ = 1,152 SF|
|Roof||32′ × 32′ = 1,024 SF||2nd story walls||128 PF × 9′ = 1,152 SF|
|Roof||32′ × 32′ = 1,024 SF|
|Total skin area||=3,200 SF||Total Skin Area||4,352 SF|
|Floor area, single-story home||Floor area, two-story home|
|Floor area||32′ × 32′ = 1,024 SF||1st floor area||32′ × 32′ = 1,024 SF|
|2nd floor area||32′ × 32′ = 1,024 SF|
|Less 96 SF lost in stairwell||-96 SF|
|Floor area||= 1,952 SF|
Gain in skin area with two-story house: 4,352 SF – 3,200 SF = 1,152 SF
Percentage gain in skin area: 1,152 SF ÷ 3,200 SF = 36 percent
Gain in useful floor area with two stories: 1,952 SF – 1,024 SF = 928 SF
Percentage gain in floor area: 928 SF ÷ 1,024 SF = 91 percent
Bottom line: Adding the second story increases usable floor space by 91 percent with only 36 percent more skin area. And that’s not all. Warm air rises. We may as well use it twice before it leaves us. If the primary heat source warms the air in the lower story, we can use the heat again upstairs. Strategic placement and use of floor registers, internal doors, and the stairwell itself will allow passive delivery of this heat, and the effect can be controlled further with a simple fan in the ceiling of the first story.