Green Building for Tough Times
Squeezimus Sanguinem ex Turnipibus (Butchered Latin for We squeeze blood out of a turnip)
April 29, 2013
This online-only article is a supplement to the May/June 2013 print edition of Home Energy Magazine.
In my roughly 35 years of building energy-efficient homes, I’ve had the pleasure of learning from building scientists, designers, and clients. Building science, of course, is focused on the physics of energy flow, but it ignores the human factors of how we use energy and space. I believe both are important. In this article, I will share some of my insights with you.
No doubt we live in a tough economy, one where we have to wring every dollar to meet our goals. The same goes for building the most energy efficiency into our homes. But how do we find that sweet spot—that peak of the curve where we get the most benefit for our buck in both efficiency and livability? It’s a tall order, especially when some of the best new materials, equipment, and programs can magnify the cost of traditional methods of homebuilding.
Affordability is the limiting concept here. Clients’ budgets have limits. Affordability is central to how successful we are in achieving our goals. If our goals focus on finishes, they can consume much of the budget for energy efficiency. If our goals focus on being comfortable, we can achieve that best by focusing on energy conservation. Clearly, building one demonstration home—such as a net zero energy home—will prove a point, but that home probably had expensive components that were subsidized by grants, partners, or donors, making it a home that most ordinary buyers couldn’t afford. To make the benefits of sustainability and energy efficiency available to large numbers of home buyers, the price of admission has to be within reach.
I build homes in east central Iowa, a predominantly heating climate, where in winter, maintaining a warm interior temperature and comfortable relative humidity (about 35% or more) is desirable. Iowa also has hot, humid summers, where we need to reduce interior humidity. In each case, a well-insulated, airtight envelope is needed to control humidity. From my experience, I’ve found that focusing on energy conservation nets greater rewards than focusing on efficient energy production. It costs roughly $10,000 more to build a house using sprayed-foam insulation, structural insulated panels (SIPs), and energy recovery ventilation than it costs to build the same house using sticks and fiberglass—and the payback is about 8 years. It costs an additional $10,000 to $15,000 for a geothermal system, which comes with a 25- to 40-year payback.
What Comes First
Our eyes can be bigger than our stomachs, as my dad used to say, and that applies to all the energy-saving upgrades we may want to use. If we insist on wanting everything, we may end up getting nothing—or very little—and moving into a poorly built house. I favor concentrating the budget for energy upgrades on things that would be very expensive to upgrade later, like windows and wall or subslab insulation. The better the building envelope keeps the interior at its conditioned state, the less it matters how efficient the HVAC equipment is.
My heating contractor once asked me, when I demanded the most energy-efficient furnace for a new home on a modest budget, “Don, which client gets the better deal—the one who gets 95% of the heat from an 85% efficient furnace, or the one who gets 60% of the heat from a 95% efficient furnace?” Furnaces don’t last forever, and when it comes time to replace them, we may be in a better position to install a geothermal system.
In a similar way, we may want to include the most durable roofing or siding or flooring, but if including those things means the whole house will be unaffordable, we might want to consider holding our noses and installing the more-affordable materials, knowing that, yes, they will make one trip to the landfill, but by then, we may be able to afford something more durable. Sure, good-quality steel roofing can last for a very long time, but it can cost 5 times as much as composition shingles.
As a general contractor and project manager, I’m involved with the client from concept to commissioning. As someone informed about building science, I find that my job places me at a crossroads. I want to provide the greatest comfort and sustainability while staying within the client’s budget. So what guides can we use to give us the greatest energy efficiency at the lowest cost? We have to follow building science, but we have to consider design and lifestyle as well.
Stick to the Basics
I start with the basic principles that govern how energy crosses a building enclosure: convection (air leakage), conduction (movement through walls, for example), and radiation (of sunlight through windows, for example). I choose building components that best address energy flow by design, and that require proper installation, but not extra labor and skills, to make them work.
Can we build an energy-efficient, stick-framed envelope insulated with fiberglass? Sure, but it takes a lot of work and requires skill, persistence, and a ton of caulk. Air leaks through stick-framed walls at the top and bottom plates; between the drywall and the sheathing; around windows and doors; and through light fixtures, switches, and outlets.
We can still use stick framing and dramatically reduce air leakage with properly applied sprayed polyurethane foam, reducing the need to caulk holes from wiring or plumbing. Foam costs 3 or 4 times as much as fiberglass, but if it’s applied as directed, it fits tightly, insulates, and doubles as an excellent air seal—far better than fiberglass. If we’re concerned about heat loss through studs, we can either sheathe the exterior with rigid foam sheathing, or better yet, use SIPs, which eliminate a great deal of framing lumber.
I spray open-cell foam directly to the underside of the roof deck, from the ridge down to the tops of the walls, creating a conditioned attic. This stops air leakage to the outside through any penetration in the ceiling, eliminates the need for roof ventilation, and does not, in my opinion, lead to premature deterioration of the shingles. All HVAC supply and return ducts are within the conditioned space, access to plumbing and wiring in the attic is simplified, and recessed ceiling lights need not be airtight or protected from insulation. Admittedly this insulation method costs more, both because foam costs more than fiberglass, and because there’s more surface area to cover. Nevertheless, foam seals out air leakage better than fiberglass, and the home’s energy performance is greatly improved.
Framing with SIPs is faster and simpler than stick framing. An additional benefit at gables is to install SIPs that are continuous from the top floor up to the roof deck. This eliminates thermal bridging through the top plates, and the need for gable end trusses.
Are there yet other ways to build even more energy-efficient envelopes? Sure, but let’s always keep the client’s budget in mind. PV panels for a net zero home or using extra-large amounts of insulation are expensive choices and come with a very long payback. Installing 14 inches of rigid foam under the basement floor alone cost about $10,000 in one Passive House project I read about.
It is crucial for someone, such as the designer, the general contractor, or the project manager, to understand how one subcontractor’s work affects the performance of the whole project. A few years ago I was called to remedy an energy performance problem in a very large and beautiful home. The home had three geothermal systems and zoned heating, and yet the bills for heating alone were about $1,000 a month in the winter. Furthermore, the humidity, even with humidifiers, hovered around 10%.
The owner had wanted to be involved hands-on in building this home, so he decided to be his own general contractor, hiring a draftsperson and all his own subcontractors. The owner understood the need for structural framing, insulation, attic ventilation, and efficient heating systems. Most of the subs were competent in their own respective roles, but none of the subs understood the building science of the home’s envelope, or how each one’s work affected the entire project.
Poking our heads above the main-level vented soffit, we could see the tops of recessed ceiling lights in the kitchen, and see all the way across the house to the opposite side. The air barrier was entirely missing, allowing outside air to wash across the whole ceiling. The second floor had air leaking through fiberglass insulation on the ceiling, down interior cavities, and throughout the whole house. Most of the return ducts in the upper level were open to the attic, sucking cold outside air into the house. And finally, the three heat pumps had been improperly installed, so that the whole HVAC system was operating inefficiently. Either all three operated simultaneously, or only one operated at all, recruiting the electric-resistance heat when it was on.
I wish I could tell you how it all turned out, but after we sealed the air leaks in the envelope, the owner turned the issue over to the heating contractor and the heat pump engineers. Clearly, a good understanding of building science on the part of anyone in the process could have prevented this debacle.
Clients usually care much more about the aesthetics of the home than the envelope technology, as well they should. A lesson I learned from a client about blending aesthetics with energy efficiency started me on a journey learning about the value of design. In 1995 an owner wanted me to build a Victorian home, but decided to orient the long axis north-south, resulting in a large amount of glass due east and west (picture a floor-to-ceiling, wall-to-wall sunroom window, unshaded and facing due west). What little glazing faced south was also either unshaded, or behind the roof overhang of a 12-foot- deep veranda.
I was perplexed, thinking the house had to follow all the rules about overhangs and the proper amount of glass facing each direction. However when we had the home HERS rated, it became the first 5-star home in Iowa—thanks to the other details of the building envelope, and the energy-efficient heating, mechanical ventilation, and sealed-combustion water heater. I had to admit that the owner’s decision to take advantage of the view and natural light, rather than choose the optimal orientation and amount of glass, made the home more enjoyable to live in.
While this next example is for remodeling an existing home, the same principle of squeezing the most use and value out of every square foot applies to the design of new homes as well.
Architect Sarah Susanka, author of the Not So Big House book series, expanded my appreciation for design as a tool for increasing the efficient use of a client’s budget and the enjoyment of the space. She tells of a client who hired her to design an office addition to his home. Upon visiting the home, a simple, one-and-a-half-story Cape Cod, she learned that the owner had a desk that he frequently used for working, reading, paying bills, and so on. This desk was an heirloom, handed down through several generations.
Susanka suggested that rather than adding on and going through the expense of building a whole new room, the client add dormers to the upper level. The dormers were designed with a half-round window and a barrel-vaulted ceiling. Susanka designed the windowsill to be the same height as the desktop, so that when the desk was slid next to the window, the desk and window seemed to become a single unit, and the soft reflection from the barrel vault illuminated the whole area.
So without adding one square foot of floor space, she made the existing space much more attractive and useful, and did it at a fraction of the anticipated cost.
Here are some of Susanka’s ideas for reducing the size of a home while making it feel more spacious.
Diagonal view. The diagonal view is the longest possible view in a house. Having an unobstructed diagonal view gives the feeling of spaciousness.
Focal point. Create a focal point at a distant location to attract the eye. Use a contrasting design, a photo, a geometric shape, or even the bright light of a window.
Double duty. Save floor space by doubling up on function. Widen a hallway to include a washer, dryer, and storage, thereby saving space that would otherwise be used for laundry. You can also save space by using an area such as the dining room to double as work space.
Multiple lighting schemes. Borrowing from Susanka’s ideas, we once enabled a client to afford things he would otherwise have had to forgo simply by trimming 4 feet from a house plan. The client wanted window seats across the entire length of a 28-foot wall. By reducing the wall to 24 feet on the first floor, second floor, and basement, and including one window seat in an adjacent wall, we saved the owner well over $33,000. With the savings he was able to purchase a geothermal system, high-efficiency appliances, and custom cabinets. See Figure 1.
If we plan to stay in our home after our children are gone, after we retire, or if our mobility changes, we may want to renovate that home. Here are some ideas that we can incorporate into a new home that will improve our lives and save considerable renovation costs.
To make the entry and hallways more accessible, we can
- provide t least one no-step entry, preferably from the garage;
- design all hallways with a 60-inch turning diameter; and
- combine uses for hallways by adding storage closets with adjustable shelving, a washer and dryer, or a shelf to hold packages.
To make the stairs more accessible, we can
- design them 48 inches wide, to accommodate a future stair lift;
- plan for a future elevator shaft by stacking closet spaces basement to top floor; and
- design a U-shaped, carpeted stairway to reduce the chance of falls.
To make the kitchen more accessible, we can
- install full-extension drawers for easy access;
- design pull-out counters from base cabinets with knee space underneath;
- design a base cabinet on casters that rolls out from under the sink, for knee space;
- install cooktops and ovens with controls in front;
- install a wall oven; and
- design low countertops, or counter tops of different heights, with rounded edges.
To make bathrooms more accessible, we can
- mount sinks on a wall or pedestal, or close to the front edge of the counter;
- install toilets, with seats 17–9 inches the floor ;
- design low- or no-curb shower stalls with built-in seats; and
- preinstall lumber backing for future grab bars.
And for general accessibility throughout the house, we can
- install electrical switches 42 inches, and electrical outlets 18 inches, above the floor;
- design all doors, including pocket doors, to be 36 inches wide;
- install casement windows; and
- install windows designed to provide natural lighting.
Are our homes energy efficient, or are we? It’s not often that we get to see data that demonstrate the relationship between lifestyle and energy use (see Figure 2). The data shown in this figure raise many questions as to what strategies designers and HVAC contractors can use to balance occupants’ energy use with their lifestyle, and make homes more affordable to buy and maintain.
In 2011, the South Mountain Company in Martha’s Vineyard, Massachusetts, built eight Cape Cod-style, two- or three-bedroom homes, all with the same floor plan, except that half of them had the third bedroom added to the back of the house. All of the homes had a 5kW PV array and were heated with a single air source heat pump (ASHP) designed to condition the entire home. Bedrooms had auxiliary radiant-heat panels. All of the homes were oriented alike, were exceptionally tight, had double outside walls with cellulose insulation, and were built to be potentially net zero energy. After the homes were sold and occupied, they were monitored for itemized energy use for a full year.
The results showed that two of the homes achieved net zero; some were a little over; and some used as much as 75% above the 5kW PV output.
One might expect that the two-bedroom homes, being smaller, would have used the least amount of heating energy. But in fact, both the greatest and the least amount of heating energy were used in three-bedroom homes. Two-bedroom homes are most often occupied by couples without children; three-bedroom homes by couples with children. With children, the parents would more likely keep the bedroom doors closed, requiring the use of radiant panels and eliminating the benefit of the single ASHP.
Given the disparity, what could the designer and heating contractor have done to accommodate the different lifestyles?
Get more information on Sarah Susanka’s Not So Big House book series.
Proskiw, G. Identifying Affordable Net Zero Energy Housing Solutions. Report prepared for Alex Ferguson, Sustainable Buildings and Communities (Housing Group), CanmetENERGY, and Natural Resources Canada, 2010.
Here are some possibilities:
- Integrate the third bedroom deeper within the floor plan to reduce the amount of cold wall surface, especially on the north side.
- Install jumper grilles with ultraquiet fans to circulate air through the bedrooms, and engineered to eliminate or greatly reduce the need for radiant panels.
- Install another ASHP instead of the radiant panels.
In these projects, how could the roughly $35,000 cost of PV have been otherwise applied?
My point is not to criticize the developer’s efforts; they were remarkable; and the data are a lesson for us all. For me, those lessons were: Get to know the client better and accommodate the client’s particular needs. Don’t waste material or floor space that won’t get used, but try to get the greatest value out of the client’s budget.
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