©2013 Green Building Advisor. From The Taunton Press, Inc., publisher of Fine Homebuilding Magazine.
[Editor's note: Roger and Lynn Normand are building a Passivhaus in Maine. This is the 18th article in a series that will follow their project from planning through construction.]
Is it possible to tweak the design of EdgewaterHaus to simultaneously get more energy performance from the building, pay less to build it, and still keep about the same square footage and floor plan?
We liked the aesthetics of the design and floor plan, except for a few niggling concerns. To maximize solar heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss. for the Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Planning package energy analysis, our architect Chris Briley made the windows on the south facade as large as possible. The bottom of the windows are set just high enough off the floor so we don’t need safety glass, and the top of the windows are less than one inch from the ceiling. We never really liked that look; it doesn’t leave any room above the window to install interior shades. A lesser concern was the roof truss over the family room limited the depth of ceiling insulation we could apply near the eaves; we’d have to substitute higher R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. but more expensive spray foam to maintain a consistent R-value in the ceiling.
But these were quibbles. So why, you ask, would we want to change anything besides replacing the Unilux windows we have now rejected because of their poor customer support?
Cost. Costs have grown — a lot — since we started putting dollar signs in front of the many building categories. More than we expected or felt comfortable with. It wasn’t a matter of affordability, but a decision of how much of our assets we wanted to sink into EdgewaterHaus, vs. other desires such as world travel. The cost of EdgwaterHaus was on a bad upward trend, and we hadn’t even started construction yet!
We had to put EdgewaterHaus on a diet. Where to start? We asked Chris, Marc Rosenbaum our energy consultant, and Symphony Construction, our notional (we never did sign a contract) builder, for ideas.
Some things were easy to spot. The amount of stonework had nearly doubled. The stone plus installation cost about $40 per square foot. We eliminated the stone flanking the upper portion of the family room bump-out and the less visible east side of the house.
There were six stone planters leading to a trellis made of five parallel stainless steel cables stretched above the windows along the south facade. Ivy would grow along the trellis to shade the windows in the summer. The leaves would die in the fall to again allow the sun to penetrate through the windows to heat the interior of the house. But we’re talking Maine, and the PHPP identified only a few weeks of potential overheating. The minisplit heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump. system we will use for heating also provides air conditioning; overheating solved.
More importantly, have you ever tried to tame ivy? You can’t. It spreads uncontrollably, and grips tenaciously. I pictured myself perched on a ladder several times each year yanking ivy off the stone, the siding, the metal roof , the solar collectors, and the windows. I have seen ivy grow through a closed window into the house!
Good-bye trellis. We could also pass on etching a color into the concrete for the lower level.
Symphony suggested we abandon the Passivhaus standard and cut back on the “excessive” insulation levels: reduce the amount of rigid foam under the basement slab and the depth of cellulose in the walls and ceiling. Lynn and I talked about that, but I wasn’t ready to give up on Passivhaus. Still, we felt the need to identify other savings opportunities.
I kept looking at the study on the west wing of the house. With its unique foundation, slab-on-grade, and roof trusses, the study seemed like a misfit appendage to the west wing of the house. The deep, sandy soil on the site would likely require excavating this area to nearly equal that for a full depth basement. Its small floor-to-wall ratio and four exterior corners hurt PHPP energy performance.
We would have to bury a tube in the concrete slab to carry condensation from the minisplit (HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building.) wall cassette on the exterior wall of the study to the plumbing in the basement. Would that buried tube become a future headache?
Could we redesign the west wing of the house to pull the study within the rectangle of the house while also reducing the width of the entire west wing, so the square footage stayed about the same? That would simplify excavation, erecting the foundation, framing the walls, and eliminate one type of roof truss.
From a PHPP perspective, the study would now be part of the larger, rectangular floor to wall ratio. The consensus was this was no home run, but perhaps a base hit on energy performance and another on cost savings for material and assembly. Chris said it would be a small redesign effort. So let’s do it!
Image #2 (below) shows the revised floor plan. Note how the study is now part of the rectangle of the west wing of the house. It’s now excavated the same way as the rest of the house, with the same approach for the footers, foundation, walls, and trusses. That should cost less for material, time and labor. The floor-to-wall ratio is better, and there are four fewer corners to improve energy performance.
It turns out this redesign led to other positive benefits. I suggested we flip the position of the his/her closets with the master bath. That brought the plumbing runs in the master bath some 35 feet closer to the core of the house, nearly above the mechanical room in the basement. That helps PHPP energy performance more than you might think.
Ready to take a hot shower in the morn? You turn on the hot water and wait to purge the cold water in the pipes before the hot water arrives and you step into the shower. You just wasted all that cool-to-warm-to-now-hot water down the drain. Now why did none of us think of this before? Walking a few extra feet to the bathroom will also provide better sound isolation when one person is showering and the other still asleep.
We ended up with an small net increase of 87 square feet – we cut 25 square feet from the main floor, but added 112 square feet to the lower level. In Passive House parlance, we reduced the main floor's “treated floor area” (a measurement that excludes walls and stairs) by 70 square feet, and added 112 square feet of TFA to the lower level.
Chris also revised the window dimensions on the south facade. Reducing the window height cut 25 square feet of south facing glass. That will hurt us on PHPP, but allows us to install interior shading devices above the windows and still show about 6 inches of wall. It also allowed Chris to have the trusses bear on the top of the south wall rather than hung on metal hangers, which will provide more head room for cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection. in the ceiling.
But wait, there’s more. The “her” closet had become too big — much too big, Lynn agreed. It was big enough to be a bedroom. There didn’t seem any convenient way to reduce its size without creating other layout conflicts. Hmmm... In a moment of seeming clairvoyance, the problem became the solution: let’s make it a legal bedroom. We will likely use it as a closet/storage area, but future owners could use it as a bedroom — say to monitor an infant sleeping nearby. At 4,400 square feet, a five-bedroom house is more appropriate than one with four bedrooms. Conveniently, this will also help us on LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. scoring and the revised green appraisal we are awaiting.
So did the redesign simplify construction, improve energy performance, and reduce cost?
We haven’t run a cost analysis or energy performance calculation yet, but we are confident we have been successful. Perhaps more importantly, we like this revised layout even better than the previous one.