The Design Choices
SITING THE HOUSE
Early in the design we determined that we wanted to take advantage of the slope of the land to allow a larger window wall along the south side to support passive solar energy design. Once we chose the design-build team and discussed our thoughts, we all agreed that using this slope was important but we changed from a passive solar design concept to a LEED/Green/high efficiency house. After further discussion with the design-build team we agreed to push for Passive House certification.
THE FLOOR PLAN
Our original concept for the house was a ranch style house with all living spaces on a single floor so that as we age we did not have stairs to negotiate. The advantages provided by a due-South facing slope on our property and our desire to avoid clear-cutting the hardwoods made us migrate the design to a ranch with walkout basement. In the early stages of design the basement was going to be about 1/2 the size of the main living floor with a poured slab on the other half of the house. During the process we found that drainage issues and the grade of the land meant a slab would not be the best option since it would require as much as 8' of backfill. We also found that building the walls as a single unit from the footings to the top of the main floor was much more desirable and cost effective.
The biggest departure from the normal Passive House construction that we are making is our choice of wall systems. Our builder has teamed with Ideal Building Systems to construct pre-cast concrete walls with several layers of insulation to form the envelope in passive house construction. The use of this system provides an the foundation for an air tight envelope because the panels overlap slightly and the entire butt-joint is sealed with an air and water tight sealant. For our application these panels will be varying width but will typically be 20 feet tall. The R-factor for these walls is planned to be around R-40 which is important to maintain near-constant temperatures in the house without the wide temperature fluctuations like those in our current rental house (and yes, the recent GBA Blog on sealed crawl spaces looked like someone took a photo our crawl space!). One of the benefits (or limitations depending on your viewpoint) with this type of system is that any envelope penetration has to be planned in advance. Cutting reinforced concrete for job-site changes is very difficult and time consuming (but not impossible). This includes any penetrations for doors and windows, ventilation ducts, and any other large openings required so our early planning included constantly reviewing the design for placement of all those openings.
Having lived in Europe for 5 years, we developed a strong liking for the tilt and turn windows common in Germany and Belgium. For those that aren't familiar with that design, it is essentially a casement window which also opens like a hopper window (both in-swing on the same movable part of the window). As part of or PassivHaus certification we are specifying high efficiency, high solar heat gain triple pane windows that are also low-E. We have been unable to find windows manufactured in the US that meet our requirements so we are currently narrowing our choices down from several suppliers in Germany, Lithuania, and Canada. Cost and quality concerns have narrowed our search criteria to vinyl or fiberglass windows. The drawing shows a 4-lite window which nearly every manufacturer has told us significantly increases costs. The costs are related to having to build essentially an individual window for each of the lites; in a double-pane construction the manufacturer simulates the lites by inserting mullions between the two panes but they don't have that ability for triple-pane windows. An additional cost driver is the tilt and turn hardware. Both of these choices are important to us and we are willing to adjust the number of lites in our windows to ensure they are not budget busters. As for skylights we are still researching but we have found that the majority of skylight manufacturers simply don't offer high-efficiency units. One positive find in recent days is nanogel which is a silica gel product that provides high R-values (1" = R-10) and it available in one or two manufactured skylights but there is also an after-market producer of custom sheets that can be used to increase the efficiency of skylights. The product does act like a light diffuser and reduces the visible light transmission to some degree so we have to evaluate the benefit cost of using that gel.
We do not like the appearance of asphalt shingles and therefore we researched alternative roofing systems. We have always liked metal roofs and after discussion with our architects we all agreed that this design deserved a standing seam metal roof. We chose standing seam because we like the looks but also because it uses a concealed fastener system. We are only installing gutters at the main entrance and one walk-off area along the west end of the house - the dogs simply refuse to walk through a wall of water to do their thing! We are also going to install mounting plates for future addition of solar devices (PV or hot water) should we find the need.
We are currently anticipating a mixture of cork and hardwood flooring (but no shoe molding!) and marmoleum flooring (sheet) in the bathrooms. One of the early concessions we made was to forgo the underfloor heating systems in the majority of the house but that concession did not extend to the master bath. There are just some things one doesn't give up. For the laundry room we are looking at marmoleum and that may also be installed in the workout room due to the moisture resistant qualities. Stained concrete isn't in our current plans but as we progress in the finish planning that may change.
During the majority of the design phases we had 10' ceilings in all but the family room which housed the clerestory but we recently changed that design to vaulted ceilings in all but the main (East-West) hallway. This change was important to eliminate the 'dead space' between flat ceilings and the super-insulated roof which could trap unwanted moisture and grow "funky stuff" in the words of our build team. The main hallway is currently envisioned to have 10' wood-slatted ceilings interrupted only by the cross-hall from the front entry to the 6' x 12' window on the south wall. A skylight is currently planned for the central hall and glulams will be used to accent/define the rooms. For those wondering, the roof is a 4:12 pitch so the slope of the ceilings won't be too dramatic - though this will present some potential challenges in the lighting design. Our intent at this time for lighting is to use LED lights wherever possible throughout the house. We had the opportunity to view a local manufacturer's product (CREE) and the brilliance of the colors on everything was remarkable when viewed under the LED lighting as opposed to under the incandescent lights.
I've already talked about the glulams and the wood-slat hallway ceiling inside the house for highlights. We are using wood grained vinyl for the door and window interior surfaces and the other trim will all be natural wood. For the exterior of the house we are having the pre-cast broom finished. The red color you see in the artist's rendering are intended to be stand-off panels while the "wood" will be hardi panels spaced to provide an interesting shadow detail. We have chosen not to go with standard garage doors but have rather chosen to install a set of recycled oak carriage house doors. The current plans are to put those on a track system so that both can be moved to one side using an automatic gate opener to avoid the manual strain of moving 300-plus pound doors. The colors are still under consideration but we believe the pre-cast panels will be painted with an elastomeric paint in a light brown, the wood in a darker wood-color, the doors in a burgundy while the window sashes will be a golden oak. The roofing is currently planned to be a light gray color both for the reflectivity characteristics as well as the intent to blend it with the surrounding trees. Landscaping is being designed by a local architect to compliment the design of the house and blend into the natural surroundings. We are also well aware that deer frequent the property and that ticks and chiggers thrive in this area of the country. Our landscape plans are to use the natural "deer-resistant" nature of some plants and to do our best to provide a tick-repellant border to areas we will frequent with the dogs. We also have several nice white oak and magnolia specimens that will figure into our landscaping plans.