What makes the Batesville residence 'net-zero' or 'energy-positive'?

Passive measures

• a well-insulated, airtight but vapor-open building-envelope to minimize energy-losses (R28 above ground walls, R24 basement walls, R26 slabs, R54 roofs, windows and doors with R11 triple-pane glazing and R7 wood-clad frames, Airtightness 0.34ACH @50Pa)
• generous overhangs for shading to prevent over-heating but allow solar gains in the winter
• exposed concrete floors, insulated from below, to provide thermal mass to help the house stay comfortable by equalizing temperature swings
• window and door openings are designed to allow for solar gains in the winter from morning and mid-day sun, minimize energy losses by being less in number or smaller on the north side, support cross-ventilation and natural cooling, and also allow for generous daylight, framingviews and providing generous indoor-outdoor connections in all directions

Active features

• the space conditioning system is comprised of two 1t ducted mini-split heat-pumps with variable speed compressors (a similarly sized to-code-home would need 4-6t of air-conditioning capacity), an ERV to provide continuous fresh-air ventilation, while preserving and transferring the energy of the conditioned exhaust-air to the incoming fresh-air
• a wood-burning stove with direct air supply and a sealed combustion chamber serves as back-up and atmospheric heat source on cold days
• hot water is generated by an electric heat-pump hot-water-heater that uses room temperature air to generate heat for domestic hot water, simultaneously dehumidifying the air in the basement
• LED lighting throughout
• energy-efficient appliances such as an induction cooktop and an electric heat-pump dryer
• the electric consumption is estimated to be 7,000-10,000 kWh/year
• a 7.2kWp photovoltaic array adjacent to the house is calculated to generate 10,000 kWh per year of solar energy. It will feed the grid with excess energy on sunny days, while the house will draw from the grid at night or on cloudy days. 
• the installed inverter already allows to plug-in vital appliances during a power outage. Upon market availability the owners plan to install a lithium-ion battery bank allowing the pv system to supply the house for several days.

Batesville House achieves 0.34 ACH50 in first Blower Door Test

Last week our passive house colleague John Semmelhack of Think Little, who has been assisting us with our mechanical design and is performing the quality control testing, performed the pre-insulation blower door test. Thanks to both meticulous planning and excellent execution with an outstanding result of 0.34 ACH50 / 0.023 ELA50!

(For reference, the Passive House Certification threshold is 0.6 ACH50 or 0.05 ELA50).

Airtight Construction: Don't buildings need to breathe?

No / it depends what 'breathing' means.

First of all, the buildings' occupants need to breathe: Fresh air, either supplied through windows and doors, or by a fresh-air-ventilation system in connection with an energy recovery ventilator (ERV).

'Breathing' in the context of the building envelope, especially in connection with energy-efficient construction, is not just a waste of energy, but can actually cause problems, if breathing means air, and therefore moisture infiltration, through cracks and holes in the building envelope. Scientific testing has proven that the amount of moisture traveling through a one square-inch hole in a wall, equals 100 times the amount of moisture traveling by means of diffusion through a 4'x8' sheet of drywall. In older poorly insulated buildings with thin walls, this usually doesn't cause much of a problem, since there is enough drying potential in either direction, but in buildings with a higher degree of insulation, thicker walls and possibly vapor retardant components, this can lead to moisture being trapped, and therefore to rot, mold and decay. 

That said, for a mixed-humid climate as present in Virginia and the mid-atlantic states, we recommend vapor-diffusion-open envelope assemblies, which are often described as 'breathable', meaning that the wall or roof can dry either to the outside in winter, or to the inside in summer. 

So, what components function as an air-barrier, and where is it located in the Batesville house?
The concrete in slabs and basement walls is naturally air-tight. The continuity of this air-barrier to the air-barrier in the exterior walls is ensured through special tapes and sealants. In this house, the plywood sheathing functions as an air-barrier. The studs are glued and nailed to the sheathing boards, and all seams sealed with a sealant. We actually do have a belt-and-suspenders approach, because the 'black stuff' which we are mainly using as 'weather-resistive barrier' or 'bulk-water-membrane' also is an air-barrier. What is the 'black stuff'? It is a vapor-open, water-proof, weather-resistive-air-barrier-membrane. It is in place of house wrap, which usually functions as bulk-water-membranke, but isn't air-tight or water-proof. The product we used is actually new on the American market and the Batesville house is the first house where it is applied: It is called the 'Solitex Adhero' Membrane, essentially a polymer fabric, and made in Germany.  The original product, the Solitex Mento or Solitex Mento Plus have been on the market on both sides of the Atlantic for a long time. The Adhero is a self-adhering membrane, using the adhesive from the tescon air-sealing tape line, which are available in different perm ratings, depending on the application. Originally conceived as a roofing membrane, we are using the Mento Plus membrane in the roof both as air-barrier and as secondary water-proofing layer between dense-pack cellulose insulation and the vent-channel below the decking.  The entire Solitex line of WRBs, including ADHERO, is stocked and exclusively distributed here in North America by 475 High Performance Building Supply.

Concrete

Exposed, board-pattern concrete is an architect's favorite, however it often is cut out of the budget, since its the execution in a project demands meticulous planning and detailing, knowledge and experience of chemical reactions, influenced by the type and age of wood used for the forms, the aggregate size, amount of water, speed and continuity of pour, weather and much more. Once it is poured, it is what it is, and it takes a few days wait and taking of the forms to see, whether it was successful or there will be a tear-down and do-over. Daniel, even though he is a carpenter by trade, was thankfully up for the challenge - with an excellent result!

The concrete slabs - both interior and exterior - where poured by Danny Herring. Originally, the plan was to acid stain the interior floors, but now, that it is cured, the natural variation in color is so beautiful that we decided to leave it natural, as it is!

Basement Pour

On October 15th, after some torrential down pours earlier in the month, it was the most perfect fall day for the basement concrete pour! 

It is a little hair-raising to think 2 3/4" of foam are holding tons of concrete, which is usually poured into heavy wood, steel & aluminum forms, in place during the pour. However, Daniel and his crew had done excellent work in bracing the ICF to prevent blow-outs and to keep the walls from deforming during the pour, and everything went well and stayed in its place.

Styrofoam Lego

One half of the home will have a basement, the other half will be built over a slab on grade, which will be finished and exposed as acid-stained concrete floor in the kitchen, dining room and master suite. 

The basement gives us an opportunity to highlight the iterative design process and also the compromises it takes in order to built a beautiful home within a set construction budget. 

Over the course of the design process, we explored multiple options for both the method of construction and the finishes and appearance. We explored ICF (insulated concrete forms), finished in natural stone veneer; exposed, core-insulated, board-pattern concrete; concrete block with interior insulation and stucco finish. The exposed board-battern concrete would have been  visually and energetically preferred, however, since it is not common practice in residential construction in the U.S., it proofed to be over budget. Concrete block with interior insulation would have been least expensive, however, in matters of energetic and moisture performance, this was an inferior option. This lead us back to ICF with an EIFS (Exterior Insulation Finish System) Stucco finish for the less prominent basement terrace level. The carport walls, which are of high visual importance, will still be constructed in exposed board pattern concrete.

ICF are essentially like large blocks of Lego. Multiple options in regards of foam thickness are available on the market. Since we are not going 'all the way' to passive house, the standard 2 3/4" eps + concrete + 2 3/4" eps form, which equals about an R24 total, was sufficient.  The floating basement floor slab will be insulated with 6" of eps (expanded polystyrene), which gives us an equal R value and in connection with the ICF allows for thermal bridge free construction.

Breaking Ground on Plus-Energy Residence in Batesville

We are so excited! After 12+ months of planning we have been breaking ground in Batesville on September 4th!

In the architectural style of a contemporary prairie house, capturing mountain and meadow views, the energetic performance of this home is designed close to passive house standard, balancing cost of insulation with the cost of photovoltaics, in order to reach both optimal comfort and a net-positive energy balance within our clients' budget. 

We are excited about working with Daniel Ernst of Promethean Homes in taking the plans to reality!

Over the course of the construction we'll keep highlighting the steps of creating a super-insulated  airtight building envelope for a modern home in this blog! 

follow the project

New Form