Category Archives: Energy Efficiency

A New Way to Build


Published :    By : Merle      Cat :    Comments : 2

image 1

BT has always recognized the importance of energy efficiency in its building projects but it was obvious that we were going to have take our game to a whole new level for the Davis house. The main motivation for us was that the Davis project was going to powered by electricity only…no natural gas or propane was used because of the propane tragedy that caused the rebuilding!! Some of you might remember our dalliance in the early 2000′s with the “open stud”; in some ways, this is a continuation of that journey that had been on hiatus for awhile. See Image 1.

For some time now, BT has been exploring the concepts and working models of the Passive House concept.  A Passive House is a house that is built to use 90% less energy then a conventional house because it is built to such high energy standards that it can heated passively through solar gain and heat produced by the lights, appliances and humans that reside in the building. (see www.passivehouse.us/passiveHouse/PassiveHouseInfo.html‎ for more information) The Davis house is not a Passive House but it is a step in the direction of building with airtightness and conservation of energy as the primary goal.  Perhaps in the future, the Davis’s might decide to make the house a Net Zero House http://www.invisionzerohome.com/netzerohome/   by producing electricity with photovoltaic panels or they may decide to install a solar hot water heating unit to preheat water for the radiant floor heating and domestic hot water systems.

  image 2

The Davis home was a combination (hybrid) of a new stick framing system and a traditional timber frame with wood joinery. As with all stick frames, no one would know how the building is framed after the walls are covered. One can see clearly that the timber frame with its 3 interior posts are supporting the ridge of the building and carrying both roof load and second floor load.  See Image 2.

   image3  image 4

Here are the factors that helped us determine how the Davis project would be built: 

  • - We wanted to build a double wall house without actually having to build two walls–therefore we decided to let our local truss plant (Kenyon Noble Lumber Company) build our wall components and cut each piece to its finish length–thus allowing our carpenters to be assemblers rather than fabricators. See Image 3.
  • - We designed the system to use small dimension material primarily (2×4′s) and looked to minimize thermal bridging as much as possible. 
  • - We used advanced framing techniques (everything is lined up with rafters and floor joist landing exactly on top of stud) in this balloon frame to eliminate double plating and 11.25″ wide plates. 
  • - We worked on 24″ centers for all exterior wall and roof framing with 5/8″ exterior plywood sheathing and 5/8″ drywall on the interior of the exterior walls.
  • - We chose a system that was mechanically fastened rather than glued.  
  • - We wanted a thick wall for the architectural effect with deep shadow boxes on the exterior of building. 
  • - We chose to use dry-packed cellulose insulation (as opposed to foams) as much as possible to achieve R-values of 44 in the wall and 64 in the 18″ cathedral ceiling. 
  • - The insulation system is designed to be a continuous element between the wall and the roof. More insulation be added easily to the ridge of the building if there is settling in the walls. See Image 4. 
  • - We also aimed for an infiltration rate that was less 1 air change/hr at 50 pascals of pressure. Most modern houses average in the 3-5 air changes/hr…
  • - Because of the tightness of this home, we planned on using a fresh air system (Venmar AVS with ERV system) to supply  the house with fresh clean air. 
  • - The heating system is radiant embedded in a polished concrete floor that is powered by a Thermolec Electric Hot Water Boiler with a Napoleon Wood Stove as a backup heart source. 
  • - We used Sierra Pacific Windows (made from Douglas fir) that averaged near .30 U value. 

image5     image6     image 7     image8

How did it work out?

  • - The framing went fast and was fairly predictable for the time required to complete. The new version of the “open stud” worked great and saved a ton of time versus building two walls. 10% of the open studs has twist issues although most could be used. The framing details proved effective at using the minimal amount of wood possible and eliminating thermal bridging as much as possible. 
  • - The walls were amazingly straight and true despite the fact our walls studs were up to 20 feet long. The truss manufacturer counter balanced all the bows and then mechanically fastened them in a straight position. Amazingly they stayed straight. 
  • - The electrician loved the system because it required almost no drilling to run the wires. We did discover that his wires which sat on top of the interior stud connectors provided to be a choke point during the installation of the loose fill cellulose insulation. This was especially true if there were more than 2 wires on top of the connector. See Image 5. 
  • - The insulator learned that he couldn’t fill the wall cavity from the top of the balloon frame  wall-instead they had to fill in lifts. We’ll check the insulation level at the ridge this coming summer to see if it has dropped below the 18″ that we put in. If there is significant settling, we’ll add some more. See Image 6. 
  • - We had 10 days of below zero temps in December and had almost no condensation and subsequent freezing on the inside of the windows. That means that the fresh air system is getting rid of the humid interior air effectively. 
  • - On winter days with sun, the indoor temperature seems to be averaging 4 deg. higher than the temperature setting on the thermostat. That means that we are collecting some passive solar heat on our south windows and its being stored effectively in our 6″ concrete slab. 
  • - The house is very quite because of the positive sound dampening qualities of the dry packed cellulose insulation. 
  • - The jury is still out on the electric bill for powering the 3900 square foot house. Since the house is not being used this winter, the power company is not reading the meter because of a locked gate. Our first bill was $139 for a month and a half but we don’t know if that is  guess or based on an accurate meter reading. 
  • - The wood stove has proven an effective tool to warm the house up quickly when the radiant heat thermostat has been set low (60 deg.) when the home is not in use. 
  • - The thick wall detailing has proven to be a positive detail in the architectural appearance of the building. See Figure 7 and 8. 

Conclusion: We’re already planning our next project with this new “open stud” framing system. Now that we’ve successfully completed the Davis project, we’ll be able to improve some details and fine tune the product for maximum efficiency. The material costs are more when using this product but the labor cost is dramatically less than building a double wall building. Stay tuned for updates in the future……!!!!