So I just returned from today’s LEED Design Charrette and everything went very well. The bottom line is that we found out that reaching Platinum is possible with our design, but we have a few issues to clarify and iron out. Rob from MaGrann was extremely knowledgeable and taught us all a lot about the LEED process in the matter of a few hours.
Rob tallied a total target score of 87.5 points that would enable us to achieve LEED Platinum. Our square footage for the 100K House is just over 1,100 sf so we need a total score of 84.0 to reach LEED Platinum once the thresholds are adjusted for our home. There are two major hurdles we must pass in order to achieve this target score though.
- We must hit a HERS Index of 50 or below
- We must get credit for having a 2 bedroom home with our open floorplan
Achieving a HERS rating of 50 or below means that our home will be 50% more energy efficient than code or half way to being a zero energy home. Energy Star only requires a rating of 85 so we are significantly below this. The HERS Index works on a sliding scale with 100 being a standard home built to code and 0 equals a home that is zero energy. Each point represents 1 percentage point better than a code home in terms of energy efficiency. Getting a score of 50 is no easy task without a PV or small wind system to generate power but it is possible.
One of the things that is hurting us in the current design is the fact that we have spec’ed out a full electric house. While this simplifies the home, reduces the cost and allows us to convert to a truly zero energy home in the future, it is less energy efficient than using gas for water heating. For this reason, we are pretty sure that we will need to squeeze a solar thermal system into the budget. Other things that could be tweaked include the SIPs (going with thicker panels for higher R-Values) and the windows (lower U-Values). Either of these last two should not hit the budget too hard if we only need a minor push to get us over the edge. Alternatively we will need to consider gas for the water heating.
The other hurdle is getting the LEED raters to consider our plan to be a 2 bedroom home. According to code each bedroom must be a separate, closed off room with it’s own door and a closet. Our bedrooms do have closets but they lack doors. Even more troubling is that both bedrooms are open to the ground floor even if it is a small opening. If we are only considered a one bedroom home then our Platinum target rises to 95.5 based on our square footage and we are no longer within reach of the highest, shiny rating the USGBC offers.
The two bedroom dilemma is most disconcerting to us as we purposely designed the open spaces to facilitate natural airflow. This allows us to keep our HVAC system very simple, efficient and cost-effective. To remove those elements, destroys the design we worked so hard to create and the associated efficiencies. It also becomes a much more traditional home that will not have nearly the same appeal to those seeking modern architecture and design. Our main hope here is to submit a Criteria Requirement Interpretation (CRI) request to determine if the USGBC will interpret our home as two bedrooms regardless of what code says. Rob from MaGrann will be helping us out with this but the response time is not very fast, so we may not have an answer to this critical answer for some time.
So now the top priorities are to get our HERS form filled out with all of the current design elements and see where we stand. Rob will also begin investigating the probability of our home being considered two bedrooms also. Once we have more insight into these two issues, we should have a good idea if we can tweak our design into the platinum realm without exceeding out tight budget. Either way, I’m pretty excited as I never thought we would be able to even approach platinum on such a meager budget!