Lessons Learned

I thought I would share my experience with the Passive House (PH) design system, and relate how it works with LEED.  I had been enamored with PH for some time as a rigorous energy design system.  Having many years of experience in construction and being reasonably computer savvy, I ordered the PH software about six months before I began construction, thinking I could work through the logic and design my own home. 

I gave up after six months of trying to deconstruct the logic and hired John Semmelhack of Think Little.  As it turned out, John is the chair of the Technical Development committee for Passive House US (PHIUS).  He is familiar with a number of the different energy modeling software applications, and was able to complete the modeling on our home in about one day.  With his facility in performing the calculations, I have no reason to attempt to learn the software as I can rely on his expertise.

Though John was able to get our design to comply with the PH requirements of less than 0.6 Air Changes per Hour (ACH), and 4.75 kBTU/(ft²yr), the cost of achieving that exceeded our budget.  The primary driver of that cost was the building geometry.  Since a primary objective was to build a barrier free home, we designed it all to be on one level.  This meant that the ratio of exterior wall and roof area to the floor area was not optimal for thermal design.  It was more important to us to have the barrier free design that to meet the PH requirements, though we came very close.  We exceeded the air infiltration requirements by getting down to 0.44 ACH, but only got down to 7.20 kBTU/(ft²yr).  The only changes we made from the original PH design was to reduce the thickness of the perimeter walls from 22” to 19”, and specify a window that was not quite as high performing as the one that would attain the PH rating. 

The savings allowed us to purchase a ground source heat pump which performs both heating and cooling for us.  Due to the efficiency of the thermal envelope, the heat pump we purchased was the smallest one made, and we are only using half of that capacity.  If the next owner chooses to finish the attic, the heat pump will be more than adequate to the task.  As we get older, our thermal comfort will become more and more important, and having this thermal control will be a benefit.  I also work out of our home, and my productivity is tied to my thermal comfort.  The PH design did not include any cooling, so this was ultimately a good choice for us for the long term. 

There is some tension between the advocates of Passive House and LEED, though there need not be.  Passive house is strictly a building energy model that deals with the energy efficiency of the home.  It operates beautifully within the Energy and Atmosphere section of LEED to maximize energy efficiency.  However it does not deal with any of the other environmental best practices described by LEED.  LEED is more holistic as an environmental standard, considering other tangential energy inputs such as the energy costs of commuting to the site and material delivery.  However LEED does not mandate the strict energy requirements of Passive House. 

My goal in implementing Passive House standards was to develop a return on investment that would pay for all of the energy costs of the building for the lifetime of the building (which I hope to be 100 to 200 years) within the first 5 to 10 years.  We implemented the most energy efficient envelope, appliances, and alternative energy sources we could afford in a coordinated effort to achieve that goal.  Time will tell what the actual return will be. 

Things we would do differently:

The dual stud wall was designed to eliminate thermal bridging.  With the 4” of rigid insulation on the outside, we do not have any thermal bridging, so we had some added labor for the wall construction.  Constructing the walls out of 2x10 material would have simplified the erection process, but the materials would have cost about $500 more. 

I would have been more adamant about the concrete sealer.  Due to poor communication on my part, the material we have is like a hard shellac.  It scratches easily, and in the space of a couple of years is going to look terrible.  At 9:00 every night our two cats start chasing each other around the house.  When they try to get traction on the smooth floors they look like Willey E. Coyote spinning his legs and they leave scratch marks on the finish as they skid to a stop.  What I had wanted was a concrete hardener which would have served roughly the same purpose, but not have been as shiny.  This would look like the concrete floors you see in most of the large box retailers like Home Depot.  We could apply a wax to it to prevent staining and would produce the same polished finish.

I wish we had thought of the cedar shake shingle as a siding material earlier.  We committed a lot in labor and material cost for the installation of the plaster lath.  The cedar looks much better than the stucco would have, and the whole house sits much better on the site for the change in materials.  In hindsight, the stucco would have been a boring finish. 

Things we love: 

We love the clear span concrete in the basement.  Not having a beam and columns in the basement provides a lot of options for use.  We had designed the basement for use as a storm shelter, storage, and mechanical room, but it is going to take on a more prominent role at some future date. 

We love the concrete floors.  The finish notwithstanding, cleaning the floors is a breeze.  About five minutes with a dust mop cleans the whole house, then a little bit of damp mopping here and there periodically as needed.  We do have some area rugs for color, comfort, and acoustics in a few areas, and we need to drag out the vacuum for those, but it only takes about another five minutes to finish the vacuuming.

We love the Serious windows.  These are extruded fiberglass windows, and have a somewhat commercial storefront design to them.  They perfectly frame the views we had hoped to capture, and the thermal comfort is superb.  We have tested the temperature at the window ledge at one degree of difference from the center of the home when the outside temperature was 50^o F lower. 

We love not having any drafts.  After living in homes that were over 100 years old for the last 30 years, we have had no complaints about drafty conditions.  Even though there is a lot of glass, the thermal efficiency of the window does not even generate any noticeable convection to cause any discomfort.

We love the radiant floor heating and cooling.  Warm toes make a great difference in thermal comfort, and we really enjoy the even heat that is distributed throughout the house without the air currents of a forced air system.  The same goes for the cooling.  This summer was especially hot, and we could feel the coolness radiate from the floor.  After working outside installing the siding this summer it was a welcome relief to come in and recover on the cool floors.

We love the Energy Recovery Ventilator.  We had some issues with the installation.  We had some testing done to see if it was delivering the proper amount of air, and found that it was short about 30%.  When the power failed once during the summer, we felt as if we were suffocating within about 8 hours from lack of oxygen.  We had installed flexible ductwork in the basement to the ERV, which is not as efficient as metal ductwork.  When we changed it to the metal ductwork, we were able to operate the fan speed on the low setting and feel just as comfortable as we felt previously when it was operating on the high setting. 

We love our yard.  We opted not to have a lawn and enjoy nature right up to the edge of the house.  We installed a six foot gravel rainwater collector around the perimeter of the home to hold back the vegetation, and planted a no mow native plant species for the first 20’, then planted prairie grasses over the rest of the disturbed areas of the site.  Some of the grasses are designed to attract wildlife, and one is designed to be shallow rooted wildflowers for over the drainfield.  Though we have not experienced a full year of growth, and it takes about three years for a prairie to mature, we are really looking forward to seeing this develop.

The rainwater harvesting system is something I wanted to do to test the economic efficiency of the technology.  I knew the economics would be marginal for our use as we only intended to irrigate the garden.  I did however really want to eliminate the need to clean out gutters on this tree lined site as we get older, and this presented itself as a solution.  We normally get 36” of rainfall in this region which is more than enough for any native plant life.  This year we experienced a drought that lasted nearly 8 weeks, and our cistern ran dry.  The next 8 weeks we had rainfall every few days and required no irrigation.  The right mix of capacity and need seems to be a function of rolling the dice.