From the start, we intended to have an air-to-air heat exchanger in our new home. Regular exchange of inside (stale) air with outside (fresh) air is necessary in any building to maintain good air quality. Bringing in some fresh air and exhausting moisture, odors, and gasses that accumulate minimizes problems with moisture and maintains good air quality, without opening a window. This transfer of air between inside and outside causes a loss of heat in cool weather and an increase of temperature during warmer weather and affects the inside temperature.
Regardless of more stringent building codes, a standard, stick-built house has numerous cracks and crannies that allow exchange of inside air with outside air. An owner doesn't have much control over this. In the numerous vent holes and spaces around pipes and wires, there is an abundant transfer of air, regardless of the weather.
However, when done according to specifications (mastic between and tape over all seams), SIP construction greatly reduces air leaks and heat transfer. So in a home like ours, with SIP floor, walls and roof, seams sealed, we needed to balance the need for fresh air with loss of heat on cool days. After all, we are seeking efficiency in every way. Also, we have hydronic radiators, not a ducted, forced-air heating system.
We wanted and specified to our contractor a cross-flow, air-to-air heat exchanger , which is a heat recovery ventilator for the entire house. It would transfer heat from the outgoing indoor (stale) air to the incoming outside (fresh) air. This results in significant savings in the cost of heating or cooling a house and conditions the inside air. And this influx of fresh air is controlled: the fan is relatively low power but runs continuously, or on a timer, or other schedule.
Our general contractor's adamant refusal to install a heat recovery ventilator wasn't just strike one in our relationship with him. At that time, we rationalized that there wasn't all that much efficiency and cost saving of having one. But what we noticed later was that there was no provision for whole-house ventilation and that the construction of our house would not meet the Washington State Ventilation and Air Quality Code.
Too late by our judgment, but nevertheless, after attempting to gain compliance with our requirements, we terminated his contract (for numerous reasons) and with a house half complete we began making the best of a difficult situation.
Our own contractor now, we talked with a heating subcontractor about meeting the code, and most importantly, maintaining indoor air quality. We agreed on a relatively simple solution. We installed four vents at critical places in the outer walls. And we programmed the heating control system to cycle the two bathroom exhaust fans on and off on a regular schedule to push stale air out and pull in fresh air through those vents. We also measure indoor relative humidity and CO2 levels, and when either of these rises past s suitable level, the control system runs the fans until the level subsides.
Our results so far:
Given the values indicated by the indoor sensors, we feel our solution is working well. We are tuning the schedule for cycling the fans. Given there is no way to reduce indoor RH when outdoor RH is above 90%, we are considering a dehumidifier for the spring and fall times when the outside temperature is above 50 degrees.
When Maura and I dreamed about our house-to-be years ago,, we though of engaging local craftsmen and managing the construction project ourselves. We read books by contractors and learned about all steps and the paperwork that is necessary. We knew that the sum of our experiences would help us be successful in a project as complex as building a house.
We learned several things that changed our plans. First, at that time banks were reluctant to finance an owner-builder construction loan. To compensate for the additional risk, the lending officer insisted on additional points (a fee that is a percentage of the entire loan amount) as well as charging a higher interest rate over the life of the construction loan and the mortgage. That amounts to quite a premium.
We learned also that the local craftsmen were not visible to us except through the phone books, and we had poor luck in contacting those listed there. We learned only later in our project how to find them.
We worked with a big-city contractor to formalize our house plans. We were amazed at how much money it took to realize such a small amount of value as we refined existing plans. Then we looked at the size of construction loan that a “time and materials” contract would require (this was the only type of contract they would offer). It was clear we needed to look for a way that would fit our incomes.
We began to work with a Seattle franchise of national construction consulting business, thinking that we could manage construction with some assistance. The short story is that this company was unresponsive and really not up to providing assistance with building the type of custom house we planned. Then we looked for recommendations from the manufacturer of the SIP materials we would use. Even then, we continued a search for local craftsmen who had experience building an SIP house. It was only after much frustration and with reluctance and deep concern that we agreed to work with a specific general contractor.
In short, we had chosen a predatory mercenary who bullied us to do things his way whenever we got specific about the construction plans and requirements of the SIP. In addition the work of some subs was obviously, even to us, shoddy and thoughtless (confirmed by later examination by experienced construction people), and unsuitable for a house in our climate. We terminated that contract after we were unable to gain compliance with specs and plans.
After 12 months of sloppy and intermittent work done by the subcontractors we had 45 per cent completion of the house – and were faced with additional fees from the bank for extensions, as well as continuing rental on the house where we were living. In the four months after we took over the project and engaged local craftsmen, we completed the entire house, and did so with much greater quality and with finish and features much more to our liking. There is no question that the house is so much more than the general contractor was willing to provide.
So, there are a couple of lessons, that we would take to heart if we ever built another house. First, be patient. Allow plenty of time just for getting started, and don't feel you need to push to beat the rainy season (for example). If we felt pressured by impending events we would attempt to adjust those events rather than rush the planning or the construction.
Second, we would take more time to find local subcontractors. Hindsight taught clearly that once we found a good craftsman, he or she knew others with compatible skills and attitudes. Even though we tried before we broke ground, we just didn't allow enough time to find good local contacts. For example, well into our project we asked a local carpenter to look at the library with the thought of anticipating needs for cabinets and bookshelves. From him we learned of the plumber and the electrician who completed the shoddy and incomplete work done by the general contractor's subs, and he designed the stairway using our lumber claimed from deadfall hemlock and maple. Also from our independent solar contractor we learned of a project manager and carpenter who provided exactly the craftsmanship and personal service we needed, as well as other local people who paid attention to what we wanted. All these craftsmen did good work, listened to what we wanted, and worked at a fair rate.