38 Stonewall Lane – Greene Building at High Cove
One day a month, a piece of mail arrives at our mailbox on Rebels Creek Road. It is an eagerly anticipated event. It isn’t a check, although it might as well be. This envelope contains a monthly pat on the back, an acknowledgment of a job well done. Yes, it is our bill from Progress Energy.
There were a number of goals and desires we hoped to achieve as we started planning our house at 38 Stonewall Lane. Building an energy efficient structure was probably our top priority, although it is hard to rank our priorities retrospectively. The focus of this article is on how we put together the pieces to meet that goal.
We knew we wanted a gold rating on North Carolina’s Healthy Built House green certification checklist, then the highest rating given. (The checklist has been renamed North Carolina Green Built, and now provides for a top rating of platinum. High Cove houses are required to reach at least a silver rating.) With that in mind, I turned to books, the internet, magazines, conversations, trade shows, and any other resource, including the checklist itself, which came to my attention. (See the end of this article for an annotated list of selected sources I found most helpful.)
Arranging the Puzzle Pieces
The wide-ranging research I was doing led me to identify two key areas of the energy efficiency puzzle – siting and building envelope. Grouped under the general heading of building envelope, I identified materials and methods of construction, insulation, and windows as pieces which would require attention. I made decisions about siting and building envelope my priorities because they are essentially permanent, at least for the period of our lifetime in the house. Other factors which play into energy efficiency – heating and cooling, appliances, lighting, hot water heating, and source or sources of energy are more easily changed. I plan to devote a future article to our decisions in those areas.
Free is the cheapest form of energy and for us, that means the sun. Choosing to site the house so that we could get as much – or as little – from the sun as possible was our first consideration. Here that translates to as much exposure to the sun in winter as can be managed. Facing true south, with the sun unimpeded by obstacles, is ideal. Deciduous trees do interfere, but a lot less than evergreens or ridges.
Most of High Cove, including our lot, is pretty heavily treed. High Cove’s woods are central to its identity and their preservation is key to our commitment to live sustainably on this land. The community’s Design Guidelines acknowledge this by requiring that any plan to remove trees be approved prior to cutting. One of the justifications for cutting is to gain southern exposure. (My first article in this series dealt with the selective clearing of our lot, largely to open up our southern exposure.)
A scientific detour is warranted here. There is a difference between true and magnetic north or south. In some parts of the world the two are quite close to each other, while in others they are far apart. At High Cove, we fall somewhere in the middle. There is currently about a 6 degree, 45 minute difference between the two readings, and it is increasing at about 4 minutes per year. So, if you are trying to orient your house towards true south, you will need to adjust the compass reading for south about 7 degrees west. This only becomes critical at the margins as the experts say that orientations within 15 degrees east or west of true south are in the appropriate range to take practical advantage of solar energy.
Having a southern exposure was a prime consideration in choosing our lot. The final orientation of our house is about 4 degrees west of true south. On our lot, this orientation suits the general lay of the land, meaning we could minimize the amount of site preparation work needed. What it means to us in the winter is that on the frequent sunny days, the sun’s rays penetrate up to ten feet or more into rooms with a south wall. All but four rooms in our house have south-facing walls and one of those, the kitchen, has south-facing clerestory windows which wash the ceiling with light. In summer, all the south-facing windows are shaded by appropriately sized overhangs, limiting any heat gain from the sun.
Taken in combination with other decisions we made, the choice of orienting our house to the south contributes significantly to our energy efficiency and it cost us nothing to make that choice. While we take advantage of passive solar, our orientation allows for future consideration of photo-voltaics and/or solar thermal panels.
One of the areas of green building which seems to have changed the most since we were making our decisions is in the number of materials and construction methods which are now being utilized to achieve energy efficient, “tight” building envelopes. Tight in this context refers to air tightness. Great lengths are justified to prevent air leaks and to avoid thermal bridging, which could be defined as the undesirable transfer of heat from a conditioned space to an unconditioned space.
Construction Materials and Methods
In the course of my research, I investigated a number of materials used to construct a tight envelope. One which particularly interested me was AAC, autoclaved aerated concrete. (See http://www.sungardenhouses.com for a NC company which makes use of this material in really cool ways.) AAC led me to Faswall, a variant on the same theme (www.faswall.com) which incorporates recycled wood. Both of these and other similar products appealed to me because they are vapor permeable, fire- and mold-proof, insect resistant, hypoallergenic, sound-absorptive, and can replace wood framing, insulation, house wrap, and drywall with a single material.
The drawbacks for us proved to be shipping the materials from fairly distant points, some lack of familiarity with the materials on the part of contractors, and lower r-values (a rating for insulation effectiveness) than we were hoping to achieve. I discovered Faswall, my favorite among the choices, after our house had been designed and using it would have necessitated a reworking of that design, another impediment to its use.
We also looked at Hemcrete, a product new to the US, which uses hemp shiv as its aggregate. The company chose Asheville as its US launch site. Had we proceeded with that, we would have been the first house built in this country using the product, which is one of several reasons why we didn’t go that route.
In the end, balancing all the factors and adding in budgetary considerations, we decided to go with 2×6 frame construction, utilizing advanced framing techniques. Advanced framing differs from traditional framing in a number of ways which minimize the amount of lumber used while providing increased area for insulation. (Advanced framing is described more fully in the section on insulation.) Our house is built on an insulated slab and incorporates Superior Wall for the below grade portions of the envelope. Superior Wall utilizes 5000 psi concrete panels which are put in place by crane and bolted together. Watching that installation was one of the highlights of our build.
Insulation is all about r-value, which is how insulation effectiveness is rated. The higher the r- value, the better the insulation. By code in our area, the walls must be insulated to an r-value of 18 and the ceiling/roof to 38. The recommendation in Green from the Ground Up is that code numbers be treated as minimums; one should aim to exceed them by 50%.
Achieving insulation levels 50% over code was considered the gold standard in 2008. Current green builds, especially those using photo-voltaics and/or being built as net-zero (producing as much energy as the house uses) would seem to be at least doubling the code r-values, judging from what I see in accounts of more recent construction. Some green houses are being built with two sets of wall framing, one inside the other, the whole space between the two, including the depth of the individual walls, filled with insulation. In other words, insulation is not a place to skimp, according to experts, if energy efficiency is the goal.
I took this advice to heart and went searching for the best insulation we could get, given the constraints of budget. While the idea of a natural material like cotton bats or wool was really appealing and the “green-ness” of using recycled newspaper, blown into the voids of the walls and roof was obvious, in the end the higher r-value we could get from petroleum-based sprayed in foam won the day. I chose an open-cell (also called low density) foam because it is more vapor permeable than the closed-cell variety. The formulation I chose incorporated soy for some of the petroleum. (Closed-cell foam has a slightly higher r-value per inch but I was warned that especially in roof applications, it can create problems with noise as it apparently amplifies sound; for example, from rain hitting it.)
Filling the spaces between the studs in our 2×6 walls, we were able to achieve an r-value of about 30 from the spray foam insulation. Our exterior walls were also faced outside of the sheathing with 1″ of “blue board”, adding about another 5 to the total and helping to limit any thermal bridging. The foam sprayed between the rafters gave us a total r-value for the roof of a little over 60. The fact we chose to use advanced framing techniques means that there is less wood, not a very good insulator, and there are larger cavities to be filled with insulation, since the studs are 24″ apart, instead of 16″. Unlike in standard framing, the corners are constructed in such a way that there is a pocket for insulation. Similarly, in advanced framing, LVLs (laminated veneer lumber) replace the usual ganged studs over window and door openings, so that there is additional space which can be insulated.
One fact about foam insulation which did not turn up in the research I did is that carpenter ants seem to enjoy tunneling and nesting in it. We found a nest of ants in our attic during the first year we were in the house. We were able to get rid of them, mostly it turns out, with persistent use of a portable vacuum cleaner. The problem probably occurred because we did not remove the leaves from the valleys of our roof over the period of the winter, which gave the ants a ready source of moisture. We recommend that if the roof of your house at High Cove has valleys, make sure to routinely remove the leaves which gather there. By the way, we later found that it took a flea “bomb” set off to rid the house of a flea infestation to completely exterminate the ants. Far better to avoid the necessity, for ants or fleas, if you can manage that.
I had to laugh recently when I ran across a blog about building a net zero house in Maine. I was surveying the titles of the posts which had preceded the one I was reading. The first couple of posts dealt with planning and design. The next six or seven posts were about windows, with titles that suggested steadily increasing levels of frustration with the search for the “right” windows. It is indeed complicated.
Windows and doors are key parts of the all important building envelope. As with insulation, the experts stress that getting the best you can afford is the way to go if energy efficiency is a priority. This advice too I took to heart. I saw little sense in undercutting a good effort at insulating by letting all the potential energy savings flow out through less than optimum windows and doors.
During my research into windows, I discovered Serious Windows. I am completely sold on these windows. They have very high r-value series – ours is 925, with an r-value of 9 for fixed windows – as well as 725 and 525 series, with somewhat lower r-values, but still much higher than many Energy Star rated windows. Every window is custom made, so sizes are pretty much unlimited, and they can be specified for higher or lower solar heat gain. We have higher solar heat gain windows on the south to maximize the passive solar heat gain in the winter, and lower solar heat gain on the other three exposures. Unlike triple pane windows, which are the norm for most highly efficient windows, our windows are not thick or heavy. Instead of glass panes, Serious uses two sheets of film between the outer layers of glass. The frames are fiberglass, which expands and contracts at virtually the same rate as glass. And I could go on. (Note that Serious Windows have recently been sold to Alpen, from whom the window technology was purchased by Serious Materials.)
There is no better evidence for the value of these windows than standing by them on a sunny day, temperatures in the teens outside, and feeling the heat coming off them or conversely, standing by them on a cold night and feeling no cooler than if you were 10 feet away from them. I am completely satisfied. Were they expensive? They cost more than some other windows, but were not out of line with typical costs as a percentage of the building envelope, while providing far greater value as far as we are concerned.
We were not able to get doors from Serious Materials, which at the time was producing only sliders, which we did not want. Alpen is now producing a full line of doors. As strongly as I feel about the windows, I might replace our current doors with Alpen at some point in the future.
Not everyone will place energy efficiency as high on their list of priorities as we did. Still, it is a significant part of what “green” is about, and without some attention being paid to the issues of siting and building envelope, a house built at High Cove would probably not meet the minimum standard required. These two elements are fundamental. They are difficult and expensive to change later.
We are happy with the choices we made – they work well for us and we think they will benefit future residents of 38 Stonewall Lane. Our choices have paid off in comfort and low energy bills which have averaged about $65 per month over the last 2-1/2 years. And yes, we did get our gold certification with 309 points, enough to have gotten platinum on the new rating system. We were also awarded the Energy Star 5 Plus rating and given a 5% discount by Progress Energy on our electricity bill for the life of the house.
There are so many exciting developments occurring in the world of green building. Those of you who follow us and build in this and future years will have more and better options to choose from as you put together the puzzle pieces in your own way. Good luck to you!
—————————————————————————————————— Selected Resources
Green from the Ground Up, by David Johnston and Scott Gibson was published in 2008, just in time for our build which started in 2009. Building technologies and materials are constantly changing and expanding, but I think the book still provides an excellent summary of the inter- related systems which are factors in determining the energy efficiency of a house. I found it to be technical enough to allow me to understand most of what I read in the builders’ forums that I followed, but not overwhelming. (The subtitle of the book is A Builder’s Guide.)
By far my favorite online resource was (and is) http://www.greenbuildingadvisor.com. It was very worthwhile to become a subscribing member which gave me access to all kinds of information about specific products and new strategies being tried, as well as the ability to ask questions of experts who were very helpful and expansive in their replies. I benefitted immensely from the various points of view and range of experience that the answers represented.
But even without subscribing, there is an extraordinary amount of information on the Green Building Advisor site. One of the features I especially enjoy are the case studies which describe in delicious detail the whys and the hows of various green projects. Each includes a sidebar with product-specific listings of such pertinent items as insulation, lighting, windows, HVAC equipment, etc. The sidebar also lists projected and actual energy performance numbers and, often, cost per square foot. The comments section which follows the case study is enlightening.
There are several magazines which I found particularly useful. Fine Homebuilding is one of them. The articles were often on target for something I was researching, but equally helpful to me was a close reading of the advertising. From that source, I got leads on a number of materials and/or techniques which eventually ended up being used in our house. Mother Earth News also provided valuable information on energy efficiency topics.
While not exactly a magazine, the Western North Carolina Green Builders Council (WNCGBC), the group which administers North Carolina Green Built certification, publishes the WNC Green Building Directory annually. It is a valuable guide to local businesses and resources. Most of the businesses are in or near Asheville, but in many cases the guide provides a starting point for locating materials and services in our area. It also features a wide variety of articles. The WNC Green Building Directory can be picked up free from newsstands in the greater Asheville area. See http://www.wncgreenbuilding.com and http://www.wncgbc.org.