As a group, builders in the state of Maine take a wide range of positions on energy efficiency. At one end of the spectrum are a handful of companies focused on ultra-high-performance homes (the zero-energy, Passive House crowd). At the other end are a few builders who still aren't happy with the state's decision to adopt the 2009 International Energy Efficiency Code (a move that was required for states who wanted their share of stimulus package money after the 2008 housing market collapse). In the middle are the mainstream builders and remodelers who are sticking to whatever the code requires.
And then there's the "pretty good house" movement. "Pretty good house" is the handle coined by a subset of the homebuilding industry who are aiming for the cost-effective "sweet spot" where the cost of energy upgrades will pay itself back through a reduction in the cost of heating systems, along with reductions in operating energy cost. It's hard to be sure where that sweet spot lies, of course, but in Maine, the typical recipe calls for R-20 insulation in the floors, 2-40 in the walls, and R-60 in the roofs. So while "pretty good" falls a tad short of a full-on Passive House, it's well beyond code minimum requirements. Building shells have to be air-tight, but there's no bright-line blower-door requirement. And of course, the design and construction details have to manage the risk of moisture condensation or bulk water leaks.
This month, JLC has started to follow a "pretty good" project on Peaks Island, a neighborhood of Portand, Maine, that is a 20-minute ferry ride away from the city's "Old Port" downtown. The existing house, like most houses on the island, was built as a three-season vacation home in the early 1900s with light wood framing, a simple foundation, primitive plumbing, and no insulation. There have been improvements over the years, but nothing that would bring the house all the way into the 20th century — much less the 21st. But that's about to change: Peaks Island design/build firm Thompson Johnson Woodworks has just kicked off a full modernization makeover of the house. Designed by island architect Rachel Conly with engineering from local engineer Andy Jackson, the project involves enclosing porch areas to add living space, finishing part of the dirt-floor, low-ceilinged basement, creating an open-plan first floor, and punching out a few dormers and skylights in the second story. (See Slideshow)
Along the way, Thompson Johnson will also turn the dwelling into a modern, well-insulated building. Walls will get three inches of rigid foam on the exterior and six inches of dense-pack cellulose in the interior framing cavities; the roof will get three inches of spray foam against the sheathing, and a foot of dense-pack inboard of that. The exposed portion of the masonry block basement walls will also get clad with foam, and the new footing will be frost-protected with horizontal wings of rigid insulation below grade. The resulting envelope will cut heating loads low enough that the main heating plant will consist of two air-source heat pumps, rated at 12,000 or 18,000 Btus apiece.
The job starts with two structural measures: first, excavating beneath the existing foundation to construct a new load-bearing footing; and second, jacking, straightening, and reinforcing the existing wood frame walls and roof.
The existing block walls were laid directly on soil, with no structural footing. But they've held up well over a century, supported by strong sandy soil over ledge, and holding up only a lightly framed house. Now, however, Thompson Johnson will excavate to the base of the block wall, dig underneath the block, and place new structural footings, one four-foot section of wall at a time.
Upstairs, Thompson Johnson has been jacking up sagging floor joists, splitting the longer spans into shorter joist runs, and supporting the floor system using engineered beams. Where the balloon-framed walls have splayed outwards, the crew has winched the walls inward, jacking up the hip roof's ridge at the same time, and inserting new posts into the existing wall framing. Next they'll strengthen the roof, adding depth to the existing hip rafter system for more insulation, and installing a system of collar ties and heavy trusses to stiffen and reinforce the structure.
This week, we start with a look at the foundation work. In a coming issue we'll follow some of the wall and roof framing action.
