14. Building (really) Green in Vermont

“If we do not have an economy capable of valuing in particular terms the durable good of localities and communities, then we are not going to be able to preserve anything. We are going to have to see that, if we want our forests to last, then we must make wood products that last, for our forests are more threatened by shoddy workmanship than by clear-cutting or by fire. Good workmanship – that is, careful, considerate, and loving work – requires us to think considerately of the whole process, natural and cultural, involved in the making of wooden artifacts, because the good worker does not share the industrial contempt for ‘raw material’. The good worker loves the board before it becomes a table, loves the tree before it yields the board, loves the forest before it gives up the tree. The good worker understands that a badly made artifact is both an insult to its user and a danger to its source. We could say, then, that good forestry begins with the respectful husbanding of the forest that we call stewardship and ends with well-made tables and chairs and houses, just as good agriculture begins with stewardship of the fields and ends with good meals.” 

Wendel Berry, Home Economics, 1987

While “green” building is taking root in Vermont’s construction landscape, it’s ironic that almost none of the builders who are pioneering this branch of the sustainability movement would even consider using green, rough-sawn, native lumber.

Green lumber delivery from local sawmill

Vermont is a state that was hewn out of its primeval forest, significantly cleared for farming and now returned to nearly 80% forested – about 15% of that in public ownership and 85% in private hands. Hemlock, white pine and spruce make up most of our softwood forests – all excellent for framing and trim lumber. Our forest product industry employs more than 6,000 people and brings $1 billion into Vermont’s economy every year. More than $31 million go to Vermont’s landowners in stumpage fees, and wood provides 6% of the state’s energy needs (heat and electricity).

With the forest being such an important part of Vermont’s economy, you might think that the state’s builders would want to support the segment that creates 16% of all manufacturing jobs. Yet nearly all of our pine and fir is sent to Canada for processing rather than used in-state. While the more than 100 small sawmills have traditionally been competitive in hardwood and white pine, competition in the spruce and fir markets has forced mills to grow larger and more automated. Old sawyers are retiring and their children move on to easier and more lucrative endeavors. Nearly half of Vermont’s softwood sawlogs are exported.

A sustainable economy is one that supports local production, community employment and value-added processing and manufacturing within the region. It isn’t necessarily contained by political lines, such as state borders, but by bio-regions and watersheds. Certainly, the nearer a material is sourced to its end-use, the more ecolocally (to coin a word) responsible it is.

Honoring the spirit of the Hemlock

What about dressed and kiln-dried lumber versus green or air-dried? An important measure of the environmental impact of building materials (or any consumer product) is its embodied energy – all the extraction, processing, manufacturing and transportation energy that goes into getting a resource to its intended use. Embodied energy is also directly related to pollution and global warming.

Kiln-dried (KD) lumber contains approximately eight times as much embodied energy as air-dried rough-sawn. In addition, a rough-sawn hemlock 2×4 has 50% more wood and is up to 80% stronger than its KD equivalent. Though there is not much price difference anymore between KD and rough lumber, at least from the bigger commercial mills, the KD lumber still costs about 34% more per actual (as differentiated from nominal) board foot of lumber delivered.

Yet, because residential builders are focused today on production timetables and profit margins, easily-available and uniform KD lumber has become the standard for almost all construction. A house framing book says about green lumber: “The wood is heavy and hard to work with, and it cracks and splits as it dries. Native green lumber is inexpensive, however, and you might want to use it to frame rough structures like sheds or barns.”

This attitude, however, reflects a modern prejudice and lack of experience with native lumber. The one true part of that critique is that green lumber is heavy. Since KD or SD (surface-dry) lumber is required to be milled at no more than 19% moisture content (by weight), green lumber can be nearly 70% heavier when fresh off the mill. But green lumber is far easier to cut and nail, though longer galvanized nails are required which might mean hand nailing rather than relying on pneumatic nail guns. Not many framers these days enjoy the acoustic pleasure of hearing the rhythmic impact of hammer on nail. In my experience, hand-nailed frames are almost always more carefully assembled.

Because wood does not shrink or warp until it dries below the fiber saturation point – about 28% – green lumber is typically much straighter than KD lumber. The trick is to nail it into the house frame, and block it in place before it dries enough to warp. A frame that is exposed to sun and wind for a couple of months during the construction process, can not only dry to the same moisture content as KD lumber but also dry straighter and stronger. If the green lumber comes off a computer-controlled bandsaw mill, not only will it have smoother faces than a circular-sawn stick but will likely be almost as uniform in dimension as that pile from the lumberyard. Lumber sawn on smaller circular-saw mills may vary somewhat in width, depending on the condition of the mill and the skill of the sawyer.

But there are ways to use rough-sawn lumber in which only one face of an assembly needs to be aligned. A first floor deck over an unfinished basement or crawlspace, or a roof which is not also a cathedral ceiling are two such examples. My frames have an inner and outer “skeleton”, each of which requires only one-face alignment, and which results in a 12″ thick wall assembly that can be filled with another excellent wood product – recycled newsprint insulation, or cellulose – for an R-45 wall with almost no thermal bridging from inside to out.

Frame Matrix – Charlemont MA 1998

Because each framing stick is stronger than KD lumber, it’s sensible to frame on 24″ centers rather than the more common 16″. This not only reduces lumber consumption but also increases the effective R-value of the walls by leaving more space for insulation. Rough-sawn is not only suitable for framing but also for sheathing and even exterior trim. Diagonal board wall and roof sheathing is not only an excellent way to create shear-bracing, but leaves a more breathable exterior that allows greater drying potential of the thermal envelope. All wood-frame buildings start out wet and take on moisture, from the interior and from the exterior, daily and seasonally over the life of the structure. Breatheability creates a more forgiving building that can be less susceptible to moisture problems.

Living Wood: A Monarch Butterfly Emerges from Cocoon on Green Hemlock

And, while it’s true that a green lumber house frame will shrink more than a KD frame, even a conventional KD 2-storey frame will lose about 7/8″ of height as the wood reaches equilibrium with its environment. So all frame designs need to take shrinkage into account, and clever planning will allow the entire frame to “settle” consistently. With adequate drying time during construction, I’ve never experienced drywall nail-popping or joint cracking due to shrinkage of green lumber. In fact, by the time I’m ready to “weather in” my frame, the wood is as dry or dryer than KD lumber.

When I use band-sawn hemlock, I stack and sticker some boards to air-dry for later use as exterior trim. The cross-grain saw marks create a wonderful texture which is not only visually appealing but also absorbs more stain for better weather protection. If I’m siding with ¾” horizontal shiplap boards, I will sometimes forgo the sheathing layer (using metal T-bracing for shear) and apply the siding directly over the housewrap on the exoskeleton of my truss-wall. This allows me to build a 12″ thick wall with less lumber than a conventional 2×6 frame sheathed with plywood.

Building with native lumber, then, can be more resource-efficient, is definitely more embodied energy-efficient, less costly, supports our neighbors and our regional economy, and offers a more sensual experience (fresh lumber has a wonderful smell). So not only is using green, native lumber more “green” in the sustainable sense, but also requires less “green” as in dollars & cents. More sensual, more eco-sensible and more dollars and cents-able. What’s not to like?

Riversong Truss house frame for Energy Star 5+ home in Warren VT – all native, rough-sawn, green hemlock and pine

For a deeper exploration of What Does “Green” Really Mean? click on this link to my other blog: Turning the Tide : Shifting the Paradigm of Human Culture

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by Robert Riversong: may be reproduced only with author attribution for non-commercial purposes and a link to this page
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