How Green is Timber Framing

How Green is Timber Framing?

Since two areas of specialty for me are: 1- sustainable building practices, and 2- timber framing, this has been an important question for me to answer in my own mind. Let me define what "green" and "timber framing" are to me. In order to be green, a dwelling must: 1- be well above average in terms of energy efficiency, 2- consume a minimum of natural resource in its construction and upkeep, and 3- provide a healthy and non-toxic environment for its occupants. I define timber framing as the design and construction of a frame, made of wood, which is structural and stable without sheathing, and which is held together with ascetically pleasing joinery, primarily variations on a mortice and tenon.

To start with, I'll list what I believe is inherently "un-green" about timber framing. Timber frames tend to use large amounts of wood and the wood is often from large trees - thus consuming more than its fair share of natural resource. Well, that's it. I can't think of anything else un-green about timber framing, but the quantity of large trees consumed is a very important consideration. I have some strategies to minimize this quality, and some other strategies to offset it.

First of all; I like to design frames which spread the load evenly over a foundation - either with a large number of piers or a wall or slab foundation. I try to use plenty of posts, to eliminate long spans which need timbers that are long and large in diameter. Where posts can't be used, I'll try to use truss shapes which are built of smaller pieces of wood. Careful planning of knee braces and points where many pieces of frame come together can minimize wood use and timber size. Secondly; I use SIPs (structural insulated panels) wherever possible to minimize the need for structural elements in the frame. SIPs provide the "skin" of the house - sheathing inside and out with insulation in between the sheathing panels. I attach the panels to the outside of the frame - leaving the frame exposed. SIPs can absorb a large load with a minimum of other framing, allowing me to make a frame that's far undersized from what it would have been without SIPs. The panels themselves typically use less than 55% of the amount of wood that goes into a stick frame house, so we're lowering wood consumption here.

SIPs also provide a super-tight and very well insulated skin around the house that very few building systems can compete with, certainly stick framing can't, giving the well designed timber frame house very high marks for energy efficiency. Back to wood consumption; because a timber frame is such a "woody" look, I tend to dramatically minimize the amount of naturally finished wood in a timber frame house. I'll use plaster, or painted MDF (medium density fiberboard) on ceilings and walls). For floors I'll use alternate materials; concrete, cork, painted lower quality wood, tile, etc. For cabinets and furniture, I'll use painted, sustainable materials to contrast with the frame.

I don't use asphalt shingles because they don't tend to last long on a house and they last a long time in a landfill. My two favorite roofing materials are steel, and recycled rubber shingles that look like slate. They both last 50+ years if installed correctly.
I design almost all of the houses that I build to be both passively and actively solar in heating, cooling, electricity, and domestic hot water. I often use rainwater collection systems, grey water reclamation, composting toilets, and passive geothermal heating and cooling.

One aspect of timber framing that often gets overlooked in the green debate is that a good timber frame takes a substantially higher degree of skill and planning to execute than most other building systems. Because builders need a higher than average level of commitment to their skills, it naturally follows that they will have a higher level of attention and commitment to their trade in general - producing products that are higher in quality and thus more green than they would have with a lower commitment level.

Below is a frame which will be built primarily of 6x6 hemlock (locally grown and sustainably harvested), in which no span is over 9'6".