Seattle - Framing

Since this whole project is about environmental protection, its clear what side we're on, but we're also pragmatic: we can't deny we're using wood to build a house, but it can still be used as wisely as possible. 

The strategies we used are as follows:

• Keep the size of the structure down - although its not clear how well we succeeded, we did at least try, by using "just the right size" principles (see needs in the design section).
• Keep the shape of the structure simple - the house is essentially a box with a few bump-outs, and removing any of the bump-outs would clearly be a detriment to the house.
• Layout the rooms so that structural loads could be carried simply - while we did line up all the stairs in the center of the house and use the stair walls as load bearing walls, there are still quite a number of headers and posts, most of which appear to be the result of having to carry loads from the peak of the roof down through the center of the house, instead of on the exterior walls.  I still believe that much of this support system is unnecessary, even with a 25lb snow load (see structural section for more on  engineering), although after seeing how the SIP roof attaches to the house, the extra support adds a little confidence (more on SIPS below).
• Use engineered lumber/avoid big beams - since almost everyone does this anyhow, it can hardly be counted as a "green" feature.  I did ask the engineer to avoid the use of big beams that would come from old-growth, but of course a bunch of 4x8's and 4x10's ended up in the house anyhow.  When you make changes that affect structure during construction (as many people, including us do), your choice is to put in oversize beams or call the structural engineer to spec a size.  Needless to say, you're not likely to call the structural engineer, because (a) it takes a while for him to get back to you (b) he costs a lot.  The one "engineered" product we used that is atypical, is finger-jointed 2x4s for interior framing.
• Use FSC certified wood - we would have used all FSC wood if we could have gotten it, but alas its not generally available.  We did get some of it (statistics coming some day), and we did learn that if we ordered it well ahead of time, we could have gotten a bunch more.  We also got a bunch of SFI certified wood, under the assumption that we're sending the message that good forestry practices are important
• Use reclaimed wood - our intent had been to use about 400 reclaimed 2x4s, but we only got up to about 150 of them before we ran out of steam running around collecting them.  Virtually no one carries them (except the re-store), and even for them, there big market for them is up in Bellingham, so the re-store ships most of them up there.  We ended up using a lot of finger-jointed 2x4s where we would have otherwise used reclaimed.

Even though our framing fairly different from conventional, it was still close enough that there were no significant glitches.  The biggest difficultly is getting corners and interior wall intersections right.  The framer used the reclaimed studs without complaint (although we did pre-select only straight ones). The SIPs had a bit of a learning curve, and in the future the contractor will probably be able to install them faster.

	Non-load bearing walls are made of finger-jointed and reclaimed lumber (left). TGIs when laid on edge they are so floppy they bend under their own weight, but are very strong on edge (below, center). FSC wood comes branded with their logo (at right).

Double wall  construction:  the exterior wall is a normal load bearing 2x4 wall, while the inner just makes space for more insulation and holds sheetrock.

Materials use .vs. energy use
While we were trying to use wood efficiently, we were also trying to built a very energy efficient house- one that is dramatically better than the energy code requires, and in fact better even than required to be an "energy star" certified home.  There are a number of ways to do this, but the obvious way was to use double 2x4 wall construction, creating a 9" thick wall cavity, which significantly increases the amount of wood used to make walls.  The outer wall is load bearing, so the studs are on 16" centers, while the inner, non load bearing wall is on 24" centers, reducing the extra wood use somewhat.  The downside of 24" centers is that you then have to use 5/8 sheetrock (instead of 1/2), which makes standard door jambs 1/4" too small.  In the case of main floor and the roof, there is little to no extra framing material required since the floor is TGIs and the roof is an SIP.

The scrap pile kept growing bigger than we'd like.  This was the first of three big piles.

Minimizing Waste
One strategy we didn't apply very much was working to minimize waste.  This can be done as a design strategy by laying out the house to be even increments of standard wood sizes, but in a house this is purposely kept small, everything is squeezed into as little space as possible, making most things odd sizes rather than even increments.  Alternatively, we could have been every careful about using cutoffs when ever we needed a short piece, but this makes much more work for the framer, who was open do doing it, but it would incurred additional labor costs (how much is unclear).  Instead, cutoff pieces were reused when it was convenient, but otherwise ended up in the recycle pile.

Framing requires much temporary cross bracing (later reused).  Window holes are cut out later resulting in small, hard to re-use pieces (below).

The best way to minimize waste would be to lay everything out ahead of time (like with a CAD program), and then each piece of lumber can be subdivided in a good way.  Alternatively, it would seem like keeping a cutoff pile sorted by size would allow the framer to grab the closest piece to what is needed.  Some wood ended up getting wasted when we change our minds about how something should be framed (sometimes because we didn't think thru a particular detail well enough in the planning stage, but more often because seeing the building in 3D gave a better sense of what size things should be) We ended up sending about 8 cubic yards of scrap to a "recycler" who actually just grinds the wood up and use it for a very low value purpose, like compost.

SIP (Stress skin panels)
Our roof system is all 12" SIPs from Enercept, which uses 1/2" OSB on on both sizes and TGI spline every 4 feet.  Although there are many claims about how much wood use is reduced by using SIPs, in our case there appears to be no savings.   The SIP system uses two layers of 7/16" OSB and TGI splines every four feet, while a stick framed roof would use TGIs every 16" and be sheathed with 1/2" plywood: its two times as many TGIs but half as much plywood.  The SIPs roof is very straight and very stiff in spite of being made out of inherently weak materials and spanning 22 feet.  Looking at the product sitting on the ground does not inspire confidence, since its just a chunk of styrofoam sandwiched between two layers of 7/16" OSB, and it looks like a couple of good smacks and you'd break a panel in half, but when walking on it, it feels very strong, and does not creak or flex..  Still, the fact that the SIP is only strong as long as all three layers remain glued together, can lead one to imagine various accidents, such as inadvertently slicing into one of the OSB layers leaving one or more SIP panels completely useless.  For the most part, the SIPs are attached to the framing with very long screws, but the attachment at the bottom was non-intuitive and in places was done wrong.  The right was that little metal plates are supposed to be slid under an extra 2x4 plate nailed to the attic subfloor, and then bent up and nailed to the bottom of the SIP.  While this undoubtedly makes good engineering sense, its a pain in the ass in reality because the 2x4 has to be pried up to slide the metal plate under it.  Its not clear why they shouldn't just be screwed down into the 2x4 plate, just like the rest of the connections.

SIPs stacked in order for assembly (far left).  To put them in place on the roof, a hole is drilled in the SIP and then it is lifted by a crane into place (center).  The tails of the TGI splines stick out so they can be cut to make the proper overhang.  In our case, the overhang is to be boxed in with a soffit  (right).

Cost wise, the SIP roof was estimated to be about the same as stick framing, and although experience could make installation go faster, the panels don't go together all that easy. First of all they're a pretty tight fit (which is great for reducing air infiltration), and then there is just the issue of manipulating a 4 foot wide, 22 foot long, 500lb panel hanging from a crane.  Finally, because SIPs are made off site and must be joined to existing framing, the usual fudging around that a framer will do to make everything come out right is much harder.  At one point, we ended up peeling the LVL end cap off the last panel, shaving about 2" of stryrofoam off, and then putting the LVL back in.

Lowering  the SIP in place (far left).  The crane holds the panel while its attached in place (center).  Most of the panels in place: the opening in the center is for a dormer (right).  The boom of the crane is visible in the upper right corner.

Pressure treated wood
Since the EPA banned CCA treated wood last year, we were easily able to get alternative treated wood products, but of course we have no idea if they also will be banned some day, or whether they are also toxic, but just less so.  The two competing new product, ACQ, and copper azole, has no arsenic in them, just copper, but more of it. Treated wood comes in varieties now, depending on how much copper is in it.  Wood suited for ground contact has more preservative than wood suited for outdoor use, and both have more then wood which is normally dry.  These new products require special nails, as they will corrode normal nails, and although they say the copper doesn't leach out, they said that about CCA also, and of course it did leach out.

All of our sill plates are treated, as well as all the porch lumber and the supports for the two bump outs that sit on concrete piers, and the bottom plate of every wall in the basement: overall it seems like we used a lot of pressure treated wood.  In some cases we have wood in contact with the ground for no obvious reason (I'd better ask), a situation that would seem like a design flaw, as you would think you could always keep the wood off the ground with brackets in the footing.

TGI floor framing sitting on a pressure treated sill plate. Underneath the sill plate is a foam gasket that keeps water from wicking up through the concrete.  Code requires the use of pressure treated, but not the gasket, and apparently doesn't allow substitution of the gasket for the use of pressure treated.

Framing Summary

Floors: all 11-7/8 TGI, except two of the bump outs are 2x6.  The surface is 3/4" plywood.

Walls: mostly double 2x4 walls, both 24"o.c. All load bearing walls have double top plates, because the upper framing doesn't always line up with the lower floor.  Most of the corner are three stud "advanced framing" style, except where the engineer requested PHD hold downs in the corner.  There are 4 short sections of 2x6 wall, in the two window seat bump outs.  Most of the non-load bearing 2x4s are either reclaimed or "finger jointed".  The surface is 1/2" plywood.

Roof: all roofs over heated space are 12" SIPs, while porch roofs are stick framed with what ever size is necessary.

Posts and Headers:  as mentioned previously, we seemed to end up with a lot of these, and some of them were pretty big pieces of wood, although by request, most headers were either engineered wood or double/triples of smaller lumber.  We can only hope that the house lasts for a very long time.

Blocking/extra wood: since sheetrock isn't strong, you end up needing a bunch of blocking to hold up or stiffen things that go on the wall: ceiling fans, lights, switches, cabinets, towel bars and so on.  We used also extra wood to help form the low voltage electrical chases, and to stiffen up pocket door walls.

Wood Use Summary

(to be supplied)