After months of planning looking at our flat property ... finally, we have walls!!! After months of digging, leveling, digging some more, laying out the rooms for the millionth time, and pouring concrete, we finally started to go 3 dimensional with WALLS !!!
Initially, we wanted to use Structurally Insulated Panels to save construction time, increase the tightness of the walls, and save materials. Because of the curvature of the walls in our design, this was not possible or at least not economical. So we framed with dimensional lumber ... stick built. The method used by our contractor Barrett Burr is called advanced framing, because approximately 25% less wood is used.
In the past homes were built with 2x4 inch lumber, with a stud every 16 inches. This limited the amount of insulation that could be added to a bit less than 4 inches. Because of building and energy codes and the need to increase the insulating performance of walls, 6 inch walls have become the norm. Unfortunately for our forests (not to mention contractors budgets), the industry has not moved off of 16 inch studs.
With 2x6s it is possible use less dimensional lumber by going to 24 inch studds ... 24 inches on centers. From personal experience with builders, 24 inches on center is the exception rather than the rule. Ask most builders about this and they will simply say that it won't work. I even had a discussion with the former Executive Director of a local builders association who said that it was against the building code.
Rubbish!! With thicker walls, fewer studs are needed, to achieve a structurally sound building. There is the same amount of wood in the studs as with 2x4x16, but the overall effect is stronger. However, most important, 25% less wood is used and more insulation can be put into the wall for better performance.
Barrett Burr, Polar Bear Construction, has been using advanced framing for nearly 15 years which is one of the reasons Barrett Burr is building my house.
The contact point of the wood wall with the concrete foundation deserves a discussion. Water will travel in concrete by capillary action ... moving upwards through microscopic cracks in the concrete. It is important to put a moisture barrier between the foundation and the wood, as we have done. It also is useful to make certain that the base plate on the foundation is pressure treated to kill any mold that might get into the framing at this point.
When building corners, and intersecting interior walls, advanced framing techniques call for enough space for insulation to be packed into the wall. Air pockets and gaps are minimized.
Finally, to be environmentally friendly the wood used should ideally be sustainable, eg the forest from which the wood is harvested will continue to produce wood into the future without degrading the water and plant resources within the forest. The Forest Stewardship Council (FSC) has an international certification program that provides confidence that the final wood product has been harvested from forests managed to a high environmentally conscience/sustainable manner.
The timber industry is fighting FSC certification and has launched its own Sustainable Forestry Initiative (SFI) Program. The critical difference between the two is accountability. FSC requires a third party to monitor that the forest and company are complying with the program. There is an independently verified paper trail from the forest to the consumer for FSC wood. SFI is self regulated, with no independent auditing. If you want to know the difference you can take a look at the FSC/SFI Comparative Analysis.
FSC Certification is expensive and the demand for FSC wood is growing as consumers and retailers like Home Depot and Lowes push their environmental programs. Thus, FSC certified lumber can increase costs significantly. We decided to use FSC certified wood for doors and trim, and not for the framing.
However, for the framing, there is a third option, which is to use finger jointed dimensional lumber ... lumber that is composed of shorter pieces, glued together to create longer boards, as shown in the pictures.
In addition, we used Oriented Strand Board or OSB rather than plywood for the roof and wall sheeting. OSB is an engineered, mat-formed panel product made of strands, flakes or wafers sliced from small diameter, round wood logs and bonded with an exterior-type binder under heat and pressure. If you want to learn more about OSB go to www.osbguide.com/ . According to the industry, in 2000, for the first time, OSB production marginally exceeded plywood production. By 2004, OSB production is expected to grow to nearly 60% of the North American panel market share.
It is just as strong and rigid as plywood but I cannot attest to the type of resins used to make OSB. The industry says "Resin binders and waxes are completely cured and stabilized, so there is no measurable off-gassing from panels." On balance, OSB is probably superior to plywood from an environmental perspective.
One final point however is that OSB can be made from smaller diameter trees. As we over harvest our forests, trees are cut at smaller and smaller diameters to increase the timber industry's cash turn. The increase in OSB use should be viewed with this in mind.
In the likely event that you have never built a house, the trusses are commonly built off-site by a truss manufacturing company. They are then delivered to the construction site and hoisted into position. Supposedly this saves time building the trusses, and saves material because dimensional lumber is cut to the exact measurements of the truss package.
The truss company will be responsible for the engineering calculations to make certain the trusses can support the weight of the roof.
To get a building permit we had to have every truss defined for the counties permitting department. There are 12 different truss configurations in our home. As the walls got closer to completion, the truss company visited the site and made field measurements to guarantee that there were no changes.
In fact, they visited and measured 5 times. When the big day arrived and trusses were hoisted onto the house, we discovered that ever single truss was wrong ... wrong overhang, wrong roof pitch that did not line up, wrong pitch angle, and some were too short to span the walls. This comedy of errors cost us 2 weeks fixing the problems so we could start laying the roof decking.
Remember a GreenBuilt Home is also Quality Built Home !!
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Sunday December 17, 2006 05:34 PM -0800
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