This is part 2 of the wood feature wall on the Skyline Project. The first part dealt with the aesthetics and the simple and real fact that wood is a natural product and will move with changes in the weather.
This wall faces south west and will receive a great deal of sun in the spring, summer, and fall. The basic structure of this wall is a 2x6 stud wall. The added depth of the 2x6 allows more room for insulation. Two layers of R13 batt insulation were used in the stud bays. Two layers of R13 is less expensive than one layer of R19. The double R13 is not equivalent to R26 due to some compression of the insulation. However, it is probably around R19 or R20. The interior is drywall. This wall is the exterior of an office where computers are used. This is the main reason there are no windows on this wall.
The wall has a layer of 3/8" plywood required by the structural engineers for shear. This plywood is designed to help resist lateral movements (think falling dominoes). The plywood does provide a good backing for the siding. It also provides a better seal against the elements. All of the plywood joints were sealed with either polyurethane sealant or spray foam.
Construction practices tend to be regional. Here on the west coast we are no different; we do things the way we always have. In the colder climates, such as the northeast and Canada, they have their ways, as well. Much of the way they do things is in response to the weather they have. Here on the west coast, our weather is much more temperate (warm and dry). Hence, we have not payed as much attention to the weather in the development of our construction methods.
One of the construction features of this wall is the use of a rain screen. This is simply the incorporation of an air space behind the wood siding to allow it to breathe. This is accomplished by adding furring (or adding a spacer) strips behind the siding that holds the siding out away from the wall. If any water should get behind the wall (and it will), the water has a clear and easy path to get out from behind the wall. And once the water has drained away, the area behind the wall can dry easier (breathe).
The sealing of the wall (from the habitable space that is conditioned) from the weather elements takes place behind the wood siding. The wood siding is not the "seal" from the weather. Sandwiched between a layer of plywood and a layer of rigid insulation is a weather resistant barrier (WRB-a critical component of any building envelope) layer of Typar. There is a vast quantity of discussion around which type of weather resistant barrier should be used. I will reference one of those discussions here:
Each of the manufacturers present a great case for their products. Users vigilantly take sides on which product is best. In the end, it's important to know why you are using the product and install it properly.
The WRB keeps the water out. It is not water proof. In fact, it has the ability to breathe in case water (or water vapor) gets in.
In front of this WRB is a layer of 1/2" rigid foam. I wanted to increase the insulative properties of this wall as well as give the wall one more layer against the weather. Rigid foam can be used as a WRB. But doing so effectively is a little tricky. Here it is simply another layer that aids in protecting the surface of the wall from the weather.
On top of the rigid foam are 1/4" wood furring strips. These strips, as discussed above, allow the back of the siding to breathe. Here again, there is a great deal of discussion on the way in which the furring is installed. The main point is that the wood is held off of the wall. See the following reference for a detailed discussion on rainscreens:
Finally, the sidding is attached to the furring strips.
Here again, there is a great deal of discussion of how to attach wood siding: nail or screw. Most carpenters will attach wood siding with a nail gun. I generally prefer screws over nails. Screws allow for easy disassembling.
Douglas fir was used for the siding. The material is durable and far less expensive than Cedar or Redwood. The siding will be stained a dark chocolate brown. This stain is opaque and will not allow the grain to show through. If I wanted the grain to be a part of the aesthetic, I would have chosen Cedar as my first choice and Redwood as a second. However, the dark, opaque stain will fair better against the sun.
A note on finishing. The wood siding can be finished in place or pre-finished. With finishing in place, the wood is installed and then it is given its final finish. Or the wood can be finished before it is installed. Pre-finishing allows both sides to be finished adding greatly to the life of the wood. This siding was pre-finished. It was given two coats of stain on the back and front. These two coats were applied by brush. A final finish coat was sprayed on the front side of the siding. There is a major difference in the look of stain when applied by brush versus spray. If you are going to have wood finished with a stain, make sure you see samples of both the brushed and the sprayed finish before making a final decision on which to use. There is also lots of discussion about the quality of the application when using a brush versus spraying. My technique of brush and spray resulted in the benefits of both methods as well as the final aesthetic I wanted.
The sequence of rows down the face of the wall is a flat 1x4 followed by a horizontal 1x2. The flat 1x4 was face screwed with stainless steel screws. The horizontal 1x2 was blind screwed.
There are many ways to detail how the two pieces of wood come together at the corner. I like both the alternating butt joint and the 45 degree tight mitered corner. In the end, I chose the tight mitered detail. The corners were simply cut to fit, finished with stain, and then attached to the furring strips.
Here are a few examples of corner details:
At the bottom of the wall is a layer of screen mesh that folds back from the wall under the siding. This mesh allows air to move up behind the wall but prevents insects from entering the space. This is standard practice. I do wonder, however, if this really does much good. Ants, termites, and other critters always manage to get into the walls. I think this is probably more of a deterrent than an absolute prevention.
Once the wall is complete, it will require regular maintenance to keep it looking good. This will involve cleaning and re-staining. The horizontal 1x2 acts like a little shelf to collect debris. This needs to be cleaned to avoid a build up and premature rotting. The wall will need to be re-stained once a year as well. It could probably go longer, but will look better with more frequent staining.