Online Blog > Previous Entry 5/1/2015 > 6/09/2015 - Shop framing construction almost complete > Next Entry 7/10/2015
We have been framing a 40' x 95' shop that contains an apartment. This is
the largest building we have built as a firm. It is a traditional stick framed
building on a concrete stem wall. Unlike pole buildings, this will last
forever, and it is varmint proof.
Stick framed buildings are also already to go as far as insulation. There are no special construction needs in the regards. Like all of our buildings, we raise the heel of the truss to at least 16", so that there is room for blown in cellulose to an insulation factor of R-50 right at the outside plate, while still maintaining the ability to ventilate at least a 2" or more space immediately below the roof deck. This ventilation is provided with intake air from the eaves and exhausts at the ridge. Thermal convection keeps the air moving, and the main purpose of ventilation is to control moisture, especially moisture that would otherwise condense on building materials.
In the walls of this building, we will be insulating to R-21 with high density fiberglass batts. The walls do present special challenges during construction as they are 16' tall and 16" on center. There is a lot of lumber in a wall, and as it is being raised it rotates on its axis to a very uncomfortable-to-maintain pivot point, where most of the weight is centilevered far above the framers' heads.
To facilitate this extreme difficulty, we simply used forks on a skidsteer loader to raise the wall above the awkward pivot point.
In the picture below, we had already used a crane service to set these trusses in a short amount of time. They are a 40' span, and it would have been difficult to establish staging down the middle 16' above the shop floor below. Before we left on the day we set the trusses, we added the catwalk 2x4's that run horizontally across the trusses, and we added the diagonal braces. That way if we were going to be away during a windstorm on a long weekend, the trusses would still be in position on Monday.
We had already installed plywood shear wall as far up the walls as we could go before we installed the trusses. This braces and stiffens the building and makes it ready for adding the trusses and other parts of construction. The remaining plywood shear wall will be used to tie the trusses to the walls.
The catwalks and cross bracing will be removed as we install the 5/8" plywood roof deck:
A lot of builders will use OSB for their shear wall and for their roof deck. Typically for a few hundred dollars more we always opt instead to use CDX plywood. While the American Plywood Association says that they are interchangeable as far as application and strength, our real world experience is that OSB can easily puncture if you hit it with equipment or a board, whereas plywood is much stronger in penetration resistance.
Also, we have noticed that OSB will swell more severely when exposed to moisture, which it typically is exposed to during the construction season (we have seen a sheet or two of plywood delaminate because of moisture at a spot where the glue was not adequately applied between layers).
I have had other builders tell me they would use plywood if the homeowner would pay for it. I naturally include plywood in my bids with no option for OSB, except for interior shop walls. I really like 7/16" OSB in that application.
Our posts and beams on the covered porch in the below photo are dead Douglas Fir milled at Specialty Beams in nearby Noxon, Montana. Dead Douglas Fir are trees that had died of beetle kill or other disease. As such, they tend to be more stable trees for milling and hold their shape more reliably over time.
On the roof deck, code would allow us to use as little as 3/8" CDX plywood (CDX means there is a C and a D graded side to the plywood, and X means it will stand up well to the elements of the exterior during the construction phase of the building). However, we always opt for 5/8" 5 ply since it is so much stronger. The 5th ply gives it more structural capability than a typical 4 ply board.