Thursday, September 8, 2016

Construction - Second Line of Interior Bearing Walls

As explained in the previous post, it made sense to erect the interior bearing walls before starting the exterior walls.  Accordingly, that post went on to describe the first bearing wall -- situated a few feet inside the concrete earth-contact north wall.

This post details the second east-west line of structures, more or less in the middle of the house, that will support the front wall of the second story and the roof above it. This line is 55' long and comprises a complicated combination of a 2 x 4 wall, 15" thick truss wall, a header and a post and beam span over the living room-dining room-kitchen open floor plan.

(For a better understanding, it might help to consult the architectural drawings.  Click on them, as well as on photos here, for exploded views.)

Central Bearing Walls
The central bearing wall nearly complete; truss wall in foreground, post &
beam section in the middle; bathroom framing next and a dual header last
The south wall of the bathroom area comprises the 2 x 4 bearing wall section. Consequently, my first task was to build out the bathroom framing, including the joists that form the ceiling for the bathrooms and the floor for the second floor balcony office. The second story exterior wall will rest on the sub-floor on top of the joists.
Another view of the central bearing wall for better visualization of the
bathroom framing and the dual header to the left

Next, I had to build the north wall of the laundry area and a short section of the exterior truss wall extending east of it -- the section that will house the main entry eventually. Unfortunately, the wall contained pre-made wall trusses with plywood gussets that needed to stay dry and an imminent threat of rain caused me to wrap this section of wall in plastic before taking any photos.  Just as in the bathroom area, the second floor exterior wall will sit on the subfloor of the second story bedroom. Consequently, I had to install floor joists and
The subfloor on which the second story exterior wall will rest; the
narrow isthmus comprises the catwalk between the balcony office
in the foreground and the bedroom in the distance 
tie them into the front wall after it was under the plastic.

The second story exterior wall will also rest on the subfloor of the catwalk that bridges between the two second story rooms and extends westward over the master bedroom. The bridge portion of the catwalk is supported by two beams.  The short section of the catwalk that will overlook the bedroom will be supported by a combination of a header, a joist and a beam.  None of the catwalk could be built until all of the
Pre-made wall sections under cover
beams were in place.  Early on, the pre-made wall sections for the windows were stored under plastic in the master bedroom area.  Now they are in the way of completing the west end of the catwalk. I plan immediately to call in volunteers and lift most of them to the new second story for use in the south exterior wall. Then the remainder of the catwalk can be framed and subfloored to complete the central bearing wall.

Post and Beam Section
When designing the house, my fondest dream was to use salvaged barn timbers for the post and beam supports.  And my step-son and I were able to salvage a few good timbers and many not-so-good timbers from a 19th century barn.  We used the better ones for his house several years ago and the rest would be unsuitable for our needs.  So, in the interest of time and probably money (salvaged timbers can be pricey), I decided to scrap
Friends and family volunteers installing the heavier beam
the barn timber idea in favor of the man-made variety of which there were two options.

The plans called for 3 LVL's (laminated veneer lumber) fastened together to make the main beam.  They do not come in "appearance grade", meaning they are not pretty enough for a natural finish look and must be hidden behind something like drywall. An alternative was Glulams, another man-made product.  A natural finish on them became moot when the manufacture recently quit offering the option of a clean product with no identification information stamped on it.  To use them would involve much sanding to erase the markings for a natural look that even then would have been marginal at best.  The plans called for two sizes of beams. For the larger one, a Glulam beam would cost 28% more than an LVL's; for the smaller, a Glulam would cost 32% more than LVL's.

The posts specified by the drawings were 6 x 6s and the options at my lumberyard were pressure treated yellow pine, cedar and kiln-dried pine.  I chose the latter for a several reasons.  Pressure treated posts were unnecessary, more expensive than the pine and more likely to warp. Cedar, although it could have a natural finish, would not fit in with the other natural woods used in the house and it would be twice as expensive as pine.  The disadvantage of pine is that its natural look does not fit well either and will therefore need a drywall covering.  The robust hardware used to join the post and beams is anything but aesthetic and is best hidden behind drywall as well.   

Beam Construction
For bridging the 20+ foot gap between the bathrooms and the laundry area there needed to be two beams -- the "main" beam, to carry the second story wall and the "catwalk" beam, to carry the north edge of the catwalk.  The plans called for three 1 3/4" thick LVLs fastened together for the main beam supported on posts at both ends and one post midway.  Two LVLs were specified for the catwalk beam with no intervening posts.  

According to information online, the LVLs could be fastened together with through-and-through bolts, with construction screws or could be nailed together with 3 1/2" nails.  For
expediency and to save costs, I chose nails.  The longest nail my Paslode framer shoots is 3 1/4" which is just long enough for fastening 1 3/4" thick LVLs back-to-back.  The nailing pattern for a 12" tall beam was as follows:  Either two or three rows of nails (I chose three) with the nails in each row no further apart than 12" and no closer to the edge of the boards than 2".  Furthermore, the nails in each row should be driven from both sides so that the nails on a given side would be 24" apart in an alternating pattern with the opposite side.   In the case of the main beam that involved three LVLs, I nailed two together 24" OC then flipped them over, laid on another LVL and nailed it in an alternating 24" OC pattern.  The photo shows clamps to align the LVL's for nailing and the chalk lines guiding nail placement.

Despite manufacturer-applied "weatherization", I doubt that the integrity of the LVLs -- much like other manufactured wood products like plywood and OSB -- would hold up under my snail-like construction schedule that postpones getting them under cover for several months.  Therefore, my intention was to caulk any cracks and openings on the topside then paint them with Kilz undercoated in order to buy some extra time.  However, only the larger beam got painted; before I could l paint the smaller beam, we had the subfloor installed and I am assuming that its 500 hour rating against the weather will protect the beam sufficiently.  I do not regret having painted the larger beam because it is more vulnerable to sideways rain coming from the southwest and southeast.

Post and Beam Hardware
The hardware needed to join the posts with the beams was simplified by having beams long enough to span the entire 20' distance.  All that was required were off-the-shelf post bases to anchor the posts to the floor and keep them from touching the concrete and "T" braces (stand-alone post) and "L" braces (end posts) to secure the posts to the beams. The braces were pretty robust -- 1/4" thick -- and were fastened with the substantial 1/4 x 2 1/2" hex screws that came with the braces.

No comments:

Post a Comment

As a do-it-selfer-in-training, I welcome your comments.