Sunday, December 11, 2016

Construction - First Exterior Truss Wall

The actual "first" exterior wall was described in the previous post  but its ten-foot-plus height from the second story floor and a preponderance of windows caused it to be a hybrid instead of a pure truss wall.  The wall described here provides an opportunity to detail the building of an 8' wall using trusses made ahead of time in a jig. Rather than going over the details of truss wall construction when blogging on the rest of the exterior walls, I will link back to this post as a reference.

The wall is the exterior wall between the garage and the living quarters.  By not having windows like most of the other stick-built exterior walls, it allows us to focus on the use of trusses instead of 2 x 4s or 2 x 6s for framing.  The fact that it has a door only means that a couple of trusses are positioned differently than would be the case for a plain wall.  While the garage will be insulated and passively conditioned to a higher comfort level than most garages, the design for the wall is no different than for the rest of the exterior walls, i.e., 15" thick and an R-value of just under 50.

Although I intend to refer back to this post in the future for the details of truss wall construction, it is atypical in one respect.  The wall was put together on the floor of the garage and tipped to place from the exterior side.  The remaining truss walls will be assembled on the house floor and tipped up from the interior.  I will try to nuance the difference during this narrative.

Building the Wall
I took eleven trusses for the wall from the stash of pre-made trusses and built the wall on the floor as is typical of most wall construction.  I failed to photograph the wall while it was laying on the floor so I've included the following photo from the most recent post as an example of horizontal assemblage.  

After cutting the 2 x 6 pressure-treated bottom plates (mud sills) and the salvaged lumber 2 x 6 top plates to length, I laid them side-by-side and used a tape measure to mark lay-out lines on 24" centers as if laying out stud positions for traditional walls. The future pedestrian door to the garage was laid out in the process, centered over the mini-ramp that had been formed into the garage floor to make the doorway ADA compliant.  I stood the trusses on edge in the approximate positions they would occupy in the lay-out. I stood straight pressure-treated 2 x 6s on edge against the bottom of the trusses with the lay-out lines facing the trusses.  The trusses were moved to match the lay-out lines more closely and "eye-balled" perpendicular to the 2 x 6 longitudinally. Then, starting at one end, I aligned each truss accurately with its lay-out line on the mud sill and nailed it with one nail.  I then used a rafter square to make sure the truss was perpendicular to the sill before adding more nails.  

Digressing for a moment.  The rest of the 8' exterior walls will be framed on the floor of the house as opposed to the garage floor.  For them, getting the framing as flush as possible on the interior profile for smoother drywall would be more important than for the sheathing and cladding side of the wall. So, the following procedure applies specifically to the other walls but I used it for this wall while knowing that any minor discrepancies would be reversed and face inward and the garage wall would be the smoothest. A smooth interior profile is another reason for using the straightest 2 x 6s next to the floor which puts them on the interior side when the wall is raised.  

I slipped enough shim(s) under the 2 x 6 and the end of the truss for the truss and the 2 x 6 to be in simultaneous contact with the shim(s) before sending home the first nail  Since the trusses, having been assembled in a jig, are quite true and uniform, the shims merely compensate for any unevenness in the floor that might cause misalignment of the straight 2 x 6 with the trusses and result in a rougher interior profile.

The next step was to attach the interior-most (current situation; exterior-most for the rest of the walls) top plates in exactly the same manner.  (I use the plural form "plates" because the pressure treated 2 x 6s would have had to have measured 20' to have spanned the entire length of the wall.  It is hard to find straight pressure treated two-by-sixes this long so, I used two boards of varying lengths for each plate so that the junction between them on one side of the wall did not fall opposite the junction on the other side of the wall.  The top plates were salvage lumber so I used two of varying lengths such that the junction of one set of top plates were staggered not only with each other but with those of the bottom plates. 

Finally, it was a simple job to nail the second set of 2 x 6s to the trusses.  The trusses were already properly aligned as for perpendicularity and therefore already matched the layout lines on the top plates.  Although the 2 x 6s were salvaged lumber, the two used for the exterior-most top plate were pretty straight while the one of them used for the inner top plate was bowed slightly.  I made sure the bow was facing towards the center of the wall so that it would not hang over the top of the wall and interfere with proper mating to the floor joist as described below.  For the other walls, a plate that bowed outward would make for bumpy drywall or sheathing so I have made it a practice to fasten all crooked plates with the convex profile facing inward towards the middle of the wall.  Since the second set of plates had to be suspended while nailing, I cut spacers to fit over the plates nearest the floor that held them in place but slightly too low.  Then it was a matter of shimming them a little into a nailing position flush with the edge of the truss.

Only one other job remained before the wall was ready to raise.  I scabbed together the segmented plates with short boards and drywall screws.  This maneuver stiffened the wall for raising; the scabs were removed later.  In fact, one of the scabs interfered with proper placement of a truss so its installation was delayed until after the wall was raised and the scab had been removed.
The wall aligned, secured and ready for covering (click on the image
to enlarge it for more detail)

Raising and Aligning the Wall
I used a spirit level to check the north concrete wall and the south truss wall and found that they were both plumb.  Therefore, I could use the distance between them at the floor as the measurement for the length for the wall while allowing a 1/4" tolerance.  The three guys helping me raise the wall were skeptical about such a close tolerance only to have to witness me puffing up and strutting around when it went to place exactly as planned.  

After it was in place, I secured the top by clamping it to the adjacent floor joist to which it would eventually be nailed after the wall was aligned.  The wall had no choice but to be plumb in a north-south direction as it fit tightly against the concrete north wall and the truss south wall.  And fitting against the floor joist took care of its straightness at the top. All that remained for alignment was getting it plumb in an east-west direction after fastening it to the joist.  Plumbing also automatically aligned the bottom longitudinally. The top of the wall ended up being pretty level despite the concrete floor being anything but (see Major Concern below).  Minor differences will be handled as the rest of the rake wall is stick-built on top of it. 

Fastening the Wall To Place
I nailed the top of the wall to the second story floor joist and to the existing south wall. Fastening to the joist took the place of a second layer of 2 x 6s commonly found in double top plates to bridge over joints in the first layer and to tie together intersecting walls.  The need for a double top plate was further diminished by having two top plates side-by-side to begin with.

I fastened pressure treated two-bys to the north concrete wall with robust (1/4") Tapcon screws and nailed the north end of the new wall to them.  I supported any gaps between the bottom plates and the insulated concrete foundation or the concrete floor with composite shims under each truss.  I then used the 1/2" galvanized anchor bolts, that were installed into the top of the foundation when the concrete was poured, to tie down the bottom of the wall.  Because one of the bolts fell in the doorway and had to be cut off, there were only three bolts for the entire wall so I added three more using 1/2" concrete anchors.

Shielding the Wall from the Weather
Since the trusses have gussets made from interior plywood and OSB board and, since my
snail-paced construction schedule means they will be exposed to rain and snow unduly long, I immediately covered the wall with lumber wraps.  I expected to be using relatively expensive 6 mil plastic sheeting (at nearly $100 for a 100' x 24' roll) until realizing that the lumber wraps were free for the asking from my local lumber yard.  I used a lot of staples and a few batten boards to fasten the wrap. How well it resists the wind remains to be seen.  At least I get to test it on this short and easily-accessible wall before using it for the tall wall described in the previous post.
The inside to the left also needed covering

Looming Problem
The concrete floor on which the wall sets is not level, in one area being 1/2" out of level over a distance of only 6' or so.  Nor is the concrete foundation perfectly level within itself or level with the floor in many places.  Consequently, there were some serious spaces under the bottom plates that have to be air-sealed in some manner.  At the time of this writing, I am not entirely sure how to do it, whether to use mortar or spray foam or caulk or ???????.

This will be a common problem for all of the exterior walls so I will have much to say about it in future posts starting with the next post on building the short truss wall on top of the earth contact north concrete wall.  The top of the concrete wall is decidedly unlevel so the challenge of standing a level wall on it without gaps between will be addressed.

2 comments:

  1. So much work! At the end of the day, the level of satisfaction to see your truss wall erected must have been immense in comparison! Thanks for sharing all this process you've undertaken!

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