Friday, February 3, 2017

Construction - Short Truss Wall (Cont'd)

The first post on the short truss wall zeroed in on the unusual handling of the mudsill. This post is about building the rest of the wall then raising it onto the mudsill for alignment and nailing.  (Note: click on any photo to enlarge it for more detail.)

Pre-made Trusses
The jig as modified for the short trusses; notice the
pre-cut components in the background and the long
radial arm saw table for gang-cutting them
The trusses that will support the roof will extend from the south wall of the second story to the short north wall under discussion here.  The fact that I elected to erect a internal bearing wall in between before the back wall was in place meant that a line from the front wall to the bearing wall had to be continued on to the future back wall in order to know the height of the back wall. Since the tape measure would sag too much over such a span, it was necessary to scab together a couple of  2-bys on which to lay the tape measure.  I took the measurement in three places -- in the middle and at both ends.  Fortunately, the results did not vary more than half of an inch -- 43" plus or minus 1/4".

A truss prior to removal from the jig; gussets have
been nailed on
An earlier post detailed the use of a jig for pre-making trusses for the exterior walls.  I used the same jig for the short wall trusses by installing a divider that restricted the working part of of the jig to 43". I have an excellent job-site sliding compound miter saw but the handiest tool for gang-cutting truss components is the radial arm saw in the shop with its long and wide table. In short order, the side rails and short pieces that form the ends for 31 trusses were cut from salvaged 2 x 4s followed by the OSB gussets from new material.

Then I used the jig and two Pasload nailers to assemble the trusses.  Without thinking, all four gussets were nailed to place only to find out later that one on each truss had to be removed in order to have access for nailing the trusses to the mudsill after the wall was raised.

Building the Wall
Trusses made from recycled lumber except for new OSB gussets
The 2 x 6 tandem top plates were laid side-by-side for laying out the wall.  After the lay-out, one set was set aside and the trusses arranged at a 90 degree angle opposite the marks on the other set. As described in an earlier post, I stood the top plate on edge and nailed the trusses to it flush with its bottom edge. Then I nailed a parallel set of top plates to the trusses using spacers and shims on top of the first plates to position them for nailing. Overall, the wall was built in three +/- 20' sections that a friend and I raised in sequence starting from the east end.

Since the mudsills had already been installed, they were not available for nailing to the
The short wall upon completion
bottoms of the trusses before raising the wall.  So, in order to stabilize the bottoms for the raising, I attached a 1-by temporary brace.  The scaffold railings interfered with raising the two end sections directly into place.  Instead these sections had to be raised off-position and slid along the mudsill into the correct position.  As a precautionary measure, I nailed a second horizontal brace to the other side of the trusses before attempting the slide.
Once the wall
The last section ready to raise; notice
the 1-bys bracing the bottoms of the
trusses for raising
was in position, the temporary braces were removed and the individual trusses were aligned flush with the edge of the mudsill, plumbed in an east-west direction and nailed to the mudsill with only one nail close to the exterior side.  The interior side would be nailed after the wall was plumbed in a north-south direction and braced. The decision to nail the outside first instead of the inside was dictated the tendency for the wall to lean slightly inwardly.

The plastic sheeting that was stapled to the mudsill on the day it was installed (first post on the short truss wallwas left in place under the trusses.  Eventually, after the pressure treated wood has dried sufficiently and the roof shades the sill from the sun, the plastic can be cut away without worry about the sill warping due to uneven drying in the heat of the sun.

The concrete contractor placed the anchor bolts in the middle of the 10" wall so they ended up only a couple of inches from the inside edge of the 2 x 12 mudsill when it was cantilevered 4" outward in order to be flush with the stucco.  I added an equal number of anchor bolts an inch or so from the outside edge of the concrete.  The extra anchors at least fell in the
The completed wall from the inside except for replacing
the gussets at the bottom that were removed in order
to have access for nailing the trusses to the mudsill; to
have built the wall without the scaffolding would have
middle of the 2 x 12 and moored the outside half of the sill before the wall was plumbed in an north-south direction.  In conjunction with plumbing, both sets of bolts were loosened or tightened as needed.

So much anchorage may seem like overkill but our location carries three types of risk: tornadoes, earthquakes and subsidence. We have tornado alerts every year, sometime several times, and actual tornadoes nearly every year. Seismologists say that the odds are pretty high for another major earthquake at the New Madrid fault near the Mississippi River in southeastern Missouri.  If one should happen, the seismic waves will follow the gelatinous river floodplain to St Louis with the potential for major damage. Finally, subsidence from cave-ins of abandoned underground coal mines occur regularly in southern Illinois, including in Collinsville where a reasonably new school had to be razed a few years back due to subsidence damage.  The old mine under our site is a little over 200 feet down and, even at that depth, we have to worry about subsidence.

Just like the other 15" exterior walls, the short wall will be insulated with rice hulls to an R-48. The 5" space between the tandem top plates will provide access for blowing the hulls into the wall cavity after the sheathing and drywall are in place.

The first set of top plates were nailed to the wall before raising.  Consistent with common practice, a second set of top plates were necessary to bridge the joints in the first set and establish continuity and alignment. The roof trusses will rest only on the outside-most "top" top plate. Because of the pitch of the roof, there will be space between the inside "top" top plate and the trusses. Consequently, I used less-than-perfect salvaged 2 x 6s for the inside "top" top plate but bought new 20 foot long 2 x 6s for the all-important outside "top" top plate to which the trusses will be fastened.
The jig for pulling the measurement for the roof trusses

Measuring for the Roof Trusses 
Working alone, it would have been impossible to pull an exact measurement for the roof trusses without some sort of jig. One of the new twenty-foot 2 x 6s for a top plate was perfect for making a jig.  I scabbed an extension to it and used it to span the distance between the front and the back walls. Beforehand though, I put a shallow saw kerf in one edge and tacked opposing keepers to the sides of the board in several places.  After hoisting the 2 x 6 to the top of the walls and standing it on edge near the west end, I used a level to make the saw kerf even with the outside edge of the front wall framing and clamped the 2 x 6 to the middle wall to steady it on edge.

Then, to pull the measurement for the trusses, I hooked the end of the tape measure in the
The vertical lines on the 2 x 6 flush with the wall framing; notice that
the variance between locations is only 1/4"  (to see the lines better,
click on the photo for blow-up
kerf and stretched it along the top of the 2 x 6. The task was simplified by having the keepers tacked to the sides of the board that kept the tape measure from sliding off of the edge.  I used a level to mark a vertical line on the 2 x 6 that was flush with the outside framing of the short wall and recorded the length.  
I repeated the measurement at the middle of the wall and near the east end.  Instead of using the tape measure each time, I could compare plumb lines with the original mark on the board.  To my surprise, the variance between the three locations was only 1/4".

I might say parenthetically that the technique for measuring just described is only one example of many techniques that my working-alone mindset comes up with after having read early on John Carroll's book, Working Alone.  I recommend it for any serious DIYer.   The triangular braces in the nearby photo that are clamped to the mudsill while I was using it as a straight edge to assess the levelness of the concrete wall (previous post) was suggested by Carroll.  The four that I made exactly to his prescription have been enormously helpful in many ways.  (Ever tried planing a door while holding it between your legs?  Try using Carroll's braces.)

I needed two other measurements for the trusses. One was the difference in height between the front and back walls, the value of which gives the roof pitch.  This task was made easy by the rotary laser. The other measurement was the horizontal distance between the walls which I obtained in one area only.  Since the situation is a right triangle, the difference in height and the distance along the slope would be sufficient to calculate the horizontal distance between the walls .  But as a DIYer, I was more comfortable pulling all three measurements.  And for added comfort, I asked my mathematician brother-in-law to make the calculation and found that his calculation coincided with the measured distance.

1 comment:

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