Truss Uplift

As I mentioned earlier, our roof was constructed using trusses rather as opposed to being stick-built in the field:

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I don’t know if using roof trusses is less expensive than a roof built in the field.  But I do know that the trusses allowed us to construct the house without any load bearing walls on the second floor (the second floor floor was constructed using floor trusses, and did require a single load bearing wall on the first floor).  This made it much easier to seal the second floor ceiling (with Zip sheathing) because it gave us the ability to do it before any interior walls were constructed.  But it also raised (at least with me) two concerns.

The first concern was something that I happened upon by accident, when I encountered an article that mentioned “truss uplift.”  Evidently, truss uplift is a condition that can (but does not always) occur when the bottom chord of a roof truss (which is buried beneath the insulation) absorbs moisture at a rate that is different than the top chords (that run along the roof line).  If my understanding is correct, when this happens (usually in winter), the upper chords bow causing the bottom chords to lift.  If the interior walls and the drywall ceiling are attached to the bottom chord, this “uplift” can cause damage to the walls (which are presumably also attached to the floor.  It can also cause the drywall ceiling to separate from the drywall on the walls.

Simpson makes a bracket that is used to attach the interior walls to the trusses in a way that prevents this problem (if the drywall ceiling is installed without using screws near the seam).

The problem is that these brackets can’t be used in our house because the Zip sheathing is attached directly to the trusses.  So that left us with two options; either hope that it doesn’t become an issue, or come up with a way to allow the ceiling to move without tearing up the interior walls.

The solution that I came up with (which I hope will work should the problem occur) is as follows:

First, I screwed the top plates for the interior walls to the Zip sheathing and trusses (or blocking between the trusses where the walls ran parallel to the trusses):

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Then I constructed the interior walls, screwed them to the floor, and attached them to the top plate with four-inch Timberlok screws, which I did not screw in completely:

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If you look closely, you can see a couple of the Timberloks in the above photo.  They have two inches of thread.  The other two inches is a smooth shank.  Therefore, if they are left slightly less than a half-inch “out,” all of the threads are embedded in the top plate and Zip sheathing, and there is room for the top plate to rise 1/2″ independently of the wall that is attached to it.

So that’s part of the solution.  The other part was to ensure that the drywallers did not screw the drywall to the top plate and that they kept the ceiling (drywall) screws back, away from the interior walls.  As with the Simpson brackets, the idea is to allow the trusses to move up, without forcing the drywall to separate at the seams.

Hopefully all of this was unnecessary.  That may be the case because a) the interior of our house was unfinished for a year, (giving the trusses to dry completleyl) and b) unlike a typical house, our house isn’t going to allow any moisture to move into the attic during the winter months (or any other time during the year, for that matter).  But then again, maybe the upper chords dry out more than the bottom chords in the winter.

 

 

 

Problems With the Siding

Early in the project, my wife and I decided that the exterior of the house would be covered with fiber cement siding.  Lap siding would be used below the gables, and board and batton would be used in the gables.  I had considered vinyl and fiberglass siding, but ruled them out because neither was approved for installation over 1×4’s placed 24″ on center.  All things being equal, I would have preferred to use wood, but decided against it for several reasons.

The first reason was cost, particularly with regard to cedar.

The second reason was durability.  We currently live in a house clad in cedar lap siding.  We also have a garage clad in wood (board and baton), though I’m not sure if it’s cedar.  The problem has been woodpeckers and carpenter bees.  I didn’t want to have to deal with either in the new house.

The final reason centered on paint.  The thought of painting another house was not enticing.  And I didn’t want to deal with the added expense of having to back-prime every board during installation and then paint them after they’re installed.  I purchased the fiber cement siding pre-painted, and my hope was that the paint would last longer on fiber cement than it would last on wood.

So fiber cement it was.  Once that decision was made, it came down to a choice between Hardi and Certainteed.  We settled on Certainteed because my wife liked the color they offered (Cyprus).

The siding was purchased in December 2013, and installed the next month.  Seams between siding boards were butted without gaps.  Gaps were left around window trim (generally about 1/8″) and caulked.  The installation looked great.

But problems started surfacing a couple of months later.  In March, cracks started developing around some of the windows; usually at a lower corner, but in a couple of instances at an upper corner.

Here’s a piece that feel off of the upper left corner of a second floor window on the west side of the house (I placed a piece of coil stock over the hole to keep the rain and bugs out):

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Here’s a crack that developed at the corner of a window that is under the porch roof on the north side of the house:

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This crack developed at the corner of a first floor window on the west side:

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Eight instances of these issues have since developed.  They’re on all four sides of the house.  There was some initial speculation that the cracks may have been caused by expansion of the Azek window trim.  But I’ve discounted that for several reasons.

First, per Azek, the expansion rate of their product is 1/8″ per 18 feet.  This is consistent with the 38 feet of skirt board on the south side of the house.  It consists of three pieces, and two one-eighth gaps were left between them.  No issues have developed:

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Also, gaps of 1/8″ were left (and caulked) between the siding and the window trim, and none of the trim pieces are anywhere near 18′ long. Even on the widest window,the Azek expansion shouldn’t have been more than 1/16″.

In addition, as the temperatures have risen, we’ve noticed some obvious cupping of the siding on the east and west sides of the building when the sun hits the surface:

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As seen in the photo, the cupping has occurred on all the boards, even those below the window.  The same issue hasn’t developed on the south side of the building.  But my guess is that this is due to the roof and pent overhangs, which keep almost all of the surface in the shade.  Here’s a photo of the same (east wall) area when the sun is not hitting it:

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The most obvious explanation for the above photos (in my opinion) would be that an insufficient gap was left between the boards at the time of installation, particularly since the installation occurred during the January, when the temperatures were generally below freezing.  However, leaving gaps would have run contrary to Certainteed’s installation instructions, which contain the following note on page 36:

“Note: It is never acceptable to leave a gap of any size at a butt end/joint.”

My conclusion is that the cracks are developing at the windows simply because they are the weak points in the siding.  And one thing that surprised me about the siding was it’s brittleness.  There appears to be absolutely no give in the product.  I’m surprised that it can even be nailed.

This prompted me to do a bit of research, during which I discovered the following:

– In November 2013 (one month before we purchased the siding), Certainteed entered into a $100 million settlement pertaining to this lap siding.  The settlement covered any siding installed prior to October 1, 2013.

– The siding on our house was manufactured in December 2012.

– On February 1, 2014, Certainteed stopped selling fiber cement lap siding.

Needless to say, all of this is concerning.  Certainteed has no comment on the cause of the issue.  I’ve got the siding sub coming out next week to replace the boards that have cracked, and I’m hoping that more do not develop.  I don’t yet know what I’ll do about the bowing issue which, at this point, is only cosmetic.