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.

 

 

 

Extending the Gables

As previously discussed, the exterior walls are covered with 4″ of polyiso foam.  On the gable sides of the house, that foam extends up about 18″ past the second floor ceiling.  This places the top of the polyiso in line with the top of the 18″ of blown-in cellulose that will be placed above the second floor ceiling.  Since the remainder of the gables will have no exterior foam, we had to build out the gable walls five inches to place it in line with the wall below it…actually, we built it out five-and-five-eights inches so the gable siding (fiber cement board and batton) would be a bit proud of the siding on the building below (fiber cement lap siding).  I’m sure that some (many) might think it over-kill, but we accomplished the build-out with 2x4s.  First, we “Timberloked” vertical 2x4s into the vertical truss members.  To do this, we placed the 2x4s on edge, attached a 2×4 to it on-the-flat to create a “nailer,” and attached a strip of 5/8″ plywood to the back.  This was then screwed through the sheathing and into the vertical studs in the wall truss.  That brought us out 4 1/8″.  Then we nailed horizontal 2x4s to the verticlals every 12 inches.  That brought us out to 5 5/8″.  We also used horizontal 1x4s to provide us with nailers over the 18″ of foam that extends into the gables.  To keep it in line with the walls above, that was also packed out with 5/8″ plywood strips, and the plywood was notched to allow air to circulate and travel up the wall (behind the siding), into and through the gables, and out the triangle gable vent that will be placed at the top.

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Exterior Door Extension Jambs

As with the windows, we used Azek to build five-inch extension jambs for the doors.  However, unlike the window extension jambs, which used 3/4″ material, we used 5/4 thick Azek for the doors, and pocket screwed it into the door jambs (giving us a 1/4″ reveal).  We also used Wolf decking for the sill extension; which will match the decking on the wrap-around porch, and was just wide enough to extend 1/4″ past the final skirt trim (which will be 6/4 Azek below the door threshold).  The doors will use the same type of nailers and trim as used on the windows:

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Window Extension Jambs

Because of the four inches of exterior foam board and full one-inch-thick strapping to hold it on and provide a nailer for the siding, we needed to create extension jambs for the windows and doors.  As with most tasks, there are a number of ways in which that task could have been handled, and the solution is partially dependent upon the location of the window within the exterior wall.

In our case, the architect decided that the windows should be installed within the 2×6 framing (i.e. flush with the Zip sheathing), rather than even with the exterior plane of the wall/siding structure.  The architect did this to achieve better thermal performance, and also to provide a more appealing exterior by providing depth and shadow lines.

Given that position, we had to come up with a method for extending the window (and door) jambs five inches to place the exterior jamb surface to a place where it could be properly trimmed out; trimming the jambs out that far, would put them in the same plane as the surface of the 1×4 strapping.

Rather than building plywood extension jambs that extend into the rough opening and attach to the wide surface of the 2x6s that form the opening, we decided to use Azek, and build the boxes so they would attach to the outside of the building structure, with screws driven through the sheathing and into the 2x6s that form the rough window opening.

The jamb extension boxes are glued and tacked together.  We cut a 3/8″ wide by 7/16″ deep rabbet into the inside rear edge of the sides and top of the boxes.

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This allows the Intus windows (which don’t use a flange) to be installed 1/2″ proud of the wall sheathing and fit into the extension jamb and over the sill.  We also put a 5 degree pitch on the box sill, and made the sill a half inch wider than the sides and top to allow water to drain over the trim sill.

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Attachment flanges (1 x 1 3/4″ Azek strips) are tacked and glued to the sides of the boxes to allow the boxes to be screwed through the sheathing and into the studs.  On the smaller windows, we only put these flanges on the sides of the boxes (as shown above).  On the larger windows, we also put them on the top and bottom for added support.

Here are a couple of photos of the boxes installed (no nailers or trim yet):

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Once the box is attached to the house and the 4″ of foam board is applied to the exterior of the walls, we glued and pocket screwed 1×8 Azek “nailers” to the sides and top of the boxes to serve as an attachment point for both the trim hoop and the siding. A 1 x 3 “nailer” is attached to the bottom.

Here’s what the nailers look like when attached:

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And here’s what they look like on the house:

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Once the nailers are attached, we’re ready to attach the trim.  The trim, which will be in the “Arts and Crafts” style, will look like this:

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The sides are 5/4 x 4 1/2.  The top is 6/4 x 5 1/2, and the sill is 1 1/2 x 2 1/2, with a 15 degree pitch. The inside dimension of the sill is 1/8″ wider than the sill on the box.  When installed, the trim sill is pushed up against the bottom of the sill on the box.  The trim hoop is sized to result in a 3/8″ reveal all the way around.

All in all, it’s an extremely sturdy structure, and they’re very quick to build (much quicker than this explanation conveys).  However, care must be taken to ensure that they’re installed square (as we built them, there is about a quarter inch of play each way that can result in an out-if-square installation if you don’t pay attention).  Also, the Azek is flexible enough that variations in the sheathing (e.g. where the wall bows slightly) can result in a bowed front edge on the box.  If the bow is in the sides or the top, the 1 x 8 nailers will take it out when they’re attached.  But if the bow occurs in the sill, the 1 x 3 nailer may not provide enough rigidity to remove it.  The easier solution might be to shim between the attachment flange and the sheathing if necessary.

 

External Framing Completed

The basic frame and all Zip sheathing was completed on September 16th.

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In the two photos below, you’ll see how the Zip is being wrapped over the top of the second floor walls.  Once we prep for the future attic insulation (we need to install some type of baffle to retain the 18″ of cellulous),  Zip will be installed on the rest of the second floor ceiling and the seams will be taped.  As can be seen in the following photos, the finished side will face down.  It could have gone either way, but since the tape will be placed on the bottom, this seemed to make most sense.

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That’s 1/2″ Zip in the photos above.  The same thickness we used on the exterior walls (we used 5/8″ Zip on the roof).  Looking back, we could have saved a bit of weight and money by using 7/16″.  I was a bit concerned with the ability of the roof trusses to hold the weight of the drywall, zip, and 18″ of insulation.  But they’re engineered to support 10lbs/sqft, which provides a reasonable margin of safety, as the weight of the drywall, Zip, and insulation amounts to less than seven.

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The combination of perspective, background lighting, and lack of windows and porch make the house look mighty small.  Hard to believe that its over 2,000 square feet.

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The rest of the Zip was taped a couple of days later.  The Zip tape dispenser/roller proved difficult to use effectively.  The roller seems to have a slight crown that makes it difficult to seal the edges and causes the roller to drift.  But the job was completed:

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The Framing Continues

By September 5th, most of the necessary framing materials had been purchased and assembled, and the framers started working up from the first floor decking.

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The longest wait was for the trusses that will be used for the roof, porch, pents, and the second floor.  Unlike the first floor (where we used Flack Jacket I-Joists), we’re using floor trusses for the second floor because we’re figuring that they will make it easier (than I-Joists) to route the pluming, the heat pump lines, and the ERV ducting.  The following photo shows the floor trusses, along with a bit of post and beam work created by the builder, Hugh Lofting Timber Framing, that will define the division between the kitchen and dining area (and also the fir beams that will be above the kitchen/living area):

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As shown in the photos, a number of the key principals of “advanced framing” are being applied to the shell structure; framing 24″ on center;  joists, studs and trusses will be “stacked” (i.e. line up); single headers; single top plates, and two-stud corners.  This is new to everyone involved in the project.  So the pace was slowed down to ensure that the essential details were correct.  We lost count on the number of tubes of polyurethane caulk used.

We’re using Huber’s Zip System for the exterior sheathing, which  think is pretty common these days.  But since we are framing at 24″ on center, and I wanted to ensure a bit extra structural support, I opted for the half inch Zip for the walls, rather than the more common 7/16″.  That decision resulted in an upcharge of approximately $1.30 per sheet ($21.75 vs $20.45).  Basically, the entire shell will be covered with the Zip sheathing.  The 1/2″ product will be installed on all vertical exterior walls and the second floor ceiling.  A 5/8″ version of the product will be used for the roof.  Of course, all of the seams will be sealed with the Zip tape, at about $26 per roll.  The estimated use is one roll for every 7.5 panels.

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As the photo indicates, when initially completed, the shell will only have one opening, which will be for the front door (the basement windows and the door in the Bilco well will also be installed).  Once the blower door test passes the Passive House standard of .6 ACH @ 50 pascals, the windows and the two remaining doors will be installed, and the shell will be retested.

By COB on September 11th, the framers were closing in on completion of the second floor.  Here’s a couple of photos from earlier in the day:

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The First Floor Decking and Backfill

On August 5th and 6th the framers came out and framed out the first floor decking.

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The sill plate went on over the sill gasket with two beads for caulk, and the rim boards, I-Joists and subfloor followed.

We used Weyerhauser 1 1/8″ TJ Rim Boards.  I don’t like them.  We’ve been experiencing a lot of rain, and some of them swelled to anywhere from an-inch-and-a-quarter to an inch-and-three-quarters.  Everyone tells me that it’s fine. But I’m still convinced that I want to use 1 3/4″ LVLs for the 2nd floor  rim boards.  They’re three times as expensive (about $1.50/lf vs. $4.50/lf).  But that only amounts to a few hundred dollars.  And since the porch roof will be cantilevered off of the 2nd floor rim boards with blocking (more on that later), I’ll feel a lot better about the connection.

It took a bit of effort, but I got the building inspector to OK the use of Weyerhauser Flack Jacket I-Joists (for the first floor).

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This allowed me to avoid having to drywall the basement ceiling to achieve the fire protection rating required by the 2009 International Residential Code (IRC).  In addition, it actually appears to be a money saver.  For instance, considering the 360 Series 11 7/8″ I-Joists, when we checked on pricing, we found that the Flack Jacket version runs about $3.40/lf, while the regular version runs about $2.53.  Figuring that we had about 500lf of I-Joist in the first floor, that amounted to an increased cost of approximately $565.  However using the Flack Jackets would preclude the need for drywalling the basement ceiling, which I am told would be about $42/sheet installed, or about $1,300.  So we figure that use of the I-Joists will result in a savings of approximately $700.

The inspector’s initial concern was that, while the evaluation report that I provided him said that Flack Jacket I-Joists were approved under the 2012 IRC, it said nothing about the 2009 code, which is still in force in Pennsylvania.  His thinking seemed counter-intuitive to me.  So I contacted one of the Tech Reps at Weyerhauser, who was extremely helpful, did the research, and provided me with the following explanation:

“I dug into this a little and it is an interesting issue. PA is enforcing the 2009 IRC code with a couple of legislative changes. The base 2009 code does not require fire protection of floors over basements. This is new requirement in 2012 IRC. The base 2009 IRC does include a controversial requirement for sprinkler systems in residential construction. The PA legislature decided to add the fire protection requirement- based on the 2012- while allowing the sprinkler requirement to be waived . So while it is true that our code report does not comply with the 2009 IRC, it is only because membrane protection was not required in the 2009 BASE code. I have attached the bill related to this issue. It begins on the bottom of page 10. Our code reports list only the base codes and do not include special state provisions or amendments. Flack jacket does provide the 2×10 equivalence as the provision intends. Ultimately it is up to the code official in each jurisdiction to determine what he will accept, but we are certainly willing to work with him and address any concerns.

Based on the above explanation, I provided the inspector with a letter of explanation together with the Pennsylvania legislation, and he gave his approval.

I should also note that, prior to giving his approval, the inspector suggested that I use a product called No-Burn.  It’s a spray-on coating that achieves the same purpose.  But it just seemed like more work, and more of a mess, than the Flack Jacket alternative.

When it came to the sub floor, I was particularly concerned with its ability to hold up in the rain (given that we’ve had a particularly wet summer and things were moving forward rather slowly).  I was also concerned with floor bounce, which we had experienced in our last home and just seemed to detract from a feeling of quality.  To combat the latter problem, I’m certain that I over-killed the issue by using the 360 Series 11 7/8″ I-joists for the longer (16′) spans (we used the 210 series for the shorter spans, and their specs showed that it would have been fine to use them throughout).  But to avoid any issue that might be caused by the rain, and to provide double insurance against bounce (particularly since the I-Joists are 24″ on center) I decided that I wanted to use Advantech flooring.  The floor is rock solid, and looks like it would support an elephant.  And since it was installed, we’ve had at least a half-dozen days of rain.  But it looks like it’s holding up well.

The Advantech sub floor (we used 1″) ran about $41 per sheet, while the 2nd choice, 7/8″ Weyerhauser EdgeGold, came in at about $34 per sheet.  At approximately 80 sheets,that resulted in an increased cost of approximately $560.

Once the decking was on, we had the precast Bilco well installed.  It’s a $3,200 unit (with primed steel doors), and bolts to the foundation in four spots (two high and two low).  In our case, we had it bolted right to the exterior foam, ensuring a complete thermal break.  The only issue encountered was a couple of pieces of rebar right where the fourth hole was to be drilled.  After several hours of struggling, they were able to cut through it and get the well installed. We then covered the seams with Resisto peel and stick, and wrapped the dimple board around the inside corners, and we were ready for back-filling.

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I still don’t quite understand how Bilco sizes these wells.  We ordered (and received) a size “E” well, which is supposed to be used for applications where the distance from the footer (i.e. the bottom of the well) to final grade is anywhere from 83″ to 91″.  But given that the outboard edge of the well casting is only about 5″ inches thick, that simply doesn’t seem possible; particularly when considering that the grade should fall away from the house.  Our final grade will be about 4″ above the dimple board (which is about 86″ from the footer). With a bit of creative landscaping, I’m sure we can make it all work out fine.             IMG_0073

It took three of us a day-and-a-half to backfill; using a jumping-jack tamper for every two-foot layer.  We didn’t bring it all the way up to final grade because the EFIS still has to be installed everywhere other than under the porch.

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Then we sealed every seam, inside and out, with Sica Polyurethane Caulk.  I think it took somewhere around two dozen tubes at just under $6 each:

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