Exterior Foam Insulation

Just to backtrack a bit…For the exterior insulation, we used two two-inch sheets of Polyiso held to the sheathing with 5/4 by 4″ poplar furring strips and six-and-a-half-inch Fastenmaster Headlok screws.  The one-by-fours cost us about 25 cents per linear foot.   That seems like a decent price, particularly since they’re a full 1″ thick (actually the thickness varied a bit, but was generally about 1 1/8″, so we planed them down to 1″).


We’re using Polyiso because it has a higher R-value than EPS (which is what the ICFs are made of) or XPS (which is what we added to the outside of the ICF foundation).  Polyiso has an R-value of just over 13 for 2″.  Tuff-R and Super Tuff-R are Dow’s Polyiso panels.  Super Tuff-R has a more durable facing than does Tuff-R.  R-Max Thermasheath 3 is another brand of Polyiso that Home Depot stocks, and appears to be less expensive than the Dow products.  The R-value is the same for all three products (i.e. R-Max reports 13.1 and Tuff-R reports 13).

Home Depot in our area stocks R-Max.  It is $30.25/sheet off the shelf and on the Interweb.  I went to the local store and told them I needed 150 sheets.  They put it through their “bid room” and came back with a quote of $26.73/sheet, which is an 11.6% discount.  So the total cost ended up at just over $4,000.

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.


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:

IMG_0360 IMG_0361 IMG_0362 IMG_0363 IMG_0364

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.

IMG_0158 1

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.

IMG_0157 1

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):



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:

IMG_0293 IMG_0292

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

IMG_0373 IMG_0372

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:

IMG_0284 IMG_0286

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.


Choices in Window Installation

The window installation has been one of the more difficult issues to deal with.  The first part of that issue was deciding which product/method to use to flash the windows and achieve the necessary level of air-tightness.

We tested three products/methods on the basement windows.  The first was Tremco’s ExoAir Duo Membrane.  This is basically a flashing tape that is applied to both the inside and outside of the window jamb gap.  Half adheres to the window, and half adheres to the jamb, thereby completing the seal.  Spray foam is applied in between the two (before the second side is applied.  This product seemed to be the least favorable.  First, it was difficult to get the tape to seal to both surfaces without undesirable waves.  But the bigger issue was that it seemed almost impossible to get the spray foam to fill the gap without pushing the tape outward.  It was obvious that this would make it difficult to properly trim out the window box; at least not without significant difficulty.  We estimated that it would have cost approximately $750 for enough of this product to do all 19 windows in the house.  Here’s the best and worst of what it looked like:

IMG_0249 IMG_0246

The second product that we considered is also made by Tremco.  It’s called the Exo Air Trio, and seemed to be a much more effective product.  It basically consisted of a a compressed foam band with adhesive on one side.  It is applied to either the window or the jamb.  Once unrolled, it begins to expand, so you have to plan out the installation a bit.  But the expansion rate is rather slow, so it’s not a mad rush.  Once fully expanded, the foam completely seals all of the gaps between the window and the jamb.  It looked pretty effective, if not a bit amazing.  The biggest downside was the estimated $1800 price tag to do all of the windows.  Here’s what the installed product looked like:


The third option (the option that we went with) uses a three-part solution by Prosoco.  Unlike the other two products, the Prosoco solution seals the gap and flashes the window.  The first part of the process involves the application of Prosoco R-Guard Joint and Seam Filler, which is described as  “a fiber reinforced fill coat and seam treatment.”  It basically appears to be a pink, fibrous, rubber caulk.  It’s applied to all of the seams in the rough opening.  After that, the R-Guard Fast Flash was applied to the entire opening (and the exterior of the opening).  Like the Joint and Seam Filler, it’s applied with a caulk gun.  But then it’s smoothed out with a spatula to create a consistent rubber-like covering over the entire area.  Once dry, it really leaves one with the impression that the opening will be impervious to water and moisture:


Then the window is installed, and an appropriately sized backer rod is installed in the gap surrounding the window on the interior surface.  The final step is the application of the R-Guard Air Dam product to the face of the backer rod:

IMG_0344 IMG_0346

All in all, it appears to be a pretty bullet proof system that interplays well with the Zip System sheathing, and should serve us well.  On top of it all, we estimate that it will cost us somewhere around $500 to cover the installation of all of the windows.