With framing complete and signed off from the inspector, sheathing was up next.
The sheathing is all ZIP R-Sheathing R-6, which is roughly 1/2” OSB with the ZIP system Weather Resistant Barrier (WRB) on the outside, bonded to a roughly 1” thick piece of poly-iso foam. This gives me a continuous thermal barrier on the outside of the house, adding directly to the effective R-value of the inter-stud insulation and wood studs. This puts the house at an effective R-value of roughly 19, which is taking into account the comparatively low R-value of wood detracting from the higher R-value of the rockwool insulation that will go between the studs.
One downside of the R-sheathing is the higher fastener schedule demanded - Huber (manufacturer of ZIP) requires a 4 inch edge and 12 inch field nailing schedule, which comes out to somewhere near 100 fasteners per 4x8 panel. With construction screws running ~$0.2 per and taking 20+ seconds to run down, nailing was the way to go for the sheathing. We rented a nailgun for $200, purchased $200 in nails, and were able to hang 44 panels with 3000 nails in one week. I was able to borrow a Track Saw which proved immensely useful for cutting the panels down to non-standard sizes when needed. I recommend a high quality circular saw or corded version as the foam tends to pinch the blade and bog down the saw.
With 2 people we stayed busy with decent efficiency with a procedure that went something like this:
(1 person) Measure gap/space to get the panel edge to sit on a stud
(1 person) Cut panel to size with track saw
(2 people) Hang panel and use clamps/screws to tack it into place
(1 person) Nail panel according to fastener schedule
We also notched the rafters with a jigsaw to get that thermal barrier all the way up to the roof, and cutout the window openings with the jigsaw (these were later trimmed using a router).
With the sheathing installed we could seal the seams and prep the rough openings.
For seam sealing we used the following products:
ZIP Flashing Tape (3.75”) for seams
ZIP Liquid Flash for all over-driven nails/fasteners
Prosoco R-guard Joint and Seam Filler for the rafter-panel-roof cutouts
And made sure to shingle all the tape (generally working bottom up, horizontal seams before vertical).
Prepping the rough openings was a little more involved. We roughly followed these steps:
Trim the sheathing to the frame using a flush trim bit with bottom bearing (this made an immense amount of dust, another downside of the foam-backed sheathing)
Lay a flexible sill pan using ZIP System Flex Tape (6” wide). For doors I additionally had 22 gauge stainless steel sills pans made that laid over the flex tape.
Apply flashing tape to the sides, folding around the frame to create an air barrier between the frame and sheathing.
Apply a head flashing tape, shingled over the side tapes
To actually install the window, we followed this process:
Check floor in window vicinity for level - level trailer if not level
Tape two shims in place, thick side out (remember that the sills are sloped 4 degrees out at the framing stage)
Place window in opening, center side to side, check level on top of window, check diagonals for square. Adjust shims as needed. Trace window flange onto side and head flashing tape. Remove window.
Apply continuous bead of sealant (DAP Dynaflex Utlra - Black) inside the traced line around sides and top, but not the bottom to allow for drainage should water get back there.
Re-install window. Check level again, fasten screws through the flange (we used GRK #8x3-1/8” cabinet screws which have a large pancake head that works well with the flange). We fastened through all top and side holes but left the bottom at every-other.
Apply side flashing tape, folding 1/2” onto the window frame. Apply head flashing tape, folding 1/2” onto the window frame.
A drawing for the sill pans I had made are below - they were not cheap but it feels good to have a solid pan underneath the doors as insurance to water intrusion. The sill pans shown in the photos below are just placed in as a test fit before the flexible pan and side flashings were installed, after which the pan was permanently attached.
240729 - SILL PANS.PDF
One detail that I regret not doing is boxing out the door openings using solid wood instead of having the sheathing extend to the opening edge as I had it. This could have been be easily accomplished on the sides of the opening during framing by using a 2x6 jack stud ripped down to 5” (3.5” frame + 1.5” sheathing). The solid wood box gives doors with a nailing fin a better structure to mount to, but more importantly allows longer screws to be installed through specifically the top hinge going directly into the framing. On the back door, these screws went directly into the foam, doing nothing. On the big front door, I wound up trimming away the sheathing and installing ~1.5X1.5” wood strips on either side of the door.
Installing the doors was nerve-wracking. The back door is fiberglass and pre-hung, but without a nailing flange, so we had to do a lot of shimming to get the jambs straight, plumb, and the door closing with consistent clearance. However, we were able to lift and install it with two people and it turned out pretty good. I taped the gaps between the opening and jambs just like the window, being careful to limit the extent of the tape onto the jamb as part of the jamb will be visible after exterior trim. The back door opens into the bathroom and thus has frosted glass, and it diffuses light very nicely into the space.
The bigger front door required 4 people to lift and install, but fortunately had a nailing flange to enable tacking it into place easier. I think the door fits and swings well in the opening, but some adjustments need to be made to the latching hardware to get it to latch consistently without missing the strike plate (it is a multi- point locking door, so there are a total of 4 strike plates between the sill and head jamb). Since it had a nailing flange we were able to apply sealant to the opening just like the windows, and did the same taping strategy on the sides and head.
With the whole house sealed (except the bottom), and R-6 insulation from the sheathing, it started to get pretty toasty inside! I took this as a good sign as there was no inter-stud insulation yet installed, and it wasn’t even that hot out. The next steps are exterior trim and siding, roofing, and then plumbing/electrical.
