Monday, May 20, 2019

Construction - Standing Seam Steel Roof - Part II: Installation

The prior post covered the preliminary steps leading up to the actual installation of the steel.  This post details the installation of the garage roof that was actually the third section of roof that I had installed but I am using it as exhibit A because, by being a simple rectangle, it is easier to describe. In a subsequent post, I will deal with the hip-roofed porch which is far more challenging.  

Installing Moisture Barriers
After I identified the truest eave-rake corner, I proceeded with the installation in the following order
1.   Metal drip edge over the junction of the sheathing and the fascia (eave side only; the rake sides would be handled with a steel rake trim over the roof panels later); the drip edge is installed first so it can be overlapped by the ice shield in step two.
2.  Two courses of stick-down ice shield paralleling the eave; the ice shield covered the drip edge; code requires that the ice shield extend 24" beyond the interior face of the exterior wall and, since our eaves overhang 24" and the wall is 15" thick, two 36" courses of shield were necessary to meet code.  Unfortunately, the installation was being done on warm-ish winter days that were still too cool for proper adhesion of the shield to the sheathing so we used a torch to seal the edge at the eave then held our noses and used roofing nails to secure the remainder, hoping that the hot summer sun will activate the adhesive later; ordinarily, the ice shield would be unnecessary for an unheated garage but, since ours will be seriously insulated and warmed considerably by the AGS system, I decided to error on the side of caution.
3.  Roofing nails to fasten as many courses of 30# felt paper as it took to reach from the ice shield to the wall of the second story (first photo below (clicking on any of the photos will enlarge them for better viewing)); the junction between the future steel siding on the second story wall and the steel roofing panels would eventually be protected from moisture by a metal trim piece called "dormer flashing"; however, rather than depend on it alone, I continued the felt paper from the roof up the wall a ways as a secondary barrier, taking care not to bend it so abruptly as to compromise its integrity; most roofing contractors use staples in a slap stapler in a rather random fashion but I like the idea of using roofing nails along the overlapped edges of the felt because, when driven tightly, the heads help to seal the hole in the felt against water in a way that staples may not, especially when the paper is damaged by the head of the slap stapler should it be held at an angle to the surface of the paper.
4.  A mason line paralleling the eave to which the ends of the panels could be referenced for a straight installation (second picture).  In our case, the line was positioned for the 1 1/2" overhang specified for the  Rain Handler system that we are using on all sides of the house in lieu of conventional gutters.

It is important to point out that the virtually impervious 30# felt can be used in this situation only because the sheathing, which will inevitably collect moisture, will be able to dry from underneath even though the roof is of cathedral design.  The trusses supporting it are 12" thick and I plan to hold the insulation down from their top edges several inches to allow air to circulate between the insulation and sheathing.  (For a in-depth discussion of moisture abatement, check out the previous posts on Design - Vapor and Air Barriers and Design - Vapor and Air Barriers (Cont'd)). 

Major Problem
As described in the post preceding this one, the metal panels for the garage were the wrong length and had to be reordered.  Unfortunately, I did not catch the mistake until the moisture barrier was in place and, as luck would have it, a strong wind soon had its way with the 30# felt despite its toughness.  A small section blew away but most of it stayed in place even after pulling loose in many areas.  I re-nailed it with Grip-Rite Round Cap Roofing Nails which held it reasonably well until the replacement 
Green arrows = felt paper being unrolled just ahead of
the installation of the steel panels; red arrow = felt paper
extending up the wall a ways for better protection of the
wall-roof interface

panels were available but knowing that it would not be wise to leave the Grip-Rites under the metal panels because they would be proud enough possibly to dent the steel from below if it were stepped on.  Consequently, it was just easier at little additional cost to pull the Grip-Rite nails and lay down another layer of felt but doing both a little at a time just ahead of the next panel to be installed rather than laying it all down at once and risking another wind event.

Observation of Note
I bought 30# felt paper from our local (traditional) lumber yard as well as from one of the big box retailers and, despite only a small price spread, found a significant difference in quality.  Fortunately, I found the discrepancy early enough on the first roof to replace the big box paper with the better quality lumber yard paper before the first panel went down.  And, of course, I used the heavier paper for the rest of the roofs.

Installing the Steel Roof Panels
After the taut mason line has been installed along the eave as a reference for the ends of the steel panels, the panels can then be installed from left to right or from right to left, depending on the location of the truest corner
The mason line is tautly strung so that it designates the
amount of overhang for the steel panels but situated just
low enough that the panels do not touch and distort it
that was identified by using the 3-4-5 method (actually, 9-12-15 or 12-16-20 for more accuracy if the roof is large enough).  Knowing which corner forms the best right angle is a starting point but it is probably not accurate enough to install the first panel without further checking.  If the first panel is not aligned perfectly perpendicular to the mason line, the rake edges of the panels will not align with each other, forming an amateurish saw-tooth edge to the roof, the jaggedness of which is directly proportional to how much the first panel is off.  

To satisfy the 9-12-15 right triangle, the lower end of the
 first panel is anchored with one screw then the "0" end of the
 tape measure is held at the 12' mark on the mason line (red);
 the other end of the tape measure is held on the outside
 edge of the panel at the 9' mark (green) while the upper end of
 the panel is swung in or out until the 9' mark on the panel 
precisely underlies the 15' mark on the tape measure

I installed the first panel next to the rake with the standing seam side towards the rake.  In order to verify the absolutely critical right-angle-ness of the first panel to the mason line, I drove a screw through the predrilled hole in the panel closest 
to the eave then, with help from a neighbor, redid the 9-12-15 measurement.  Any right-angle discrepancy could easily be corrected by moving the top end of the panel slightly left or right to align it with 15' on the tape measure.  As long as care was taken to align succeeding panels with the mason line, the ends of the panels were nice and even.  By contrast, our first installation was the smallish rectangular roof on the west side of the house that we did before cold weather.  I did not think to double-check the right-angle-ness of the first panel as just described and ended up with a little sawtoothness.
Resulting smooth, versus 
saw-toothed, edge

The leading edge of each panel contains a row of holes to receive the screws that are furnished by the manufacturer (for a better understanding of the components, visit ProSnap Steel Roofing on Menards website).  The screws should be no further than 2' apart which meant one in every other hole.  The next panel is lined up with the mason line at the lower end and its standing seam ridge is aligned over the lessor ridge of the preceding panel.  It is then a simple matter of snapping the panels together by pressing on the ridge of the second panel, starting at the eave, until it snaps to place over the ridge of the first panel then repeating the process up the slope of the roof until the panel is fully seated on the prior panel for its full length.  The snapping can be done with the heel of the hand or with a rubber mallet.

Installing the Rake Trim
After the panels were in place, it was time to add the trim pieces that divert water from the rake edges and the junction between the house wall and the roof.  First, the rake trim.  On the side of the roof where the first panel was installed, the trim fits against the surface of the fascia in a vertical direction and overlaps the standing seam ridge in horizontal direction.  It is fastened to the flat part of the panel with screws having neoprene grommets under the heads that keep water from penetrating around the screws.  Since the trim overlaps the standing seam, any water that runs under the edge of the trim is caught by the standing seam so that it is unnecessary to use any sort of caulking under the edge of the trim.

The installation of the rake trim on the opposite
The panels nearly installed; notice the block on the
 fascia to hold the ladder off of the mason line and
out of the way of installing the panels behind it; notice
that the felt paper extends up the wall a ways to be
covered later by the house wrap and cladding
side of the roof is complicated by the fact that there is no standing seam under the trim to divert water.  Therefore,
 to serve as a water barrier, so-called "tape mastic" that has the consistency of very dense plumber's putty but looks like weather stripping is applied to the under-edge of the trim before the latter is screwed to place.

The rake trim came in 12' lengths so I started the first piece at the eave and overlapped it for a few inches with a second
The rake trim did not fit snugly against the fascia; it had
to be tightened down with screws after painting the
 fascia with the final coat of paint
12-footer.  It took still another shorter piece to reach the second story wall.  The trim did not fit the facia tightly in several areas, especially where two pieces overlapped, so I resorted to a few grommeted screws to snug up the vertical part of the trim after the fascia had been painted.


Installing the Dormer Flashing
The dormer flashing is used at the top of the roof to divert water from the junction of the second floor wall and the roof panels.  It slips up under the house wrap and the wall cladding and overlaps the ends of the steel panels.  In doing so, it rests on the tops of the standing seam ridges leaving gaps under it.  In order to keep water from blowing in through the gaps, the latter are filled with so-called "closure strips" that are die-cut to fit the contours of the flat part of the panels and coated with adhesive. They are pressed to place between the ridges just inside the lower edge of the dormer flashing to prevent, or at least minimize, water penetration.  Once the closure strips are in place the flashing is secured with grommeted screws long enough to penetrate through the tops of the standing seam ridges and screw into the sheathing.  The vertical flange of the flashing is also screwed or nailed to the wall sheathing before the house wrap and wall cladding are installed.

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