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Glazing a Custom Sunroom, continued

Assembling the Parts

Before installing any of the extrusions, we pressed the EPDM gasket material into its intended raceways (Figure 3). Each gasket should seal tightly against intersecting and adjacent pieces. Therefore, it's a good idea to allow the gasket material several hours' rest before final trimming to recover from possible stretching.

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Figure 3.The crew used soapy water as a lubricant to help seat the gaskets in their raceways (left). Because the gasket material has memory, or a tendency to shrink back to its original form after stretching, it's important to install the gasket strips long and let them shrink for several hours before final trimming. The top perimeter bar is installed first, with mitered ends, then the side bars (right).

The first extrusion installed is the head member, which runs across the top of the openings, the full length of the glazing area. We predrilled the base of the perimeter bar with a series of holes, starting 2 inches in from each end and spaced 15 inches apart, for fastening the bar to the framing with the #10x2-inch stainless-steel screws provided. The prescriptive spacing ensures that there'll be no conflict with the cap-bar screws that are installed later, on 12-inch centers. The inscribed centerline in the underside of the bar helped prevent the 7/32-inch drill bit from wandering off center. Each end of the head piece gets mitered to the perimeter sides.

The perimeter sides are square-cut at the bottom ends, while the intermediate vertical members are square-cut at both top and bottom.

Bottom perimeter members are cut to fit between the mullions. It's important to drill the required 3/16-inch weep holes, one at either end of each bottom bar, before installation. Drilling later risks punching through the extrusion and chipping the glass edge. Nicking the edge of tempered glass courts disaster, as the sheet may spontaneously shatter into thousands of glittering "dice." The weep holes drain the interior gutter system and prevent condensation from overflowing onto and staining the supporting wood frame. Because of the importance of positive gutter drainage, the Pro-Seal system should not be installed on roof pitches less than 3 in 12.

Glazing

With the complete base-bar layout screwed to the frame and the gaskets set, we're ready for glazing. We use 1-inch insulating glass, with a laminated interior panel and a tempered exterior panel. If, by chance, the glass is hit and breaks, the exterior panel will break into small, harmless pieces; a bonded plastic sheet prevents the interior panel from shattering and catches the fragmented outer panel, preventing harm to anyone below. We ordered the interior panel with a low-e coating on the side facing the insulating void, as much to help reduce interior condensation as to control heat loss.

Pro-Seal uses a pair of 4-inch-long rubber setting blocks, screwed to the bottom perimeter bar of each panel section, to fully support the double edge of the glass panels. Neglecting to support the entire edge of an insulating glass panel — both the inner and outer panes — is a major cause of seal failure in sloped glazing. If only the bottom (inner) pane is stopped at the base of the panel, the upper panel may "creep" downward and rupture the seal. Generally speaking, thermal glass fabricators will not guarantee against seal failure in sloped glazing applications, especially when they're not in control of the installation.

The glazing panels are heavy as well as fragile; four of us working together boosted them onto the staging and lowered them into place. We used glazier's vacuum cup grips to handle the panels (Figure 4). A pair costs around $150, well worth it if you frequently install glass panels or mirrors.

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Figure 4.Vacuum cup grips make large, heavy glass panels easier and safer to move.

Flashing

Because of the custom nature of each installation, flashing isn't included with the glazing bars. Pro-Seal recommends using minimum .032-gauge aluminum flashing to prevent rippling. We bent the profiles on a 10-foot brake, using bronze coil stock to match the system components. The manufacturer provides good detail drawings in its design manual.

The eaves flashing goes on first, before the extrusions are installed (Figure 5). After the glazing panels were in place, we installed side flashings, which overlap the apron flashing with a 45-degree end cut, giving the appearance of a mitered joint. The overlap is set in silicone caulk and secured with a few stainless-steel screws. The design manual offers two methods for sealing the side flashing to the glazing system: by running it flat beneath the side perimeter bar, or by making up-and-over right-angle bends and clamping it under the glazing cap and gasket. We decided to go with the second, more surefire method.

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Figure 5.Because every overhead glazing job is different, flashings are custom-bent on site. The first installed is the eaves flashing (top), which goes on before any glazing bars. After the glazing is in place, the side flashings are installed (bottom).

The head flashing breaks up and over the top perimeter bar to fully cover the glazing cap. A strip of foam-backed tape between the flashing and cap bar closes any gaps and serves as a backer rod behind a final bead of silicone caulk.

Glazing Caps

The gasketed glazing cap serves as the primary barrier to water intrusion around the glass. Because you can expect aluminum to expand in hot weather, the design manual requires butt joints in the cap to have a minimum 1/8-inch expansion gap, to be filled with silicone caulk. However, the EPDM gasket must be cut long to bridge the gap and butt snugly against adjacent gasketing. The glazing cap gets drilled every 12 inches for the 1/4-inch gasketed stainless-steel machine screws that connect it to the base extrusion (Figure 6).

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Figure 6.Attaching the gasketed glazing cap makes the installation watertight. A snap-on cover trim will hide the screw heads.

A running depression in the cap creates a recess for the fastener heads. The heads are finally concealed by a snap-in trim cover strip that must be gently tapped into place with either a wood block and hammer or a rubber mallet. A good grade of silicone caulk on all the joints and intersections tops up the glazing system.

The Pro-Seal design manual is detailed and clear. When properly installed, the system will remain leak free for a long time. We've been using this system for 15 years and have many satisfied clients.

John DeCiantisowns DeCiantis Construction in Stonington, Conn.