Building Fixed-Glass Windows

While building a house a few years ago, we experienced the usual number of surprises at material costs and delivery times. One of the worst surprises concerned fixed-glass windows. The home is a passive-solar design, so it includes many such windows. We reasoned that because these windows were substantially simpler in construction than the wooden casement windows used elsewhere, they would cost less.

A typical wooden casement is a marvel of precision construction, maintaining airtight weather-seals over many linear feet of sash and through years of winter storms and summer heat. In the San Francisco Bay Area, casement windows typically cost $20 to $30 per sq. ft. of glazed area, including screens. Although window wholesalers told us not to rely on this approximation, we found it to be generally accurate.

We were shocked to discover that a fixed-glass equivalent would run $35 to $45 per sq. ft. of glazed area - an assembly without moving parts or weather-stripping. Adding insult to injury, the first company we contacted quoted a 14 week delivery time. Other companies promise slightly better delivery times, but could not break the $35 per sq. ft. price barrier.

We did not consider ourselves window craftsmen. And it remains true that casement window require so much special tooling that we could not reasonably compete with a production window shop. But the project architect convinced us that we could build quality fixed-glass window in a reasonable amount of time and do so at a price (including our labour, of course) far below the alternatives.

Simple frames
The house is a single-story contemporary with opposing shed roofs and a clerestory. Because the fixed-glass windows follow the roof lines they are trapezoidal. Altogether there are 12 of these windows scattered around the house. We started by laying out all the windows full-scale on the sub-floor.

By far, the most important detail in any window is the sill. The sill is the last stopping point for water before it either drips harmlessly off the house, or is pulled destructively into the walls by capillary action. The 15o bevel on the front of the sill directs water away from the building, while the drip kerf underneath the sill guarantees that capillary action will not pull the water into the house. Milling the jambs and sills from solid stock and incorporating integral stops (rather than using applied stops) similarly prevents water from migrating past the glazing.

The window sills are 1.75 inch thick altogether, with a 0.75 inches thick integral stop, a 0.75 inches thick centre section and a 0.25 inches rabbet in the bottom that fits over the rough opening and further discourages water from entering the house. The head and jamb pieces, which are identical to each other in cross section, are essentially sill pieces without the bevel and kerf details, but they are only 1.50 inches thick altogether because they do not need the 0.25 inches rabbet. The jambs and sills are made of #1 clear white pine and were milled on a table-saw with a dado blade.

All the surfaces that would show after installation were first sanded, and then the pieces were cut to the proper length and angle. The integral stops on the end of each piece had to be cut back (notched) in order to butt the side jambs into the headers and sills. We cut the sills so that the bevelled portion extended past the side jambs on both sides by the width of the exterior trim. The frames were glued and screwed together, and then each was laid on top of its respective chalk-line template on the sub-floor to check the dimensions.

Setting the frames
After the glue had cured, we painted the window frames, the exterior stop and the exterior trim with two coats of primer. After cutting the exterior trim, we attached it to the jambs and heads with a pneumatic finish nailer, driving 8d aluminium finish nails. We stay away from electroplated galvanized nails because they seem to lose their plating and eventually bleed. If we were hand-nailing, though, hot-dipped galvanized 8ds would have been fine. The nail holes were puttied and sanded smooth.

The finished (but unglazed) frames were then set in the rough openings, plumbed and nailed into place. We use standard flashing details, but for good measure, we always run a bead of caulk between the top of the trim and the building paper. After installing the siding, we caulked again between the siding and trim.

Fitting the glass
To make sure the insulating glass would fit into our frames, we cut cardboard template 3/8 inches smaller than the width of the window opening and 3/16 inches smaller than the height and gave them to a glass company. When installing the glass, you can either seal it with glazing tape or with caulking. But if you use caulking, make sure it is compatible with the seal used by the insulating-glass manufacturer. In this case, we used caulk and applied it against the vertical face of each integral stop. We followed with a second application on the outside between the glass and the exterior stops. We used redwood for the exterior stops and nailed them up with 6d aluminium nails. For extra protection, we cut 15o bevels in the sill stops.

We set the glass directly on the sill and have had no problems with it in the two years that the windows have been in place. We have since learned, however, that the Sealed Insulating Glass Manufacturer's Association (SIGMA) recommends setting fixed glass on a pair of small neoprene blocks (called setting blocks), which help distribute the weight of the glass and prevent water from being trapped behind the glass. SIGMA also recommends drilling a pair of weep holes in the exterior sill stops.

Corner sidelight
At the front entrance of the house we built a large sidelight with two panes of glass meeting at right angles. In this case only one header - supported by an exterior wall on one end and by an interior partition on the other - was needed to carry the roof loads. It is conceivable that two headers could be required in circumstances where two load-bearing walls intersect at the window. Several manufacturers of metal connectors make a framing clip for headers that intersect other headers. Because of the unusual glazing detail, it was critical that the rough opening be plumb on either side of the window's corner.

The corner unit was built with the same jamb, sill and head sections as the other windows. First the sill and jamb stock were fabricated as described in the previous sections. Then the sills and heads were mitered and cut to length in matching pairs. Accuracy in cut length was important to guarantee a square opening for the glass. The jambs were cut to matching lengths and the whole unit was assembled near the rough opening.

Before the glue had a chance to set, we placed the unit in the rough opening, aligned the corner of the sill with the corner of the framing, shimmed it level and tacked it in place. We used a plumb bob to align the mitered corner of the head jamb to the identical point on the sill below. Next, the sill was tacked near each jamb and the head adjusted in or out until plumb. Then we stepped back and double-checked that everything was plumb and level.

It was not critical that the corner be exactly 90o. The critical requirement was that the jambs were plumb so that the two panes of glass would meet neatly at the corner. If small adjustments were needed, this was the time to make them. Once everything was plumb and level, we set the nails, puttied the holes and sanded them smooth.

Because of the proximity of the window to the door and to the floor, we had to use safety glass. And to achieve a clean line at the intersection of the glass, we used single panes (1/4 inches thick) rather than double-pane insulating glass, which would have made an awkward corner. We installed the glass exactly as before except that we applied a bead of clear silicone between the mating glass surfaces at the corner. After the silicone set, we trimmed off the excess inside and out with a razor blade. The final step was to miter the exterior stops and nail them into place.

Number crunching
When the windows were finished, I calculated how much they had cost us. We paid $4.34 per sq. ft for the insulating glass, $3.29 per sq ft for the tempered glass and billed our time at $40 per hour. The cost for all 12 windows and the corner side-light averaged just under $15 per sq ft.

Building fixed-glass windows is simpler than you might think. After making and installing the window frames, a bead of caulk is run around interior stops and the double-pane insulating glass is set in the opening and held in place with wooden stops.

Tip: Working on the job site with the tools at hand, you can easily beat the cost of special orders.