The Only Way to Trim Exterior Windows
The key to durable trim and minimal trips up the ladder is to assemble it first and install it later.
Synopsis: Trimming exterior windows can be an ordeal, unless you learn the lessons that Seattle builder Mike Vacirca presents in this article. Vacirca’s process for exterior windows begins by assembling the trim first, then installing it as one piece. He starts by measuring every window to be sure he has correct dimensions. Vacirca then mills the windowsills, and is sure to keep the casing square during assembly. Finally, he installs the unit, nailing in the casing but screwing in the sill.
I can no longer call myself a trim carpenter because these days, I do a little bit of everything. I was a trim carpenter for most of the past 15 years, though, and a boat builder before that, so I feel comfortable saying that I know a thing or two about trimming out a window, and about how water affects wood.
Every time I dropped a piece of window trim from scaffolding 30 ft. in the air, I found myself remembering another career past, the days I spent working in a cabinet shop, where work is easy to control and weather isn’t a concern. Finally, I came to my senses when I was presented with 27 windows to trim for one house. That job helped me to develop a method for installing exterior trim that’s easier on my body, that is safer and faster, and that also yields more durable results. To make this process as efficient as possible, I even prime, putty, and paint the casings before installation.
Cutlists and stations add efficiency
When I worked in the cabinet shop, I organized my projects with cutlists and made shop drawings that showed how everything was going to be built before a saw ever touched wood. The process I created for assembling window trim in the shop starts with that premise. As with the cabinet work, I organize the shop into efficient workstations to build the trim. I want the workflow to move so that the pieces are cut and the assembly happens in such a way that a few folks can work at the same time and not get in each other’s way. The process, however, begins on site.
When the windows arrive, I grab a tape measure, get a notebook, and make a list of all the windows. I measure each to determine the finished height and width so that I can make a cutlist. I add 1⁄8 in. to each dimension to allow for caulk and to be sure the casing units will install easily by just slipping over the windows. Finally, I break everything into a formula. To keep track of which window is which, I use the lettered labels attached to them at the factory. Once the casing unit is built, I mark the respective letter on its back.
I install painted trim, so I build everything with primed stock. I cut all the pieces first, then assemble each unit with biscuits, glue, and screws to ensure that joints won’t open over time. Once all the units are built, and the nail and screw holes are filled, I prime any exposed wood and give everything a first coat of finish paint.
Get the proportions right
The windows on the project featured here are a mixture of Marvin (www.marvin.com) double hung, casement, and fixed units. All of the windows have aluminium-clad exteriors and primed wood interiors, and they are installed with a nailing flange. The nailing flange is set 1 in. back from the face of the unit, which in turn ends up 1 in. proud of the unsided building.
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