Modern Parallam Window Stools

Parallel Strand Lumber or “PSL” is an engineered wood product made up of parallel veneers of wood that are compressed and laminated together with glue to form structural members for construction. PSL offers more strength and dimensional stability than solid lumber and because it is manufactured, can be easily sourced in lengths that would be impractical (think 70 feet long) with solid wood.

In the United States, PSL beams are marketed and sold by Weyerhaeuser under the brand name Parallam and at least in this designer’s mind, are often under-appreciated for their striking, visual beauty.

Some time back I ripped down a Parallam left over from a job site and used it to create a modern mantle for my fireplace. It remains one of my favorite Makeshift Modern DIY projects, so recently I decided to take the off-cut from that project and create two matching window stools for an adjacent room.

Before I proceed, I should take a minute to address what you are probably already wondering and hopefully assist in containing a pervasive misconception about window anatomy. Although often used interchangeably, the window stool and the window sill are not the same thing. I should preface this by saying that if you scoured the confusion-feeding land of the internets, you may think that this is a topic of some debate, but among architects and building professionals, this is essentially a settled matter. Mind you, I have found countless numbers of industry insiders who are happy to argue to no merciful end about whether any particular door should be described as left-handed or right-handed, because this is something we have no consensus on, but among professionals, the sill being the angled, water-shedding, exterior portion of a window and the stool being the flat, shelf-like interior portion of a window is a topic that enjoys no contention.

So the next time you are at a party and want to alienate your friends and coworkers with your geeky, architectural tidbits, feel free to correct anyone describing the last known location of their cocktail as being on that window sill when they clearly mean on that window stool. It’s now your job, you’re welcome. Incidentally, if they describe the last know location of their cocktail as being on that window seal, you should just punch them in the throat and then email me about it. We’ll both feel better.


Based the before photo and my sweet sketch above, you will note that my existing windows have no casing. In project specifications, they would have been described as having “drywall jambs and paint-grade stools and aprons” a common, albeit painfully unimaginative detail I imagine you are familiar with. I removed the existing stool and apron and carefully undercut the drywall jamb to allow the Parallam to slide into place. I measured the window carefully to ensure the new stool would not be taller than the frame and ripped the beam into an “L-shape” on a tablesaw. By sliding the stool under the drywall, I did not have to cut the new stool exactly to fit the opening, since the drywall overhang essentially provided all the trim necessary for a clean installation. A little construction adhesive, some light sanding with 120 grit sandpaper, 2 coats of water-based poly, and some paintable caulk and I was done.

I apologize that I don’t have better progress photos of this particular project, but now that this blog is up and running, future improvements will be documented more thoroughly.



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