Bucking, sort of…

Back to the basement windows! The basic masonry repairs are taken care of and I would like to get the final measurements, which allows me to get a final bid on the windows.

First, though, I have to frame out the masonry opening with what is called a buck. The buck is the wooden frame that sits inside the opening of the brick and holds the window in place.  I will get the final measurements for the window from measuring the interior of the buck.


My friend Ben from the 168 Elm Ave. project was kind enough to stop by and offer his advice on the buck installation. He pointed out that nine out of the 16 window openings were almost the same size. Rather than tailoring each individual buck, he recommended that I pre-assemble nine of the same size for those openings.

I have a bunch of lumber to cut, although ending up with a number of same sized window bucks expedites the process.

The basement windows are rather close to the ground, therefore close to moisture sources such as splashing rain water. To add to the longevity of the window buck, we purchased 2 by 6 treated lumber for the sides and top, and 1 by 6 composite lumber for the sill plate.


The sill plate will have the most severe exposure to moisture, thus our decision to use the composite lumber, which provides an excellent rot resistant material.

The hardware also influences the longevity of the assembly. I have to use coated screws to put the buck together. Uncoated screws would corrode in the treated lumber.

The lumber is cut and I’ve got the hardware; time to put the bucks together.

It is important to assemble the buck as square as possible. To add rigidity and keep it square while I am moving it around, I stiffened the top corners with triangular plywood pieces and added another plywood piece along the bottom.

Here is another subtle detail that helps with moisture management and should increase the longevity of the buck assembly.

I cut the bottom of the two sides at a two degree angle, which gives the sill plate (the composite lumber piece) a slight slope outwards. This, so I hope, prevents any water from sitting on the sill plate or at the bottom of the window.


It’s time to install the buck.  I set it into the masonry opening and shim on all four sides. While doing that, I check several times that the assembly is level, plumb and square. The easiest way to check for square is to measure diagonally across the buck from corner to corner. Both diagonals must measure the same distance.

This is somewhat important as the window units will come perfectly square, and we want them to fit into the buck opening.

The last step requires attaching the buck with ¼ inch masonry screws into the brick opening.

Once that is done we can take a closer look at how it all fits.


Yes – what you see there is a gap between the brick opening and the buck – and it is intentional.

The triple-glazed windows we are about to install will have a U-value of 0.20, which is about R-5. The assembly surrounding the window should meet, or preferably exceed R-5. If not, we will have paid good money on high efficiency windows but lose energy through the sides, defeating the whole point of the investment.

The pressure treated lumber (pine) has about an R-value of 1 per inch. The gap gives me a thermal break between the masonry and the buck, which I can spray out with foam to increase the thermal resistance to an R-5 or greater. This is a subtle detail that will have a significant impact on the thermal comfort.

All right, now I am ready to take the final measurements and get the bids for the windows. I hope we won’t end up cost-shocked again!


About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

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