What Is A Window Or Door Buck?
Openings in buildings are frequently not exact and are referred to as rough openings for that reason.
When window products are placed into openings, they often need to be shimmed into place to properly fit the opening.
Sometimes, windows come with a ‘fin’ that requires a buck to serve as a support for this lip surrounding the frame.
When a large amount of shimming is required, 1x or 2x pieces of wood are utilized and are referred to as door bucks.
Code References
Product evaluations issued by accredited entities specify how to fasten window products to host substrate with a maximum shim thickness.
However, if the window is only fastened to the buck, then the buck needs to be securely fastened to the host structure.
According to Section 1710.3 of the 2023 Florida Building Code (8th Edition).
“where the wood buck thickness is 1 ½ inches (38 mm) or greater, the buck shall be securely fastened to transfer load to the masonry, concrete or other structural substrate…”.
In the 2021 International Building Code more loosely covers buck attachment in Chapter 23.
More On The Topic of Wood Bucks
It’s typically up to the Window or Door Product Manufacturer to specify whether bucks can be used and how they may be installed.
A general rule is that a 2X wood buck (1.5″ actual thickness) should be installed at least as securely as the window or door anchorage being installed to it.
In the case of impact windows, the maximum force shall be used and not reduced for a lesser force or opening area.
for 1X wood bucks (0.75″ actual thickness), it is possible that the window or door anchors may pass through the 1X buck and provide equivalent embedment to provide a ‘solid shim’ condition and equivalent anchorage*.
Wood bucks also provide an aesthetic finish and assist in flashing & waterproofing of the building envelope.
Stucco finishes typically encase wood bucks and sealed with caulk.
* Always consult a design professional before installing wood bucks as there are many factors to consider that are beyond the scope of this article.
Contact us to discuss your need.
From Our Plan Store
Engineering Express provides pre-engineered certified plans to assist in permitting wood bucks in our online plan store.
View these plans which describe 2x & 1X wood buck installation.
Purchase engineer-sealed copies to be used with your project for plan review and construction documentation. Plans are sealed for use in your state throughout the US.
Last Update: August 7, 2025