The Buck Frame is the wood that sits between a window and the structure. Its main purpose is to transfer the load from the window to the structure. Impact windows require a different sized Buck Frame than regular non-impact windows. Many impact windows companies in South Florida attempt to skirt the issue by not changing the Buck Frame or simply reinforcing it when installing impact windows. Some companies even have an addendum to their contract warning that if they have to change the Buck Frame there will be an additional charge. To install impact windows correctly, you must always change the Buck Frame unless of course the pre-existing Buck Frame is made out of concrete.