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Installing a window seat can take anywhere from three to 20 hours, depending on the complexity of the project. A professional carpenter can complete a basic installation in as little as three hours if no modifications are needed. If they need to remove cabinets, shelves, or baseboards, it can extend the work to a full day. If you're tackling a DIY project, expect it to take a full day for a basic seat and several days for more advanced designs that involve extra structural adjustments.

A built-in window seat that measures four feet in width will seat two adults comfortably or let one person stretch out. Ideal dimensions are 17 to 20 inches in depth and 16 to 21 inches in height to ensure a balanced design and optimal comfort. Make sure your window seat isn't higher than the bottom of your window for a harmonious look in your space.

You might need a building permit to install your window seat. Even though it's an indoor modification, some municipalities require permits for any built-in seating that is added to residential properties. Check with your local building authorities and your professional carpenter to ensure you're in compliance and avoid any potential penalties.