A window assembly includes first, second, third, and fourth frame pieces connected together to form a rectangular frame. Each of the frame pieces has an inside face defining a glass-receiving groove and a muntin-engaging face orthogonal to the inside face and defining a muntin-receiving channel. A first muntin is oriented in the first frame piece muntin-receiving channel and the second frame piece muntin-receiving channel, and a second muntin is oriented in the third frame piece muntin-receiving channel and the fourth frame piece muntin-receiving channel. The first and second muntins cross over to engage at a first half lap joint. The frame pieces are connected to each other with rabbet joints. The window assembly can be part of a garage door arrangement. A method of making a window assembly includes connecting together the frame pieces with rabbet joints and orienting first and second muntins to engage at a lap joint. Methods of retrofitting existing windowless garage doors to include windows includes cutting a hole in the garage door and dropping a window assembly into the hole. The window assembly can then be removably secured to the garage door with fasteners.