The single hole nest box securely fastens to a wooden wall using screws and fender washers supplied with this complete heavy-duty unit. No additional bracing or supports are required or recommended. The 6 opening in the cover is large enough for most chickens and it may be increased to 8 for heavy breeds, if needed. In some climates vent holes may be beneficial. They can be added as needed. There is also an alternate installation plan that allows for vent holes in the back. Assembled units are 20.25 x 12.5 x 12.5.For heavy breeds the cover hole may be increased to 8, if needed. Ribbing on the inside of the cover reveals the outline of the area that is specially designed to be cut out for this purpose.Comes with template to drill holes in bucket for mounting.