Many home builders just cantilever the bay from the foundation wall. The cantilever is the reason why it’s not a good idea to just attach to a deck to the bay window with additional support.  The architect that designed the home probably only designed the cantilever to support the weight of the bay window itself. The additional weight of a deck could add too much stress onto the homes floor frame that supports the bay.  It’s not that much cost to add an 8 foot beam with two more support columns to help with the load of the deck in front of the bay.

This may seem a little over the top as far as being precautions.  We only recommend this because we have seen many times under engineered bays that barely support the weight of the walls and windows above. If you feel that your bay has been properly framed then feel free to just attach to it and move on.

If you do decide to just attach to the bay you may find that the cavity of the floor frame under the bay is inaccessible from the basement and the bottom has been enclosed for a finish look or to hold in insulation. We recommend the easiest way to get a nut on the back of a ledger bolt is to remove the plywood that encloses the bottom and replace it afterwards. Many times lower quality builders will just install lag bolts thru the deck ledger into the bay house band and move on. We recommend you use carriage bolts throughout the deck ledger.