Ask the Architect

Too much second-floor overhang?


Q. We’ve been discussing adding a room on the second floor, behind our kitchen, with views of the water. We spoke to two contractors, and one told us that we can’t use our existing deck to make the floor of the new room because it has an overhang that he called a cantilever, which is too far out beyond our existing deck beams. Is this true that we have to start over, instead of saving money by using our existing deck?

A. What you heard may or may not be true, but unless someone with the ability and training to calculate the load distribution and confirm it with building codes can check it, you’ll probably never know if you could have saved the structure or not. The unwritten rule, compared with the code standard, is typically that repetitive floor joists shouldn’t span more than 2 feet beyond a support beam. If calculations show that the bending moment, fiber stress and moment of inertia are within a safe range, however, then the existing structure may be able to be saved.
It gets more complicated, though, because most decks have inadequate spread footings for the weight distribution underground, especially because people assume, incorrectly, that sandy soil is very stable. They also generally have little understanding of what freezing conditions can do to the entire structure. In other words, most decks are built based on many assumptions, but aren’t considered as big an issue if they move, since cracking and uplift generally aren’t a noticeable concern.
It really doesn’t matter if a design professional is working on a big building or something as simple as a deck, because the ability to cause deadly problems and mistakes is still the same. It’s understandable that people want to save money by not hiring an architect or engineer for something seemingly so simple, but you may want to consider that most municipalities require plans prepared under the direction and review of a licensed professional, and not guessed at by someone with power tools who builds. Many people learn the hard way, especially when they go to legalize a deck long after it has been built and used for years, that the way it was built won’t pass and get a permit without expensive changes.
There are many regulations, codes and laws regarding every kind of structure, from where it can be placed to the materials and methods of putting it together. It doesn’t take much, just a consultation with an architect or engineer, to find out the answer to your question. Building an addition close to water means making a little more effort to only do things once, especially with exposure to the conditions of higher wind and water force, corrosive salt air, saltwater and unstable soil. You may end up with a new structure, but when you think about the investment and your safety, it will be worth it. Good luck!

© 2022 Monte Leeper. Readers are encouraged to send questions to, with “Herald question” in the subject line, or to Herald Homes, 2 Endo Blvd.,
Garden City, NY 11530, Attn: Monte Leeper, architect.