Floor Span Sizing Calculation of Old Hardwood Timbers

Hello Everyone,

I am an electrical contractor by trade in the process of purchasing a 1780’s Federal Colonial timber framed home located in New Jersey. The years and previous owners haven’t been so kind to the structure. My primary concern is a 20’ x 20’ living room area that sits over a full basement and has two bedrooms above. The ceiling has 6 1/2” deflection at the midspan which is evident at the floor above as well. The ceiling/floor joists are all hand hewn hardwood timbers that measure minimum 4” wide x 8” height. The spacing is approximately 19” on center. The wood appears to be an Oak or Chestnut species.

I recently hired a structural engineer to evaluate my concerns. I received his report the other night and have questioned the recommendations. His recommendations are to sister new 2x8s to the existing ceiling joists. Although, I realize that the existing lumber has not been professionally identified or graded; I am having a difficult time accepting his recommendations as adequate. In my 20+ years of construction experience, I typically see 12” deep joists or greater for such spans without supports. I have not found published span tables that deal with old growth timber beams. Additionally, modern span tables typically reference structural, #1, & #2 Southern pine or Douglas Fir, or TGI joists.
I have contacted him over my concerns and have not received an answer back that supports his recommendations. Please let me know if my concerns about his recommendations are warranted or there is some complex mathematical formula that qualifies such work. Thank you,
Brian

 

[Ron247]

I think it is a cut or notch. It is not a full depth cut. Used to weaken a member for straightening.

 

[racookpe1978]

The kerf is the width of the sawblade. Most often, the kerf is the width of the sawcut left after a piece of wood or metal has been sliced, but not all the way through. So, a kerfed beam has been sliced into many smaller sections by cutting from one side, but not all the way through. Obviously, the beam now has much less resistance to bending, can be bent both more open (kerf on outside of the bend) or more closed (kerf on inside of the bend.) Because you have lost strength of the beam, you MUST replace that strength with a sister pair of pieces of good wood, a sister piece of two plates, or something else underneath like a metal beam held up by multiple posts. If the kerfed bend is made in drywall or the kerfed slots are on the back of the bend (not exposed) you need to smooth and fill and sand the visible sides of the kerfed bend to hide the slots and their texture.

 

[mmarlow]

Thank you Racook

-MMARLOW EIT