I probably will have to notch at about the 6' area of a 25' joists.
Redsy,
I assume there must be a load bearing wall or beam somewhere around midspan underneath this floor, as dimensional lumber this size will not carry 25' clear span loads at allowable code deflections(there would be, at minimum, serious deflection problems). Based on this assumption your 6' measurement would place your notches in the
middle of a 12'
supported span. This isn't going to be a problem, especially with the sistered joists---I just brought it up for clarification.
Joist width
does affect
strength. The depth of a joist affects its
stiffness(deflection). Allowed loads, for a constant joist depth and deflection at a certain span, are based upon formula that yields a maximum load per inch of joist width. This must then be factored in with joist spacing, etc, to achieve the desired performance values for the floor. From a lumber usage standpoint deeper and narrower is more efficient - but there is a point at which lateral bowing, lack of deflection, nailing, and other factors make it a poor design choice. The equation, of course, can be configured to give allowable loads per inch of joist depth based on a constant width.
The best examples of this compromise between depth and width are found in timber framed structures(homes, bridges, ships, etc.)
Standard dimensional lumber dictates the use of 2x material, and most of us have simply become accustomed to going no further than the span table.
Len
[This message has been edited by Len_B (edited 02-12-2003).]
