Kitchen renovation--NEED HELP w. joist!!

Brad_Blazer · Sep 3, 2008

Link to NC plumbing code on this topic:
http://ecodes.iccsafe.org/nxt/gateway.dll/Plumbing/chapter01246/section%20head01247/subsection01248.htm?fn=main-nf.htm$f=templates$3.0

"Notches on the ends of joists shall not exceed one fourth the joist depth. Holes bored in joists shall not be within 2 inches (51 mm) of the top or bottom of the joist, and the diameter of any such hole shall not exceed one third the depth of the joist. Notches in the top or bottom of joists shall not exceed one sixth the depth and shall not be located in the middle third of the span."

Davitk's rule agrees but holes and notches are not the same thing i.e. properly placed holes in the center 1/3 are permissable, notches are not. The principles in play are that bending stress is highest at the center of a span and that the top and bottom fibers of the joist carry the majority of the stress.

Check the code in your state.

davitk · Sep 3, 2008

Brad_Blazer said:
Link to NC plumbing code on this topic:
http://ecodes.iccsafe.org/nxt/gateway.dll/Plumbing/chapter01246/section%20head01247/subsection01248.htm?fn=main-nf.htm$f=templates$3.0

"Notches on the ends of joists shall not exceed one fourth the joist depth. Holes bored in joists shall not be within 2 inches (51 mm) of the top or bottom of the joist, and the diameter of any such hole shall not exceed one third the depth of the joist. Notches in the top or bottom of joists shall not exceed one sixth the depth and shall not be located in the middle third of the span."

Davitk's rule agrees but holes and notches are not the same thing i.e. properly placed holes in the center 1/3 are permissable, notches are not. The principles in play are that bending stress is highest at the center of a span and that the top and bottom fibers of the joist carry the majority of the stress.

Check the code in your state.

Good post. And may I add, which may or may not help to clarify, that one of the reasons notching is so potentially dangerous in a joist is that wood tends to split along the grain where it is nicked (i.e. a saw kerf), while a round hole is OK midspan (think knothole)

To further muddy the waters, when notching joists or stair stringers, some carpenters advocate drilling a whole at the inside corner, then cutting the notch

Danno1 · Sep 4, 2008

davitk said:
To further muddy the waters, when notching joists or stair stringers, some carpenters advocate drilling a whole at the inside corner, then cutting the notch

Actually, that's not necessary as the corner is in compression in that situation. The purpose of the round hole is to relieve stress when the corner is in tension.

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davitk · Sep 4, 2008

Danno1 said:
Actually, that's not necessary as the corner is in compression in that situation. The purpose of the round hole is to relieve stress when the corner is in tension.

.

Top or bottom?

Danno1 · Sep 5, 2008

davitk said:
Top or bottom?

In a house, the joists/stringers are all loaded fr the top. That puts the top in compression and the bottom in tension. Since stair stringers are notched on the topside, there's no need to drill a round hole at the corner of the tread/riser. In a machine the stresses could come fr various directions. The carpenters are confusing this situation w the stair stringer situation. I could explain better w a picture but don't have a convenient way to do that right this minute.

Do a Google for stress concentration factor, notch strength, notch sensitivity, or stress riser.

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davitk · Sep 5, 2008

Danno1 said:
In a house, the joists/stringers are all loaded fr the top. That puts the top in compression and the bottom in tension.

Stringers aside, plumbers do not know top from bottom

when it comes to boring and notching wood joists; tops and bottoms get equal mistreatment. Their job is to make the pipes pitch downhill, the carpenter's job is to fix it. More often than not the sheetrock covers the mess and the project is called done.

TomSr · Sep 6, 2008

Since you are talking about a vent I assume you mean a ceiling Joist. You might consider going up and over the top of joist. When I built my house I ran a vent line using 4" pvc from vent to vent and put one pipe through the roof. Just tide all vents together in the attic.