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brick1930 08-21-2009 05:19 PM

removing block between joists for 6" heat duct?
Can block in joist bay between basement and main floor be removed to allow 6" heat duct to pass from furnace side of house to far wall?

Currently space between joists appears completely blocked in, about midway across span.

Have gotten conflicting info about purpose of block-
1) required structurally to maintain spacing and support of joists
2) required by code as fire block
3) needed only during construction as support until floors and walls were completed.

If 3), a new heat duct/register is possible. If 1) or 2) are true, I've been told to consider radiant floor heating (electric mats).

And what about cross-bracing between joists? Can they be removed?

House was built in 1930.


Wildie 08-21-2009 08:15 PM

You can knock this out, run the pipe and then 'scab' a piece of 1X4 across the bottom of the two joists!
The block has two functions! One is to stiffen the floor and the other is to stop the joists from twisting, as they dry out! In a house as old as yours, I'm sure they are well dried by now!

Gary in WA 08-21-2009 09:08 PM

Joists >2x12 blocked or bridged at 8' on center.......502.7.1 (In solid-sawn rectangular lumber beams, rafters and joists to prevent rotation or lateral displacement in accordance with the ratio of depth to thickness of six to one-- unless both edges are held in line. Otherwise, the allowable stresses shall be reduced by a slenderness factor for single span beams or cantilevered beams). Under 2x12, not required. Fire-stopping--- every 100 square feet required. In a joist space, 14-1/4" wide, it would need to be over 85' long!
Be safe, G

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