wall strenght under large ducts


Old 10-16-06, 08:16 AM
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wall strenght under large ducts

I need to build a wall in my basement directly under some wide hvac ducts. The wall will be about 15 feet and the ducts are about 6 feet wide. The wall will be parallel to the joists but perpendicular to the ducts. Iím not sure how to proceed, but Iím thinking I need to build a structure, like a sideways ladder connected to the joists on either side of the ducting then connect my wall top plate to it. Iím concerned since the ducts are so wide that the top plate will not have much to connect to for wall top strength. Would this ladder concept work, or should I consider something more elaborate. I plan to hide this with a suspended ceiling later.
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Old 10-17-06, 11:05 PM
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I am not sure what you are saying. Are the ducts in the ceiling (horizontal) or in the wall (vertical)?

I thought they were in the ceiling, but could not understand the concern about the "top strength" or what you meant by a ladder concept.

I'd just sister 2X4's, or 2X6's in between the wall joists to span the duct, if it is in the ceiling. I'd look at it as a window or a door, and frame it accordingly.
Old 10-18-06, 07:17 AM
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Hopefully I'm reading this right....

Hopefully I'm reading your post correctly.

What I think you are saying is that your proposed wall will not only be parallel to the joists, but between the joists and therfore have nothing to nail the top plate of the wall to for an attachment point.

What you are describing as a "ladder" is simply blocking. Use 2x4s on the flat between the joists spaced 16" or 24" on center and this will provide plenty of attachment points to nail the wall to. Just make sure the bottom face of the 2x4 blocking is flush with the bottom of the floor joist.

When you get to the ducts, run a 2x4 from the floorplate all the way to the top plate making sure the 2X4 is right next to, but not touching the ductwork. Do this on both side of the duct. Heating and cooling of the duct will cause it to expand/contract and might result if excessive noise if it is rubbing on this 2x4. Make sure there is a piece of blocking between the joists right at the duct. This will allow you to secure the wall tight at this point.

Under the duct, you will just nail the top plate in between the two 2x4s you run up along the side of the duct and fill in with 2x4s to complete the wall under the ducts maintaining your 16" o.c. spacing for the studs.
Old 10-19-06, 10:10 AM
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Thanks for your responses and sorry for not being more clear. The ducts are in the ceiling and perhaps the way to express my concern about the wall strength is that I plan a 15 foot wall but, approx 6 feet of the wall will be under this large ductwork, so I will not have a joist visible to nail the top plate to for this 6 foot stretch.

I can install blocking on both sides of the ducts and nail the top plate to that blocking, and then have a top plate travel along the bottom of the duct to connect the studs, but it just seemed like having such a large section of wall not connected to the joists would cause an issue of not enough support at the top of the wall. Is this description any clearer ? Thanks again ! sgtgerryf - I agree with your idea, just wonderaing about some extra support idea, if you think it's necessary ?
Old 10-22-06, 06:17 PM
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You could double up the studs at each side of the duct work that extend all the way up to the joists, and then use a double top plate like a door or window header. 6 ' is not that far to span unbraced.

explaining this in words is much more difficult that it would be in a sketch or just building it. : )
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