There was significant Shrinkage...

[Darren Emery]

Anyone have experience with the requirements of 2009 IBC 2304.3.3 - Shrinkage?

We have a four story wood apartment building just underway, and the PE has called for a "flexible connector" at the slab for the plumbing stacks. The code section simply says that the analysis shall show that no adverse effects shall occur. The plumber has no idea what or how to install.

The fact that the PE called for a flexible connector tells me that there may be adverse effects.

Any input would be appreciated.

 

[globe trekker]

Can the RDP specify the type of "flexible connector"?

.

 

[mark handler]

Clamped flexible connectors or hubless couplings, have been used years.

For example, placed in risers between floors of tall buildings, expansion and contraction compensation has been achieved by leaving a 1/8-in. to 3/8-in. gap between the ends of the pipe within the flexible connector

 

[mark handler]

The International Building Code (IBC) 2009 Section 2304.3.3, addresses shrinkage concerns for multi-story wood frame construction:

2304.3.3 Shrinkage. Wood walls and bearing partitions shall not support more than two floors and a roof unless an analysis satisfactory to the building official shows that shrinkage of the wood framing will not have adverse effects on the structure or any plumbing, electrical or mechanical systems, or other equipment installed therein due to excessive shrinkage or differential movements caused by shrinkage. The analysis shall also show that the roof drainage system and the foregoing systems or equipment will not be adversely affected or, as an alternate, such systems shall be designed to accommodate the differential shrinkage or movements.

 

[TheCommish]

I have seen expantions fittng used in PVC drian pipe, when the run is around 2 inside corners, web reasher tund up a recomendatin for an expantion coupling at 25 foot intervals http://www.plumbingsupply.com/images/pvc-coupling-3-4.jpg

The idea make sense for a 4 story wood building, Simpson makes spring loaded take up couplings for their sheer wall products that at slack in a wood building due to wood shrinkage ATS: CTUD Coupling Take-Up Device

 

[Darren Emery]

Thanks for the info so far. Let's tweak the question a bit. If the plubming stacks offset lateraly at first ceiling level, so we have no stacks that run vertically through all four floors, do we need still need to provide for movement at the slab?

 

[mark handler]

No pipes should be embedded in the slab, there will be a differential of movement between the slab and the wood.

Ant stacks including vents that extend greater than two floors need flex connectors

 

[Mark K]

While the code is neutral the problem can be addressed in a number of ways. The total shrinkage can be greatly reduced if engineered lumber is used for the floor framing. Engineered lumber has low moisture content and has low shrinkage. In any case dry lumber should be used.

You could disconnect the floor from the riser and accommodate the movement in the laterals. You could also offset the riser at each floor. In either case the drain pipes should still have the proper slope after the shrinkage. If the pipes are offset they should be able to accommodate the expected shrinkage without damaging the pipe.

You might find that normal flex connectors will be inadequate if the expected shrinkage is high.

Some engineers will provide an estimate of the expected shrinkage thus putting the plumbers on notice as to how much movement they have to accommodate.

This is a well understood problem. The fact that the plumber has a problem implies either the plumber is not experienced with this type of construction, the designers have not done a good job of addressing the problem, and or the communication between the contractor and the designers is inadequate.

 

[Yikes]

Agree with Mark. The shrinkage won't be in the studs, it will be int he floor framing. 2x floor joist will shrink - -either use joist hangers or switch to engineered lumber for 4 stories.

 

[DRP]

I wouldn't disregard it entirely for low rise, log homes get into settlement considerations as soon as you leave the foundation.

 

[Darren Emery]

This is a well understood problem. The fact that the plumber has a problem implies either the plumber is not experienced with this type of construction, the designers have not done a good job of addressing the problem, and or the communication between the contractor and the designers is inadequate.

And Mark gets a prize for hiting the nail right on the head.

 

[Paul Sweet]

Wood shrinks far more across the grain than with it. That is why most of the shrinkage occurs at the floor levels, unless you're in a log cabin as DRP pointed out. I usually figure on 1/8" to 1/4" per story. This can cause problems at window sills & heads, as well as plumbing.

 

[Mark K]

It has been years since I ran the numbers but I recall that for 2x12's we can be talking of 1/2 to 3/4 inches with green lumber.

If one is assuming 1/8 to 1/4 inch shrinkage the sill and top plates in the wall need to be dry lumber.

 

[DRP]

The Shrinkulator

remember these are averages of a natural material there' ~15% variation. They are also based on very thin clear, normal, wood sections. Internal stresses usually reduce the overall shrinkage compared to these numbers. Then, when you get into heavy timber, the wood often checks, rather than the shrinkage causing overall change in the timbers' dimension at least a portion of the shrinkage is in the check.

 

[Phil]

The WWPA also has some documents on shrinkage and a spreadsheet for western lumber species.

http://www2.wwpa.org/Portals/9/docs/PDF/TN10.pdf

Shrinkage