Shrinkage measurement of multi-family buildings!

[design62713]

How much shrinkage can we expect for wood multi-family buildings (e.g. 4 story building)? Is there any section in NDS that refers to this requirement? Are there any requirements that a designer needs to consider? Thanks in advance.

 

[msquared48]

Really depends on the type of framing and wood materials used.

With solid wood joists, beams, and plates, you could get about 3/4" to 1" per story.

Using TJI or engineered wood, but still using solid wood plates, that should be l/4 to 1/2" per story max. And that is exactly why engineered wood products are3 better fur multi-story wood structures.

Mike McCann
MMC Engineering

 

[lsmfse]

I remember a three story apartment building built in the 60's. Several years later, the 3rd floor toilets were sitting 2+ inches above finish floor. Back then, the drains were plumbed with cast iron. It was determined the successive wood shrinkage was the cause.

 

[msquared48]

A lot of solid wood framed structures were baloon framed for the first two stories to help mitigate this too. Not done so much now.

Mike McCann
MMC Engineering

 

[efsinc]

There are formulae I believe based upon the difference between moisture contents at time of construction and in the final equilibrium state (or perhaps it's just rules of thumb based upon years of experience, but at any rate, easily available from AWPA or similar) which I don't have at my fingertips. Generally wood shrinks very much less along its length than its depth. Therefore the preponderance of shrinkage in a 4 story will be in the depth of the joists at the floors as opposed to the studs. As noted above, Engineered joists, TJIs, wood trusses, glulams, due to their dryness or orientations, mostly mitigate this, and of course as also noted, balloon framing dodges it entirely where useable.

 

[design62713]

Thanks all for your input.

 

[wannabeSE]

Here are a couple articles on wood shrinkage and building design

http://www2.wwpa.org/TECHGUIDE/Shrinkage/tabid/858/Default.aspx

http://www.woodworks.org/wp-content/uploads/5-over-1-Design-Example.pdf‎

 

[design62713]

Thanks wannabeSE. This is great.