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RE: Timber Frame Construction Tolerances

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>From a manufacturing perspective consider variability in the manufacturing
process and the performance of the end-product.

If process variability is say +/- 10mm, then that process is only suitable
for an end-product with a performance that can tolerate a larger variation
say +/- 12mm. If the performance of the end-product can only tolerate +/-
8mm then that process is unsuitable for making the end-product.

The tolerances in the structural codes always strike me as being pulled out
of thin air: arbitrary and subjective. Though some are relevant to
minimising eccentricities and secondary forces not otherwise considered.

Acceptable performance is always subjective. The issue is whether the
subjective judgement is made with respect to a characteristic of the system
relevant to the end-user, or otherwise functionally relevant and critical to
the performance of the system.

Most floors require a certain fall for drainage of water whether or not
intended to have water present, some fall is beneficial. However, do not
want tables with 2 legs several inches shorter than the others so that table
top level on sloping floor. Users may tolerate a small amount of unevenness,
slightly larger may use packers, and if possible may plane legs of timber
table to suit. To make a table more quality robust, would provide with
leveling screw adjustment on the legs.

Whilst a floor has a slope on it, do not want users to perceive they are
walking up hill, or that there is a noticeable ridge or peak in the floor
when the floor is meant to be seen as flat.

The performance requirement for the floor should be independent of the
materials used in its construction.

If cannot achieve the required performance for a floor using timber
construction, then timber construction is unsuitable for the floor. It is
not really acceptable to say this is as good as the timber industry can
achieve, so this is the accepted tolerance. Same applies to any industry and
the materials they use. Methods suitable to the material and the required
performance of the end-product have to be developed.

If the slope in the floor is perceived as a defect: then its a defect. It
doesn't really matter if the construction codes permit higher or lower
variation in the associated construction: such as joists up and down all
over the place. Unless have contract issue based on some ill defined
"industry standard practice".



The Canadian document mentioned earlier.

http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-171.html



Regards
Conrad Harrison
B.Tech (mfg & mech), MIIE, gradTIEAust
mailto:sch.tectonic(--nospam--at)bigpond.com
Adelaide
South Australia




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