Vertical Holes Through Wood Decking.

[RARWOOD]

Are there any "rules of thumb" which would give guidance on how large of vertical hole you could cut in a 2x6 wood deck before additional support was required?

I not sure if I am correctly remembering a rule that you generally could cut a vertical hole through the wood deck as long as it didn't remove over 50% of two adjacent pieces.

 

[SlideRuleEra]

RARSWC - For vertical holes in glulam the rule is:
"The section modulus at the vertical hole is based on the width of the member minus 1.5 times the hole diameter"

IMHO, unless you find other more definitive info, sounds reasonable for sawn lumber too.

See "AITC Technical Note 19", pages 2 and 3

https://www.aitc-glulam.org/shopcart/Pdf/aitc_tn_19_ may_2002.pdf

http://www.SlideRuleEra.net

 

[RARWOOD]

Thanks for the information.
May be I worded the question wrong. What I am asking is if you use 2x6 tongue and grooved wood decking to span between purlins spaced 6' o.c. how large of a vertical hole could you cut through the deck with out calculating the stresses or adding additional information.

For example if someone cut a 1 1/2" diameter hole through 2x6 wood deck laid up in a random length pattern would you need to run calculation to determine if that was acceptable? I probably would not worry about a hole that didn't exceed 2 3/4" in diameter for 2x6 decking ( removed 50% of the cross section of a single piece).

The person who asked me the question is looking for some basic guidelines to tell a contractor not to exceed. From experience I know that contractors are cutting penetrations through the deck all the time.

In a lot of ways the answer depends on the system. For example with plywood laid over the deck or nail base you probably can tolerate a large hole.

In evaluating it through calculations I would agree the 1.5 times the hole diameter is a good guideline.

One thing about wood decking, the spans generally are controled by deflection not strength. In a lot of case strength wise you could cut out a 5" x 5" area in a single piece of decking transfering the load to the two adjacent pieces. In that case you would have a soft spot in your deck where you would get more deflection. However in the course of things that probably would not be a problem.

The interesting thing is that considering all the time I have spent in the wood industry, no one has asked me this question before. I've been asked plenty of times about notching and boring beams and purling but never the deck.