Use of tongue and groove boards for loft construction

[BakingDude]

Hello -

I am new here.  I live in a post and beam home built 30 years ago, which has a loft floor over beams and girders on a 5'-4" square layout.  The subfloor is made up of 1-5/8" actual thickness double tongue and groove laid on the supports, and plywood over that.  This is a full loft with bedroom and bathroom.  The beauty of the design is more headroom below, and the natural wood finish.  A bit more labor to install.

I am designing a new house, with a storage-only loft, which will be accessed by a ladder, not stairs.  I am using the same company.

I am told by my sales rep that they no longer design homes using loft floors made of tongue and groove, due to "a code issue".

I observed that timber frame companies continue to design using tongue and groove loft floors.  One I noticed is on 4' spacing, and 1-1/2" thick boards.

In looking at some span tables, it looks like the "code issue" may have been the thickness of the boards, as opposed to some other factor.  3" nominal double tongue and groove looks like it would work over 5'-4" spacing, whereas 2" may be marginal.

Since I do not have access to engineers at the home design company, I am asking here if anyone has input one way or the other if insufficient board thickness may indeed have been the "code issue" - or can you see some other factor.  While my expectation would be they could solve the issue by switching from 2" to 3" nominal boards, for whatever reason they ditched this technique and now offer I-beam joists/drywall only for loft floors.  I am trying to see if they will design specifying the thicker boards, to be supplied locally.  (They supply stamped plans, wall and subfloor elements, as well as the columns and beams).

Thank you in advance,
Don

[beenthere]

Welcome to the Forestry Forum. 

Fill in some of the blanks, such as what location and which "codes" you reference. A bit more about the wood you are using, or plan to use. 

A lot of the codes are written around grades of material, and what species may end up in those grades. 

Would like to hear more from  you.