Timber beam floors with perpendicular timber floorboards as indicated in the drawing below are common throughout northern Europe. The floorboards are nailed onto the beams and are quite substantial with a thickness of around 25-30 mm. The floorboards are typically connected with one another with longitudinal tongue and groove joints.

I wonder if the floorboards serve a structural function? Specifically, I could imagine that they could serve to distribute loads or to brace the beam structure.

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As pointed out by Solar Mike the floorboards are indeed typically connected with one another with longitudinal tongue and groove joints.


2 Answers 2


Most of the wood floors of that type tend to be tongue and groove so they do "interlock" with each other as it helps to prevent squeaking.

They are structural as they need to spread the load and be sufficiently strong so you don't put your foot through when you step on it.

Also the floor needs to support the furniture like chair feet and bed feet as they will not always be located directly above a joist.

  • $\begingroup$ Thanks for the reply. I particularly mean if the floorboards play a structural role for the overall timber beam floor (distribution of loads among beams, bracing), not solely that they have to withstand their intended loads. $\endgroup$
    – sba222
    Commented Jun 5, 2020 at 10:25
  • $\begingroup$ @Steve222 check paragraph 2. $\endgroup$
    – Solar Mike
    Commented Jun 5, 2020 at 10:26
  • $\begingroup$ Yes, the boards and beams form and integrated structural diaphragm. $\endgroup$
    – Phil Sweet
    Commented Jul 5, 2020 at 18:00

The floorboards functions are supporting and distributing loads on beams. Another function is to brace the beams. In the design of the beams we only consider the rectangle section beam, not I section. As you described in the question, the floorboards are nailed to the beam. Thus, if you cut the section of the beam, the connection between the boards and the beams are pinned connections.

Even the floorboards are glued to the beams which result in fixed connection between the two members, conservatively we only consider the rectangle section in beam design.


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