Expansion joints in timber floors

In short, the ATFA manual defines floor width as "measured at right angles to the run of boards".

I suppose an easy way to describe this is on some examples.

If your room is 7m x 9m, obviously both dimensions are greater than 6m and there is a need for EJ across the width of the floor. So, what is the width of the floor in this case? The answer depends on which way you lay the boards.

If you lay the boards so that they (longitudinally) follow the 7m wall, then the floor width is the other wall, which measures 9m.
Similarly, if you lay the boards so that they (longitudinally) follow the 9m wall, then the floor width is the other wall, which measures 7m.

So, using the above pic, the blue arrow is at the right angle to the run of boards - so that's your "width".
If boards on my pic were laid the other way, then the lime arrow would be the floor width.

I think it's easiest to remember this if you understand why are the EJs required across the width of the floor and not the length of the floor. It's because timber boards have far greater movement (expansion/shrinkage) across their width. Longitudinal movement is very small, in most species it's almost negligible.
That's also the reason why narrower boards are generally more stable than wide boards.

We have photos of our expansion gaps (1 or 2 mm every metre) but I don't know how to post pics here. If you can tell me how to do it I can load some for you if you like.

Thanks very much, Tracy! Here is the thread that has lots of explanations on the issue:
http://forum.homeone.com.au/viewtopic.php?f=13&t=1272&hilit=post+photo

In short, the steps are:
1. Create your account on imageshack image hosting site
2. Add your photos there
3. Then go back to h1 and insert the link to the photo inside your post. Eg. (this is from memory), for the pic that you want to show, inside imageshack, copy the image code (I think it's called Forums or mentions that word) and then simply paste it into your post here. Test. If it doesn't work and you can't make it work, it doesn't matter, as long as you give us the code, we could probably fix it for you

By drif at 2010-08-04

By drif at 2010-08-04

By drif at 2010-08-04

Hi Lex, Hope I've done this right. The first 2 show the actual expansion gaps and the last gives you an idea of the room size. I think this room was 9x8 metres roughly and expansion gaps of 1 or 2mm (can't remember now) were left between boards every metre (because I didn't want a cork strip). They are noticeable but not unpleasantly so I don't think and only really if you are looking directly along them. They were laid in January this year but not sanded or polished until early march by which time they had almost completely closed up. Now that the weather is cooler some have openend up a bit again. I'm guessing they will close up again when it warms up. Hope this is helpful for you.

Hi Tracy, thanks for this. I realise that I failed to register that you said gaps, not joints, in your original post, so I was looking for cork in the pics before reading the rest
Was there any particular reason why they left the floor for so long, more than a month?

And a question for our timber flooring experts - why would installers leave visible 1-2 mm gaps, isn't it possible to "add" some room for expansion by laying al boards loosely (instead od leaving 1-2 mm gaps every so often) or not cramping the boards hard together? Or ... ?

The house was being built and we wanted to have the floors laid before the kitchen was put in and doors and skirtings etc were installed. We waited until after completion however to have it sanded and polished so that it wasn't damaged by the builders/tradies.

Oh, I see, thanks. Makes sense, plus it's better for the floor to stand a bit.