Foamboard base board and flex

On the O14 Yahoo chat group I was recently asked a question by Dave Eggleston about how much does the foamboard baseboard flex, so I set about measuring it.

The first experiment was to prop one corner of the baseboard up by 2cm, and measured the flex under just the weight of the baseboard itself, no weights added, the unsupported corner was then 11mm off of the desk, giving a flex of 9mm, this was over a width of 600mm, and length of 1650mm. The diagonally opposite corner stayed flat on the desk.

The next test was to place a hard back book on top of the unsupported corner, this then put the corner flush to the desk, although the diagonally oppostire corner needed to also be weighted with a similar book or it would raise into the air. This gives the flex of 20mm. The book weighs about 900g.

I then repeated the above two tests but swapping the unsupported and raised corners, this time the flex unweighted was 5mm, and I had to weight the opposite corner down to stop it raising. With the book (900g) on top of the unsupported corner the flex increased to 17mm. I believe the bracing under the board to be the reason for this, the diagonal bracing on the unsupported section went into the unsupported corner on the second test, whereas on the first it went into the supported corner. I suspect that adding an additional brace into each section so that both diagonals are braced would have improved the first set of measurements.

To test for end to end flex I raised each end up on to 1cm pieces of foam board, and measured the height in the middle, here, just under the weight of the foamboard itself was no measurable flex, certainly less that 1mm over 1650mm of length.

Adding on a couple of books (1250g) made it flex by 2mm over the 1650mm length. 

I did try to measure the flex on the deck, by pushing down on the top when the baseboard was flat on the desk, however there was no appreciable movement, no more than pushing down on a plain piece of foamboard.

Overall I feel the results are certainly adequate for my requirements, and hope that they have been helpful to anyone else considering this type of construction.