"Tim S" wrote in message
news

the pack says overlap by 30cm so hopefully thats easy enough.

My roll of foam didn't say so and I didn't. I would have thought that the
overlap would have caused some uneveness despite the fact its
compressible. However, the manufacturer said do it, so best to go with the
instructions in your case - might be a different foam to the one I used...

I interpret that as overlapping the boards 30cm from the joins in the
underlay.

Mary