Walked into a a renovation jobsite today where the builder had installed in-floor heating in the basement. I am familiar with the type of heating system that has tubes that fit into routered channels within the plywood or substrate. However............

The problem with THIS particular system is that the builder has nailed 8" wide strips of 3/4" plywood to the existing floor (OSB on purlins over concrete)and left 4"-6" spaces between the strips in order to accomodate the heating tubes (3/4" diameter). He wants me to install 5/8" bamboo perpendicular to the strips of plywood which is okay except for the fact that I'm spanning over the 4"-6" spaces. I'm not comfortable with that span. The other problem is that the bamboo has been manufactured with only 2 different lengths in the carton (3' & 6' pcs). I'll have an end joints falling on that 4"-6" span without any support unless I screw small strips of plywood underneath the joint.

Any suggestions?? I'm inclined to tell him that he needs to cover the entire area with plywood thick enough to protect the heating tubes from my floor cleats before I prcoeed with the work. Thanks for any feedback.

With bamboo, I'd want a solid subfloor. Suggest at least an additional 1/2" plywood. The bamboo will flex too much between those spaces.