We're renovating our condominium. My contractor intends to charge us extra for some of the blocking on the walls, because we don't know exactly what is going to go on all the walls. The contractor seems to think we need to know where our heavy paintings or Murphy bed will go, even though we will only buy these well after the renovation. In fact, he would have liked us to point out what items what size we have, so he can put the minimum amount of blocking based on these items. The rationale is that the things we may want to move are light items, and these can be moved without trouble to areas that have no blocking. What constitutes standard in terms of number of blocking "panels"?