These shapes have a property such that when the shape is selected the shape's dimensions are displayed. It's possible to override this (but there is a side-effect) - I assume here that you are using, say, the shape "room" from` the "Walls, Shell and Structure" stencil. Select the shape, then menu Window -> Show Shapesheet. There is a cell called User.visBESelected which will be set to the value "1" hopefully (as the shape has been selected. You want to change this to "=guard(1)".
What's the side-effect? Well, once you've forced this as the selected shape then selecting a different shape with this type of property will no longer display the dimensions so you have to set the User.visBESelected cell to "=guard(1)" in all the shapes where you want to show the dimensions.