Query: If I fit the top box below the lintel, how much height will I lose?
Context: We’d recommend that alongside the space for the top boxes (205mm square for TD55 and 300mm square for TD77), you should also account for about 50mm extra for the protrusion of the last slat to fit into the guide runner, so totalling about 255mm square for the TD55 range and 350mm square for the TD77 range.