The central fallacy here is that, unless I missed something, the moveable walls and drawbridges and such all rely on electricity.
Well ~snort~ when corpses reanimate in homocidal search for human feast, power grids will soon fall silent as their operators become prey to the undeed appetite. So you could be all chillin at your swank pad, sippin a cocktail, when suddenly you're made aware of the zombie pocalypse. You race to your house controls and find only failure and a flashing light reading "LOL" "LOL" "LOL" "LOL" "LOL"
You then have several luxurious minutes to review your life's work before decaying hands crash through your wall of windows.