[quote=sdcellar]As I understand it, you have to build like an 18-inch thick wall to conform to their architectural guidelines. This means that each wall has to actually be two walls; i.e. it comes down to building a house within a house.

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Twice the framing really is not that much of a cost addition: Houses cost much more than the wood or the labor of nailing the framing together, as you can guess by the time that framing takes relative to the rest of the construction time. A house may take four months to build; framing takes four days.

Still, no way would I build a custom house, unless there was something specific I just had to have. Not only is custom construction expensive, it is one hell of a headache.