Just try to ask, is the specs is so important that have to following 100%? or is only a minor diff? do you try to communicate with the contractor why this is happen? may be there is some problem on site which the person who make the spec do not realise?

ok, ic, if you already have the specs detail b4 work started and the contractor aware of it, then he is responsible to make sure giving everything acording to the specs, you have a right to ask then to re-do, but is really strong enough or not, then have to refer back to architect, let say architect also say is actually is strong enough, then u can choose want to ask them to re-do or not.

well, from what i know, mostly are actually like that. because if a minor house extention, they will just ignore the spec since they think they had done a lot and no problem so far, and they normally will think architect always giving a spec more then what should they use simply becoz architect not the person work on site.

But if you looking for a formal designer company which have own architect to build a bangalow house, they will of coz following all the spec but of coz the price must be extreamly higher compare to the contractor around.