We are having a sip extension built but keeping the external doors in to access the extension. Do we need building regs for the new extension? The company who are fitting the sip only mentioned building regs if we were to open up the space to our house to make one big room. Obviously a sip is very quick to put up, like 2 weeks if that makes any difference (I read somewhere that for building regs they usually come and inspect at various stages of the build, but not sure if that was based on a traditional build which is usually a longer period of time). Going to make a few calls on Monday but wanted to hear other people's experience:)