Is it the customer responsible for building control?

Can't see why you need BC MM. Is any structal work involved or are you concerned about uprating insulation to the walls etc?
A lot of window fitters that claim to be Fensa registered just polish the badge along with their spurs! Someone I know is forever correcting Fensa registered fitters work due to poor installation...usually down to lack of lintels and sagging windows causing plenty of havoc.

 

I recently installed my own windows in my parents house (first time).

Because I am not a FENSA registered fitter, I involved BC from the outset. I agree with CGN that being FENSA doesn't mean that the job will be done any better, in my experience worser.

Building control department in my council charge £120 to come out and inspect the works (upto 10 windows or doors), they will then issue a compliance certificate if the work is fine. Upto 2 visits can be made, so an initial inspection before work is carried out is a good idea to make sure things are being specified correctly.

They will look to see that the glazing fitted in the door is toughened as well as any adjacent glazing to the side window.

The responsibility for getting BC involved would be yours as you will be installing the windows, and it may not be cost effective to install just 2 fixtures to warrant a job, unless the cost of BC has been factored in. As a rough guide; in my area to install a window costs £100-120, and a door costs £150 to install from a FENSA co.

If a fitter is FENSA it probably costs them a couple of quid to register the window, but they will have to issue a 10 year warranty on any install.

 

Technically, anyone can breach building regs, but the onus will most likely land on the Building Owner. (The Building Act 1984 s.35)

Although if you haven't applied for Building Regs, you have breached the Building Act, not Building regs (or both if the installation doesn't comply!)

 

I have seen some guys call in BC when they are working for a picky or awkward customer and think they will try and wriggle out paying the quoted amount. Once BC have been out and issued a certificate then the majority of the time they back off

 

They could be arguing about a matter not relating strictly to building regulations, often the matter is about the quality of the work or non-compliance with the clients requirements. - good point though.

 

If you replace a window sash it is like for like and no notification, if you replace the frame you then have to go to current building regs, so d/g and notification, fee and inspection from B.C.
An unglazed door should be no problem.
Just noticed the porch bit, shouldn't be a problem if there is an exterior door between th