No partition wall in new build garage loft

[Dave]

I would appreciate some help.

I purchased and moved into a "detached" new build six months ago and recently fitted a hatch in the ceiling of my adjoining garage to get access to the sizeable loft space there. I soon realised that there is no partition wall between my garage loft and the neighbour’s garage loft (unusually, their garage is attached to our property, but the rest of their house is not).

I spoke to the developers and they basically said: "The loft is not designed to be accessed. The ceiling is fireproof, so we are not failing any regulations. You shouldn’t have put a hatch in; it will need to be removed and plastered over".

Is this true or should they have finished the wall in the roof space?
I guess they are probably right, but I feel angry about it because they are basically preventing me from using a large part of my house, which I need for storage. Thanks.

[New Home Expert]

It is quite unusual as both garages need to have the ceilings plaster boarded with 2 layers of plasterboard and jointed and edges sealed with fire proof mastic.   
More commonly, the party wall in the garage is built up to the underside of the roofing felt, meaning the roof space is useable.

My guess is the roof was covered before the bricklayers were able to build the party gable wall.
On snagging it was spotted so they opted for plasterboard to comply instead.

Now you will need to replace you loft hatch with a fire rated metal one to ensure the fir resisting integrity. If you have a door from your house to your garage, this is even more important.

I would ask why a gable wall wasn't built and suggest it was forgotten.