Don't know why it won't load, I managed to get it up on my phone.
Anyway, I googled 'RAF bomber specification B12/36' and it comes up about halfway down on the 3rd page as a PDF. The thesis is entitled 'RAF operational requirements 1923-1939' by Colin Sydney Sinnott submitted in 1998 and is archived by KCL. As you would expect the author has used PRO documents as references. He points out that some contemporary RAF hangars had door openings well in excess of 100ft, and some were considerably shorter, and posits the theory that any limitation imposed in size was due to the forthcoming treaty limitations.
I searched the document using 'hangar' it turns out that earlier, in 1932 Salmond had expressed concern regarding allowing designers free reign that may result in 'these machines may become so large that we cannot get them into any of our sheds; e. g., the bomber transport machine will not fit into any shed we have at home or abroad. "
It is actually quite an interesting read and certainly gives a lot of context as to why the Air Ministry specified requirements as it did.
I've appended the link again here just in case I didn't do it right earlier.
LINK