Permitted development subdividing 1 flat into 2?

Last time I did this was 2008, and I nearly did it again in 2013. Both were the two floors of accom. above a shop (aquarium/pet shop and hairdresser) I decided to keep the second dwelling as one because the payback period for the subdivision work was too long. In retrospect I wish I'd left the first one as one dwelling, for that reason. Less total rent of course, but I thought one bed flats would be more in demand than two storey/three bed homes. Thats true, but as I said the expenditure will not be recouped for flippin' ages.

Anyway, in both cases the architect liased with Building Control and it was all a formality. I had the impression that it was just a case of applying for permission to modify, and complying with the expected requirements. On that basis I'd suggest you speak to your local Building Control dept.

Thanks for the reply Gunga
What sort of building costs were you looking at?
Also what were the most expensive items of work? I am expecting insulating the outside walls to bring the newly formed flats up to current regs to be pretty high

This was when I was still on the learning curve, not very good trade accounts with builders merchants, running it from a distance with periodic visits and other hindrances. They're in the north-east.

Purchase cost £140K (three story 1890s terrace, shop in ground floor, one dwelling above). I eventually got through £30k, including stud work, plastering, internal wall insulation, soundproofing floors, rewiring, two new CH systems, two gas supplies, splitting the Elec supplies, split water supplies, two kitchens, two bathrooms etc.

The next property, very similar, which I left as one dwelling over two floors, cost £15 to renovate. No soundproofing required, CH system is original, minimal rewire, plaster/paint and a new bathroom + kitchen.

The latter rents for £450 a month, the former brings in £700 so I'll let you do the maths. The eggs on 1 basket argument swayed me. With 2 flats - unlikely they'll both be empty. With the one dwelling, more difficult to find a tenant wanting so much space so longer voids. I now have a foot in both camps, but I would look at the increased income with two flats vs. the payback period for the work.

Reply to the comment left by "Gunga Din" at "20/01/2017 - 12:21":

Great perspective for both scenarios. By basic maths, you are having 10% gross rental return on 30k spend vs 3.8% on the first 140k. In addition, the conversion might have some capital return by increased the market value. So it seems the conversion might be more value for money. Am I missing something?

No, your probably NOT missing something! Yes it will have increased the property's value and I hadn't mentioned that in my previous. The way you've broken it down, the decision to split doesn't seem quite so disadvantageous!

The numbers im working with are...
As is value 240k with rent of 1200 pcm
If split value would be 350k with rent of 1700 pcm
So if costs were 30k it would be 20% return on rent to cost of work and 80k capital.
Obviously there is still the cost to get freeholders permission to do the split, and to my knowledge that is no exact science.
What did you have to pay for freeholders consent gunga?

I own the buildings so not a factor for me.