EXtension - adding value?

I am looking at adding a ground floor 18sqm extension to my 2 bed mid terrace house. The current size is about 52 sqm - so the extension will add a fair bit to the overall size. The kitchen is currently a small galey kitchen (4.25 sqm) - the extension will increase this and have room for a modest dinner table. All in all I can achieve all of this in a 16 sqm area (current 4.25 and another 12). That still leaves a bit of space - I was thinking of using that space to have a 6sqm single bedroom beside the kitchen area. I know this isn't the most conventional way of doing things, but adding the bedroom will be cheap (plasterborad, insulation, and possible a window).

Simply - will the bedroom be overkill? I'm not looking at it as a way of upping the house to a 3 bed house value, but to give a 10k or 20k edge over an equivalent 2 bed with a big enough kitchen. I don't see the need for a 22 sqm kitchen/dining area in the house.

Am I overthinking it? Should I just have a kitchen/diner and keep it at that???

Honest advice appreciated...

Delboy - It depends on a number of factors. As you are querying whether it will 'add value' I'm assuming your plans for extending are not to do with needing more space or amenity for self/family? Presumably the house is adequate and habitable currently? There will be planning restraints if the property is one of a terrace of houses. Is it in the middle of a town and might there be conservation issues? You need to check, and a good indication is what neighbours have or have not done at the rear of their properties. What is the soil like? There will be other considerations - about appropriateness and scale - if for example the house is pre-1900. You will need to investigate what the foundations are like; in some properties existing foundations don't conform to modern safety standards and putting extensions entails strengthening these. There are also building regulations which you need to research. For example on your remark about possibly putting a window - if windows are not present in a room there are legalities about adequate ventilation etc. Your Planning Department of your Local Council will be able to advise.

Thanks Marie.

From a planning perspective my next door neighbour has the exact same extension dimensions (also mid terrace) - so I don't forsee much hassle in that way. I only want to build out as far as their extension. To be honest some houses in the estate (a late 1920's council estate) have managed to get permission for 2 storeys so I'm not really pushing the envelope from a planning perspective.

I will be employing an architect friend soon, so hopefully he will be aware of the things like the need for windows, soil composition for foundations etc. The fact that so many houses have put on extensions recently (with full permission) in the estate I'm not expecting too many unusual problems. I am expecting some - but hopefully not too many...