When adding value there are couple of routes to take cosmetic or structural. Here is a list of what kind of return you can expect from what kind of investment:
Conservatory 5% of value increase
Kitchen 5-10% of value increase
Extreme cosmetic makeover 20% of value increase
Quote taken from http://blogs.telegraph.co.uk/finance/ianmcowie/100022974/newbuild-homebuyers-beware-period-properties-enjoy-quadruple-house-price-gains/
By contrast, every hour spent adding to the value of your home can produce tax-free gains because of what HM Revenue & Customs (HMRC) calls the prime residence Capital Gains Tax (CGT) exemption; profits on your home are tax-free.
However, even that lack of transparency is likely to make period property a better bet than newbuilds for bargain-hunters. Or, as Mr Hooper put it: “For those investors who wish to outperform the market as whole, the period property market is much more inefficient, and will produce more opportunities to buy below market value and increase value through planning and refurbishment.”