Primairly because old houses are on bigger plots and allow for extensions and conversions.

ah interesting! That's quite different from the areas I've lived in the US. If you're in or near city lines the lots on older houses are small. It's not uncommon to see .15 acre lots. Newer houses aren't much better, but you can see .2 to .25 acres relatively commonly, though those are nearly always on the outer city or outside city lines so it could just be proximity to the city that's the factor there rather than age.

▲

happyopossum 20 hours ago | parent [-]

That is highly location dependent. Many cities had/have large lots in older neighborhoods and have transitioned to zero-lot-line construction or smaller lots in the past 30-40 years as demand for housing grew.

In fact in most of the western US that’s the norm…

	▲	jimnotgym 18 hours ago \| parent [-]
		The UKs green belt laws haven't helped here. Since you can't make the settlement bigger, the only course is to build in the gardens of houses with big gardens. In my view it has ruined many nice villages