A 1930s semi has a side return that is often a metre and a bit wide. Under the old permitted development rules the outdoor unit had to sit at least a metre from the boundary, which on a return that width meant there was nowhere legal to put it — and that was the end of a lot of conversations. That rule was scrapped on 29 May 2025. The unit can now go right up against the fence, and a great many Timperley semis went from impossible to straightforward overnight.
What decides it now is noise, and here it is a real constraint rather than a formality. The MCS 020 sound calculation is assessed at the nearest noise-sensitive premises, which on a semi means your neighbour's window — and on these plots that window is a few metres from where the unit wants to go. It has to come out at 37 dB(A) or below. On most Timperley semis it does, with sensible placement and mounting. On some it does not, and we would rather run that calculation before you have paid for anything.
The other thing to know is that a semi-detached house is capped at one outdoor unit under permitted development. That is not usually a problem for a three-bed semi — the heat loss does not need two — but it removes the fallback that a detached house has.
The stock itself is honest to work with. Cavity walls where the builder got round to it, suspended timber ground floors that make pipe runs easy and also leak heat, and radiators that are usually original enough to need upsizing. Timperley is also the one part of our patch where we still routinely pull out back boilers.
