Extension cost.

[pete01]

If it doesn't have a window how can it lose light.

The utility does

 

[Ivor Windybottom]

If it's the sole source of light to the kitchen that adjoins that utility room then I suppose they could argue that it is indirectly a window to a habitable room.

But if it hasn't been there for 20 years then that may mean it has no right to light anyway. In which case who knows... should it be assessed based on where their kitchen window was before they built the utility onto it? Edit: Or is this window their original kitchen window? In which case it's a habitable room despite the new internal wall if it's a wall that allows light through.

Is this a planning permission application? If so speak to them. I had objections to mine, with a list of tenuous nonsense reasons for objections. I phoned the planning officer, I just asked if it made any difference to anything. He said no, it's still being approved. So I didn't need to bother even thinking about their arguments, just ignore it and move on.

 

[Valeriu2]

For a quick sanity check: outside London, single-storey build costs in 2026 are running at roughly £1,800–£2,800 per m² for a standard finish, with the shell alone at about £1,200–£1,700 per m². A full-width extension on a typical semi is about 6m × 4m = 24m², so the build-only range is roughly £43k–£67k, and £45k sits at the bottom of that. So it's not a cowboy price if the builder is known to you, but it will be a tight spec, so check what's excluded: foundations in bad ground, floor insulation and screed, electrics, plumbing, the bifolds themselves, and making good inside.


Add fees (architect, structural engineer, building control, around £5–10k), a 10% contingency, and VAT if the quote is ex-VAT. That's usually what turns a £45k quote into £70k+ by the end.


If it helps, I put the 2026 per-m² rates and the extras into a free calculator so you can see the full range for your size: https://uktoolcalc.uk/extension-cost-calculator/