Renovation Hidden Costs Estimator

The items most often excluded are skip hire, scaffolding, Building Control fees, party wall agreements, structural engineer fees, temporary site facilities (toilet, power, water), and the final builders clean. Some quotes exclude waste removal beyond what fits in a single skip. Others quote labour and materials but list 'plus statutory fees' without pricing them. None of this is necessarily dishonest — it is often a way to keep the headline number low so the quote looks competitive. Your job as the homeowner is to ask: is X included, and if not, roughly what should I budget for it? A good builder will give you honest numbers on the spot.

Building Control fees are charged by your council (or a private approved inspector) to check that the work complies with Building Regulations. Most homeowners do not realise the fees are separate from planning permission. For a typical extension, expect £500–£900 for full plans approval and inspections. For a loft conversion with structural work, it is similar. The fee is based on project value. Some builders include it in their quote, others list it as 'paid by client'. If your quote does not mention Building Control at all, ask why — it is legally required for most structural and extension work.

If your neighbour signs the Party Wall Notice agreeing to the work, the cost is just the notice itself (often free if you do it yourself, or £150–£300 if a surveyor drafts it). If they dissent, you appoint a surveyor and they appoint a surveyor, both at your expense. Expect around £1,100 per neighbour in typical cases, rising to £1,500–£2,500 if the work is complex or the neighbour is difficult. Terraced properties have two shared walls, so you often deal with two neighbours. Semi-detached have one. Detached houses usually need no party wall agreement unless work is within 3–6 metres of a neighbouring foundation.