Badly renovated houses: what we find behind the new finishes

A newly renovated house is the easiest kind to buy and sometimes the most expensive to own. Fresh render, microcement floors and new kitchens photograph well. Whether the work behind them was done properly is a different question. Here is one house we inspected this year, with names and the address left out, and what it cost to put right.

The house

A two-storey terraced house in Porto, renovated within the last few years, with external insulation (capoto) on two elevations, a sandwich-panel roof over a concrete ceiling and microcement throughout. It looked finished. The owner called us in because of mould.

What we found

• Capoto that was never built properly. No proper mesh reinforcement in the base coat, cracking across both elevations and water getting in behind it. Patching wouldn’t work. It had to come off and go back on as a proper certified system.
• No ventilation at all. No extract in either bathroom or the kitchen, nothing whole-house. In a house sealed up by insulation and new windows, that produced black mould in the wardrobes, the bathroom, the window reveals and under the roof.
• No fire separation between houses at roof level. You could see daylight through an open void above the party wall, running its full length. That breaches the fire safety rules and leaves no thermal or acoustic separation either.
• Windows bedded with open voids and no continuous perimeter seal.
• A roof without its end caps or proper flashings, with water dripping onto structural steel that was already rusting at a welded joint.
• A hot water cylinder standing on a plastic crate, with its pressure relief discharge made from a garden hose and plumber’s tape. We rated that critical and recommended isolating it straight away.
• Lighting circuits that didn’t work in a house renovated only recently.

What it cost to put right

For the work a builder could cost without an engineer, the total came to roughly €60,000–110,000 ex IVA. The biggest lines were replacing the roof system with insulation (€22,700–35,700), stripping and replacing the capoto (€11,000–20,500), re-bedding the windows (€4,800–10,000), whole-house ventilation (€4,300–7,500) and an electrical audit and remediation (€3,000–8,000). A structural engineer had to assess the steelwork before that part could be priced at all.

How to spot it before you buy

• Ask for the renovation file: the project, the contractor’s alvará, invoices, the electrical certificate and any warranty.
• Look for extract fans in every bathroom and the kitchen, and check they actually run.
• Look at render corners and around windows for fine cracking on capoto.
• Get into the roof space if there is one.
• Be suspicious of fresh paint in one corner of one room.

Our pre-purchase inspection is built for exactly this: a builder reading a renovation for what it hides. If you’ve already bought and need a technical record for a claim, see how the defect warranty works.

Figures are from our own inspection reports in 2025 and 2026, ex IVA, with names and addresses left out. Every house is different, so treat them as a guide to scale, not a quote.

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