Vetting a renovation contractor before you sign

September 16, 2026
5 minute read
By Betsy Hines

A homeowner vets a renovation contractor by checking the firm in the public registration records first, then reading the licence document and the classes it carries, and only then comparing quotes line by line rather than by total. The order matters: registration and licence tell you whether the firm is allowed to do the work at all, while the quotes tell you what the work will cost and what is excluded. Signing before those three steps is done leaves the homeowner with no way to tell a qualified bid from an unqualified one. The useful work begins by looking closely, naming the trade-offs, and keeping the next decision visible. This guide is a starting point for a conversation, not a substitute for a site visit or qualified professional advice where the work requires it.

Start with the public registration record

In Portugal, construction firms that take on private works must hold an alvará, a licence issued and recorded through the IMPIC system. The record is public, and it is the first thing to pull. You are looking for the firm's legal name, its registration number, the classes it holds, the value limits attached to those classes, and whether the licence is active or suspended. A practical sequence: ask the contractor for the full legal name and the alvará number, then search that number in the public register yourself rather than accepting a photocopy. Compare the name on the record with the name on the quote and the name that will appear on the contract. Mismatches are common and are not always dishonest, but they need an explanation before anything is signed. Registration is a technical and administrative condition. It says the firm is entitled to contract for certain works up to certain values. It does not say the firm builds well. Keeping those two ideas apart prevents a clean record from being read as a guarantee of quality. A useful companion to the register is a plain-language guide to how these documents work in practice, such as the Caderno de Obra in Portugal, which explains contractor records, licence classes and quote comparison for readers who are not specialists. Reading that kind of material before you call anyone makes the register search faster and the questions sharper.

How do you check a contractor in the public IMPIC records?

The IMPIC register is searchable by firm name or by alvará number. Search both ways. A name search can reveal related companies, previous names and branch records; a number search confirms the specific document you were shown. What to note down: The exact legal name and the registration number. The alvará number, its issue date and its validity. The classes recorded, and the maximum value attached to each. Any suspension, cancellation or limitation shown on the record. The registered activity, which should match the work you are asking for. If the record shows a class whose value ceiling sits below your project budget, the firm cannot legally contract for that work on its own. It may be able to work as a subcontractor under another firm, or the project may need to be split. That is a question for the contractor, not an assumption. Screenshots help. Save the record page with the date visible, and keep it with the quotes. If the record changes between the first visit and the signing date, you will see it.

How do you read a construction licence and its classes?

An alvará is not a single permission slip. It is a document that lists classes, and each class corresponds to a type of work and a value band. Reading it means reading those two columns together. The classes describe categories of construction activity, such as building construction, rehabilitation, installations or specific specialist works. The value band attached to each class sets the maximum contract value the firm may take on within that class. A firm can hold several classes at different levels. When you read the document, ask: Does the class cover the type of work in my project? Does the value band cover my budget, including VAT and any likely extras? Is the licence valid for the whole expected duration of the works? Is the firm listed as the holder, or is it named as a representative of another entity? A licence that covers the work type but not the value is a real limitation, not a technicality. It affects who can sign the contract and who carries responsibility if something goes wrong. Keep the distinction between the licence and the work itself in view. The licence is an administrative condition. The quality of execution is a separate matter, judged by references, site visits and the clarity of the quote.

How do you compare contractor quotes for a private renovation?

Compare quotes line by line, not by the total at the bottom. Totals hide scope. Two bids for the same room can differ by thousands because one includes demolition, waste removal and finishing, and the other lists them as extras. Build a simple table with one row per work item and one column per contractor. For each row, note whether the item is included, excluded, or priced separately. Then compare. What to look for: Scope: Which works are inside the price and which are excluded. Exclusions are where budgets move. Quantities: Square metres, linear metres, number of units. A low unit price on a wrong quantity is not a low price. Materials: Brand, model or specification. "Ceramic tile" and a named tile with a reference number are different offers. Labour and access: Scaffolding, lifting, protection of common areas, working hours. Waste removal: Who removes rubble, where it goes, and whether the cost is included. Payment schedule: Tied to completed stages, not to dates alone. Deadlines and penalties: Start date, completion date, and what happens if the schedule slips. VAT: Confirm whether each line is quoted with or without VAT, and at what rate. Contingency: How variations are priced and who approves them in writing. Once the table is filled, the totals become meaningful. A higher total with a complete scope is often cheaper than a lower total with open exclusions.

What documents should be in place before signing?

Before signing, the file should contain the registration record, the licence details, the itemised quote, the contract, the payment schedule and the works timetable. Ask for the insurance documents that cover the works, and confirm who is responsible for site safety. Read the contract against the quote. The scope in the contract should match the scope you compared. If a line item disappeared between the quote and the contract, that is the moment to raise it. Keep everything in one folder, dated. If a dispute arises later, the dated record is what you will rely on.

Common mistakes and how to avoid them

Checking the licence after signing: Do it before. The record search takes minutes. Accepting a photocopy: Search the number yourself in the public register. Comparing totals only: Build the line-by-line table. Ignoring value ceilings: A class limit below your budget is a legal obstacle, not a detail. Leaving exclusions vague: Ask for exclusions in writing, item by item. Paying on dates rather than stages: Tie payments to completed and inspected work. Treating the licence as a quality mark: It is an administrative condition. Quality comes from references and site visits. None of this requires technical expertise. It requires reading documents in a fixed order: registration, licence, quotes, contract. Done in that order, the decision rests on records you can check rather than on impressions you cannot. A window contract is checked the same way, and reading a window contract before signing follows the rule set out here.

Close detail showing renovation contractor checks in context — Details are easier to judge when context and next steps stay together.

Second detail showing a practical New England home decision — Details are easier to judge when context and next steps stay together.