Before the Deposit Goes Down: A 10-Minute Double Glazing Installer Check

Double glazing is one of the bigger cheques you will write for your home, and most of the grief starts before the fitters arrive. A rushed deposit, a vague quote or an unverified guarantee can turn a straightforward job into a long argument. The good news is that a ten-minute check before you pay anything can tell you a lot.

1. Confirm who you are actually dealing with

Start with the basics. Does the company have a real trading address, a landline and a company number? Check the name on Companies House and see how long it has been trading. A mobile number and a glossy leaflet are not proof of a stable business.

Ask who will fit the windows. Some firms use their own teams, some use regular subcontractors and some sell the job on. None of those is automatically bad, but you deserve to know. If a subcontractor will be in your home, ask who is responsible for snagging and guarantees.

2. Verify FENSA or TrustMark registration

In England and Wales, replacement windows and doors are usually notified through a competent person scheme such as FENSA. TrustMark is another useful sign that a firm has been vetted for good practice. Ask for the registration number and check it on the scheme website yourself. Do not rely on a certificate PDF alone; a logo on a quote is easy to copy.

If the company is not registered with a scheme, ask how it will arrange building regulations approval. Some firms do this through the local authority, which is legitimate but may add time and cost. What you do not want is a vague answer about it all being covered.

3. Ask about insurance-backed guarantees

A ten-year guarantee sounds reassuring until you ask who is standing behind it. A company guarantee is only as strong as the company. An insurance-backed guarantee, sometimes called an IBG, is backed by a separate insurer or provider. Ask for the policy wording and check what is covered, how long it runs and whether it survives if the installer stops trading.

Also check whether the guarantee is transferable if you sell your home. It is not essential, but it can be a nice detail for buyers. Make sure the guarantee is registered in your name after installation, not left in a drawer at the office.

4. Protect your deposit

Never pay a large cash deposit on the spot. Ask whether the company uses a deposit protection scheme or an escrow arrangement. If you pay by credit card, you may have Section 75 protection on purchases over £100, though the rules are specific and the card provider is the one to ask. Debit card chargeback is another possible route, but it is not a guarantee.

A sensible payment schedule is tied to progress: a modest deposit, a payment on delivery or before fitting, and the balance after you have inspected the work. If a salesperson demands most of the money upfront before a survey, treat that as a warning sign.

5. Get a written, itemised quote

A proper quote should list the window and door sizes, frame material, glass specification, energy rating, hardware, trickle vents, handles, cills, installation, making good, waste removal and VAT. It should state the lead time and the payment schedule. If two quotes use different glass or different installation methods, they are not really comparable.

Ask what is excluded. Scaffolding, plastering, blinds, curtain tracks and moving furniture may sit outside the price. None of that is necessarily unfair, but it should be clear before you sign.

6. Check the survey and building regulations

A survey should happen before the final order is confirmed, especially if you have bay windows, unusual openings or a flat roof above. Ask who handles building regulations notification and what happens if the work fails inspection. For replacement windows, ventilation and fire escape requirements can matter, particularly in flats and upstairs bedrooms.

If a fitter says regulations are not needed, ask them to put that in writing. Then check it. It is a lot easier to sort out before the frames are made than after they are in the wall.

7. Read the small print for red flags

Look for a clear cancellation period, a delivery date or estimate, and a complaint procedure. Be wary of today-only discounts, pressure to sign on the night, blank contracts, verbal promises that are not written down and requests for large cash payments. A genuine firm will not collapse because you want to sleep on it.

Check whether the price can change after the survey and under what circumstances. Ask what happens if the installation is delayed. And read the guarantee exclusions: condensation inside the glass is usually covered, but accidental damage, poor cleaning and settlement cracks may not be.

8. Ask these five questions

Who will actually fit the windows, and are they employed or subcontracted?

Who handles the FENSA or building regulations notification?

What exactly does the guarantee cover, and is it insurance-backed?

What is excluded from the quote, and what could add cost later?

Can I see a recent local installation or speak to a past customer?

If any answer is evasive, pause. A good installer will not mind being checked. In fact, they will usually make it easy for you.

The ten-minute version

Check the company address and company number. Verify FENSA or TrustMark on the scheme website. Ask for insurance-backed guarantee wording. Confirm how your deposit is protected. Get an itemised written quote. Ask who handles building regulations. Read the cancellation and guarantee terms. If the paperwork is vague, do not pay a deposit. The best double glazing job is the one you checked properly before anyone picked up a drill.