The short version
- The contract must state the total price, the fitting date and the payment arrangements.
- For a contract signed at home or online, you are owed a copy of the signed contract before fitting starts.
- Keep the deposit to 25% or less and pay the balance on completion.
- Promises the salesperson made become contract terms when you relied on them, so get them written in.
What should a double glazing contract include?
A double glazing contract should include these 11 items, drawn from the Consumer Contracts Regulations 2013 (Schedule 2), the Consumer Rights Act 2015, Citizens Advice and Which?. Print the list and tick each one off against the installer's contract and the quote you accepted.
| # | Check before you sign | Done |
|---|---|---|
| 1 | Every window and door, with size, style, frame material, colour and glass specification | ☐ |
| 2 | The total price including VAT, and any extras priced separately | ☐ |
| 3 | The start date and the fitting date | ☐ |
| 4 | The deposit, the payment stages and the accepted payment methods | ☐ |
| 5 | Removal of the old frames and the rubbish | ☐ |
| 6 | Whether subcontractors will do the fitting | ☐ |
| 7 | The guarantee, its length and the insurer if it is insurance-backed | ☐ |
| 8 | Who registers the work under Building Regulations (FENSA, CERTASS or building control) | ☐ |
| 9 | The cancellation information and how to complain | ☐ |
| 10 | Every promise the salesperson made, written into the contract | ☐ |
| 11 | A copy of the signed contract for you to keep | ☐ |
A spec, price or date that differs from the quote needs an explanation in writing before you sign. Never sign a form with blank sections. Line the contract up against your other written quotes using our guide on how to compare double glazing quotes. Own a flat? Get the freeholder's written consent before you sign, as our guide to windows in a leasehold flat explains.
Need written quotes to check against?
Get free quotes from local installers who cover your postcode, then compare them on spec, price and terms.
The paperwork you are owed before work starts
You are owed three pieces of information before a double glazing contract binds you. They are a description of the goods and services, the total price including any extra charges known at the start, and when the work will be done. Which? lists these as the legal minimum, and the installer must stick to them.
- Signed at home or online: the information must be on paper, unless you agree to another durable medium such as an email or text message.
- Copy of the contract: for a contract signed at home or at a distance, you get a copy of the signed contract, or confirmation of it, before delivery and before work starts.
- Signed at the installer's showroom: the installer can give the information in any medium it chooses, so Which? advises asking for it in writing before you leave.
Do not let fitting begin until you hold your copy of the signed contract.
How long is a double glazing quote valid?
A double glazing quote is valid for the period printed on it, because the law sets no minimum. Neither the Consumer Contracts Regulations 2013 nor the Consumer Rights Act 2015 gives quotes a fixed lifespan. Ask for the validity date in writing if the quote does not show one.
A quote and an estimate are different documents. Citizens Advice explains that "a quote is a fixed price", while "an estimate is just a rough guess, so you might end up paying more". Make sure the paper you hold says quote.
"Only valid today" is a sales tactic
A price that expires the same day is pressure, not a validity period. The Digital Markets, Competition and Consumers Act 2024 (Schedule 20, paragraph 7) bans one tactic outright. Falsely claiming that a price or its terms last only a limited time, to force an immediate decision, is always unfair.
Get the fitting date in writing
The contract should state when the windows will be fitted, because the Consumer Contracts Regulations require traders to give "the time by which the trader undertakes to deliver the goods, to perform the services". Where no time is fixed, the Consumer Rights Act 2015 (section 52) requires the trader to perform the service "within a reasonable time".
A named date or week is easier to enforce than "a reasonable time". Agree in writing what happens if the date slips, such as notice of the new date and the right to hold back a payment stage until fitting starts.
Payment terms: deposit, stages and the balance
Payment terms should keep the deposit to 25% or less and leave the balance until the work is finished. Citizens Advice gives that 25% ceiling and says stage payments mean "problems can be put right before you make the final payment".
- Deposit on signing, written on the contract
- Any interim stage tied to a piece of finished work
- Balance after you have inspected the fitted windows
Pay at least part by credit card for Section 75 cover. Our guide on whether your double glazing deposit is protected covers payment methods and deposit insurance.
Guarantee and certificate terms
The contract should name the guarantee length, state whether it is insurance-backed and name the insurer. A company-only guarantee usually ends if the company stops trading, as our guide on what happens if your double glazing company goes bust explains.
How long should the guarantee be?
The guarantee should run 10 years on frames, 5 to 10 years on glass and at least 2 years on hardware, with a 10-year insurance-backed guarantee. That is the combined advice of nine Which? Trusted Trader installers, not a legal minimum, so treat it as a benchmark for comparing contracts.
The contract should also say who certifies the work under Building Regulations. A competent person scheme installer gives you a certificate and notifies the local authority within 30 days of completion, under regulation 20 of the Building Regulations 2010. Scotland has no FENSA, so our page on double glazing quotes in Edinburgh shows what to get in writing instead.
What the salesperson said counts
Spoken promises become contract terms when you relied on them. Section 50 of the Consumer Rights Act 2015 makes statements about the trader or the service binding where you took them into account when deciding to sign. That includes the pre-contract information under the Consumer Contracts Regulations.
Proving a spoken promise is harder than pointing to a written one. Ask for every promise to go into the contract: the glass rating, the fitting week, the colour, the making good inside and out. Our questions to ask a double glazing salesman help you draw those promises out during the visit. Section 49 adds that the installer must perform the work "with reasonable care and skill".
Cancelling a double glazing contract
If you sign at home, you usually have at least 14 days to cancel, but made-to-measure windows can be an exception, so check the contract before you sign. Our guide to the double glazing cooling off period explains the rules. Havering Trading Standards also covers doorstep-sale cancellation rights, as our page on double glazing in Romford notes.
Red flags in a double glazing contract
Six clauses or gaps mean you should stop and ask before signing:
| Clause | Why it matters | Ask for |
|---|---|---|
| Blank sections | Anything can be filled in after you sign | Every section completed or struck through |
| Deposit over 25% | Above the Citizens Advice ceiling | 25% or less, balance on completion |
| No copy of the signed contract | Contracts signed at home or online need one before work starts (Which?) | Your copy before fitting begins |
| No fitting date | You fall back on "a reasonable time" | A named date or week |
| Guarantee with no insurer named | It may end with the company: see what happens if your double glazing company goes bust | The insurer's name and policy terms |
| Price "valid today only" | False urgency is an unfair practice under the DMCC Act 2024 | A written validity date |
Questions people ask
Is there a double glazing contract template?
No, the installer writes the contract, and you check it. Print the 11-item checklist on this page and tick it off against the installer's document and your accepted quote.
Can the price change after the survey?
A quote is a fixed price and an estimate is not, according to Citizens Advice. Ask the installer to confirm in writing that the contract price will not change after the technical survey, or what would change it.
What if the installer misses the fitting date?
The installer is bound by the date in the contract. With no date fixed, section 52 of the Consumer Rights Act 2015 requires fitting within "a reasonable time". Raise the delay in writing and keep any unpaid stage until fitting starts, if the contract allows it.
