New windows guarantee what’s covered in the UK

Replacing the windows in your home is one of the most significant investments you can make as a homeowner, with a typical three-bedroom semi-detached property spending anywhere from £4,000 to £10,000 on a full window replacement. Given that kind of outlay, the guarantees and protections that come with your new windows are every bit as important as the windows themselves.

When buying new windows in the UK, you should receive two separate written guarantees — one from the manufacturer covering the product itself and one from the installer covering the quality of the fitting — along with a FENSA or CERTASS certificate confirming Building Regulations compliance and an Insurance Backed Guarantee protecting you if the installer later ceases trading. A reputable installation in 2026 will include a minimum of ten years on sealed glass units, ten years on frames, and at least one to two years on hardware, with all remedial labour included at no additional cost.

Understanding Window Guarantees and Why They Matter

A window guarantee is simply a written promise that protects you if something goes wrong — and understanding exactly what kind of promise you are receiving, from whom, is the foundation of buying wisely.

A manufacturer’s guarantee is a written commitment from the company that made the window product — the frames, the sealed glazing units, and the hardware such as handles, hinges, and locking mechanisms. This guarantee covers defects in the materials or manufacturing process. If your uPVC frame begins to warp or discolour due to a production fault, or if a sealed unit fails and condensation appears between the panes, the manufacturer’s guarantee is what entitles you to a remedy.

An installer’s guarantee is a separate written commitment from the company or tradesperson who fitted the windows into your home. This covers the quality of the workmanship — the way the frame was measured, secured, sealed, and finished. Poor fitting can cause draughts, water ingress, or frames that sit out of square, and these faults should be remedied at the installer’s expense under their workmanship guarantee.

In 2026, most reputable window companies will provide both types of guarantee, and in many cases they present them as a single combined document. However, it is important to understand that these are legally separate instruments. You should receive both in writing, ideally before or at the point of completion, and you should check that each document clearly states who is responsible for honouring it.

It is also worth knowing that your guarantee exists alongside — not instead of — your statutory rights under the Consumer Rights Act 2015. This legislation requires that goods must be of satisfactory quality, fit for purpose, and as described, and that services must be carried out with reasonable care and skill. These rights apply regardless of any written guarantee and give you an important legal safety net. If a company tries to rely solely on a weak or exclusion-heavy guarantee to avoid their responsibilities, your statutory rights remain in place independently.

Practical tip — always ask for both the manufacturer’s and installer’s guarantee as separate written documents before you sign off on the completed installation.

What a Standard New Window Guarantee Should Cover

A well-structured guarantee from a reputable UK installer in 2026 should cover the four main areas where windows commonly develop faults — the sealed glazing unit, the frame, the hardware, and the workmanship of the installation itself.

Sealed glazing units

The sealed unit is the double or triple-glazed glass pane, which consists of two or three sheets of glass bonded together with a hermetically sealed cavity filled with air or an inert gas such as argon. The most common failure is seal breakdown, which causes moisture to enter the cavity and produce visible condensation or misting between the panes. A ten-year guarantee on sealed units is the widely accepted benchmark in 2026, and you should be cautious of any installer offering significantly less than this.

Window frames

Whether your frames are uPVC (unplasticised polyvinyl chloride, a rigid plastic), aluminium, timber, or composite, the guarantee should cover structural defects, warping, discolouration caused by manufacturing faults, and failure of the frame to maintain its weathertight seal. Ten years on uPVC frames is standard; premium aluminium products are increasingly guaranteed for fifteen to twenty-five years given the material’s inherent durability.

Hardware

Handles, hinges, multipoint locking mechanisms, and tilt-and-turn operating systems are grouped under hardware. These components are subject to daily use, so it is reasonable that their guarantee periods are shorter — one to two years is common on entry-level products, though many mid-range and premium installers now extend hardware cover to five years or beyond.

Workmanship

The installer’s guarantee should explicitly cover any defects arising from how the windows were fitted. This includes remedying gaps, cold bridges, water ingress, or frames that have shifted out of alignment due to poor installation.

Critically, the guarantee should confirm that both parts and labour are included for any remedial work. A guarantee that covers replacement components but excludes the labour to fit them can leave you with a significant bill, since a glazier or window technician’s call-out and fitting time will often cost more than the part itself.

Practical tip — read the guarantee document carefully for any mention of labour exclusions, and if the document is unclear, ask the installer to confirm in writing that all remedial work including labour is covered.

link to related article on how to compare window installation quotes UK

What FENSA Registration Means for Your Guarantee

FENSA registration is one of the most important signals that your installer is operating to a recognised professional standard, and it has direct implications for both your legal protection and your ability to sell your home in future.

FENSA, which stands for the Fenestration Self-Assessment Scheme, is a government-authorised scheme under the Building Regulations Competent Person framework. It allows registered installers to self-certify that their replacement window and door installations comply with Building Regulations in England and Wales, without the homeowner needing to pay for a separate local authority inspection. This is not merely an administrative convenience — Building Regulations set minimum standards for thermal performance, ventilation, and safety, so FENSA registration is confirmation that your windows meet the law.

FENSA registration does not in itself provide you with a product guarantee. What it does provide is a framework of consumer protections. Registered installers are required to offer a deposit indemnity scheme, which protects any deposit you pay if the company goes out of business before completing the work, and a guarantee protection insurance policy — commonly known as an Insurance Backed Guarantee — which ensures your guarantee remains valid even if the installer later folds.

At the completion of your installation, your FENSA-registered installer is required to notify your local authority and to issue you with a FENSA certificate. This is a legal document confirming that the installation meets Building Regulations, and it is a document you will need to produce when you sell your home. Missing FENSA certificates are one of the more common complications that arise during residential conveyancing, and resolving the issue retrospectively can delay a sale and cost money. Keep your certificate safe from day one.

You can verify any installer’s current FENSA registration at the official FENSA website (fensa.org.uk), where you can search by company name or postcode. Do this before signing any contract, not after.

Practical tip — check your installer’s FENSA status yourself at fensa.org.uk before you agree to any work, even if the company displays the FENSA logo on their website or vehicle.

What CERTASS Registration Means and How It Compares to FENSA

CERTASS is equally valid to FENSA for all legal and practical purposes, and homeowners should feel entirely confident with an installer registered to either scheme.

CERTASS is the Certification and Self-Assessment Scheme, the other principal competent person scheme for window and door installers in the UK. Like FENSA, it is government-authorised under the Building Regulations Competent Person Scheme and allows registered installers to self-certify compliance with Building Regulations in England, Wales, and Scotland. CERTASS registration also requires member installers to provide guarantee-backed insurance — meaning your protection is equivalent whichever scheme your installer belongs to.

The practical differences between the two schemes are minimal from a homeowner’s perspective. Both issue certification that satisfies conveyancing requirements. Both require member companies to carry Insurance Backed Guarantee provision. Both are searchable online — CERTASS via certass.co.uk. Neither is legally “superior” to the other, and any installer or salesperson who claims otherwise is being misleading.

In practice, the scheme a particular company belongs to tends to reflect regional industry preferences, historical business relationships, or the preferences of the trade association they are members of. What matters to you as a homeowner is simply that your installer is registered with one of these two schemes, that you can verify that registration independently, and that you receive your compliance certificate upon completion.

Scottish homeowners should note that window installations in Scotland are governed by Scottish Building Regulations, which differ in certain technical requirements from those in England and Wales. Both FENSA and CERTASS operate in Scotland, but it is worth confirming with your installer exactly which regulatory framework applies to your property.

Practical tip — ask your installer at the initial quote stage whether they are FENSA or CERTASS registered, and make their answer and your independent verification of it a condition of proceeding.

link to related article on Building Regulations for replacement windows UK

Insurance Backed Guarantees Explained

An Insurance Backed Guarantee — commonly abbreviated to IBG — is arguably the most underappreciated element of window consumer protection, and it is one that every homeowner should understand before signing a contract.

An Insurance Backed Guarantee is a separate insurance policy, provided by a specialist insurer, that steps in and honours your original guarantee if the company that installed your windows goes out of business, ceases trading, or is dissolved. The guarantee you receive from your installer is only as durable as the installer itself. Without an IBG, if your installer folds five years into a ten-year guarantee, you are left with no one to contact if your windows develop a fault — unless you pursue your statutory rights, which may involve court proceedings.

The UK window and glazing industry has historically seen a significant number of company failures over the years, including some well-known national brands. This is not a rare or hypothetical risk. It is an ordinary commercial reality that makes IBG cover genuinely valuable rather than a theoretical extra.

Reputable installers in 2026 include IBG cover as standard. Before you sign any contract, ask the installer to confirm the name of the IBG provider and the policy number. You should receive a copy of the policy document directly — not merely a reference to it in the guarantee booklet — so that you know exactly who to contact if you ever need to make a claim against it.

IBG policies for window installations are typically administered by specialist providers. Names you may encounter include QANW (which provides guarantee insurance through many glazing industry members), as well as schemes administered through FENSA and CERTASS themselves. Some IBGs are also arranged through general building warranty providers. The homeowner’s key requirement is simply to have the policy document in their possession, with a clear claims process explained within it.

Some installers charge a modest additional fee for IBG cover — typically in the range of £50 to £150 — and this is a legitimate cost. What would be concerning is an installer who presents a very limited basic guarantee and then asks for a significant premium to make it meaningful.

Practical tip — do not accept verbal reassurance about IBG cover; ask for the insurer’s name, the policy number, and your own copy of the policy document before work begins.

What a Good Guarantee Does Not Cover

Understanding the limitations of your window guarantee is just as important as understanding what it includes — and being realistic about exclusions will help you avoid unexpected disputes.

Almost all window guarantees exclude damage caused by misuse, accidental damage, or failure to carry out routine maintenance. For uPVC windows, this typically means keeping moving parts clean and lightly lubricated and keeping drainage channels clear of debris. For timber windows, maintenance requirements are more demanding — many timber frame guarantees are conditional on the frames being repainted or re-stained at specified intervals, often every three to five years, and failure to do so can void the guarantee entirely. Read these maintenance requirements carefully and keep records of any maintenance work you carry out.

Normal wear and tear on hardware — meaning gradual deterioration from ordinary everyday use rather than a manufacturing defect — is commonly excluded after the first few years. Surface scratches, minor chips to frames, and slight fading of frame colours that occur after installation are generally not covered, since these are considered cosmetic issues arising from environmental exposure rather than product failures.

One exclusion that catches many homeowners off guard is the third-party alteration clause. If a builder, plasterer, or renderer subsequently works in close proximity to your windows — rendering an external wall up to the frame, for instance, or removing and refitting an internal window board — your installer may consider the guarantee voided on those particular units. This is a legitimate clause since the installer cannot be held responsible for damage or displacement caused by someone else’s work. Before allowing any contractor to work near your windows, check whether this clause applies and, if necessary, notify your window installer in advance.

Homeowners choosing coloured frames, woodgrain foil finishes, or RAL-painted finishes should check the small print carefully. The decorative finish on these products often carries a shorter separate guarantee — typically five to ten years against peeling, flaking, or significant colour change — even where the structural frame guarantee runs for longer. This is particularly relevant for anthracite grey and other dark-coloured aluminium or uPVC windows, which have become extremely popular and which can show colour degradation more visibly than white frames.

Practical tip — read the maintenance obligations in your guarantee document on the day you receive it and set a reminder to carry out any specified maintenance at the required intervals, keeping dated records as evidence.

link to related article on maintaining uPVC windows

How Window Guarantee Coverage Compares Across Different Window Types in 2026

The guarantee you receive will vary depending on the type of window you choose, the price point you buy at, and the individual policies of the manufacturer and installer. The table below sets out the typical guarantee durations homeowners should expect across the main window types available in the UK in 2026.

In terms of pricing, budget window installations — where the cost per casement window including fitting falls roughly in the range of £300 to £500 — may come with shorter or more limited guarantees, and Insurance Backed Guarantee provision may need to be confirmed explicitly rather than assumed. Mid-range installations, typically in the region of £500 to £900 per window installed, generally represent the point at which comprehensive guarantees become standard practice. Premium aluminium and timber products, which can range from £900 to £1,500 or more per window installed, typically carry extended frame guarantees reflecting the longer design life of the materials involved.

It is worth noting that some installers charge a small additional fee — typically £50 to £150 — for IBG cover as a separate policy. This is an acceptable approach, but homeowners should always check that the base guarantee without the IBG is itself robust, covering parts, labour, and all four main areas described earlier in this article.

The following table provides a broader comparison of what homeowners at different investment levels should reasonably expect in 2026.

Practical tip — always compare guarantees alongside prices when gathering quotes; a cheaper window with a weak guarantee may cost you more in the long run than a slightly more expensive window with comprehensive cover.

link to related article on how to get accurate window replacement quotes

Available Grants in 2026 and How They Affect Your Guarantee Entitlements

For eligible homeowners, government grants can significantly reduce the cost of window upgrades — but grant-funded installations carry exactly the same guarantee entitlements as privately funded ones, and homeowners should not accept anything less.

The two principal grant schemes relevant to glazing upgrades in 2026 are ECO4 and the Great British Insulation Scheme (GBIS). ECO4, which stands for the Energy Company Obligation in its fourth phase, is a government programme delivered through energy suppliers and local authorities that funds energy efficiency improvements — including window upgrades in certain circumstances — for eligible low-income or vulnerable households. Eligibility is typically linked to receipt of qualifying means-tested benefits or to living in a property with a low Energy Performance Certificate rating. The Great British Insulation Scheme takes a broader approach, targeting homes with poor insulation ratings across a wider range of income groups, and may include glazing work where this forms part of a broader fabric improvement package.

For completeness, the Boiler Upgrade Scheme administered by Ofgem covers heat pump and biomass boiler installations and does not extend to window or glazing work.

When your windows are installed through either ECO4 or GBIS, the full range of consumer protections described in this article still applies. You should still receive FENSA or CERTASS certification. You should still receive a manufacturer’s guarantee and an installer’s guarantee, both in writing. You should still receive IBG cover. Grant funding does not reduce your entitlement to these protections, and any installer who suggests otherwise is not operating to the expected standard.

There is one additional layer of protection specific to grant-funded work. ECO4-funded installations must be carried out in accordance with PAS 2035, which is a publicly available British Standard specification governing the retrofit of energy efficiency measures in domestic buildings. PAS 2035 requires that a qualified Retrofit Assessor assesses the property before work begins and that a Retrofit Coordinator oversees the project to ensure that improvements are appropriate and correctly installed. This adds an independent layer of quality assurance on top of the standard installer guarantee framework.

Homeowners receiving grant-funded window installations should check that their installer holds the relevant TrustMark registration. TrustMark is the government-endorsed quality scheme for home improvement work, and installers carrying out ECO4 or GBIS-funded work are required to be TrustMark registered. You can verify any installer’s TrustMark status at trustmark.org.uk. This is separate from and in addition to FENSA or CERTASS registration.

Practical tip — if your windows are being funded through ECO4 or GBIS, ask the installer specifically to confirm their TrustMark registration number before work begins, and verify it independently at trustmark.org.uk.

link to related article on ECO4 and GBIS eligibility for window upgrades

How to Check and Protect Your Guarantee From the Start

Knowing what you should receive is only useful if you take practical steps to secure it — and the best time to do that is before you sign anything, not after the windows are in.

A thorough approach to protecting your guarantee rights breaks down into a clear sequence of actions:

1. Verify the installer’s FENSA or CERTASS registration before agreeing to any work. Use the official online registers — fensa.org.uk or certass.co.uk — rather than relying on logos on literature or vehicles. Registration status can lapse, and a logo is not proof of current membership.
2. Ask for both guarantee documents in advance — the manufacturer’s guarantee and the installer’s guarantee — as part of the written quotation or contract pack. If an installer cannot produce these before you sign, treat that as a warning sign.
3. Confirm that labour is included in any remedial work covered by the guarantee. Ask the installer to confirm this explicitly in writing if the guarantee document does not state it clearly.
4. Request the IBG policy document including the insurer’s name and your policy number. A responsible installer will provide this without hesitation. If this proves difficult to obtain, escalate by contacting the relevant FENSA or CERTASS scheme directly.
5. Read the maintenance obligations in the guarantee on the day you receive it. Set calendar reminders for any specified maintenance tasks — particularly relevant for timber frames — and keep dated photographic records of any maintenance you carry out.
6. Store all documentation safely — your FENSA or CERTASS certificate, both guarantee documents, the IBG policy, and your receipts. When you come to sell your property, your solicitor or conveyancer will ask for these, and tracking them down years later is avoidable stress.
7. Check the third-party alteration clause before allowing any other trades near your windows. If a clause exists, notify your window installer in writing before any adjacent building work takes place, and request written confirmation that the guarantee will remain unaffected.

According to the Energy Saving Trust, windows and doors account for a significant proportion of heat loss in older UK homes, making replacement glazing one of the most impactful improvements many homeowners can make. Protecting your investment through robust documentation of your guarantees is simply good financial sense.

The guarantee on your windows is only as strong as the documentation behind it. A verbal promise costs nothing to give and nothing to break. A written guarantee, backed by insurance and issued by a registered installer, is worth keeping safe for the life of your home.

When gathering quotes from multiple installers — and you should always gather at least three — compare the guarantee terms alongside the price. A company offering a significantly longer or more comprehensive guarantee at a similar price point to a competitor may be the better choice, even if the product specifications appear similar on paper. Conversely, an unusually long guarantee headline figure is worth scrutinising carefully; check whether it applies to the whole window system or only to specific components.

Finally, it is worth remembering that the guarantee framework described throughout this article applies to replacement windows — windows fitted into an existing aperture in an existing building. If you are extending your home or having windows installed in a new building or substantial conversion, different Building Regulations processes may apply, and you should confirm with your installer and your local authority how compliance will be certified in your specific case.

Practical tip — treat your window guarantee documents with the same care as your property deeds; file them somewhere permanent and accessible, and make sure a second household member knows where they are kept.