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Window and door supply specification: what to put in the contract
A practical B2B guide to the technical and commercial items of a window and door supply specification between retailer or contractor and manufacturer. What to demand in writing.
- Mirko Vanzo
- Author
- 18 February 2026
- Published
- 12 min
- Reading time
Most disputes between a window and door retailer and a manufacturer don’t stem from fraud. They stem from something far more mundane: something neither party put in writing, and each assumed in their own way. The colour of the hardware. The acceptable dimensional tolerance on an out-of-standard order. Who pays for the return transport. Exactly when “delivery” is deemed to occur for the purposes of the agreed lead time.
A supply specification — or a framework supply contract, which is the same logic formalised — exists precisely to remove these ambiguities before they turn into a tense phone call with a site standing idle. This article is a practical guide to what to demand in writing, item by item, when you order windows and doors from a manufacturer. It isn’t a template to copy, nor legal advice: it’s a map of what, in our experience as a manufacturer, makes the difference between a smooth relationship and a litigious one.
Here we’re talking about the document: what it contains and why. If you’re still working out who to trust, that’s a different stage — we cover it in the checklist for choosing a reliable window and door supplier. And if the point is volume discounts, that’s the territory of price list negotiation. Here we stay on the text of the contract.
Why a specification, and not just an order by email
An accepted quote is already a contract, legally speaking. But an accepted quote is also a thin document: it describes what you’re buying and how much it costs, rarely how, when and what happens if. The specification covers exactly that gap.
It matters most in three situations:
- Ongoing supply — if you work with the same manufacturer all year round, a framework contract sets the rules once, and individual orders sit on top of it.
- Complex or out-of-standard orders — special colours, unusual dimensions, particular glazing: the further you move from the standard, the larger the grey area to clarify.
- Significant amounts — where a dispute would be costly, it’s worth investing half a day in writing it well.
For clauses with legal effect — penalties, jurisdiction, retention of title, limitations of liability — there’s one rule, and we won’t repeat it in every paragraph: have them validated by a legal advisor. What follows is the technical and commercial substance to bring to them, not a substitute for their work.
The technical items: describing the product with no room for interpretation
This is the part genuine manufacturers appreciate and improvised ones fear. The more precisely the product is described, the less room there is to deliver “something similar”.
Profile system
Writing “5-chamber PVC” isn’t enough. Demand the make and code of the system: for example, knowing whether it’s a Salamander BluEvolution 82 or a GreenEvolution 70 changes the thickness, the thermal values and the range of available accessories. A supplier who won’t put that in the specification is a supplier keeping the door open to switch profile without telling you. For a practical comparison between systems, see the comparison of Salamander profiles.
Performance values: Uw, Ug, and what they mean in the specification
There’s a classic trap here. The supplier declares a “catalogue” Uw, but that value applies to a specific reference size. On a smaller or larger window, the real value changes.
| Item in the specification | What to demand |
|---|---|
| Glazing transmittance (Ug) | The glass unit’s value as stated on the glazier’s delivery note |
| Window transmittance (Uw) | A value referred to a declared size, not a generic one |
| Air permeability | Class according to EN 12207 |
| Watertightness | Class according to EN 12208 |
| Wind load resistance | Class according to EN 12210 |
These performance figures aren’t a nicety: they’re the parameters that CE marking under EN 14351-1 requires to be declared, and that you’ll find in the Declaration of Performance. Putting the expected class in the specification means having an objective benchmark if something doesn’t add up.
Glazing and hardware
The glazing package needs to be described in its make-up (for example low-emissivity, any gas fill in the cavity, any acoustic or laminated safety pane). It sounds pedantic, but “double glazing” and “low-emissivity double glazing with warm-edge spacer” have different prices and different performance.
Hardware is the item that generates the most aesthetic and functional complaints. Put in the specification:
- make and range of the hardware;
- finish/colour (silver, white, black, brass-effect…);
- any security fittings (number of locking points, anti-tamper cams);
- micro-ventilation, if required.
Dimensional tolerances
A hugely underrated item. Every window and door unit has manufacturing tolerances: the question is which ones are accepted. Stating an order of magnitude in millimetres for the accepted tolerance, consistent with what the system provides for, avoids the “it’s crooked” / “no, it’s within tolerance” argument once the tape measure comes out. The exact value depends on the system and must be agreed: there’s no universal figure to pass off as law.
CE marking and DoP
It’s non-negotiable, and it’s worth writing anyway: every supply must be accompanied by the Declaration of Performance (DoP) required by EU Regulation 305/2011 (CPR) and by CE marking under EN 14351-1. Put in the specification that the DoP is delivered with the goods, not “on request” three months later when you need it for testing and acceptance. On how to manage this documentation on the retailer’s side, we’ve dedicated a piece to CE marking and DoP certifications.
The commercial items: where the disputes really start
The technical items define the product. The commercial ones define the relationship — and that’s where relationships break down.
Prices and volume brackets
The price must be referred to a precise configuration. If you have volume brackets, put the bracket table in the contract, along with the criterion: does it apply to the single order? To the cumulative annual total? With what balancing mechanism? Also define the validity of the price list (for example, until a certain date, or with notice of revision), so you don’t discover a price increase once the job has already been sold to the end customer.
Delivery times
“Fast delivery” isn’t a clause: it’s a wish. What you need is:
- a delivery time expressed in working days from order confirmation (or from measurement confirmation, which is different);
- a definition of what starts the clock;
- a distinction between standard and out-of-standard products, which have different lead times.
Real lead times depend on seasonality, complexity and material availability: they should be treated as a contractualised order of magnitude, not a to-the-minute promise. To frame the logistics of supply, see the article on supply lead times and logistics.
Late-delivery penalties
Penalties are a tool, not a club. If you include them, the typical structure is a percentage of the value of the delayed supply per unit of time, with a maximum cap — but amounts, thresholds and allowances depend on the contract and need to be calibrated with your legal advisor. A disproportionate or badly worded penalty clause can be ineffective, or even backfire against the party who imposed it. Include it if it makes sense for the value at stake, not on principle.
Transport, damage and passing of risk
Who pays for transport, and above all, from what moment does the risk pass to you? A window that arrives chipped is a problem for whoever held the risk at that moment. Define:
- terms of delivery (who arranges and who pays for transport);
- the moment risk passes (on leaving the factory? on delivery to site?);
- the obligation of inspection on delivery and the time frame for reporting transport damage, typically immediately and with a written reservation on the delivery note.
Returns and non-conformity
Distinguish two things that are often confused:
| Case | Nature | Who typically bears it |
|---|---|---|
| Manufacturing defect | Manufacturer’s non-conformity | The manufacturer |
| Customer measurement error | Error by whoever ordered | Whoever supplied the measurements |
| Change of mind | ”Convenience” return | To be agreed, often at a cost |
A made-to-measure product is, by its nature, not easily resold; demanding a free return of an out-of-standard window “because it’s no longer needed” isn’t realistic. Put the dispute procedure in the specification: how it’s opened, within how many days, with what photographic documentation, and the supplier’s response times.
Warranties
The statutory warranty exists regardless. What the contract can add is a commercial warranty: duration, what it covers (profile, hardware and glass often have different durations), what voids it (for example, installation not carried out to standard). Writing down who guarantees what stops each party pointing at the other the moment a first defect turns up.
Brand ownership
A crucial item if you work in private label / third-party manufacturing. Define who owns the brand applied to the product, who can use it, and what happens at the end of the relationship. If you want the end customer to see your brand and not the manufacturer’s, it needs to be written down. We go into this in the piece on private label margins and on the dedicated private label / third-party manufacturing page.
Summary checklist for the specification
| Area | Minimum items to contractualise |
|---|---|
| Technical | Profile system (make+code), Uw/Ug, EN classes, glazing, hardware, tolerances, DoP+CE |
| Timing | Delivery time, the event that starts the clock, standard vs out-of-standard |
| Commercial | Price referred to a configuration, volume brackets, price list validity |
| Risk | Transport, passing of risk, inspection on delivery |
| After-sales | Returns and non-conformity procedure, warranties, penalties |
| Brand | Brand ownership and use (relevant for private label) |
When it’s NOT worth it
A detailed specification is a tool, not a universal obligation. There are cases where locking everything down is counterproductive:
- A single, low-value order for a standard product. For two catalogue windows, a good quote with clear terms is enough: forcing a twenty-page framework contract just wastes both parties’ time.
- A relationship built up over years with well-worn practices. If, with that manufacturer, returns, lead times and disputes have always been handled without friction, suddenly formalising everything can stiffen a relationship that works. Better to put in writing only the points that have historically caused doubt.
- When the specification becomes a weapon for offloading every risk onto the other party. An unbalanced contract, one that lands the supplier with liability for things it doesn’t control (for example, responsibility for installation carried out by someone else), or the customer with disproportionate penalties, doesn’t prevent disputes: it sets them up. The aim is mutual clarity, not winning on paper.
- If you have no way to get it validated. Inserting complex legal clauses copied from elsewhere, without review, can give false reassurance. Better a few clear, correct items than many ineffective clauses.
FAQ
Does an accepted quote count as a contract? Yes, legally, accepting an offer forms a contract. The issue isn’t validity, but completeness: a standard quote rarely covers lead times, passing of risk, returns and penalties. The specification exists to fill that gap, not to “make valid” something that already is.
What’s the difference between a specification and a supply contract? In industry practice, they overlap. The specification is traditionally the technical-descriptive part (what I’m supplying and with what characteristics); the supply contract adds the commercial and legal framework (prices, timing, liability). A good supply document contains both elements.
Can I demand a penalty for delays? You can propose and negotiate one. Amounts, thresholds, allowances and caps depend on the contract and the balance of the negotiation, and a badly worded penalty risks being ineffective. That’s why it needs to be calibrated with a legal advisor: the aim is a tool that works, not an intimidating figure.
Who pays if the windows and doors arrive damaged? It depends on where the risk sat at that moment, and that’s exactly why it needs to be written down. If risk passes on delivery to site, transport damage stays with the sender; if it passes on leaving the factory, it doesn’t. Either way, there’s an obligation to inspect the goods on delivery and note a reservation on the delivery note.
Do I have to receive the DoP? Yes. The Declaration of Performance is required by EU Regulation 305/2011 for CE-marked construction products, and for windows and doors the reference is EN 14351-1. Demanding it with the goods, not on a subsequent request, is a concrete safeguard, especially ahead of testing and acceptance checks.
Does the specification replace legal advice? No. This article describes the technical and commercial substance to focus on; clauses with legal effect — penalties, retention of title, limitations of liability, jurisdiction — need to be drafted and validated by a trusted legal advisor.
In summary
A well-drafted supply specification isn’t there to help you argue better: it’s there so you don’t argue at all. It describes the product so there’s no room for “something similar”, and it defines in advance who does what when something goes wrong — because sooner or later, something goes wrong. The difference between a manufacturer with whom these documents get written in half a day, and one who dodges every item, is, in itself, valuable information.
If you’re looking for an Italian manufacturer willing to put systems, performance and terms in writing — and discuss them item by item — let’s talk, starting from the proposal for wholesalers and retailers or from our production page.