This is what a buyer checks before they shortlist a construction and building products supplier.
What does a buyer check before specifying windows or doors?
They check the whole-window thermal value rather than the glass alone, the air and water tightness classifications, and the security rating where required. Whole-unit performance is what regulations reference, and a glass-only figure will not satisfy them.
A housebuilder is specifying windows that must pass both a regulatory calculation and a site air tightness test.
Reviewed 4 August 2026 · Written for door and window manufacturers selling to business buyers
What does a buyer check before specifying windows or doors?
What a buyer needs to identify the product
These are the fields a buyer scans before deciding whether you are worth contacting. Missing one of them usually ends the visit without an email.
- 1
Product type and material
Aluminium, timber, steel and composite frames differ in every property.
- 2
Whole-unit thermal transmittance
The value regulations reference, not the glass value.
- 3
Air permeability classification
Directly affects the building's air tightness test.
- 4
Water tightness and wind resistance
Determines suitability for exposure and height.
- 5
Security rating
Required by regulation and insurers in defined applications.
- 6
Maximum sizes and configurations
The design constraint.
- 7
Acoustic performance
Frequently required near roads and railways.
The documents buyers ask for
Not all of them belong on a public page. Naming the ones you can issue is what separates a supplier who can be audited from one who cannot.
| Document | What it proves | Where it belongs |
|---|---|---|
| Test report for the window systemAsked at: specification — the primary evidence | Air, water and wind performance under the system standard | Publish it |
| Declaration of PerformanceAsked at: regulatory compliance | Regulated declaration of the product's performance values | Publish it |
| Thermal performance calculationAsked at: building compliance calculation | Whole-unit thermal value for the configuration specified | Publish it |
| Security certificationAsked at: where regulation or insurance demands it | Testing against the security standard the application requires | Publish it |
| Acoustic test reportAsked at: noise-exposed sites | Sound reduction under a named method | Name it, share on request |
| Installation guidanceAsked at: installation — the performance depends on it | How the tested performance is achieved in the opening | Publish it |
| Warranty termsAsked at: purchase | Coverage for frame, hardware, finish and sealed units | Publish it |
Where doors and windows sites lose the enquiry
Each of these is common, cheap to fix, and costs an enquiry that never arrives — so nobody ever reports it.
Glass thermal value published instead of whole-unit value
Regulations reference whole-unit performance. A glass-only figure looks better and cannot be used in the compliance calculation.
Air permeability classification omitted
Buildings are tested for air tightness on completion, and windows are a main source of failure. Buyers now check the classification before specifying.
Installation guidance separated from performance data
Tested performance is achieved only with correct installation. Publishing one without the other invites failures at the site test.
What the enquiry form should ask
A form that collects these can be answered properly the first time. A form that collects a name and a message cannot.
Enquiry form — doors and windows
Enough to reply usefully, short enough that a buyer finishes it.
- Building type and application
- Determines the requirements.
- Performance targets
- Thermal, acoustic and security values required.
- Sizes, configurations and quantities
- The basis of the quote.
- Exposure and building height
- Determines wind and water requirements.
- Finish and colour requirements
- Affects lead time and cost.
- Programme dates
- Windows sit on the critical path of a build.
Questions suppliers ask
Why does whole-unit performance matter more than glass performance?
Because the frame is where heat is lost and where regulations focus. Whole-unit values are what compliance calculations use, and a manufacturer quoting glass values is either unaware of the requirement or avoiding it. Buyers can tell which.
How should installation guidance be presented?
As part of the performance claim rather than as a separate document. Air and water performance depend on how the unit is fixed and sealed into the opening, and the manufacturer who explains it clearly is protecting their own product's reputation on site.
What convinces a large housebuilder?
Consistency evidence and supply capability alongside performance: test reports for the systems actually offered, production capacity, and the ability to hold a delivery programme across a site. Performance gets you considered; supply reliability gets you the contract.
Documents and standards named here are the ones buyers in this industry commonly ask for; requirements vary by market, customer and contract, so treat this as a starting checklist rather than a compliance list. Clearer pages can help discovery and evaluation. They do not guarantee rankings, AI citations, enquiries or revenue.
Illustrative
An enquiry from this search looks like: Sizes, configurations and quantities · Programme dates · Building type and application · Performance targets