What does a buyer check before specifying windows or doors?
Answer
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.
Information to make clear
Use the fields that affect this buying decision. Leave unsupported claims out.
- Product type and material
- Aluminium, timber, steel and composite frames differ in every property.
- Whole-unit thermal transmittance
- The value regulations reference, not the glass value.
- Air permeability classification
- Directly affects the building's air tightness test.
- Water tightness and wind resistance
- Determines suitability for exposure and height.
- Security rating
- Required by regulation and insurers in defined applications.
- Maximum sizes and configurations
- The design constraint.
- Acoustic performance
- Frequently required near roads and railways.
Documents to prepare
State what can be published, shared on request or issued with an order.
| Document | What it supports | Suggested handling |
|---|---|---|
| Test report for the window systemMay be requested at: specification: the primary evidence | Air, water and wind performance under the system standard | Publish |
| Declaration of PerformanceMay be requested at: regulatory compliance | Regulated declaration of the product's performance values | Publish |
| Thermal performance calculationMay be requested at: building compliance calculation | Whole-unit thermal value for the configuration specified | Publish |
| Security certificationMay be requested at: where regulation or insurance demands it | Testing against the security standard the application requires | Publish |
| Acoustic test reportMay be requested at: noise-exposed sites | Sound reduction under a named method | Share on request |
| Installation guidanceMay be requested at: installation: the performance depends on it | How the tested performance is achieved in the opening | Publish |
| Warranty termsMay be requested at: purchase | Coverage for frame, hardware, finish and sealed units | Publish |
Details to ask in an enquiry
Collect only the information needed to assess the request and respond.
- 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.
Related questions
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.
This is an editorial checklist, not a compliance standard. Requirements vary by market, customer and contract. Confirm current requirements with the responsible technical and commercial teams.
Plact Research. Plact's editorial desk for buyer-evidence guides. The guides organize common buyer questions, documents and enquiry fields. Requirements should be checked against current standards, regulations and contracts.