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A Bill of Quantities should make competing tenders easier to compare. Yet glass and aluminium packages are often specified so broadly that two contractors can price completely different systems while appearing to tender for the same item.
A BOQ item such as “Supply and fix aluminium windows complete” may leave unanswered questions about aluminium profile series, wall thickness, finish, glass type, glass thickness, hardware, drainage, seals, testing and installation. One bidder may price a lightweight basic system while another prices a heavier-duty system with better glazing, hardware and weather resistance.
The result is a familiar procurement problem: the lowest tender may not represent the lowest price for the same quality.
For consultants, architects, quantity surveyors, project managers and developers, a good BOQ glass specification creates a measurable scope. It defines the minimum acceptable materials and performance while allowing genuinely comparable bids.
This guide explains how to write clearer aluminium BOQ clauses and tender specifications for glazing in Kenyan construction projects.
Ali Glaziers Limited supplies glass, aluminium, hardware and building materials for projects in Nairobi, Eastleigh, Malindi and other parts of Kenya. For project sourcing and product comparison, consultants can explore the Ali Glaziers catalogue and identify relevant materials before finalising tender documentation.
Glass and aluminium tenders become difficult to compare when the BOQ describes only the finished element without defining the material, dimensions, glazing, finish, hardware and performance requirements. Comparable bids require the consultant to specify the minimum technical standard, not merely the name of the product.
Glass and aluminium work is rarely a single material.
A completed aluminium window or glazed partition is an assembly of components that may include:
If the BOQ simply says:
Supply and fix aluminium sliding windows.
different bidders can legitimately interpret the item differently.
One contractor may price:
Another may price:
Both may claim compliance with the same short description.
The BOQ has therefore failed to create a common basis for pricing.
A good BOQ specification should identify exactly what is being measured, define the minimum acceptable technical requirements and state what is included in the rate. The objective is to prevent bidders from reducing quality through unspoken assumptions or exclusions.
A well-written clause should help answer five questions.
For example:
Specify:
Depending on the project, requirements may include:
For example:
The unit of measurement should match the nature of the work.
Examples include:
A contractor cannot price accurately when the BOQ and drawings describe different scopes.
The phrase “supply and fix complete” is useful only after the specification clearly defines what “complete” includes. Without technical requirements, the phrase can hide major differences in glass thickness, aluminium quality, hardware and installation scope.
The problem is not the phrase itself.
The problem is using it as a substitute for specification.
Consider these two clauses.
Supply and fix aluminium sliding window complete.
Supply, fabricate, deliver and install aluminium sliding window to approved drawings, including specified aluminium profiles, minimum glass type and thickness, glazing gaskets, beads, drainage provisions, rollers, handles, locks, screws, anchors, perimeter sealants and all accessories necessary for a complete installation.
The second clause still needs project-specific technical information, but it establishes a clearer scope.
An aluminium BOQ clause should define the profile system, alloy or material requirements where relevant, wall thickness or approved system reference, finish, opening configuration, hardware, glazing method and installation requirements. These details help prevent bidders from pricing visibly similar but technically different systems.
A practical aluminium specification can include the following.
State whether the contractor must use:
Where alternatives are permitted, define the minimum technical criteria.
Do not assume that all aluminium extrusions have the same wall thickness.
The relevant thickness should be appropriate to:
Avoid inserting an arbitrary thickness without considering the system design.
Specify the required finish.
Examples may include:
The specification should define the required appearance and, where applicable, durability requirements.
State clearly whether the window or door is:
Do not leave the opening mechanism to tender interpretation when it affects cost.
Glass should be specified by type, nominal thickness, safety requirement and application rather than simply described as “glass.” The specification should also identify whether the glass is clear, tinted, laminated, toughened, insulated or otherwise treated.
The word glass is too broad for procurement purposes.
Different glass products can have very different cost and performance characteristics.
A BOQ should distinguish between, where applicable:
The exact glass specification should match the application.
For example, the requirements for a fixed internal partition may differ from those for:
The consultant should avoid copying one generic glass clause across all applications without considering safety and performance.
A useful glass clause identifies the exact glass type, thickness, safety classification where applicable and installation method. The clause should also state whether glazing materials, setting blocks, gaskets and sealants are included in the rate.
A model structure could read:
Supply and install [glass type] glazing, nominal thickness [X mm], to locations shown on drawings, complete with compatible glazing gaskets, setting blocks, beads, sealants and all accessories required for a secure and finished installation.
The project-specific information should then be inserted.
For example:
The consultant should not insert technical values unless they are supported by the design and relevant product requirements.
Toughened and laminated glass are different products with different failure characteristics and should not be treated as interchangeable in a BOQ. The specification should identify which safety performance is required for the particular application.
Toughened glass is heat-treated to improve its strength and, when broken, it typically fractures into relatively small pieces.
Laminated glass consists of multiple glass layers bonded together with an interlayer.
The interlayer can help retain fragments after breakage.
The correct choice depends on the application and required safety behaviour.
For example, a glazing element where post-breakage retention is important may require a different specification from one where toughened safety glass is appropriate.
The key procurement lesson is simple:
Do not write “safety glass” without defining the required glass construction or applicable performance requirement.
Yes, nominal glass thickness should normally be identified, but thickness alone is not a complete safety or performance specification. Glass selection should consider the panel size, support conditions, location, loading and intended application.
A clause that says:
10 mm glass.
still leaves unanswered questions.
Is the glass:
The thickness should therefore be combined with the glass type and installation condition.
For example:
10 mm clear toughened safety glass, polished exposed edges where indicated, installed in accordance with approved fixing details.
The correct wording for a real project should be developed from the design requirements.
Aluminium windows are commonly measured according to the project's agreed measurement rules, but the BOQ must make clear whether rates include glazing, hardware, installation and perimeter finishing. Consistency between drawings, schedules and BOQ descriptions is essential.
Measurement disputes often occur because the schedule and BOQ are not aligned.
For each window type, the consultant should establish:
A window schedule can provide technical detail while the BOQ provides quantities and pricing structure.
For example:
Drawing/Schedule: W-01, aluminium sliding window, dimensions and technical configuration.
BOQ: Supply and install W-01 windows in accordance with window schedule and specification.
This can be more effective than repeating a long technical description for every individual item.
However, the BOQ should still clearly state what the rate includes.
Unless specifically excluded, a complete aluminium window rate should state whether it includes fabrication, glazing, hardware, transport, installation, anchors, sealants and finishing. Leaving these components ambiguous can create variation claims after tender award.
A complete installation may include:
Not every project will include every element in the same BOQ item.
The important point is to allocate each responsibility clearly.
Aluminium door specifications should define the opening type, profile system, glazing or panel infill, hardware and locking requirements. Door performance depends heavily on the combined specification of the frame, leaf, hinges, locks and closing hardware.
A door clause should clarify whether the door is:
It should also define the required:
A simple phrase such as “aluminium door complete” leaves too many variables.
For hardware sourcing, consultants can also review Ali Glaziers hardware-related products when preparing procurement schedules.
Hardware should be identified either within the aluminium item or as separately measured items, but it should never be left unclear. Locks, handles, rollers, hinges and closers can create significant price differences between bids.
There are two common approaches.
The clause states that all required hardware is included.
This can simplify pricing.
However, the minimum hardware quality must still be defined.
This may be useful when:
Whichever approach is used, avoid double-counting or leaving items unpriced.
For example, if a door BOQ item says “complete with all ironmongery”, but the hardware schedule separately measures locks and handles, tenderers may interpret the scope differently.
Aluminium finish affects appearance, durability and cost, so tenderers should know exactly which finish is required. A generic reference to “finished aluminium” does not create a reliable basis for comparing powder coating, anodising or other finishes.
Finish clauses should clarify:
For high-visibility commercial projects, physical samples can be useful before full production.
The consultant should also coordinate finish specifications with:
This helps prevent inconsistent colours across the completed building.
Tender glazing specifications should define the exact glass build-up and performance required for each application. Bidders should not be asked to price “equivalent glass” without a measurable minimum standard.
A useful glazing schedule can include:
| Glazing Reference | Location | Glass Type | Nominal Thickness/Build-Up | Safety Requirement | Notes |
|---|---|---|---|---|---|
| G-01 | Fixed external window | Project specified | Project specified | As required by design | Clear/tinted as scheduled |
| G-02 | Door vision panel | Project specified | Project specified | Safety glazing where required | Coordinate with door system |
| G-03 | Internal partition | Project specified | Project specified | As required | Edge finish where exposed |
| G-04 | Shower enclosure | Project specified | Project specified | Safety glass | Coordinate with hardware |
The exact values should be determined by the designer or competent technical professional.
The table format prevents bidders from guessing which glass applies where.
A model clause for an aluminium sliding window should identify the approved profile system or minimum requirements, opening configuration, glass, hardware, finish and installation scope. The clause should refer to drawings and schedules for dimensions instead of relying on generic descriptions.
A model procurement clause could read:
Supply, fabricate, deliver and install aluminium sliding windows to the types, sizes and configurations shown on the drawings and window schedule. Form windows from approved aluminium profile systems suitable for the indicated opening sizes and service conditions. Include specified glazing, glazing beads, gaskets, weather seals, drainage provisions, rollers, handles, locks, fasteners, anchors and perimeter sealing. Finish aluminium in the scheduled finish and colour. Submit product data and samples where required. Rate to include all labour, cutting, fabrication, transport, installation, accessories and incidentals necessary for a complete installation.
The project should then define:
The purpose of the model clause is to establish scope, not to replace engineering or design.
A fixed-glazing clause should define the glass construction, framing or support system, setting method and all glazing accessories. The clause should make clear whether the rate includes perimeter sealing and finishing to adjacent construction.
A model clause could read:
Supply and install fixed glazing to locations indicated on drawings, comprising the specified glass type and build-up, installed within the approved aluminium framing system or support arrangement. Include compatible glazing beads, gaskets, setting blocks, sealants, fasteners and all accessories required for a secure, weathertight and finished installation where applicable.
Again, the project documentation should define the exact glass.
Frameless glass should be specified with particular care because glass type, thickness, edge treatment and fixing hardware are all critical to safety and appearance. The BOQ should not rely on the phrase “frameless glass complete” without defining these requirements.
A model clause could include:
Supply and install frameless glass assembly to drawings, comprising specified safety glass construction and thickness, with exposed edges finished as indicated. Include all approved brackets, clamps, channels, gaskets, fasteners, sealants and associated hardware necessary for a complete installation.
Depending on the application, the specification may also need to define:
These should not be treated as incidental when they significantly affect fabrication cost.
Shop drawings allow the contractor and consultant to confirm dimensions, opening arrangements, interfaces and fixing details before materials are fabricated. This reduces the risk of expensive site modifications and conflicting interpretations after production begins.
Shop drawings can help coordinate:
For aluminium and glass packages, fabrication often begins off-site.
Discovering an error after glass has been cut or profiles have been fabricated can create avoidable cost and delay.
The BOQ or specification should therefore state whether:
“Or equivalent” should only be used when the specification defines measurable minimum criteria that an alternative must meet. Without measurable requirements, the phrase can allow bidders to substitute lower-grade materials while claiming equivalence.
A better approach is:
Approved system or technically equivalent system meeting or exceeding the specified requirements for material, profile performance, finish, glazing capacity, durability and installation suitability.
Then define the actual requirements.
For example:
The goal is not necessarily to restrict competition to one supplier.
The goal is to ensure alternatives are genuinely comparable.
Where the final system is not fully designed, the BOQ should identify provisional allowances or provisional quantities rather than pretending the scope is complete. Uncertainty should be visible in the tender documentation so bidders price risk consistently.
A project may go to tender before every glazing detail is finalised.
This can happen with:
In such cases, options include:
The chosen approach should make uncertainty transparent.
It is better to identify an unresolved design issue than to allow every bidder to make a different assumption.
A named brand can provide a clear reference point, but the specification should state whether alternatives are permitted and how equivalence will be assessed. Brand names alone may not define every technical requirement required for a comparable tender.
A brand may help establish:
However, the consultant should still define the relevant project requirements.
A named aluminium system does not automatically define:
These may need separate treatment.
For product sourcing and market comparison, consultants can explore Ali Glaziers' manufacturer listings where relevant.
Sealants and gaskets should be specified as part of the glazing and installation system because they affect weather resistance, appearance and long-term performance. Leaving them unspecified can lead to inconsistent products and installation methods across competing bids.
A glazing package may require:
The BOQ should make clear whether these are included in the window, glazing or separate sealing item.
The specification should also require compatibility between:
Compatibility matters because an unsuitable sealant can affect adhesion, appearance or long-term durability.
Aluminium and glazing work must be coordinated with masonry, plaster, waterproofing, cladding, flooring and finishes before fabrication. Many site disputes arise because an opening or interface is assumed to belong to another trade.
Typical coordination points include:
For example, the consultant should establish:
These responsibilities should not be discovered during practical completion.
A glazing schedule should give each glass application a reference, location, type and minimum technical description. This allows bidders, consultants and contractors to trace every glazing requirement back to a common document.
A useful schedule may include:
This can be used together with the BOQ.
The BOQ provides quantity and pricing.
The glazing schedule provides technical clarity.
Quantity surveyors can improve tender comparability by separating technically different systems, referencing schedules consistently and clearly stating what each rate includes. The objective is to ensure bidders are pricing the same quality and scope rather than different assumptions.
A practical approach is to avoid combining different systems into one vague item.
Instead of:
Aluminium windows, various types – Item.
use:
Each item can then reference the appropriate schedule.
Where dimensions vary substantially, the measurement structure should remain consistent with the project's measurement rules.
Procurement teams should compare compliance as well as price. A bid that is cheaper because it excludes specified glass, hardware or finishing should not be treated as directly comparable with a complete compliant tender.
A bid comparison should review:
A simple tender comparison matrix can help reveal exclusions.
| Requirement | Bidder A | Bidder B | Bidder C |
|---|---|---|---|
| Specified glass type | Compliant/Check | Compliant/Check | Compliant/Check |
| Glass build-up | Compliant/Check | Compliant/Check | Compliant/Check |
| Aluminium system | Compliant/Check | Compliant/Check | Compliant/Check |
| Hardware included | Yes/No | Yes/No | Yes/No |
| Sealants and gaskets | Yes/No | Yes/No | Yes/No |
| Installation included | Yes/No | Yes/No | Yes/No |
| Shop drawings | Yes/No | Yes/No | Yes/No |
| Exceptions | List | List | List |
The lowest price should then be assessed against actual compliance.
Avoid vague descriptions that name a finished product without defining the minimum materials and performance. If bidders can reasonably price different systems, the clause is too broad for a genuinely comparable tender.
Examples include:
Too vague unless supported by a detailed schedule and specification.
Too open for tender comparison.
Not measurable.
Not sufficiently specific unless supported by a defined system or measurable criteria.
Incomplete unless the required glass construction or standard is defined.
Weak unless the basis of equivalence is defined.
Before issuing a tender, check that every glass and aluminium item can be traced to drawings, schedules and technical requirements. If a bidder still needs to guess about a major component, the documentation should be improved before procurement.
Use this checklist.
Profile system defined
Opening type defined
Finish defined
Hardware responsibility defined
Glass interface defined
Installation scope defined
Glass type defined
Thickness/build-up defined
Safety requirement identified
Tint/appearance defined
Edge treatment defined where required
Glazing accessories included
Site measurement responsibility defined
Shop drawings required where appropriate
Anchors included
Gaskets included
Sealants included
Perimeter finishing responsibility clear
All bidders receive the same schedules
Alternatives are controlled
Exclusions are declared
Product substitutions require approval
Rates include the stated scope
A BOQ glass specification defines the glass type, thickness or build-up, application and installation requirements so tenderers price the same minimum glazing standard. It prevents broad descriptions such as “glass complete” from creating different assumptions between bidders.
Yes, but thickness should be specified together with glass type and intended application. Thickness alone does not define whether glass is toughened, laminated, clear or otherwise suitable for the required installation.
Reference the window schedule and define the required profile system or minimum criteria, finish, opening type, glazing, hardware and installation scope. The BOQ should also state what is included in the rate.
Bids are genuinely comparable when every bidder prices the same minimum technical requirements and scope. Differences in glass, aluminium profiles, hardware and exclusions should be identified before comparing tender prices.
It can be included within the window rate or measured separately, but the responsibility must be clear. Leaving hardware unspecified can create major cost differences between bids.
Yes, but only when the specification defines measurable minimum criteria for equivalence. Otherwise bidders may propose products that appear similar but provide different technical performance or durability.
This depends on the project's measurement method and procurement strategy. Separating them can improve price transparency, while combining them into a complete window or façade system can simplify responsibility when the technical scope is clearly defined.
The biggest mistake is allowing major technical components to remain undefined. If bidders can choose different glass, profiles or hardware without violating the written BOQ, the resulting prices are not directly comparable.
A reliable glass and aluminium BOQ should describe the minimum system being procured, including materials, glazing, finish, hardware and installation. The clearer the scope before tender, the less likely the project is to face substitutions, variations and disputes after award.
For consultants preparing a BOQ glass specification, the central objective is not to write the longest possible clause.
It is to eliminate material ambiguity.
A tenderer should understand:
For an aluminium BOQ clause, avoid relying on terms such as complete, heavy duty or best quality unless the measurable technical requirements are stated elsewhere.
For a tender specification for glazing, define the actual glass type and construction required for each application.
Where drawings, window schedules and glazing schedules are used, reference them consistently.
The strongest procurement documents allow flexibility where it is useful while controlling the technical minimum that every bidder must meet.
That is how consultants create genuinely comparable bids.
Ali Glaziers can support project teams sourcing glass, aluminium and associated hardware by providing product information and material options for Kenyan construction projects. Consultants can explore available glass-related products, review the wider structural products range, or contact Ali Glaziers when preparing material requirements.
Business and project purchases are supported with eTIMS-compliant invoices, helping contractors, consultants and commercial clients maintain appropriate procurement and tax documentation in 2026.
Ali Glaziers Limited: Your one-stop hardware, glass and building-material supplier for residential, commercial and construction projects.
Nairobi – Funzi Road: +254 716 259682
Eastleigh Branch: +254 722 522452 | +254 723 354299
Malindi Branch: Imadi Shopping Mall | +254 722 671352
Email: [email protected]
Website: Explore Ali Glaziers
Delivery: Same-day in Nairobi. Next-day delivery to Mombasa, Kisumu, Eldoret, Nakuru and beyond, subject to product availability and delivery arrangements.
For project procurement, contact Ali Glaziers for product guidance and availability before finalising your BOQ or placing material orders.
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