How to estimate an aluminium window and façade tender from drawings

A tender for aluminium windows, doors or a curtain wall usually arrives as a bundle: an invitation, a specification, a set of drawings and, if you are lucky, a window and door schedule. Turning that bundle into a price you can stand behind is a sequence, not a single calculation. This guide sets out that sequence step by step, with the checks that catch the expensive mistakes.

1. Read the invitation and the specification first

The drawings show what the building looks like. The invitation and the specification tell you what you are actually being asked to price. Read them before you open a single elevation, and note down the answers to these questions:

What to find	Why it changes the price
Scope: supply only, or supply and installation	Installation, access equipment and site time can be a large share of the total.
Scope boundaries: sills, window boards, flashings, membranes, fire stopping, scaffolding, cranes	Each item is either in your price or someone else’s. Unclear boundaries are the most common source of disputes.
Required performance: thermal transmittance, wind load, watertightness, air permeability, acoustics, burglar resistance, fire	Performance targets decide the profile series, the glass make-up and the hardware.
Named system or “equivalent”	A named system may not be the one you fabricate. An equivalent must be proven equivalent.
Colour and finish, inside and outside	Dual colour, special RAL shades and anodising carry surcharges.
Contract terms: programme, payment schedule, retention, penalties, warranty	Cash flow and risk belong in the price as much as materials do.
Documents required with the bid	Declarations of Performance, test reports and references take time to collect.

2. Collect and index the drawings

A typical package contains floor plans (where each unit sits and how many there are), elevations (sizes, divisions and opening types), sections and details (how units connect to the structure) and a window and door schedule. List every drawing with its number, revision and date. Price only from the latest revision, and state the revisions you used in the proposal. If a drawing is referenced but missing, ask for it.

3. Build the position list

The position list is the backbone of the estimate. Give every unique unit type one row and record:

• the mark, for example W-01 or D-03, and the quantity, split by floor or elevation if the drawings allow;
• width and height, and whether they are structural opening sizes or frame sizes;
• the division into fields and the opening type of each field: fixed, tilt-turn, side-hung, top-hung, sliding or lift-and-slide;
• the glass make-up, the profile system and series, and the colour inside and outside;
• hardware, and special requirements such as burglar resistance, fire rating or acoustic performance.

If the tender has a schedule, use it as the starting point, but do not trust it blindly. The next step exists because schedules and drawings often disagree. Our guide on how to read a window and door schedule covers the notation in detail.

4. Reconcile the counts

Count the units on the floor plans and on the elevations independently, then compare both counts with the schedule. Differences are common: a unit that appears on a courtyard elevation but not in the schedule, a door type that was changed on the plans but not in the table, a mirrored unit counted once. List every difference. The contract documents usually say which document takes precedence. If they do not, ask the client in writing and state your assumption in the proposal.

5. Check that the system can do the job

For each position, check the limits of the profile system you intend to use: the maximum sash size and weight, the load the hardware can carry, the deflection under the design wind load and the thermal target. Glass weight is simple to estimate: float glass weighs about 2.5 kg per square metre for every millimetre of thickness, so a triple-glazed unit with three 6 mm panes weighs about 45 kg per square metre. Oversized or heavy units may need a stronger series, different hardware or a split into two units. These are the positions that move the price most, so flag them early.

6. Take off the quantities

• Profiles: the length of each profile code per position, converted into supply bars with an offcut allowance based on your own cutting records.
• Glass: square metres per make-up, the number of units, and any units that are oversize, shaped or need special handling.
• Hardware: one set per opening field, by type.
• Accessories: gaskets, corner cleats, brackets, screws, sealants and drainage parts.
• Installation: perimeter metres for membranes and foam, the number of fixings, and the access equipment needed.

7. Price each position

Build the price of each position from its parts: profiles (by weight or length, plus the finishing surcharge), glass (per square metre, plus size and processing surcharges), hardware, accessories, fabrication labour and installation. Then add transport, lifting, site overheads, company overheads and margin. Keep the structure visible. If a client questions one line, you should be able to explain it in a minute. Our article on what drives the price of aluminium windows and curtain walls covers each cost driver in more detail.

8. Compare with your own past jobs

Before you trust the total, compare the price per unit and per square metre of each type with completed projects of a similar specification. A large difference is either real (a different specification, size or site access) or an error. This is the fastest error check an estimator has, and it works only if past proposals are stored in a form you can search.

9. Write down assumptions, exclusions and questions

Every estimate rests on assumptions. Write them down: which drawing revisions you used, which document prevails, what is excluded, the price basis of the aluminium and the validity of the offer. Send unclear points to the client as questions early enough to get answers before the deadline. A short list of precise questions also shows the client that you read the tender carefully.

10. Review before you send

A second person should check at least the quantities, the ten most valuable positions, the units (millimetres against metres), the exclusions against the scope and the totals. Most expensive mistakes are simple ones: a missing position, a wrong count, a decimal in the wrong place.

Common mistakes

• Pricing from an old drawing revision.
• Missing units that appear only on one elevation or in a section.
• Confusing frame sizes with structural opening sizes.
• Forgetting installation materials such as membranes, foam and fixings.
• Ignoring glass weight and sash size limits.
• Using one rate per square metre for every size and opening type.

Frequently asked questions

How long does it take to estimate an aluminium window tender?

It depends on the size of the project and the quality of the drawings. A small residential package can be priced in a few hours. A façade tender with hundreds of positions can take several days of estimator time, most of it spent on the position list and on reconciling counts.

Should aluminium windows be priced per square metre or per position?

Per position. A rate per square metre is a useful check, but small units cost more per square metre than large ones, and opening types, glass and hardware differ between positions. A single square-metre rate hides those differences.

What should I do if the schedule and the drawings disagree?

Follow the order of precedence in the contract documents. If there is none, ask the client in writing, and state in the proposal which document you priced from.

What should a proposal for aluminium windows include?

A position list with quantities, sizes and specifications; prices per position and the total; what is included and excluded; the assumptions and drawing revisions used; and the validity period and payment terms.