What a Main Contractor Owes an Architect at Tender

When you send a scheme to a main contractor for a tender, you already know what the number needs to be. What you are actually testing is whether the contractor understands the work, and more importantly, whether the contractor will protect your detail on site.

Most tender responses hand back a price and a programme. That is the minimum. What separates a contractor you can trust from one you cannot is what arrives in that tender pack alongside the number.

1. A Clear Bill of Quantities

A bill of quantities is not decoration. It is your first evidence that the contractor has read the drawings properly, and crucially, that you can interrogate the proposal before anyone signs.

The bill should break down every measured item: wall areas, linear metres of joinery, individual soil stacks, electrical circuits by zone. Provisional allowances should be called out separately, with their basis stated. "Unforeseen structural works" buried under a blanket contingency is not a provisional allowance, it is an excuse to add money later.

The bill should also state what is excluded. If the contractor is not supplying and fixing architectural ironmongery, it should say so. If the supply chain for bespoke bronze hardware sits with you and you are handing over finished items for fixing, the bill needs to separate the cost of fixing from the cost of the goods. This is where disputes start, and they start because the bill was vague.

You should be able to read that bill line by line and say, "I agree with that, I disagree with that, and I did not know that would cost that much." That conversation happens before the contract, not during inspection.

2. Confirmation of Your Building Control and Party Wall Interface

Your scheme may carry party wall works, or it may require consultation with a planning officer after the formal application. The contractor's tender should clearly state whether party wall surveyor costs sit with the client or the contractor. The same for any building control liaison that goes beyond standard notification.

If the works affect a neighbouring property, a timber party wall, a flue that serves the neighbour's boiler, the contractor should flag it and confirm who is managing the surveyor appointment. A vague "we will agree this on site" is not good enough. You need it stated before work begins, because the dates matter. A party wall award can take four weeks from instruction to agreement, and if the contractor assumes you will handle it and you assume the contractor will, the programme slips by a month before anyone notices.

3. A Detailed Method Statement for Critical Sequences

A good tender pack includes a method statement for the sequences that will kill a building if they go wrong. Basement waterproofing does not happen by accident. Taking down a party wall and rebuilding it around new beams requires planning. These are not optional things a competent contractor will just "work out on site."

The method statement should describe how temporary support will be installed, where the waterproofing membrane goes relative to the new structure, and crucially, where the architect's sign-offs fit into the sequence. If a tanking inspection happens at a particular stage, the method statement should say when, because if it does not, a competent main contractor will do it when he thinks it is right, which may be after the plasterboard is already up.

This is where your detail survives or dies. Not in the specification, but in the order in which things happen on site.

4. Shop Drawings Acknowledgement and Sign-Off Process

If the scheme carries bespoke joinery, cladding panels, or any item that is made to order, the contractor's tender should commit to a shop drawing process, with timescales and sign-off points.

This is not the contractor trying to be helpful. This is the contractor saying, "I understand that if I cut 40 metres of walnut joinery and the dimension is wrong by 5mm because I did not submit a shop drawing for approval, the joinery does not go in the building."

The shop drawing sign-off should confirm: the drawing will be submitted by a date you both agree beforehand; you will have a specified number of days to review and annotate; the contractor will not cut anything until the drawing carries your approval stamp. That process protects you. An architect who does not insist on it is accepting the risk that the joinery arrives wrong.

5. A Clear Site Protocols and Inspection Schedule

The contractor's tender should set out how you will access the site, how inspections will be scheduled, and critically, what authority you hold as the architect. If you have the right to stop a piece of work because it is not building to the detail, the contractor's tender should acknowledge that explicitly. If the contractor believes he can proceed without your say-so, that disagreement needs to be resolved in the tender phase, not on site.

Site protocols should confirm: how the contractor's foreman and your inspector will communicate; how defects will be logged and rectified; what constitutes "sign-off" on a completed element (a site visit, a photograph reviewed off-site, or a measured inspection with the architect present); and crucially, who decides whether a deviation from the drawings is acceptable or not.

If these are not addressed in the tender, they will become problems during the works, and problems on site cost money and time.

6. Confirmation of Subcontractor Appointments

Who is doing the MEP work? Is it the main contractor's in-house team, or is it sub-let to a specialist? Is it a team the main contractor has used for 10 years or a new relationship to a firm he found online a week ago?

Your tender should confirm the key sub-contracts: MEP design and installation, structural work if it is not the main contractor's own team, bespoke joinery (or at least the principal trades). And it should confirm that those sub-contracts carry the same quality standard and inspection protocols that bind the main contractor.

A main contractor who sub-lets everything to the cheapest bidder and hands you a "we are not responsible for their site performance" clause is passing the risk to you. That is fine if you are happy with it, but it should be explicit, because it changes what you are actually buying.

Why This Matters

The contractor's tender is often the only formal document that sits between your drawings and what actually happens on site. If the tender is vague, or if it answers the question "how much does it cost" but not "how does it build," you have already lost the ability to hold the contractor to your standard.

A detailed, site-literate tender does two things. First, it tells you whether the contractor actually understands the work. Second, it gives you something to point to six months in, when there is a disagreement about whether a particular detail should be built as drawn or adapted on site. The answer is almost always in the method statement the contractor already agreed to.

The tender is where your control lives. If the tender is shallow, your control ends.

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If you are pricing a renovation and want a contractor who reads the drawings and then builds them as drawn, not as they think would have been easier, call 020 7731 6841 and we will talk you through how we price work open-book and what that means for site control.