How to Compare Waterproofing Quotes and Tenders

Direct answer

Waterproofing quotes and tenders can only be compared after they have been normalised - adjusted so that every bid prices the same scope, the same BS 8102:2022 performance grades, the same lines of defence and the same design responsibility. As submitted, tender returns on a commercial basement are almost never comparable: each contractor prices their preferred system, their own exclusions and their own allowance for the risk the documents leave with them. Comparing the bottom-line figures before normalising them rewards whichever bidder excluded the most, and it is one of the most reliable ways to buy a defect. The fix is structural: tender against an independent, product-neutral performance specification, then have the returns reviewed by someone with no stake in any of them.

Full explanation

Why are waterproofing tender returns not comparable as submitted?

Because in the absence of an independent design, a waterproofing tender is really an invitation for each contractor to design the works themselves and then price their own design. Three bids means three different designs - different systems, different grades assumed for each space, different views on what is included. The numbers on the final page are answers to three different questions.

What are the six things that make quotes non-comparable?

1. The performance grade assumed for each space. One bidder prices the plant room at Grade 1B, another at Grade 2, a third has not graded the spaces at all. The grade drives everything downstream - what grade each space needs is a design decision, and if the tender documents did not fix it, every bid has taken its own view.

2. The number of lines of defence. A single line of protection is cheaper than combined protection. If the risk assessment demands Type B plus Type C for the habitable levels and one bidder has priced Type B alone, their bid is not cheaper - it is for a different, riskier building.

3. Scope boundaries and exclusions. Junctions with the piling, penetrations, movement joints, the interface with the podium or ground-floor waterproofing, temporary works dewatering - the expensive, failure-prone details are exactly the ones most often excluded, qualified or left to “others”. Attendance on QA, commissioning and any independent monitoring requirement is another quiet exclusion: a bid that has priced no engagement with inspection is cheaper than one that has. The exclusions list is where a low bid earns its headline number.

4. Design responsibility and liability disclaimers. Some bids include genuine in-house design with drawings; others carry a supplier’s standard details and a warranty that disclaims design liability. A bid that transfers design risk to you is cheaper for a reason.

5. Product lock-in and guarantee small print. A bid built on one supplier’s system is also a bid for that supplier’s future pricing - remedials, extensions and maintenance are captive once the system is in. And the guarantee that appears to underwrite the bid needs reading: conditions on installation, exclusions for workmanship, ground conditions and consequential loss routinely reduce a “20-year guarantee” to something far narrower than the tender summary implies.

6. The risk premium and the commercial structure of the bid. Where the documents are ambiguous, a competent contractor prices the ambiguity - invisibly, distributed through the rates. Separately, a bid light on measured work and heavy on provisional sums, or carrying low headline rates with aggressive rates for variations, is priced to win the job and recover the margin later. The commercial structure is part of the comparison, not an afterthought.

What does a hidden risk premium look like in practice?

You rarely see it labelled. You see its symptoms: a spread between bids far wider than the contractors’ overheads could explain; rates for below-ground concrete work notably above the same contractor’s above-ground rates; heavy qualification of ground conditions; or a bid that undercuts the field by 20% from the one contractor who asked no questions during tender. In CLW’s quote due-diligence work, the widest spreads consistently trace back to the tender documents, not the bidders: where an independent performance specification fixed the grades, the systems philosophy and the scope boundaries, the returns cluster; where a supplier’s document went out to tender, they scatter. Removing the premium is procurement arithmetic, not luck - it is a large part of why an independent appointment typically pays for itself before any defect is ever avoided.

What are the six checks to run before comparing the numbers?

Work through each bid against the same checklist, and only then rank them:

1. Confirm the grade assumed for every space - in writing, against BS 8102:2022 Table 2.
2. Confirm the lines of defence per zone, against what the risk assessment requires rather than what the bid proposes.
3. List every exclusion and price the gap back in - junctions, penetrations, interfaces, dewatering, QA and monitoring attendance.
4. Identify who carries design responsibility for what, in writing - and read the guarantee small print against the claim on the front page.
5. Strip provisional sums and rates back to a common basis, and note the variations posture.
6. Note the questions each bidder asked during tender. A contractor who asked nothing about a complex basement has either done it a hundred times or has not read the documents - find out which.

It is routine for the ranking to invert once the gaps are priced back in - the “cheapest” bid becoming the most expensive compliant one. If you are appointing the reviewer as well as the contractor, how to appoint an independent waterproofing consultant sets out the independence checks that make the review worth having.

Who should do this review?

Someone independent of every bidder and every product. The review is technical before it is commercial: whether a proposed system meets the required grade for each space, whether the proposed details survive the ground conditions, whether the installer’s competence matches the system. That is waterproofing design specialist work. If you would like the fast version: the Waterproofing Wisdom agent’s quote-comparison pathway will take the quotes or tender returns you upload and produce a like-for-like read - what each bid actually includes, where the gaps are, and what to ask each bidder before you award. It is free, and it is the same framework we apply in a full appointment.