Why do low bids in Qardho hide trade interface gaps?

Interface coordination underbidding risks in Qardho appear when every bidder prices their own package and nobody prices the joint between packages. Each tender looks complete. The blockwork price covers blockwork, the render price covers render, the plumbing price covers pipe. The strip where they meet belongs to no one, and the cheapest bid is often the one that assumed someone else would handle it. The client pays twice: once for the missing work, and again for the argument about who should have allowed for it.

Where does the gap between trade packages come from?

A gap opens wherever two packages share one surface, one level or one sequence. A blockwork subcontractor may stop at the face of the wall and leave the chasing and making good to the electrician. The electrician prices conduit in the slab, not cutting cured block. The plumber assumes a sleeve is cast in. Someone else assumes it is drilled later. None of these assumptions is dishonest. They are each reasonable inside one package, and unreasonable once the packages meet.

The same gap appears at levels. If the earthworks bidder finishes 50 mm low and the slab bidder prices a fixed thickness, the slab bidder either absorbs the extra concrete or asks for a variation. General practice is to fix a single level datum and a single responsibility for bringing the formation to it, then confirm that arrangement against the project specification or the engineer's instruction. Ask each bidder, in writing, which package finishes the surface their work meets.

What does underbidding do to the work in Qardho?

Once the joint is unpriced, the contractor on site has three choices: stop and ask, do it badly, or do it and claim later. Stopping costs programme time. Doing it badly shows up months later as a leak, a crack at the wall-render junction, or a floor that ponds. Whether a claim succeeds depends on what the contract allows, so read the variation and notice clauses before the work starts.

The effect does not depend on the town. It follows from the omission itself. A joint left out of the price still has to be built, and the party who builds it will look for the cheapest way to close it. The temptation is to reduce what cannot be seen: less compaction under a floor, a thinner bed, fewer fixings. A supervisor can catch some of this by walking the work before it is covered, and by asking for test records for compaction and concrete rather than a verbal assurance. Ask the municipal engineer's office what records it expects to see on a project of this type, then write those records into the inspection plan. Confirm every limit against the project specification or the engineer.

How do you detect an interface gap during bid review?

Total the bids per package only to rank them, never to conclude. Then read each package against a single list of interfaces: wall to floor, wall to roof, wet area to dry area, buried pipe to slab, external level to internal level, and one trade's finished surface to the next trade's start. For every interface, ask the bidder to state who prepares the surface, who finishes it, and what allowance covers it.

A bid that leaves an interface blank is a question, not a saving. Compare the lowest bid against the next one on those interfaces alone. If the gap between them sits in exactly the items nobody described, the low number is likely an omission. Where the answer is unclear, ask the bidder to price the interface as a separate line, and check whether the contract allows you to add that line before award. A written clarification request costs nothing and closes the gap before it reaches site.

What to do next

Pick one interface your project cannot avoid, such as the wall-to-floor junction or the buried pipe entering a slab. Send every bidder the same written question: which package prepares and finishes this surface, and what allowance covers it. Keep the replies with the tender file, and put the confirmed answer into the contract before you award the work.