Every building has clashes between structure and services. Paying to find them on a screen or letting the site find them is a real choice with real numbers.
Mechanical, electrical and plumbing services compete for the same space as structure and ceiling voids. That competition is resolved either during design, through coordinated drawings or a model, or during construction, through site decisions taken by whoever arrives first. Both approaches end with a working building. They differ in cost, quality and how much of it is documented.
Coordinate during design at a glance
Services are laid out and checked against structure and architecture before construction, either through overlaid drawings or a coordinated model with clash detection. Routes, void depths and penetrations are fixed and drawn, and the contractor installs to a resolved design.
Resolve on site at a glance
Services are designed in principle and routed in detail by the trades as work proceeds, with conflicts settled between foremen as they arise. It is fast, it needs no coordination fee, and on simple buildings with generous voids it frequently produces an acceptable result.
When the cost appears
Coordinate during design: Early, as a coordination fee and a longer design period.
Resolve on site: Later, as rework, cut penetrations, dropped ceilings and delay to following trades.
Effect on structure
Coordinate during design: Penetrations are designed and cast in, with reinforcement adjusted where needed.
Resolve on site: Holes are cut after casting, which sometimes means cutting reinforcement and always means an argument.
Effect on ceiling heights
Coordinate during design: Void depths are proven before construction, so heights are deliverable.
Resolve on site: Heights are protected by lowering ceilings locally, which shows in the finished rooms.
Quality of as built records
Coordinate during design: Good, because the coordinated design becomes the basis of the as built drawings.
Resolve on site: Poor, because what was installed exists only in the memory of the people who installed it.
Programme effect
Coordinate during design: Longer design, shorter and more predictable installation.
Resolve on site: Faster start, with unpredictable stoppages when two trades need the same space.
Who carries the risk
Coordinate during design: The design team, who are paid to resolve it and can be held to it.
Resolve on site: You, in practice, because site resolution generates variations and claims from several parties.
Value to an absent owner
Coordinate during design: High, since decisions are documented and reviewable before anyone builds.
Resolve on site: Low, since the decisions happen daily on site and you learn about them through their consequences.
When coordinate during design wins
- Buildings with dense services such as hospitals, hotels, laboratories and data facilities.
- Projects with tight floor to ceiling heights where void space is genuinely scarce.
- Builds where penetrations must be cast in rather than cut later.
- Owners who will operate the building and need accurate records of what is where.
When resolve on site wins
- Small residential buildings with straightforward services and generous ceiling voids.
- Projects with an experienced main contractor who sequences trades tightly.
- Refurbishments where the existing conditions cannot be known until opened up.
- Builds where speed matters more than documentation and the owner will not operate the asset.
How to decide
Coordinate in design wherever services are dense, voids are tight, penetrations must be cast in, or you will operate the building yourself. Accept site resolution only on simple buildings with generous voids and a contractor you trust to sequence trades, and even then require penetrations through structure to be agreed with the structural engineer before anyone drills. The middle path that works on many private projects is coordinating the congested zones such as plant rooms, risers and corridors, and letting the simple areas resolve themselves.
The evidence that coordination happened is a set of drawings or a model showing services in three dimensions with void depths dimensioned, plus a clash report with items closed. The evidence that site resolution is being controlled is a penetration register approved by the structural engineer and a marked up drawing set updated weekly. If neither exists, the services in your building are arranged in a way that nobody has recorded, which you will discover the first time something needs replacing.
Domira designs, builds and manages projects across Saudi Arabia for owners who are based abroad: land appraisal, feasibility, design, construction, handover and asset management under one accountable contract. Send us the plot or the brief and Domira will put the numbers in front of you before you commit.
Frequently Asked Questions
Is BIM coordination worth paying for on a small building?
It depends on service density rather than on floor area. A small clinic or restaurant with heavy mechanical and drainage requirements benefits more than a large villa with simple services. If you are deciding, ask the design team to identify the congested zones and price coordinating only those. Partial coordination of risers, plant rooms and corridors captures most of the value at a fraction of the fee.
Who pays when services clash with structure on site?
It depends on whether the design should have resolved it. A clash between two properly drawn systems points to a design coordination failure, while a clash created by a trade installing outside the drawn route points to the contractor. Most disputes are murky, which is why a penetration register and a weekly marked up drawing set are worth maintaining even on a site being coordinated informally.
Can holes be cut through concrete for services after casting?
Sometimes, but never without the structural engineer approval, because the position and size relative to reinforcement and to the structural behaviour of the element decide whether it is acceptable. Cutting first and asking later is one of the few site errors that can affect safety rather than only cost. Make written structural approval a hold point before any penetration is formed in a structural element.
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