Construction vibration: BS 5228 and BS 6472 in practice

A construction vibration assessment answers two different questions with two different standards, and confusing them produces reports that satisfy nobody. BS 5228-2 deals with vibration from construction and demolition works, including the guidance most people quote on when a building might be damaged. BS 6472-1 deals with how people inside buildings respond to vibration over time. Damage thresholds sit an order of magnitude above the levels at which residents start telephoning the council.

That gap is the whole subject. A scheme can be perfectly safe structurally and still be stopped by complaints.

What the two standards each cover

BS 5228-2 is the vibration half of the code of practice for noise and vibration control on construction and open sites. It gives source data for common activities, prediction methods for piling and ground improvement, and guidance in its annexes on both human perception and the onset of cosmetic damage.

BS 6472-1 is a guide to evaluating human exposure to vibration in buildings, for sources other than blasting. Its metric is the vibration dose value, which accumulates over a day or a night rather than describing a single event. Two sites with identical peak levels can produce very different dose values if one works for two hours and the other for ten.

Damage assessment also draws on BS 7385-2, which sits alongside BS 5228-2 and is the reference for guide values on damage from groundborne vibration. Where a report cites damage thresholds without naming which standard they came from, that is a finding in itself.

Peak particle velocity and the damage thresholds

Peak particle velocity, in millimetres per second, is the measure used for damage.

The guide values in BS 5228-2 for transient vibration distinguish between building types. Reinforced or framed structures of industrial or heavy commercial type tolerate a good deal, with a guide value at 50 mm/s across the relevant frequency range. Unreinforced or light framed residential and commercial structures have a lower guide value, starting around 15 mm/s at 4 Hz and rising with frequency.

Three points that matter in practice.

Cosmetic damage means hairline cracking in plaster and opening of existing cracks. It is not structural damage, which sits well above it.

The values assume a building in reasonable condition. A listed building with lime plaster on lath, or a Victorian terrace with existing settlement, warrants a lower project-specific limit set by the structural engineer.

And frequency content matters as much as amplitude. Low frequency energy from vibratory sheet piling couples into building structures far more readily than high frequency energy from a breaker.

Human response and vibration dose values

The vibration dose value is expressed in m/s to the power 1.75, and BS 6472-1 gives ranges describing the probability of adverse comment in residential buildings, with lower ranges applying at night than during the day.

Construction work is temporary, which is the argument every applicant makes and the argument every environmental health officer has heard. It carries weight where the exposure really is short and where the programme says so in writing. It carries much less weight over a three-year build.

The dose value approach rewards programme management directly. Concentrating percussive work into defined hours, with quiet periods either side, can bring a scheme inside an acceptable band without changing a single piece of plant.

Piling method selection and its effect

Method selection is the largest single lever, and it is a decision taken by the contractor long after planning permission unless the application ties it down.

Ranked roughly by vibration generated, from highest to lowest: driven precast concrete and driven steel bearing piles, vibratory sheet piling, vibro stone columns, driven cast in-situ piles, continuous flight auger piles, rotary bored piles, and pressed or jacked sheet piles.

Continuous flight auger piling is the usual answer on constrained urban sites, and it costs more per metre than driven piles. Where an application relies on a low-vibration method to demonstrate acceptability, the method has to be secured by condition, because the tender process will otherwise find the lower-cost option.

Ground conditions decide whether the choice is available at all. Dense granular layers or shallow rockhead can rule out CFA, and that is a question for the Geotechnical Assessment rather than the acoustician. Get the two teams talking before the assessment is written.

Monitoring, trigger levels and stop works procedures

A monitoring regime that only records data is useless. The regime has to have consequences.

1. Install triaxial geophones at agreed positions on the nearest sensitive structures, plus a control position away from the works.
2. Set an amber trigger below the guide value, at which work continues and the method is reviewed.
3. Set a red trigger at the project limit, at which the activity stops.
4. Define what happens on a red exceedance: who is notified, within what period, what inspection follows and who authorises restarting.
5. Log everything, and make the log available to the local authority on request.
6. Report monthly to the council in a format agreed before works start.

Amber and red triggers should be set with a margin below the damage guide value, because a geophone on a foundation records something different from what the plaster on the third floor experiences.

Real-time alerting is worth the cost. A trigger discovered when the data is downloaded a fortnight later has already failed.

Pre-condition surveys of neighbouring buildings

Photographic and written schedules of condition on neighbouring properties, taken before works start, protect everybody. They give the developer a defence against opportunistic claims and give neighbours a record if damage does occur.

Cover the properties within the predicted zone of influence, plus any listed building, retaining wall, or third party asset such as a railway structure or a public sewer. Note that a party wall award under the Party Wall etc. Act 1996 requires a schedule of condition in its own right and runs on a separate legal track from planning.

Offer surveys rather than waiting to be asked. A refusal by an owner should be recorded in writing, since it becomes relevant if a claim is made later.

How the assessment is secured through conditions

At application stage the vibration work usually appears inside the construction environmental management documentation rather than as a standalone submission. A Construction Management Plan covering hours, plant, monitoring, triggers and complaint handling is the document councils condition, and the technical vibration analysis sits behind it as an appendix.

Where noise and vibration both arise, the Noise Impact Assessment and the vibration analysis should share the same receptor list, the same survey dates and the same programme assumptions. Reviewers check that.

There is a separate statutory route worth knowing. Section 61 of the Control of Pollution Act 1974 allows a contractor to apply for prior consent for construction works, agreeing methods, hours and limits with the local authority in advance. Consent gives protection against an abatement notice for works carried out in accordance with it, and it is normally handled by the contractor once appointed.

For specialist technical reports, qualified professional input may be required. Vibration prediction and monitoring is specialist work, and structural limits for sensitive buildings should be set by a structural engineer.

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