Temporary Works in Demolition: Designer Approval, Prop Loads, Deadshore and Flying Shore Details

Summary

Temporary works in demolition are frequently underestimated. The instinct is to see them as a minor cost — a few props, some timber, a bit of acrow — but a failure in temporary works during demolition can be catastrophic. The structural system of a building under demolition is inherently compromised: connections are cut, walls are removed in sections, floors lose their lateral support, and the load paths change continuously as work progresses. Temporary works are the engineered response to these changing load paths. Get them wrong and the structure comes down at the wrong time, in the wrong direction, with workers in the way.

BS 5975:2019 (Code of Practice for Temporary Works Procedures) is the primary standard. It was updated in 2019 (superseding the 2011 edition) and sets out the roles, responsibilities, and procedures that must be in place before any significant temporary works are installed. The standard applies beyond demolition — it covers all construction temporary works — but demolition is explicitly addressed and presents particular challenges because the structural condition of the building is constantly changing and the loading applied to temporary works is harder to predict than in typical construction.

Contractors who operate without a formal temporary works system in demolition are not only breaching industry standards — they are operating without any reliable means of knowing whether a prop, shore, or propping system is safe. The consequences of under-propping during demolition are well evidenced in accident records: partial collapse is common, and fatal collapses have occurred on UK sites where temporary works procedures were absent or informal. HSE prosecutions following demolition collapses routinely identify absent or inadequate temporary works as the primary cause.

Key Facts

• BS 5975:2019 is the current code of practice for temporary works procedures — supersedes 2011 edition
• Temporary Works Coordinator (TWC): the person responsible for managing and coordinating all temporary works on a project — must be competent and appointed in writing
• Temporary Works Designer (TWD): the engineer who designs the temporary works and produces calculations — may be an in-house engineer or an external specialist
• Temporary Works Design Checker (TWDC): independent person who checks the design — required for Category 2 and 3 schemes
• Category 1 schemes: low-risk, straightforward temporary works (simple propping, standard proprietary systems used within manufacturer's guidance) — can be self-certified by TWC without independent check
• Category 2 schemes: moderate complexity — require an independent check by a competent engineer not involved in the original design
• Category 3 schemes: high-risk or complex temporary works (large span, high load, novel design, adjacent to public) — require independent check by a suitably qualified and experienced engineer
• Permit to Load: written permit issued by TWC authorising loading of temporary works — must be obtained before any load is applied
• Permit to Strike: written permit issued by TWC authorising removal of temporary works — must be obtained before any props, shores, or supports are removed
• BS EN 1065: European standard for adjustable steel props (acrow props) — specifies safe working loads by prop type and extension length
• Deadshores (vertical props): support vertical load from floors and roofs above — must be designed for the actual load they will carry, not assumed from prop label
• Flying shores: horizontal timber or steel members spanning between two parallel walls to provide lateral restraint — used when one wall is demolished but an adjacent retained wall needs support
• Raking shores: inclined struts propped against the face of a retained wall to resist lateral movement — used for walls that have lost lateral support from removed floors
• Safe Working Loads (SWL) for acrow props: vary significantly by extension — an acrow prop at minimum extension may have SWL 4–5× higher than at maximum extension; always check the manufacturer's load table for the actual extension being used
• Headroom clearance: temporary works on demolition sites must not restrict emergency egress — minimum 2m headroom in escape routes
• Temporary roof/weather protection: required when retained elements (historic facades, listed structure) must remain weathertight during demolition — designed as temporary works, not improvised

Quick Reference Table

Detailed Guidance

BS 5975:2019: What Has Changed From 2011

BS 5975:2019 updated the 2011 edition with clearer guidance on roles, more explicit requirements for competence, and expanded coverage of higher-risk scenarios. Key changes relevant to demolition:

The category system (1, 2, 3) is more clearly defined, with practical examples to help classify temporary works. The TWC role is more precisely specified — the TWC must be competent to assess whether a scheme requires a Category 1, 2, or 3 check, which requires understanding of structural behaviour that goes beyond site management. Many contractors appoint a TWC without equipping them to make this judgement — the standard addresses this by defining minimum competence expectations.

The 2019 edition also strengthens requirements for the permit-to-load and permit-to-strike system, making it clear these are not optional paperwork exercises but the primary safety control. A permit-to-load ensures that someone with appropriate knowledge has confirmed the temporary works are properly installed before any structural load is applied. A permit-to-strike ensures that someone has confirmed it is structurally safe to remove the support — checking that the permanent structure has reached adequate strength or that alternative support is in place.

The standard also clarifies that proprietary systems (scaffolding towers, acrow props, Peri Gridflex, Alsina, etc.) used within the manufacturer's published load tables and guidance do not necessarily require a bespoke structural design, but the TWC must verify that the proposed use is within the manufacturer's parameters. Using a proprietary prop in a way not covered by the manufacturer's data (unusual load angle, soft ground conditions, eccentric loading) makes the use non-standard and requires an engineered design.

Deadshores: Vertical Propping Principles

Deadshores (vertical props) are installed to support gravity loads — floor loads, roof loads, and the weight of walls above — while structural elements below are removed or temporarily weakened. They are the most common form of temporary works in selective demolition and strip-out.

The fundamental design requirement is that the prop must carry the load that will be applied to it. This sounds obvious, but it is frequently done incorrectly by assuming a prop "looks about right" or using a standard grid without calculating the actual load. The load on a prop depends on: the area of floor tributary to the prop; the floor's dead load (self-weight) and live load; any additional loads from walls or structure above; and whether loads are shared between multiple props in a grid.

Once loads are calculated, the prop selection follows from BS EN 1065, which specifies SWLs for standard adjustable steel props at different extension lengths. A 3m acrow prop (Typ 3) at minimum extension has an SWL around 30–35 kN; at maximum extension the SWL reduces to 17–20 kN. The SWL also assumes the prop is plumb and on a solid base — on soft ground, a baseboard must be used to spread the point load. On suspended floors being propped below (to relieve the floor from load), a headboard distributes load at the top.

Prop grid spacing is the other key variable. Closer grid spacing reduces the load per prop but increases the number of props and the risk of workers encountering them. The structural engineer's prop layout drawing must be followed — reducing spacing to "save money" or increasing it to "give more room" are both potential causes of collapse.

Raking and Flying Shores: Lateral Support to Walls

When a floor slab is removed during selective demolition, the wall it was spanning between loses its lateral restraint. A masonry wall without lateral restraint at floor levels is a slender free-standing panel that can be unstable under wind load, dynamic loading from demolition plant vibration, and horizontal forces from remaining floor slabs.

Raking shores are inclined steel or timber struts propped against the external face of the wall, transmitting horizontal forces down to a ground-level soleplate (which must be founded on ground capable of resisting the horizontal thrust). The angle of the raking shore is typically 60–75 degrees from horizontal. The design must account for the horizontal force applied by the shore to the wall face — if the wall is weak in bending, the shore itself can cause local failure.

Flying shores span horizontally between two parallel walls (typically street frontages or party walls) at floor level. They are used when one building between two retained walls is demolished — the flying shore maintains the relative positions of the retained walls and prevents outward deflection. In timber, a traditional flying shore uses a main horizontal strut (the flying shore itself), needle pieces through the wall at each end, and inclined straining pieces to distribute the load. Steel flying shores using tubes and couplers or proprietary systems are more common on modern projects.

The critical design parameter for flying shores is span. Timber flying shores are typically limited to 9–10 metres; longer spans require steel. The shore must also be positioned at a level where the wall is strong enough to transfer the thrust into the masonry — not near openings or at points of structural weakness.

Façade Retention: The Most Complex Temporary Works in Demolition

Retaining a historic or architectural façade while demolishing the structure behind it is one of the most demanding temporary works scenarios in demolition. The façade is a masonry panel, often with multiple openings, that was designed to be supported by the internal structure — floors, party walls, and roof. When those supports are removed, the façade becomes a free-standing panel of masonry that may be several storeys high.

Façade retention systems are typically designed by specialist temporary works engineers and installed by specialist contractors. The system consists of a steel space frame or grillage of horizontal and vertical members that connects to the back of the façade at multiple points and transfers its weight and lateral forces to an independent foundation system. The foundations of the façade retention system must be independent of the building being demolished — if the building's foundations are removed as part of demolition, the façade retention system cannot rely on them.

Dynamic loading is the most critical issue in façade retention. Machine demolition immediately behind a retained façade causes significant vibration — percussion tools, tracked plant manoeuvring, and material drops can induce forces in the façade that far exceed static wind load assumptions. The demolition method immediately adjacent to the façade must be agreed with the façade retention engineer. In many cases, final hand demolition within 3–5 metres of the façade is required.

Permit-to-Load and Permit-to-Strike: Operating the System in Practice

The permit-to-load and permit-to-strike system is the day-to-day operational control of temporary works safety. In demolition, where the structural condition is constantly changing, this system must be actively managed — not treated as a one-time box-ticking exercise.

Permit to Load: issued by the TWC before any significant load is applied to the temporary works. The TWC (or a competent delegate) physically inspects the installed temporary works against the design drawing: are props at the correct spacing? Are they plumb? Are baseboards in place on soft ground? Are headboards fitted? Is the extension within the designed range? Only when these checks are confirmed in writing does the permit to load get issued. No structural demolition should begin in an area until the relevant temporary works are confirmed as loaded (or loaded and confirmed adequate if they are pre-loaded).

Permit to Strike: issued when the TWC is satisfied that the temporary works can be safely removed. In demolition, this typically means the structural engineer has confirmed that the remaining permanent structure is self-supporting, or that alternative permanent support has been installed. The TWC physically inspects the condition before issuing the permit. Props must be struck progressively (one at a time, in the order specified by the design) not simultaneously — removing all props at once removes the opportunity to detect settlement or unexpected structural behaviour.

Document all permits as they are issued. The permit book is the evidence that the temporary works system was operating correctly — it is the first document the HSE will request following any incident involving temporary works.

Frequently Asked Questions

Who can be the Temporary Works Coordinator on a demolition project?

The TWC must be competent to fulfil the role — BS 5975:2019 defines this as someone with appropriate training, experience, and knowledge. In practice, the TWC on a demolition project is often the site manager or a senior engineer who has received formal TWC training (typically a 1-2 day course from a provider like CITB, ICE, or ISTRUCTE). The TWC must be formally appointed in writing by the employer. On large or complex demolition projects (Category 2 or 3 schemes), the TWC should have relevant structural knowledge or access to the designer, as they need to be able to assess whether the temporary works are installed correctly against the design. A site manager with no structural background cannot adequately TWC a façade retention scheme or a complex multi-level propping system.

Can I use acrow props without a structural design for simple floor propping?

For straightforward, low-risk Category 1 schemes where standard acrow props are used within the manufacturer's published load tables on a solid, level base, a full structural design is not always required — the TWC can self-certify. However, this only applies when all of the following are true: the load being carried is clearly within the published SWL for the prop at its actual extension; the props are on an adequate base; the props are used at the manufacturer's recommended spacing; and no unusual loading (eccentric, dynamic, or inclined) is present. In demolition, "simple floor propping" frequently turns out to involve loads that are not straightforward to estimate, ground conditions that require spreading bases, or adjacent plant that induces vibration. When in doubt, commission a structural calculation — it is far cheaper than a collapse.

How long in advance must I appoint a Temporary Works Designer?

Ideally at pre-contract or early tender stage, certainly before the demolition method statement is finalised. Temporary works design takes time — a façade retention scheme for a listed building can take 4–8 weeks to design, specify, and get approved. Leaving temporary works design until site start means either a rushed design (risking errors) or delayed start while the design is produced. On CDM-notifiable projects, the temporary works designer is a designer under CDM 2015 and must contribute to the pre-construction information pack. This means they need to be involved before mobilisation.

What triggers a Category 3 temporary works check?

BS 5975:2019 defines Category 3 as schemes where the complexity or risk is such that a detailed independent check by a suitably qualified and experienced engineer is required. Demolition scenarios that typically trigger Category 3: façade retention systems for multi-storey buildings; propping that transfers load to ground-bearing structures adjacent to live highway or underground services; temporary works with spans exceeding 12 metres; schemes where failure would likely result in fatality or major structural collapse; and any scheme the TWC or designer considers to present novel or unusual risks. Category 3 independent checkers are typically Chartered Engineers (MIStructE or MICE) with specific experience in temporary works, appointed independently of the original design team.

Regulations & Standards

• BS 5975:2019 — Code of Practice for Temporary Works Procedures (primary standard)

• BS EN 1065:1998 — Adjustable telescopic steel props — product specifications, design, and assessment

• BS 5628-1:2005 — Code of practice for the use of masonry (structural use of masonry in temporary works context)

• BS 6187:2011 — Code of practice for full and partial demolition (references temporary works)

• Construction (Design and Management) Regulations 2015 — temporary works designers are designers under CDM; Construction Phase Plan must cover temporary works

• Health and Safety at Work etc. Act 1974 — general duty to ensure safety of temporary structures

• HSE HSG151: Protecting the public — your next steps — includes guidance on structural stability during demolition

• CIRIA C703 — Façade retention — a guide to good practice [verify full title]

• BS EN 12811-1:2003 — Temporary works equipment — scaffolds — performance requirements [verify applicability]

• Eurocodes EN 1990, EN 1991, EN 1997 — load combinations, actions, and geotechnical design applicable to temporary works foundations

• BSI — BS 5975:2019 overview

• HSE — Temporary works guidance

• NFDC — Guidance on temporary works in demolition

• IStructE — Temporary works: principles of design and construction

• CIRIA — Façade retention guide

• HSE — Collapse of buildings and structures

• structural demolition sequence — Top-down vs bottom-up sequencing and how temporary works support the demolition programme

• demolition adjacent structures — Party Wall Act requirements and temporary support for neighbouring buildings

• cdm regs demolition projects — CDM 2015 duties including temporary works designer as CDM designer

• selective demolition and strip out — Propping requirements during soft strip when structural elements are exposed