Can I just put a prop under each end of beam after cutting?

No — masonry above doesn't 'stick together' enough to span the opening before beam installed. Wall above will crack/collapse the moment opening cut without supported needles above. Needles transfer load above to props before opening is created — this is the whole point.

How long can needles + props stay up?

Days to weeks — depends on cure time of masonry + beam grout. Typical sequence: needles up 3–7 days. Long-term propping (months): Mabey Quickshore systems suitable + inspected weekly per CDM. Domestic project should remove needles within 1 week of beam install — risk of accidental dislodgement, lost time, prevention of finishing trades.

What if I can't get props underneath (cellar, void below)?

Alternative methods: prop from solid floor below (basement floor or external ground), strut from external pavement (requires highways licence if pavement obstruction >24hr), or specialist 'wall-fixed' temporary support (cantilever needle from solid wall both sides without ground prop). Engineer judges case-by-case — adds £1,250–£4,500 to temporary works on tricky sites.

Needle and Prop Temporary Works London 2026 | Builderr

What Is 'Needle and Prop' Temporary Works in a London Renovation?

Needle and prop is the temporary works technique supporting masonry above an opening while a permanent beam or lintel is installed. Method: cut horizontal pocket through wall, insert short RSJ ('needle') through, support each end with acrow prop or Mabey strong-back, take load off masonry below, demolish wall section, install permanent steel beam, transfer load to permanent beam, remove needles + props. Cost £450–£1,250 per opening. Designed under CDM 2015 by Temporary Works Coordinator on larger projects.

Method + sequencing

Required wherever existing load-bearing masonry is removed for new opening (door, window, knock-through, beam installation). Sequence: (1) Survey + design — structural engineer specifies needle size + spacing + prop locations + load capacity required. (2) Cut horizontal pocket through wall at level above future permanent beam (typically 300–600mm above) — masonry chiselled or chased. (3) Insert needle (typically 100×100×100 or 152×152×23 UC short section) through pocket extending 600–1000mm beyond wall each side. (4) Position acrow prop or Mabey shore tube beneath each end of needle bearing onto floor (usually with timber sole plate + wedge spreading load). (5) Wind prop tight transferring masonry weight from wall to needle to props. (6) Cut + remove masonry below needle to create opening. (7) Position + bed permanent beam onto padstones at correct level (typically 50mm below needle). (8) Pack out + grout space between beam top + remaining masonry (typically slate packers + mortar). (9) Wait 24–48 hours for grout cure + masonry mortar reset. (10) Carefully release prop pressure transferring load from needle to permanent beam. (11) Remove needles + repair pockets.

Spacing + load

Engineer specifies needle spacing based on masonry self-weight + floor/roof load above. Typical: needles at 1.2–1.8m centres for single-storey wall above opening; 0.8–1.2m centres for double-storey wall above; 0.6–0.9m centres where significant point loads (column or beam landing above). Standard acrow prop (Acrow Mk II): SWL 2.5 tonnes at full extension, 5 tonnes at 1.2m extension. Mabey 'Strong Boy' (one-piece needle + prop assembly): SWL 3.0 tonnes per needle. Heavy loads (multi-storey above, RC slab): Mabey Quickshore or RMD Slimshore propping systems — SWL 10–30 tonnes per leg. Floor support beneath props: timber sole plate (225×75 minimum) spreading load to 2+ floor joists; suspended timber floors may need additional propping from below to avoid joist failure.

Design + responsibility

Construction (Design + Management) Regs 2015 + Building Safety Act 2022: temporary works require designer + competent supervision. Project >£1m or HRB: appoint dedicated Temporary Works Coordinator (TWC) — typically qualified under CITB scheme. Smaller domestic project: structural engineer signs off temporary works as part of permanent design + competent main contractor implements. Design check: TWC or independent engineer verifies prop sizing + load path adequacy. Risk assessment + method statement mandatory. Common failures: undersized props (acrow at full extension SWL drops dramatically — check engineer's chart), missing sole plate (point-load punctures suspended timber floor), inadequate pocket bearing (needle bears on lime mortar joints not brick — needle slips), removal of props too early (mortar not cured — beam crashes onto opening). Cost typical 2m opening: 2 needles + 4 props + sole plates + 4 hours labour + engineer design = £450–£1,250 incl. design fee allocation.