Transfer structure and podium design for mixed-use buildings
Design of the transfer beams, slabs or podium that carry homes above over open-plan shops, offices or car parking below.
About this service
Mixed-use buildings in London often put flats above shops, offices or parking. The flats want closely spaced walls and columns, while the commercial space below wants wide open floors and shopfronts. A transfer structure resolves that conflict by picking up loads from the residential floors and carrying them sideways to fewer supports. Getting it wrong shows up later as cracking, sagging floors and sticking doors in the flats above.
We design transfer beams, transfer slabs and podium structures for new mixed-use buildings and for projects that convert or extend above existing commercial units, up to five storeys and 15 m. Typical schemes include flats over a high street shop in a town centre such as Croydon, residential floors above an open-plan office, and homes over a ground floor car park where columns must suit parking bays.
We carry out the load take-down, design the transfer elements and their bearings, and coordinate with the commercial fit-out and services that pass through or below them. Calculations and drawings go through our three-step quality control process with final sign-off by our Head of Engineering. Design of the residential floors is not included unless we are appointed for the full building. Fees start from £1,800 + VAT.
When you need it
- Your building has shops, offices or parking under flats
- Columns or walls above do not line up with the space below
- You are converting or extending above an existing commercial unit
What's included
- Load take-down from the residential floors
- Transfer beam, slab or podium design
- Connection and bearing details
- Coordination with the commercial fit-out and services
How it works
- Map loads and gridsWe overlay the residential layout on the commercial plan to find where walls and columns above do not line up with supports below, and establish the loads to be transferred.
- Choose the transfer formWe compare steel beams, plate girders, concrete transfer beams or a thick podium slab against depth, cost, fire protection, programme and the ceiling height available.
- Design for stiffnessWe design the transfer elements for strength and, crucially, for stiffness, so movement under the full residential load stays within limits that masonry, partitions and finishes above can tolerate.
- Detail bearings and connectionsWe detail bearings, connections and the interface with columns and foundations, including temporary support during construction where an existing building is being altered while partly occupied.
- Coordinate fit-out and servicesWe agree service routes, penetrations, fire protection and ceiling zones with the commercial fit-out and services designers before issuing the package to Building Control for approval.
What you receive
Deflection, not strength, usually decides transfer beam size
A transfer beam can be strong enough and still cause problems. Brick or block walls sitting on it are brittle and crack if the beam deflects even modestly under several floors of load. That is why transfer beams are often sized by stiffness limits much tighter than an ordinary floor beam, and why long-term creep matters for concrete. The resulting depth needs agreeing early, because it eats into shop ceiling height and the services zone.
Converting above an existing shop adds another layer. The existing frame and beams were sized for the original building, not new floors, and records are often missing. A structural investigation and opening-up usually comes first. Where the scheme adds storeys, robustness checks also apply, and the whole building can be designed under our new residential and mixed-use design service.
Not included
- Design of the residential floors above unless appointed for the full building
Frequently asked questions
What is a transfer beam?
A transfer beam carries walls or columns that do not continue straight down to the foundations. It picks up their load and transfers it sideways to supports elsewhere. Transfer beams are common in mixed-use buildings where flats above have a different layout from shops or parking below, and in conversions where ground floor walls are removed.
Can you build flats above an existing shop?
Often yes, but the existing structure and foundations must be checked for the new load, and the shop layout may need a transfer structure to carry the flats. Fire separation, acoustic separation and services routes also matter. We start by investigating the existing building and confirming what it can support.
Is steel or concrete better for a transfer structure?
Steel is lighter, quicker to install and suits alterations to existing buildings, but needs fire protection. Concrete transfer slabs and beams offer inherent fire resistance and stiffness, and suit new-build podiums. The choice depends on spans, loads, available ceiling depth and construction sequence, and we compare options with you.
Why do flats above a transfer structure get cracks?
Usually because the transfer beam or slab deflects more than the masonry and finishes above can tolerate, or long-term movement was not allowed for. Cracks often appear over openings or at partition junctions. Designing for stiffness and detailing movement joints prevents most of this.