Retrofitting is repair work that makes a structure stronger, not just better looking. Plastering over a cracked beam hides the problem; retrofitting fixes it. It is designed by a structural engineer and carried out by a contractor who has done this kind of work before.
What's included
| Method | What it is | Typical use |
|---|---|---|
| Column jacketing | New steel and concrete cast around an existing column to make it bigger and stronger | Weak or damaged columns; before adding a floor |
| Beam strengthening | Extra concrete and steel, or steel plates bolted or bonded to the beam | Sagging or cracked beams |
| Slab repair and strengthening | Removing loose concrete, treating rusted steel, adding steel and new concrete; or adding beams under the slab | Spalling slabs under bathrooms and roofs |
| Fibre wrapping | Bonded fibre sheets around columns or under beams | Where adding size is not possible |
| Steel frames and supports | New steel columns or beams to take load off weak members | Open halls, removed walls |
| Foundation underpinning | Extending or deepening existing foundations | Settlement; extra floor |
| Crack injection | Filling cracks with resin or grout | Where the engineer confirms the cause is controlled |
The engineer chooses the method based on the audit and the load the building must carry.
When you need it
- After a structural audit finds a weak or damaged member.
- When concrete is falling and steel is rusting, typically in old roofs and bathroom slabs.
- Before adding a floor to a house that cannot carry it as built.
- When a wall or column has been removed during renovation.
- After fire damage.
- When changing use to something with heavier loads, like a school, store or gym.
Step-by-step process
- Audit first. No retrofit should be designed without an inspection, and tests where needed.
- Design. The engineer prepares repair drawings, materials and the order of work.
- Temporary support. Props are installed before any member is opened up.
- Surface preparation. Loose concrete removed, rusted steel cleaned and treated or replaced.
- Strengthening work as per drawings: new steel, formwork, concrete, plates or wraps.
- Engineer inspection before each stage is closed up.
- Curing and removal of props only when the engineer allows.
- Finishing and handover with as-built notes.
Approvals and documents
Small repairs to existing members usually do not need new approval. Structural changes are different. Under the LDA Building and Zoning Regulations 2019 (as amended), any structural change after the plan is approved counts as an addition/alteration needing its own plan. Check with your authority whether your work falls in that category. Keep the audit, repair drawings and site records together for future buyers.
What affects the cost
There is no fixed public rate. Get written quotes for both design and works. Main factors:
- Number and size of members to be strengthened.
- Method chosen (jacketing, plates, fibre wraps).
- Extent of rusted steel and loose concrete.
- Whether the building is occupied during the work.
- Temporary propping and access needs.
- Tests needed before and after.
- Engineer supervision visits.
Questions to ask
- Is the repair based on an audit? Can I see it?
- What load will the building safely carry after the work?
- Which members need propping, and for how long?
- How will rusted steel be treated or replaced?
- Who supervises on site, and when do you sign off each stage?
- What guarantee is given on the works?
Red flags
- A contractor who proposes "patch and plaster" for exposed, rusted steel.
- Work started before temporary props are in place.
- No drawings, just verbal instructions.
- Removing a column or wall "because the slab will hold".
- Resin injection promised as a cure for every crack, with no cause identified.
FAQs
Is retrofitting cheaper than rebuilding? Often, but not always. The audit should compare the extent of repair against the value and life of the building.
Can we live in the house during work? Sometimes, if work is phased and the engineer approves. Areas under repair must be propped and kept clear.
Can retrofitting make my house strong enough for another floor? Possibly. The engineer checks foundations and columns and designs strengthening where needed.
How long does a retrofit last? It depends on design, materials and workmanship. Ask the engineer about expected life and maintenance.
This page is general information; confirm with the relevant authority or a qualified professional before you act.
Sources
- LDA Building and Zoning Regulations 2019 (amended), PDF copy reviewed: https://khalidzafar.com/wp-content/files_mf/1685711737LDAAmendedBuildingRegulations2019.pdf