Adding Floors to an Existing Building: The Structural Checks You Cannot Skip

Land is scarce and expensive in Bangladesh, so adding floors to an existing building is an attractive way to gain space. It is also one of the most common reasons buildings become unsafe. Every new floor adds weight to every column and foundation below it, and increases the earthquake forces the whole structure must resist.

Was the building designed for more floors?

Some buildings were genuinely designed for future floors — the original structural drawings and calculations will say so explicitly. Many were not, even if the owner was told otherwise. The only reliable evidence is the original design documentation, checked against what was actually built.

The checks an engineer will carry out

1. Verify the existing structure

Measure column and beam sizes, locate reinforcement with ferro-scanning, and test concrete strength with cores. Construction rarely matches drawings exactly, and concrete strength is often lower than specified. See our guide to the Detailed Engineering Assessment.

2. Check the columns

Ground-floor columns carry the most load. Adding two floors to a five-storey building can increase their axial load by roughly 40% — often more than their reserve capacity.

3. Check the foundations

Footings and piles must carry the new load without excessive settlement. This usually needs the original soil report, or a new investigation if none exists.

4. Check seismic and wind resistance

A taller, heavier building attracts larger lateral forces. The lateral system — frames, shear walls, bracing — must be checked against BNBC 2020.

5. Check the roof slab that becomes a floor

An existing roof slab was probably designed for roof loads, not floor loads with partitions and occupancy.

If the structure is not adequate

Vertical extension may still be possible with strengthening — for example, jacketing ground-floor columns, adding new shear walls, or underpinning foundations. Alternatively, a lightweight steel extension can reduce the added load considerably compared with a concrete storey. The engineer should compare options on cost and disruption.

Approvals

Vertical extensions require approval from the relevant development authority (such as RAJUK in Dhaka) and must comply with planning rules on height and floor area. A structural assessment report is an essential part of a responsible application.

Never add floors on the basis of a contractor's assurance alone. The cost of an engineering assessment is small compared with the value of the building — and the lives inside it.

Book a consultation to discuss a planned extension, or read about our retrofitting and strengthening service.