Facade Retrofit and Recladding: Replacing an Envelope in Use

Investigation comes before design

On a new building the facade engineer starts from the architect's intent. On a retrofit they start from what is already there — and what is already there is rarely what the drawings say.

Opening up at representative locations is the single highest-value early spend on a retrofit. Every rupee saved by skipping it tends to return as a variation.

Overclad or replace

There are two routes: add a new outer layer over the existing envelope, or remove the existing envelope and build a new one.

The deciding question is usually: is the existing envelope merely tired, or is it failing? Building over a failing layer preserves the problem.

Loads have to be re-established

A new facade transfers load through its fixings into the existing structure. Design wind pressure comes from IS 875 (Part 3) for the building's actual site, height and terrain — and may differ from what the original design assumed, particularly if surroundings have changed.

Whether the substrate can accept those loads is an assessment, normally including pull-out testing of trial fixings in the actual substrate. Those values are the structural and facade engineers' output, not something to carry over from the original construction.

Keeping the building dry and in use

• Work in controlled zones, with temporary weather protection
• Sequence so no area is open longer than necessary
• Plan around monsoon conditions rather than hoping
• Maintain the interior environment — cooling, or its absence, in opened zones
• Protect interiors even where work appears external

A partly removed facade during heavy rain damages interiors at a cost far exceeding careful sequencing.

Requirements for an altered building

What an existing building must achieve when altered depends on the extent of the work, its classification and the applicable rules — including envelope performance under ECBC 2017 and fire requirements under NBC 2016, Part 4.

This has to be established at the outset by the project's consultants and the authority having jurisdiction, because it determines what the new envelope must deliver and therefore what it will cost. Establishing it late is how a retrofit budget doubles.

Occupants and access

Working at height on an occupied building brings safety requirements addressed in NBC 2016, Part 7, plus practical matters: access equipment outside windows, exclusion zones below, agreed working hours, and clear communication to occupants about what happens to their area and when.

Standards referenced

Wind loading to IS 875 (Part 3); envelope performance in ECBC 2017; fire and life safety in NBC 2016, Part 4; construction practices and safety in NBC 2016, Part 7. Structural capacity, fixing design, applicable performance requirements and safety arrangements for a specific retrofit must be established by the project's facade engineer, structural engineer and fire consultant, and confirmed with the authority having jurisdiction.