# Facade Retrofit and Recladding: Replacing an Envelope in Use

> A facade retrofit replaces or upgrades an existing envelope, usually while the building stays in use. It begins with investigation rather than design, because what is behind the existing cladding — the substrate, the fixings, the insulation and the structural capacity — determines what is possible.

## 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.

| Investigate | Why |
| --- | --- |
| Substrate type and condition | Determines what can be fixed to it |
| Existing fixings | Reusable, or must be replaced entirely? |
| Insulation present and its state | Wet insulation indicates a water path |
| Structural capacity | Can it take the new system's loads? |
| Existing water paths and defects | The cause, not just the symptom |
| Legacy materials | Some require particular handling |

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.

| | Overcladding | Replacement |
| --- | --- | --- |
| What it is | A new outer layer over the existing | The existing envelope removed entirely |
| In its favour | Avoids opening the interior; faster; less disruptive to occupants | Addresses the actual condition; new build-up designed properly, not around an unknown |
| Against it | Adds load; thicker wall affects reveals, sills and roof edges; leaves whatever is underneath in place | More disruptive and more expensive |

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.

## Frequently asked questions

### What has to be investigated before designing a retrofit?

The substrate and its condition, how the existing cladding is fixed and whether those fixings can be reused, what insulation is present and its state, the structural capacity available for a new system, and whether there are any legacy materials requiring particular handling. Opening-up investigations at representative locations are what turn assumptions into facts, and skipping them is the main cause of retrofit cost escalation.

### Is overcladding cheaper than replacement?

Often, and it avoids exposing the interior, but it is not always possible. Overcladding adds load to the existing structure and fixings, increases the wall thickness which affects window reveals and roof edges, and does nothing about a defective layer left underneath. Where the existing envelope is failing rather than merely tired, leaving it in place can mean building over the problem.

### How is the building kept weathertight during the works?

By working in controlled zones with temporary weather protection, sequencing so that no area is open longer than necessary, and planning around the weather rather than hoping. Monsoon conditions in particular require planning: a partly removed facade during heavy rain damages interiors, and the cost of that far exceeds the cost of sequencing properly.

### What changes for occupants?

Noise, temporary loss of daylight where panels are removed, access equipment outside windows, and sometimes temporary relocation from the immediate work zone. The programme has to account for working hours, and occupants need to be told in advance what will happen to their area and when. Most complaints on occupied retrofits are about surprise rather than disruption.

### Does a retrofit have to meet current requirements?

What applies to an existing building being altered depends on the extent of the work, the building's classification and the applicable rules, and it is determined by the project's consultants and the authority having jurisdiction. This must be established at the outset, because it affects what the new envelope has to achieve thermally and in fire performance, which in turn affects the system selection and the cost.

### What about the existing structure's capacity?

A new facade imposes loads through its fixings into the existing structure, and design wind pressure derives from the building's actual site, height and terrain under IS 875 Part 3. Whether the existing substrate and structure can accept those loads is an assessment, usually including pull-out testing of trial fixings. Those values must come from the project's structural and facade engineers rather than from the original design assumptions.

## Sources

- [IS 875 (Part 3)](https://standards.bis.gov.in/website/published-standards/department-wise) — Wind loads on buildings and structures
- [ECBC 2017](https://beeindia.gov.in/) — Building envelope
- [NBC 2016, Part 4](https://www.bis.gov.in/standards/national-building-code/?lang=en) — Fire and life safety
- [NBC 2016, Part 7](https://www.bis.gov.in/standards/national-building-code/?lang=en) — Construction practices and safety

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Source: https://hagerstone.com/services/facade-glazing/facade-retrofit-and-recladding