# Cold Storage Construction: What Decides the Building Envelope

> A cold store's envelope is a continuous insulated, vapour-sealed box: insulated panels for walls and roof, an insulated floor protected against frost heave, and doors and junctions detailed to keep warm, humid air out. Most failures are not in the panels but at the gaps between them, where heat leaks in and moisture condenses or freezes inside the construction.

## Thicker panels do not make a better cold store

When a cold store underperforms, the first instinct is to blame the insulation
and specify thicker panels next time. In practice the panels are rarely where it
went wrong. **A cold store fails at the places where the insulated box is
interrupted:** panel joints, the wall-to-floor junction, doors, steel passing
through the envelope and every pipe and cable that enters.

At those points warm, humid outside air meets cold surfaces. Moisture condenses,
soaks into insulation and, in frozen rooms, turns to ice. Wet insulation
insulates poorly, so the refrigeration runs longer, which makes the surfaces
colder, which draws in more moisture. For the business the cost is a rising
power bill, ice on floors and doors that becomes a safety hazard, damaged stock,
and in the worst case a frozen-store floor that heaves and has to be broken out.

The envelope is decided by what the room holds. Cold stores are usually described
in two broad categories, and the difference changes more than the panel
thickness.

| What changes | Chilled store (held above freezing) | Frozen store (held well below freezing) |
| --- | --- | --- |
| Panel thickness | Typically thinner | Typically thicker, from the heat load calculation |
| Vapour drive into the envelope | Present | Stronger, because the temperature difference is larger |
| Floor | Insulation often used; frost risk low | Insulation plus frost heave protection beneath it |
| Door frames and seals | Standard seals | Usually heated frames so seals do not freeze shut |
| Pressure relief | Rarely needed | Usually needed, as air contracts on cooling |
| Drain lines from evaporators | Plain | Usually trace-heated inside the room |
| Ice at junctions | Condensation risk | Ice build-up if any junction leaks |

The categories are descriptive. The room temperature, panel thickness and
protection measures for a project are set by the refrigeration and envelope
designer.

## The vapour barrier belongs on the warm side

Moisture moves from warm, humid air towards cold. In a cold store that means
from outside, inwards. In most Indian climates the outside air carries a lot of
moisture for much of the year, so the drive into a cold store envelope is
strong and constant.

The rule is to stop moisture **on the warm side of the insulation**, before it
reaches the cold zone where it would condense. With metal-faced sandwich panels
the outer skin is the barrier, which makes **the joints the critical detail**:
every panel joint, corner and penetration needs sealing on the warm face, and
the seal has to be continuous with the barrier under the floor. Sealing only the
inside face, which is easier to reach, traps moisture inside the panel joint.
[Interstitial condensation](/glossary/interstitial-condensation) explains the
mechanism, and the same dew point logic behind
[office window condensation and mould](/blog/office-window-condensation-and-mould)
applies here at a much larger temperature difference.

Panel selection still matters. [PIR insulated panels](/materials/pir-insulation-panel)
give high thermal performance per millimetre, and the panel system as a product
is covered by **EN 14509**. **IS 661** is the Indian code of practice for the
thermal insulation of cold storage. Neither replaces sealing the junctions.

## The floor: insulation and frost heave

The floor is the part of a cold store that is hardest to fix later, because it
sits beneath the racking, the stock and the traffic.

**Floor insulation** has to carry rack leg loads and forklift wheels without
crushing, so it is typically a high-compressive-strength board such as extruded
polystyrene, chosen from the manufacturer's data against the loads the
structural engineer calculates. A vapour barrier sits below it, and a reinforced
wearing slab above it spreads the loads.

**Frost heave** is the slower risk. Under a frozen room, cold works down through
the insulation over months and years. If the ground below falls below freezing,
water in the soil freezes and expands, lifting and cracking the slab. Frozen
stores are therefore typically built with **underfloor heating** (electric or
fluid-based) or a **ventilated underfloor** that lets ambient air through pipes
or a void beneath the insulation. Which method suits depends on the site, the
ground and the room temperature, and is the cold store engineer's decision. The
wearing surface on top is a separate choice; [PU concrete flooring](/materials/pu-concrete-flooring)
is commonly used where washdown and thermal shock are part of the duty.

## Doors, air curtains and the loading face

Every time a door opens, warm humid air rolls in at the top and cold air spills
out at the bottom. In a busy store the door is often **the largest single source
of heat and moisture**, larger than the conduction through all the panels.

The design tools are well known: fast-acting doors that are open only while
traffic passes, insulated sliding or hinged doors for less frequent use, strip
curtains and air curtains to reduce exchange while a door stands open, and an
anteroom or chilled dock between the outside and the coldest rooms. Frozen-room
doors usually have heated frames so seals do not freeze to the frame. Where the
store loads trucks directly, the dock seal and leveller become part of the
envelope too.

Frozen rooms also need **pressure relief**. When a room is pulled down to
temperature the air inside contracts, and when a door opens and closes the
pressure swings. Without relief valves, panels can be pushed or pulled out of
shape and joints opened.

## Thermal bridges and the refrigeration interface

A thermal bridge is any path that lets cold travel through the insulation. In
cold stores the common ones are steel columns or beams passing through the
envelope, panel hangers from the roof structure, the base of the wall where it
meets the floor, and fixings through both skins. The cold end of the bridge
chills the warm end, and moisture condenses or ice forms on it. Keeping the
structure entirely outside or entirely inside the insulated box avoids many of
them.

The refrigeration interface adds more penetrations: refrigerant pipes, drain
lines, power and control cables, and the supports for evaporators hung from the
ceiling. Each needs a sealed sleeve detail agreed between the panel installer
and the refrigeration contractor before panels are cut, not after.

## Fire is an envelope decision too

Insulated panels with foam cores are the usual cold store envelope because they
combine insulation, vapour control and a cleanable face in one product. The cores
are combustible, and fires in cold stores have shown how a fire can travel
through panel cores where it is hard to see and hard to reach. Cold stores are
also often unoccupied for long periods and full of packaging, which adds to the
fire load.

That makes the panel core a fire decision as well as a thermal one. The core's
reaction-to-fire class to **EN 13501-1** should be named in the specification,
and what the building requires, including any compartmentation and whether
non-combustible cores are needed at particular lines, is decided by the fire
consultant under **NBC 2016, Part 4**. Insurers frequently take their own view,
so it is worth asking them before the panels are ordered.

## Common mistakes

- **Specifying thicker panels** while leaving joints sealed on the inside face
  only.
- **No frost protection under a frozen room**, because the floor was designed as
  a normal warehouse slab.
- **Floor insulation chosen for thermal value alone**, without checking it
  against rack and forklift loads.
- **Refrigeration penetrations cut on site** without a sealed sleeve detail.
- **Steel structure passing through the envelope** without a thermal break.
- **Panel fire class left unstated**, then raised by the insurer late.
- **No pressure relief** on frozen rooms.

## What to ask your designer and contractor

- What room temperatures and loads were used for panel thickness?
- Where is the vapour barrier, and how is it continuous at joints and the floor?
- How is the floor protected against frost heave, and who designed it?
- Which doors, curtains and anterooms are proposed for the traffic expected?
- What is the panel core's reaction-to-fire class?
- How are refrigeration penetrations sealed, and who is responsible for them?

## Standards referenced

Thermal insulation of cold storage under **IS 661**; metal-faced insulating
panels under **EN 14509**; reaction-to-fire classification under **EN 13501-1**;
fire and life safety under **NBC 2016, Part 4**. Room temperatures, panel
thickness, floor protection, refrigeration design and fire strategy for a
specific cold store must be established by the project's refrigeration engineer,
structural engineer and fire consultant; nothing on this page replaces that
design.

## Frequently asked questions

### What thickness of panel does a cold store need?

It follows from the room temperature, the outside climate, the insulation's thermal conductivity and the refrigeration load the designer is willing to accept, so there is no single answer. Frozen rooms typically use thicker panels than chilled rooms. The thickness should come from the refrigeration and envelope designer's heat load calculation and the panel manufacturer's data, not from habit.

### Why does ice form on the outside of cold store panels or around doors?

Ice and frost on the warm face, or around a door frame, usually mean cold is escaping through a thermal bridge or an air gap, chilling the surface below the dew point of the surrounding air. Moisture condenses and, in frozen areas, freezes. The cause is generally a junction, a penetration or a door seal rather than the panel itself, and it should be traced before it soaks the insulation.

### What is frost heave and does every cold store need underfloor heating?

Frost heave happens when the ground beneath a frozen room slowly cools below freezing, water in the soil turns to ice and expands, and the slab lifts and cracks. Frozen stores are typically protected by underfloor heating or a ventilated underfloor beneath the insulation. Chilled rooms held above freezing carry far less risk. Whether protection is needed is the cold store engineer's decision.

### Where should the vapour barrier go in a cold store?

On the warm side of the insulation, which in a cold store is the outside. Moisture moves from warm, humid air towards cold, so a barrier on the warm face stops it reaching the insulation. Metal skins of sandwich panels act as the barrier, which makes the joints between them the critical part. In the floor, the barrier sits beneath the insulation and must be continuous with the walls.

### Are PIR or PUF panels safe to use in a cold store?

Both have combustible foam cores, and cold store fires are known to spread through panel cores and be difficult to fight. The panel's reaction-to-fire class to EN 13501-1 should be stated, and what the building requires is set by the fire consultant under NBC 2016 Part 4 and often by the insurer. Some designs use non-combustible cores at fire-critical lines.

### Can an existing warehouse be converted into a cold store?

Often, by building an insulated panel box inside the existing structure, but the floor is usually the hard part. An existing slab has no insulation or frost protection, so frozen use generally means a new insulated floor build-up above it, with the loss of height and the level change at doors that implies. The structure, floor and refrigeration should be assessed before committing.

## Sources

- [IS 661](https://standards.bis.gov.in/website/published-standards/department-wise) — Thermal insulation of cold storage - code of practice
- [EN 14509](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Self-supporting double skin metal faced insulating panels - factory made products
- [EN 13501-1](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Fire classification of construction products - reaction to fire
- [NBC 2016, Part 4](https://www.bis.gov.in/standards/national-building-code/) — Fire and life safety

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Source: https://hagerstone.com/blog/cold-storage-building-what-decides-the-envelope