Insulated panels are widely used in external & internal roof & wall cladding in retail outlets, warehouses, distribution centres, factories, industrial units, food factories, cold stores, offices, along with airports, leisure, health & education buildings.
Types of Structural Insulation Panel (SIP) Systems
There are two types of prefabricated structural panel insulation (SIP) systems, either the:
- Insulation material is formed and clad with outer facings using adhesive - the most common type, or
- Outer-facings are prefabricated and the core is injected with the insulating material - typically Polyurethane
In a structural insulation panel construction, each panel consists of:
- An insulation material (low density core material)
- An outer covering material / metal facing (high-density thin-skin to provide structural strength)
- Adhesives to stick the insulation & metal facings together
- Joints to assemble the panels into multi-panel walls, floors or roofs
Due to their construction, structural insulation panel are sometimes referred to as "composite" or "sandwich" panels. These panels typically possess an interlocking tongue & groove system that allows the panels to be easily assembled into a multi-panel wall.
In a multi-panel construction, the junctions between panels are vapour sealed so that a continuous barrier - impervious to moisture - enveloping the insulated structure e.g. in a cold store or food factory building.
Some cold store panel systems use a key-operated interlocking system that allows multi-panel walls to be reconfigured for changing use cases. Other jointing systems include cassette systems - whereby the panels are tightly supported in a frame (i.e. a H-bar struts or similar metal extrusions that form a grid to interlock panels).
There are numerous advantages to using prefabricated structural insulation panels:
- High thermal insulation - using low density insulating core material
- High structural rigidity - due to the high density thin-skin
- Rapid installation - due to the prefabricated nature of the SIPs
- Lightweight - due to their composite design
- Few Defects - due to prefabrication in the factory
- Low Shrinkage - comparable to timber frame structures
- Minimal waste - off-cuts can be recycled
- Wide-range of external finishes are available
Types of Insulation Panel Core
Common types of insulation material include:
- Polyurethane (PUR) rigid foam
- Polyisocyanurate (PIR) rigid foam
- Mineral wool (i.e. fibrous glass, stone or ceramic materials)
- Expanded Polystyrene (EPS) bead
- Extruded Polystyrene (XPS) rigid foam
- Phenolic (PF) foam
Over 90 % of external structural insulation panels possess either a Polyurethane (PUR) rigid foam core (pre-2004) or Polyisocyanurate (PIR) rigid foam core (post-2004).
Approximately 75 % of structural insulation panels are used externally for the roofs and walls of a steal portal frame structure e.g. for a warehouse, manufacturing facility or a distribution centre etc.
The remaining 25 % of structural insulation panels are used in internally, for example in cold stores, smaller internal structures, lining panels in existing structures, or in fire resistance walls to isolate sections of a building.
Expanded Polystyrene (EPS) core panels were commonly used internally for the cold store and food industries until the mid-1990s.
All these insulation materials are low density & offer little or no structural rigidity by themselves. They are also water permeable & dirt or debris can easily ingresses into the material. Consequently, insulation materials are used in the sandwich panel configuration, whereby the low density core (insulation material) is given structural stability & protection from the environment by a thin-skin or outer casing of high-density material.
Types of Insulation Panel Coverings / Metal Facings
The most common types of insulation panel coverings are:
- Galvanised steel sheet
- Galvanised steel sheet with Plastic coating e.g. Polyvinyl-chloride (PVC) or Polyvinylidene fluoride (PVDF)
- Galvanised steel sheet with Polyester coating
However, the following types of coverings for specialist or architectural uses are also available:
- Stainless steel sheet
- Aluminium sheet
- Steel sheet with Aluminium/Zinc coating
- Fibreglass reinforced plastic
These high-density materials offer the structural rigidity missing in the low density insulating cores. They also protect the low density core from the ingress of dirt & are easily cleaned. Note that because of the structural properties that the metal sheet adds to the composite panel, they should not be confused with insulation boards that possess only thin aluminium foil facings: insulation boards or foil-faced boards should not be wrongly referred to as "panels" because do not offer any structural properties.
Internal facings do not typically require durable weatherproof coatings & can instead be simply coated with a thin layer of paint. The plastic or polyester coatings on external metal facings are essential to weatherproof panels.
For permeable facing materials - such as glass reinforced plastic - an additional vapour seal over the covering is necessary to prevent permeation of water into the insulation material - something that is particularly important for cold store or food factory structures.
The metal facings may be either flat, or lighting profiled - common in walls, or deeply profiled - common for all roof panellings / some wall panelling.
Vapour Sealing Insulation Panel Wall Constructions
When constructing a multi-panel insulated wall structure, it is crucial to vapour seal the joints to prevent permeation of water. A vapour seal is typically achieved using one of the following sealant materials:
- Butyl Mastic Sealant (Non-Hardening)
- Silicone Sealant (Acetic Acid Curing)
- Polyurethane Sealant
- Intumescent Sealants (for passive fire protection)
It is crucial that the joint and vapour seal materials:
- Accommodate movement of the structure without compromising the integrity of the joint
- Have good adhesion, are compatible & elastic to accommodate joint movement
- Age well & are able to maintain the previous two characteristics over a long time
- Achieve the previous three requirements in the temperature bands used
- Are easily repairable without dismantling the panel structure
In the food industry, it is also crucial that the materials used throughout the insulated panel & joint construction do not taint food e.g. through degassing of solvents, plasticisers etc.