Introduction
Insulation materials are a part of a building’s fabric and serve the purpose of reducing heat transfer. In order to create a comfortable thermal environment in our buildings, we need to maintain a constant temperature within them. This is especially important because temperature directly impacts user health, productivity, and comfort.
Without proper insulation, prolonged exposure to excessive heat can lead to issues such as heat stress and fatigue, while extreme cold may cause hypothermia and stiffness, among other issues. Suffice to say, both extremes heighten the risk of illness and negatively affect productivity. This is why the Health and Safety executive guidance titled, ‘Temperature in the workplace,’ outlines that the reasonable working temperature in workrooms is to be at least 16°C, or 13°C for strenuous work.
Temperature fluctuations may also weaken the building’s structure and damage equipment which could result in potential safety hazards and higher maintenance costs. The continued exposure to extreme conditions may cause materials to expand, contract, or degrade over time, which may further lead to cracks, warping, and structural failures.
Insulation materials are made from poor conductors of heat which tend to trap warmth, reduce heat loss, and thus maintain a more stable indoor environment. Although heat transfer is inevitable, the reduction in the rate at which it happens can be quite important to the efficient functioning of the building.
Good insulation will improve the thermal performance of the structure, keeping the building warm in winter and cool in summer (providing solar gain and ventilation are designed correctly).
The best type of insulating materials will have a low density, with atoms spaced well apart. Since gases have atoms that are widely spaced, air is considered a good form of insulator. This is why it is a key factor in insulating materials, as the materials allow for ‘pockets’ of air that function as insulators. The examples of this include closed cell insulation like PIR boards and glass fibre.
By designing a building fabric that keeps heat within the building for as long as possible we can conserve energy, reduce heating demands, and further lower costs.
In this post, we will be exploring the different types of insulation materials and key compliant build ups to help you understand how to properly insulate your buildings and projects.
[Check out the post below for a refresher]
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Insulation Material Performance
Generally speaking the best performing insulation materials in terms of thermal conductivity or K-values (see this article for a refresher on K-values) are the materials with the highest embodied energy or carbon. However, this can sometimes be offset by the reduced requirement of space heating and less material being required for the same performance of a lesser material.
The natural plant/animal-based materials tend to have good environmental and performance benefits (such as acoustic) and a lower embodied carbon. They do, however, tend to have higher K-values and much greater wall thicknesses are required to achieve a suitable overall U-value. The best scenario is to find a good balance between a material that has a low K-value and low environmental impact.
Table of Thermal Conductivity of Insulation Materials
The following table outlines various insulation materials with their K-values and embodied energies:
Table adapted from Greenspec.co.uk.
Types of Insulation Materials
There are many forms of insulation used in construction, with a wide variety of properties and applications. They include:
- Rigid preformed insulators – aerated concrete blocks
- Flexible materials – fibreglass quilts
- Loose fill materials – expanded polystyrene granules
- Materials formed on site – foamed polyurethane
- Reflective materials – aluminium foil
They generally fall under three main categories as follows:
- Organic (or plant/animal derived)
- Mineral
- Petrochemical derived (oil based)
Let’s explore these further.
Organic or Natural Insulations
Organic insulations come from naturally derived sources such as plants or animals. They include cellulose insulation, cork insulation, hemp, wood fibre, hempcrete and sheep’s wool.
Composition wise they are open cell in nature containing numerous air pockets that can trap heat and regulate moisture.
The advantages of organic insulations:
- Usually low, zero or negative embodied carbon
- Often waste or by products
- They are recyclable or reusable
- They can be made airtight with good acoustic performance
- Suitable for breathing or timber framed constructions
- Do not release harmful VOCs
- Some materials, like hemp and cork, can sequester carbon during growth
The disadvantages of organic insulations:
- They don’t always have the best K-values with a range of 0.038 to 0.1 W/mK
- Some materials can rot if exposed to high levels of humidity or moisture
- Not suitable for installation in flood areas at low levels
- Not generally suitable for wet construction such as masonry cavity walls
- Not generally suitable for high load areas like foundations, floors, green roofs
- A breather membrane must be used if it is adjacent to a ventilated cavity
- They are often more expensive since they may not be mainstream in the market
- They may require extra treatments to meet fire safety regulations or pest control
- Often more is required to achieve the right U-values which leads to thicker and heavier walls
Natural Insulation: Sheep’s Wool Focus
Sheep’s wool rolls and batts are used as insulation between rafters, joists and timber studs in a breathing or ventilated construction.
Benefits:
- Sheep’s wool insulation is a waste produce from a renewable source
- Wool sequesters CO2 during animal growth
- It is a hygroscopic material which helps to control the temperature throughout the season
- Absorbs moisture without loss of thermal efficiency
- Is possible to reuse if recovered carefully
- Does not release harmful chemicals or irritants
- Can help support local farmers
Limitations:
- The polyester binder used to create the material is non renewable
- Needs to be fire treated but these contain a boron-based flame retardant
- If wool is imported it adds to the embodied energy
- Is more expensive than synthetic options
You can read a more in-depth exploration of this insulating natural fibre in our post from our Natural Materials Series:
Sheep’s Wool as a Building Material
Mineral Insulations
Mineral based insulations originate from naturally occurring inorganic materials, such as rock, slag, or glass. They include rock wool, glass wool, cellular or foamed glass, or aerogel.
Similar to organic insulations these are also open cell in composition and great at trapping heat.
The advantages of mineral insulations:
- Average k-values in the range of 0.036 to 0.05 W/mK, with aerogel being 0.013 W/mK
- Vapour permeable apart from glass foam and aerogel
- Usually contains recycled or waste products
- Good fire resistance
- Recyclable or reusable (except mineral fibre)
- Work to reduce noise transmission
- Do not absorb water
- Maintain insulating performance over time
- More cost-effective than organic and oil based
The disadvantages of mineral insulations:
- Embodied energy is average
- Can contain formaldehyde
- Some materials are not hygroscopic and therefore any moisture will reduce insulation performance
- Aerogel reuse and recycling is difficult due to installation method
- Fine fibres if exposed to can cause itching and respiratory issues
- Production requires high temperatures, leading to a larger carbon footprint
- Loose-fill applications may compact and lose some insulation efficiency
Mineral Insulation: Rock wool Focus
Rock wool is made from quarried rock and recycled steel slag. It is available in a variety of densities which produces varying thermal conductivity. It is versatile in its application and can be used in masonry cavity walls, timber frame walls, roof rafter insulation and lofts and floors.
Benefits:
- Uses up to 23% secondary industrial waste
- Can be reused if in a good condition
- Can be recycled
- Inherently non combustible and is able to resist rot
- A formaldehyde version has been developed but not yet available in the UK
- Absorbs sound
- Does not absorb moisture
Limitations:
- Quarrying results in land degradation
- Emissions from production include carbon monoxide, formaldehyde and phenol. UK emissions are within legal limits
- Only formaldehyde brands are available in the UK at present
- High embodied energy
- Fine fibres can cause irritation upon exposure
- Requires strong structural support and may be difficult to install in some applications
- More expensive than fibreglass or polystyrene insulation
Oil-Based Polymer Insulations
Oil-based polymer materials or petrochemical derived materials include expanded polystyrene (EPS), extruded polystyrene (XPS), rigid polyurethane (PUR/PIR) and phenolic foam.
These synthetic insulations can have either an open cell or closed cell structure, depending on their formulation. The closed cell structures offer superior thermal performance as they are created through controlled foaming processes that create uniform, gas-filled cells within a synthetic polymer matrix.
The advantages of oil based polymer insulations:
- Good insulators, with k-values ranging from 0.028-0.04 W/mK, with PIR and phenolic foam able to achieve 0.018-0.024 W/mK
- Can be recycled and reused
- Good fire resistance although not always suitable for rainscreen cladding
- Suitable for damp conditions – i.e. masonry cavity walls
- Suitable for high impact areas such as foundations, floors, and green roofs
- Lighter and easier to install
- Durable and long lasting
- Their closed cell structure works to reduce air movement within the insulation
The disadvantages of oil-based polymer insulation:
- Highly combustible
- High embodied energy
- EPS thermal performance may be reduced by moisture
- Off gassing particularly with phenolic foam
- Vapour impermeable so not suitable for use in breathable constructions
- Closed cell /surface insulation not suitable for timber frame construction as moisture will only be able to escape through the timbers
- Phenolic insulation can shrink over time so not suited to render finishes
- Most materials excluding EPS, suffer from reduced performance over time
- Petroleum-based materials contribute to landfill waste and have limited recycling options
Oil Based Polymer Insulation: Extruded Polystyrene (XPS) Focus
Extruded polystyrene (XPS) is an extruded foam, by mixing polystyrene with a blowing agent and forcing it through a die. It is slightly stronger than EPS and most commonly seen in below ground applications where high loading or impacts are expected.
Benefits:
- Recyclable and reusable
- High compressive strength
- Water impermeable due to closed cell structure
- Generally resistant to both rot and vermin
- In the UK most blowing agents used in manufacture are zero ozone depletion agents
- Low thermal conductivity provides effective insulation
- Has minimal degradation
- Easier to handle and cut
- Has versatile applications, commonly used in basements, foundations, roofs, walls, and external insulation systems
Limitations:
- Derived from petrochemicals which leads to resource depletion, pollution risks for the production of oil and plastic.
- HBCD which is used as a fire retardant is considered to be hazardous
- Can ignite and release chlorofluorocarbons or toxic fumes if not treated
- Relatively high embodied energy
- Can trap moisture within wall assemblies if not properly ventilated
Building Assembly Examples for Thermal Performance
Refer to our Building Fabric 01 – Thermal Performance Guide article below for refresher on U-values and thermal performance.
You may also benefit from reviewing The Approved Document Part L: Conservation of Fuel and Power (Volume 1: Dwellings), which outlines the current requirements for U-values in notional dwellings (new builds).
According to Part L 2021 Edition, incorporating 2023 amendments, the recommended U-values to aim for in a new dwelling are illustrated in the diagrams and table below:
Table adapted from Approved Document Part L: Conservation of Fuel and Power (Volume 1: Dwellings).
The following diagrams and tables demonstrate different building assemblies that comply with the required U-values. We have provided examples using both mineral wool and rigid insulation materials. You can see the thickness requirements of the different types of materials and how the performance has an impact on the overall assembly thickness. These examples are for information purposes only. All construction assemblies must be calculated on a project by project basis to ensure project specific compliance.
Walls:
Full Fill Masonry Wall
Partial Fill Masonry Wall
Floors:
Roofs:
Checklist for Specifying Insulation Materials
When specifying insulation for buildings, it is important to consider the requirements of the material. Some of the properties to take into account are:
- Is the insulation suitable for the purpose?
- Does the insulation have sufficient strength or rigidity for the application?
- What is the moisture resistance like?
- Is it fire resistant or treated to reduce fire risks?
- What is its resistance to pests and moulds?
- Is it compatible with the materials adjacent to it?
- Is the insulation harmful to occupants or the environment?
- Does the material have a high R-value for better heat resistance?
- Does it have a low U-value to minimise heat transfer?
- Does it allow controlled moisture movement (breathability) to prevent condensation?
- Are there any additional benefits like sound insulation?
- Is the material recyclable or made from sustainable sources?
- Does it have a low carbon footprint and minimal environmental impact?
- Will the insulation retain its performance over time?
- Is it easy and safe to install?
- Will it require specialist equipment and skilled labour?
- How much does it cost?
The choice of insulation products is vast and there is not a ‘one size fits all’ insulation that is suitable for all applications. For example, a sheep’s wool insulation performs well in a ventilated wall construction but is not suitable for unventilated cavities. The choice of insulation must go hand in hand with the overall construction method.
Helpful Links
Temperature in the workplace: Managing workplace temperatures (HSE)
Conservation of fuel and power: Approved Document L (GOV.UK)
Insulation materials and their thermal properties (Greenspec.co.uk)
Books
Here are some recommendations for some hemp related further reading for you to indulge in:
You Might Also Be Interested In…
We have loads of other incredible posts in our Building Fabric Series. Be sure to check them out.
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Conclusion
In summary, insulation is a part of the building envelope that plays a great role in its overall energy efficiency and thermal comfort. Its right use can help reduce heat loss, lower energy consumption, and enhance occupant wellbeing.
Having the awareness of different insulation materials and the knowledge of their unique properties can allow you to make more informed design decisions. It is also essential that you stay in the know about new and innovative insulation materials alongside updates to current regulations.
This post just touches the surface of the topic of insulation materials, but we hope we have provided valuable insights on the subject and that you find our checklist useful in your projects.
You can read all of the architecture and environment related posts here:
Architecture and the Environment
Thank you for reading!
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Author
Written by Emma Walshaw, Architectural Technologist and founder of First In Architecture and Detail Library. Emma has written a number of books about construction and architectural detailing.
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