Thermal insulation

Anybody considering a building project of any size knows that it has to be insulated. They should be aware that building regulations aim to limit energy use, but they may not fully understand what determines the amount of thermal insulation required. That has a knock-on effect for the correct use of rigid PIR insulation.

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What is thermal insulation?

When someone talks about ‘insulation’, arguably they are usually referring to thermal insulation - a material that is chosen for its ability to restrict the movement of heat energy, helping to keep buildings warm in winter and cool in summer.

There are other types of insulation, however. There are materials that insulate against sound and provide acoustic insulation. The word insulation is also used in connection with fire performance. Architects and other building design professionals choose materials for a reason, and that reason is linked to how they need the materials perform in the chosen type of construction.

Adopting a principle of using the right insulation for the right reasons can help in achieving a successful building design and construction project.

What type of thermal insulation materials are available?

Common thermal insulation materials include rigid foam products like polyisocyanurate (PIR), polyurethane (PUR), phenolic foam (PF), extruded and expanded polystyrene (XPS and EPS), and vacuum insulation panels (VIP).

PIR thermal insulation boards, offer a range of benefits, including:

  • One of the most efficient thermal insulation products available.
  • Reliable long-term energy savings.
  • Lightweight for easy handling and transport.
  • Fast and easy to cut to size and install.
  • Takes up minimal internal space within the structure.

Mineral wool insulation includes glass mineral wool and stone mineral wool products. The benefits of these include:

  • Good thermal insulation properties.
  • Excellent acoustic insulation.
  • Non-combustible for excellent fire performance.
  • Easy to handle, cut and fit.

Other materials, such as cellulose, wood fibre, hemp, sheep’s wool and straw bales, can also be used as to thermally insulate buildings.

What is the correct thickness of thermal insulation?

Generally speaking, it is good practice for thermal insulation to be specified to the maximum level to help a project exceed current energy efficiency regulations. Where a project is not subject to specific requirements, it can be a case of accommodating as much insulation as there is space for, or that can be afforded.

Where a particular thickness of insulation has been specified to meet a target, however, it is for a reason. If a specification features, say, a 110mm PIR board in a floor, that is what will achieve the required U-value. A contractor ordering materials may decide that 100mm is fine because that is what the merchant has in stock. They may think, ‘what difference does 10mm make?’

That 10mm could mean the floor doesn’t achieve the required U-value, with the knock-on effect that other energy efficiency calculations suddenly do not meet their targets. In theory, it’s possible that changing the insulation specification could lead to the whole building failing to comply with building regulations.

Project planning, and ordering materials in sufficient time to ensure correct thicknesses are available when needed, are key to getting the best from the insulation specified, and indeed the building fabric in general.

Insulation products to consider
Product Name Thickness Range Sizes Lambda
Celotex GA4000 50-100mm Width 1200mm, Length 2400mm 0.022
Celotex PL4000 25-65mm (+12.5mm Plasterboard) Width 1200mm, Length 2400mm 0.022
Celotex TB4000 20-40mm Width 1200mm, Length 2400mm 0.022
Celotex XR4000 110-200mm Width 1200mm, Length 2400mm 0.022