How to insulate a basement


There is currently a greater emphasis on creating more space in homes, rather than moving to larger ones, especially in areas where space for properties is limited. There are several methods of doing this; either up into the attic, out into the garage or down into a basement, the subject of this blog post.

Either refurbishing an existing space or digging down in order to create a new basement is becoming an increasing achievable method of adding more space, and value to a property without having to move house. A key factor in making a basement a warm liveable area is insulating it properly to keep it at an appropriate temperature throughout the year and to avoid issues with condensation. In this blog post we will look at how to achieve this with our insulation.

Building Regulations

When building or refurbishing a basement into a habitable space there is still a requirement to meet Building Regulations / Standards for the walls and floors. More information on these can be found at One of the key considerations with the basement floor is the type of insulation used. As a basement is usually surrounded by earth it is important that the insulation is resistant to the passage of moisture and has a high compressive strength such as Kingspan Styrozone.

Waterproofing Systems

The next consideration would be the waterproofing system used. Waterproofing BS 8102: 1990 (Code of practice for protection of structures against water from the ground) provides guidance on protection of basements against ground water. The level of protection needed by a new basement in housing, offices, restaurants, leisure centres etc. is Grade 3 which consists of one of the following waterproofing options.

  1. Tanking System – A continuous waterproofing membrane surrounding the exterior of the basement structure, preventing ground water from penetrating the basement construction. Available in mastic asphalt tanking, cementitious renders, self–adhesive membranes and liquid applied membranes.
  2. Waterproofed Concrete – A continuous waterproofed concrete, mixed in accordance with BS 8007: 1987 (Code of practice for design of concrete structures for retaining aqueous liquids). The waterproofed concrete is used as the exterior of the construction to prevent water penetration.
  3. Drained Cavity & Damp Proof Membrane (DPM) – An effective drainage system where moisture that seeps through a monolithic wall, into the cavity is collected and channeled away under the floor. Using a DPM in conjunction with the drained cavity prevents any water penetrating the structure. This type of system can include the use of cavity drainage membranes.


The next consideration is the thickness of insulation required to meet the target U-value. These depend on the size and height of the basement and the calculation is slightly different for walls and floors.

Basement Walls

U-value calculations for basement walls are based on the height of the basement, the P/A ratio of the basement floor and the thermal performance of the basement floor. These obviously vary considerably depending on the basement size and shape.

Basement Floors

For basement floors the U-value depends on the P/A ratio of the floor area as well as the height of the walls. We’ve included calculations for these on our online U-Value calculator with an assumption that the basement walls are 2.5m high. Take a look at the online U-Value calculations for basement floors here.

For full details about insulation for basements read our brochure which has full details, including installation sitework.

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Kingspan Insulation is a market leading manufacturer of optimum, premium and high performance rigid insulation products and insulated systems for building fabric and building services applications.

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