Insulation R Value

If you hadn’t yet guessed it a shipping container in its raw state has pretty poor insulation values, and as such needs some help to create a comfortable space internally.

If you are just learning about insulation there are two main terms that are used in the building world that relate to insulation and they are intrinsically related to each other.

  • Insulation R Value - high number indicates a good insulator (for raw materials - glass, brick etc)
  • U Value - low value indicates a well insulated element (wall, floor or ceiling - a combination of materials )

Here is their basic meaning without having to get too mathematical on you..

U and R Values

  • R value  - measure of the thermal resistance of a material -  how slowly it transfers heat or cold from one side to the other. So it is the R value of a material that gives us an idea of whether a material makes a good or a poor insulator.
  • U value -  measure of heat loss in a building element. To get the U value it equals  1 divided by the combined R values of the materials that make up the element*

    *By element I am referring to a wall, ceiling or floor as these are the three main elements to go together to produce a building envelope - but each of them will be made up of various building materials

For example most people would know that glass and steel are poor insulators – you can see their low R values below

Similarly fiberglass batts, foam, and strawbales (which also hold a good amount of air) all have good insulation properties, as is shown by their higher R values.

There are many good insulators available in stiff (rigid foam), flexible (batts) and spray forms. The space available and budget will influence which insulation materials are chosen for each building.

You also need to consider how materials sit next to each other and whether 'thermal bridging' is occurring.

* Note - earth is also a great insulator, which is why earth/green roofs perform extremely well as a thermal barrier.

Working Out R and U Values

There is software to help you work out these value calculations, and tables exist with the R values of materials.

For example the R value of the following materials (per inch);

Single Glazing

Double Glazing (with ½” air gap)

Air Space  Between Materials  (½ to 4”)

Fibreglass batt

Steel (used in containers)

Strawbale (450mm width without render)


0.91

2.04

1.00

3.14

0.33

4.8


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