The amount of insulation you should have in your loft will depend on a few factors, including the type of insulation you use and the thickness of the insulation. The recommended depth of loft insulation in the UK is currently 270mm for glass wool or mineral wool insulation.

The recommended thickness of insulation for other types of insulation may vary slightly, but in general, you should aim for a minimum of 250mm of insulation to achieve the recommended thermal resistance (R-value) for loft insulation.

It's worth noting that the recommended amount of insulation may also depend on the age of your property and its location. In colder areas or older homes, you may need to increase the thickness of the insulation to achieve optimal energy efficiency.

It's also important to ensure that the insulation is installed correctly and does not have any gaps or areas of compression, as this can reduce its effectiveness.