Part L of the building regulations govern the conservation of fuel and power used by buildings. It’s a long document with multiple sections covering different components and materials used in order to ensure buildings meet with Part L.
How heat loss from homes is measured
The unit of measurment used to represent heat loss is known as the ‘U’ value. The U value is specified in W/m²k and represents the amount of heat lost in watts (W) per square metre of structure (Glazing, insulation, wall, ceiling etc) when the exterior temperature (k) is 1 degree lower. This means the lower the U value, the better.
Current U Value requirement for Loft Hatches under Part L building regulations
The current requirement for a loft hatch to comply with Part L of the building regulations it needs a U value of 0.35 or better. This is achieved with the use of insulation on the inside of the loft hatch and draught seals on the contact surfaces to keep warm air in the building below and cold air in the loft above.
What makes a Part L compliant Loft Hatch different?
In order to meet or exceed Part L a loft hatch will need to be insulated, either with a mineral wool insulation, or a polystyrene slab. A better and therefore lower U value (0.35 or lower) is achieved by using a better type of insulation, or a deeper type of insulation. Insulation is pointless if air can leak through gaps between the loft hatch frame and the lid. To eliminate draughts, the tolerances between the size of the frame and the size of the lid need to be close. In addition compression seals are fitted to the contact points on the frame and the loft hatch lid.
Please note, insulation and draught seals do not necessarily make a loft hatch Part L compliant. If your loft hatch was installed before 2002 it’s probable it will have a U value in excess of 0.35 W/m²k.
Types of Part L compliant Loft Hatch
There are two main types of loft hatch available…
Push up loft hatches where the lid is separate from the frame and is pushed up into the loft space when opening.
Hinged loft hatches where the lid hinges at one end of the frame and opens downwards.
The lowest U Value Loft Hatch currently available
Currently the lowest U vaule we’ve measured is 0.15 W/m²k which is 80% lower than 0.35.
You can find more information on Insulated Loft Hatches and Insulated Fire Rated Loft Hatches here.