Home Contractor's Corner Knauf Insulation Tech Talk: Top tips for insulating a loft

Knauf Insulation Tech Talk: Top tips for insulating a loft

Faced with rising energy bills, many homeowners will be looking to increase the energy efficiency of their homes by insulating their lofts. So this month, Bradley Hirst, Technical Services Manager at Knauf Insulation, gives his six top tips for a successful loft installation.

Bradley Hirst, Technical Services Manager at Knauf Insulation.

• Meet the minimum standards for thermal performance
The minimum standards for thermal performance are listed in Approved Document L of the Building Regulations. From June 2022, renovated roofs – which includes lofts insulated at ceiling level – must achieve a U-value of 0.16W/m2K. For a typical loft, this can be achieved by installing Knauf Insulation’s Loft Roll 44 at a depth of 270mm or Loft Roll 40 at a depth of 250mm.

• Always unwrap Mineral Wool insulation in the loft
Our Glass Mineral Wool insulation is compressed so there’s more product per pack, which means you can fit more insulation into your van – which also reduces transport-related carbon emissions. But when you unwrap it, our Loft Roll insulation will recover to up to ten times its compressed thickness. So always unwrap it where you plan to install it!

Layer insulation at right angles
The first layer of insulation should be installed between the joists to the same depth as the joist. So, if your joist is 100mm deep, your first layer of insulation should also be 100mm deep. Subsequent layers should be installed at a right angle to the first layer, completely covering the joists.

Make sure there are no gaps
Unintended air gaps reduce thermal, fire safety and acoustic performance, so make sure the insulation is fitted tightly against the joists and that rolls are butted together. Remember to tuck the insulation down at the roof perimeter so it meets the insulation in the wall head to prevent thermal bridging.

Above: Knauf Insulation Loft Roll 40.

Don’t block ventilation
To prevent condensation, make sure air vents are unobstructed and if the roof is lined with sarking felt, leave an air gap at the eaves to ensure continuous ventilation of the roof void.

Watch out for electrical cables
High voltage electrical cables should be rerouted and laid over the top of the insulation to prevent risk of overheating or fire. One of the benefits of our Mineral Wool insulation is that it is non-combustible with the best possible Euroclass A1 and A2-s1,d0 reaction to fire classifications. This means it will not contribute to the development or spread of fire should it occur.


Read Bradley’s previous column here.

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