Get on top of loft insulation

Demand for insulation is ‘through the roof’ as homeowners are desperately looking for ways to improve energy efficiency of their homes. Loft insulation is one of the most beneficial methods of improving energy efficiency, but it has to be done right.

Top-up insulation or replace it? 

If there’s already some mineral wool installed, assess whether it can be topped up or should be replaced. If it’s in good condition and has been correctly installed, mineral wool insulation lasts for over 50 years, so it’s fine to insulate over the top. But if it’s been torn, compressed, fitted incorrectly, or disturbed so there’s gaps between rolls or the joists, it will need replacing.

Maximise performance

Under Northern Irish Building Regulations, renovated roofs, including lofts insulated at ceiling level, must achieve a U-value of 0.11W/m2K.

For a typical loft, installing Knauf Insulation’s Loft Roll 40 or Loft Roll 44 at a depth of 400mm will meet these standards. But we know that the thicker the insulation is, the more effective it will be at preventing heat transfer. That’s why, housebuilders are installing loft insulation to a depth of 500mm in new homes. So, to help your customers cut their bills as much as possible, advise them to do the same. 

Start at the eaves 

Always start in the eaves and work towards the loft hatch. Ensure your first layer of insulation is slightly wider than the joist to ensure a tight fit and the same depth (i.e if the joist is 100mm deep the insulation should be too). 

Position the end of your insulation between the joists and curve it down around the edge of the loft floor, into the wall head until it meets the top of the wall insulation. Always leave a 50mm gap between the top of your loft insulation and the roof to ensure air movement and prevent condensation. 

Make sure the ends of the insulation are butted together so there are no gaps that can reduce performance. 

Layer insulation 

Once the first layer is complete, you’ll need to cover the joists with the subsequent layers of insulation, which should be installed at a right angle to the first. Installing the second and third layers together means you can achieve a depth of 500mm without compressing the insulation, which reduces its thermal performance.

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