VIEWPOINT THE DO’S AND DON’TS OF
LOFT ROLL INSULATION Matt Neary, head of marketing, Knauf Insulation
WITH THE WARM Homes Plan expected to drive more retrofit activity, merchants are likely to see growing demand for loft insulation. It’s a familiar product for most customers, but best practice has evolved in recent years, with many housebuilders now installing significantly deeper insulation.
That shift creates an
opportunity for merchants to guide customers towards better outcomes. Loft roll remains one of the most cost-effective energy efficiency upgrades available, but only when it is installed properly. Understanding the do’s and don’ts of installation will help ensure customers achieve the performance they expect.
DO maximise insulation depth New homes are commonly built with loft insulation to a depth of 500mm to achieve Part L requirements and maximise energy efficiency. Your customers should consider taking a similar approach when topping up, replacing or adding loft insulation to take advantage of the relatively low cost and significant thermal performance boost.
When installing additional layers, the first layer should match the depth of the joists. Subsequent layers should then be laid perpendicular to the joists, covering them fully and reducing thermal bridging. Rolls should be tightly butt-jointed with no gaps or overlaps to maintain consistent coverage across the loft.
DON’T ignore the preparation stages Preparation is essential for achieving the best results. Before any insulation is installed, installers should check the loft space for signs of damp or poor ventilation.
DON’T crush the insulation
Dark patches or mould at the edges of ceilings can indicate thermal bridging in the eaves, while damp timbers, stained felt or a musty smell in the loft can point to ventilation issues. Sealing gaps and service penetrations in the ceiling is another important step. These openings allow warm, moist air from the home to enter the loft, increasing the risk of condensation and reducing thermal efficiency.
Electrical safety also needs careful attention. Downlights should be fitted with suitable protective covers, while high-load cables should be routed above the insulation to avoid overheating. Even with modern mineral wool products designed to minimise
May 2026
www.buildersmerchantsjournal.net
dust, installers should still wear appropriate PPE, including gloves, eye protection and a dust mask.
DO pay extra attention at the eaves
The eaves area is particularly important for maintaining thermal continuity. Insulation should be carefully detailed so that it meets the wall insulation without leaving gaps, helping to prevent cold bridges.
At the same time, ventilation must be preserved. A gap of around 50mm between the insulation and the roof underlay allows moisture to escape and helps keep the loft space healthy. If the insulation depth makes this difficult, ventilation trays can be used to maintain airflow.
Knauf Insulation’s Loft Roll works by trapping air within its fibres. Compressing it reduces those air pockets and dramatically reduces its thermal performance. This commonly happens when loft boards or stored items are placed directly on top of the insulation. If customers need storage space, raised loft boarding systems should be used to create a platform above the insulation without compressing it.
A simple upgrade done properly
Loft insulation remains one of the simplest and most cost-effective retrofit measures available. However, it still requires attention to detail to deliver long-term performance.
With retrofit activity expected to increase, merchants who understand best practice will be well placed to support their customers and ensure installations deliver the comfort and energy savings homeowners are looking for. BMJ
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