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Loft Insulation: It’s Not Working

There’s a big problem with loft insulation.

In the UK, there are 23 million houses with lofts and several million non-domestic properties that also have loft spaces.

According to Government figures, around 15 million of the houses have insulation of over 100mm (though often nowhere near the current building regulations of 270mm) but there seem to be no figures for insulation levels of non-domestic properties. For many of the buildings without adequate insulation, access and storage requirements are cited as the reason, because the owners want to be able to access M&E equipment or they want to use the loft as a space for storage.

Well, at least we have over half of the country’s properties with properly working insulation… except, alas, no we don’t.

That’s because recent research by the National Physical Laboratory and Carbon Trust shows that in 80% of insulated properties, the insulation isn’t working, and that the reduction in thermal resistance from what is expected is at least 50%.

Why is There an Issue?

The issue is one of compression: for mineral wool-type insulation, it needs to retain its full depth to work properly. Ask the insulation manufacturers how performance is diminished if the insulation is squashed and they will simply tell you that it’s an abuse of the product to squash it, which is correct.

Loft Insulation
Source: NPL

But, in both the residential and non-residential sectors, insulation is regularly squashed. Carbon Trust sponsored the biggest ever survey of loft users, with 6,000 responses, and the results are eye-watering:

  • 82% use their loft for storage
  • 78% say the loft is greater than half full
  • 76% say loft storage is important or essential
  • 65% have fully or partially boarded their loft at joist height (typically squashing or removing the insulation down to 75 or 100mm)
  • only 26% knew that squashing loft insulation was bad for it.

In effect, 82% of lofts users have compromised their insulation, and only 26% of users knew this was reducing its effectiveness.

What is the effect on the U-value from compressed insulation? Tests by the National Physical Laboratory on the market-leading mineral wool insulation found:

  • Compression from 270mm to 100mm (4” joist height) results in a reduction of the thermal resistance of 50%
  • Compression from 270mm to 75mm (3” joist height) results in a reduction of the thermal resistance of 61%.

Add this up over the whole UK and this is a massive in-use reduction, equivalent to switching on one whole power station. After millions of pounds of CERT and CESP funding for insulation over the past few years, this is depressing reading.

What Are the Alternatives to Loft Insulation?

Historically, one way to protect the insulation is to raise the joist with extra timber. The materials for this are relatively cheap, but the labour is not, and the timber places significant extra weight on the joists.

Another historical approach is to lay rigid foam insulation, with boards placed, or bonded, above these. But fitting these in a loft is not easy; large insulation boards can be difficult to get into the loft, they have to be cut to size in the loft and gaps between them, and the (often irregular) joists need to be carefully sealed. It is also preferable to leave space for a flow of air between the top of the insulation and the underside of the boards, to allow moist air to be removed and stop any risk of condensation, which may require extra timber in addition to the boards.

More recently, a suite of raised loft decking products have come to market, which all consist of supports or a supporting structure that lifts the boards up above the insulation by between 180-280mm. Some of these are strong enough to walk upon, whilst others are more for storage; some allow for an air-gap between the insulation and the boards whilst others do not; some also allow for cables and other services to be raised above the insulation too, whilst others do not.

They are typically sold by LoftZone, B&Q and Wickes, and some builders merchants. Increasingly they are being specified as standard by architects for new build and retrofit, conscious that without them, the insulation is going to be working well below par.


So, in summary, when designing energy efficiency programmes, it’s necessary to quite simply assume significant in-use reduction factors for loft insulation unless mitigating measures have been put in place.

Most of the UK’s loft insulation simply isn’t working as well as promised, and many people refuse it in the first place as they value access and storage more highly.

You wouldn’t specify external wall insulation on a building and then not insist upon render on the outside to protect it from damage.

So why would you not protect loft insulation from damage, too?

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Dave Raval is CEO of LoftZone, which has brought to market a raised loft deck for safe access and/or storage purposes for both domestic and non-domestic properties.

Check out their website, Facebook, Twitter and YouTube channels, or download their product information from SpecifiedBy.


SpecifiedBy Editor