Full Fill for the Full Facts

By Steve Smith: Product Manager (Glass Mineral Wool) – Knauf Insulation Northern Europe

When I used to speak to people about insulation of cavity walls, I couldn’t help but leave the conversation thinking that partial fill was the most popular solution of choice. It was only after doing a little research that I found something quite opposite, and that full-fill solutions actually account for more than 85% of the market according to Construction Markets Report published last year. Now that includes insulation of existing homes where the only option may be to use injected full-fill insulation such as blown mineral wool, but even when I looked at new build in isolation, the figure was showed 55% used some form of full-fill solution. This got me looking into why there might be such a preference for full-fill.

The main reason I could see would be cost – especially in the current economic climate where every penny counts. Having looked into the SPONS Architects and Builders Price Book, and called around a few local distributors, it became apparent that some full-fill glass mineral wool solutions can provide substantial cost savings per plot when compared to partial fill solutions – as much as £535.00 per plot*, which is significant, especially when building multiple plots.

When I looked at some of the reasons given by those that actually prefer partial fill solutions, I found that some of those may not be totally accurate and that there are what you might consider ‘myths’ regarding full-fill insulation. If customers were to believe some of these myths, they could potentially be losing out on significant savings – something which could make a major difference in the current economy.

One of the main perceived benefits of a partial fill solution seemed to be a thinner product. However, there are several full-fill solutions which can achieve comparable thermal performance at a much lower price point, clearly a major factor in its favour. For example, Knauf Insulation’s Earthwool DriTherm Cavity Slab 32 Ultimate in a 100mm cavity, which is currently the most common cavity width, will provide an equivalent U-value to the best performing partial fill solution, but in a less expensive and more convenient format.

Another potential misconception is that full fill solutions cannot be used in very severe exposure zones. Even when building to NHBC standards, full-fill solutions can be used in all exposure zones – including”very severe” when render or other claddings are used.  Instead, specifiers should firstly check a product’s third party certification which may well cover the product for use in all exposure zones – there are products in the market with such certification.

All in all my research showed me that there are savings to be had in the market, savings which can make a big difference to the bottom line. Specifiers just need to be willing to look a little closer and not necessarily believe everything they are asked to believe.

* Costings based on SPONS Architects and Builders Price Book 2011. Insulation costs based on 1000m2 of product available from a national insulation distributor. Target U-value of 0.25 W/m2K.

5 thoughts on “Full Fill for the Full Facts

  1. The traditional function of a cavity wall is not to receive full insulation but to keep out the possibilty of water/dampness occuring on the interior face. Cavities and the wall ties must be kept clean as a result to also avoid dampness creeping acrross the cavities to the inner face.I would not want to accept a certificate that mantains full fill will not contribute to dampness.

    • From Dave Khan; Technical Product Manager at Knauf Insulation

      All of Knauf Insulation’s full fill mineral wool cavity wall insulation products are treated with a special additive to ensure their water repellency, and they are covered by a British Board of Agrement (BBA) Certificate in order to provide confidence to end users, architects, specifiers and building control authorities that they are fit for the purpose for which they are intended to be used.

      Before any product is awarded its BBA Certificate it is put through a very rigorous set of rain penetration tests to ensure that liquid water is not able to pass through the product and wet the inner masonry leaf, additionally, all products are tested on site, in the laboratory, and the manufacture of the product is also examined.

      • Only filling part of the cavity is a waste of money you would pay to have the insulation installed, heat loss will take the easiest path of resistance.

      • From Dave Khan; Technical Product Manager at Knauf Insulation

        Nigel, You make a very valid point, in these days of continually and ever increasing fuel costs it makes economic sense to fully fill the cavity and maximize the thermal efficiency of the wall construction. The insulation will be effective for the lifetime of the building and the installation cost will be recouped many times over by the year on year reduction in heating bills .

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