Knauf Insulation on zero carbon homes

Stephen Wise, market development manager at Knauf Insulation, looks at how Gordon Brown's plans for zero carbon homes will affect the construction industry.

Stephen Wise, market development manager at Knauf Insulation, looks at Gordon Brown's pre-budget speech and how his plans for zero carbon homes will affect the construction industry.

As you are aware, the Chancellor proposed that all new homes should be zero carbon by 2016 in his pre-budget statement in December.

This ambitious target reconfirms the Government's strong commitment to tackling climate change, a step that is welcomed by Knauf Insulation - the UK's leading manufacturer of glass and rock mineral wool, extruded polystyrene (XPS) and extruded polyethylene (XPE) insulation.

But what are the implications on the building and construction industry and how are we going to meet these targets? Most people recognise that we have to act now to fight the effects of global warming, but how do we go about achieving the results?.

The Chancellor's announcement is a real challenge for the industry, and associated product manufacturers such as Knauf Insulation - but a very achievable one, providing the right action is taken, which has been proven through the Promotion of European Passive Houses (PEP) document produced in 2006.

The document recognises that to be able to achieve a zero carbon home, we need to drastically reduce the U-value of a building with roofs, floors and walls all achieving U-values of 0.15 or below - drastically lower than the levels outlined in the revised Building Regulations released in 2006.

So, how can these new targets be achieved?.

The starting point has to be high levels of fabric insulation to minimise the space heating requirement.

The roof has to both contribute towards the minimisation of fabric heat loss, and is also likely to be the location for the energy generation technologies such as Photovoltaic Cells and Solar Water Heating.

The insulation specifications required to achieve these U-values in certain types of roof, are already familiar, however other roof types require significantly higher levels of insulation that has hitherto been common.

Pitched Roof Cold Attic.

A U-value of 0.15 W/m2K in a cold attic can be achieved by simply installing two layers of Mineral Wool such as Crown Loft Roll 44 between (100mm) and over (200mm) the ceiling joists.

In fact, a superior performance can be easily achieved by upgrading the Mineral Wool to a product such a Crown Loft Roll 40 which, used in the same thicknesses, achieves a U-value of 0.13 W/m2K.

Of course, extra performance in a roof will only serve to reduce heat losses still further.

Pitched Warm Roof.

Achieving really low U-values in Warm Pitched Roofs (where the insulation runs in the plane of the roof) is a bit more problematic.

The popular method is to install insulation between the rafters, but thickness is restricted here and to achieve the required U-values is likely to require a two layer solution.

This can include a high performance Mineral Wool product such as Crown Rafter Roll 32 between the rafters, with a second layer of insulation either above or below them.

For instance, if 200mm Crown Rafter Roll 32 is placed between the rafters, then either 50mm Rocksilk Pitched Roof Slab (as a sarking type insulation) above the rafters, or 45.5/9.5 Polyfoam Linerboard (insulated Plasterboard) below the rafters, which will achieve 0.15 W/m2K.

Flat Roofs.

A U-value of 0.15 W/m2K in a flat roof would require a significantly greater thickness of insulation than is currently used.

For instance, using a Mineral Wool slab such a Rocksilk Krimpact Flat Roof Slab requires a thickness of 245mm, and while this depth of insulation may seem high, it is not a problem if the architect is aware of it when designing the roof details.

To keep heat loss to an absolute minimum it is also necessary to restrict heat loss through the thermal bridges that occur at junctions and openings within the structure, for instance wall roof junctions and around roof lights.

The designer will need to design and assess details to calculate the heat loss for each detail.

These methods combined with zero or low carbon energy technologies will not only help reduce emissions to meet the Chancellor's targets, but most importantly will increase the environmental payback of insulation within the modern home.

What's more, increased insulation will inevitably help to cut people's fuel bills.

Knauf Insulation has been preparing for these challenges for a long time now, and is ready to meet the inevitable increase in demand not only for insulation products, but also for expert help and advice to help fulfil these new requirements.

To this end there are a number of useful calculation tools on the website to help everyone from architects to specifiers and builders calculate how to achieve the right level of insulation in any type of building or construction - including SAP and U-values calculators.

Back to top