Roof terraces and balconies are clever ways of utilising existing footprints to create private spaces that interact well with outside. Whether taking advantage of an existing flat roof or building a new home or extension, the key is to find a design which gives you the right balance of aesthetics, accessibility and thermal performance.
As with any other building work, the specific thermal performance requirements for roof terraces vary depending on which home nation your property is located in and whether you are refurbishing, extending or building from scratch. In most cases though, a U value of 0.11W/m2K provides a good starting point for a compliant and well-insulated roof.
Where to Insulate — A Stumbling Block
So far, so good. However, while insulating a flat roof to this level is relatively straightforward (providing you use the right materials), roof terraces provide additional access considerations. These considerations make the process of insulating a balcony or terrace more challenging as, even with premium performance insulation, achieving a compliant U value requires a substantial insulation thickness to be fitted.
The obvious way to make space for this thickness is to raise the floor level of the terrace or balcony above that of the floor level of the internal rooms. This can result in a somewhat clumsy (and hazardous) step between the internal and external spaces.
The alternative route of insulating underneath the roof or balcony deck will often mean lowering the ceiling height in the room below. This loss of headroom can make rooms feel much more constricted, as well as creating unsightly discrepancies in room height.
Insulating below the deck also does not adequately solve the issue as, unless a thicker layer of insulation is also applied above, it can lead to problems of interstitial condensation (which happens when a material is warm on one side and cold on the other, causing moisture to be deposited in liquid form within the material).
Vacuum Insulation Panels
One solution which has become increasingly popular on the Continent, particularly in Germany, Switzerland and Scandinavia, is to install an insulation system incorporating vacuum insulation panels (VIPs). VIPs are particularly well suited for applications where construction depth or space is critical. The minimal thickness of the insulation allows consistency of ceiling height and avoids the necessity of a step between the terrace and the adjacent room.
With an aged (in service) thermal conductivity as low as 0.007W/m2K, VIPs can offer optimum thermal performance, at a fraction of the thickness required for other commonly available insulation materials. This can ensure that balcony or terrace build-up thicknesses remain manageable from both a design and an accessibility point of view.
VIPs systems typically consist of vacuum panels with high-performance insulation infill strips of a matching thickness. These infill strips are usually fitted on the outer edge of the balcony or terrace as they can be cut to fit any irregular spaces or penetrations. VIPs manufacturers can supply a layout beforehand, demonstrating where all of the VIPs panels and infill strips should be placed — therefore maximising the ratio of VIPs to infill strips and keeping the required system thickness to a minimum.
To limit thermal bridging, a 25mm thickness of high-performance insulation should be fitted on the inner face of parapets and rooflight kerbs. A further thin layer of insulation can then be overlaid on the system to receive the waterproof membrane. As with any flat roof, it is important to maintain adequate drainage and by fitting a tapered layer of insulation above the VIPs system, this requirement can easily be met.
Kingspan: 01544 387384
Adrian is Head of Marketing and Product Development at Kingspan Insulation and is one of the UK’s leading experts on insulation