Fabric First and Tapered Roofing

Time to put fabric first

‘Fabric first' means exactly what it suggests: first and foremost concentrating on getting a building's fabric right. It means achieving healthy, comfortable, high quality buildings that perform on site as well as complying with regulations on paper.

Designing and constructing thermally efficient building elements that consistently give their intended level of performance is vital to reducing heat loss, energy consumption and carbon emissions. And, of course, cutting energy bills!

Some consumers are becoming wiser and asking for more efficient buildings. Some, though, want to continue living how they want, when they want. That means we need to keep things simple, with minimal input from occupants. Fabric first is essential to a ‘fit and forget’ philosophy that building users will appreciate without even realising it.

Maintenance-free energy efficiency is built in to the building fabric for the life of the building.

It removes the need for what some term as ‘eco-bling’ – complicated renewable technology that can be expensive, difficult to operate or maintain, less efficient than claimed, or have a service life shorter than the building's lifespan. By contrast, once good building fabric has been constructed there is no need to worry about it. Fabric first can therefore be employed on projects of any size, from the largest public building to the smallest domestic extension.

Case studies exist of houses with an annual heating bill of £50, or a school that saved the equivalent of a headteacher's salary from its energy costs. But while it helps to safeguard the Earth's future, fabric first does not have to metaphorically cost the Earth. Some aspects cost more, some cost less; getting the balance right is the key. By focussing on the available budget, the required standard can be met.

Fabric first in flat roofing

For buildings where height restrictions are not an issue, a warm flat roof often presents the most straightforward means of achieving increased thermal performance. It’s not uncommon for projects to require a U-value of 0.10 W/m2K or better, meaning a rigid insulation thickness in excess of 220mm.

With a simple construction comprising structural deck, vapour control layer, insulation and waterproofing finish, a warm flat roof lends itself to the fabric first concept. Running services below the structural deck ensures that the vapour control layer and insulation are untouched once installed, ensuring continuity of the layers and reliable performance.

Insulation manufacturers can advise on the theoretical performance of building elements that feature their products, but usually have little control over how those products are used on site. That is where the waterproofing membrane manufacturers come in, offering training for site operatives to ensure correct installation of warrantied systems.

Some projects, however, are larger and more complex, or require a solution that will reduce the installation time; a tapered insulation scheme allows manufacturer involvement from an early stage.

Single layer tapered insulation

Tapered insulation creates the necessary falls on a flat roof, instead of traditional solutions like a screed or timber firrings. Specially prepared versions of flat roofing insulation boards are supplied for new and refurbishment projects, offering a quality-assured process that provides the required levels of thermal performance, and reliable drainage too.

New buildings simply require the architect-drawn plans, while existing roofs are surveyed in detail to establish the position of rainwater outlets and other features that will influence the design. Insulation boards can be adapted on site, but the project will run more smoothly if issues are identified and addressed in advance.

An experienced design team draws up a scheme taking into account required U-values and establishing the pattern of drainage across the entire roof. From the completed scheme drawing, a list of components is produced ready for factory production. Where substantial thicknesses of insulation are required, thinner boards are bonded in the factory to produce a single layer for on-site installation.

The component pieces are marked and labelled before delivery to site, where the roof effectively becomes a jigsaw puzzle – but one where the solution is provided! Off-site manufacture is quicker and more accurate: the ‘single layer’ concept saves time and reduces the margin for error, while bespoke mitres, fillets and deflector boards help to achieve faster installation and – crucially – better continuity of the insulation layer.

Even with the best will in the world, sites find a way to throw up a problem or two. Good tapered insulation manufacturers provide support throughout a project, being available to advise clients, architects or contractors as required. The manufacturer becomes a member of the design team, and their surveyors can provide guidance on different deck types, installation techniques and waterproofing finishes.


Producing genuine performance improvements, whether in flat roofing or other areas of construction, means communication is vital. That might be through educating clients, designers and specifiers in the benefits of a fabric first approach, or ensuring that contractors are trained for and understand the expected quality of work.

Insulation has the biggest role to play in improving the thermal performance of buildings, but fabric first is about achieving continuous insulation, minimal thermal bridging and high levels of airtightness in combination. Addressing these aspects of construction means Building Regulation targets can be met and designed performance levels translated to the finished building.