Tapered insulation systems deliver both insulation and a fall for drainage in a single solution, helping to prevent water ponding and support improved building energy performance. They can offer a range of clear benefits over alternative methods of creating a fall on flat roofs, providing a lightweight solution which is fast and easy to install, can be fitted on both new and existing roofs and can reduce maintenance needs whilst extending the lifespan of the roof.
In this article, we’ll look at why tapered insulation might be the right choice for your flat roof project including:
- when to use tapered insulation;
- the benefits of tapered insulation; and
- what is the thinnest type of tapered insulation.
What is tapered insulation?
Tapered insulation boards are wedge-shaped. These angled boards can be used to create the fall needed which allows water to drain effectively. In our Thermataper system, these boards are manufactured from rigid polyisocyanurate (PIR) insulation.
In addition to the tapered boards, our Thermataper systems also include flat packer boards. These are typically 80 or 120 mm thick and are laid below the tapered boards. As shown below, this creates the necessary height difference in the tapered boards to achieve the desired fall. They can also be used to increase the thickness of the insulation layer where this is needed to achieve the project U-value. This combination of tapered and packer boards can be seen in the diagram below. Pre-mitred hip and valley boards are also used for areas such as internal or external roof corners.
Learn more about our Thermataper range of tapered roof insulation
We also provide a tapered roofing design service to ensure our Thermataper systems provide a sufficient finished fall of at least 1:80 in accordance with BS 6229:2018 – Flat roofs with continuously supported coverings. Code of practice. Our design team can either use existing roof plans, or organise a survey of the roof to develop a system layout (shown below) which provides the most cost-effective solution for your requirements.
Why use tapered insulation?
Virtually all flat roofs need to be laid to a fall to prevent rainwater from ponding on the roof deck. Guidance set out in BS 6229:2018 states flat roofs should have a finished fall of at least 1:80 including internal guttering.
Where an insufficient fall is provided, or other drainage issues are present, water can accumulate (pond) on the roof deck.
Where ponding occurs, it can:
- Lead to algae and mould growth – creating a potential slip hazards/ health & safety issue;
- Cause deterioration of the roofing membrane and leaks;
- Contribute to thermal stress on the water proofing system; and
- Cause structural damage to, or progressive deflection of, the roof deck.
These issues can significantly reduce the lifespan of the roof, leading to costly remedial work.
At the same time, roofs need to be insulated to achieve increasingly ambitious U-values. This can require substantive thicknesses of insulation to be laid both on new flat roofs, or as part of refurbishment projects.
Tapered roof insulation systems can help to deliver on both of these requirements.
What are the benefits of tapered roof insulation?
Tapered roof insulation systems offer a number of benefits:
- Lightweight – our Thermataper systems use lightweight rigid insulation boards. This limits any structural load placed on the roof deck, making them suitable for refurbishment applications.
- Accurate performance – as the systems are designed bespoke to your project, you can have confidence that the final system will deliver both the required fall and insulation performance.
- Fast installation – the insulation boards can be laid with a dry installation process following the clear layout provided by our design service. This can allow rapid installation on all sizes of roofs.
- Reduced waste – a number of our tapered roofing systems are available single picked, pre-mitred and pre-bonded to reduce on site waste.
- Compatible with range of coverings and fixing systems – the range of products in our Thermataper range cover can both mechanical and fully adhered applications and are compatible with all commonly used waterproofing systems and most green roof systems.
How do I order a tapered roofing system?
You can request a tapered roofing design from our tapered roofing service page.
As part of the enquiry form you will be prompted to provide a range of information including the project address, scheme type and U-value targets. Based on this, the tapered roofing team will develop an initial quote and design to meet your specific requirements.
Our UK wide team of tapered roofing surveyors and area technical managers are also available to carry out on-site tapered surveys for new or existing roofs. All of the team have completed CITB Rooftop Safety Training and are on hand to provide any project assistance. Based on this information, the final tapered design will be developed and submitted for approval. Once agreed, this will be supplied along with the insulation system for installation by the roofing contractor.
Once works are complete, our team can also carry out final phase checks to ensure the system is performing as expected.
Can tapered insulation be fitted above the existing waterproofing system?
Yes, in some cases. To fit insulation on an existing build up, it will have to be determined if the existing roof area is acceptable to overlay. This will be dependent on the installing contractor carrying out core samples and moisture tests and considering the weight load of the existing waterproofing. The risk of interstitial condensation within the construction will also need to be assessed based on the building use as this will impact the humidity class. This will be carried out by our design service team.
Are tapered insulation systems expensive?
As our tapered insulation systems need to be designed and cut specifically for each application, the upfront cost will typically be higher than for a project where screed or timber firrings are used to create the fall and flat roof insulation is laid separately. However, tapered insulation systems can provide significant programme savings, removing the need for project teams to design and create their own structural fall. The light weight of the boards can also avoid the need for additional structural support of the roof deck in refurbishment applications.
We also offer a range of flat roof insulation boards where this approach is preferred.
Discover our range of flat roof insulation.
What is the thinnest tapered insulation system?
All tapered roof insulation systems fitted on new and existing roofs must meet certain U-values set out in the Building Regulations and supported with the guidance in BS 6229:2018. The specific U-value will depend on the building and work type. In almost all cases, no single point of a tapered insulation system should achieve a U-value worse than 0.35 W/m2K and the area weighted U-value will typically need to be much lower than this.
Learn more about the energy targets in the Building Regulations
Our standard Thermataper systems use PIR insulation which offers a high level of thermal performance. This can typically allow the desired U-value to be met with a thinner overall system thickness than lower performing alternatives such as EPS and rock mineral fibre.
Where a project team is looking to achieve especially ambitious U-values, we can provide our Thermataper TT44-K and Thermataper TT47-K systems. These use a premium performance Kooltherm phenolic insulation packer board which can help to reduce the overall system thickness when compared with the standard PIR Thermataper systems.
In certain problem applications, however, a very thin construction may be needed. This typically occurs where the height of parapets is set or where an even transition is needed between internal and external spaces on a roof terrace. In these cases, we can provide a design using our Thermataper TT44-O and TT47-O systems. This features our OPTIM-R vacuum insulation panel (VIP) packer board which can provide optimal thermal performance, allowing for a very thin construction.
Learn more about OPTIM-R Vacuum Insulation Panels
On site training and support
Build your team’s knowledge with onsite training and support from one of our Product Technicians. The presentations cover the full range of Kingspan Insulation products and applications from flooring to roofing and everything in-between with both internal and external wall insulations.
