Flat Roof Types
There are three traditional flat roof system build ups: Warm roof, Inverted roof and Cold roof. A warm roof is the most common flat roof used in the UK because of the inclusion of insulation which is installed above the waterproofing encapsulating this within the system, and also an Air and Vapour Control Layer (AVCL). Although the most common, it is still important to understand the purpose of the roof area from a manufacturers perspective to ensure the most suitable system is specified.
What is a warm roof?
Warm roofs can be very effective for energy reduction and building performance. However, the thermal insulation type and thickness is critical. We carry out thermal and condensation risk analysis for every project. Furthermore, a bespoke designed system eliminates any performance and design issues.
In a warm roof construction, the Sika waterproofing system and Sikatherm insulation is installed above the structural deck. This keeps the structural deck, any voids, and the ceiling at approximately the same temperature as the building’s interior. An air and vapour control layer (AVCL) is required below the insulation to prevent interstitial condensation from occurring. The amount of insulation should be enough to maintain the AVCL above dew point temperature. Warm roof voids are not ventilated. Condensation can be calculated to BS 6229 and BS 5250.
Is a warm roof appropriate for your project?
- Most thermally efficient method of insulating a flat roof
- Protected insulation due to positiong within the waterproofing system
- Thinnest roof build up
- Most common roof build up in the UK
- Can be used with a variety of different insulation materials
What is an inverted warm roof?
In an inverted roof construction the Sika membrane is installed directly on the structural deck and the Sikatherm insulation is installed on top of the waterproofing membrane. A high performance, non-woven polyethylene WFRL (Water Flow Reducing Layer) membrane is installed over the insulation to minimise the ‘cooling effect’ associated with rainwater flowing down through the insulation and draining away, reducing the insulations’ thermal performance. It is critical the WFRL layer is installed correctly, as this significantly reduces the insulation thickness required for a given U-Value. An air and vapour control layer is not required.
This type of roof is generally used where there is going to be a requirement for paving (or another surface finish) for use as a roof terrace or balcony area. A minimum ballast weight of 80kgs/m² is normally required in order to resist wind uplift forces and adequately secure the loose laid insulation. The ballast requirement may increase in some locations, depending on the specific type of building, exposure/location and surface finish.
Is an inverted roof appropriate for your project?
- Life expectancy of inverted roofs is oftern substantial, meaning they may never need to be replaced
- The waterproofing is protected by other layers above (i.e. ballast, insulation), meaning it is far less susceptible to mechanical dmanage
- Can be a cost effective solution for larger roof areas
- Ideal solution for trafficable areas
What is a cold roof?
In cold roof construction, the waterproofing is installed directly to the structural deck. Sometimes designers prefer to install the insulation beneath the structural deck, however to achieve this there must be an adequate air void between the deck and the insulation below to allow free movement of air, and to prevent water vapour being transmitted from the building outwards where it could condense in the roof construction, causing harmful interstitial and/or surface condensation. A suitable breather membrane is required under the thermal insulation and needs to be continuously sealed. Even though a cold roof construction can be specified where appropriate for the building, the British Standard 6229:2018 states that a cold roof is not recommended due to the high risk of condensation.
Is a cold roof appropriate for your project?
- If Sika have provided a condensation risk analysis to confirm system suitability
- If no other method of thermal design is suitable
- If no insulation is required e.g. bin store/outhouse
Roofing Specialist Application Systems
What is a green roof?
A green roof is a system that provides numerous benefits to the environment of which it is installed including improving the overall thermal performance of the building itself. However a green roof does not watertight the building, for every green roof there still requires a waterproofing system beneath it.
All of Sika's roof waterproofing technologies, hot melt structural waterproofing, reinforced bituminous membranes, single ply and liquid applied waterproofing systems are all compatible with Sika's green roof systems.
What is Solar Photovoltaic?
A roof was once seen only as a means of protecting a building from the elements. But now through the introduction of insulation to increase thermal efficiency, followed by the ability to generate renewable energy from the roof space, it has become a valuable resource for building owners. By using solar photovoltaic (PV) panels on your building you can generate a yearly income that could pay off the initial cost of completing the roof work and installation, and in subsequent years will give you a return on your investment.
The use of solar PV panels also results in lower roof surface temperatures, which can have many benefits such as reduced internal heat gain in summer and can lead to lower air conditioning costs, reduction of the Urban Heat Island Effect (UHIE) and improved performance of photovoltaic panels. All the roofing systems we offer can accommodate the addition of crystalline panels secured on a frame that may be weighed down with ballast or fixed to the deck.
What is a blue roof?
Blue roofs are flat roofs designed to provide temporary storage and controlled release of rainwater during storms as part of a Sustainable Urban Drainage Systems (SuDS) good practice policy. Rainwater is released at a managed and controlled rate directly into sewer waterways and river systems.
Green spaces incorporated onto blue roofs can be irrigated using the free storm water to create a multifunctional area that building occupants can use.
A blue roof can be created at roof or podium level or by combining both in a cascade design above the waterproofing membrane in a warm roof application, or above the water flow reducing layer (WFRL) in an inverted application.