Creating a Sound Roof
Ahead of the launch of a new webinar series, Simon Downe, an area business manager with IKO Group Plc, compares the performance of mastic asphalt against cementitious screeds used in roofing applications.
When installing a flat roofing system on either a new build or refurbishment project, contractors must ensure a sound, solid substrate is created prior to applying the chosen waterproofing system.
In many new build and refurbishment projects, mastic asphalt is often a preferred option to traditional cementitious screeds, as it offers advantages both at design stage and during installation, and creates a solid foundation for any subsequent roof build-up.
Mastic Asphalt Considerations
There are a number of key considerations to make prior to applying the chosen waterproofing system on the roof, and although it may seem like a small detail within the overall project, the correct specification of mastic asphalt screed can be vital to the success and durability of the roof.
Traditional cement screeds have been used for many years, yet, mastic asphalt alternatives have many advantages which are becoming increasingly appealing to specifiers and contractors alike.
Alongside its quick and easy application, mastic asphalt is a flame free application, which is advantageous in many settings, particularly on occupied refurbishment projects.
The versatile qualities of mastic asphalt means it can be used in both refurbishment and new build projects, and can create the perfect substrate for warm roofs, cold or inverted roof build-ups. Almost any waterproofing solution can be laid on top of mastic asphalt, which can be used to provide drainage falls or level out an uneven deck before the next element of the roof is installed.
Mastic asphalt is seamless and quick curing. Only a handful of manufacturers’ products, including IKO Permascreed, can be trafficked within hours after application - meaning contractors can continue the roof build-up the same or next day, limiting any delays on site.
The growing need to create zero carbon buildings combined with BREEAM requirements, a preference for local and responsible sourcing of labour and materials. and the Considerate Constructors Scheme, mean it is increasingly important to establish greener approaches to construction.
This is why mastic asphalt is often the preferred choice for specifiers and building owners because the UK mastic asphalt is the first industry in the world to achieve the CarbonZero™ standard. IKO, for example, has been offsetting the carbon footprint of mastic asphalt projects for more than a decade, using internationally approved carbon credits.
Prior to applying mastic asphalt screeds, very little preparation is required, the roof just needs to be swept clean and surface dried.
Mastic asphalt screeds can provide a temporary waterproofing solution for the roof prior to applying the specified waterproofing system, meaning that the building can be in the dry without undue delays. Consideration just needs to be given to detailing items such as rainwater outlets, abutments and penetrations.
Working during the winter months can present its own challenges, and can potentially affect application and drying times of cementitious screeds.
Because mastic asphalt screed is hot applied and simply just needs to cool before it can be trafficked, in most circumstances, it will be cool and ready to use within an hour of application, compared to days if not weeks with traditional cementitious screeds – especially during winter months when drying out times will be extended because of the inclement weather.
Mastic asphalt screed solutions are sometimes referred to as a ‘fit and forget’ solution, as it is quick cooling and can be covered almost straight away. Because cementitious screeds are more porous than mastic asphalt, it can cause issues during the drying period if wet weather is predicted. On some occasions, contractors have erected tarpaulins on site to try and keep the cementitious screed as dry as possible, which as a result, creates further costs and project extensions.
The minimum thickness of a mastic asphalt solution is also less than a cementitious screed, typically 10 mm compared to 60 or 70 mm meaning weight savings and less product to get to site. Mastic asphalt can arrive on site hot in purpose built hot charge tankers capable of holding up to 18tonnes of material, or contractors can prefer to re-melt blocks on site.
With cementitious screeds, best practice would also require a site visit to ensure there is five per cent or less moisture content within the screed prior to the waterproofing layer being applied, especially during wetter, winter months. This causes time delays and extra cost, which is eradicated with mastic asphalt as once it has cooled sufficiently, contractors will be safe in the knowledge it will provide an excellent bond.
Project Spotlight: Barking Riverside
Situated between the A13 and the river Thames within the Borough of Barking and Dagenham, Barking Riverside is one of the largest new mixed-use urban developments in the country.
A joint venture agreement between Bellway Homes and the Homes and Communities Agency, the 443-acre development has created 10,800 new mixed tenure homes together with community facilities, new schools, and access to two kilometres of the Thames River frontage.
Bellway Homes was looking for a solution to help smooth-out the undulations in the structural roof decks on a number of three and four-bed houses with flat roofs, where precast concrete planks had been specified.
Although the planks were installed within the manufacturers’ tolerances, the step level between individual units was deemed unsuitable to receive the specified hot melt waterproofing system.
It was critical that the developer did not fall behind on the construction schedule and so a fast track solution to the problem was essential. A traditional concrete screed layer wasn’t suitable for this project, as the weight of it would impact the foundation design, and would take too long to cure.
Therefore, IKO Permascreed mastic asphalt solution was specified because of its quick application and drying qualities, meaning delays on site were kept to a minimum. Once cured, the IKO Permascreed layer was robust enough to accept the traffic and concentrated loads associated with the installation of a flat roof waterproofing system.
A total of 8,000 sq. m of IKO Permascreed was laid on the Barking Riverside project at a thickness of 40mm, a reduction of 33 per cent when compared with traditional screeds as the overall weight of the finished roof needed to be considered.
This fast curing solution provided the developer with a level surface, and enabled them to keep the construction programme on schedule. The finished roof, including the IKO Permatec solution also provided a 20-year guarantee.
Why We Can’t Overlook the Screed Layer
Mastic asphalt solutions, like the IKO Permascreed offered by IKO Plc, is sometimes referred to as ‘just a screed’ which enables work to continue on a roof.
There is truth in this, yet, choosing the right screed is paramount to the overall success of the project’s waterproofing, and needs to form a sound foundation for subsequent materials.
Specifying mastic asphalt is an opportunity for the roofing contractor to control the destiny of that roof and how quickly they can continue to waterproof it for the benefit of the end client, and themselves.
Sign up for the webinars at IKO Permascreed: Bituminous Screed - Levelling and Falls Solution Tickets, Multiple Dates | Eventbrite.