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Advice on Bituminous Flat Roofing, Underslating, and Shingles

Installation of flat roofs has undergone significant advancements in recent years, resulting in improved durability and maintenance. Modern bitumen felt membranes now boast a lifespan of up to 20 years, showcasing their high-performance capabilities. The introduction of superior felts with innovative application techniques, such as torch-on and self-adhesive methods, has revolutionized traditional bituminous flat roofing practices, which relied on the laborious “pour and roll” approach involving heating bitumen to extreme temperatures exceeding 200ºC.

Compared to traditional fiber-based felts, these cutting-edge felts are less prone to rapid aging, brittleness, and damage caused by weathering. While temporary repairs can prolong a roof’s lifespan to some extent, a complete re-covering is ultimately the most effective long-term solution.

Contemporary roofing felts are commonly referred to as “bituminous reinforced membranes.” Although they may visually resemble their predecessors, their performance and material composition have undergone remarkable improvements, significantly enhancing resistance to aging and weathering. These advancements ensure that roofing felts meet customer expectations and align with Building Regulations.

Among the latest breakthroughs in roofing felts is the advent of high-performance “cold applied” self-adhesive systems like Wickes Easy Seal. These systems eliminate the need for hot bitumen, gas torches, or liquid roofing adhesive, simplifying the installation process.

The purpose of this guide is to acquaint you with the wide range of roofing materials and application methods currently available. It aims to provide advice on common issues and offer guidance on flat roofing systems, empowering you to make informed choices. With these resources at your disposal, you can confidently utilize our products safely, efficiently, and cost-effectively.

Roof Design and Good Practice

It is recommended to conduct inspections of flat roofs every six months, ideally during the Spring and Autumn seasons. Before stepping onto the roof, ensure that it is safe to do so. It is important to have someone reliable present either as a lookout or to periodically check on your well-being.

During the inspection, pay attention to various components such as outlets, projections, gutters, rooflights, and flashing. If you notice any displaced surface chippings, gently sweep them back into their proper position.

In Autumn, take the time to verify that fallen leaves have not obstructed the gutters and outlets, as this can lead to water ponding. Avoid flushing any debris down the outlets.

During Spring, it is crucial to examine the pointing for signs of frost damage, which can result in moisture infiltration into the roof structure.

Before ascending to the roof, inspect the area from below and from overlooking windows for indications of sagging, leaks, condensation, or decay. If the roof decking is visible from below, test its integrity by applying pressure from underneath using a blunt pole. Decks made of chipboard, particleboard, wood fiber, or wood wool are especially susceptible to decay. Even if a roof has not exhibited any leaks, certain types of decking (such as specific grades of chipboard) may have been significantly affected by condensation, making them unstable and fragile. It is possible to fall through a weakened roof structure and sustain injuries. If you are uncertain, seek expert advice before accessing your roof.

Do’s and Don’ts

  • Take immediate action to address any detected leaks.
  • Consult the original specifications to determine the composition of the roof.
  • Consider timely repairs instead of incurring expensive replacements in the future.
  • Prior to and after any work carried out on or in the vicinity of the flat roof, conduct thorough inspections. This way, any damage caused by others can be easily identified.
  • Avoid using the roof as a working platform for adjacent buildings.
  • When access is necessary, ensure that the waterproofing membrane is adequately protected to prevent damage.
  • Seek proper advice before allowing anyone to install units through the waterproofing membrane, particularly when installing television aerials, satellite dishes, or telephone cables.
  • Refrain from dropping cement, paint, or solvents on the roof, as these substances can harm the surface.

Leaking Roofs

If you discover a leak, don’t panic. There are various roof repair products available that can provide a temporary solution, allowing you to plan for a more convenient time to address the issue. However, it’s essential not to ignore the leak, regardless of its size, as it can worsen rapidly.

  • Decide whether to hire a professional, tackle the job yourself, or seek assistance from a friend.
  • Plan and estimate the cost of the repair.
  • Create a shopping list of necessary materials.
  • Assess if the deck needs replacement.
  • If it’s a new flat roof on a habitable building, contacting your local building control office may be necessary.
  • Avoid taking shortcuts, as this can lead to increased time, effort, and expenses later on.
  • Focus on doing the job correctly from the start, using proper preparation and quality materials for long-lasting results.

Choosing the Right Roofing System

There are various options for roof coverings, ranging from traditional bitumen-based felts to modern, technologically advanced, and easy-to-use self-adhesive coverings. A recommended solution is the cold lay method using a self-adhesive product like ‘Easy Seal.’

Important Considerations

When re-covering a roof, it’s crucial to remove all old felt and thoroughly inspect the underlying surface. If the roofing felt has been defective for a while, there’s a possibility of damage and rot. Any damaged timber or boarding, including fascia timbers, angle fillets, drip battening, decking, and occasionally supporting joists, should be replaced. It’s a costly mistake to install new roofing over an imperfect surface.

Building Regulations

It’s important to be aware of the existing Building Regulations related to the design and construction of flat roof structures. For new constructions and some re-roofing projects, consulting with your local council’s Building Control office may be necessary to ensure compliance with regulations. Refer to Part L1 and L2 for information on current insulation requirements.

Design Considerations

Flat roofs always have a structural roof deck that supports the waterproofing. Typically, this is a timber boarding supported by joists. Except for garages, most roofs above habitable parts of a house require insulation. The common method is to place insulation immediately above the ceiling, known as a cold roof. Proper through-ventilation is crucial to prevent condensation during cold weather (refer to BS 6229:2003). Alternatively, insulation can be placed above the roof deck in a warm roof design (Fig. 2). If using the preferred Easy Seal System, ensure the insulation used is a urethane/plywood composite board with the plywood face on the top surface.


Roofing Deck Materials

When constructing or strengthening a flat roof deck, it is essential to choose the appropriate materials. Here are some commonly used types:

Plywood Roofing Deck (Recommended)

  • Opt for exterior grade type WBP plywood, adhering to BS 6566: Part 8: 1995.
  • A minimum thickness of 18mm is recommended.

OSB 3 Bituminised & Conditioned Roofing Decking

  • Oriented Strand Board (OSB) should have a minimum thickness of 18mm.
  • Ensure it is manufactured in accordance with BS EN 300: Part 3: 1992.

Timber Roof Boarding

If the existing deck consists of close boarded tongued and grooved timber with a minimum thickness of 18mm, it is advisable to use exterior grade WBP 6mm plywood as an overlay. This creates a smooth surface for bonding with the Easy Seal System. In case of damage, replacing a few boards may be sufficient, provided they are easily replaceable. The 6mm plywood overlay is still required.

Extensive damage to the timber decking might necessitate the removal of all close boarded timber and replacement with 18mm plywood.

Note: If any rot is discovered or suspected, the affected timber must be removed, and surrounding wood should be treated before fixing new timber or decking.

Chipboard Roofing Decks

Although chipboard is frequently used for garden buildings and some garages, it is generally unsuitable for habitable building roofs and roofs with ceilings. If chipboard is to be used, ensure it is a moisture-resistant P5 grade.

Concrete Roofing

Concrete is commonly found in roofs of flats and pre-war houses, providing stability and reliability as a deck material. When repairing concrete decks, allow for proper drying before applying any priming or waterproofing covering.


Essential Considerations for a Flat Roof

To ensure a successful flat roof construction, it is important to take into account various factors. Here are some key considerations:

Protection from Rain & Snow

  • The roof should have a slope of at least 1 in 80 for proper drainage.
  • It is advisable to design the deck with a 1 in 40 fall to be on the safe side.
  • Drain the roof towards one or two edges.
  • Conventional eaves gutters are preferred over internal outlets.
  • Adequately size internal outlets to handle storm conditions and equip them with clamping rings, leaf and gravel guards.
  • Extend the waterproofing up adjacent walls by at least 150mm from the roof surface and protect the top edge of the felt with a cover flashing.

Protection from Sun and Frost

  • Insulation is beneficial for reducing heating bills in winter and keeping rooms cooler in summer.
  • Ensure that insulation of new flat roofs complies with Building Regulations, Part L1 and L2.

Protection from Condensation

  • Cold roofs require sufficient through ventilation in the void space.
  • All insulated roofs need a vapor control layer.

Protection from the Wind

  • Construct roofs to withstand wind forces.
  • Seek additional advice from the local Building Control Office for buildings in exposed locations or areas prone to extreme weather.

Protection from People

  • Take precautions to protect the roof surface and support the structure when people need to walk or work on the roof.
  • Consider strengthening the structure if the roof’s use is changed.

Weather and Temperature

  • Check the weather forecast before starting the roofing job and aim for dry conditions and warm temperatures.
  • Do not remove existing roof coverings until weather conditions are confirmed and all materials are assembled and checked.

Make Good and Mend

  • Inspect the condition of the existing roof structure and deck before starting the roofing project.
  • Make necessary structural repairs and ensure the roof surface is obstruction-free, smooth, clean, and dry.

The Right Sequence

  • Plan the sequence of the roofing job to ensure the availability of the right materials at the right time.
  • Read the instructions thoroughly to understand the recommended sequence for using the materials.

Safe Working Practices

  • Follow safety guidelines when working at heights.
  • Erect a safety guardrail around the roof perimeter and secure ladders to prevent slipping.
  • Seek professional advice or consult the Health and Safety Executive (HSE) for further information on working safely at heights.

Working at heights – Key Facts

  • Approximately 4,000 people suffer serious injuries and 50 are killed annually due to falls from height.
  • Falls are the leading cause of fatalities in the workplace.
  • 60% of major injuries are caused by falls below 2 meters.
  • Nearly a quarter of fatalities and major injuries result from falls from ladders.

The Working at Height Regulations (WAHR) aim to reduce accidents associated with working at heights. The regulations focus on avoiding working at height when possible, using appropriate equipment to prevent falls, and reducing the consequences of falls through fall arrest systems.

Employers, employees, and self-employed individuals involved in working at heights are affected by these regulations.


Wickes have put a helpful PDF guide together here…

Wickes Flat Roofing Guide