Choosing the right materials for your flat roof

Flat Roofing in Hertfordshire

Over the years, the standard of material used for flat roofing has been considerably improved. The options are now even more to choose from. The assurance of satisfaction will be guaranteed when high quality materials are used for the roofing project.

The Structural Flat Roof Deck

There are special requirements that should be met for the installation of different types of waterproofing.


The choice of Plywood should be exterior grade per British Standard (BS) 5268-2, WBP (Water & Boil Proof) to BS EN 636-2:1997. It should have a minimum thickness of 18mm. It can be used for the project once the roofing contractor confirms its suitability for the work.


The recommendations for this should be tongued and grooved, and expertly treated with a preservative. The usual practice the usual practice is that the first layer of bitumen felt is always nailed to timber boarding.


OSB has almost the same application and usefulness as the plywood, it is made from wafers of timber, rather than full sheets of veneer. The usual recommendation is that OSB/3 or OSB/4 (BS EN 300) should be used in flat roofs. Ensure that the product has been duly certified by the British Board of Agrément (BBA) before it is used for your project. Thickness: a minimum 18mm is usually recommended.


This board is not frequently used except in rare cases for residential flat roofing. The main reason it is usually avoided is because it has a low ability to absorb moisture when used for roofing. BS 7916:1998 permits its use for cases where there is no threat of condensation happening or for structures that have no ceiling.


The use of concrete is very common because it is reputably strong and durable. The maintenance is usually done by ensuring the complete removal of moisture before installing the waterproofing and insulation.


It is highly recommended that all warm roofs should have a vapor control layer installed in between the deck and the insulation. The ranges of materials that can be used for this include bitumen membrane, metal foil cored felts and loosely laid polythene.

The right methods will involve the selection of the appropriate vapor control layer that is most suitable for the insulation that will be used. It should also be able to withstand the level of humidity that is to be expected.


There is a wide range of options of insulation materials that can be used for warm roofs. The eventual choice will be made depending on the planned use of the roof. Considerations for power saving should also be made.

The most common choice of materials is:


Insulation rating:****

This is a very reliable insulator. It is commonly used by roofing contractors because of its light weight. It is available in different sizes and thickness. This should be considered for the best results. The choice should be suitable with the material that is going to be used for waterproofing according to the British Standard 4841 Part 3: 2006.


Insulation rating: ***

This is a reliable fire resistant product that comes in varying sizes and thickness. The choice to be used should be strong enough to carry the weight of people who will walk through on it.


Insulation rating: ***

In the case of this insulator, it has been reported to be very good but it will fall apart under harsh weather conditions like extreme heat. If this is the preferred choice, it should be covered with a protector like the bitumen felt. Its use should follow the provisions made by BS 3837: Part 1.

Only HD (high duty) and EHD (extra high duty) products should be used for flat roofs.


Insulation rating: ***

There are some special single boards that possess the qualities of two different materials. (E.g. Cork / Polyurethane (PUR))


Insulation rating: **

The materials to be used should come as slabs with recommended sizes of 500mm x 1000mm in the range of thickness. It can be reliably used as an insulator good for stronger bitumen membrane waterproofing. The recommended nominal density is 120kg per cubic meter.



The Reinforced Bitumen Membrane is a very common material used for flat roofs on residential buildings and other building projects. This product has undergone a lot of changes over the years. The method of application involves placing two or more layers that have been bonded with bitumen over the roof. The waterproofing material is formed from the combination of polyester covered with bitumen. The warm roof is ensured by the placement of the membrane on the insulation which is attached to the part of the building that is linked with the vapor control layer.


The process of attaching the membrane to the roof can be done in many ways.

Pour and roll: The pouring of heated bitumen over RBM will create a layer that acts as an adhesive that seals the laps.

Torching: this method involves the use of a gas torch to heat up the RBM without the addition of bitumen for bonding. This method is used for carrying out repairs and for doing minor works. Care should be taken to avoid the outbreak of a fire while the torch is being used.

Cold applied: this method will require the application of a cold adhesive over the surface of the roof. The RBM is placed in the right position and the laps are sealed by the adhesive. It is a safer method because it does not require the use of a source of heat.

Self-adhesive: There are special membranes that have been coated with adhesives and sealed with a sheet which will be peeled off before application. The exposed adhesive on the membrane will attach the membrane to the surface. A disadvantage of this method is that it will not be effective for uneven surfaces or cold surfaces.

Surface protection

Many roofs that have been built with RBM should be made inaccessible except in cases of an inspection. The following can be done

Stone chippings (12+mm): These materials should be bonded with the waterproofing using a good material other than bitumen.

Mineral finish: This is done during the initial production process. The bonded pieces to the felt come in varying colors which can be appealing to the customers.

Reflective paints: the reflective paint looks very astonishing when it has just been done. The finishing is very attractive, but unfortunately this beauty will quickly wear off with time. Customers who love this work will have to settle for frequently doing it again when it wears off.

You will get all the necessary information concerning fire protection regulations from your local authority.

For roofs that will subsequently be used for family gatherings and parties, or if the customer desires to have heavy materials like tiles and concrete slabs in their roofs, there must be adequate plans to fortify it for this purpose.

The structure of a building from the foundation up to the roof has already been fore planned by a qualified architect so the plans for the roof will already be written down on paper. There are instances where subsequent owners of the property might decide to make some changes to the pre-defined uses of the roof; the advent of this happening is enough reason to fortify the roof of every building to support an average amount of weight at the least.

Is it possible to make changes to an already existing roof in line with modern designs?

The answer to this question yes. It is possible to make any changes required but these conditions must first be considered:

  • Does the current roofing have a membrane attached to it?
  • has there been a collection of water noticed on this roof?
  • What is the status of the deck, wet or dry?
  • What are the actual reasons for this proposed change?

The life span of a roof can be remarkably prolonged if an extra layer is attached to the existing roofing

A case of a badly deteriorated roof will require an entire replacement with RBM and a new insulation for a property that will receive a good amount of heat energy.

Any case of ponding needs to be addressed by the professional contractor who will proffer the right solution to the ponding problem.

Polymer-Modified Materials

The polymer modified materials have been highly patronized by the roofing contractors because they are very durable and reliable. They are essentially polymer modified bitumen that meets the approved standards for use.

A good example is the Elastomeric felts also known as the SBS modified felts. They are perfect for properly insulated warm roofs. The following considerations should be made before these materials are used:

  • The product has a polyester core / base
  • The materials must have a certificate from the British Board of Agrément
  • The material is suitable for the bonding method.

Model Specification

Basically the specifications must meet the approved standards prescribed by the British Standard 8747 that regulates pour, roll and touch on products. Many manufacturers also indicate their approved standards before their materials are purchased and used for any project. This will guarantee the products purchased by the customer.

Caution should be exercised not to use the material close to a source of heat.


What is Single Ply?

An introduction to single ply is easy because it is very popular in the UK. It has been in use for roofing for a very long time. They are known to prevent water absorption and this is what has made them to be widely used for private owned properties as well as commercial structures and public places. They are basically composed of polymers that have been originated from oil which is resistant to the radiations from the sun and harsh weather conditions generally. They are produced as sheets with varying thickness ranging from 1.2mm to 2.0mm. For commercial use, they come from the factory as rolls measuring about 1.2 m wide and approximately 20m in length.

The single ply is most suitable for use on warm roofs. This means that it will have to be placed over the installed insulation and held firmly by the decking. The occurrence of condensation is checked by the use of a vapor control layer. Warm roofs like this are very reliable and high in demand.

Methods of application

There are three specific ways to protect the single ply against wind:

Mechanical fastening: in this method, the single ply is secured by the use of plastic fasteners. These come as steel screws that are screwed into the roof deck through the sheets. The finishing is neat because the next ply used will cover the fasteners from being visible. The advantages of this method are that it is affordable and very quick to use.

Adhesion: In this method, specially produced polyurethane adhesives are used to hold the single ply and insulation in place. The adhesives are reliable and effective but very expensive.

Ballasting: This is a creative method which entails the use of the stone ballast or paving to hold the single ply securely. There might be a need to use some fasteners as well for more reliability.

What forms of renovation can be carried out on an existing roof?

There are two major ways that an existing roof can be renovated, they are:

Covering the existing waterproofing with the single ply membrane - this is a straight forward process; the waterproofing is simply covered with the single ply membrane. The only drawback is that there will be no added improvement in terms of a cooler interior.

Roofing can also be improved by using extra insulation and fresh single ply membranes- the effects of an extra insulation will be experienced by the cooler temperatures that will be enjoyed in the interior during the summer and the use of the single ply will definitely prolong the life span of the roof.

What is the life span of the single ply membrane?

It has an estimated life span of between 25 to 30 years. This is guaranteed only if the products used are the purchased form a reliable source, and the installation has been done by an experienced roofing contractor.


Types of liquid systems

There are many types of liquid systems; we will consider the Glass Reinforced Plastic (GRP) in this paper because it is one of the most commonly used and most reliable of all the brands. They are used for only Oriented Stran Board decking only. Just to mention a few other liquid systems we have – polyurethane, acrylic and flexible polyester materials.

The use of the liquid applied systems will generate a good membrane ready for use on roofs. They are supplied ready for installation after being prepared with the information that details the area of application. They can also be enhanced with the use of a catalyst to ensure at a much quicker rate.

Fiberglass Reinforced Liquid Applied Membranes: They are basically made up of a liquid based gum and glass fiber mat fortification.

Fleece Reinforced Liquid Applied Membranes: these materials are just like the fiberglass liquid based but the reinforcement is effected with the use of a fleece.

Other Liquid Applied Membranes: the resins used for these materials are not likely to have been fortified with fiber. They are applied in repairs and they also form a part of the roof.

What standards must the liquid systems meet according to the regulations?

The two basic requirements that must be met to be used in the UK are the regulations of the British Board of Agreement (BBA) and the European Technical Approval (ETA).

It is important to not that many of these materials are sold in the open market without meeting the required standards. The use of substandard products will end up making the roof compromised in many aspects.

Generally, the liquid materials are used for only repair works. It should be noted that they have not been fortified enough to be used as the roofing for a structure.

What kind of projects requires the use of liquid systems?

These liquid systems are excellent for renovations and they are best studied for the warm roof. They are usually applied by placing them over the insulation held firmly by the structural decking. They can be used on any project that is a renovation or the building of a market.

There are two basic ways in which an existing roof can be renovated and improved, these methods are:

Installing them over the existing waterproofing. This is an effective method of improving the roofing. The decision to use the existing waterproofing will be dependent on its condition. It is important to consider ensuring that condensation will not occur when the liquid system is used.

The use of extra insulation in addition with a fresh liquid applied membrane- an extra insulation will be a very good idea for shielding the interior from harsh weather conditions especially during the summer. It is also a good way to improve the existing roofing.

How safe are liquid system to be used as balconies?

There are liquid systems that have passed the necessary tests for use on balcony finishing. In this case, the material which can be sand, slate or bauxite is applied on the surface to create enough friction before it is used on the balcony.

What is the life span?

The life span estimated for the materials accredited in the UK is between 25 to 30 years. This is guaranteed with authentic products that have been properly installed.