GRP Roofing Systems and How They Differ - Hambleside Danelaw Ltd


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Welcome to GRP roofing systems and how they differ.


Corporate Background

In this seminar we’ll be looking at different types of GRP roofing systems, but before we start, I'd like to give you a brief overview of Hambleside Danelaw, who we are as a company and how we approach our business as a responsible manufacturer. We're a British company and have been a leading manufacturer of GRP products and roofing systems for over 35 years. We have two state of the art production and administration facilities, one in Daventry in Northamptonshire and the other in Inverness Scotland.


Environmental impact is a core concern for Hambleside Danelaw and the wider construction industry. Since 2004 we've reduced our carbon footprint by 78%. It now stands at 272 tons per year, that's for an industrial manufacturer making 1.5 million square meters of GRP and many thousands of injection moulded products each year. The ultimate target is carbon neutrality.


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Agenda - GRP roofing systems and how they differ

In this seminar we will cover:

  • The use of GRP as a roofing material and the basic process of manufacture.
  • The different types of GRP roofing systems, which are the wet-lay system, which as the name suggests, is the hand application on site of a liquid resin with an activating catalyst onto a glass reinforcement mat.
  • Component based systems which come as a kit of factory manufactured parts or mouldings which are mechanically fixed to the roof substrate.
  • Finally, we'll go through some case studies and then we'll do a quick summary.


What is GRP?

Well GRP stands for glass reinforced polyester, in essence its glass fibre reinforcement encapsulated in a thermostat hardened resin. GRP was first used over 60 years ago and has since been developed for a wide variety of industries including the construction sector. As the material GRP offers a long service life, in some applications it can last over 50 years, it delivers a very high strength to weight performance, it can be used in internal and external applications, it's available opaque and translucent in a range of colours, fire retardant from general purpose right up to FAA for flat roofs SAA for sloping roofs class 0.


Lightweight and easy to handle during installation it's UV resistant, and its safety using grey water systems. It's easy to repair and at the end of its service life it's recyclable. It's versatile, flexible and gives an aesthetically pleasing finish. In short, it's an ideal roofing material.


How do we make GRP?

Well GRP is produced by combining thermosetting polyester resin and glass fibre. These photographs show our process which is carried out under strictly controlled factory conditions, as opposed to wet-lay on site process.


Glass fibres are made from mixing sand, soda ash and limestone. After processing these are extruded into very fine filaments of 10 to 25 microns. These filament's can be chopped to form roving’s or used as continuous filaments which can be woven into reinforcement fabrics or used as windings for electrical insulators etc. As glass roving’s their most commonly used as the reinforcement element for composite material and particularly GRP or glass reinforced plastics. The roving’s can be used to make a reinforcement fabric like this chopped strand mat which has randomly patterned fibres, or specifically woven fabrics for a stronger lighter end-product.

Now, in isolation, each glass fibre is relatively weak across its axis but by placing layers of fibre on top of each other with each layer of fibres facing in selected directions, we can control the stiffness and strength of the finished material. In a GRP product the glass fibre is saturated with a liquid resin which is then cured hard to provide the form and the structural strength we need in the finished product.


GRP in the Building Industry

GRP has been used in the building industry for over 60 years and it has a vast array of applications. It's very commonly seen as translucent roof lights. It can be formed to produce roof edge trims and flashings. It excels as a replacement for metals like lead, for example in Valley troughs and gutters, and most appropriately for this seminar it can be used for roofing systems and membranes. And of course, we shouldn't forget that it's also commonly used in liquid storage tanks, lifeboats and even minesweepers for the Royal Navy, so it has a great track record.


Types of GRP Roofing

Let's move on then to consider GRP specifically as a roofing system material. Well there are two main types, there's the traditional wet-lay system this involves a liquid resin being directly applied to the roof. The glass reinforcement is then manually laid into the resin, and then it's rolled into the resin to expel any air pockets in the construction and saturate the mat. This is a process called consolidation.


The alternative option to this is a component based system for which all of the component parts including the membrane are factory manufactured. This system is mechanically fixed on site to the roof substrate and can often be fixed over the existing roof, if the existing roof is sound. For both systems are correctly installed GRP roof should have a service life of at least 30 years.


The Wet-Lay Process

Let's take a closer look at both systems starting first with the wet-lay. For this system a liquid resin is hand mixed on site with a catalyst to start the curing process, which is what will ultimately cause the mixture to solidify and harden to become the finished roof. Then the glass mat is introduced, and the construction is consolidated.


Curing time can vary depending on a number of factors like the environmental conditions and the amount of catalyst used. Mixing the catalyst can be a tricky process, get it wrong and the performance of the roof will be compromised because the operative then has a limited time to, one make sure that the compound has been properly consolidated and all of the air expelled and, two lay any additional mat or resin required.


It can become a bit of a race against time before the resin cures, but it has to be done carefully and efficiently to avoid product failure. In wet-lay roofs the resins and glass are applied directly onto the substrate.


For the successful installation of a wet-lay roof the following things have to happen. Ideally the decking needs to be replaced usually, within 18mm exterior ply or sterling board. Next weather conditions need to be dry and the temperature must be above 5°C.


Due to the nature of the process you need to be sure that these conditions are going to continue for sufficient time to finish the roof. After the deck has been replaced the roof edge trims are fitted and then the board joints need to be reinforced, to prevent the risk of stress cracking in the finished roof. Now that's necessary because the finished GRP roof once adhered to the deck through partial absorption, has a markedly different expansion coefficient than the timber deck. This means that the deck joints become high stress points and have to be reinforced. The liquid resin is then mixed with the required amount of catalyst to give the right curing time.


There's a series of guidelines to help the installer decide what the mix should be, the reinforcing mat is then laid onto it and the whole thing is consolidated. It's critical at this stage to ensure the right resin to glass ratio is used to give the right long term performance for the finish roof that's usually 2.5 kilos of resin to each kilo of glass.


The final stage is then to topcoat the system after it is cured. That's got to be done as soon as possible preferably on the same day as the unprotected laminate shouldn't really be left exposed overnight. The optimum thickness for the topcoat is between 500 to 700 microns, and once the topcoat has cured the roof installation is complete. 


So that's an explanation of the process for wet-lay, but what are the things that need to be considered to ensure a successful installation? We're dealing fundamentally with a series of chemical reactions here and a number of potential issues can arise from that.


First fumes can be released from the resin during application. Next the resin and glass laminate can emulsify, failed to cure and failed to adhere to the deck, if there is any moisture in or on the deck during the application process.


The top coat can cause the glass fibres to lift to be pulled up if it's applied while the laminate underneath is still wet. The laminate can cure too quickly if the ambient air temperature is too high for the catalyst mix used and that can result in a weakness in the finished roof. The glass fibre pattern can be overly prominent in the finish roof if the wrong resin to glass ratio is used. And, as we've already said the weather window has to last long enough on one day for the whole process to be completed from start to finish for either the whole roof or a designated working area.


Component Based GRP Membrane Systems

So, let's move on then and take a look at a component based GRP membrane system. Our system is very different from wet-lay although it does still require a small amount of manual lamination at joints and at periphery detailing.


The key difference is that the GRP membrane which covers the main roof area is factory made and tested in a controlled environment and, then delivered to site. It doesn't therefore depend at all on curing, catalyst mix, resin ratio or weather for the installation of the main roof construction. Also, the fact that the membrane is mechanically fixed and not bonded means that if the existing deck is sound our system can be fixed over the existing roof. Mechanically fixing the membrane also eradicates the potential issues caused by expansion coefficient differential. There is a small amount of lamination work required at joints and periphery detailing, but this is much easier to control and manage.


Another key difference is that the topcoat on a component based system does not need to be applied on the same day. In fact, as a general rule the topcoat can be applied up to 28 days after the membrane has been installed and, that allows the contractor are much greater flexibility of program. It also means that adverse weather conditions would have a much reduced impact on the projects critical path. In manufacture the membrane and trims for our component based system are factory produced under strictly controlled manufacturing conditions.


Our sophisticated production line in Inverness pulls the glass saturated in resin through the machine to make profile GRP products. This production method is called pultrusion. The production process is automated and monitored for quality.


Consolidation happens at tightly controlled rates under factory conditions, and the product finish and tolerances are consistent. They are made from high grade resins and glass fibre reinforcement, and their fire retardant achieving external FAC rating to BS 476 Part 3. All of which means that the membrane has unrestricted use as a roof covering under all UK building regulations. 


In terms of the installation process for a component based system, the membrane and trims are mechanically fixed using a range of proprietary fasteners for specific substrates. The joints are sealed using a purpose design GRP tape saturated in resin, and finally affine jointing tissue is applied to the laps. By using the same materials as the roof membrane there is no differential of expansion or aging between the components and, at this point the roof is now waterproof. It doesn't rely on the top code for weather tightness, the topcoat is applied for additional UV protection but, as we've already mentioned it isn't critical for that to happen on the same day as the roof is installed and, there are a few other things to bear in mind with the component based system.


It offers a wide selection of trims to suit most details, there's a choice of flat or ribbed membranes, there's a comprehensive range of specialist tried and tested fixings, it offers real design versatility. We’ll look at this more closely in the case studies. A range of topcoat colours is available subject to quantity, and finally it has been tested and approved for fire performance. 


From the point of view of durability, it goes without saying that for a roof to last as well as be weathertight it has to be inherently strong. It has to be able to accommodate thermal expansion and contraction. It has to perform well against the effects of UV light.


Generally, most modern materials do perform well, although there are some common performance issues such as oxidization and corrosion, UV and ozone degradation, plasticiser migration, vulnerability to mineral oils or solvents or, in the case of some specific metals the cost and the attractiveness to thieves once the roof is finished and everyone's gone home.


GRP has been around and in use for nearly three generations now, it's known to be resistant to most forms of chemical attack and degradation and, because it can be made to look like some of the more expensive metal finishes, it's much less attractive to your local scrap thief and, that may well bring a positive benefit in terms of the building insurance premium. Because the component based system still involves a small amount of lamination work, there are still areas of the installation that need to be considered. The joints between the membrane sheets and details need to be laminated but, the fact that the lamination is applied to factory produced and mechanically fix sheets means that it is much easier to control and, can be applied very quickly indeed.


A topcoat still needs to be applied to the finished roof but the potential issues that can arise from applying topcoat to uncured laminate just aren't an issue when you're dealing with a factory produced ready cured membrane. Topcoat curing is much less of a potential issue as the dry seal system does not require the topcoat to be applied immediately, as we've already discussed the gap can be as much as 28 days.


As with any roofing system weather conditions are an important factor but, as we've already shown the flexibility of this system means that the weather can be much more readily accommodated and dealt with, because it involves much less on site wet working. The mixing of the resin and the catalyst can still potentially release fumes and that has to be incorporated into any method statement or risk assessment. Again, though this element is dramatically reduced by using a component based system as it applies to the joints only or, to put it another way less than 10% of the roof.


Punctures and Repairs

But what happens then if your roof is damaged or if it needs to be altered say, to introduce a penetration for a new internal process. It's very rare that one or the other of these things doesn't happen during the life of a building. Now depending on the roof covering on a building repairs and changes can be either costly or, problematic or sometimes just plain impossible.


As we've already said roofs can corrode or they can become brittle or, they can lose adhesion all of which can make repairs a really difficult proposition. GRP roofs don't suffer from these aging or weathering effects. GRP roofs remained stable from the moment they are installed and, both wetly and component based systems can be repaired or adapted even many years later.


Achieving Safety

Let's just take a moment out to think a bit about the safety of the operatives during the installation phase of the roof. This is now the number one consideration for any aspect of working at heights and we need to stress a couple of points. Firstly, roof operatives must follow health and safety rules and guidelines for working at height.


Second, they must be fully trained in the use and installation of the specified materials and, they must understand the competent management of all recognised risks. And finally, construction design and management CDM requires designers to be aware of these risks and design and specified with them in mind.


Achieving Specification

So, turning to the specification itself, as with any system there are a number of key points which feed into the selection of the right GRP roof system and the right contractor and we’ll run through a few of them here: 

  • First does the manufacturer provide thorough installation and materials training?
  • Is the contractor registered with for example the National Federation of roofing contractors NFC, or another recognised Trade Organization?
  • Does the manufacturer provide a written guarantee for their system?
  • Does the contractor provide a written guarantee?
  • Do the guarantees have any substance, in other words are these guarantees backed by any independent warranty?
  • And finally do the manufacturer and contractor comply with recognised and defined quality and environmental standards?


Safety in Use

Another safety consideration for roof works is any potential fire risk. A major risk to both building and operatives can be avoided by eliminating the use of naked flames or intensive heat sources during construction. GRP does not need to be torch applied. It doesn't need to be hot air welded and so from this point of view the risk is minimal. And, of course the fire rating of the proposed roofing materials should be checked for compliance. Most GRP roofing should be rated to FAC grade 3 to allow for use in all flat and low pitch applications.


Toxicity and Run-off Water

Another consideration is toxicity and run off water after the roof has been installed and during its service life. Many roofing materials have implications in terms of the run-off water they produce, due to contamination, due to leaching, due to chemical migration or just general toxicity. GRP is one of the very few materials which have been certified for potable water storage, so it has no problems in addressing this issue.


Material Hazards

Turning to a key environmental issue the production of harmful chemicals during manufacture was one of the first targets for the early environmental movement. The harmful factors associated with the extraction, smelting and refining of some metals are well known. The industrial processes involved in producing modified bitumen’s are also widely recognised as harmful. The harmful effects of PVC production are perhaps less well known. It uses benzene and vinyl chloride both of which are known to cause cancer and PVC’s principled by-products include dioxins, which can cause serious illness.

But GRP production is not whiter than white on this issue either, the industry in general produces some styrene and other VOC’s but in our production processes at Hambleside Danelaw, we've reduced these from an industry standard of 4 kilograms per tonne to less than 15 grams per tonne. These figures stand as a measure of our commitment to addressing the key environmental issues surrounding manufacture, that can sometimes fly under the radar.


Case Studies

The next few slides are case studies that show examples of the Hambleside Danelaw dry seal component based GRP roofing system.


Case Study 1 - St John the Baptist, Bromsgrove

The first one is Saint Johns the Baptist church in Bromsgrove which is a 12th century grade one listed building the church had suffered 7 instances of lead theft despite a range of security measures. They’d finally run out of patience and were adamant that they wanted to use a replacement material with no value to thieves. The church approached Hambleside Danelaw regarding our dry seal GRP system after many months of discussion and negotiation involving the diocese and English Heritage of faculty was granted by the chancellor to use dry seal for cost reasons, saving over 200,000 pounds compared to the lead alternative.


The top left photograph was taken within a few weeks of the installation being completed, as you can see the dry seal is not yet weathered down to the matte finish which will increase its similarity to lead, a process that takes 6 to 9 months. But, it doesn't look out of place in this setting.


Below that is a really good example of using preformed components and in situ lamination. On this window detail the installer has laminated over the existing lead window flashing and laminated around the base of the window mullions. 


The GRP is chased into the joints then pointed with lime mortar and the original timber roles have been laminated back into position. Reverend Wingfield of Saint John’s Bromsgrove was very happy with the finished product, he commented, "it looks like lead, it's got longevity and it will save this church for generations to come. We had to fight our corner, but we were caught between a rock and a hard place. It was not cost effective to use lead or turn coated steel. In the current financial situation, you need to use the most cost effective material. The church spent £51,000 to replace the roofs with dry seal rather than the £275,000 it would have needed to raise to use led. All in all, a very satisfactory result."


Case Study 2 - Durlston Castle, Dorset

This newly restored Victorian Castle forms the gateway to a World Heritage site in Dorset. The grade two listed Durlston Castle received a £5.5 million facelift, helped by a grant from the Heritage Lottery Fund. Originally intended to be waterproof by a PVC single ply system the architects and the principle contractors chose dry seal for its robust quality, compatibility with differing substrates and, the ease with which intricate detailing can be formed on site. The contractor achieved first class results with the system by forming the required complex detailing around the masonry abutments below a spiral staircase and rear fire escape staircase.


The building is unusual in that all rainwater drains from the outside in, discharging through outlets in the base of the wall into an internal gutter system. The centre image shows the mouth of these drain water outlets and the internal gutter which is all water proved in dry seal. In the two images on the right you can see the lower roof terrace at the rear of the Castle where the dry seal installation has been completed and, then overlaid with timber decking to provide outside seating for restaurant customers.


Case Study 3 - Hotel Du Vin, Poole

This is the boutique hotel du van on the edge of Poole Harbour in Dorset. Dry seal was used for the roof covering for a new extension to this hotel, which is on various levels and installed under the stripped wood flooring on the balconies at the front of the building. This project also involved working around air conditioning plant and as you can see, they've replaced some low level roofs with simulated lead roles and a very good job they've done with it too.


Case Study 4 - The Bank of Scotland, Southampton

Here we see a GRP roofscape with a lot of ducting and air conditioning plant on a Bank of Scotland building in Southampton. The point to note on this project is that all of the roof mounted plant and ducting remained at roof level throughout the project being raised off the roof by jacks and, the dry seal semi rigid sheet slid underneath. The ability of the system to cope with his awkward detailing including the parapet encapsulation without the need for a crane and road closure led to a large cost saving and, was the principle reason why dry seal was chosen to replace the original failed felt roof covering.


Case Study 5 - Orient Place, Four Oaks, Sutton Coldfield - Bellway Homes Plc

This thousand square metre project was designed by Bellway homes in early 2012 to provide stylish two bedroomed apartments in the popular Sutton Coldfield area of Four Oaks in the West Midlands. Situated close to the railway station the development which was completed in early 2013 has attracted Birmingham City centre commuters. Hambleside Danelaw were consulted at an early stage and the dry seal system chosen due to its lightweight and robust nature. Previous experience of dry seal on other projects made this a straightforward choice for Bellway homes. A J42 specification drawings and technical information were provided to Bellway to assist in the design process. Dry seal covers all the roofs on this prestigious modern development over all apartment’s stair cause and ancillary buildings.


Review of Learning Aims

All of which brings us to the end of our presentation on GRP roofing systems and how they differ.


Just a quick recap of the key points we've covered today, we've talked about:

  • How the material is produced,
  • The two main GRP roofing systems and the practicalities of each, just to recap these are wet-lay and component based and,
  • A small selection of case studies where the product has been used successfully.


We hope you have found this presentation to be interesting and informative and for more information on dry seal please don't hesitate to contact us on the details provided.

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