Flat roofing system review

Sprung a leak? A review of flat roofing systems and the pitfalls of appointing a roofer in the UK by experts Carma UK Roofing and main contractor Carma UK Construction.

 

Background

We inspect a lot of failed roofs. Carma UK Roofing spends much of its time in the Oxfordshire area appointed by residential and commercial property owners to remedy their roof issues or supporting developments for sister company Carma UK Construction. We also travel the length and breadth of the United Kingdom to carry out facilities management roof repairs for our care home and restaurant chain clients. Given the significant expense of a roof, most wait until it is too late (storm damage or neglect) and the roof has already failed and others tend to address their roof at point of sale or purchase based on a surveyor’s report to avoid price negotiation. Here’s our experience over the last few years:

GRP roofs


What is it?

GRP (Glass Reinforced Plastic), also commonly known as fibreglass, is a robust roof covering material. It is the same material used by many power and sailing boat manufacturers given its ability to be formed into intricate shapes and its strength. It’s the same material used to make many wind turbine blades given its lightweight characteristics and its ability to take incredible loads and forces along with extreme changes in temperature due to variable weather.

  • Cost: Circa £100 per m2 plus insulation requirements.

  • Durability: High level of durability, if not the highest level available. 20-30 year lifespan when installed correctly but expected to last far longer.

  • Appearance: Seamless finish, albeit often with small ridges and trims visible. Feature details can be added like “fake” standard seem. Wide choice of colours.

  • Great For: Medium-sized flat roofing projects, such as large garages or extensions, and commercial projects.

Inspection defects

“Hairy” ends of matting visible through coatings – This is a clear sign that not enough resin has been used and or it hasn’t been rolled to flatten/ensure full matting saturation and remove air bubbles post resin application. This can be remedied by sanding the existing system and applying a new system over the top, or fully stripping the existing system and reinstalling. Patch repairs can also be attempted but warranty is likely to be limited. Best solution is to get your installer back to remedy their poor install.

Not enough matting used –Often we find this issue out where cracking has occurred in the roofing after a hot summer and cold winter which causes stresses to the covering leading to failure. Attempts to overcoat the existing could be proposed with limited warranty or strip off the poor work and reinstate. Once again, we’d suggest you start with the original installer as the remedy will be expensive!

Boards not fixed down correctly. Its all very well when you apply a fantastic GRP finishing system, but if the sub structure is loose then the roof is going to move under wind, rain and snow load leading to early roof failure as well as being a risk from uplift (your roof could literally take off!). We’ve found roofs in gardens due to lack of fixings after storms. New fixings can be applied through the existing build up, the existing system sanded back to provide a key and a new system applied over the top, or preferably the system removed and reinstated. If budget is very tight, then apply fixings through the existing build up, and patch repair each screw hole.

Pin holes visible. This is a clear sign not enough resin has been used and the resin applied hasn’t been rolled leading to air bubbles. The system can be sanded back and additional resin applied to ensure a fully watertight solution. This should be carried out by the original installer to ensure you receive your paid for warranty. Failing that, an alternative supplier may offer warranty, but it is unlikely with their preference to apply a new system in its entirety.

 

Asbestos roofs

Asbestos was typically used in the flat roofs for a wide range of building types. Flat roof asbestos corrugated sheets is one of the most common in the UK containing 10-15% white asbestos fibres mixed with cement. The insulation inside the flat roof may also contain asbestos.

Asbestos as a building material (ignoring its enormous now known negative health aspects) is without doubt brilliant!

Its strong, cheap, insulating (heat, sound), fire, chemical, water and electrically resistant. These are excellent qualities for construction. It’s a shame it also has the deadly property also!

  • Cost: No longer available. The cause of 1000’s of deaths per annum. The single biggest construction industry killer.

  • Durability: High level of durability with roofs known to last for several decades.

  • Appearance: Typically corrugated sheets with a grey colour.

  • Great For: Nothing any longer. It is a banned material for good reason.

 

Inspection Defects

Many asbestos roofs were installed with a 25 year guarantee but remain sound several decades later. It really is a wonder material. Being a simple material to install very few installation defects are present, but general degrading can be seen on older roofs.

Whilst asbestos remains intact and undisturbed it is not a health hazard and should be left alone.

Splitting or crumbling locally. Asbestos sheets can begin to split (often at fixings). These can be locally patch repaired offering little warranty. The roof can then be overcoated with a specialist (often liquid plastic) overcoating system where installed with a trained specialist can be guaranteed for 15+ years.

General loss of waterproofing. Asbestos sheets can over time lose their waterproofing properties. These can be renewed with specialist sealants and overcoating systems. There are various systems available, often with 10-20 year guarantees.

Where the roof has extensive or multiple failures, either its time to remove, or the roof can be overclad with a new lightweight roofing system. Any additional loading should be reviewed with a structural engineer to ensure the structure is capable of taking the additional load.

Once notable degrading occurs (breaking up, crumbling, splitting) or need to remove for other construction works to occur, it is time to remove it. This needs to be done safely with a firm carrying the correct licences to remove this hazardous waste and dispose of it correctly.

 

Felt Roofs

Roofing felt is perhaps the most common flat roofing material available. A felt roof is easy to install, providing a weatherproof seal to protect any correctly graded flat roof. A roof covered with felt can also be repaired cheaply and easily. Torch on felt types are the most common for flat roof installations.

On the underside of the flat roofing torch on felt you’ll find a thick layer or pre-installed bitumen designed to be melted with a roofers blowtorch whilst being rolled out onto your roof. This melting process isn’t for the faint hearted. With a naked flame present, without careful precautions it is dangerous not only to the installer and those in close proximity, but also to the building itself. Take head and use an experienced professional that carries the correct level of insurance including protection for hot works which many cheaper insurance policies do not provide.

  • Cost: Circa £45-£60 per sqm.

  • Durability: Torch-on felt is a robust felt type, and many three layer systems come with a 20-30 year guarantee where installed correctly

  • Appearance: Typically black or grey with a slate grit finish. Be mindful some felt top capping layers can be very thin and susceptible to impressions such as footprints. Be careful with cheaper felts if you wish to avoid looking at your roof for the next few decades with a trampled over look.

  • Great For: Most suitable for larger roof spaces and for applications during colder periods where GRP installations may prove problematic.

 

Inspection defects

Problems can occur if felt layers are not properly laid and bonded. Joints can negate the fall of the roof and encourage ponding. If water penetrates defective joints then adhesion between layers can deteriorate. Joints can be reheated and rolled to improve adhesion and where necessary additional layers laid over the existing. If the defects are significant, it may be prudent to strip back to the substrate and reapply a new three layer system.

Problems can occur which are caused by the decking below the felt. Boards may have moved or warped, or interstitial condensation may build up between the gaps in the boards. Where this is the case you will have little choice but to strip the roof back, repair the substrate and any vapour barriers and then reinstate the felt finish.

 

EPDM Roofs

EPDM rubber is a type of synthetic rubber that is used in many applications. EPDM is a relatively low-cost flat roof material. It has some great properties such high strength, a long lifespan, and a clean, smooth refined finish. It’s simplicity to install on straightforward roof shapes make it a favoured DIY roofing material.

  • Cost: Circa £60-£80 per m2.

  • Durability: Fully waterproof with high resistance to weather, temperature changes and strong impacts. Expected to last 40-50+ years.

  • Appearance: It’s a flat rubber sheet. What can we say, it doesn’t look overly appealing if in plain sight. Best suited to locations where it is not seen. Typically black or grey.

  • Great For: Projects of any size, ideally with few challenging upstand or down stand details.

Inspection defects

Whilst the membranes themselves can be relatively indestructible and being a flat sheet, its not overly difficult to install on main flat sections, it is the details where we find the greatest defects.

Peeling details. Roofing details and joints are glued typically with a contact adhesive. It is these details where failure normally occurs. Some may simply require regluing, but often they have been installed poorly where perhaps a thinner more flexible detail or prefabricated detail would be better suited. Cut out and reinstall. Once again, best place to start is with the original installed to maintain your warranty or guarantee.

Peeling joints. Similar to above, it is often the joints that fail. These may be possible to reglue by first cleaning off any residue before applying a new high grade contact adhesive suitable for use on a roof environment.

Puncture hole. On occasion objects may fall onto roofs causing a puncture hole. These can be patch repaired with an EPDM patch with a high grade contact adhesive.

Sub board not fixed down. If the roof is moving and creaking when its windy or with foot traffic it may be the sub boards have not been correctly fixed down. Its time to strip off the EPDM covering I’m afraid to address this property before reapply the EPDM covering. You may find that if the substrate has been installed badly, so has the EPDM covering allowing it to easily be peeled back and reused.

Delamination. EPDM roofs are typically installed with a water based adhesive on the main flat runs. Where no adhesive has been used or it has failed and the roof covering is starting to lift with the wind loading, it is time to remove the EPDM covering and reinstall or replace. You may find that its peels back with no issues, but often the edges will have been fixed with a higher grade contact adhesive which will not remove without mechanical intervention.

Single Ply Roofs

Single ply roofing is a popular flat roof covering with growing recent popularity. A single ply membrane roof is a flexible sheet or either thermoplastic or synthetic rubber (for EPDM see above). PVC single ply membranes have become the favoured option for many commercial and green roof installations installed mechanically, ballasted or fully adhered with heat welded seams.

It is a robust roof covering resistant to UV, natural elements, chemicals with TPE variations seen as one of the most eco-friendly variations available at present.

  • Cost: £100-150 per m2.

  • Durability: Fully waterproof with high resistance to weather, temperature changes and strong impacts. Expected to last 20+ years.

  • Appearance: Typically, light grey or black in appearance with welded regular seams. Quite unattractive but easily covered with ballast, green roof build ups or pedestal slabs for a more aesthetically pleasing finish.

  • Great For: Large commercial, industrial or residential flat roofs. Often warranties require inspection by the supplier which push these installs for larger budget projects.

Inspection defects

Spongy substrate. Often found in locations where regular foot traffic has caused the insulation boards beneath to fail or where long standing leaks have caused the boarding to fail. Localised sections can be removed to allow substrate repair before reapplying and welding the new membrane to the existing. Warranty for this work may be a challenge with old to new membrane weld details potentially being defective or incompatible. Once carried out, an overcoating system may be the preferred method to complete the repair.

Unknown leak. Leak detection systems can be used where the membrane is scanned from above to locate potential leaks. Once identified these leaks can be patch repaired with new compatible membranes heat welded to the existing.

Multiple failure. Where multiple seam failure is discovered, often by poor quality installers who have closed their businesses through large warranty claims and overcoating system can be applied. Seams are reinforced before a PU overcoating system is applied to the entire membrane creating a new seamless membrane. These overcoating systems are often offered from competent installers with a 15+ year warranty.

 

Lead Roofing

A lead roof is where sheet lead is used to completely cover a roof area. Lead has been used for roofing for centuries and is used on many of the historic buildings in the UK, such as Cathedrals, Churches and historical university buildings. However, it is not limited to heritage buildings and can be used on residential properties also.

Lead has been used in the building industry for centuries because it is extremely durable and is highly resistant to corrosion and other environmental factors. Lead roofing is used on historic buildings as lead roofs have been known to last over 100 years, proving to be the material of choice when longevity is required. That is where it is installed correctly and treated with Patination oil to prevent Lead oxidation.

Lead is 100% recyclable. In fact, most lead used in today’s building sector is made from recycled sources. It also enjoys the lowest carbon footprint among hard metals like copper, zinc and stainless steel. All these put lead on the list of eco-friendly building materials. Picking lead roofing for your building restoration project, thus, allows you to contribute to promoting a greener environment.

  • Cost: £100-200+ per m2.

  • Durability: With lead roofs having stood the test of over 100 years on many historical buildings, it is the winner of durability of flat roofing materials.

  • Appearance: With its soft mouldable characteristics, lead can be shaped and detailed unlike any other roofing material. Where some skill and care it taken, lead roofs can be one of the most attractive of roof finishes. Remember to apply patination oil once completed to stop ugly white lead oxidation staining.

  • Great For: Any flat roof, but given its cost, perhaps only the most prestigious or where highly visible. It is also the ideal material for interfaces with other materials like parapet wall abutments or chimney skirt flashings.

Some tips from us when carrying out a roof repair:

Collect 3+ quotes and inspections. There are a lot of rogue roofing companies in the UK who may recommend far more work than you really need to carry out, or not know of a potentially cost saving repair technique/solution. Equally some roofers charge far more than others. Ensure you balance your quotes out with a review of the robustness of the company you have chosen. Will they be around to honour their guarantee?

Ensure the scope of the work is clear. Whilst text messages and emails form informal contracts, they are not as robust as a formal contract. We’d urge a contract to be drafted with a clear service, cost, warranty and process should a dispute occur through the work.

Check insurance. Many roofing companies will skimp on the basics leaving you exposed during the building works. Ensure they have suitable levels of insurance whilst also checking your home insurance policy allows for maintenance and building works. Often you will need to extend you own insurance as well.

Do you need building control approval. Some roof installations require building control approval along with insulation upgrades. We’d suggest a quick call to your local building control office to check before proceeding.

What warranty is offered. Is it a third-party warranty or is it backed by the company themselves. If it is themselves, how long have they been trading and how robust is the company’s balance sheet? Essentially attempt to work out what the warranty is worth. If the company is small, we’d suggest asking for a third-party warranty for their installation. You get what you pay for!

Material warranty documentation not provided as part of handover. Ensure you know what the material is and what was used along with receipts or itemised brands on the invoice/receipt/warranty statements to ensure you have a claim against the material supplier where the installer is no longer trading if a material defect occurs within the guarantee period.

No financial protection – unprotected deposits. Paying deposits in advance for any building work means you are taking credit risk form the supplier. Do your homework and protect yourselves. Contracts are a good place to start with a company’s house background check. Using credit cards for even £100 of a deposit towards your building work will give you significant consumer credit protection should you not receive the material and or service you have paid the deposit for. Construction payment protection systems are also available such as Pay Trade who provide construction escrow project accounts to protect both consumers and their chosen suppliers from bad or undelivered work and bad payment.

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Team progress January 2023