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Two of the most common enquiries we receive from property owners are ‘I’m having fibreglass flat roof problems’ and ‘I have just had a fibreglass flat roof installed and I think there is a problem although the contractor is saying this is normal’.
This article attempts to provide answers to these two queries, so you have enough knowledge to identify problems with your GRP roof. Below we will focus on the most common problems with GRP roofing. And what needs to be done to put the problem right.
• Pinholes on the Fibreglass Flat Roof’s Surface.
• Cracks on the surface of the GRP Flat Roof.
• Alligatoring of the GRP top coat (this is where the roof shrivels up).
• Pools of Water sitting on the surface of the GRP roofing (this is referred to as ponding).
• Leaks coming through the fibreglass roof.
• Noise Problems with a GRP Roof.
• Problems with the Flashing on the Fibreglass Roof.
• Swollen timber board causing crack in GRP roof.
• Not using OSB Board.
• Collar details not finished correctly.
• Cracking Expansion Joint.
• Cracks in the render of the wall the roof is attached to.
• Moss and lichen growth on the roof and capstones.
• Faulty capstone joints at the point they meet the wall.
• Failing Guttering.
It is hard to identify pinholes from afar. But upon close inspection pinholes on a fibreglass flat roof are unmistakable. As the name suggests this problem resembles the roof having been pierced repeatedly by a pin.
The reason this problem develops is because not enough top coat resin has been applied during the installation of the flat roof. Although it may seem as though such small holes could lead to no damage to the roof, in fact they can.
These pinholes can lead to the development of leaks which have the potential to cause significant damage. The time when a roof with pinholes is especially vulnerable is when there is heavy rain and high winds. During these times water ingress is likely to occur.
Thankfully if your GRP flat roof is suffering from pinholes it is possible to fix it. It is recommended you hire a professional flat roofing contractor with expertise in fibreglass roofing systems to do this to prevent any further problems with your roof.
The contractor will apply fresh resin to your roof to fill the pinholes. Although this sounds straight forward is important both the correct mixture of GRP resin is prepared and the resin is applied in the correct quantity.
Once this resin has been applied correctly the pinholes will be sealed and no water ingress will occur through this part of the GRP roof.
Cracking on a fibreglass roof in most cases can be identified from the moment you look down on the flat roof. The roof will either have a typical crack going through it or a flaking effect.
The most common reason for a GRP roof to suffer from cracking is because of a poor installation. Most GRP systems are very rigid (the exception is UltraFlex1). This rigidity means there must be room let between the perimeter edges and the timber boards.
If this is not the case cracks will occur in the surface of the GRP flat roof. The reason for this is due to thermal movement. As the roof is exposed to changes in temperature such as during the day in summer and then the cooling down during the night. The roof expands then contracts. As this process repeats pressure is put on the GRP surface and cracks will eventually form due to no movement being allowed for in the boards underneath.
Cracks can also appear in the surface of a GRP roof if the incorrect timber boarding is used. Due to the rigidity of GRP systems OSB boarding2 should be used. We go into more detail about this later in this article.
Another reason for cracking is if the top coat of GRP resin was applied to quickly or on top of the laminate whilst still wet.
If a roof is suffering from cracking due to a problem with the top coat, the best thing to do is to cut out and replace the affected area. Once the area which is suffering from cracking is removed. New resin should be applied by an accredited GRP roofing specialist.
If there is a problem with the boards, unfortunately it is a possibility the boards will have to be re-installed correctly. This could be using the correct boarding or making sure the correct movement is allowed for. Before making any decision about replacing your roof it is a good idea to get an opinion of a GRP specialist to advise you on the most cost effective way to solve your problem. You can contact one of our fibreglass flat roofing specialists by calling us on 01277 375 511 or get in touch by clicking here.
Like any other roofing system, one in GRP has a life expectancy. As time goes on the elasticity in the roof diminishes. Fibreglass is a rigid system from the beginning, so once the top coat loses any elasticity it did possess the top coat begins to shrivel. This shrivelling effect makes the roof look quite literally like the skin of an alligator (this is obviously where the term alligatoring derives from).
Once your roof is suffering from this alligatoring effect the only lasting solution is a complete roof replacement.
If you see one or more pools of water forming on the surface of your GRP roofing this is called ponding. If your roof is designed for zero falls this may not be a problem. But if your roof is not designed for zero falls this is likely to be a problem. A problem which can result in water ingress and leaks.
You won’t always spot pools or water on your roof but may notice some of the big clues your roof has been suffering from ponding. These clues come in the form of dark or light circular patches where the water was present. And often you see a dirt stained ring around the perimeter of these patches.
The problem is created by a low point or dip somewhere in the flat roof which is preventing the water from draining off correctly. If the roof is sound this may not pose any immediate threat but if there are other problems in the roof water ingress is likely.
To fix the problem of ponding you cannot simply apply more top coat to remove the dip or low point. The reason for this is the GRP top coat will be too thick and will crack. The way to remedy this is to remove the affected area and use firings to build up the area then reapply the fibreglass matting and topcoat.
If you notice your fibreglass roof leaking the first thing you should do is contain the. The next step is to identify the cause. And the final step is to repair the leak.
You can view a comprehensive guide on dealing with leaking roofs by clicking on the following link:
Leaks are caused in a fibreglass roof for a multitude of reasons. Water ingress has developed into a leak, this could be from a crack in the top coat, pinholes, faulty flashing or cracked rendering. You will need a GRP roofing specialist to conduct a roof survey to trace the fault or faults. Once the cause of the leak is diagnosed, the necessary repair work can be conducted.
It is common to hear noises coming from your GRP roof. The most reported noises are those which sounds like cracks or creaks.
The reason for these noises coming from a fibreglass roof are due to the rigid nature of a GRP roofing system.
Temperature plays a big part in causing these noises. In general, noises are more prevalent in the summer months due to a large change in temperature from the high during the day to the low in the night. This thermal expansion causes the expansion and contraction of the rigid GRP system resulting in noises.
These noises can be annoying but are a perfectly normal phenomenon with fibreglass roofing. If you want to minimise any noise made by a fibreglass roof you need to design the roof to allow maximum movement.
This can be done by installing special expansion joints which allow the fibreglass more flexibility. Another thing you can do is to use a fibreglass roofing system like UltraFlex which has more flexibility than the other systems which are rather rigid.
By taking these measures your GRP roof will be more equipped to deal with thermal movement3. The result will be less sound effects from your roof.
On a fibreglass flat roof a common problem is the flashing needs replacing or re-fixing. This can be down to several reasons. One reason is the flashing has cracked and made it possible for water ingress to occur. If this happens the solution is to remove the defective flashing and replace it with a new one.
Another problem is the flashing has pulled away from the wall. This again creates an opportunity for water ingress. The reason for this happening is normally down to wear and tear or subsidence breaking down the mortar which attaches the flashing to the wall. To fix this problem the flashing will need to be re-attached to the wall.
If you have any leaks faulty flashing are always prime suspects as to where the leak originates from. And even if you have no leaks a faulty flashing is likely to develop into a leak over time. If you ever spot a problem with your flashing call a roofing contractor and get the necessary flat roof repair work before it becomes a bigger problem.
A swollen timber board can cause a crack in a GRP Roof. This is normally easy to identify. It is very unsightly and leaves an ugly crack or a hole where you can see the timber board. In its early stages a swollen timber board may not be so easy to spot.
There are two reasons this problem can occur. The first is the roof being badly designed allowing for no ventilation. This causes trapped moisture which begins to build up in the timber board which causes it to swell. Once it swells past a certain price the strain on the fibreglass will be so much it causes a crack to occur.
The other reason is water ingress this can be caused by any number of reasons. Nearly every problem listed on this blog post can be the reason for water ingress. No matter how the water ingress develops the result is the same. A building up of water in the timber board which will eventually swell to a point which puts enough pressure on the GRP top coat to make it crack.
Water ingress can occur around the collar details on a GRP roof. The most common reason for this is an incorrect dressing of mastic. Mastic around any details on the roof should be at least 150mm high.
To remedy this problem a new mastic dressing to 150mm must be applied. Also, separation should be put in and around any lead junctions.
A GRP roof can suffer from leaking if the render4 of the wall where the roof meets the wall is failing. Failing render can be identified by cracks along the surface of the render. What happens here is in high winds and heavy rain water hits the wall and penetrates the cracks in the render. This moisture will then trickle down the wall and underneath the roofing system which will eventually result in leaks.
The way to fix this problem is to re-render the wall in the area which is failing.
Moss and lichen growth around capstones or on the GRP roof are indications of dampness or standing water. It is more common to see moss on shaded areas and on the north side of a roof. It is important to remove moss and lichen to prevent any damage to your roof coating which can take years of your fibreglass roofs lifespan.
Problems you can encounter from moss and lichen growth are as follows. Growth into the guttering preventing the proper drainage of water from your roof. Causing water to pool on your roof. Growth into small impressions in your roof which can expand due to thermal movement. This can develop into cracks in the roofing system and allow water ingress. If you have a problem with your GRP roof moss and lichen growth could be the problem. To prevent any problems from moss and lichen growth it is a good idea to carry out an annual roof maintenance survey.
As mentioned above moss and lichen growth can be the reason for a capstone failing and allowing water ingress on your GRP roof. However, the most common reason for capstone failure is thermal movement and subsidence. This happens at the point where the capstone meets the wall. Due to the movement, the mortar breaks away causing the capstone not being secured to the wall. This allows the potential for water ingress. Which can cause the roofing system to fail and develop leaks.
Like any other flat roofing system GRP roofs can fail due to the guttering. If a gutter becomes blocked on a GRP roof water will build up in the gutter and potentially overflow. Eventually this can lead to the gutter needing to be replaced. Thankfully, in most cases gutter problems are caused by a build-up of debris or leaves. Therefore, it is important to get regular maintenance checks on your roof and to get any debris on your roof or guttering cleared away. If a guttering problem is not fixed it can lead to leaks or a replacement gutter being needed.
A badly laid GRP roof can cause cracking along an expansion joint. The cause of this is room not being let between the perimeter edges and the timber board. Another reason for this occurring on large roofs is if an expansion joint is not inserted for every 60 square metres of roof.
An OSB board has a rough surface which allows the GRP resin as it is laid to create a good bond that does not de-bond. If OSB board is not used the GRP resin can de-bond. This can lead to the roof system failing. If this happens the solution is to cut out the failing area and replace the boarding with OSB board and re-applying the GRP system.
Fibreglass is a popular system of waterproofing for a flat roof. And for good reason. There is nothing inherently problematic about fibreglass flat roofs if installed and maintained correctly. In the only reason a correctly installed and maintained flat roof should fail is because it is at the end of its service life.
Therefore, as a homeowner to prevent problems with your roofing system and maximise the lifespan of your roof there are two things you can do. The two things you can do are as follows.
1) Get your fibreglass flat roof installed by an accredited GRP roofing specialist.
2) Make sure your roof is properly maintained. You can do this with an annual maintenance survey and by quickly resolving any roofing problems you identify.
These two simple steps will prevent nearly every type of fibreglass flat roof problem you may encounter.
We hope this blog post has helped you identify the source of your fibreglass flat roofing problem. If you would like help fixing the problem you have identified or you still cannot identify the source of your problem you can contact us on 01277 375 511 or you can send an email to email@example.com .