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Flat Roof Repair

In the past flat roofs have had a reputation for being leaky and unstable, high maintenance and costly. However, repairs to flat roofs need not be expensive and, depending on the extent of the problems, can be undertaken on a DIY basis. Add to this advances in flat roof technology, the fact that many manufacturers of flat roof coverings now offer lengthy guarantees, not to mention the potential flat roof structures have in contemporary architecture, and the idea of a flat roof really becomes rather attractive.

Flat roofs are made up of a covering and joints, thermal insulation, a structural deck, drainage outlets, guttering, a parapet, an abutment, flashing, vapour barriers, surface coverings and sometimes reflective treatments to prevent overheating.

Detecting Problems

If you suspect the roof is leaking it will probably be obvious in the room below. The leak in the top layer, which you will be able to see up on the roof, will probably not be directly above where the leak appears in the room below. This is because water will find its way under this top layer and run between any subsequent layers before finding a way through the boarding in your ceiling.

Leaks are caused by a number of factors and it is important to determine what is causing the leaks before taking any action to rectify the problem. Begin by inspecting the roof covering and check that no ‘ponding’ is occurring. Ponds in excess of 25mm will be a problem and regular ponding can be detected by obvious water stains as well as plant growth.

It may be that bad design is leading to a leaking flat roof, so check for cracks at joints and corners, around chimneys, ventilation slits or tacks, where the roofing may have moved, and around rooflights too. Commonly, roof nail heads are missing or have rusted and cause leaks, or gutters may be obstructed or punctured. Carefully inspect seams and other joins and be sure to look out for problems around junctures with other roofs as these are prime areas for cracks to appear.

If the roof has a gravel covering, pay attention to areas where the gravel has lost colour. This is usually a sign that water is filtering through and leaking, discolouring the stones. Also check for blisters. This is a common problem caused by moisture finding a way between the deck of the roof and the membrane and is a common cause of leaks if not treated.

It should also be noted that the reason many flat roofs failed in the past was not just down to faulty membranes, but due to rotting and failure of the structure beneath, caused by condensation. To avoid this the outer roofing membrane should be placed on top of external insulation with a void beneath the timber decking and the ceiling beneath. This is not only ideal for containing services and lighting but also vital for roof ventilation.

If there are no obvious problems but leaks are occurring, a specialist will be able to use other methods of detection, such as infrared thermography, endoscopes or electronic detection methods.

Repair or Re-cover?

There are various inexpensive DIY repair kits available which contain adhesive and tape for making localised repairs. Providing your roof is otherwise sound these are the best option for those 'Moving On'. Repairs are best made after a spell of dry weather, particularly in the case of flat roofs with a felt covering, so they can dry out.

Of course patch repairs are just that, and where the roof has started to deteriorate, you may find yourself up there regularly making repairs. So, if you are a 'Fixer Upper', consider a new overlay. This is advisable where the existing deck of the roof is sound, but where the waterproof membrane is a problem. A new membrane should be placed over the existing one, complete with a layer of insulation and ballast over. Another option is to use the existing membrane as a vapour check, adding insulation and a new waterproof membrane. However, if this is your 'Forever Home', by far the best way to deal with an old flat roof that is starting to fail is total renewal, stripping the deck and water - proof membrane away and replacing them.

Regardless of what you decide, experts advise checking your flat roof twice a year and clearing leaves, debris and dirt away so that drainage is free-flowing.

What is Smart Renovating?

The concept of Smart Renovating is based on the idea that renovation is not a one-size-fits-all subject. Different renovation solutions and design ideas make sense for different people depending on their situation. We’ve outlined the three basic situations:

Moving On: You plan to live in the house for less than two years, with the aim of making a profit as opposed to a home for life.

Fixer-Uppers: You intend on staying in the house for four to five years and see it more as a stepping stone to a bigger, better home as opposed to a ‘Forever Home’.

Forever Home: You would like this to be your home for the foreseeable future and are willing to invest time and money in order to transform it into your dream home.

Your Flat Roof Covering Options

If you find that your flat roof is beyond repair or that the number of repairs required make it an impractical task, then you will need to have it re-covered.

There is a wide choice of coverings for flat roofs, ranging from the very cost-effective mineral felts to the more costly metal sheet coverings. For those Moving On (SEE ABOVE), felt coverings make sense, although with their expected lifespan of just 15 years they will not be suitable for everyone. Fixer Uppers may wish to consider EDPM (ethylenepropylene- diene terpolymer) or TPO (thermoplastic polyolefin) membranes which are not much more expensive than felt, but have a longer life expectancy (they’re both a form of rubber). Asphalt roof coverings are considered stronger than felt and can be walked on. Those looking to create a Forever Home should take a look at a lead covering which is once again generally considered more durable than some of the cheaper materials and costs around £50/m². For a really smart modern look, consider zinc or copper.

Finally, flat roofs lend themselves perfectly to being transformed into green roofs. Not only will a green roof protect the membrane below, but they are also good-looking, have fantastic insulative properties and are good for the environment.

1. Built-up Felt Roofing: This type of flat roof consists of a waterproof membrane constructed by bonding two or more layers of bitumen felt or hot bitumen. Built-up roof coverings usually use bitumen roofing membranes or high-performance membranes, including polyester-based versions, with a life expectancy of 15-25 years respectively.

These roofs are suitable for patch repairs where there are just isolated faults, but where there are lots of separate problems or the membrane has started to deteriorate, total replacement will be required.

At the cheapest end of the market lies mineral felt, which costs around £10/m² supplied and fixed.

2. Single-Ply Membrane: This is made up of single sheets of material in which synthetic polymers are the main component. EDPM or TPO membranes are either loosely laid or fixed directly to the ‘deck’ of the roof. This type of covering is quickly fitted and easy to repair. Their life expectancy is 25+ years.

3. Polymer Modified Mastic Asphalt: Mastic asphalt is mixture of inert mineral aggregate and an asphaltic cement. According to the British Building Research Establishment mastic asphalt has a life expectancy of 50-60 years, used on cold deck roofs that have been correctly installed and maintained. Expect to pay from approximately £25/m².

4. Sheet Metals: Although zinc is currently the fashionable material, stainless steel and copper are thought to be more durable. In general, this type of roof covering is expensive, coming in at around £100/m² supplied and fixed by a specialist contractor.

Green Roofs

ABOVE: 1. Planting; 2. Growing medium; 3. Moisture retention fleece; 4. Aqua drain; 5. Sarnafil membrane; 6. Insulation; 7. Vapour control layer; 7. Structural deck.

Also known as ‘living’ roofs, this type of roofing is ideal for those with flat roofs. Modern green roofing systems are made up of a series of functioning layers to recreate growing conditions up on the roof. ‘Extensive’ green roofs are made up of a shallow layer of substrate planted with lowgrowing, stress-tolerant grasses, mosses and alpines and require little or no maintenance. ‘Intensive’ green roofs consist of a thick layer of soil in which a variety of plants, vegetables and even trees can be grown. They do require frequent maintenance comparable to that of a normal garden.

Green roofs trap moisture on the roof – which initially sounds like a negative feature considering the aim is to keep pools of water off flat roofs – but keeps the water up in the soil and plants rather than letting it pool on the membrane surface.

The cheapest green roofs are ‘extensive’ and are generally considered to double the cost of waterproofing and insulating a roof. They cost (excluding insulation and waterproofing) around £20-70/m².


I'm fond of unique house plans, and I have already quite a huge collection of pics (downloaded by torrent search engine).I love soft and fluid lines combined with masculine lines; a perfect marriage; Space, or the illusion of it; The feel; the natural flow; and most importantly, the human factor. Cost is always a factor, whether or not you are planning to build a tiny house or a mansion. No matter the size of the house plan or the budget.
Good information provided related to roofing.

I must point out that the prices quoted for the various roofing systems are misleading and incorrect.

The descriptions are quite good.

For specialist flat roofing advise don't hesitate to contact Hambro Roofing.

Hi Jon,

We'd be happy to hear your take on the prices we've used in the article. Potentially just an inflation issue (the article is from December 2009) or is it more than that?


Samuel, there's a few points on the above. Costs of felt and single ply are not much different. Also I must point out that it says felt has a 15 year lifespan, felts have BBA certificates of 40-50 years (more than single ply membranes). All of the above systems have their place in the market, in my honest opinion I don't think that you can beat a high performance felt roof. We install a number of systems (felt, asphalt, single ply pvc/EPDM, liquids, etc and I still think that bitumen based products take some beating.

If the budget isn't an issue and the construction is right then lead, copper and zinc are the best hands down and over the lifespan of the roof they will actually work out cheaper.

Budget costs I would say starting from £55-£75m2 for single ply or felt system, £60-80m2 for mastic asphalt and £50-£70m2 for liquids. Bare in mind that these are budgets and every job is different (access, details, etc). There is no inclusion for stripping up existing, installation of decking, insulation, vapour barriers, outlets, lead cover flashings etc. which all need to be taken in to consideration.

If you are stripping up more than 50% of a roof then insulation has to be installed or upgraded to comply with current building regulations (as of October 2010).

Feel free to contact me if you need more information or visit/google Hambro Roofing - Competent Roofer verified.

Thanks Jon for your comments, some really useful info there.