building valuations


The Rolls Royce of Roofing

Asphalt flat roofs


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On our way to carry out a building survey in the London area we noticed a cloud of smoke and the smell that goes with it which could only mean one thing that an asphalt roof was being installed. We were particularly pleased to see this as we do believe that asphalt roofs are the best of the best when it comes to flat roofs and almost an art form with the skill required installing.

It takes a skilled craftsman/trades person to be installing asphalt roofs properly.

The kettle that warms up the asphalt blocks

Asphalt blocks on the lorry waiting to be put into the kettle to be warmed up

You can always tell if asphalt is being carried out due to the smokey environment.

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Is a flat roof just a flat roof?

Even for people that have not lived in a house or worked in an office or factory or warehouse with a flat roof the reputation goes ahead of flat roofs. If you mention a flat roof people often think you are talking about a problem roof. We would have said that this phrase was so true many years ago however interestingly if you go back even further flat roofs were common used roofs and used to be finished in lead, copper or other metals. Interestingly if we now come back to this era whilst metal flat roofs are a rarity and all sorts of new materials have come in for use asphalt is still a good flat roof material.

Newly asphalted flat roof


The question we are always asked about flat roofs is?

The question we always are asked about flat roofs is should flat roofs be flat?

Generally the answer is no as you need to drain rainwater off flat roofs as soon as possible. The problem with rainwater sitting on a flat roof is it becomes susceptible to freeze thaw action which is the freezing of rainwater in the winter and then the thawing. Expansion occurs as rainwater freezes and causes any weaknesses in the flat roof to open up even further and ultimately cause a leak in the roof.

The great thing about asphalt roofs is they are joint-less and such do not split as easily however they do split if rainwater is left to sit on them. Therefore the answer is that flat roofs should have a fall on them.


Please see our surveying articles on

Asphalt Roofs

Flat Roofs

Structural Survey, What does a Chartered Surveyor do?



If a flat roof is not meant to be flat what pitch should it have?

Whilst we believe that the Building Regulations requires 12 to 15 degrees (if you know the answer please email us) but it is far more important to use Common Sense and ensure that there is enough fall to get the rainwater off the flat roof and avoid any ponding/puddling occurring on the flat roof so the angle of the fall differs depending upon the size of the flat roof. When we use the term flat roof we mean a roof with a shallow pitch.


What is ponding?

Ponding is puddles on flat roofs which are almost common place. Unfortunately if there is not enough fall present on a flat roof a small pond appears and the weight of the rainwater that collects in our experience tends to increase the size of the pond by depressing the area of the roof. Gradually over the course of several years the depressing of the roof due to the volume of rainwater collecting becomes larger and larger.

The worse flat roof we have even seen was on a very famous designer building where the flat roof had dropped approximately 150mm or 6 inches or half a foot. How did we know this flat roof had a problem? The internal downpipes that take the rainwater away were standing this height above the roof level. Even more unfortunately there was a large, very expensive restaurant located beneath this flat roof.

Whilst we are discussing unbelievable flat roof issues we were called in to look at one roof on a snowy day where the downpipes were blocked and there was approximately 300mm (or 12 inches dependent upon which measurement system you prefer) rainwater on the roof which is a large weight with a shop below. From what we could see the large amount of rainwater sitting on the roof had been caused by the adjoining property rearranging the windows in the flats to allow people to be able to open the windows (originally the windows were sealed to this particular room) and from this point onwards people in the flats had thrown cigarettes out of them and all sorts of other things which had blocked up the drain points on the flat roof.

Ironically it was the landlord that made the changes to the windows who owned the building as a whole and was trying to get our client, the tenant or leaseholder of the shop, to completely replace the roof. This actually led to a court case.



Flat roofs truth or fiction?

Let us consider something that we have never known whether it is true or not and are sure that we have read a long time ago that a surveyor, when carrying out a structural survey, found fish in a pond on a roof. We are sure we are not talking about a very large fish but apparently the fish had been brought onto the roof via birds that had landed on the roof after being on a lake or pond then travelled onto the roof with fish spawn on them. We are never sure if this is a true storey or an urban myth? If anyone or any surveyors reading this article have seen similar things then please kindly phone us on free phone 0800 298 5424.


Other things you need to know about asphalt roofs

Whilst we are reiterating what we said earlier to install an asphalt roof is a craft and art and as such you require someone who is skilled in carrying out these types of flat roofs. You also need to understand that an asphalt roof is more expensive than any other sort of flat roof but in turn it lasts longer. In our experience an asphalt roof lasts longer but there is a reason for this please read on.

Excessive ponding on a felt roof

This is not a sales person talking but an Independent Chartered Surveyor who has surveyed many properties over many years and has found again and again that asphalt roofs last longer.


Are asphalt roofs repairable?

We, as Independent Chartered Surveyors, would respond to the question are asphalt roofs repairable that they are more repairable than most roofs as asphalt can be heated up and bonded into the existing roof. On the other hand if you look at a modern high performance felt or traditional felt or a mono-ply or single layer roofing system you are literally sticking on a sticking plaster type of patch repair whereas with asphalt you are bonding into the existing material.

Asphalt roof

Large asphalt roof


Please see our surveying articles on:-

Structural Surveys

Roof Problems and Information

Leaking Flats Roofs



What does asphalt look like?

For those of you who have never climbed onto a flat roof asphalt looks very similar to the tarmac that we drive on and walk on.


Problems with asphalt roofs

As you can imagine, with any material that is exposed to the elements and is protecting a building in an exposed location it does deteriorate and wear. However from looking at our life tables that we use that were compiled by other building surveys and surveyors carrying out surveys on properties typically asphalt has a life of twenty five to thirty years.

Property can be exposed to the elements and thereby the roofs


Cracks in asphalt

The cracks in asphalt often are known as crocodiling and lead to all sorts of problems such as rainwater getting into the property. Cracking is simply lines of cracks within the asphalt and the crocodiling or crazing is where you get a pattern similar to a crocodile's skin with many lines and cracks.

All these cracks are repairable the main problem however with an asphalt roof is that it is so reliable that you tend to forget about the roof. It is tempting not to carry out any surveys to check an asphalt roofs condition.


Blistering and crocodiling

A typical example of this would be an older public house which was extended in the 1950s/1960s with the addition of toilets (believe it or not we were still in the era of having outside toilets back then). This extension work was carried out to include asphalt flat roofs which had been left and left over the years and not checked nor maintained. In fact it can become worse than this if the toilets are then amended and altered over the years and become say part of a restaurant area and the first time that anyone is aware of a problem it affects the trading area.


Similarly with houses of the Art Deco era which was a great era for design and also for the use of large areas of flat roofs which were often carried out in asphalt have had problems.


Blistering in asphalt

An asphalt blister is very similar to the blister that may occur on your finger which often has moisture within the blister as the dampness in the structure is being drawn up and causing the blister. These blisters can effectively be popped or cut out and repaired. 


Asphalt is not a quick fix

We would say that asphalt is not a quick fix as the number of skilled trades' people that can carry out this work is limited and sometimes you will have to queue to wait for their services. There are a number of people who can install roofing felt, particularly with the newer products that are torch on, which require less skill.


Please see our surveying articles on:-

Buying a house

Why have a residential survey

What is an independent survey?


Hot, buckets of tar

Remember with asphalt roofs the roofer is moving around hot buckets of tar and will require his own kettle to warm up the tar. You literally cannot rely on a DIY store and purchase the products.

Buckets of tar



How do you use asphalt?

Heat up the tablets in a kettle and whilst the asphalt is in liquid form you then apply this to the roof in three coats . You can produce a proper, solid flashing all in the same material. Asphalt has flexibility too which is inherent in the material. You can also carry out flashings also; see adjoining photo with flashing circled in red.


Asphalt flat roof and flashing

Flashings Defined

Flashings prevent dampness from entering the property, usually at junctions where materials change. Such a junction is the one between the chimney and the roof.


Asphalt in summary

In summary asphalt is initially more expensive but lasts longer so you could say that on a day to day payback rate it is the cheapest flat roofing material (although we appreciate that most people look at the initial cost only). Asphalt is very repairable and the repairs are far better than the stick on sticking plaster repairs that you can achieve with other materials.

Detailing to areas such as parapet walls, roof windows and flashings are generally much better on asphalt flat roofs.


Please see our surveying articles on:-


Homebuyers Report or Structural Survey

Builders, building problems and roofs and how a Chartered Surveyor can help



Independent Chartered Surveyors

If you truly do want an independent expert opinion from an Independent Chartered Surveyor with regard to building surveys, structural surveys, structural reports, (and yes we do talk about flat roofs) we also carry out engineers reports, specific defects report, (and we can carry these out on flat roof problems if you so wish) dilapidations (yes, we do look at problems associated with flat roofs) or any other property matters please contact 0800 298 5424 for a friendly chat.


Commercial Property Surveyors

If you have a commercial property, be it leasehold or freehold, then you may wish to look at our Dilapidations Website at and for Disputes go to our Disputes Help site .


We hope you found the article of use and if you have any experiences that you feel should be added to this article that would benefit others, or you feel that some of the information that we have put is wrong then please do not hesitate to contact us (we are only human).

The content of the website is for general information only and is not intended to be relied upon for specific or general decisions. Appropriate independent professional advice should be paid for before making such a decision.

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