Flat Roofs - Part 2 - Built up Felt - Problems to look for

A well constructed and properly maintained flat roof should remain in serviceable use for approximately 15 – 20 years. Life expectancy can vary depending on a number of different factors however if not regularly inspected and maintained there are numerous problems that can occur

In my last article I provided a brief summary of typical UK flat roof construction together with an explanation of different roof coverings.  As a result of the design/form of a flat roof they are often more vulnerable than pitched (angled) roofs to problems due to their reduced ability to discharge rain and other surface water adequately. A well constructed and properly maintained flat roof should remain in serviceable use for approximately 15 – 20 years. Life expectancy can vary depending on a number of different factors however if not regularly inspected and maintained there are numerous problems that can occur.  Below I will discuss a number of typical problems that can be found when inspecting a flat roof and how these can be identified.

You do not need to be a surveyor or have any detailed knowledge of property or construction to realise that there are clearly issues with the flat roof shown in the images below.  Some of these images show us the extent that people will sometimes go to carry out temporary ‘repairs’, when it is clear that there is a much bigger problem. 

Source: http://grandvalleyservices.ca/

Source: http://www.diychatroom.com/

Source: http://www.showalterroofing.com/

Built up Felt Flat Roofs

Water Ponding – Water ponding can occur on a flat roof for a number of different reasons, for example the roof was not designed or constructed correctly in the first place and is not allowing water into guttering our outlets, there could be impact damage (possible people walking across) or heavy loadings such as plant or materials that have resulted in ‘depressions’ in the roof, outlets or guttering could be blocked etc.  In any event prolonged standing water on a flat roof can result in degradation of felt, stress and failure of joints, increased risk of condensation (as the internal roof surface temperature is reduced), and the build-up of moss and lichen.  Standing water will also freeze in sub-zero temperatures, further increasing the possibility of condensation as well as becoming a health & safety risk if there is a need to gain access to the roof at that time.

Source: Google Images

Although not the nicest of conditions, the best time to inspect a flat roof is in poor weather conditions particularly whilst it is raining.  This will highlight many of the problems with design, workmanship and general deterioration. Even in the warmer months when it may not have rained for a long time a surveyor will still look for visual clues that may indicate water ponding, such as a build-up of moss and debris, general staining of the roof covering or damaged coverings etc.  The image to the left provides an example of this.

Simple regular maintenance such as clearing gutters and outlets will help to reduce water ponding however this is something that is often overlooked by many property owners/occupiers.  This is likely to be because many flat roofs are out of sight (and therefore out of mind!) and unless the roof starts to exhibit problems many will choose to ignore it. Water ponding problems as a result of poor design or poor workmanship are often more problematic to deal with and consequently more expensive.  Again, many people will choose to live with these problems until of course the roof starts leaking and causing consequential damage to other parts of a building.

Source: http://thermalimages.ca/

Blistering of Felt – A fairly common issue identified by surveyors when inspecting a built up felt flat roof is blistering of the felt roof surface.  This occurs where water vapour pressure becomes trapped underneath the roof covering between layers of felt that have been inadequately bonded.  Any trapped water or moisture will evaporate and expand.  As it is trapped and cannot escape it will force the felt to form a blister. The source of any moisture will need to be addressed before any repairs are undertaken otherwise the problem will re-occur.  Blistering sometimes occurs when the felt covering is laid onto a substrate that is not fully dry, possible when roofing works are being undertaken either after or whilst it is raining.

Source: http://www.newcastlene1.co.uk/

Cracks and Tears - Cracks and tears to felt roof coverings can be caused by thermal or moisture movement, saturation of insulation or sagging of the roof deck. Cracks and tears can also occur when there is thermal or moisture movement between the roof substrate and membrane. In most cases the impact of thermal movement is not visible to  the naked eye, however even though we cannot see it, building materials expand and contract by varying amounts when they heat up and cool down. This is due to their differing coefficients of thermal movement. Materials expand because an increase in temperature leads to greater thermal vibration of the atoms in a material, and hence to an increase in the average separation distance of adjacent atoms. Due to the fact that roofs in the UK can experience a significant temperature difference due to the varied climate, the roofing felt material will be reacting to these ever changing conditions by expanding and contracting continually.  This can sometimes result in crack or tears appearing in the felt surface which can often be repaired by cutting back the existing felt and allowing the area to dry before applying a new layer of felt with a suitable overlap between the new and existing material.

Other issues such as de-bonding at up-stands can also be encountered by a surveyor during an inspection of a built up felt flat roof as well as numerous other problems that occur as a result of poor workmanship.  In my next article I will discuss problems associated with mastic asphalt flat roofs, where some similar issues to those described above will be explored together with some other problems that may occur as a result of using a different material.

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Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

Flat Roofs – Part 1 – Different Types

I often find that the choice of flat roof construction is usually one of convenience and cost, however, this really is a false economy as the costs of maintenance, repairs and replacement of a flat roof, from a life cycle cost perspective, usually work out more expensive than constructing a pitched roof in the first place

Source: http://www.angleseyroofing.co.uk/gallery/

Flat roofs are commonplace throughout many parts of the World and are regularly used throughout the UK.  One of the primary functions of any roof is to keep the internal environment dry and it is essential that water is prevented from entering the internal environment.  Whereas pitched roofs readily allow rainwater to drain into gutters and downpipes due to their design, flat roofs tend to be more problematic particularly if not designed and constructed appropriately.  The use of flat roof construction in warmer parts of the World which experience limited rainfall is less problematic than in a varied climate such as that encountered in the UK, where the potential for extensive prolonged rainfall is highly likely.  I often find that the choice of flat roof construction is usually one of convenience and cost, however, this really is a false economy as the costs of maintenance, repairs and replacement of a flat roof, from a life cycle cost perspective, usually work out more expensive than constructing a pitched roof in the first place. The problem we seem to have in the UK is that property owners and occupiers do not think long term and most will not reap the benefits of longer term investment because people tend to move on a regular basis.

I am sure that many Building Surveyors (and others who inspect property on a regular basis) will agree that flat roofs are something that warrant a particularly close inspection and is an element where regular problems are identified.  In next week’s article I will focus on some typical defects/problems to look for when inspecting flat roofs however for the remainder of this article I want to focus on different types of flat roofs typically found in the UK.  When we refer to different types of flat roofs we can basically consider these in terms of both construction and coverings.  

Figure 1 - Source: Source: http://www.diynot.com/

A flat roof is defined in BS 6229 as having a pitch (gradient) of 10 degrees or less.  Therefore a flat roof is not actually completely flat and should be constructed with a subtle gradient which will allow any rainwater to find its way to gutters or outlets.  Even a small gradient of a few degrees will allow rainwater to become mobile by gravity, although clearly the greater the gradient the better.  There are a number of ways of achieving this subtle gradient on a flat roof such as the use of timber firing strips onto of joists (as seen in figure 1), however I have stumbled upon many examples when these have been incorrectly installed and in numerous cases completely omitted. In fact the vast majority of problems I encounter with flat roofs were a result of either poor workmanship during installation or lack of general maintenance.

In terms of flat roof construction there are two common types used in the UK, cold roof construction and warm roof construction (I will discuss flat roof coverings a little later). Buildingregs4plans.co.uk (online) provide a concise explanation of warm and cold roof construction which is used below;

Warm roof construction - In a warm deck roof the insulation is positioned above the structural deck and no ventilation is required. Throughout the course of the year the roof deck and all below it is kept at a temperature close to that of the inside of the building, therefore the roof structure is protected from extremes of hot and cold, lessening the potential for damage caused by thermal movement.

Figure 2 - Source: Source: http://www.buildingregs4plans.co.uk/

A warm deck also provides added protection from the dangers of condensation as the structure is kept warm, at a temperature above dewpoint, by the insulation above it. Therefore water vapour which enters the roof structure from the room below will not have a cold surface on which to condense. NHBC recommend that this type of roof be considered as the standard form of construction. (Figure 2)

There are two forms of warm deck roof, sandwich and inverted.  The sandwich warm deck roof is the most common type of flat roof. The insulation is placed below the waterproof covering and is either mechanically fixed or bitumen bonded on to the top of the deck.

Figure 3 - Source: Source: Chudley R. & Greeno R (2005), Building Construction   Handbook.  

The insulation boards in an inverted warm deck are laid over the structural deck and the waterproof covering. The insulation is secured by a layer of ballast or paving slabs to prevent wind uplift. The waterproofing membrane has the added protection of the insulation from foot traffic and degradation caused by exposure to solar radiation. However, it may be a more difficult to locate defects in the membrane (insert image 4)

Cold roof construction - In a cold roof the thermal insulation is laid between the joists below the structural deck. As the insulation is not required to take any loads, quilts and other loose fill materials can be used as well as rigid insulation. Because the structural elements of a cold roof are not protected by from the heat of the sun by a layer of insulation they are liable to suffer the damaging effects of thermal movement. Ventilation is required above the insulation in a cold roof to prevent the build-up of moisture vapour in the roof void. (Figure 4).

Figure 4 - Source: Source: http://www.buildingregs4plans.co.uk/

In addition to the construction types described above, flat roofs are also often referred to by the type of covering that is used.  In the UK, built up felt, mastic asphalt and single ply are the common types of coverings installed.  Some of the typical problems with flat roofs that I will discuss next week are a direct result of the type of covering selected.  It is therefore essential that an appropriate covering is considered during design and installation.

Built up Felt Roofing - involves the installation layers of tar impregnated roofing felt which are rolled out onto a roof.  Each layer overlaps the previous layer and in between the deck material and each layer of felt a layer of hot tar is applied over the surface.

Mastic Asphalt Roofing - premiermasticasphalt.co.uk (Online) define mastic asphalt as; comprises suitably graded aggregates bound together with an asphaltic cement (primarily refined bitumens) to produce a dense voidless material.  It cannot be compacted and is spread rather than rolled. As mastic asphalt is installed as a ‘hot liquid’, when it cures (cools down) it provides a continuous impervious membrane with no joints making it extremely waterproof.

Single Ply Membranes - everybodyneedsaroof.com (online) define Single-ply membranes as; factory-manufactured sheet membranes. which are generally catagorised as thermoplastic or thermoset. Thermoplastic materials can be repeatedly softened when heated and hardened when cooled. Thermoset materials solidify, or "set," irreversibly after heating. Single ply membranes commonly are referred to by their chemical acronyms, such as ethylene propylene diene terpolymer (EPDM). Single-ply membranes can be installed fully adhered, mechanically attached or held down with ballast. Most single-ply roof systems do not receive surfacings. 

The information above provides a brief introduction into UK flat roof construction and flat roof coverings and should be used as a reference point for the problems/defects associated with flat roofs that will be discussed next week.

Please feel free to share this article and other articles on this site with friends, family and colleagues who you think would be interested

Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

Listed Buildings – Why should we protect our past?

We have a wonderfully diverse range of buildings in the UK and an equally diverse built environment which has responded to many years of change, development and progress. We clearly need to embrace change however our unique heritage in the UK would be quickly lost if all of our important and historic buildings were to be demolished and replaced with new modern buildings

Source: http://www.geograph.org.uk/

In 1709 Jonathon Swift, an Irish Cleric, Writer, Poet and Politician once commented; ‘nothing in the World is constant, but change’. In this fast moving World this is particularly true of the built environment which continues to find ways of re-inventing itself to keep pace with technology, innovation, population growth and to respond to issues such as depleting resources such as fossil fuels as well as global warming. 

We have a wonderfully diverse range of buildings in the UK and an equally diverse built environment which has responded to many years of change, development and progress. We clearly need to embrace change however our unique heritage in the UK would be quickly lost if all of our important and historic buildings were to be demolished and replaced with new modern buildings.  It is for this reason that selected buildings in the UK are given statutory protection, which makes it a criminal offence to alter, develop or demolish, depending on the protected status of the building (discussed below), without permission.  You will often hear protected buildings referred to as ‘listed buildings’. 

Listed buildings were first introduced during World War II as a means of deciding which buildings should be rebuilt if they were damaged by bombing. Not long after World War II had ended the introduction of the Town and Country Planning Act 1947 resulted in the compilation of the first list of buildings of special historical or architectural importance. Since then more and more buildings, monuments, site, landscapes and other miscellaneous items have been added to the list in order to preserve our heritage. Currently, listed buildings are designated by the Secretary of State for Culture, Communications and Creative Industries, acting on advice provided by English Heritage.  English Heritage will assess a building’s suitability for protected status and will then make a recommendation to the Secretary of State for Culture, Communications and Creative Industries, who can then decide to either accept or reject the recommendation.

If a building is designated for statutory protection (Listing), then it will be allocated into one of the following categories:

Categories of listed buildings (Source: English Heritage)

-   Grade I buildings are of exceptional interest, sometimes considered to be internationally important; only 2.5% of listed buildings are Grade I

-   Grade II* buildings are particularly important buildings of more than special interest; 5.5% of listed buildings are Grade II*

-   Grade II buildings are nationally important and of special interest; 92% of all listed buildings are in this class and it is the most likely grade of listing for a home owner.

The selection process for protected status is much wider than you would imagine.  When I ask my students ‘what is a listed building?’, the usual first reaction is an ‘old historic building’ where they usually provide examples such as Tudor timber framed buildings with thatched roofs or medieval castles.  Whereas, these examples given are not bad ones, the scope and selection of listed buildings is much wider than age and appearance.  The older a building is and its rarity will be a strong influencing factor in respect of whether it will receive protected status in addition to its appearance, both in terms of its architectural merit and whether the building is part of a collection of similar buildings.  Architectural merit will not always relate to ‘older’ buildings as there are examples of many more ‘modern’ buildings that have been listed as a result of their unique structure and form.  

Source: http://www.newrailwaymodellers.co.uk/

A good example is the signal box at Birmingham New Street Station (see image).  Many people are surprised to when they find out that the signal box is listed and therefore protected, as it does not follow the conventional perception of what people think a listed building should be.  An article in the Birmingham Post on-line (Link) describes the unique features of the signal box; ‘Designed by Bicknell & Hamilton and W.R. Healey and completed in 1965, the unapologetically bunker-like structure is an honest expression of its utilitarian function. Standing five storeys high above track level, the building gives no clue of the hive of activity that exists within its four walls. The technology inside is of the same era as the exterior façade and was revolutionary for its time. The Relay Room sits just above street level and houses enormous banks of algorithmic electronic relays, known as Wespacs, which are programmed to calculate legal routes for the trains to take.’

A building may be also listed because it represents a particular historical type.  A good example of this is the prefabricated houses that were erected in the 1940’s as a means of providing housing quickly for those affected by bombing during the war.  I have previously written an article on 1940’s prefabs which you may find of interest (Link).  These houses were only designed to solve a short term problem, however as the majority have now been demolished the ones that remain provide a permanent insight (because they are now listed) into a unique form of simplistic construction, one that I have to admit I find fascinating.  If we did not have the ability to protect these types of buildings then it is likely that they could have all disappeared without a trace, which would have been a real shame.  Occasionally English Heritage will also select a building because the building has played a part in the life of a famous person, or as the scene of an important event. 

In order to ensure that our heritage does not get lost in this modern World it is fundamentally important that we provide a level of protection that ensures that future generations can appreciate the built environment of their predecessors. Statutory protection and listed status allows this protection and whilst many may not approve of every building, structure or monument that is given this protection, it's importance cannot be understated.

Please feel free to share this article and other articles on this site with friends, family and colleagues who you think would be interested

Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

UK Housing Market - What's in Store for 2015?

The UK government acknowledge the importance of the housing market to the UK economy and over the last few years have tried to ‘push it along’, with the introduction of a number of initiatives and policies, such as the help to buy scheme, changes to planning policy and recent changes to stamp duty thresholds

Source: http://www.theguardian.com/

Trying to predict what will happen in the housing market over the next twelve months and beyond is always a topical subject, which generates a wide range of debate particularly as we enter a new year.  Any decision on whether to enter the market or to buy or sell will be dependant upon many different factors and particularly by an individual’s current position on the housing ladder.  There will be those who are looking to get onto the first rung of the ladder and those who want to move further up the ladder who may be looking to ‘upsize’ or even ‘downsize’ depending upon their circumstances.  There will also be those who may be stuck in negative equity as a result of decline in the market over recent years and are looking for the first opportunity to escape. In any event the housing market affects a lot of people who will be watching closely to see what happens before making any decisions.

The UK government have acknowledged the importance of the housing market to the UK economy and over the last few years have tried to ‘push it along’, with the introduction of a number of initiatives and policies, such as the help to buy scheme, changes to planning policy and recent changes to stamp duty thresholds. Over the course of 2014 there has clearly been some positive momentum in the UK Housing market undoubtedly influenced by continued low interest rates and no doubt the impact of initiatives such as the help to buy scheme. However, as ever, opinion seems to be split (depending on what you read) on the effectiveness and impact of these initiatives and policies and only time will tell whether they prove to be a benefit or otherwise.  This really is the crux of the matter; will these types of initiatives and polices create sustainable growth in the housing market progressively or will the benefits be only short lived? Well, as identified at the beginning of this article, the answer is undoubtably one of perspective and will depend on individual circumstances and where a person is on the housing ladder.  An advantage for one person may be a disadvantage for another. Rising house prices is a prime example.

Source: http://www.thisismoney.co.uk/

Telegraph Online (Link)recently reported; ‘The average British homeowner saw their property wealth grow by £15,000 this year (2014) – or an astonishing £81,000 for those owning homes in London. The data, from property website Zoopla, is the first to put a figure on house price growth for the year 2014. A tranche of similar numbers from other property price analysts are due in the next few weeks. They are expected to confirm Zoopla's figures and highlight what has been an "extraordinary" year in the British housing market, characterised by a booming first half and then a rapid cooling off. Zoopla said prices across the country rose 6pc bringing the average value to £268,895.’

House Prices - Those who are eager to enter the housing market for the first time may have been biding their time while they save a deposit and no doubt become increasingly frustrated as house price steadily increase. As house price start to increase so does the deposit proportionally, possibly delaying the point at which they can enter the market.  Increasing house prices become less of a problem for those who are already on the housing ladder, because although the purchase price of the next property may increase, so will the price of their existing property, although not always at the same rate.  This is particularly an issue for those who plan to relocate to a different part of the country due to regional price differences, which can be significant.

FT Advisor Online (Link)predict that; ‘House prices will continue to rise in 2015 as gross mortgage lending hits a five-year high next year, Ray Boulger, senior technical manager at mortgage broker John Charcol has predicted. Mr Boulger also said he expects house prices to rise by 4-5 per cent in 2015. He believes that the rate of house price increases will continue slowing, but on-going low interest rates mean that for most people affordability will continue to be more around the deposit than the monthly payments’

Interest Rates – Telegraph Online (Link) recently reported; ‘Rates have remained at a record low (0.5%) since March 2009. The Bank now expects inflation, as measured by the consumer prices index, to fall below 1 per cent next year, from October’s rate of 1.3 per cent. Most economists believe interest rates will start to rise in the second half of next year (2015). Bank of England policymakers are increasingly divided over the best time to start raising interest rates without putting the recovery at risk’

In a previous article I discussed the implications of interest rate rises (Link) and explained that even a small increase in interest rates will pose difficulties for many with variable rate mortgages, particularly those who have borrowed to their absolute maximum.  As an example the table below provides an indication of the financial impact of an interest rate increase on a variable rate 25 year repayment mortgage loan of £150,000, assuming and existing current interest rate of 3%:

Mortgage amount	£150,000	£150,000	£150,000	£150,000
Current Interest Rate	3%	3%	3%	3%
Interest Rate Increase	0.25%	0.5%	0.75%	1.00%
Existing Monthly Payment	£717.85	£717.85	£717.85	£717.85
New Monthly Payment	£737.99	£758.43	£779.15	£800.15
Increase per Month	£20.14	£40.58	£61.30	£82.30
Increase per Year	£241.72	£486.92	£735.57	£987.61

With house prices predicted to continue to rise in 2015, although much more sedately than in 2014, and interest rates predicated to increase for the first time since 2009 in the second half of 2015 this is likely be another challenging year for the UK housing market.  Although the housing market is showing signs of life we need to ensure that the pace of recovery is sustainable.  This will not be achieved by positive publicity (or spin) alone, but must be underpinned by realistic and tangible means.  Building more homes seems logical, however this is impacted by planning policy, skills shortages, funding and numerous other issues that the government need to sort out to enable us to address our massive housing shortage.

Whichever way you look at it the issues inherent in the UK housing market are not new and have existed for many years, so what are we going to do differently in 2015?  Well, it is likely that we will see very little will change in the space of one year, however if we can continue to make steady measured progress in the housing market in 2015, (rather than short term gains) then we may be on the road to a sustainable recovery which in the mid to long term future will be to the benefit to everyone.

Please feel free to share this article and other articles on this site with friends, family and colleagues who you think would be interested

Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.