Basement Construction - Part 1 - Design Considerations

When considering whether to construct a basement it is first worth weighing up the advantages and disadvantages, and then also thinking about a number of design considerations which will undoubtedly impact on the construction method, waterproofing, safety, usability and ultimately, costs

Source: http://basementwaterproof.com/

A recent article in the London Evening Standard (link) highlighted the growing popularity of basement construction, particularly where land is at a premium or restricted above ground.  The scale of the proposed basement construction in the article was extensive to a point where it generated a section 106 contribution of £825,000!:

A millionaire hedge fund boss digging out a basement eight times the size of a typical London home has been ordered to pay £825,000 towards affordable housing in his area.

Kensington & Chelsea council planners said the two-storey, 9,160sq ft basement — complete with cinema room, swimming pool and whirlpool spa — is the biggest they have been asked to approve. The scale of the extension, below two large Notting Hill villas which have been turned into a single family home, means it has fallen foul of rules that normally apply only to major commercial developments.

The fashion for digging out super-size basements to create so-called “iceberg homes” in London, and the prospect of years of disturbance during excavation, has pitted residents against each other in some streets ......... neighbours are said to be horrified by the scale of the works which will involve scores of lorry loads of earth being removed from the site. One said: “It will certainly be one of the ‘iceberg houses’ and sadly, our house will probably be the Titanic.” The number of applications for subterranean spaces in Kensington & Chelsea has soared in recent years.......

Source: http://www.kitchentoday.net/

Although the news article identified above is a rather extreme example of a basement construction it does demonstrate an alternative way of providing valuable useable space when above ground construction may be restricted or unavailable. Basement construction is still considered a less conventional method of adding space compared to above ground construction and is often instigated by those who are prepared to challenge the conventional norm and think outside the box.  There are however many examples of residential buildings throughout the UK where basements were constructed as a normal part of the building process. Houses built during the Victorian period provide a typical example of where basements were commonly constructed.  Nowadays, these Victorian basements are often converted and refurbished to made them part of the useable habitable space within a dwelling.

When considering whether to construct a basement it is first worth weighing up the advantages and disadvantages, and then also thinking about a number of design considerations which will undoubtedly impact on the construction method, waterproofing, safety, usability and ultimately, costs. Clearly basements can add space and value to a property and it could also be argued that security can be less of an issue as there will be less accessible entry points into a basement, as by its very nature the structure in buried in the ground.  Also, as long as the basement is waterproofed appropriately (something I will be discussing in my next article), and insulated correctly, you could argue that a basement can be made energy efficient more readily that an above ground building. Conversely, the perceived disadvantages and the impact that these may have on costs will prevent a lot of people proceeded beyond the initial enquiry stage when considering basement construction.

Source: http://restorationeze.com/

One of the key things to consider is that by placing an enclosed structure such as a basement in the ground you are subjecting the structure to a number of different forces. The first is the presence of water in the ground.  Water is a naturally occurring element in the ground and the level of this water will vary from location to location.  Many will be familiar with the term ‘water table’ which can be understood as the layer below which the ground is completely filled up (or saturated) with water. Try to imagine a basement like a boat which is surrounded by water in the ground.  The problem is that boats leak, and so do basements!  A basement is unlikely to sink like a boat, but because the basement is an enclosed structure it has the ability to hold a lot of water if the basement is not adequately waterproofed.  Water in the ground also has the ability to exert a lot of force onto the structure of the basement depending on the head or height of the water.  This is something known as hydrostatic pressure.  This is better defined as ‘the pressure at a point in a fluid at rest due to the weight of the fluid above it’. Basement design therefore needs to take into account the height of the water table because that will influence the amount of hydrostatic pressure that a basement structure will be exposed to.  The method of waterproofing will also need to be designed to consider hydrostatic pressure.

In order to design and construct a basement correctly it is first necessary to establish ground conditions. This will require a thorough ground investigation which although will have a cost attached to it, is essential at the very early stages of a project. This will also highlight the type of ground and any contaminants present together with information of water in the ground and importantly the height of the water table. Other design considerations will include; protection and stability to adjacent structures, basement depth, boundary issues including Party Wall etc. Act implications, method of excavation, temporary support, method of construction in addition to exclusion of ground water.  Of course all of this will have an impact on costs and there is no getting away from the fact that constructing a basement can be very expensive. 

In my next article I will consider a number of methods of waterproofing of basements and explain that the correct choice of which method to use is crucial to ensure that the internal environment within a basement remains dry.

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.

Thatched Roofs – Roofs that have stood the test of time!

There is no doubt that a timber framed building with lightweight infill walls of wattle and daub and a thatched roof provides an element of charm and there are many examples of similar buildings throughout the UK

Source: Own

I was recently driving through a rural village located approximately two miles from where I live in the West Midlands when I can across the building on the right, where you will note that the thatched roof was in the process of being renewed.  There is something fascinating about thatched roof buildings which give a real sense of history and I could not drive past without taking a few photographs. There is no doubt that a timber framed building with lightweight infill walls of wattle and daub and a thatched roof provides an element of charm and there are many examples of similar buildings throughout the UK. Wattle and daub was a method of weaving small branches between parts of the timber frame and then 'plastering' onto the weaved branches a mixture of clay, horsehair and sometimes horse dung! with water,  This would be smoothed when wet and when it dried out it provided an effective wall finish that would be reasonably weather tight. 

Thatched roofs were the main form of roof construction for many hundreds of years throughout many parts of mainland Europe and were particularly popular in the United Kingdom. Early forms of thatched roofs in the UK can be traced back to Celtic Roundhouses (circa 750BC to 12BC) where a combination of straw and mud were used in order to try to provide a watertight environment. The Romans (circa 43AD to 410AD), Anglo Saxons (circa 420AD to 650AD) and the Vikings (circa 700AD to 1000AD) all continued to make use of natural resources such as timber for buildings and straw and reeds for thatch for their roofs. However the Medieval Age (circa 1066AD to 1500AD) is arguably the period of UK history where the use of thatch really accelerated and there are many examples of these types of building still in existence today.  Many Tudor Buildings (circa 1485AD to 1603AD), continued to make use of timber frames with thatched roof however toward the end of this period other types of materials such as clay tiles were starting to be introduced in place of thatch.

Source: http://gogermany.about.com/

It is clear that thatched roofs were popular, primarily because they were light weight (compared to modern materials), and could easily be supported from timber frames and subject to appropriate installation, would be watertight for many years.  The use of thatch began to decline with the evolution of transport, particular rail, during the early Victorian Period (Circa 1837 to 1901), which allowed the transfer of materials such as Welsh slate across the UK as an alternative to thatch.  The decline in the use of that is identified by the Diseworth Heritage Trust (Online): ‘It is estimated that the number of thatched buildings in England decreased from one million in 1800 to about 35,000 by 1960, due mainly to lower transport costs and new techniques enabling other materials (such as cheap slate from Wales, or mass produced clay tiles) to be used, with less skilled labour. The onslaught of combine harvesters had much to answer for too. With a far shorter cut, the wheat straw became unusable for anything other than grain production. Today, there are around 24,000 listed thatched buildings in the UK, and about 1500 individuals engaged in thatching.  Thatch is also being used on some new builds, so there is something of a revival in progress’

It is easy to wonder how thatch is able to provide a watertight roof surface given that it is fundamentally straw or reeds placed on top of a building that is exposed to the elements often over a long period of time.  The answer lies in the manner in which the thatch is installed and the pitch (angle) to which the roof is constructed. In fact if you compare a thatched roof to a roof constructed with concrete or clay tiles you will often find that the thatched roof will have a much steeper pitch, typically 50 to 55 degrees, which allows rainwater to be shed much more readily.

The Conservation of Traditional Thatch Group (Online) provide a useful insight of the thatching process: 

‘Most underlying roof structures are formed of timber with the thatch supported by battens spanning between rafters. The main coat of a thatched roof is formed by fixing bundles of thatch, with their lower ends aligned, in overlapping courses from the eaves and verges upward towards the ridge, to form a thick layer (or coat). For most roofs this will be about 250-300mm (10 – 12 inches) thick, although in some techniques much thinner coats are used. For a new thatched roof, the thatch is fixed by tying to the rafters, battens or other support. Subsequent coats can be applied over the remains of underlying coats and fixed using spars and sways or metal fixings. 

Thatch was traditionally fixed down by clamping the bundles to roof timbers. Sways (long hazel or willow rods, about 2-3cm (1 inch) in diameter) were laid across the bundles of thatch and held in place with twine or rope passed down through the thatch by means of a hook or large ‘needle’ and tied round the support. In the earliest roofs, plant stems were used, but by the 18th century hemp rope or twine (sometimes tarred to discourage damage by rodents) became the norm. Wire netting was introduced in the late 19th century to provide additional protection from birds and rodents. Nowadays, plastic netting is often used. Netting can be applied to either just the ridge or over the entire roof’

As you would imagine from reading above, thatching a roof requires a skilled craftsman who has undertaken their ‘apprenticeship’ over many years, and this is not something that should be attempted by anybody. We must ensure that we protect this craft to ensure that traditional thatching skills are not lost and in the process help to ensure that we can continue to enjoy the many wonderful thatched roof buildings that we have throughout the UK.

Take a look at the series of youtube videos below which show the thatching process in excellent detail:

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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.

Dry Rot – An ‘Intelligent’ Fungus requiring intelligent diagnosis

The reason that dry rot is often so devastating is because of its ability to travel long distances as it searches for more and more timber to remove moisture from

Source: http://www.timberwise.co.uk/

As a Building Surveyor there are certain words that you know, just by saying them will strike fear and panic into the majority of members of the public.  Words such as subsidence or asbestos are examples which regularly appear in the news due to significant cost or health implications. In many cases however, potential subsidence or the identification of asbestos often result in relatively simple and cost effective solutions although it seems to be a natural human reaction to automatically think the worst.  The ‘term’ dry rot is also generally well known by members of the public, however unlike subsidence and asbestos the implications of the discovery of dry rot are often serious, depending upon the stage at which it is actually identified.

I was recently watching a well know property renovation programme on TV a few weeks ago where the Presenter had identified what looked to be dry rot on the ground floor of semi-detached three bedroom residential property.  Although, I agree that what he was looking at did appear to be dry rot, his description included, ‘feeding off concrete’ which is completely inaccurate as well as some of his terminology being confusing and wide of the mark.  TV programmes should be mindful of the information that they provide, as it is possible, dare I say likely, (just by the nature of the amount of viewers), that someone will act on what they are being told which could result in loss/damage.  In order to identify if or where dry rot may be present, it is useful to understand the conditions that dry rot needs to grow and thrive. 

Source: http://livingtherusticlife.com/

Dry rot is a fungus, often referred to as an ‘intelligent fungus’.  The reason dry rot is referred to as intelligent is because of its ability to travel across non-timber surfaces and to take moisture from timber.  What is left behind is dry friable timber that can easily be broken up with moderate hand pressure.  The reason that dry rot is often so devastating is because of its ability to travel long distances as it searches for more and more timber to remove moisture from. It is worth noting that when the dry rot fungus travels across non-timber surfaces such as bricks, mortar, concrete etc. it is just using these as a route or bridge to find other timber.  Dry rot does not ‘feed’ off these types of surfaces but carries moisture with it in strands which allows it to grow and spread. If left untreated dry rot has the ability to affect vast amounts of timber within a building, often resulting in extensive specialist remedial works which are not cheap.

Dry rot is a living fungus which will continue to grow by feeding off timber, which it will completely destroy be removing all of its moisture.  Without being too technical, there are four primary stages in the dry rot lifecycle.  The first stage is Spores. The spores are constantly present in the atmosphere however are only activated in certain conditions, which include timber and moisture.  For dry rot to thrive it’s ideal environment will include timber with a moisture content of between 22% and 25% warm humid temperatures of between 24⁰ and 30⁰, poorly ventilated areas and dark concealed spaces. This is why dry rot will often spread undetected in basement, floor voids, roof voids, behind plasterboard in timber stud walls and the like. As the spores start to become more concentrated they develop into small white strands known as Hyphae, which look a little like small white cob-webs.  These are reasonably easy to identify and a good indication of dry rot.

As the hyphae feeds off the timber it will extract further moisture from the timber as it continues to grow and become more concentrated in volume to a point where the hyphae mass develops into the next stage of the dry rot cycle, know as Mycelium. Visible large white mycelium strands can travel large distances in search of more timber and as previously stated can travel across non-timber surfaces in order to find new timber. In suitable conditions, mycelium will continue to exist and grow at a considerable rate within a building. Fungi prefers dark and damp areas with little or no air movement, therefore where these conditions change and threaten the fungus; its natural response is to create a Fruiting Body (Sporophore), and this is the final stage of the dry rot lifecycle.  Visually the fruiting body can take a number of forms, however will generally appear in ‘mushroom like’ form. The fruiting body is the fungi's response to a threat to its survival and its reaction is to throw out spores into the air which can be transferred to other vulnerable areas within the building, which allows them to germinate and create a new attack of dry rot, thus restarting the dry rot life cycle right from the very beginning.

The dry rot lifecycle described above demonstrates how the fungus can spread so quickly and how much damage that can be caused if left undetected. It is possible to treat dry rot however this requires specialist knowledge and something that should not be attempted ‘on the cheap’.  If all traces of dry rot are not dealt with then all that will happen is the fungus will continue to grow and spread and start to affect any new timber that may have been installed. The steps below provide an indication of remedial works to deal with dry rot, however please bear in mind that this is indicative only and specialist advice should be sought in all situations:

1.   Deal with the moisture source

2.   Brush down any exposed masonry to remove visible surface fungal growth

3.   Deep-drill masonry at regular centres and irrigate with fungicidal wall solution

4.   Sterilise all exposed masonry surfaces with fungicidal wall solution

5.   Remove all affected timber including a minimum of 1m past the last identifiable location

6.   Dispose all affected timber from site

7.   Provide new treated and primed timber where previously removed

8.   Spray all new and adjacent timbers including cut ends with fungicidal spray

9.   Re-plaster where required using a cement and sand render mix

10. Ensure adequate ventilation is used

Dry Rot is easy to misdiagnose and I would always recommend that you engage the services of a professional such as a Building Surveyor for advice and guidance.  The short video below provides a good example of dry rot occurring in a residential dwelling and is well worth look. Many thanks to Bryan Hindle who has provided his kind permission for use of the video. Please also take a look at Bryan's excellent article on the following link

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.

Built Environment Professions - Part 3 - Mentoring - A Professional Necessity

New members of staff require time and if a mentor does not allocate sufficient time to train and supervise them then the consequences are likely to result in a demotivated member of staff who is not developing and likely to make mistakes. If this is the case an employer should question their selection of mentor or ask themselves if they have made provision to fulfill the role effectively with the mentor’s workload.

Source: http://caithnesschamber.com/

Any successful business will undoubtedly have staff development as one of their core business objectives and understand the importance of the continued professional development of their employees.  Although training and development should occur at all levels of a business, a key part of the process involves training of new and junior members of staff when they are embarking on their new profession/role for the first time.  These are the type of people who will be extremely ‘green’ and have maybe decided on a career change or just left education and think they are now ready to enter the stresses and strains of the professional world.  If we take a second to think back a few years (in some cases, like myself, more than a few years) to the time when this was us, you may remember feeling lost, often alone and generally overwhelmed at times. 

If your experience was anything like mine, you were thrown in at the deep end and allowed to sink or swim and basically learn by your mistakes.  Unfortunately, times have moved on and the litigious nature of the professional world, no longer affords us this luxury.  Nowadays organisations appear to be much more inclined to take the training of their newer employees much more seriously and often attach individuals to mentors.  Mentoring is defined by Eric Parsloe, The Oxford School of Coaching & Mentoring, as: "Mentoring is to support and encourage people to manage their own learning in order that they may maximise their potential, develop their skills, improve their performance and become the person they want to be’. The role of a mentor is therefore a significant one, usually allocated to an extremely busy individual who will be expected to work closely and oversee the activities of a new member of staff for a defined period of time.

Source: http://shetakesontheworld.com/

For mentoring to be effective it requires time and commitment from the mentor. However time is often a commodity in short supply and if the mentor is not aware or does not take account of the time needed to adequately fulfill their role then the results can be disastrous. Employers need to select mentors very carefully and try to ensure they are appropriately trained, they know what is expected of them and importantly the extra time needed to fulfill the role is taken into account in the mentor’s workload.  If an employer does not take account of these things when selecting a mentor then a number of things will happen.  Firstly, the allocated mentor will immediately feel that the employer is allocating them an additional responsibility with no consideration for their current workload.  Secondly, the new member of staff may be seen as a hindrance (which is actually true in the early days!). Finally the new member of staff, will pick up that they are unwanted, which will make them feel disillusioned and unhappy. This is unfair on the mentor and the employee and creates a situation where nobody achieves what they want.

A good mentor however is invaluable and will realise that every minute that they spend with a new member of staff will be repaid tenfold.  Having acted as a mentor on many occasions I soon realised that the first few weeks required some intensive supervision, which meant that I needed to put certain things on hold so that I could make enough time to allow this to happen.  In these first few weeks I would set a weekly timetable, which would also include time slots where I had arranged for members of staff in other parts of the organization to facilitate certain activities.  For example, I would allocate a day with administrators, so that an appreciation of filing, photocopying, incoming and outgoing post and other policies and procedures could be attained.  All of these are fundamentally important activities within the business.  I also arranged for time to be spent in other departments, so that an appreciation of the wider business activities was also attained.  If you do take the time in the early weeks to spend time to train and supervise appropriately, then you will find that your new colleague becomes an asset who you can allocate ‘real work’ too, which will help to develop them and ease the burden on you.  The problem with a lot of people, however is that they focus on the here and now and are too short sighted to see this!

It is also very important to make new people feel welcome and at ease in their new role.  Always remember that one day you had been in this position and that no matter how busy you are politeness and courtesy costs nothing.  As stressful as a work environment may be, there is absolutely no excuse for shouting or being rude to your colleagues.  I say this because in the past I have seen a number of members of staff almost reduced to tears as a result of being inappropriately spoken to by more senior members of staff.  This is totally unacceptable and in most cases was due to the fact that the member of staff had not been given adequate support and supervision from their mentor, which had resulted in a number of mistakes/issues occurring. New members of staff require time and if a mentor does not allocate sufficient time to train and supervise them then the consequences are likely to result in a demotivated member of staff who is not developing and likely to make mistakes. If this is the case an employer should question their selection of mentor or ask themselves if they have made provision to fulfill the role effectively with the mentor’s workload.

If you are currently acting as a mentor, I refer to the definition stated earlier and ask you to consider whether you are encouraging and supporting your colleague to help them manage their own learning in order to help them to develop skills to maximise their potential. Or, do you see them as a burden that has been thrust upon you, where you have no time to help them.  If it is the latter, then I suggest that you speak to your employer and see if they can find someone more suitable, as this is not fair on the person you are mentoring.

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.