Septic Tanks – An alternative to mains drainage

Guest article from Duncan - www.propertyhive.org

Under the Water Resources Act 1991, it remains a criminal offence to discharge effluent that is not of a sufficient quality into a watercourse without the consent of the Environment Agency. This can result in a three month prison sentence or a fine of up to £100,000. Therefore it is important to ensure your installations are up to date.

Source: http://www.mtmdrains.co.uk/

Consideration of drainage is an important part of any development and in the vast majority of cases UK developments will enjoy the benefit of being able to connect to ‘main drainage’.  In rural or more isolated areas, where mains drainage is not generally available, alternative methods of controlling and disposing of drainage, particularly foul waste, need to be considered.  Septic tanks are one such option:

The first recorded septic tank was installed in 1896 by Donald Cameron who was the city Surveyor for Exeter. This septic tank served the entire town and was 20 x 6m to a depth 2.1m. Since then there has been some progress in the development of septic tanks, but the principles are basically the same.

Source: http://www.septicrepairny.com/

Septic tanks are covered in UK Building Regulations under Approved Document H, and it is an offence not to build new structures to the standards as set out in the Building Regulations under the Building Act 1990. However as long as the British Standards are followed or bettered this should not be a problem. See BS6297:2007 for further guidance. Building Regulations do not apply retrospectively and so septic tanks that pre-date the 1985 Building Regulations are not affected. This is despite the fact that many septic tanks are no longer fit for purpose due to the increase in water usage rates over the last fifty years. However under the Water Resources Act 1991, it remains a criminal offence to discharge effluent that is not of a sufficient quality into a watercourse without the consent of the Environment Agency. This can result in a three month prison sentence or a fine of up to £100,000. Therefore it is important to ensure your installations are up to date.

Treatment  - All foul drainage should enter a tank including water from W.C’s, showers, sinks, baths and domestic appliances such as washing machines etc. Washing machines and dishwashers are often discharged into rainwater pipes as it is easier, but this can have a significant impact on the local environment and should always be avoided.

A Septic Tank is a self contained installation that processes and treats raw sewage. It is a tank which stores the waste allowing enough time for the organic matter to decompose through natural processes. The sewage becomes liquefied, with a thick oily scum forming on the top and sludge that settles on the bottom. What is left is a central layer of clear liquid, which in older tanks is often emptied straight to a watercourse (which is illegal and harmful to the environment), but in new installations it is treated further before been discharged. The sludge at the bottom is made up of everything that is too heavy to remain in suspension and the oily layer that sits atop is the matter that can decompose naturally.

The secondary treatment usually comes in the form of a soakaway, where the water is drained into a hole formed underground, using plastic formwork that can be described as looking like milk crates, where the water will be soaked up slowly by the ground. Soakaways come with their own set of legal requirements.

The other type of secondary treatment comes in the form of a bio-filter. These have sweeper arms that drip the effluent over clinker beds. Please note that a septic tank is not the same thing as a cess pit, which is a container that stores sewage until it can be emptied and treated elsewhere. Older tanks are often square in shape with brick walls, although modern installations are often pre-fabricated uPVC units that can be square or circular. The septic tank is made of either two separate tanks or one tank split into two

Capacity - A septic tank should be 180 litres in size for every person it serves, with an additional 2000 litres of capacity regardless of the number of people using it.

Litres = 180P + 2000

Where P = the amount of persons served by the tank.

The above calculation should treat children as adults and allows for emptying on an annual basis.

This is so the sewage can be stored long enough that the decomposition of the waste can occur. Anything smaller than this will mean untreated sewage is discharged and solids may cause blockages in the pipework, or if installed the bio-filter. If untreated sewage is allowed to drain into the local environment, there is likely to be an increase in disease, rat infestation and damage to the local environment.

End Product - One of the end products of a septic tank is sludge. This is raw sewage that remains in the tank, and then emptied periodically. The other is water that consists of nitrates and tiny fragments of sewage.

General Problems - An excess of detergent will inhibit separation of the three layers. An excess of disinfectants will kill of the bacteria involved in the treatment process. Day to day domestic use should not cause any problems in a well designed and maintained system. Water softeners however produce salts which in excess can kill of the bacteria required to make the system work.

De-sludging - How often to de-sludge depends largely upon the occupancy of the household and size of tank, but for an average household of 4 people it would be reasonable to assume an annual de-sludging would be sufficient.

Mains Drainage - If there is a nearby sewer you have the right to connect to it. Just contact the local sewerage company and they will give you further details on how to arrange for a connection.

Construction Requirements - Reference should be made to BS6297:2007, which contains recommended materials for use. Rain and groundwater must be prevented from entering the Septic tank, as clean water should not be contaminated. Therefore the tank should be covered, which also helps with the safety issues of having an open tank. Access must be maintained with an access hatch of at least 600mm square. This access should allow for inspection of the inlets and outlets, and should be large enough to allow rodding. Tanks should be situated;
1. Not within 15 metres of the dwelling in question.
2. Not within 10 metres of a watercourse.
3. Not on land that it is regularly flooded, or land that has a high water table.
4. So that a tanker can access for emptying (e.g within 30 metres of vehicle access).
5. Downwind of nearby dwellings if at all possible.

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

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Commercial Leases - Dilapidations Liability – Tenants beware!

Once a lease is signed a legal contractual relationship is formed.  It is no defence for a tenant to claim that they were not aware of what they were signing as ignorance is no defence in law! 

Source: http://brisbanecommercialproperty.com.au/

A tenant occupier of a commercial building has a legally binding contractual obligation through their lease to return a building to the landlord in a state of repair that is stipulated within the lease, when the tenancy ends.  Now it may seem obvious that a landlord would expect to have a building returned to them in such a condition so that they can re-let the building immediately, however in reality this very rarely is the case.  This can then lead to protracted dilapidations claims where the costs to the tenant can start to escalate due to a landlord’s a claim for loss of rent and service charge and additional professional fees in addition to the costs of repairs, reinstatement and decorations that are associated with the lease covenants.

In my professional career I spent many years negotiating dilapidation claims (acting on behalf of both landlords and tenants) in the whole spectrum of the different commercial sectors, such as office, industrial, retail, leisure etc.  During this time I have encountered many tenants who did not understand the significance of meeting their lease obligations and in fact entered into a lease arrangement without seeking professional advice or indeed reading the lease in any detail before signing!  The gravity of the situation did not dawn onto these types of tenants until they were served with a schedule of dilapidations accompanied by a summary of claim which often ran into tens of thousands of pounds and sometimes even more. 

Source: http://commercialpropertyforsalewall.blogspot.co.uk/

Once a lease is signed a legal contractual relationship is formed.  It is no defence for a tenant to claim that they were not aware of what they were signing as ignorance is no defence in law!  Therefore a tenant should be aware of what they are entering into and in particular their repairing and other obligations BEFORE they sign the lease.  Although there would be a fee involved it would always be advisable for a tenant to seek professional advice to enable them to understand the lease and in particular their likely dilapidations liability once the lease comes to an end.  Good professional advice may identify obligations and clauses in a lease that may be particularly onerous to a tenant and negotiations may be possible to have clauses removed or at least re-worded.  Also, a professional advisor may recommend that a schedule of condition is taken prior to occupation which can later be used to help limit liability when the lease comes to an end.  In my experience I have found that many tenants are reluctant to pay professional fees for some of the services/advice previously discussed because they do not have the foresight to appreciate the benefits and especially the amount of money it could save them in the future.   Avoiding professional fees, particularly in relation to a tenant entering into a commercial lease arrangement really is a false economy.

A few of years ago I was asked to carry out a dilapidations liability assessment on a number of branches of a mid-sized DIY retailer’s stores which had been put up for sale.  I was acting as Consultant for the prospective purchaser.  The stores were located in many parts of the UK for which each one was occupied under a commercial lease arrangement.  Basically, my Client was considering acquisition of the business, however before being in a position to negotiate a fair price for the business it was necessary for them to understand the likely financial impact (their dilapidations liability), to them when each of the leases came to an end.  Each of the leases were unique, with a variety of remaining terms, (some had a few years remaining and some were much longer). There were also a variety of different repairing, re-instatement and decorations covenants within the leases. 

Prior to undertaking any type of dilapidations inspection it is important to read and understand the lease, which is what I did, and on completion of each inspection I was able to prepare a schedule of dilapidations for each branch.  The difference with dilapidations liability inspections compared to interim or terminal dilapidations inspections is that you need to have an eye on the future.  So I therefore had to take account of the length of term remaining on each lease and to make an assessment of the likely dilapidations that would occur at that point (the end of the term) and not just in the here and know.  I was then able to cost/quantify the lease obligations which would also factor in likely future inflationary cost increases.  I cannot remember the exact overall dilapidations liability however I do remember this totalling in excess of £1 million.  Not exactly the type of money you want to ignore if you are proposing to purchase a business!  My Client then went onto to use this to help negotiate a purchase price.

Not all dilapidations liability will be as costly as the example I give above, however it is worth educating tenants about the benefits of seeking and paying for professional advice before they enter into a commercial lease arrangement.  In most cases larger companies will have there own professional advisers so the pitfalls discussed above are much more likely to be avoided.  In my experience it is the medium and particularly the smaller size companies or even individuals who are less familiar with commercial lease arrangements and worse are much more willing to avoid paying professional fees.  Perhaps it is to these companies/individuals that we need to focus our education?

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.

What is Underpinning? - Part 2 - Other Methods

Underpinning is often considered as a solution for subsidence however the need to stabilise ground could warrant underpinning for other reasons therefore underpinning is not a solution exclusive to subsidence

Source: http://www.mason-mason.co.uk/

In last week’s article (Link) I discussed traditional underpinning and explained that this is often a solution to ground movement (subsidence), which will stabilise a building or structure in the event that movement is continuing.   I also explained that dealing with ground movement is not always disruptive or expensive however professional advice is always recommended to ensure that an appropriate remediation method is adopted.  In this week’s article I will consider a number of different methods of underpinning as alternatives to traditional underpinning that may be selected to suit individual circumstances.

Underpinning is often considered as a solution for subsidence however the need to stabilise ground could warrant underpinning for other reasons therefore underpinning is not a solution exclusive to subsidence.  For example, the use of a building may change which would add load.  The original foundation design may not have been designed for this additional load, this could warrant underpinning.  Adding an additional storey/s to a building would be a good example of this.  Also, the construction of nearby structures may warrant additional support to an existing foundation for which underpinning may be selected.  For whatever reason underpinning is used it is important that the correct method is selected.  Traditional underpinning was discussed in last week’s article however this week will I discuss needle beam underpinning, cantilever beam underpinning and an underpinning raft.

Source: www.gbanksltd.com

Needle Beam Underpinning – This method of underpinning stabilises existing foundations with the installation of concrete ‘needle beams’ supported by concrete mini-piles.  The amount, distance between needles and diameter of the mini piles will be determined by the design. Concrete mini-piles can be either cast in-situ (this is where wet concrete is used with steel reinforcement) or pre-cast (made off site a delivered as a dry solid concrete component).  A small hole or pocket is broken out below ground level and just above the existing foundation as detailed on the image at the left.  Concrete mini piles are then installed into the ground adjacent to the newly made hole. We will consider cantilever beams in a moment, however a common method of installing needle beam underpinning is to install a concrete mini pile either side of the newly formed hole, one inside the property and one on the outside.

www.gbanksltd.com

The concrete mini piles, once installed will have short steel reinforcement bars projecting at the top.  These are referred to as starter bars and allow further steel reinforcement to be attached which will connect each of the concrete mini piles to each other as they pass through the hole/pocket that has been made in the wall.  The next stage is to provide temporary timber formwork around the reinforcement bars to accommodate and hold the wet concrete until it has cured (hardened).  Once the formwork is complete the wet concrete is poured and allowed to cure, after which the timber formwork is removed, leaving behind a single solid concrete beam supported off the concrete mini piles.  The hole/pocket, which the new concrete beam now passes through, is made good with the installation of ‘packers’ to fill any gap between the top of the new concrete needle beam and the underside of wall that is being supported.  Packers will usually take the form of a masonry material or possibly materials such as slate to ensure that any voids are completely filled so that the wall has a solid support.

Needle beam underpinning is used where traditional underpinning is not appropriate due to the existing foundations being too deep, or good bearing strata is so deep that it is uneconomical to dig (depths greater than 1.5m). Concrete mini piles are typically installed in pairs at 1.0m-1.5m intervals and approximately 1.0m-1.5m apart, although this can vary with design.  The advantages of this system include suitability for restricted access, the needle beams can be constructed at a higher level if the existing foundations are too deep, it is often faster than traditional underpinning, it is more economical at greater depths, the system has a high load capacity and there is less disruption and spoil produced compared to traditional underpinning.

Source: www.gbanksltd.com

Cantilever Beam Underpinning – Firstly it is worth clarifying the term cantilever.  Freeedictionary.com provide the following definition; ‘A projecting structure, such as a beam, that is supported at one end and carries a load at the other end or along its length’ This method of underpinning will stabilise a wall foundation either internally or externally however it does not require support on both the internal and external side of the wall.  Basically all of the support is provided at just one side of the wall with the load supported off a concrete cantilever beam which passes through the wall in the same manner as the needle beam method previously described; i.e. with pockets cut into the wall and a beam cast through the wall with the use of mini-piles, reinforcement, formwork and concrete which links the two mini piles. The image above shows that two mini-piles are installed, one is a compression pile (taking downward force) and the other is tension pile (resisting uplift).   

Many of the advantages of cantilever beam underpinning compared to traditional underpinning are the same as needle beam underpinning described above in terms of speed, more economical at greater depth etc.  A further significant advantage of cantilever beam underpinning is where access is particularly restricted as the mini-piles are cast from just one side of a wall/structure.

Source: www.gbanksltd.com

Underpinning Raft – Of all methods of underpinning described the installation of an underpinning raft is by far the most disruptive and expensive as it can stabilise walls and foundations for a whole building. Mini-piles are installed within a property and capped with an integral reinforced concrete raft.  The diagram on the right shows that needle beams project from the slab into the walls below ground level. This system is used where whole rooms or whole structures are to be underpinned as opposed to individual walls or parts of a building.  Although more expensive than other methods of underpinning an advantage is that a new integral floor slab is provided at the same time as stabilising a building. The image below shows an underpinning raft just prior to concrete being poured.

Underpinning Raft before concrete is poured. Source: http://www.larsenpiling.com/

This week's article has discussed a number of alternatives to traditional underpinning as ways of stabilising walls, buildings or structures.  Professional advice should always be sought to ensure an appropriate method of stabilising is selected. This and last week’s article provide a short introduction into to some of the commonly used methods of stabilising ground, structures and buildings however there are many other ways that stabilisation can be achieved.  This is something I will no doubt discuss in a future article.

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.

What is Underpinning? - Part 1 - Traditional Underpinning

There is not a single method of underpinning which will be suitable in every circumstance and to be effective, careful considerations of things such as dead and imposed loads, ground conditions, depth of excavation, site restraints including access and ultimately costs will help to determine the most appropriate method of underpinning to use

Source: http://www.davocal.ie/

I have previously written two articles on the subject of ground movement a term more commonly referred to as subsidence, Subsidence – Part 1 – Not all it’s cracked up to be! and Subsidence – Part 2 – Factors that contribute to subsidence and what to look for. The first article explains how the very word (subsidence) seems to strike fear into most people due to the misconception that ALL instances are both disruptive and expensive to rectify.  Whilst this is true in some circumstances, in the vast majority of cases subsidence can be rectified reasonable quickly and without excessive expense.  In order to establish what correct remedial measures are necessary it is crucial to accurately diagnose the factors causing any episodes of ground movement and whether movement is continuing or has stopped.  In my previous articles I explained that when I first graduated from University I joined a Property Consultancy who’s main area of business was dealing with subsidence insurance claims as Loss Adjusters.  My role was to visit site with a more experienced Structural Engineer, who would make an initial assessment, and then I would be required to manage the claim to a conclusion.  This often involved crack monitoring to establish whether any movement was historic (had now stopped) or progressive (was still continuing).  This was a crucial part of the process as it is pointless dealing with the effect of subsidence until movement has been stopped.  On the occasions where movement was found to be progressive, it was often first necessary to undertake substantial remedial work such as underpinning to stabilise and stop any movement.  In this article I plan to explain what underpinning is so that anyone who is affected by subsidence where underpinning is suggested will have an understanding of what is happening.

So what is underpinning?  Well in simple terms underpinning is a method of strengthening weak foundations whereby a new, stronger foundation is placed beneath the original.  The whole concept of underpinning can seem mind boggling when you consider that this often involves excavating underneath of an existing foundation to strengthen whilst at the same time ensure that the building or structure that is being supported does not disappear even further into the ground!  There are a number of different methods of underpinning including traditional underpinning, needle beam underpinning, cantilever beam underpinning and an underpinning raft. The method of underpinning selected in each situation will be determined by a number of different factors, which I will discuss in this and in next week’s article.  There is not a single method of underpinning which will be suitable in every circumstance and to be effective careful considerations of things such as dead and imposed loads, ground conditions, depth of excavation, site restraints including access and ultimately costs will help to determine the most appropriate method to use.

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

Traditional Underpinning - This method stabilises existing foundations by digging under the present foundation in sequenced bays to a depth where firm strata exists and replacing the excavated material with mass concrete.  This method of underpinning is used when the existing foundations are at a shallow depth.  ‘Bays’ are usually excavated in 1.0m to 1.5m in length and generally 0.6m wide.  This method can be used to depth of circa 2.5m however due to cost an safety issues it may be worth considering a ‘mini-piled’ solution for depths in excess of 1.5m, something that will be discussed in next weeks article.

Advantages of traditional underpinning compared to other methods is that is simple engineering and generally easily understood, suitable for heavy loads and large structures, occupants can remain in the property as work can be undertaken from outside, method can be used in restricted access areas (does not require plant or machinery), it is a low cost solution at shallow depths and it creates minimal disruption and is not noisy.

Source: http://buildingandengineering.blogspot.co.uk/

You can see from the diagram on the right that each bay is excavated in sequence and then filled with concrete, which is allowed to cure (harden), before the next bay is excavated.  This is crucial to the stability of the building/structure during the process.  Once the concrete has cured the next bay in sequence is excavated, filled with concrete and cured and so the process continues until all of the bays are complete.  This method therefore provides a new deeper foundation over a short period of time but not in one operation. In order to carry out traditional underpinning it is first necessary to understand the ground conditions (via a ground investigation) to know what depth to excavate for solid ground and the to plan the sequence for the underpinning bays.

Although traditional underpinning is the simplest and most commonly used method of underpinning it is still necessary to obtain professional advice in order to ensure that the selected method of underpinning is designed and completed correctly.  It is also necessary to engage a contractor who is familiar with traditional underpinning and will take into account the various safety aspects of providing temporary support where required, supporting excavations where necessary, working in confined spaces and so on.  Excavating a bay and filling with concrete may seem a very simple process to most people and you may wonder how anyone could get this wrong, however never be surprised with the fallibility of human nature.

A common example I give to my students relates to my previously explained role as a graduate Building Surveyor, working with Property Consultancy who’s main area of business was dealing with subsidence insurance claims as Loss Adjusters.  Late one evening we received a call to a mid-terraced property in the Moseley area of Birmingham from a man who had contacted his insurance company (who then contacted us), where he had arrived home to find a problem with his house.  He had left his house in the morning as usual, shut his from door and proceeded to work.  When he arrived home he put his key in the door, turned the lock the door would not open.  After a number of attempts he promptly shoulder barged the door, which eventually opened.  When he got inside the house he realised that the front door was the least of his problems. There was major vertical cracking in three locations on the party wall (a shared wall with his neighbour), which was so bad he could see through to next door's lounge, the suspended timber ground floor had significantly dropped near the junction of the party wall, there was a 50mm horizontal crack at the junction of the top of the ground floor lounge wall and ceiling and all of the ground floor internal door frames were distorted and none of the internal doors would close properly. Not exactly what you want or expect when you come home from work!  On investigation it was established that his neighbour was in the process of an extensive refurbishment, which included underpinning of the party wall between the two properties. For reasons which we never got to the bottom of the contractor excavated underneath the party wall in one operation, rather that in sequenced bays, and unsurprisingly the whole party wall had dropped as the excavation was part way through!  How somebody was not seriously injured or even killed was a miracle.  The cost of rectifying the works and in addition the costs of temporary accommodation while the work was being carried out were calculated in the region of £75,000.  This demonstrates the significant impact of what can happen if underpinning is not carried out correctly.

In next week's article I will discuss other methods of underpinning such as, needle beam underpinning, cantilever beam underpinning and an underpinning raft.

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.