Some technical stuff, like span tables for joists and roof rafters, we just didn't have room for in the Haynes manual. Other technical aspects - like staircases and private drainage systems - will only be of relevance for a very few home-extenders, so we've put the relevant info here.
1. PRIVATE DRAINAGE - SEPTIC TANKS & CESSPITS
In remote rural areas without the luxury of public sewers, you
traditionally had a simple choice when it came to dealing with foul waste: you
had to either build your own private sewage works or be prepared to empty a lot
of buckets. The old-fashioned cesspool (or cesspit) comprised an underground
chamber storage tank into which your foul ‘solids’ and ‘soil’ waste would be
flushed. It would need to be located some way out in the garden (at least 7m
away from the house). Construction would typically be the same as a manhole, of
rendered brick walls on a concrete base, but with a reinforced concrete sealed
lid for access.
The general idea is
that, over time, the solid waste settles at the bottom and the relatively clear
liquids are drained off safely into a handy nearby field by way of a land
drain, rather like a soakaway. When full, cesspits require emptying by a
suction tanker. But in order to reduce the need for frequent emptying (and the
associated cost) one popular illegal dodge was to wait until the District
Surveyor had approved the new structure and safely departed, and then
‘accidentally’ knock out one of the bricks so fluids could seep away into the
ground. Perhaps it wasn’t fully appreciated that leaking cesspits had, not so
long ago, been the cause of fatal cholera epidemics as a result of contaminated
drinking water in nearby wells and streams.
plastic or GRP units are available, although cesspools have now largely been
superseded by more sophisticated septic tanks.
Septic tanks work in a similar way to
cesspools – the foul waste ‘solids’ settle over time with gravity, and are
partially broken down by bacteria (under a scum or crust on the surface). They
are more efficient at separating the solid and liquid matters, employing a
system of several chambers. The ‘refined’ liquid finally disperses into
approved land drainage and percolates off into the ground. This process means
that septic tanks can be smaller than cesspools and are cheaper to purchase.
The solid waste matter
that cannot be broken down further by bacteria accumulates as sediment at the
bottom of the chamber, so periodic emptying will also be required by a suction
tanker, despite ambitious claims to the contrary from some proud owners! The
tank location must therefore allow sufficient access for the emptying truck,
unless this is a DIY job that you particularly relish – in which case you may
choose to recycle the waste, which by all accounts can make an excellent
fertilizer. In Victorian times, the ‘nightsoilmen’ would empty privies in large
towns to sell the contents for just such a purpose. The nature of the subsoil
is an important factor to consider when designing private drainage systems. For
example, in clay soil the percolation rate may be poor and an extensive system
of perforated pipes over a larger area may be needed. Because the discharge is
not entirely pure, the installation must be approved by the Environment Agency
as well by Building Control.
Today, more advanced large-volume
septic tanks can be placed in an excavated pit just below ground level. These
are environmentally friendly plastic or fibreglass units, some of which are
effectively mini-sewerage treatment works that take the process one stage
further, treating the liquid by-products so that they’re discharged as ‘clean’
2. DRAINAGE - PIPE MATERIALS
Pipes of the following
materials may be encountered:
used since Victorian times in places where high strength was needed, such as at
shallow depths under roads or foundations. Iron could withstand impact and
distortion, but the joints (often caulked with lead) could be prone to leakage.
Acid conditions, such as peaty soil, can accelerate corrosion.
Most drains constructed up to the 1950s will be of
fired clay, commonly in 100mm or 150mm (4in or 6in) diameters. These were
traditionally salt glazed with a glossy, water-resistant finish. But the salt
glaze manufacturing process caused vast amounts of pollution, so from the 1970s
on clay pipes were no longer glazed and these have proved to be just as good.
The joints were caulked with hemp yarn and cement mortar forced into the
sockets, which could seep inside (hence the old custom of dragging a ball of
sacking through newly laid pipes). Such rigid joints are extremely susceptible
to damage from ground movement. Clay
pipes remain popular today because of their resistance to chemical attack and
their modern flexible plastic couplings.
and cement fibre
Mainly used for ‘big bore’ underground pipes of
150mm diameter and upwards, the weakness of concrete pipes is their
vulnerability to chemical attack from effluent on the inside (acids and
sulphates) or from the surrounding groundwater outside. Concrete pipes were
commonly jointed with cement mortar, which is unlikely to have remained
watertight. Their use should be restricted to carrying rainwater only. Now
mainly used for infrastructure projects and manufactured with protective
For generations, asbestos cement was a
wonder-material (light, strong, cheap etc) that seems to have been used
throughout the house, including soffits, flues, and even ceilings. More rarely,
it even found its way into underground pipes. Unfortunately, it was soon
discovered that asbestos pipes, like concrete, could deteriorate from attack by
chemicals. Some lasted only six years before developing serious leaks. They
must not be cut, drilled or disposed of without professional advice.
popular around the mid-1960s, there will be many existing installations with
pipes made of flexible ‘pitch fibre’ or asbestos fibre impregnated with sticky
black pitch (bitumen tar). Unfortunately these could sometimes be a little too
flexible, being squashed into an oval shape by the weight above if not properly
3. Constructing a new pre-formed concrete IC
Work starts by
laying a 150mm thick concrete base onto which half-round open gulley pipes
are laid. Any incoming branches
joining the chamber are formed at a ‘streamlined’ angle – like an
arrow - in line with the direction of flow.
Entry and exit pipes must be cut so they extend a
little just inside the walls of the chamber before terminating, and are fitted with a flexible coupling to
allow for settlement.
Next, dry-mix concrete is heaped around the base,
and the first concrete section of the IC is placed in position. Make sure it
is level on top and leave it to
set. ‘Benching’ is formed over the
surface of the base in concrete,
sloping gently inwards from the level of the entry and exit pipes at a
gradient of about 1: 12. The surface
of the benching should be topped with a
1: 1 sand
/ cement screed and then trowelled to
form a smooth surface.
The remaining sections of the chamber are then
placed on top, bedded in mortar to the required height. The finished
structure should be surrounded with about 150mm of concrete. The top section
is specially moulded to take the
frame for the airtight lid. If your
IC is located on a patio, a
special recessed ‘self- fill’
lid can be fitted, and filled with matching patio slabs or tiles.
4. Building a soakaway
1. Excavate a hole of appropriate size (typically
around 3 cubic metres) for the total
roof area and volume of water discharged, located at least 5 m away from the foundations of the house and
the boundaries, in accordance with advice from Building Control. In heavy clay soil a deep trench type
soakaway may be suitable. Always
oversize soakaways as they are prone to silt up over time.
2. Link the hole to the foot of the downpipe
next to the house by digging a shallower trench and laying 100mm underground pipes with a gentle fall of
about 1:100 towards the soakaway.
Fill the soakaway hole up to the level of the trench with large pieces of masonry, rock or rubble (e.g. broken
bricks & tiles, not sponge-like aerated concrete blocks) around the sides
to prevent the sides caving in. Leave
large gaps between the pieces as, when complete, these will need to fill with
water prior to its final dispersal into the surrounding ground through
Place the end of the pipe so it discharges roughly into the centre of the
soakaway. Then add more rubble to cover the pipe, except at the end of the
pipe which must be left clear so that
any debris carried in the water will fall down into the pit rather than
accumulating at the point of discharge and blocking the pipe.
Backfill the pipe trench, first with gravel around the pipe, then soil.
6. Place about 100mm
of gravel around the top of the soakaway. Cover this with a
heavy-gauge plastic sheet prior to covering with at least 100mm of concrete ideally incorporating some
form of inspection access. Finally, once the concrete has cured, it can be hidden with topsoil for plants
mark the soakaway location on your
plans for future reference.
MANAGING DISPUTES with contractors
mediation, litigation & terminating the contractor's employment
If you find yourself bogged down with a
disagreement that can’t be resolved, you may have a genuine dispute on your
hands. This means an independent third party will need to be
appointed as adjudicator. Exactly who this nominated person should be must be
jointly agreed in the contract at the outset. It’s normally an experienced
chartered surveyor. Never appoint the person who designed your extension, since
it may turn out that some problems are due to bad design.
should always be dealt with promptly, as they’ll only get worse if ignored. If
the problem is due to building work that’s below par, and the builder has refused
to rectify it, then a good first course of action is to ask the Building
Control Officer’s opinion (although officially they may only be at liberty to
point out any contraventions of the Building Regulations). Otherwise, arrange
for an inspection by the nominated independent surveyor, who should be able to
produce a list of defects. A site meeting will need to be held to discuss it.
both sides regard an issue as ‘a matter of principle’ it usually means they
feel bloody-minded enough to waste time trying to teach the other side a
lesson. At this point calm down! It’s silly to fritter away time and
money and to spoil a relationship for the sake of being proved right about a
few minor issues.
Of course shoddy workmanship, continually broken
promises and matters of dishonesty need to be directly addressed. The usual
solution is mediation, where a third party with expertise in the field attempts
to get both parties to agree a solution, making a judgement after listening to
both sides in turn.
the builder still refuses to co-operate, you may be forced to resort to legal
advice to enforce the terms of the contract. Consumer legislation designed to
protect customers from unfair treatment may sometimes be appropriate. If formal
court proceedings are required, it helps to retain signed photographs of the
defects in question. It is important legally that you’re seen to have given the
builder every opportunity to rectify the problem. With a possible court
appearance in mind, try to keep a cool head and always be reasonably civil.
Reported episodes of ‘site-rage’ won’t reflect well on you in court, regardless
of extreme provocation. Alternatively, you may find that a solicitor’s letter
threatening action has the effect of a warning shot, saving both parties from
having to go to court, ultimately allowing the matter to be settled more
the contractor’s employment
This is the weapon of last resort. As with the
unsavoury prospect of going to court, the mere threat to end the contractor’s
employment can sometimes be a sufficient wake-up call to him to get his ass
into gear. Termination is a major step, and only advisable if you’re stuck with
an impossible situation (and you haven’t paid them in advance). But you only have
the right to terminate if you can prove a serious breach has been committed by
the contractor, and that he has failed to put matters right after being
notified. For example:-
to start work or to deliver any materials for a considerable
time after the agreed start date. This doesn’t apply if he’s just a bit late
quality workmanship, if much of the work is of exceptionally
poor quality and he has failed to make reasonable attempts to put it right
after being formally requested to do so.
progress, if the project falls way behind schedule, with
many days of absenteeism on site, and it looks like the contract will have to
be significantly extended. He then fails to improve productivity despite formal
requests to do so.
Other serious breaches might include the contractor
going bankrupt, or extremely aggressive or abusive behaviour.
Don’t fall into
the trap of being provoked into spouting a lot of abuse back! No matter how
much you think they deserve it, a threatening attitude on your part not only
escalates the tension but could also expose you to a builder’s claim for loss
of profit. All subcontracted work is automatically cancelled when the main
contractor is terminated.
This is Big Potatoes, and legal advice will be
needed. Once the dust has settled you’ll need to appoint another builder to
finish the job, for which they may well charge a premium.