Addition Drainage Questions Checklist

Walk the elevation the addition would join and follow each downpipe to where it ends, noting whether it disappears into a gully, a small chamber or straight into the ground.

A downpipe that vanishes into the ground with no visible fitting is a different conversation from one discharging into an open gully, and the difference is easy to record now.

Note what else empties into each gully at the foot of that wall, including any waste pipe from a sink, a washing machine or an outside tap.

Gullies frequently carry more than rainwater, and the extra connections are the ones nobody mentions until the wall they hang on is being altered.

Record where the soil stack sits on that elevation, how far along the wall it stands, and whether it runs up past a window or stops below the eaves.

The position of the stack often decides whether a proposed footprint works comfortably or becomes an awkward compromise.

Where a stack runs below ground and what it serves cannot be told from the outside; ask a qualified drainage professional rather than assuming.

Note the smaller pipes on that wall as well: a boiler condensate outlet, an overflow, a vent or an outside tap supply, and write down where each one goes.

These small items are always relocated last, at the point where there is no comfortable place left to put them.

Look at the wall face for staining, moss or a green streak that shows water has been running down it, and photograph what you find with a date.

Existing marks tell you the arrangement is already struggling in one spot, which matters far more once that wall becomes internal.

Mark which of the pipes and gullies you have listed would end up inside the new space, under its floor or hard against a new wall.

Once each pipe has been placed in one of those three groups, a designer knows immediately which of them the scheme has to solve for.

Peg or chalk out the footprint you have in mind and walk it slowly, noting every cover, lid, grating and recessed tray you can see within it.

An idea on paper hides what is on the ground; marking it out is the single most useful piece of preparation at this stage.

For each cover you find, note whether it would end up under a new wall line or somewhere within the new floor, because those are not the same problem.

A cover in the middle of a new floor gets discussed openly; one under a wall line tends to be discovered by whoever digs the trench.

A chamber inside the footprint raises questions only the local authority and the responsible undertaker can settle, so put it to them before a footprint is fixed.

Note any cover just outside the marked area that would become hard to reach once a wall, a step or a paved edge sits alongside it.

Access is lost quietly, and the person who eventually needs that access is rarely in the room when the decision is made.

Record whether any part of the footprint was paved, decked or built over by earlier work, since a chamber may sit underneath with nothing showing.

Ground that was tidied by a previous owner is exactly where an unrecorded chamber tends to turn up.

Where a lid lifts easily by hand, photograph what is beneath it from above and put the date on the image, then put the lid back and leave it alone.

A photograph of a chamber tells a professional a great deal, and it takes nothing more than a careful look from ground level.

Looking from above is the limit of owner work here; entering, reaching into or altering a chamber belongs with a qualified professional.

Ask who would be responsible for locating drainage before any ground is broken, and note the answer alongside the name of whoever gave it.

Naming the person responsible for finding what is buried is a far less awkward conversation before groundwork starts than during it.

Write down where you imagine the water from the new roof going, then treat that as a question to be answered rather than as part of the scheme.

Owners often assume the new roof simply joins the existing arrangement, which may or may not be a reasonable expectation here.

Note which lawn, border or gravel the footprint would cover, since that ground is currently soaking up rain that would have to go elsewhere.

Losing soft ground is invisible on a plan but is often the change that shows itself first in heavy weather.

Record whether any gutter already overflows, any gully backs up or any downpipe splashes in heavy rain, and say where and how often you have seen it.

An arrangement that is marginal today rarely improves once more surface is added to it.

Ask whether surface water and foul drainage at this property are dealt with separately or together, and note who told you.

This single answer shapes most of the rest of the discussion, and it is not something to guess from what you can see.

Only the local authority and the responsible undertaker can confirm how the arrangement here works; treat anything else as hearsay.

Note any part of the plot that holds water after rain, whether it drains away quickly or lingers, and whether that has changed since you have lived here.

Standing water is the plainest evidence an owner can offer about how the ground behaves, and it needs no equipment to record.

Write down what you would like to happen to the rainwater from the new roof, such as a butt or a planted area, and label it a preference rather than a plan.

Preferences stated early get designed for; preferences raised late get refused for reasons nobody has to explain.

List every fitting the new space might contain, including the ones only ever mentioned in passing, such as a utility sink, a second cloakroom or an outside tap.

The fitting that was mentioned once and never written down is the one that turns up as a change when it is least welcome.

Note roughly how far each imagined fitting would sit from the point where waste currently leaves the building, and ask what that distance involves here.

Distance from the existing arrangement is the practical question behind most fitting positions, and an owner can describe it in ordinary terms.

Falls, routes and pipe arrangements are design matters for a qualified professional; nothing an owner paces out settles them.

Note whether any fitting you have in mind would sit lower than the ground around it, such as in a step down or a sunken part of the plan, and raise it early.

A fitting below the level of what it has to reach changes the conversation entirely and is far better raised at sketch stage.

Write down which appliances would live in the new space, including a washing machine or dishwasher, and where you picture each of them standing.

Appliance positions are usually settled by the kitchen conversation and then handed to drainage as a fact rather than a request.

Decide and record whether a lavatory in the new space is wanted from the outset or is being left as a possibility for later, and say which plainly.

The difference between wanting one now and possibly wanting one later changes what should be discussed, and it is often left deliberately vague.

Ask what a new fitting in this position would need in terms of ventilating the drainage system, and note the answer without acting on it yourself.

This topic is invisible to owners and routinely surfaces late, when the roof form or the elevation has already been agreed.

Note which way the ground falls on the side where the addition would sit, whether towards the house, away from it or along it, and how obvious the slope is.

Owners can describe a fall in plain terms, and doing so early stops everyone designing from an assumption of level ground.

Look for the line where the damp proof course appears in the wall and note roughly how it sits in relation to the ground outside, describing it as your own observation.

That relationship is checked early in almost every look round the outside, and having a note of it ready shortens the conversation.

What that line means and whether it is being bridged are matters for a qualified professional, not conclusions to draw yourself.

Record whether water runs onto your ground from a neighbouring drive, roof or paved area, and where it arrives.

Water crossing a boundary is a topic worth raising before a new wall stands in the way of where it currently goes.

Note whether you are hoping for a threshold close to outside ground level at any new door, and ask what keeping water out of that arrangement would involve.

Level thresholds are asked for from images and then negotiated late, when the drainage implications finally get raised.

Record any channel grating, land drain outlet or gravel trench already in the garden, including anything a previous owner mentioned to you.

Existing drainage in the garden tells you something about how this ground has behaved before, whether or not anyone kept records.

Note any spot near the house that stays damp long after rain has stopped, and whether anything grows there that does not grow elsewhere.

Persistent damp ground beside a wall is worth flagging plainly, because it may point at something that has nothing to do with rain.

Ask which of the pipes serving your property are shared with neighbours or fall under the responsibility of the undertaker, and record who gave you the answer.

Ownership determines who has to be involved, and it is a question with a definite answer that owners cannot work out for themselves.

Only the local authority and the responsible undertaker can confirm ownership and responsibility for a pipe; neighbours agreeing between themselves settles nothing.

Note whether a neighbouring downpipe, overflow or gully discharges onto or into anything on your side of the boundary.

Arrangements like this are usually long standing and undocumented, and they surface awkwardly once ground gets dug.

Look through the paperwork from when you bought the property for any drainage plan, search result or correspondence about the sewer serving the property.

Something in that bundle often shows more about the arrangement than anything visible on the ground.

Write two short lists side by side: what you actually know about the drainage here and what you have assumed, and keep them separate in every conversation.

Two separate lists stop an assumption about the drainage being quoted back to you later as something already established.

Ask what would have to be notified, agreed or confirmed locally if the new structure came close to a shared or public pipe, and note the process rather than the outcome.

Knowing which process applies, and who runs it, keeps the topic from being discovered halfway through groundwork.

Nothing in this checklist indicates whether any consent or agreement is needed; confirm locally what applies to your property.

Record any past blockage, smell, clearing visit or replaced section, along with roughly where it happened and whatever you were told at the time.

History repeats itself underground, and an owner recollection is often the only record that exists.

Sort your questions into ones for a designer, ones for a drainage specialist and ones only the local authority or the undertaker can answer.

Asking the wrong person produces an answer anyway, which is the real risk of not sorting them first.

Draw one rough plot sketch marking covers, gullies, downpipes and the spots where water is seen to stand, and take it to every conversation.

A single owner sketch that everyone marks up beats six separate recollections offered from memory.

Ask what survey of the drainage would be wanted before the footprint is fixed, who would arrange it and what would be produced at the end of it.

A survey arranged after a footprint has been agreed can only ever confirm bad news, so the order these two things happen in matters.

The condition and route of a drain can only be established by a suitably qualified professional using proper equipment, never from what is visible above.

Write down what you were told about drainage, who told you and when, rather than keeping a general impression of what everyone thought.

Drainage advice gets contradicted more often than most topics, and attribution is what lets you go back and resolve it.

Write down in advance what you would do if a chamber or a shared pipe turned out to sit inside the footprint, so the decision is not made under pressure.

Households that have already agreed their answer to that discovery handle it calmly; households meeting it for the first time rarely do.

Ask who would be responsible for protecting the drainage that stays in use while work goes on, and how a problem would be reported if one appeared.

The arrangement still has to work while everything around it is being changed, which is easy to leave unallocated.