Rear Extension Planning Preparation Checklist

Photograph the whole rear elevation from the far end of the garden and again from close up, so the overall shape and the details are both recorded.

A distant photograph shows the massing a designer needs; a close one shows the pipes, vents and repairs that shape what is actually possible.

Write down which room each existing rear window and door belongs to, and mark the ones the household actually uses to get outside.

Owners lose openings without realising which room they served, and the door people really use is often not the one drawings assume.

Note whether the back of the house is a single flat wall or already has an earlier addition, an outrigger or a lean-to attached to it.

The shape of the existing rear determines nearly everything that follows, including where an addition can join and how its roof behaves.

Record the wall finish at the back and whether it differs from the front, since the rear elevation is usually where earlier changes and repairs show.

Patched brickwork and mismatched render are useful evidence of alterations nobody documented, and a professional will read them.

Note where the existing rear roof drains, and whether its gutter joins or discharges near anything belonging to a neighbour.

A rear addition almost always interrupts this arrangement, and shared or adjoining rainwater is far calmer to raise before the design exists.

Write down anything about the back of the house you already dislike, because a rear addition is usually the one opportunity to deal with it.

Long-standing irritations rarely get mentioned in a briefing conversation and then quietly survive the whole project.

List every pipe, vent, flue terminal and grille on the wall the addition would meet, and photograph each one where it sits.

This list is one of the most useful things an owner can produce, because it converts a wall into a set of specific questions.

Anything connected to a gas appliance, a flue or a combustion vent must be settled by a suitably qualified professional before a footprint is fixed.

Note the position of the outside tap, the external light and any garden socket, and write down whether you would want each one back afterwards.

These are easily allowed for while the work is going on and irritating to add back once everything is finished.

Record where the waste pipes from the kitchen and the bathroom leave the wall and where they appear to connect below ground.

Waste routes often decide whether a fixture can move, and owners can see far more of this from the garden than they expect.

Note any alarm box, aerial cable, broadband entry or dish fixing on the rear elevation, and which provider each of them belongs to.

Each belongs to a separate organisation with its own process, and they are only a problem when discovered on the morning they are in the way.

Ask what would have to happen to any boiler flue or appliance vent on that wall before a footprint is fixed rather than after.

Terminals cannot simply be built over, and the answer sometimes moves the whole footprint or the position of the appliance.

Flue positions and appliance ventilation are matters for a suitably qualified professional; nothing here indicates what would be acceptable.

Write down whether an air brick or under-floor vent sits low on the wall, and flag it as a question rather than assuming it can be covered.

Low-level vents usually serve the floor void of the existing house, and enclosing them raises questions an owner cannot answer.

What happens to an under-floor vent when a wall is built against it is for a qualified professional to establish on site.

Walk the garden and write down every job it currently does, including drying washing, storing bins, keeping bicycles and growing things.

Gardens quietly absorb an enormous amount of household function, and none of it disappears simply because the space does.

Note where the bins actually stand and how they get to the street, because a rear addition frequently blocks that route without anyone noticing.

This is one of the most common practical complaints after a rear addition, and it is entirely avoidable at the planning stage.

Record which part of the garden the household actually sits in, and whether the proposed footprint takes exactly that spot.

The sunniest, most sheltered corner is usually right against the house, which is precisely where an addition wants to go.

Consider what happens to the shed, the greenhouse or the garden store if the footprint covers the ground they stand on.

Moving an outbuilding is a separate piece of work with its own constraints, and it needs somewhere to go before it can be moved.

Write down whether children or pets use the garden, and what the remaining space would have to allow for them.

A remaining strip that is fine for adults is often useless for the reasons a household values the garden in the first place.

Note how much garden would be left and whether it would still be deep enough to feel like a garden rather than a gap behind the house.

Owners consistently underestimate this, because the footprint is imagined from inside rather than looked at from the far end.

Note which direction the back of the house faces and record it in plain terms rather than relying on how the garden feels.

Orientation is the single most useful piece of information an owner can bring, and it is easily established without any professional help.

Write down where the sun reaches the garden in the morning and in the evening, and which part is already in permanent shade.

The pattern of sun and shade is what determines whether the remaining garden stays usable once something is built in front of it.

Consider whether a new roof would put the remaining garden or a neighbouring garden into shade that is not there now.

Overshadowing is one of the most common neighbour concerns, and thinking about it early gives a designer room to respond.

Overshadowing is assessed by a qualified professional against the relevant local requirements; nothing here indicates what would be acceptable.

Record which existing rear rooms get direct sun and at what stage, because those are the rooms most affected by building in front of them.

A room that only gets sun for a short stretch may lose it entirely, which owners often notice only after the work is finished.

Ask how the addition would affect light reaching the neighbouring property, and treat it as a question for a qualified professional.

The answer influences both the design and the way a proposal is received, so it is worth raising at the first conversation.

Effects on a neighbouring property are for a qualified professional and the local authority to assess, never something to conclude yourself.

Note whether you would rather the new space caught morning or evening light, and say which you would give up if you cannot have both.

Stating the preference early is more useful than discovering afterwards that the space is bright at exactly the wrong stage.

Walk the route materials would take to reach the rear, noting the narrowest point in rough terms and every gate, step and turn along the way.

This route determines what can be brought in whole and what has to be carried in pieces, which affects the whole approach to the work.

Note whether the only way to the back runs through the house, because that changes almost every practical aspect of building there.

Carrying materials and spoil through a hallway is a very different arrangement from a side gate, and it should be known from the outset.

Record where a skip could stand and whether that position would need anyone else's agreement before it could be used.

A skip on the street is treated differently from one on your own drive, and the arrangements vary between areas.

Placing a skip or materials on a public road is controlled locally; confirm what applies with the local authority rather than assuming.

Consider whether spoil from digging can leave by the same route the materials would have to arrive by, and how much of it there might be.

Excavated material is bulky and has to go somewhere, and a narrow route makes that a significant part of how the work runs.

Ask whether machinery could physically reach the working area, and what the alternative would be if it cannot.

Hand digging is a genuine possibility on constrained plots, and knowing that early prevents assumptions being built into the plan.

Write down whether a neighbour's cooperation would be needed for access at any point, and how you would open that conversation.

A neighbour asked early, before drawings and dates exist, tends to respond very differently from one approached once everything is already arranged.

Note every structure standing in or near the footprint, including sheds, a garage, a greenhouse or an old outside toilet.

Structures already there frequently sit on foundations or drainage that a professional will want to know about.

Write down which boundary walls or fences come close to the proposed footprint and what condition each one appears to be in.

A boundary structure that is already leaning or cracked becomes part of the conversation the moment anything is built near it.

Record whether any boundary wall appears to be holding back a difference in ground level between the two gardens.

A wall retaining ground behaves very differently from a simple dividing wall, and the difference is not always obvious from one side.

Whether a wall retains ground, and what work beside it would mean, is a question for a suitably qualified structural professional.

Note any tree, hedge or established planting that would have to be removed, including anything growing on a neighbour's side of the line.

Removing planting is often the first physical act of a project and the one most likely to cause a dispute if it was not discussed.

Trees and hedges may carry protection; confirm status with the local authority before assuming anything can be removed.

Ask what would happen to a boundary structure if the ground immediately beside it were dug out for a new foundation.

This is one of the most common causes of neighbour dispute during rear work and one of the easiest to raise in advance.

Excavation near an existing structure must be assessed by a qualified structural professional before any work is planned.

Consider what you want the boundary to look like afterwards, since a rear addition usually brings built form much closer to it.

A fence that was fine when it was distant can look very different once a wall stands close beside it.

Confirm locally what consent arrangements apply to a rear addition on your property, and write down the name of whoever tells you.

Arrangements vary between areas and between properties, and an informal opinion is not a substitute for asking the responsible body.

What proved acceptable behind one house says nothing about the next; the local authority is the only source for what applies at your own property.

Ask the local authority what it needs to know about how far the proposal would project beyond the existing rear wall, and record the answer in the words used.

Projection beyond the original rear wall is usually the measurement that decides which route a rear addition takes, and owners guess at it far more often than they ask.

Nothing about projection or its consequences can be settled from a checklist; only the local authority can tell you what applies behind your house.

Note what has been added to neighbouring houses along the row, while writing down clearly that this does not indicate what would apply to you.

What the neighbours have is useful context for a professional and a poor basis for an assumption by an owner.

Write down which neighbours would look directly at the new structure, and decide at what point you intend to speak to each of them.

Neighbours who hear about a proposal from a notice rather than from you tend to respond very differently.

Record any shared drain, shared boundary or joint maintenance arrangement that the work might touch.

Shared arrangements bring other parties into the process and follow their own route alongside any consent conversation.

Shared drains and shared structures are handled by the relevant authority or a suitably qualified adviser; ask them directly.

Write down roughly how much usable garden would remain behind the addition, since what is left outside is commonly asked about for rear work.

Owners describe the room they are gaining and rarely describe what is left outside it, yet the remaining garden is often the point a rear proposal turns on.

How remaining outdoor space is treated where you live can only be confirmed by the local authority, never assumed from another street.