Single-Storey Extension Questions Checklist

Write down whether seeing sky from inside matters to you, because that single preference often decides between a flat roof with rooflights and a pitched roof with a glazed ridge.

Owners usually describe the roof in terms of appearance from outside, when the decision they will actually live with is what the ceiling does to the room underneath.

Note where the first-floor window sills sit above the existing ground-floor ceiling, because that band of wall is what any new roof has to tuck under.

The available height between the ceiling below and the windows above quietly limits roof form, and owners are often surprised how little room there is.

Ask how each roof option would meet the existing wall, and what that junction would mean for the rooms directly above it.

A roof abutting a wall interacts with upstairs windows, with the existing gutter and sometimes with a neighbouring roof, and each option resolves that differently.

Roof build-up, insulation position and how a roof meets a wall are matters for a qualified designer and installer, not choices to settle from a photograph.

Consider that the new roof will be seen from the upstairs windows and from the garden, and record how much its appearance from above matters to you.

A flat roof becomes a permanent view from every rear bedroom, which owners rarely think about until it is finished.

Discuss with a qualified professional what access a low roof would need for clearing and maintenance, and where a ladder could physically stand once the addition exists.

Roofs tight against a boundary can be difficult to reach afterwards, and the answer sometimes changes the position or the edge detail.

Working at height and roof maintenance arrangements belong with the professionals doing the work; treat this only as a topic to raise early.

Record any strong preference about the shape of the ceiling inside, because a flat soffit and a sloping ceiling feel entirely different within the same footprint.

This is one of the few things an owner can decide alone, and stating it early stops a designer solving the wrong problem.

Identify every room that would end up without an external wall once the addition is built, and write down where its daylight would then be expected to come from.

The rooms behind a new addition are the ones owners regret, and naming them early turns a vague worry into a design problem someone can respond to.

Note each existing rear window and door, and mark which would be removed, blocked or turned into an internal opening by the proposal.

These openings also carry ventilation and escape considerations that a professional will want to look at, so listing them saves a second survey.

Consider whether an internal courtyard, a rooflight or a glazed link would matter more to you than the floor area it gives up, and write down which way you lean.

Depth and daylight pull against each other, and owners who have not decided tend to end up with the deepest plan and the darkest middle.

Sit in the room that would end up in the middle at several different times and record how dark it already feels before anything is built.

A room that is already gloomy will be considerably worse, and a first-hand note is more persuasive than a general assumption about light.

Ask a qualified professional how daylight into the retained rooms would be affected at the depth you are considering, and record what they tell you.

Daylight assessment depends on orientation, obstruction and the relevant local requirements, none of which can be judged from a checklist.

How much daylight a room needs and how it is measured are matters for a qualified professional and the relevant local requirements.

Write down whether light borrowed from the new space would have to pass through a door you would realistically want to keep closed.

Borrowed light only works while the plan stays open, and households that need doors shut for noise or heat lose it immediately.

Note whether the existing ground floor sits above the garden, and describe the step in your own rough terms rather than guessing at a figure.

That difference determines whether the new floor can run out level, and it is the single most common surprise when the ground is opened up.

Decide and record whether a level threshold to the garden is a requirement or a preference, and raise it at the very first conversation.

It affects the floor build-up, the external drainage and sometimes the whole approach to the garden, so it is disruptive to introduce late.

Whether a level threshold can be achieved here depends on ground levels, drainage and the relevant local requirements, all of which need a qualified professional.

Write down what the ground does immediately outside the proposed opening, including whether it falls towards the house or away from it.

Ground falling back towards a new threshold changes what has to be designed outside it, and owners rarely notice the direction until asked.

Consider whether the new floor finish has to match the existing one, and note exactly where a change of material would fall if it does not.

A junction line placed by accident rather than by choice is one of the most visible outcomes of a rushed decision late in the work.

Ask what floor build-up your heating choice implies before assuming the new floor can sit at the same level as the existing one.

Underfloor arrangements and insulation both take height, and the resulting level difference has to be resolved somewhere in the plan.

Record any existing step, threshold or ramp that someone in the household already finds awkward, and note who struggles with it.

Households often plan around the people who are fine and forget the person who is not, which is easy to correct while nothing is drawn.

Write down how you actually use the back of the house in poor weather, because wide glazed doors are opened far less often than people expect when choosing them.

Understanding real use tends to shift the decision towards one workable door and better glazing rather than the widest possible opening.

Note which way you want the doors to open and where the opened leaves would physically stand, since that strip is often already planting, a bin or furniture.

Folding and sliding arrangements each park their leaves somewhere, and the space they need is regularly forgotten until the doors arrive.

Consider whether you need a single door that can be opened quickly for the dog, the bins or the washing without moving a whole set of leaves.

Households without a quick door end up using a different exit entirely, which undermines the point of the opening.

Record how the opening would be shaded in strong sun, and whether blinds, an overhang or planting are part of the plan or an afterthought.

Shading added later is usually the compromise version, and it is far easier to allow for while the opening is still being drawn than once the glazing is set.

Ask what a large glazed opening means for securing the house at night, and who advises on that in a project like this.

Security arrangements interact with the door type chosen, so raising it before selection is more useful than after.

Security specification is for a qualified professional and your insurer to advise on; nothing here indicates what is adequate for your property.

Note where curtains, blinds and their fixings would go if the head of the opening sits tight up to the ceiling.

Openings taken right to the ceiling leave nowhere to fix a track, which is discovered at the point when nothing can be changed.

Mark the footprint on the ground with canes or chalk and note every drainage cover, gully and pipe that falls inside it or close to its edge.

Marking out gives you a real sense of the size and reveals features that never show up when the idea is only discussed indoors.

Note which trees or large shrubs would end up directly overhanging a low new roof, and record how close their trunks stand to the edge of the marked footprint.

A ground-floor addition sits inside the canopy of garden planting in a way an upper floor never does, which raises leaf-fall questions and ground questions at the same time.

Whether planting carries protection, and what its roots mean for ground conditions, is for the local authority and a qualified professional to establish.

Record whether the footprint covers an old patio, a conservatory base or a former shed slab, and treat reusing any of them as a question rather than an assumption.

Owners frequently expect an existing base to be built on directly, and whether that is possible depends on how it was laid and what it was originally laid to carry.

Whether an existing slab or base can form part of a new structure must be established by a suitably qualified professional after examining it.

Ask what would be needed to establish the ground conditions on this plot, who arranges that work and at what point it usually happens.

Knowing when this normally occurs helps you understand why a professional may decline to commit to a footprint before it is done.

Ground conditions and foundation solutions can only be established by site-specific assessment carried out by a suitably qualified professional.

Record whether the existing house has ever shown cracking or movement, noting where and when you first saw it rather than what you think caused it.

A factual history is genuinely useful to a professional, whereas an owner explanation of the cause tends to send the conversation the wrong way.

Note where you believe supply pipes and cables cross the garden, and flag clearly that these positions need locating properly rather than assumed.

Owners often remember a trench being dug and can point roughly at it, which is a useful starting point even when it is not precise.

Note where each existing rainwater downpipe lands and what happens to the water once it reaches the ground, including whether it simply disappears into a gully.

The existing route is the starting point for any conversation about a new roof, and it is often interrupted exactly where the addition wants to go.

Consider where water from a new roof would go, and ask that question early rather than assuming an existing gully can simply take more.

Capacity and route are technical questions with local answers, and discovering them late can move a whole footprint.

Rainwater capacity, falls and discharge routes must be established by a qualified professional and the relevant drainage authority.

Write down whether the garden already puddles anywhere after heavy rain, and mark those spots relative to the proposed footprint.

Standing water is a visible clue about how the ground behaves, and owners are the only people who have watched it over time.

Note whether the new footprint would replace lawn, border or another surface that currently soaks up rainfall.

Replacing soft ground with roof and paving changes where water goes, which is a topic the local authority may take an interest in.

Ask how the gutter along the new roof edge would be reached for clearing once the addition and any boundary planting are in place.

Gutters that cannot be reached stop being cleared, and blocked gutters against a wall junction cause exactly the problems owners fear.

Record whether a neighbouring roof, wall or gutter currently discharges onto the area you are proposing to build on.

Rainwater arriving from an adjoining property is somebody else's arrangement landing on your footprint, and it is far calmer raised before anything is built.

Write down how the enlarged ground floor would be heated, and raise as an open question whether the existing system has anything left to give.

A ground floor that grows considerably asks more of the same boiler, and the answer decides whether a second strand of work runs alongside the building.

Whether the existing system has anything left to give for a bigger floor is a calculation rather than an impression; put it to a qualified heating professional.

Note where radiators currently sit on the wall that would be opened up or removed, and where they could plausibly go instead.

Relocated radiators interact directly with the furniture layout owners already have in mind, so it pays to look at both together.

Consider how cooking smells and noise would travel once a kitchen opens into a much larger space, and whether anyone in the household would mind.

Open plan spreads both further than people expect, and it is the most common complaint after a kitchen extension is finished.

Record whether the new space has to be comfortable in the coldest and hottest conditions you get, and note what that implies for glazing and shading.

A glazed rear addition can become unusable at both ends of the year, which is designed out at the start or lived with afterwards.

Ask what ventilation the new arrangement would need, particularly where cooking moves into an open space rather than a separate room.

Ventilation requirements vary locally and by arrangement, and extract routes often influence where a hob can sensibly go.

Ventilation requirements are set by the relevant local requirements and must be confirmed with a qualified professional for your property.

Note how sound would carry in a large space with hard floors and a lot of glass, and whether any room above or next door would pick it up.

Hard, glazed spaces are noticeably louder, and soft finishes are much easier to allow for while the design is still moving.