The dining chairs are in the foreground; beyond them, a green sofa, a low coffee table and a fireplace still belong to a recognisable sitting room. At Picture Frame House in Stepney, east London, the opening is wide enough to take in that whole scene. Yet the white wall around it gives the room an edge. You can see through the house without feeling that everything has become one room.

Archer + Braun’s renovation of this terraced house included a side extension and a rearranged ground floor. The opening between the living and dining rooms was widened, while smaller, timber-framed openings connected other spaces. It is a useful distinction: a route through a wall and a view through it do different jobs.

For anyone considering a knock-through, that is a better starting point than deciding how much wall to demolish. Perhaps the real problem is a cramped doorway, an awkward route to the kitchen or a dining room cut off from conversation. Draw a generous opening alongside the fully open-plan option before choosing between them.

An empty floor plan makes almost any knock-through look persuasive. Furnish both versions to scale, using the sofa, table, storage and kitchen units you intend to keep. Draw the dining chairs pulled out, then trace the walk from the front door to the garden. If that route clips the table or cuts between the sofa and television, removing a wall has not resolved the layout.

At Picture Frame House, a smaller opening sits above the green sofa. The wall below remains available for furniture, while the framed view makes the space beyond part of the room. In a 2020 interview with The Modern House, architect and owner Stuart Archer explained that retaining some wall between the lounge and dining/play area helped give the sofa a place and the sitting area a measure of privacy.

That thinking transfers readily to a terrace or semi with two adjoining reception rooms. A retained return might accommodate shelves, a light switch or the end of a sideboard. Mark those things on the drawing; a sliver of wall that fits nothing may be an obstacle rather than an asset.

Full open plan can still win. If the dividing line leaves neither room wide enough for its furniture, or creates a stubborn bottleneck, a wider structural opening may produce a much more usable space. The comparison should settle a real problem, not preserve a partition for its own sake.

Light, conversation and quiet are different demands. An open doorway can help people feel connected, but it will also carry voices, television sound and kitchen noise. Keeping short lengths of wall at either side does not create an acoustic barrier. If someone needs to work while dinner is being made, include a way to close the rooms from the outset.

Show hinged doors in their open position so you can see what they occupy. Pocket doors need space within the wall to slide into, with services and fixings planned around the chosen system. Glazed doors can preserve a view when closed, but specify any required acoustic or fire performance rather than choosing by appearance alone.

The framed opening towards Picture Frame House’s kitchen offers another possibility. The sink remains beneath it, and the view reaches through to the garden window. It connects the rooms without turning the opening into a walkway. Where the ambition is to see greenery or bring the cook into conversation, a view through the wall may do more than another route around it.

The name of the house comes from the openings themselves. Archer + Braun worked with a local picture framer to make their bespoke American black walnut and oak surrounds. The timber gives each view a deliberate border, turning what could have been a simple hole in the wall into part of the design.

Borrowed light needs the same care. Check the opening from the seats where you will use the room, and consider the windows supplying the light. A larger aperture cannot guarantee a bright room deep inside the house.

The attractive opening is only half the drawing. The wall left beside it may be useful for a sofa, but it cannot be assumed to support the building above. If the wall carries loads, a structural engineer must check what it supports, including floors, walls above, roof loads and previous alterations, and design either option. Tapping the plaster tells you none of that.

The beam is only part of the answer. Its ends need adequate support beneath them, sometimes involving posts or strengthened foundations. The pieces of wall you hope to retain are not necessarily suitable to carry those loads. Ask the engineer to compare what each layout would require and whether the resulting beam depth or supports would affect the finished room.

The drawings also need to cover temporary support, the sequence of work and inspections. Include the required fire protection to structural steel, and identify any wiring, plumbing or heating that must move. The engineer, designer and contractor should agree these responsibilities before demolition begins.

Fire safety may affect the choice even if a partition is not load-bearing. LABC warns about opening a kitchen onto a staircase serving as an escape route. Ask the designer and building control team to assess the whole arrangement. Glazed doors are not automatically a suitable fire-door assembly, however attractive they look.

Planning and building control are separate questions. Purely internal alterations normally need no planning permission in England and Wales, but structural work still needs the appropriate building-regulations approval. In Scotland, obtain the required building warrant before starting; in Northern Ireland, check the application with the council's building control team. Listed-building consent may also be needed for internal changes.

Other requirements depend on the property. In England and Wales, bearing a new beam into a shared party wall may trigger notice under the Party Wall etc. Act. Leaseholders should check the lease and obtain any necessary freeholder consent. All of these questions belong on the drawings and quotation brief, rather than arising after a contractor starts work.

A shorter span may reduce some structural work, but it does not guarantee a cheaper finished project. A carefully lined opening with bespoke doors could cost more than a simpler, wider opening without them. Conversely, removing the whole wall can extend the repairs across floors, ceilings and decorative mouldings that looked untouched on the plan.

Architect Níall Hedderman's Edinburgh case shows how much the finishing can change the bill. Using the lowest individual prices from two 2024 contractor tenders, he put demolition and steel erection at just under £10,000. After repairing floors, ceilings, walls and cornices, plus plastering, decorating and cleaning, the composite reached £21,500 plus VAT (£25,800 if VAT is charged at 20%). These are 2024 prices, not a current quotation or a UK average. They are not even one builder's offer: Hedderman combined the cheapest items from the two tenders. The example is useful because it shows how much of a knock-through budget can go on making the rooms good again.

Ask for a separate written quotation against a drawing of each option, using the same standard of finishes and making good. Each quote should identify:

Keep an allowance for unresolved work identified by the team; do not disguise it inside an apparently fixed total. Compare what you will pay to have usable, finished rooms, then weigh that against the extra space or flexibility each option delivers. If the wider opening costs more, you should be able to point to what that extra money buys in the furnished plan.

Before signing off the demolition drawing, return to the furnished one. Can someone pull out a dining chair while another person passes? Is there still a comfortable place for the sofa? Can you close a door when you need quiet? A knock-through earns its cost when it improves those ordinary moments. Sometimes the best part of a wider doorway is the useful wall left beside it.