Architecture and interiors: facts, examples and context

The interior of a house is decided by its structure long before anyone chooses a paint color. How wide a room can be, how tall, where the windows are and how deep the light reaches, whether a wall can come out, where a bathroom can go: all of it is set by beams, bearing walls and pipes. Decoration happens inside those limits and is usually an attempt to hide them. Once you can see the limits, an interior becomes legible, and you can tell what a house can become as well as what it is.

This page is about that relationship: what the structure allows and what the interior does with it. It describes types and methods, not any particular building.

What to take away

• The section, not the plan, decides how a room feels. Ceiling height and window head height do more than floor area.
• Bearing walls and floor spans set what an interior can be. Learn to tell a wall that holds the house up from one that just divides it.
• Services are the hidden plan. Where the water goes and where the smoke went limit every rearrangement.

The section is the experience

A plan shows you where you can walk. A section shows you what it will feel like when you get there.

Ceiling height matters in proportion to room width. A tall narrow room feels like a well; a wide low one feels like a cellar; a room whose height is comfortably related to its width feels right without anyone knowing why. Older houses allocated height by importance, which is why the principal floor of a stacked house has the tallest rooms and the top floor the lowest.

Window head height decides how far daylight travels into a room. Light enters and falls; the higher the top of the window, the deeper the floor it reaches. A wide window with a low head lights the wall opposite and leaves the middle of the room dim. A tall narrow window with a high head lights the room. This is why old rooms with what look like modest windows are often brighter than new rooms with wide ones.

Wall thickness makes the reveal. A window set in a thick masonry wall sits in a deep frame that shapes and softens the light; in a thin framed wall the glass is nearly flush with the surface and the light arrives flat. Deep reveals are one of the reasons masonry houses feel solid inside, and one of the things a thin wall cannot fake.

Which walls hold the house up

Nearly every question about changing an interior comes back to this, and it can be read without drawings.

A bearing wall is doing a job for the floor or roof above it. Signs: it is thicker than the others; it sits directly over a wall or beam on the floor below; it runs at right angles to the floor joists, which you can sometimes see in a basement or roof space; openings through it have substantial lintels or beams above them; it continues from foundation to roof. External walls are almost always bearing. In a deep narrow house the side walls carry everything, as New York homes explains.

A partition divides space and carries nothing. Signs: thin, often hollow-sounding; does not line up with anything below; can be interrupted by a doorway with a light frame over it; may stop short of the ceiling structure. Partitions come out cheaply. Bearing walls come out only when something else takes over their job, which is where the beam comes from.

Framed buildings blur the line. In a house with a timber or steel frame, the frame carries the loads and the walls, including the outside ones, can be almost entirely glass. That is the structural fact behind the window wall and the open plan, and it is why the light-framed houses of the West could open their sides to a garden in a way a masonry house cannot, a story told in Los Angeles homes.

Spans decide the size of rooms

A floor is a set of joists spanning between supports, and joists of a given material and depth can only span so far. Those limits are tabulated in the residential model code that local rules descend from, described at the International Residential Code page. That limit sets the width of an ordinary room. Where a room is wider than the local span, something is helping: a beam under the ceiling, a steel member hidden in the floor, a truss in the roof above, or a column somewhere in the room.

This is worth knowing for two reasons. First, the large open volume in a modern house is a structural decision with a cost, not a simple absence of walls. Second, when you see a beam crossing a ceiling in an older house, it is often marking where a wall used to be, which is a piece of the building's history, as the reading of phases in former homes describes.

Roof structure has the same logic. A room that rises into the roof, with the ceiling following the slope, has traded the roof space for height. It is possible when the roof structure is designed for it and awkward to retrofit when the roof was built with ties at ceiling level.

Openings, and what the wall is made of

The ratio of wall to window is a structural signature.

Masonry needs solid piers between openings to carry the load down, so a masonry house has windows as holes in a wall, with wall between them. The rhythm of a masonry facade is the rhythm of its piers. Frame construction carries the load on posts, so the wall between them can be anything, including nothing. A continuous band of glass, a corner window with no post, a wall that slides away: these are frame details, and where you see them on a building that looks like masonry, the masonry is a skin.

Inside, the same logic shows in how deep the walls are around openings, how wide a doorway can be without a visible beam, and whether internal walls stack floor to floor. A house whose upstairs walls sit in different places from its downstairs walls has a frame, or a set of beams doing quiet work.

Services are the hidden plan

Water and smoke fix more of an interior than people expect.

Drainage runs by gravity to a stack, and the stack runs vertically through the house to the drain. Bathrooms and kitchens cluster around it because moving them far from it means long shallow runs that do not drain well. A house with all its wet rooms stacked over one another was planned; a house with a bathroom in a strange corner was adapted.

Chimneys were the original vertical services, and a flue rising through the house dictates where fireplaces sit on each floor. Even where the fires are gone, the stack is usually still there, a thick masonry element in the plan that cannot move. Where a fireplace sits on a party wall, the flue is in that wall, which is why the fireplaces in adjoining houses line up.

Modern services add ducts, which need routes, and a plant room, which needs space and access. In a tightly built house those ducts are also the ventilation, which turns air quality into a design decision rather than a byproduct, as the EPA introduction to indoor air quality sets out. In a large house the plant is a small building of its own, and the routes from it set the ceiling depths and the positions of the bulkheads that decoration then has to hide. The service side of a very large house, and how much of the plan it occupies, is examined under mansions.

Reading an interior

• Start with the section: how tall is the room relative to its width, and how high is the top of the window?
• Find the bearing walls: thick, continuous, over something, at right angles to the joists.
• Look for beams and bulkheads in the ceiling. Each marks a removed wall, a long span, or a duct.
• Locate the wet rooms and imagine the stack. Everything else was arranged around it.
• Find the flues. Fireplaces mark them, and so do thick walls in odd places after the fireplaces are gone.
• Check whether upstairs walls sit over downstairs walls. If not, ask what carries them.

The finishes are what someone did with these facts last time. The facts are what you can do next time.

Common questions

Can any wall be removed with a big enough beam?

Structurally, most can, at a cost that rises quickly with span and with what is above. The beam then needs supports of its own, which land on the floor below and the foundation, so the question is never only about the wall.

Why do old rooms feel taller than their measurements suggest?

Window head height and proportion. A tall window with a high head fills the room with light to the ceiling, and a room whose height is well related to its width reads as generous. Actual height is only part of it.

Is an open plan always a structural compromise?

It is always a structural decision. In a frame building it is close to free. In a masonry building it means beams, posts and foundations doing the work the walls did. Either way, what is lost is the closed room, and whether that matters is a question about the household rather than the structure. How houses in different countries reached different answers with different materials is compared in international homes.

What is the fastest way to tell if an interior was replanned?

A bathroom far from the stack, a beam crossing a ceiling with no reason in the plan above, and a cornice that stops at a wall. Any one of them says the plan you are looking at is not the plan the house was built with.