Building Structures and Forms

One question about any building

Stand in any building and ask one question. What is holding this up? There are only a few answers, and whichever one applies has already decided a surprising amount about the building you are standing in: how big the rooms can be, whether a wall could be moved, how much glass the outside can be made of, and how much of it could ever be changed. ⭐ So the three structural forms in this topic are not three things to memorise. They are three answers to that one question, and almost everything else follows from the answer. ⚠️ Which is why an exam answer that only names a form scores badly. Naming it is the start. Saying what follows from it is the marks.

Three ways to stand up

Every low-rise building you will be asked about uses one of these, or a mixture of them. Read each column as a chain: what carries the load, and then what that allows or prevents.

Follow the load to the ground

In a framed building, put the parts in the order a load passes through them, starting with the snow on the roof.

• Snow and the weight of the roof itself
• The roof structure spanning between supports
• The beams running between the columns
• The columns carrying it downwards
• The foundations spreading it into the ground

Why a repair must match

Work on a traditional building is expected to match the existing materials and keep as much original fabric as possible. Beyond appearance, why does that matter structurally?

• Because in a traditional building the original fabric is doing the structural work, so replacing it with something that behaves differently changes how the building carries and sheds load
• Because visitors expect a historic building to look consistent
• Because traditional materials are cheaper than modern ones
• Because modern materials are not strong enough for old buildings

Words for what a structure carries

Five terms that let you say precisely what a structure is dealing with, instead of saying it is strong.

Find the sentence that gives the structure away

A surveyor describes an invented single-storey building. Select the ONE sentence that tells you how it is held up.

• The building is used as a storage depot and was finished a few years ago.
• The floor is a concrete slab with a painted finish.
• Inside there is one large clear space with no supports anywhere between the two end walls.
• The doors are wide enough for a lorry to reverse through.
• The outside is clad in profiled metal sheeting in a pale grey.

What follows from choosing a frame

A client chooses a framed structure rather than load-bearing walls. Three of these five genuinely follow from that choice. Choose the three.

• Internal walls can be positioned freely, and moved later without touching the structure
• The outside can be largely glazed, because the wall only has to keep the weather out
• Much of the structure can be made off site and assembled quickly on arrival
• The building no longer needs foundations, since the frame carries the load
• Wind no longer has to be designed for, because there are fewer solid walls

Ask it of every building in the question

Exam questions here usually describe a building or a brief and ask you to choose or justify a structure. ⭐ Ask what is holding it up, then say what that allows and what it costs. Walls holding it up gives you small fixed spaces and simple construction. A frame gives you free layout and glass, and puts the load into fewer heavier points. Rigid joints give you a wide clear span, and very little else. ⚠️ Every structure is a trade. An answer that names only the advantage has given half the reasoning, and half the marks.

Match the brief to the structural answer

Two kinds of shelving

Forget buildings. Look at two sets of shelves in a shop. The first is a boxed unit: two solid sides, a back panel, and four shelves fixed between them. It is rigid, it is cheap, and it is exactly as wide as it was made. The second is a rack: four upright metal posts with holes all the way up, and shelves that clip in wherever you want them. ⭐ Now try to change each one. On the boxed unit you cannot take out a side, because the side is what everything rests on. You cannot move a shelf either, because it is also stopping the whole thing folding sideways like a parallelogram. Take out the back panel and watch it lean. On the rack you can move every shelf in ten minutes, and leave a tall gap in the middle for something big, because the uprights were always doing the work on their own. ⚠️ Notice the price of that freedom. The rack needs its uprights bolted down or braced, or it will sway, and all the weight now arrives at four small feet instead of two long edges. ⭐⭐ Nothing in that paragraph is about shelves. It is the whole of this topic, at a scale you can pick up.

Complete the building structure facts

In a _____ structure the walls themselves carry the weight down to the foundations, which is why the rooms are small and cannot be moved. In a rectangular _____ structure a skeleton of columns and beams carries the load instead, so the outer wall can become a glazed skin called _____ walling, which supports nothing but itself. A _____ frame is rigid where column meets rafter, which lets it cross a large _____ with no support in the middle. Whichever form is chosen, the building must still resist sideways wind forces, which is called _____ stability.

Build the justification

An invented client wants a single-storey sports hall with a completely clear floor. Complete the justification.

Structures quick-fire

Five quick decisions. Three lives.

Choose a structure as the brief changes

A community group wants a single-storey building on a tight site. Work through their brief.

• Their first brief is a set of small rooms: an office, a store and two meeting rooms, all fixed. What suits it?
• They come back: they now want one big hall that can be divided differently each season. What changes?
• They ask what this decision costs them. What is the honest answer?

Recommend a structure and defend it

A client wants a single-storey building containing one large open workshop and, at one end, three small permanent offices. Recommend how it should be structured.

• Say what should hold up the workshop space, and why that suits a clear floor
• Say what should hold up the office end, and why a different answer can be right in one building
• Use dead load, imposed load and lateral stability correctly at least once
• Name one thing your recommendation makes harder or more expensive
• Say what you would need to know about the ground before committing to it