The main things to know
- The floor must suit the rooms, supports and loads in the design.
- Compare the complete installed cost of suitable options.
- Plan stairs, pipe routes and large openings early.
- Temporary supports stay until the responsible team says they can be removed.
Think about the rooms above and below
Do you want a large living room without a column in the middle? Where will the stairs go? Will there be a water tank or heavy equipment above? These choices affect the floor and its supports.
Tell the architect and engineer about the rooms and features that matter to you before the drawings are settled. Moving a column later can involve much more than shifting a mark on the plan.
A solid concrete slab
This is a continuous concrete floor cast on site with steel inside it. It is a familiar method, but the thickness, steel and supports still need to be designed for your building.
Ask how it affects the ceiling below and where beams will be visible. You should understand those features before choosing room layouts and ceiling finishes.
Ribbed and waffle floors
These floors use ribs of concrete with thinner areas between them. A waffle arrangement has ribs running in two directions. Reducing some concrete can reduce weight, but the complete system still needs to suit the building.
Discuss the ceiling appearance, depth of the floor, openings and the experience of the team doing the work. A saving in concrete alone does not establish a saving on the whole floor.
Floors made with factory-produced parts
Precast systems use concrete parts made away from the final position and then installed on site. Depending on the system, more work may be needed for connections, toppings and finishes.
Check delivery access, lifting arrangements and what the supplier’s price includes. The supplier’s system and the engineer’s overall building design need to work together.
Compare the whole job
| Part of the decision | What to ask |
|---|---|
| Price | Does it include steel, supports, labour, delivery, lifting and finishes? |
| Space | How does the floor depth affect ceiling height and stairs? |
| Services | Where will pipes, cables and openings go? |
| Programme | When can the next work start, and what checks are needed first? |
| Team | Who designs, supplies, installs and inspects the system? |
Ask the team to compare options for the same layout and requirements. Otherwise, two prices may cover quite different amounts of work.
The supports underneath are doing a job
Temporary supports hold the work during construction. They need proper planning, installation and checking. They must not be moved to make room for storage or removed because another job needs them.
The responsible team decides when they can come out, considering the design, concrete strength and loads. A rule such as “remove them after a week” is not enough.
Getting a useful price
Send the plans and ask for an itemised quotation. Mention access limits and any heavy features you expect the floor to carry. Include ceiling finishes if you want to compare the finished result.
Once work is underway, do not let trades cut holes or channels without approval. A pipe route that looks convenient can pass through an important part of the floor.
Further reading
Questions we get asked
- How thick should the slab be?
- Your engineer determines that from the floor system, supports, loads and other design requirements.
- Is a ribbed slab cheaper?
- Sometimes it can be suitable and economical. Compare the complete installed cost for your building, not just the amount of concrete.
- What is the price per square metre?
- Ask for a project quotation that states the system and everything included. Access, supports, steel and finishes can change the total.
- How long do the supports stay?
- Until the responsible team confirms removal is safe under the project’s procedure.
- Can pipes run through the slab?
- Some routes and openings can be designed in. Agree them before the pour and get approval before any later cutting.
Written by
Eng. Samson Gitonga
Civil & Structural Engineer
Samson Gitonga is TimberStone’s civil and structural engineer. Based in Nanyuki, he helps clients understand how the ground, the building plans and the materials come together to create a safe, practical structure.
- Registered Civil & Structural Engineer, Engineers Board of Kenya
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