Grade 10 building construction – Ground Floors Quiz

A DPM is a continuous impermeable layer (usually plastic) placed under the slab to stop moisture rising from the ground into the floor and interior of the building.

Hardcore (crushed stone or similar) creates a stable base, improves drainage under the slab and helps distribute loads so the slab does not settle unevenly.

A suspended floor is raised above the ground on beams, blocks or piles, creating a ventilated void beneath and avoiding direct contact with potentially wet or poor ground.

Reinforcement mesh does not prevent all cracks but helps control and hold cracks that form due to shrinkage or temperature changes, maintaining slab integrity.

Beam-and-block floors use precast concrete beams with infill blocks to create a sturdy suspended floor that is quick to construct and commonly used in many climates.

Soft or compressible soil must be improved (excavate and replace, compact fill, or use deep foundations) to prevent excessive settlement and cracking of the slab.

A sand-cement screed is a thin layer used to level the slab and give a suitable surface for finishes such as tiles or vinyl; it is not the structural slab layer.

A 1:2:4 nominal mix is commonly used for ordinary concrete ground slabs, giving adequate strength for general domestic floors when properly mixed and compacted.

Overlapping and sealing DPM joints ensures a continuous barrier against moisture; gaps would allow water to penetrate up into the floor.

Perimeter or edge beams take the load from the ends of floor beams, help tie the floor together, and support the edges of the suspended floor construction.

Underfloor ventilation reduces humidity under suspended timber floors, preventing decay and extending the life of timber members.

Concrete gains strength over time; initial curing for about 7 days (keeping it moist) is commonly recommended to achieve reasonable early strength and reduce cracking.

Blinding (a thin plain concrete layer) protects the DPM from damage by sharp stones in the hardcore and gives a level bed for the membrane and slab above.

Tiles are durable, water-resistant and hygienic for wet areas; other options would suffer moisture damage or be impractical indoors.

Overdigging and filling removes unsuitable soils and replaces them with well-compacted material, providing a stable base that reduces future settlement problems.

Termites are common in many parts of Kenya; treating soil and timber prevents costly damage and preserves the structural integrity of timber floors and elements.

Compaction removes voids and increases density of the fill so the slab has a stable support and is less likely to settle unevenly, which would crack the floor.

A raft foundation is a large concrete slab that carries the loads of the building over the whole footprint, useful where soils are weak and loads must be distributed.

The slump test gives a quick measure of concrete consistency and workability on site; it does not measure final strength directly.

Concrete will crack as it shrinks; control joints create weakened lines so the cracks occur there instead of randomly, making them easier to manage.

Insulating under the slab reduces heat transfer to the ground, improving indoor comfort and reducing energy needed for heating or cooling.

Suspended floors raise the structure above ground to avoid dampness and flooding and are used where the ground conditions are unsuitable for a direct ground-bearing slab.

Murram is a lateritic material widely used in Kenya as a compactable sub-base when well-graded and compacted; it must be suitable and free of organic material.

DPC should be placed in walls at a height above external ground to prevent moisture rising into the walls and link with the floor DPM to maintain a continuous moisture barrier.

Falls ensure water runs to floor outlets rather than pooling, which is essential in bathrooms, kitchens and service areas to keep floors safe and sanitary.

Proper sequence: prepare and compact sub-base, provide blinding, lay DPM, position reinforcement, then cast the structural slab to ensure durability and prevent moisture problems.