1) Floors separate interior spaces from the exterior environment and must be waterproof and insulated on the ground level but not upper levels. Suspended floors are supported by walls while floating floors can rest on subsoil. 2) A typical floating ground floor includes removing topsoil, adding a hard-core fill and sand blinding followed by a damp proof membrane, concrete slab, and finishing screed. Insulation can replace the screed. 3) Suspended ground floors are built into walls with ventilation below and use precast concrete beams and insulation blocks for a warm, dry floor without drying time.

1. Notes to accompany 1014 “Floors”
Slides 1-4
Floors are fairly straight forward. It is important to remember that the ground floor is part of the
buildings external envelope. It separates the interior form the external environment just as
much as the roof or external walls do. It need to be waterproof and insulated. Upper floors
between ground and first floor levels are not part of the external enclosure and so do not have
to be insulated or waterproofed. They may need to be sound proofed and fire resistant. This is
especially important if the floor separates two different occupancies.
Upper floors have to be self supporting over the rooms below. They are known as suspended
floors, and are held up by the walls
Ground floors can rest directly on the subsoil, if it is strong enough, and in this form are called
floating floors, although they do not really float. Increasingly builders like to build ground floors
as suspended concrete floors, as this overcomes problems of subsidence and water penetration.
This is covered in later slides.
Slides 5-7
The typical floating ground floor is a multi-layered construction which provides a strong, level
finish for internal activities, keeps out the damp and resists the passage of heat. The main layer
is mass concrete, but this is only one layer of many. It provides the structural strength.
All topsoil must be removed from the area of the floor and all loose subsoil removed and
replaced by inert “hard-core”. This can be broken brick, broken stone or gravel. This fill raises
the surface sufficiently to ensure the finished floor level is higher than the surrounding finished
ground level, to avoid flooding and water penetration. The top 50mm of the hard-core is sand-
blinded. This means clean sand is firmly rolled into the top of the fill the provide a smooth
surface which will not puncture any membrane laid over it. Fully compacted sand blinding will
not show footprints if you walk across it.
The floating floor must not be built into the wall, it must be free to move relative to it.
Slide 8
Concrete is not water proof, it is porous. This means a separate layer is needed to keep out
ground water. This is called the damp proof membrane (DPM). This membrane can be a plastic
layer under the concrete, a water proof paint on top of the concrete or a layer of hot-poured
asphalt. Commonly it is under the slab, where it is protected frommechanical damage, except
during the building process, when it is very vulnerable. The DPM must be physically bonded to
the DPC in the inner leaf of the wall, to ensure that the damp proof layer acroos the base of the
building is unbroken. Laying a sheet DPM in strong winds is difficult, and ensuring it is folded up
correctly in corners is also a problem.

2. Slide 9
The Concrete slab should ideally be poured in one go, but often has to be laid in sections with
joints between. The slab is typically 100-150mm thick and spreads the loads from furniture and
fittings over a wide area of the sub-soil.Its should cover the DPM upturn to protect it. Great care
is needed when pouring the wet concrete not to damage the DPM or displace the sheets which
make it up. Any gaps in the DPM are almost impossible to repair later, and the floor will be
forever liable to damp penetration.
Slide 10
The top of the concrete will be quite rough. The traditional way of smoothing it is to lay a
further 50mm layer of fine concrete (cement and sand, but no coarse aggregate) which is
polished smooth like a plaster. This is known as a screed. The whole floating floor construction is
full of water, and can take months to dry out. This is one reason builders don’t like it. It slows
down the sale of the house.
Slide 11
The traditional layer cake floating floor, subsoil->hard-core fill->sand blinding->DPM->structural
slab
->finishing screed->final decorative floor finish (which must not be laid before the screed and
slab have dried out). But this provides very little insulation.
Slide 12
Insulation can replace the screed. If the concrete slab is finished smoothly, it can be topped by
dense closed cell expanded polystyrene (EPS). This must be flooring grade and fire resistant. It
must have a protective layer of boarding on top, usually chipboard. This gives a warm floor
which allows a room to heat up quickly, so is suited to buildings which are heated intermittently.
It is totally unsuitable if you are using under-floor heating, for obvious reasons.
Slide 13
Flooring grade EPS can be used very effectively under the concrete slab, and reduces the need
for sand blinding. The EPS protects the DPM from the hard-core below. Under-floor heating
pipes of wires would be laid in the slab, or the screed, and would be above the insulation, so
would be very effective. This layout provides very effective insulation, but a cold room will be
slow to heat, as the concrete slab will heat up first, before the heat meets the insulation. Very
suited to buildings which are heated continuously.
Slide 14-15
Suspended ground floors are built into the walls, have an airspace below them and do not
require significant fill or any DPM beneath them. They must be supported above the wall DPC to

3. keep them dry. The space beneath the floor should be ventilated with air bricks. The main
structures are reinforced, precast concrete inverted T beams, spanning from wall to wall. Infill
blocks are laid between these, resting on the flange of the inverted T. Blocks can be simple
concrete blocks with EPS insulation and chipboard laid on top, or they can be specially made EPS
flooring ifill blocks, which provide support and insulation, again with a chipboard finish. Such
floors are light, warm, and dry. Builders like them because they do not contain water and so
there is no extended drying out period.
Slides 16-23
Upper floors are always suspended. Wooden joists can be built into the walls, but more
commonly galvanised steel joist hangers are built in and the joists fitted later. The floor needs a
top deck of boarding and a ceiling underneath of plasterboard. Pipes and cables can be run
through the voids. Dense fibreglass can cut down on sound penetration.
Long joists will need to be braced to stop them twisting. Either solid infill blocks or open hering
bone struts, wghich allow pipes to be fitted more easily.
Openings formed as in a flat roof by doubling joists around and fitting a trimmer beam. A large
opening is always needed for the staircase.
Slide 24
Plasterboard is a cheap, easily fitted ceiling. It is skim coated with plaster to make it smooth. It is
extremely fire resistant. It is a cheap finish, but not a cheap and nasty one. It is a good material.