Whilst not the most glamorous aspect of building design, choosing the right flooring specifications can be a minefield. This is often due to the large number of options available to create the perfect flooring build up.
From structural to overlay, here we’ve tried to outline some of the key options with the advantages and disadvantages of each option.
Going underground: from beam and block to timber joists, what floor structure is right for your project?
Structural flooring options in the market broadly fall into three categories; joists, concrete slabs or beam and block.
Beam & block
Many new build houses utilise a ventilated ’floating floor’ beam and block construction for the ground floor. Although the cost of materials can be expensive, preparation is minimal and a beam and block ’floating floor’ can be quick and easy to install, thus gaining costs back through savings in the manpower bill.
Standard concrete beams are usually between 6m and 8m in length, with custom options available. The beams are laid in a similar fashion to timber joists, then concrete blocks are inserted to complete the floor.
Solid concrete is often a popular choice (particularly with DIYers) for smaller projects such as home extensions, as the materials cost is relatively inexpensive. Labour is more involved with this method however.
It’s important with this method to prepare the ground and ensure a robust and high quality hardcore base, particularly as the foundations are often very shallow. There is a risk, if the quality of ground or hardcore is not adequate, that the slab can start to crack over time.
Solid concrete floors are built in several layers, which typically comprise of hardcore, a damp proof membrane, insulation boards, and ready mixed concrete (usually 100mm thick as a minimum) then covered with conventional floor screed or power floater.
More often used on first and second floors, timber joists are available in either softwood, timber I-joists or open metal web joists. The most popular choice is timber I-joists as these do not expand and contract like softwood, which eliminates squeaking under the floor itself.
I-joists can span 6m or more and are lightweight yet strong. They cost more than softwood joists but can be installed much more quickly.
Beam & block
-Good for larger new build schemes
-Quick to install
-Quick to install
-Ideal for upper stories
-Great for DIYers
as materials costs
When best avoided
-Expensive for smaller projects,
such as extensions
-Not recommended for
-Should only be used
where the ground is well
prepared and where seasonal
soil movement is minimal
Floor Overlay: From ground up
Once you’ve decided on your structural elements for your floor, this then begs the question of what floor overlays to use.
Key considerations now come into play, such as the floor coverings desired, ideal acoustic overlay, thermal conductivity where underfloor heating is concerned and, of course, speed and cost of installation.
If we look at the market, there are two main options available, a timber or concrete screeded floor.
Both methods go back thousands of years and have both advantages and disadvantages. Timber floating floors are quick to install, low cost, and lightweight. However they are not dimensionally stable, and performs poorly as an underfloor heating overlay and acoustic overlay.
Conversely floor screed can be used to level the floor and add mass, however it has the disadvantage of a long drying time.
There are ever increasing demands on modern floor to consider too, including legislative increases in performance needed (for example acoustic floor). Plus trends towards minimalism and concealment, for example the use of underfloor heating instead of radiators, and the ever increasing options available as a finished floors – from microScreed, large format tiles, to luxury vinyls and so on.
If we look at how traditional flooring systems cope with the demands of a modern floor, timber doesn't work well as an underfloor heating overlay, it’s an insulator that resists heat transmission. In relation to floor sound insulation, a traditionally constructed timber floor consisting of 18mm OSB, 235mm x 50 Timber Joists, 100mm Mineral wall (10-11kg) and 2 layers of gypsum plasterboard (overall mass 16-17kg) could fall short of code by up to 15 dB!
The expansion and contractor of timber floor also make it unsuitable to receive tile or MicroScreed directly.
Conversely, traditional sand and cement screed floor works well as an underfloor heating overlay, meets airborne requirements for the passage of sound but fails on impact sound. In addition to the issues around impact sound, the drying time makes the use of wet floor screed more challenging, particularly on tight build schedules. British standards recommends that a traditional wet screed should be left to dry 1 day per mm of thickness for the first 40mm and 2 days per mm thereafter.
So is there a better solution?
A popular floor choice in continental Europe is gypsum fibreboard flooring, an engineered dry screed overlay board that offers excellent floor sound insulation and performance as an underfloor heating overlay, and is quick to install.
Gypsum fibre overlay floors require no long term maintenance, and will perform satisfactorily for the life of the building.
Fermacell gypsum fibre works exceptionally well as an underfloor heating overlay, as it has a low thermal resistance. It offers an optimal floor sound insulation due to its density and wood fibre absorption layer. Luxury finishes can be added as it provides a flat, dimensionally stable surface.
Regardless of whether your base floor is made up of concrete slabs, block and beam or I-Joists, gypsum fibre can be used as a dry screed overlay.