Concrete vs Timber Floors
There are 2 types of floor construction used in the building industry today; these can be classed as either Suspended or Solid. Solid floors are a lot more substantial and require the ground to be made up in layers of ground sub base, sand, compacted hard core, damp proof membrane, insulation and concrete. Suspended floors are normally made up of 2 materials, either timber joists or a concrete beam system.
There are quite a lot of variations on these types of floor, mainly depending on what use you intend for that floor area and the floor finish. In recent years the use of suspended concrete floors has become common place normally in the commercial sector, but to a lesser degree, even in upper floors of domestic dwellings. Here are some key factors to consider when choosing between a concrete or timber floor.
Suspended Timber Floors
Source: House Inspector
Suspended timber floors are normally made up of timber joists suspended from bearing walls, which are then covered with either floor boards or high quality sheets of tongue and groove. To a degree this type of floor can give more comfort when your intention is to carpet the floor and when the floor is well insulated this can create a degree of sound proofing when used in upper floors. Timber floors will deteriorate more readily and in time the boards often come a little loose and will start to get a few squeaks and creaks.
Another problem sometimes associated with this type of floor is drafts. A requirement of all suspended floors is that they have a constant flow of fresh air which is brought in by the placement of air bricks within the exterior wall. This is required to provide a good air flow under the floor. One way to avoid drafts is to install an Airtight Breather Membrane, which will allow the free flow of moisture to the ground, but will maintain an airtight seal, thus preventing drafts.
Modern centrally heated homes will cause the flooring to expand and contract and when used in conjunction with tongue and groove sheets of chip board, access to any pipes or cables will certainly create a little more work.
Suspended Concrete Floors
Suspended Concrete floors offer a lot more benefits and are normally made up of either concrete beams (more commonly known as Beam and Block) or concrete planks. Both of these systems require a lot of handling and experienced professionals when being fitted. Depending on ground conditions, these types of floors will require more support walls in your foundations and a closer eye on the details. Both of these flooring systems can be insulated and will offer greater sound proofing when installed correctly.
Suspended concrete floor systems are also suitable when your intention is to use a floor tile, as there is no movement and will therefore prevent any cracking. These types of floors are a lot more expensive, but the benefits for the future are greater as there will be little or no maintenance required. Another advantage of a suspended floor is that in some circumstances where your property is on a sloping site, using a solid floor can be very expensive as the walls to support the ground underneath would be very substantial and in turn, expensive.
Solid Concrete Floor
Solid concrete floors can have some benefits over a suspended floor because of low maintenance in the future and the fact that they are less prone to movement. They are normally made up of different layers of materials which include:
• Sub Base
• Compacted Hard-core
• Damp Proof Membrane
• Cement Based Floor Screed
There are some variances in the order depending on the ground conditions. All the layers must have great care taken to make sure they are installed correctly or, in the future you could find the floor will move or have damp issues.
This can be building rubble or other loose stone based material, make sure it is well compacted and that there are no voids.
This material should be purchased to make sure it contains the right amount of stone and sand, probably a norm would be 20mm to dust, this will help greatly when compacted and create a solid base for the above layers.
This layer should be very level and contain a moderately strong concrete mixture. At all times you should be checking the levels to make sure you allow enough height above for the next few layers. This can be achieved by marking it on the wall from an existing FFL (finished floor level). If you are going to put your DPM (damp proof membrane) on this layer then make sure the surface is smooth to avoid puncturing the membrane.
Damp Proof Membrane (DPM)
A high gauge of membrane, possibly 1000 or 1200 grade, should be used and be laid with great care. When installing the DPM on the hard core level, a 50mm layer of sand blinding should be laid to prevent the DPM getting punctured. The DPM is laid with enough lapping up the wall above FFL and all joints are overlapped and taped with a good quality waterproof tape.
This is very important in today's energy efficient society and comes in many different shapes and sizes giving different levels of insulation. At BTL we tend to use polyisocyanurate (PIR) rigid thermal insulation boards that are manufactured by companies like Celotex or Ecotherm. These rigid boards offer fantastic insulation properties and would normally be 100mm thick. Sometimes the insulation is positioned below the concrete slab but our preferred method is to fit these PIR boards over the slab as shown in the detail above.
There are many types of screed but at BTL we opt as standard for a Sand and Cement screed. This should not be laid too thin, being made up of 3 parts sand and 1 part Portland cement. Normally the introduction of a PVA bonding agent should be used if pouring a screed directly onto concrete. Underfloor heating pipes are also set into this layer of the floor and once the boiler is fired up- this makes the screed act as a large radiator. The insulation in the layer below reflects this heat back up to reduce heat loss down into the slab.
You should try to avoid walking on your screed floor for a few days or you will start to make the surface dusty. If you intend to put an impermeable floor covering on it, the floor should be given as long as possible to completely dry out before application. 28 days is normally long enough for a screed to dry out with good ventilation and ambient room temperature but when working with highly sensitive floor finishes you might need to allow 1 day per 1mm of screed which can mean 75 days before the floor is fitted!
We have talked about 3 flooring systems in this article and which you choose to go for will be dependent on many factors, including; cost, ground conditions and whether it will be going in an old or new dwelling. There are many variances to these types of floors and as always we can advise you on which system is best suited to your project.
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