Structural flooring options for a self-build home
Before you jump into picking out floor tiles or carpet colours, it’s important to know that self-build houses require structural flooring to provide essential stability, load-bearing capacity, and ultimately prevent issues like settling, sinking, and creaking.
These serve as solid, level, and safe platforms for construction. Helping with supporting walls and upper levels whilst resisting moisture, fire, and sound transfer. It’s basically what you can then put your pretty flooring options on top of. Three of the most common options for structural flooring include:
Suspended timber floor (Sawn Lumber or ‘I’ beam options)
Beam and block (concrete)
Solid concrete oversite floor
So let’s dive into these in more detail.
Suspended Timber Floor (Sawn Lumber)
A suspended timber floor is created by sawn timber joists spanning from wall to wall to support the floor decking or boarding. The joists are supported on the outside walls by means of metal joist hangers built into the brickwork. Sleeper walls of honeycomb blockwork provide interim support on the ground floor, built off foundations or in some cases a thickened oversite. This oversight is necessary in order to prevent vegetable growth and damp. Suspended timber ground floors must be ventilated by means of air bricks and cavity sleeves.
Timber first floors are supported on the outside walls by the same methods as for the ground floor, and they span to the internal load-bearing partitions. Where the unsupported span of the joists exceeds 2.5m, midspan strutting is required to prevent deflection. This can be achieved by means of traditional herringbone strutting in a diagonal cross from the top side of the joist to the bottom using 50mm x 50mm timber or proprietary galvanised steel bracing. Timber frame companies may supply flooring panels in lieu, which may use 'I' beams (see below) or sawn lumber with plywood sheathing on both sides.
Timber floors receive their decking at the same time as they are laid; therefore, any metal baffle or spreader plates required for underfloor central heating, together with the central heating pipework, will need to be laid prior to the decking being installed.
Suspended Timber Floor (‘I’ Beams)
Many houses now employ manufactured ‘I’ beams instead of timber joists. These provide greater strength and eliminate creaking. These ‘I’ beams are constructed by means of an oriented strand board upright or web fixed to top and bottom rails of glued laminated timber (known as glulam). The ‘I’ section and the lamination give greater strength.
They cannot be notched or drilled, and they therefore have knock-out sections within the web through which services can pass. ‘I’ Beams can span far greater distances than sawn lumber. Open web beams, where the OSB is replaced by steel bracing, are a good alternative when services and larger diameter pipes need to pass through.
Beam and Block
With a beam and block floor, inverted ‘T’ shaped concrete beams span from wall to wall. These walls must be founded. The beams are infilled with concrete blocks to provide a stable suspended floor, which can often support internal partition block walling.
Beam and block flooring is only applicable to masonry or ICF construction at intermediate floor levels because of the additional loads involved. A crane may be required on site in order to position the beams, especially those to upper floors. On the ground floor the void beneath the beams does not need a concrete oversite so long as the subsoil is at least 75mm from the bottom of the beam. Ventilation is required and this is provided by means of cranked ventilators that allow air to flow through and beneath the floor without letting in the light that would be necessary for growth.
A beam and block floor typically features rigid foam insulation laid on top, which is either screeded or has a floating floor as described above. If underfloor central heating is to be employed on a beam and block floor, the pipes are laid within the screed and/or the insulation at a later date.
Solid Concrete Oversite Floor
The subsoil within the building is levelled out, and each bay is filled with properly consolidated hardcore, which is then covered with a layer of soft sand. This prevents puncturing of the damp proof membrane, which is then laid under the concrete and dressed up to the DPC.
The concrete must be a minimum of 100mm thick, and it may require reinforcement mesh to be laid within it. Solid concrete oversites can be insulated with rigid foam-type insulation boarding laid below, above, or in a combination of both.
When laid below, an additional layer of damp-proof membrane is placed over the insulation before the concrete is poured. If it is exclusively below then vertical perimeter insulation is needed between the slab and the outside walling. If it is laid on top then it can support either tongue and groove flooring as a floating floor or a sand and cement screed laid on a damp proof membrane.
If underfloor central heating is to be employed on a solid concrete floor, the pipes are laid within the screed and/or the insulation later.
Still not sure on the right option for you? For a specialist build, it’s always best to speak to an expert, like us at Mayflower Mortgage. Book in for a FREE, no obligation call today, and we will be happy to chat through your plans and get you on the right path.
