Diy Conservatory Raised Floor

Conservatory suspended and raised floor

Conservatory suspended floor slabs
If you do have ground problems or if your floor level is just too high off the ground to permit a slab base or raft, you can adopt the same construction with a suspended conservatory concrete floor slab.

Here, the dwarf walls will be raised up to the floor level, allowing a reinforcing mesh or fibre-reinforced concrete to strengthen it. A truly suspended floor slab will bear on the walls and not the ground. Generally speaking, all suspended floor methods work up to a span of about 5.5 m. If your addition is any wider than this, it is likely that you will need to provide extra load-bearing walls internally to support the floor mid-span. Mesh reinforcing is used instead, as with rafts, but here it is laid near the bottom of the slab only. Fibre-reinforced concrete can be used as an alternative to steel reinforcing and should be considered if you’re looking for a polished finish to the base. Instead of steel fabric reinforcing mesh to strengthen the concrete, slender plastic or steel fibres are mixed in at the plant or on site to a given proportion, which strengthen it to a similar degree.

Conservatory Suspended timber floor
Not the best choice for a conservatory, given the high humidity and dramatic temperature changes, timber does, however, make a sound floor structure for a garden room or sun lounge where solid roofing offers a degree of shade and insulation against solar overheating. If you are using this method for your ground floor, some precautions are needed to avoid rot and decay. The ground beneath it should be covered by a blinding of concrete, around 75 mm thick cast on polythene, to prevent vegetation growth and damp. At least 125 mm of air space should exist beneath the floor joists and the ground and this void should have a good cross-flow from air bricks on both sides, one every 1.5 m of wall. Plastic periscopic air vents are best at achieving this. If you are supporting the joist ends on the inner leaf of the cavity wall, a DPC must be placed beneath them to keep them dry.

Noggins
Timber floor joists need cross-bracing if they aren’t to twist and you can to this either by using offcuts of the joists as solid noggin or herringbone strutting. The latter can be bought in steel strap form or cut on site as 50 x 50 mm softwood. It needs to be positioned in floor spans between 2.5 and 4.5 m in the centre, and for joist spans over 4.5 m as two rows of struts at one-third centres.

Webbed-joist floors
Wooden joists can creak excessively in the high temperature changes of a conservatory when the board fixings are loosened by the shrinkage of the timber. Webbed or truss joists don’t because they have a much smaller volume of wood, some with plywood or OSB webs, and others even less with steel braces. They are also lightweight, making them easier to install and the steel web type can have cable and pipe services running through it without any notching or drilling needed at all, making it perfect for extending services. These joints have the additional advantage of span, which is far greater than ordinary joists, but it is the noise reduction from the absence of a creaking floor that makes them worthwhile.

Insulating timber floors
Polyurethane insulation boards can be suspended between joists on battens attached to the sides. A thickness of 100 mm or more will be needed to attain a satisfactory standard, and any pipes or cables have to be run through the void above the insulation boards, so the boards themselves need to be dropped down sufficiently to allow for this. Fixing battens to the joist sides in the strategic position will support the insulation. You can use 200 mm-thick glass fibre to achieve the same result if you have the depth of joist, but this needs chicken wire fixed beneath the timbers to hold it in place – not always an easy job to do.

Beam and block suspended floors
Precast concrete “T” beams have the advantage of being able to span greater distances than in-situ reinforced slabs or timber joists, and they don’t suffer from shrinkage or fungal or insect attack. The infill between beams can be done cheaply with standard wall blocks laid flat and grouted over, or with expanded polystyrene insulation blocks specially made for the purpose. They may be the most expensive option, but you end up with a solid and robust floor you would be happy to lay stone slabs on. It has become standard practice to sit beams directly on the DPC, and to provide a second DPC on top before proceeding with the dwarf wall structure. This seems to have come about because the placing of the beams has occasionally displaced the first DPC, but if you’re careful this shouldn’t occur.