In this article, we will look at 'how to' construct and insulate floating floors using best practice techniques.
What is a floating floor?
It is typically taken to mean a lightweight construction where chipboard, gypsum or cement fibre board floor panels are ‘floated’ across the top of the rigid insulation layer. Floating floors are used most often in domestic buildings especially when retrofitting or refurbishing an existing building. This is because they are quick, lightweight and easy to install, thinner than screed options, with no wet trades and no drying-out time. They also allow for fast heating response times.
Why use a floating floor?
Because the insulation is laid continuously across the floor there is no cold bridging through the battens, such as in timber floors. This means that a thinner layer of insulation can be used when compared to a floor constructed with timber battens, which will lead to a lower floor height when installed (which is useful if you need to match existing floors levels).
In a bathroom, you should ensure that a moisture resistant chipboard is used to construct the floating floor, and in all cases, softwood battens should be positioned at doorways and partitions.
How to insulate a floating floor?
An example of what layers you need in a floating floor can be seen below from top-down. The U-values that this will achieve are available on our online U-value calculator.
- Floor finish (eg. carpet/ laminate floor, timber boarding. As floating floors are by their nature flexible, care should be taken when specifying tile finishes that are more suited to less flexible substrates)
- Tongue and Groove flooring (typically 18 mm T&G chipboard or cement/gypsum fibre boards)
- Separation layer (500 gauge polythene)
- Insulation laid continuously (eg. Thermafloor TF70)
- Damp proof membrane if required
- Screed (if existing)
- Concrete slab
What about heavier items? For items such as bath footings or the base of toilets then a timber batten would be used. Similarly, where there are heavier point loadings such as indoor thresholds or at the bottom of stairs, then again you would use a timber batten.
How to install a floating floor?
The steps below cover how to install a floating floor. Full details of the procedure are available in the Thermafloor TF70 product literature and this should be consulted prior to starting any work.
- Concrete slabs should be allowed to dry out fully prior to the installation of Thermafloor TF70 (average 1 day per mm of slab thickness)
- The surface of the slab should be smooth, flat and free from projections. Beam and block floors should be level and grouted. In accordance with BRE Good Building Guide 28 Part 1 (Domestic floors: construction insulation and damp–proofing), irregularities should not exceed 5 mm when measured with a 3 metre straight edge
- A thin layer of cement/sand mortar, a levelling screed or a proprietary levelling compound can be used to achieve a level surface and prevent the boards of Thermafloor TF70 from slipping under the timber floorboards if required. This should be allowed to set, harden and dry (approximately 1 day per mm) before proceeding further
- If there is no damp proof membrane in the concrete floor, one (minimum 300 micron / 1200 gauge polythene) should be laid with joints well lapped and folded, to prevent the passage of groundwater, over the concrete floor slab, or beam and block floor, prior to installing the insulation boards
- The membrane should be brought up the surrounding foundation walls until it is sufficiently above the height of the wall DPC so that it will connect with or form the DPC
- To comply with NHBC recommendations, preservative-treated softwood timber battens should be positioned at doorways, access panels and support partitions. The size of the battens selected should ensure that, when installed, the top surface of the insulation boards is flush with the top of the battens.
- The insulation boards should always be loose–laid break–bonded, with joints lightly butted
- Insulation boards should be overlaid with a polythene sheet (not less than 250 micron / 1000 gauge), to act as a slip layer and a vapour control layer. Ensure the polythene sheet has 150 mm overlaps, taped at the joints, and is turned up 100 mm at the walls
- Timber floorboards e.g. tongue–and–groove 18 mm thick plywood, should then be laid over the insulation and battens with staggered cross–joints in accordance with DD ENV 12872: 2000
- An expansion gap of 2 mm per metre run of the floor, or a minimum of 10 mm overall, whichever is the greater, should be provided between the floorboards and the perimeter walls
- Where there are long (over 5 metres), uninterrupted lengths of timber floorboards, proprietary intermediate expansion joints should be installed on the basis of a 2 mm gap per metre run
- Before the timber floorboards are interlocked, apply a continuous bead of waterproof wood grade PVA adhesive to the top and bottom of the tongue and groove joints
- Once the timber floorboards have been laid, temporary wedges should be inserted between the walls and the floor, to maintain tight joints, until the adhesive has been set
- Once the wedges are removed, they are replaced with strips of cork or polyethylene foam to act as a compressible filler and to help prevent cold bridging. Skirtings may then be fixed
