Joist Floors and Flooring in Conversions

Floor Joists and Flooring in Loft Conversions

Newly laid floor joists

Before floorboards and flooring is laid loft floor must be structurally sound.

The joists in place will be ceiling joists, designed only to support ceiling boards light and attic loads.

Typically ceiling joists consist of two, narrow, low grade timbers, bolted together above a supporting wall.

Ceiling joists haven't the integral strength to take the loads of a further storey, nor of everyday household loads, e.g. people, floors and furniture.

Fitting Floor Joists

What appears to be a simple joist reinforcement solution - called sistering of joists with timber or wooden prefabricated or laminated joists - is usually acceptable since it requires ceilings below to be re-pinned.

Where sistering is used the reinforcing joist, called a sister joist is bolted onto the existing trimming joists which run the length of the attic.

The new floor structure - trimmer frame and floor joists - is the load bearing loft floor.

Modern detached, houses with trussed rafter roofs tend to have shallower and lower roofs where the roof needs to be raised.

Some attic and loft conversions - particularly open plan loft designs - require reinforced steel joists (RSJs) to support the combined weight of a conversion lacking the structural strength of an entire supporting wall below.

How we Install a New Loft Floor

The new floor system is assembled by constructing a frame (trimmer joists) to support the floor joists that will span the width of the loft and fit within joist hangers.

A basic floor system is installed in about 10 stages from preparation to floor laying.

1. Clearing the loft area of all debris, insulation, struts and temporary boards
2. Electricians 'first fix' - check and test existing ring main test for sufficient electrical power from the fuse box/consumer unit. Laying of electric power and other cables in place from consumer unit up to the ceiling according to the building plans. Positioning cables for sockets, light fittings, control units, shower point, window controls, Internet, phone, TV cable or communications.
3. Plumbers 'first fix', if plumbing is required assess existing boiler and central heating system. Identify radiator positioning and existing flow pipes and position pipes through floor for radiator supply. Position and fit inflow and outflows e.g. for en suite shower; hot-tub/jacuzzi; sauna / steam room; or bathroom.
4. Taking the level (spirit level) off the highest point of the floor transferring and spotting above existing floor joists. Bolting trimmer joists (225mm x 75mm timber) to walls and fitting joist hangers. Any slight discrepancy is packed out using slate.
5. Floor joists are dropped between both trimmer joists in hangers to span the loft area. The first joist is fixed appropriate distance away from the wall edge then spacing timbers at 400mm centres.
6. Spacer noggins are installed to reduce joist deflection, vibration and to improve floor rigidity and performance. Our floors are guaranteed for 6 months not to deteriorate: squeak, bow or warp.
7. Under floor thermal and sound insulation for energy efficiency - 250mm glass fiber insulation with half hour fire resistance is laid between floor joists in a cradle of chicken wire. This provides support should the ceiling below collapse. (see video below)
8. Before the floor is sealed the floor joists needs to be passed by a Buildings Inspector. Building to regulation standards is optional but it gives peace-of-mind that your loft is structurally sound, building work is to a high quality and work is documented for property valuation purposes.
9. Floorboards laid using tongue and groove timber or base floor materials of your choosing, e.g. high-grade hardwoods such as: Afrormosia, Ash, Beech, Birch, Mahogany, Maple, Oak, Rosewood, Sycamore, Teak and Walnut.
10. Solid flooring is protected or carpets and laminates are laid once conversion is completed.

Flooring Materials

Your loft conversion or dormer extension design need not be restricted by conventional materials and regulations.

Modern materials allow us to develop large, open plan lofts. For example, by using prefabricated, extra long joists such as the SilentFloor® system we can span very wide buildings.

For luxury loft conversions, the simple elegance of a natural wooden floor is hard to beat, practical, beautiful and exceptionally long lasting.

Luxury hardwood floorboards for high quality wooden floors heated to feel warm using efficient, electric, underfloor radiant heating. Hardwoods have a rich natural colour, great resilience and durability and are no longer required to feel cool to the touch.

Picture by Velux

To ensure preservation of finish your choice of final floor covering - carpets, wooden flooring or laminates - is not applied until all construction work has been completed.

Floor Joist Systems

We install a number of proprietary floor systems, such as: TrusJoist™ SilentFloor® system:

• SilentFloor® system guarantee squeak free floors - no dips due to the unique joist design!
• Long prefab spans for wide floor areas and design freedom
• Lightweight and resource efficient and environmentally sound
• Resistant to effects of temperature and moisture
• Free of wood defects such as knots, shrinking, bowing, twisting and splitting
• High-tech proprietary web material and laminated veneer lumber
• Roof structure and framing solution
• Ideal for floor framing, floor joist replacement
• For replacing floor joists with wide spans that are rotten or squeaking.

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