The NHBC Standards provide important technical requirements for new build homes in the UK. Chapter 6.4 specifically covers timber and concrete upper floors, establishing guidelines that builders must follow to ensure floors are properly constructed and safe. Understanding these standards can help you know what to expect in your new build home.

What Are Upper Floors?

When you walk upstairs in a new build home, you’re stepping on what construction professionals call an “upper floor” – any floor above ground level. These can be built using either timber (wooden joists and boards) or concrete systems, each carefully engineered to perform several vital functions.

Beyond simply providing a stable surface to walk on, upper floors must safely support the weight of furniture, people and fixtures while transferring these loads to the supporting walls. They need to prevent noise from travelling between floors, meet strict fire safety standards, and accommodate essential household services like water pipes and electrical wiring.

All these elements must work together seamlessly to create a safe, comfortable living space that meets building regulations. These floors separate different levels of your home and must be designed to:

• Support and transmit loads safely to the supporting structure
• Provide adequate sound insulation between floors
• Meet fire safety requirements
• Allow for proper installation of services like plumbing and electrical wiring

Upper floor design

Upper floors in new homes must be carefully designed to handle all the different loads and stresses they’ll face during everyday use. The design takes into account both permanent loads (like the weight of the floor itself, ceilings, and built-in fixtures such as boilers and water tanks) and temporary loads (like furniture and people). For a typical home, floors must be able to support a minimum load of 1.5kN/m² – roughly equivalent to 150kg per square metre.

Special attention is paid to areas that need extra support, such as where partition walls sit on the floor or where the floor connects to external walls. If your home has more demanding requirements, such as communal areas in apartment buildings, the floors will be designed to handle even heavier loads. These design considerations ensure your floors will remain stable and secure throughout the life of your home.

Fire Safety in Upper Floors

Fire safety is a crucial aspect of upper floor construction in new build homes. The floors between different levels of your home, particularly between separate homes in flats or apartments, must be built to contain fire and prevent it from spreading. This involves several important safety measures.

Your builder must ensure that any structural timber used in the floor construction is kept well away from heat sources like chimneys and fireplaces. The standards specify minimum distances – typically 40mm – between timber and these heat sources to prevent any risk of the timber becoming too hot.

Special attention is paid to any gaps where services like pipes, electrical cables, or ventilation ducts pass through the floor. These openings must be properly sealed with fire-stopping materials to maintain the floor’s fire resistance. This fire-stopping also helps prevent smoke from passing through these gaps, which is crucial for safety in the event of a fire.

Sound Insulation

Good sound insulation is essential for comfortable living, particularly in modern homes where we often have entertainment systems, appliances, and general family activity creating noise. The NHBC Standards require that timber upper floors comply with Building Regulations for sound insulation, ensuring that noise transmission between floors is kept to acceptable levels.

For homes with separate dwellings above one another, such as flats or apartments, the sound insulation requirements are particularly stringent. The floor construction must include appropriate sound-deadening materials and be properly installed to minimise both airborne sound (like voices or music) and impact sound (like footsteps or dropped items).

Concrete Upper Floors

When concrete is used for upper floors in your new home, it can be done in two ways: cast in-situ (poured on site) or using precast concrete components manufactured off-site. Both methods must meet strict standards to ensure quality and safety.

In-situ concrete floors must be properly reinforced and use the right concrete mix for their location and purpose. The finished floor should be level and smooth, particularly around doorways and where different materials meet. This is especially important as it affects how your floor coverings will look and perform once installed.

Precast concrete floors, which are made in factory conditions and assembled on site, must be installed exactly according to the manufacturer’s instructions. Any damaged components cannot be used, and proper support must be provided until the floor reaches its full strength. The joints between precast elements must be carefully grouted to ensure the floor acts as a single structural unit.

Timber Floor Construction

Timber floor joists – the beams that support your floor – come in several forms. Traditional solid timber joists, engineered I-joists (which look like a capital ‘I’ when viewed from the end), and metal web joists (which have a distinctive zigzag pattern between top and bottom) are all commonly used in new builds.

The NHBC Standards include detailed span tables that specify exactly how far these joists can safely stretch based on their size and the loads they need to carry. For a typical home with standard loads, these spans are carefully calculated to ensure your floor won’t bounce or sag over time.

Quality of Materials

All timber used in floor construction must meet specific quality standards. Each joist should be marked with its strength grade (typically C16 or C24 in the UK), and the timber should be properly dried to prevent future shrinkage. The standards specifically prohibit the use of timber that is excessively bowed, twisted, or contains large knots that might affect its strength.

Regular timber joists must be ‘regularised’ (planed to a consistent size) and graded either visually or by machine to ensure they meet structural requirements. They should be stored properly on site, kept off the ground, and protected from rain and sun to prevent warping or other damage before installation.

For engineered joists (I-joists and metal web joists), the standards require additional precautions. These components must never be exposed to external weather conditions and should be stored vertically to prevent damage. Any damaged engineered joists cannot be used, as their engineered nature means they can’t simply be cut around defects like traditional timber sometimes can.

These requirements might seem technical, but they all contribute to ensuring your new home’s floors will be stable, durable, and perform as intended for years to come.

Floor Construction and Support Methods

The way your new home’s upper floors are constructed and supported is critical to their long-term performance. The NHBC Standards specify detailed requirements for how floors should be built and connected to the rest of your home’s structure.

Basic Construction Requirements

When your floor is being built, the joists must be perfectly level to ensure your finished floor doesn’t slope or feel uneven. The spacing between joists is carefully controlled – typically no more than 600mm apart – and they must have proper clearance from walls to allow for services like pipes and cables. This precise spacing also ensures your floor decking (the boards you actually walk on) is adequately supported.

Support at Internal Walls

Where floor joists meet internal load-bearing walls, they need specific support arrangements. For traditional solid timber joists, they can overlap on top of the wall and should be nailed together. However, engineered joists (I-joists and metal web joists) require special blocking pieces or supports to ensure stability. The standards require a minimum bearing length (the amount of joist sitting on the wall) of 90mm in most cases.

Connection to Steel Beams

In modern homes, steel beams are often used to create open-plan spaces. Where floor joists connect to these beams, specific techniques must be used depending on the type of joist:

• Solid timber joists can be notched to sit on the steel beam
• I-joists and metal web joists need special support cleats or hangers
• All connections must allow for the different ways timber and steel behave over time

Joist Hangers

Joist hangers – metal brackets that support floor joists – must be carefully chosen and installed. They must be the right size and strength for your specific joists and properly fixed to both the joist and the supporting wall. The standards require particular attention to:

• The minimum bearing length on masonry walls (75mm)
• The strength of the blocks or bricks supporting the hanger
• The correct nailing pattern for secure fixing
• Special requirements for engineered joists

All these elements working together ensure your floor is stable, level, and properly supported. While you might never see these components once your home is finished, they’re essential for creating a solid, squeak-free floor that will serve you well for years to come.

The different requirements for various joist types might seem complex, but they reflect the specific ways each material behaves and needs to be supported. Your builder should understand and implement all these requirements to ensure your floor meets the NHBC Standards and performs as intended.

How these connections are made might not be visible in your finished home, but they’re crucial for preventing common issues like squeaky floors, springy boards, or uneven surfaces. If you’re having a new home built, you can take comfort in knowing these standards exist to ensure your floors are properly constructed.

Keeping Your Floors Stable

A key aspect of upper floor construction is ensuring the floors are properly tied into your home’s structure and remain stable. This involves several important elements that work together to create a solid floor system.

Wall Ties and Restraint

Your home’s upper floors don’t just provide a surface to walk on – they also help hold the building together. Galvanised steel straps (called restraint straps) connect the floor to the external walls, typically spaced every 2 metres. These straps play a crucial role in preventing walls from bowing or leaning over time. While you won’t see these straps once your home is finished, they’re essential for your home’s structural stability.

Floor Strutting

To prevent floor joists from twisting or moving sideways, builders must install strutting – additional supports that run between the joists. The amount of strutting required depends on how far your floor spans:

• Floors under 2.5m wide don’t typically need strutting
• Floors between 2.5m and 4.5m need one row of strutting
• Floors over 4.5m need two rows

This strutting helps reduce floor movement and vibration, making your floors feel more solid underfoot and preventing squeaks and creaks from developing.

Openings in Floors

Where openings are needed in upper floors (for example, for stairs or airing cupboards), the surrounding structure must be properly reinforced. This involves using special stronger joists called trimmers and trimming joists around the opening. The size and strength of these supporting joists is carefully calculated to ensure the opening doesn’t weaken the floor.

Multiple Joists

Sometimes, extra strength is needed in certain areas of your floor – perhaps under heavy partition walls or around floor openings. In these cases, two or more joists might be joined together to create a stronger support. The standards specify exactly how these joists should be fixed together, using specific patterns of bolts or special connectors to ensure they work together effectively.

All these elements are hidden within your floor structure, but they’re vital for creating a stable, long-lasting floor. They help prevent common issues like springy floors, excessive vibration when walking, or gaps developing between floors and walls. While you might never see these components, they’re working constantly to keep your home’s floors solid and secure.

The attention to detail required in these aspects of floor construction might seem excessive, but each requirement serves a specific purpose in ensuring your home’s floors perform well for decades to come. Proper installation of these elements helps prevent future problems and ensures your floors remain stable, secure, and comfortable to live with.

Accommodating Services

Modern homes need various pipes, cables, and ducts running through the floors, but these can’t be installed haphazardly. The NHBC Standards provide strict guidelines about where and how holes can be drilled or notches cut in floor joists. These rules ensure services can be installed without compromising the floor’s strength.

For traditional timber joists, holes can only be drilled through specific zones of the joist, and their size is limited to about a quarter of the joist’s depth. Engineered joists (I-joists and metal web joists) handle this differently:

• I-joists come with pre-formed holes that must be used
• Metal web joists have natural gaps between the metal webs for services to pass through
• Additional holes should never be cut without manufacturer approval

Floor Decking

The actual floor surface you walk on – called decking – must meet specific requirements depending on how far apart your floor joists are spaced. Common materials include:

• Moisture-resistant chipboard (minimum 18-22mm thick)
• Plywood (minimum 15-19mm thick)
• Oriented Strand Board (OSB) (minimum 15-19mm thick)
• Traditional floorboards (minimum 16-19mm thick)

The decking must be properly fixed to prevent squeaks and movement. This typically involves both nailing and gluing the boards, with specific fixing patterns and expansion gaps to allow for natural movement. The standards even specify the size and type of nails or screws to be used, ensuring the floor remains firmly fixed.

Floating Floors

In some situations, particularly between separate homes or where extra sound insulation is needed, a “floating floor” might be installed. This involves placing a layer of sound-insulating material between the structural floor and the final floor surface you walk on. The floor finish is literally “floating” on this resilient layer, helping to reduce impact sound transmission between homes.

These floating floors must be carefully installed to maintain their sound-insulating properties:

• The floating layer must be continuous and properly sealed
• The floor finish mustn’t touch any walls or pipes
• Special detailing is needed around doorways and stairs
• All joints in boards should be glued to prevent squeaks

All these requirements work together to create a floor that’s not just structurally sound, but also practical for modern living. The standards ensure your floors can accommodate necessary services while remaining strong, provide a stable surface for your chosen floor coverings, and meet sound insulation requirements where needed.

Remember that while many of these elements will be hidden once your home is complete, they’re essential for ensuring your floors perform well and remain problem-free throughout the life of your home. Proper installation according to these standards helps prevent common issues like squeaky floors, uneven surfaces, or poor sound insulation between homes.