Introduction to Beam and Block Floors

What are Beam and Block Floors?

There are two types of concrete floor system commonly used in residential construction; ground bearing and suspended. In this article we will be focusing on the suspended concrete floor, particularly beam and block floors.

The suspended floor does not rely on support from the ground below but instead is supported by the external walls, and therefore the foundations below.

Scroll to the end to download this article as a handy PDF guide!

01 Ground bearing floor

Ground bearing floor

02 suspended floor

Suspended floor

Suspended concrete floors can be constructed using different methods. They can be cast in situ reinforced concrete slabs, precast concrete planks or slabs, or the focus of this article, beam and block floors.

Beam and block floors are a popular type of suspended flooring system commonly used in UK construction. The system comprises precast concrete beams spanning between supporting walls or structures, with precast concrete blocks placed between the beams to create a solid floor surface.

Main components of a beam and block floor

03 beam profiles
Beams

Precast concrete beams, typically in an inverted T-shape, provide the primary structural support for the floor. These beams are designed to carry the imposed loads and distribute them to the supporting walls or structures.

 

Blocks

Precast concrete blocks, often with hollow cores, are placed between the beams to fill the gaps and form the solid floor surface. These blocks are typically lightweight yet strong, offering durability and ease of installation.

 

Concrete Infill

Once the beams and blocks are in place, a concrete infill layer is poured over the top to provide additional strength and stability, creating a monolithic floor structure.

04 beam and block layout

Why Choose Beam and Block Floor Systems?

Beam and block floors have become popular in UK house construction. Their versatility allows for adaptation to different ground conditions, structural layouts and load requirements.

It is an economical option due to off site manufacture of the beams and blocks, fast assembly and little requirement for specialist labour or equipment. The installation of a beam and block floor is not usually weather dependent and therefore specifying this form of construction can reduce site delays that other methods might encounter. Beam and block flooring demonstrates good noise reduction and fire resisting properties, and is also suitable to host underfloor heating systems.

How Beam and Block Floors Work

Beam and block floors work on the principle of distributing loads from the floor surface to the supporting walls or structures below. The structural integrity of the system relies on the combined strength of the beams, blocks and concrete. 

The precast concrete inverted T-beams are supported by the perimeter walls and internal load bearing walls. The beams vary in depth, and can be 130mm to 250mm made up to lengths of around 6m, they are usually designed and manufactured to span specific distances. Beam depth and profiles are selected according to span and loading requirements, along with the type of block specified.

Infill blocks are then positioned between the T-beams, these blocks are usually lightweight concrete. A sand cement grout is often brushed over the surface, filling any gaps providing a good load distribution and avoiding movement in the blocks. The grout also keeps insects and vermin out and assists with air tightness.

Insulation is usually positioned on top of the beam and block floor, a concrete topping or screed is then laid onto the insulation. An upstand perimeter insulation is installed around the edge of the concrete topping or screed in order to prevent thermal bridging. Some insulation manufacturers recommend a separation/vapour control layer between the insulation board and the screed to prevent interstitial condensation and the seeping of screed into insulation board cracks. 

Timber deck finish can also be used – if this is specified a vapour control layer must be included in the design under the timber deck.

A void is left under the beam and block floor of at least 150mm between the soil and underside of the beam. If heavy clay soil is present it is good practice to increase the void depth to as much as 225mm or possibly more. All organic material must be removed from the soil and the surface should be treated with weedkiller. This void must be ventilated with air bricks or ventilation sleeves positioned in the external walls in order to avoid the potential build up of gas. If radon is present, extra care must be taken to correctly detail radon barriers to prevent ingress. Ground levels under floor should be relatively level, otherwise external walls become retaining walls and would need to be designed accordingly.

A DPM or concrete oversite is not usually required, unless needed for gas or vapour protection as per the Building Regulations. Some manufacturers do recommend a DPM over the beam and block floor before insulation – be sure to check manufacturers instructions.

Expanded polystyrene (EPS) blocks are also used as infill between the beams. Not only do these blocks provide excellent thermal performance, they increase construction times as they are lightweight and easy to work with. The blocks are either designed to lap under the concrete T-beam in order to prevent cold bridging, or an additional insulation layer is positioned over the EPS infill blocks. More manufacturers are developing EPS block systems which have varying profiles and methods of construction. They are fast, efficient and would be likely to over take the concrete blocks in popularity over the years due to their enhanced benefits.

05 Beam and Block Floor Build Up examples

Principles of Beam and Block Design & Detailing

Detailing plays a crucial role in the successful design and construction of beam and block floors. Proper detailing ensures structural integrity, durability, and performance while facilitating efficient installation and coordination with other building elements. 

 

Main factors to consider during the detailing process include:

Loadings, span and reinforcement – the required beam size and reinforcement based on the anticipated loads of the structure, floors, partitions and imposed loads. This will be discussed with the structural engineer. 

Connections – ensure robust detailing of the connections between beams and supporting elements, using appropriate fixings, anchors and transfer of loads. 

Radon protection – refer to specific guidance for correct detailing of radon protection membranes. We have a selection of examples later in this post showing radon membrane taping and lapping. 

Thermal continuity – ensure that the insulation is continuous, particularly at the edges of the floor where thermal bridging is more likely to occur. Refer to insulation manufacturers for vapour control, and membrane requirements.

Airtightness – ensure airtightness is maintained between the floor and wall junctions using appropriate airtightness materials and tapes. 

Buildability – consider ease of build when designing and detailing the floor system to ensure that the arrangement can safely be built on site. 

Ventilation – Suitable cross-ventilation must be provided to allow air circulation in the void under the beam and block floor.  

Damp proof course and membrane – Correct installation and positioning of the damp proof course and membranes is key to ensure long term durability and protection against damp-related issues and moisture penetration.

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Regulatory Considerations for Beam and Block Floors

Compliance with building regulations is a primary consideration in the design and construction of beam and block floors in the UK. Key regulatory considerations include:

Building Regulations

UK building regulations govern various aspects of foundation and floor design and construction, including structural stability, ground movement, waterproofing, and thermal insulation. Compliance with these regulations is mandatory to obtain building control approval and ensure the safety and integrity of the building.

Approved Document A – Structure 
This document provides guidance on structural design and stability, including requirements for floor loading, structural integrity, and resistance to disproportionate collapse.

Approved Document E – Resistance to Sound
This document sets out requirements for the acoustic performance of buildings, including airborne and impact sound insulation between floors. Proper design and construction of beam and block floors can help achieve compliance with sound insulation requirements.

Approved Document L – Conservation of Fuel and Power
This document focuses on energy efficiency and thermal performance. It includes requirements for the insulation of floors, walls, and roofs to reduce heat loss and improve energy efficiency.

Thermal and Sound Insulation

Compliance with building regulations often requires careful attention to thermal and sound insulation properties, particularly in floor constructions. Beam and block floors can contribute to achieving these requirements through various design and construction strategies:

Insulation Materials
Select insulation materials with appropriate thermal and acoustic properties to enhance the performance of the floor system. Common insulation materials include rigid foam boards, mineral wool, and recycled materials.

Thermal Bridging
Minimise thermal bridging by ensuring continuity of insulation around beam and block floor edges, penetrations, and junctions with walls and other structural elements. Thermal bridging can lead to heat loss and cold spots, reducing energy efficiency and comfort.

Acoustic Separation
Incorporate measures to enhance acoustic separation between floors, such as resilient layers or acoustic underlays between the concrete floor slab and finishes. These measures help reduce airborne and impact noise transmission, improving the acoustic comfort of the building.

Testing and Certification
Ensure that insulation materials and construction methods comply with relevant British and European standards for thermal and sound insulation. Testing and certification by accredited bodies provide assurance of performance and compliance with building regulations.

Planning Permission & Building Control

Obtaining planning permission for foundation works may be necessary, especially in sensitive or environmentally protected areas. Engaging with local planning authorities and stakeholders early in the design process can help navigate planning requirements and ensure compliance with local regulations.

Any structural works such as foundations will need a structural design, calculation and building control approval.

More Beam and Block Detail Examples

If you are looking for reference details to use as a starting point in your own projects, our partner website Detail Library has a huge database of details ready for you to download and use. 

Below we share a few beam and block detail examples from the Detail Library.

08 DL322A DL322 EWI trench foundation with beam and block floor 3d

Masonry external wall insulation with trench foundation and beam and block floor (DL322A)

Partial fill 150mm masonry cavity wall with trench foundation and beam and block floor (DL315B)

11 DL274B 150mm Cavity masonry wall trench fill foundation - gas membrane DPC level threshold B copy

150mm masonry cavity wall with trench foundation and beam and block floor (DL274B)

14 DL185 beam and block change of span detail 3d

Beam and block floor detail showing change of span direction (DL185)

Get the books!

Emma has written a number of books on construction detailing, ranging from residential construction, to Passivhaus to Loft Conversions. Check out the full range below.

15 5 book Package R1

If you are interested in joining our community, head over to the Detail Library to learn more about our platform and get yourself signed up.

The Detail Library provides hundreds of construction details for you to download and use adjust for your own projects. The details are available in 2D Revit, CAD dwg, and 3D SketchUp. You can start downloading straight away and build your own detail reference library. Not like other BIM libraries, the Detail Library contains fully resolved details rather than individual components.

Further Reading

 

British Standards (BS)

– BS 8110-1:1997 Structural Use of Concrete – Part 1: Code of Practice for Design and Construction
– BS EN 1992 Eurocode 2: Design of Concrete Structures
– BS EN 1993 Eurocode 3: Design of Steel Structures
– BS EN 1994 Eurocode 4: Design of Composite Steel and Concrete Structures
– BS 8204-1:2003+A1:2009 Screeds, Bases and In-situ Floorings – Part 1: Concrete Bases and Screeds to Receive Floorings – Code of Practice

Approved Documents
The approved documents provide guidance on ways to meet the building regulations.

 

Guidance Documents

Concrete Centre
Provides technical guidance, design tools, and case studies related to concrete construction, including beam and block floors.

The Building Research Establishment (BRE)
Offers publications, research reports, and training courses on various aspects of building design, construction, and sustainability.

NHBC Standards
NHBC provide technical performance requirements and standards for the design and construction of new homes. A really useful document.

 

Online Courses and Webinars

Institution of Structural Engineers (IStructE)
Offers online courses and webinars on various structural engineering topics, including concrete design and construction.

Author

Written by Emma Walshaw, Architectural Technologist and founder of First In Architecture and Detail Library. Emma has written a number of books about construction and architectural detailing.

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15 Comments

  1. Amazing book!!! I will be buying.
    I’m studying a MSc in Construction but I’m also a visual person, this book really helps.

    Reply
  2. Beams are not reinforced with “steel bars” as stated. Reinforcement is provided by high-tensile, pre-tensioned strands producing a prestressed concrete unit. The pre-tensioning exerts a contracting force in the bottom of the beam which in turn creates and upward curvature, or camber, in its length. This camber is typically 1/300th of the span.

    This is important as a rigid timber floating floor can be unsatisfactory as the finished surface will displat the camber whereas an insitu screed can be laid to a flat surface.

    Reply
    • Thank you John, appreciate your comments.

      Reply
  3. Is block and beam suitable for constructing a factory floor that must carry heavy machines and a forklift truck with a lifting capacity of 2 tonnes, therefore gross weight of 7 tonnes rolling across it.

    Reply
  4. If I want to span 4.8m by 3.6m, should my T beams be 4.8m length ways of 3.6m widthways, given a 5% slope lengthways.

    Whether I use 4.8 lenghthways of 3.6 widthways, how many of each beam would I need. For each options how many 440mm block would I need.

    am being a based of a Summer residentual Log Cabin on clay soil near trees on a slight slode. The log cabin foot print is 4m x 3m

    Reply
    • hi we have a floor 4.4x26meter

      Reply
  5. Do you have a specification you could provide me for my scope of works to give to the contractor.
    I’m after 1-2 paragraphs outlining sizes, types, and BS standards and codes.
    Many thanks

    Reply
  6. How can an access hatch be formed in beam and block floor construction?

    Reply
    • Hi Chris, drop me and email and I can help you with anything block and beam floor related!

      Reply
      • Hi Luke. Is it possible to pass 2 x 68mm pipes through an existing block and beam floor? I’m interested in connecting to the indoor unit of an Air Source Heat Pump.

        Reply
  7. I’ve seen the recommended minimum void for this type of beam and block floor, but what is the maximum void recommended? Francis

    Reply
  8. I have a block and beam floor with a two storey passage floor space void underneath. The blocks have cracked in two areas leading to concerns the could eventually fall. How is this best remedied.

    Reply
  9. Hello,

    I was wondering if we could start the top of the strip foundation at the bottom of the void?
    Do we need to have the block wall with soil both sides?

    Reply
  10. Hi

    Do you have standard level change detail without having to build a supporting wall and footing inbetween as the beams are parallel to the level change?

    Reply
    • Hi Abigail, I’m afraid we don’t have an example of that detail, sorry we can’t be of more assistance.
      Emma

      Reply

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