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Posi Joist

Verified by manufacturer 26 days ago


MiTek Industries Ltd Variant:
Third party certifications:
  • EPD


    Certificate type

  • Warrington Fire

    Certificate type

Posi-Joist combines the lightness of timber with the strength of the Posi-Strut steel web, allowing you to span far greater distances than would be possible with alternative timber products.

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+44 (0)1384 451400 Website


Floor joists. Floor cassettes. Intermediate floors. Ground floors. Roof. Rafters. Stud Walls. Structural walls.

Suitable applications: residential, commercial, industrial, specialist, housing association, single family, multi family, healthcare, care homes



Are you a housebuilder or multifamily developer seeking 

a solution to reduce labour costs and overall time on site? 

Posi-Joist combines the lightness of timber with the strength of the Posi-Strut steel web, allowing you to span far greater distances than would be possible with alternative timber products.

This gives you unequalled design freedom across a wide range of applications for both floors and roofs in domestic, industrial and commercial applications. Posi-Joist allows a variety of internal room layouts within an external shell due to its clear spanning capabilities. 

Easy access for the installation and maintenance of the services in the floor zone is the clear advantage of the Posi-Joist system, and with the ever increasing need for MVHR (Mechanical Ventilation and Heat Recovery) systems, Posi-Joist provides a perfect and simple solution that just isn’t possible with alternative solid timber products.


Whilst an initial linear metre cost comparison with solid joist alternatives may suggest otherwise, Posi-Joist’s ability to span greater distances than its timber competitors, coupled with its open web design gives the contractor several important cost saving advantages. The installation of services and utilities is far simpler and quicker with Posi-Joists, reducing both labour costs and build-up time on site.Joists are manufactured in a controlled offsite environment ensuring a quality product, and are delivered ‘made to measure’ allowing for speedy erection. What’s more, Posi-Joists will often eliminate the need for load-bearing intermediate walls, dramatically cutting overall building costs.

To check a span and see a range of suitable Posi-Joist specifications visit www.mitekposi.co.uk to use our interactive span tables.


Exceptional floor performance from a wide fixing surface makes flooring easy, controls shrinkage and with precision engineering it all reduces those tiresome return visits and remedial work.

More benefits such as the unique open web design provide an area in which Plumbers, Electricians and Mechanical Ventilation and Heating Contractors will find it easy and convenient to work. The job’s done far more quickly and the contractor makes worthwhile savings.


With the largest network of licensed fabricators across the UK and Ireland, you are never too far from a Posi-Joist manufacturer. All manufacturers use the very latest BIM compliant MiTek 3D Design and Engineering software and are able to provide clear and detailed drawings. To find your nearest manufacturer visit: www.mitek.co.uk/manufacturers


Posi-Joist can adequately span for floors and for flat and pitched roofs, often allowing for increased joist centres when compared to alternative systems. It’s span capability and wide timber flanges make it the more desirable alternative to all steel systems.


Design flexibility is inherent in the concept of the Posi-Joist. The depth, length and width can be adjusted to produce an enormous number of different specifications, each with clearly defined performance criteria. In addition, end details of the Posi-Joist can be altered to give a variety of support conditions. You will never come up short with the Posi-Joist Trimmable End. Each end can incorporate a solid timber block which can be engineered with up to 130mm allowance for trimming on site. Its span capability and wide timber flanges make it the more desirable alternative to all steel systems.

No blocking or herring bone strutting is necessary with the Posi-Joist system. Instead a strongback installed near midspan provides a much more effective load transfer system between adjacent joists.


Tested by TRADA, included in ETA-20/1169 and accepted by NHBC, staggered Posi-Strut webbing reduces the material content of the joist providing economic and environmental savings. In low stress zones Posi-Joists can be designed to include single sided Posi-Strut webbing to provide considerable material savings.


Posi-Joist is a fully tested product with a European Technical Approval ETA-20/1169. Fire resistance tests for 30, 60 and 90 minutes have successfully been carried out.


Posi-Joists can be built into the inner leaf of an external cavity wall. This method of construction meets the thermal and air leakage requirements of Building Regulations provided that the perimeter of the Posi-Joist is sealed with silicone sealant as shown and the wall is insulated to the Building Designer’s specification. Alternative proprietary built-in constructions may be used, such as joist ‘end caps’, provided that they have been shown by third party tests to meet or exceed the air leakage performance of the construction. 

Posi-Joists can be supported in masonry hangers at an external masonry wall. This method of construction meets the thermal and air leakage requirements of Building Regulations.

For timber frame applications, Posi-Joist can be top hung, meeting the thermal and air leakage requirements of Building Regulations provided that the floor edge is insulated by a material with a minimum R-value of 0.75m² K/W and that a bead of sealant is placed 

between the skirting board and the floor deck and that an effective air barrier is maintained within the floor zone by means of solid noggins or header joists. The construction provides lateral restraint to the wall provided that the connection is designed and detailed by the Building Designer.


UK (excluding Scotland)

The requirement for sound resistance of floors in England, Wales and Northern Ireland is that they should achieve an airborne sound resistance of 40dB based on laboratory tests.


The requirement for sound resistance of floors in Scotland is that they should achieve an airborne sound resistance of 43dB based on laboratory tests.


There are no sound resistance requirements for intermediate floors.

MiTek has developed flooring systems to accommodate all UK regulations and details are available in our downloads section.


Floors which separate two dwellings need to meet enhanced requirements for fire resistance and sound resistance when compared to intermediate floors. Consequently the additional materials used to meet these requirements mean that the dead weight of a separating floor will be significantly greater than the dead weight of an intermediate or ground floor. The period of fire resistance required is at least 60 minutes and this is provided largely by the ceiling plasterboard. The responsibility for the plasterboard specification and fixing rests with the Building Designer. Fire resistance data is available in our downloads section.


With the exception of Scotland, separating floors in the UK need to achieve sound resistances of greater than 45dB for airborne sound and less than 62dB for impact sound and this should be Demonstrated by precompletion testing on site, or by adherence to Robust Details. Robust Details E-FT-3 & E-FT-6 are the tested, proven details for the use of Posi-Joists in separating floors in timber frame construction.


Separating floors need to achieve sound resistances of 56 dB for airborne sound and 56 dB for impact sound. These requirements should be demonstrated by pre-completion testing on site.


Separating floors need to achieve sound resistances of 53 dB for airborne sound and 58 dB for impact sound. These requirements should be demonstrated by pre-completion testing on site.


Posi-Strut webs are increasingly being incorporated into roof structures to take advantage of the many benefits on offer. Posi-Rafters are parallel chord trusses, plated together with Posi-Strut metal webs. As with Posi-Joist floor joists they are designed and manufactured offsite and tailored to the requirements of each individual project. They arrive made to measure and accompanied by full layout drawings for speed of erection. Posi-Rafters are suitable for both pitched roofs and flat roofs. They are stronger than solid timber rafters and so can span further and require less internal support.

A wide range of depths and end details provide great flexibility in their application, and the need for expensive hangers and metalwork can be eliminated through clever detailing and connections. The open web construction allows for services and utilities to be easily routed through the rafters with no need for cutting or drilling or battening out. Posi-Rafters can also offer greater thermal U values than solid timber rafters.


Posi-Attic trusses combine the solid feel of a Posi-Joist with the benefits of a conventional attic truss. The strength of the Posi-Joist floor provides greater room widths, for increased living space within the attic, delivering maximum value to the client. The Posi-Joist floor is ideal for the installation and maintenance of Heat Recovery Ventilation Systems, soil pipes and the increasingly diverse range of services installed in modern homes.


When a construction project requires an over-height wall panel, Posi-Studs have provided the ideal solution. The combination of the different available timber sections and the different Posi-Stud web sizes mean that a wide range of different wall widths can be achieved using this system. In this final section of the World of Posi Technology we provide you with indicative information regarding the thermal performance that Posi-Studs can achieve and indicative construction details for the use of Posi-Studs in wall construction.

General information



Guidance for specification option:

Natural timber colour or treated.



Guidance for specification option:

Fine sawn timber.












Warranty description

60 year


Pr_20_85_08_50 Metal web joistsPrimary
Pr_20_85_08_85 Structural wood-composite I-beams
Pr_20_85_08_86 Structural wood-composite I-joists


G20/17 Structural wood composite

G20/345 Proprietary structural wood composite

G20/341 Prefabricated structural wood composite

Specification data - Metal web joists

Factory finish

Natural (timber).


108 mm.

Manufacturer guidance

Clearance between flanges.


202 mm.

Sustainability data

Contains Red List materials


Country of material origin


Country of product manufacture

United Kingdom

Embodied carbon

A1-A3 (production stage) as defined in BS EN 15804

2.28 kg CO₂ eq/kg


In theory 100%


BIM objects


NBS BIM Object Standard

This BIM object has been authored to meet the requirements of the NBS BIM Object Standard.

Find out more about the NBS BIM Object Standard.

Platform Compatible Version




Third party certifications



MiTek Environmental Product Declaration (EPD)

Warrington Fire

Warrington Fire

Fire Resistance of Posi-Joist floors in line with EN Standards - UK & ROI

Case studies

Barratt Code Level 6 Homes Feature Posi-Joist

Barratt Code Level 6 Homes Feature Posi-Joist

Curved Trussed Rafter Roof Over Supermarket

Curved Trussed Rafter Roof Over Supermarket

Posi-Rafters - the ideal solution

Posi-Rafters - the ideal solution