The ability of a building to resist the spread of fire can come down to the weakest link and relies on the integrity of the structure’s expansion joints and their sealing mechanisms, which must also allow and accommodate the building movement over the course of its life. Determining the type of joints required and the movement that may occur is an integral part of the design process, as is the selection and installation of joint sealing systems to strict protocols.

There are three types of joints involved in almost all buildings and civil engineering structures:

Construction joints – these are typically so- called “daywork joints” and do not usually need additional specific joint sealing and fire protection.

Connection joints, also known as isolation joints – often located at the interface between dissimilar materials or units such as gaps around door and window frames, which do require additional joint sealing and fire protection, using standard fire- stopping systems and flexible extruded sealants.

Movement joints, also known as expansion joints – typically such joints allow the building elements on either side to expand into the joint, expanding and contracting in a continuous cycle. The joint must be designed and dimensioned to accommodate movement of a defined nature and extent. Additional expansion joint treatment is always required to ensure watertightness and/or to provide fire protection, plus any other demands.

Movement joints, joint sealing and fire protection

The movement in building structures is created by several factors, principally the thermal movement effects from the external environment and weathering, along with the simultaneous exposure on the inside to the controlled interior environments. There are also many other causes of building movement, including static or dynamic loading, settlement and subsidence, wind uplift forces, hail, snow and even seismic events.

While thermal movement is predominantly in one direction or plane, there is also the potential for movement in more than one direction, such as torsional/rotary movement created by dynamic loading from elsewhere, for example from machinery or traffic loading.

The anticipated extent of all potential joint movement must be calculated, then considered together with any other specific joint function and exposure requirements. This is to ensure the joints can safely accommodate the anticipated movement, are durably sealed and watertight, have the necessary fire resistance, and can meet any other defined performance demands.

Smaller movement and expansion joints BS 6093:2006+A1:2013 covers smaller, lower movement joints, generally less than 30mm in width, with a joint movement capability of around 25% (meaning +/- 12.5% of the specified joint width). The joint sealing and fire-protection materials for these smaller expansion joints should be selected in accordance with BS EN ISO 11600. This defines construction sealants into 11 classes, with joint movement capabilities up to ~25%, which is considered the maximum for smaller joint design, without imposing impractical limitations on the site construction works.

These smaller movement joints (less than 30mm in width) are generally sealed using fire-retardant backing rods/profiles, sealed in situ with suitably selected extruded joint sealants, certified for the necessary limited movement capability and fire resistance.

Unfortunately, providing durable fire resistance becomes progressively more difficult with larger or wider expansion joints, and/or higher movement joints, such as with a joint movement capability higher than 30%. The selection and specification of adequate certified long-term fire resistance for these joints, while also accommodating the necessary joint movement capability, is made even more difficult when additional joint performance factors are taken into consideration. For example, providing thermal or sound insulation, or accommodating direct vehicular traffic across the joints, such as joints in car-parking decks above or below an occupied area.

Larger movement and expansion joints

Structural design principles are the same for larger structural movement joints, but there are no unified international standards with specific guidance for their design and fire-protection treatment.

The result is that apart from joints in a few types of structures with very specific function, size and performance – such as horizontal bridge deck joints – most wider movement joints (greater than 30mm), and those with higher movement capability (in excess of 25%) of all dimensions, are bespoke. The joint design process must also consider how they interact with the rest of the structure and building envelope, which requires the use of 3D design techniques, plus the joint sealing solutions must be clearly specified and not left to chance on site. It is also important to check that the joint systems can actually be produced, delivered and installed, especially in relation to any schedule critical paths.

Larger expansion joints create smaller, simpler units that can safely respond and accommodate movement in the joints without placing additional stress on the adjacent building elements. They must also provide a continuous barrier to the spread of smoke, fumes and flames throughout these movement cycles. The absence of standards for such joints means that close attention to detail is required during the selection, specification and installation of the joint sealing and fire-protection systems for wider joints and those with higher movement capabilities.

In recent years, there have been many instances where inadequately sealed joints have allowed water ingress, causing serious damage and deterioration to the extent of structural failure; there have also been joints with inadequate joint fire protection that has meant a failure to halt the spread of smoke, fumes and flames, resulting in damage and loss of life.

The reality is that these failures can easily be prevented, simply by using the right approach and making the correct selection, specification and installation of the joint sealing and fire-protection systems on all new-build, retrofit and refurbishment building projects in the UK.

Fire protection and fire resistance of movement joints

All major building developments are to some extent sectional or compartmentalised, featuring floor and wall sections produced and assembled offsite or on site to provide functional and containment areas. These help to control the defined interior environment, maintain thermal conditions, suppress the transmission of sound, and keep the weather out, as well as to contain the spread of fire and smoke or fumes.

The fire performance of any structure is only as good as its weakest link, and historically the expansion joints have represented one of the weakest links in floors and walls. This is because while they are designed to allow the anticipated movement, expansion joints are still essentially a gap in and through the floors and walls. The wrong type of joint or joint sealant, through poor design, specification or installation, can allow smoke, fumes and flames to pass through the joint.

Fire-rated solutions for larger movement joints

Larger expansion joint sealing systems are primarily pre-formed and then assembled and installed on site. These include:

Widely used for fire stopping, particularly in long linear installations for both horizontal and vertical applications in connection joints, these work well and are tested for up to two-hour fire resistance to EN 1366-4 and BS 476, but with no significant joint movement. As the name suggests, these products are fire-stopping joint fillers, but when used in expansion joints there is a potential issue over their lack of elastic recovery and the material’s compression from cyclic joint movement. For example, in a 150mm-wide joint, even at a standard 25% joint movement capability, this would equate to a joint width movement capability of 37.5mm (+/- 18.75mm), which would soon cause failure. At any higher levels of movement, premature failure is inevitable and it will not provide an adequate barrier to smoke, fumes and flames in the event of a fire.

These are traditional glass-fibre insulation systems supplied with an integral expansion joint cap, or installed with a separate flexible expansion joint capping or cover. They are in widespread use around the UK to fill and provide fire protection in the expansion joints of many buildings, including joints in and between floor and wall assemblies. Unfortunately, any tested joint movement capability and fire resistance will reduce over time. This is because the movement cycles at the joint cause the structure of the insulation material, which has little or no elastic memory, to be progressively compressed and crushed, and so it deteriorates. Eventually it will no longer perform adequately as thermal insulation, as a watertight seal, or as a barrier to smoke, fumes and flames.

Once the most widely used expansion joint sealing systems for any wider and higher movement joints, these are increasingly being replaced. The key issues are that, firstly, they are too rigid to satisfactorily accommodate and seal substrate irregularities from installation on day one, and, secondly, that with frequent and significant movement, they tend to fail, due to compression of the material in service. This means that compression joint seals cannot be regarded as permanently watertight or as an adequate long-term barrier to smoke, fumes and flames.

This is old and outdated technology. Generally, neoprene rubber profiles are not suitable as fire-protection seals, but they are still found during some refurbishment work programmes and will need to be replaced.

Many internal wall and some floor expansion joints were traditionally sealed using so-called “strip and seal” systems (metal-track-and-rubber-gland systems), which are relatively low in cost and can adjust to cover and hide, if not fill, the joint gap. However, creating voids in the joints behind a surface sealing profile reduces fire resistance and thermal insulation (R-value) properties. Strip seals do not provide an effective long-term barrier to water, smoke, chemical vapour (gas) and flames, so are of little use for joint sealing and fire protections.

Closed-cell foams used in joint sealing and fire-stopping systems are primarily based on ethylene vinyl acetate. Closed-cell polyurethane (PU) foam systems are more commonly used for joint fillers or backing rods under elastic waterproofing and/ or fire-stopping sealants, as well as in smaller movement joints of less than 30mm wide. However, closed-cell foam systems are not ideal for use in expansion joints where elastic recovery is a key function, because when the foam is stressed by joint movement, the cells get squeezed and fracture, allowing the CO2 which initially accommodates movement to escape from inside them. The foam is squashed and permanently shrunken, which soon reduces joint movement capability. Depending on the movement and rate of cycling, elastic recovery is progressively lessened, leading to failure in tension. For the same reason, closed-cell foam profile products cannot be supplied to site pre-compressed to assist installation into the joints. They must be installed by being compressed on site so that they can be inserted into the joint, which in effect means that cell-fracturing starts right from the date of installation. This quickly reaches the point where watertightness and an effective barrier to smoke, fumes and flames is no longer assured. It is important to note that once installed in the joints, the laboratory test data on closed-cell product data sheets no longer apply.

Open-celled foam systems impregnated with wax or bitumen

These were developed to modify and overcome issues with closed-cell materials, by using an impregnation process. Originally the impregnations were mostly wax- or bitumen- based, which led to issues at higher temperatures with melting and staining adjacent surfaces, while at lower temperatures they became rigid. Limited elastic recovery also limits the ability to absorb movement, so they are not now deemed suitable for watertight and fire-resistant expansion joint systems.

Open-celled foam systems – acrylic impregnated

Fire-retardant acrylic impregnations are more expensive but strongly hydrophobic and water- repellent, plus they are stable at higher and lower temperatures. This open-celled technology was found to be ideal for use in wider and higher movement capability expansion joints, with excellent watertight sealing and fire-protection performance. As the cells are open, no cells are fractured, and this material can be factory pre-compressed and delivered to site ready to simply unwrap and install in the joints. It can be tailored to accommodate site tolerances, the installation environment, and the joint movement cycle. Another important advantage is that these systems can be bonded into position with structural epoxy, thereby eliminating the need for any potentially damaging drilling, and there is no subsequent stress imposed by tightening mechanical fixings. Open-celled foam systems have high R-values for insulation and a high sound transmission coefficient for noise reduction, so they can provide excellent thermal and acoustic insulation. Perhaps the biggest advantage of open-celled foam systems in this context is their outstanding performance in fire situations. North American fire testing in accordance with UL- and ULC-2079 achieved the maximum test classifications of three hours. In Europe they also received the maximum test certification of up to four hours’ fire rating in accordance with EN 1366-4 (which is very similar test to the former British Standard BS 476).

Fire protection, fire ratings and fire safety considerations

Without adequate fire protection, fire can spread inside a building through adjacent rooms and compartments, across floors and through doors and other openings, as well as through cavities, service ducts and pipe entries, including through and along any inadequately protected expansion joints in the floor and walls.

Fire can also spread through any voids in the structure and the building envelope, such as behind and between joint cover plates, facade cladding and glazing units, including up and along the outside of the building, where it can leapfrog back into the building on the floors above. The expansion joint gaps, especially for larger and wider joints, are like an open door, offering a direct route for smoke, fumes and flames.

All products considered for specification to provide fire protection in expansion joints should be tested and certified with the fire resistance required (normally from two to four hours) according to the joint function and location and in accordance with BS EN 1366-4 Fire resistance tests for service installations, part 4: linear joint seals.

Fire-resistant, wide and high movement expansion joint solutions

For many years in the UK – and across the rest of the world too – it has been common practice in the construction industry to specify and install several different products and materials in combined bespoke joint sealing and fire-protection systems. This was to accommodate the anticipated structural movement, to maintain a watertight seal, and to provide the necessary levels of fire protection, as well as any other project-specific performance criteria, such as weathering resistance (if externally exposed), thermal and sound insulation or direct traffic.

However, this mixed approach is not always consistent, can be confusing, and may even be impossible to install on certain sites. Certainly, this as frequently been seen as less than ideal and has caused issues on many projects. It is now possible to design, specify and install proven, certified fire-rated expansion joint sealing systems for wider joints, which accommodate higher joint movement, while also ensuring they are sealed and watertight, as well as providing high levels of thermal and sound insulation.

These systems use open-celled foam technology which is bonded into the joints with structural epoxy adhesive; no mechanical fixings are required and so there is no drilling into otherwise sound concrete. Different products are available in standard and bespoke sizes, produced and supplied to site in sections, together with factory prefabricated details, and all pre-compressed for ease of site installation.