Various issues must be taken into account when converting buildings – particularly concrete treatment regimes.
As the housing crisis continues, change of use is booming.
It makes absolute sense from both a sustainability and accessibility perspective to get the most out of existing assets, but change-of-use refurbishments are not without their challenges.
When you alter how a building is used, you also change the measures required to make that building safe: this includes passive fire protection.
The most common conversions – of former office blocks to either residential, hotels or student accommodation – all involve the need for increased periods of fire resistance.
A significant proportion of them were constructed in the 1960s and 1970s from reinforced concrete, so as contractors approach these projects it’s vital they understand concrete from a fire protection perspective.
There are solutions for most of the fire protection challenges contractors may encounter in change of use, but awareness of the issues and early engagement are crucial to preventing costly mistakes.
One of the most glaring challenges is that refurbishments come with pre-existing issues.
Dirt, damage and contamination, as well as the design of the existing structure, can all pose obstacles. Before any work begins, it’s important to establish the condition of the concrete and any existing fire protection affixed to it. Dangerous substances like asbestos also need to be identified and encapsulated or disposed of safely to protect both the operatives on site and future occupiers.
“If you’re unable to work out what you’re dealing with, a specialist primer will likely be your best option to seal in the material and create a neutral canvas for the fire protection”
Investing time at this stage may seem like common sense, but there are numerous cases where a lack of thorough investigation at the outset meant significant defects were discovered long after handover.
If a concrete slab has been painted, for example, you’ll need to establish exactly what the paint is before making any decisions, as it may be incompatible with any fire-resistant materials you apply on top.
If you’re unable to work out what you’re dealing with – and this may be tricky depending on the age of the building and the quality of records – a specialist primer will likely be your best option to seal in the material and create a neutral canvas for the fire protection.
The same applies with contamination. In a recent concrete upgrade, we were dealing with a room that had an old oil store above. For years oil had been dripping out of the tanks onto the concrete soffit; a specialist tanking system with proven compatibility with the specified fire protection system solved the issue, allowing the protection to be installed over the top.
Exceptions to the rule
Once the concrete has been prepared, there are various passive fire protection systems that can be used. The two main types are either board or spray products. Although sprays are most commonly used for larger areas, such as concrete slabs, and boards are mainly reserved for concrete columns, these are not hard and fast rules.
The most important thing when designing a passive fire protection system is to view the building holistically and think flexibly – often a combination of methods and materials works best.
It’s also worth bearing in mind early on that different areas require different periods of fire protection. In an apartment block, for example, the public areas that form the means of escape – the corridors and staircases between flats – need higher levels of fire protection than the flats themselves to allow people time to evacuate.
“The most important thing when designing a passive fire protection system is to view the building holistically and think flexibly”
An increase in loading or nearby major infrastructure also has an impact, and may require the incorporation of mesh reinforcement in sprayed fire protection systems to help overcome any negative effects caused by deflection of the concrete structure. If the problem is identified at the design stage then your installer can build the mesh reinforcement into the fire protection system from the outset.
Upgrading passive fire protection can also have an impact on the footprint of a building.
The fire resistance of a concrete column, for example, is the result of a number of factors: its size, the position of the reinforcement and the amount of concrete cover over the reinforcement. In a refurbishment, those factors are predetermined, so if you want to increase the period of fire resistance you’ll need to affix additional material to the outside of the column.
Depending on which type of solution you choose, this can have the unintended result of increasing the footprint of the column, which in turn reduces the lettable area of the flats or rooms in question – clearly a major consideration.
With space at a premium in these kinds of schemes, any underestimate of column width or intrusiveness can be extremely problematic from a commercial perspective – another compelling argument for taking fire protection into account during the design stage.
It’s also important to consider the quality of both your materials and installer. In recent years, there has been a move to drive quality standards across the built environment, boost supply chain transparency and ensure consistency through independent third-party accreditation.
“Any underestimate of column width or intrusiveness can be extremely problematic from a commercial perspective”
Cheaper, non-accredited alternatives are available, of course, but – as is usually the case – compromising on quality in the name of value-engineering is a false economy. You may also not get products that meet the requirements of the latest EN standards and structural Eurocodes.
Accreditation provides accountability long after handover is complete, giving the client or facilities management company all the information they need to manage the asset going forward.
Although upgrading passive fire protection in concrete structures presents particular challenges in change-of-use schemes, they are relatively straightforward to overcome if contractors are prepared to understand the issues and adjust their plans accordingly.
If these types of developments are to play a successful part in combating the housing crisis, it’s vital that mistakes are minimised and costly retrofits avoided.
Nigel Morrey is technical director at ETEX Building Performance UK, which includes passive fire protection specialist Promat