Amid the high-inflationary environment of the past two years, both design and commercial teams find themselves pondering a critical question: Will opting for support at every other level instead of at every floor offer a more economical solution? If so, what are the key factors I need to consider that could potentially escalate budget risks across the project?

Why masonry support is needed to start with?

Masonry support is required to introduce horizontal movement joints to prevent cracking in the façade due to several natural factors, such as heat and slab movement. The maximum gap between the vertical movement joints is 3 floors or 9m, whichever is less. In practice, this is not feasible because the weakest point in the system is the connection back to the main frame; typically into a concrete frame where the load cannot be transferred to the slab. Therefore, design teams are usually left with a decision between single storey support and double storey support.

Basic principles of support levels

Given that masonry support can typically be provided at a maximum of every two floors, there are two main options: supporting every floor or every other floor, as illustrated by the images below. We will explore the factors that govern these design choices and the variables that impact cost.

1. Channel size: Single-storey support typically utilises a 38/17 channel, offering a more economical option per meter of support. However, for two-storey support, an upgrade to a 49/30 channel is necessary, increasing costs by at least 30%. Opting for channels made from higher capacity steel, such as duplex, can mitigate this cost increase due to its 50% higher capacity compared to normal stainless steel.
2. Decrease in bracket centres: Transitioning from two-storey to single-storey support results in reduced bracket centres. Single-storey supports typically have centres between 450 to 500, whereas double-storey support can vary between 200 to 400, depending on loads. Utilising stronger channels can help increase centre spaces and reduce overall costs.
3. Increase in angle thickness: Single-storey supports usually employ a 5mm angle thickness. However, two-storey supports often require an increase to 8mm, resulting in a 30-40% rise in material costs.
4. Penetration with fire barrier: Two-storey support may offer fewer options for channel placement and bracket bearing on the slab, potentially leading to clashes with fire barriers. This limitation could lead to program delays and increased costs.
5. Corners: Two-storey support commonly encounters issues with corners due to the concentration of load in a small area and limited substrate for fixing. This may necessitate additional steelwork and pose unforeseen cost pressures.
6. Cavity size: Increasing cavity sizes, driven by enhanced thermal performance in buildings, present challenges in supporting masonry. With two-storey support, transferring loads becomes more challenging, potentially leading to increased costs.

These factors underscore the importance of carefully evaluating both single-storey and two-storey masonry support options to mitigate risks and ensure cost-effective solutions in construction projects.

Insights from a Previous Project

As demonstrated above, numerous factors can impact the design process. To illustrate this, we present data from a previous project that sheds light on the complexities involved. In a scheme examined last year, two distinct proposals were considered. The key takeaway is that reducing support does not always result in significant cost savings.

1. Initial design: Providing support for every floor, the initial design was quoted at £209K. This design featured bracket centers at 500mm and utilised a smaller profile of channel.
2. Alternative approach: An alternative approach, offering support for alternate floors where feasible, was priced at £206K. Although there was a significant reduction in meterage, the increase in angle thickness and channel size meant the price came within 1.5% of the initial design cost.

The most important consideration is to make sure you’re getting the best advice early on. By evaluating both options from an early stage you can make sure there are no hidden surprises when it comes to build which can introduce major construction risks in costs and programme certainty.

For further insights and assistance on design of masonry facades please drop me an email on henry@cfsfixings.com.