As an M&E contractor you no doubt share the frustration around the lack of clarity on the cost of roof frames for either supporting or accessing air handling services. This undoubtedly leaves you wondering if there is an unbiased explanation around the cost of these supports.
In a recent conversation with a site manager, he certainly shared this frustration.
“What I find most frustrating when sourcing roof support or access frames for air handling services is firstly that, because they can be fabricated in a variety of ways with a variety of different materials this can create a variance in the cost of the supports.
Whilst the different options all present their own pros and cons, it would be very helpful if there was unbiased information available online that outlines the factors that impact the cost so I can make an informed decision on what would be the right option for me.
Despite multiple attempts, I have not yet found an objective explanation for this online, however, it would not only help when sourcing support frames but also enable me to be informed when bidding for projects.”
This article is our effort to provide an objective source of information about the cost of a rooftop support frame. The approach is simple. We list out the reasons that make the cost go up down for an AHU frame and an access walkway then back off so then you can make that decision.
Outlined below are the article's key sections (simply click on the section you require)
What factors drive the cost up and down of an AHU frame?
Why are some companies more expensive than others?
Take me to a cost breakdown of an AHU support frame.
As the M&E industry grows towards a more sustainable and compliant future there is a greater need to replace current HVAC systems to reduce the operational carbon of a building and help the sector achieve net zero carbon emissions by 2050. To effectively access and support HVAC services (AHUs, chillers) access platform and supporting frames are required.
The dimensions of an AHU/Chiller frame will greatly influence the cost of the frame. The continual rise in cost of steel will be reflected in the price, obviously the larger the frame the more steel is required. Secondly, the cost of highly skilled welders must be considered for large traditional fabricated steel frames. Finally, larger frames may pose logistical challenges, going to and from site and this will be reflected in the cost.
Heavier AHU’s will require different frames that will contribute to the cost through the manufacturing process. For instance, supporting lightweight services such as ductwork will likely cost less than an AHU frame because it requires greater amount of material, the greater the weight the more feet required. Furthermore, labour requirements to manufacture and weld frames will be reflected on site.
For the safe maintenance and access of an AHU you will also need to consider the cost of an access platform. The dimensions, weight, design time and material will influence the cost to the consumer. For example, how many steps do you need, how much handrail do you need to order, how are you fixing the access walkway back. These are all factors that will influence the final cost.
Costs for different types of AHU frames differ. Let’s take a traditional welded steel frame, lengths of steel will be ordered from the mill, delivered to the workshop, it would then be welded to a specified design. Finally, it would be sent to the galvanisers to be hot dip galvanised and then returned to the workshop to be delivered to the customer, all of which would incur costs.
For channel-based assembly and non-welded modular steelwork frames, the cost of labour is greatly reduced as it doesn’t require hot works to assemble the frame in the workshop.
Anchors/fixings fail due to two reasons: incorrect selection and installation errors. Regardless of the type of frame you select, when fixing into a concrete slab, BS 8539 states that if an ETA-approved anchor is available for that application then it must be specified. ETA anchors typically cost more than anchors without approval, and this will impact the overall cost of an AHU support frame.
When designing a support frame for a rooftop you should always consider wind load ratings. Many organisations do not have a structural engineer in-house so to provide wind loading calculations they must outsource and this will undoubtedly impact the cost. Moreover, design time will increase as they often need to be re-drawn to accommodate the wind load calculations impacting the cost.
The environmental impact on supporting frames can’t be underestimated. Whether you are specifying secondary modular steelwork, traditional welded box section, stainless steel, or channel assembly frames in almost every case will be outdoors and according to IS0 9223 this would call for a hot dip galvanised or HCP finish. In cases where the support frames are close to corrosive environments such as coast areas a more corrosion resistant material may be necessary such as stainless steel which is more costly than hot dip galvanised finish or HCP. Hot dip galvanised tends to be more costly than pre-galvanised, however, this is very rarely suitable for roof support environments. Costs escalate further when you consider the transport cost to and from the galvanizers.
Certain companies only specialise in particular material and fabrication types, for example, some will only specialise in traditional welded steel roof supports and depending on the dimensions and weight will likely cost less when compared with other types. On the other hand, companies that stock modular steelwork may cost more initially, however, savings will be recouped during on-site assembly and installation.
For instance, the use of hot works to cut and drill welded steel on-site will incur a cost, and sending welded steel to the fabricators to be hot dip galvanised will incur further cost through galvanizing and transport to and from.
Common market forces such as supply and demand and companies’ pricing strategies will no doubt impact the cost of one companies’ frame over another. The power of the brand in the customer’s mind will also be a part of the cost, certain brands that hold trust with their consumers will likely charge a little more as they know that the frames will still be sold because of the loyal brand following.
Some organisations will only supply the product and ensure the ongoing responsibility of the support frame and its load bearing capacity is entirely in the contractor’s hands. Whereas other organisations may focus on the structure and ensuring that it can take the service load, this obviously results in more labour (design time) being attributed to the overall cost of the frame.
Finally, some companies that offer modular non-welded steelwork frames do not require a structural engineer on-site as they have traceable, independent load rating data which is not often the case for traditional welded alternatives and this convenience will be reflected in the overall cost.
For a modular non-welded steel AHU frame measuring 2.12m by 4.57m, weighing 184Kg and supporting a 2.5 tonne AHU costs between £1950 – £2,350
A list of components can be found below alongside the design and fabrication time to assemble the AHU frame.
Components
18.9 meters of Framo 80 is required, costing in the range of £46.00 to £66.00 per meter, giving a total item cost in the range of £869.40 to £1,247.40
16 connecting fittings (STA-F-80) are required, costing in the range of £20.00 to £28.00 each, giving a total item cost in the range of £320.00 to £448.00
4 end caps (ADK-F-80) are required, costing in the range of £1.00 - £1.10 each, giving a total item cost in the range of £4.00 - £4.40.
128 FLS screws (FLS-F-80) for connecting the Framo together, these cost in the range of £0.48 to £0.63 each, giving a total item cost in the range of £61.44 to £80.64.
8 Qwik feet (QFS350F) heavy-duty rubber feet for spreading the load and maintaining the integrity of the roof membrane. These cost in the range of £28.00 to £43.00 each, giving a total item cost in the range of £224.00 to £344.00.
x1 hour of design time - this would cost in the range of £69.00 - £99.00.
x1 hour of fabrication time - this would cost in the range of £63.00 to £77.00.
Total Estimated Cost would be in the range of £1,610 - £2,300 (This excludes delivery to site, however, an example dedicated vehicle to deliver to a site in the North West would be in the range of £500.00 to £550.00
The total costs should be considered alongside the necessary lead times and project deadlines. The modular frame requires minimal tools to assemble (no hot works) and can be manourvered without machinery and easily altered thanks to its design.
To conclude the price of an AHU frame differs depending on several factors already mentioned in this article. It is not only the initial cost of the frame itself but also the resources required to assemble the frame that should be considered before any decision is made.