So, if SIPs were so good in 1970, why haven’t they become the byword for modern construction over the past 50 years? To understand this, we need to look at some of the less well-publicised downsides of modular construction when compared to traditional brick and block.
The first challenge arises because you’re not building from scratch on-site. So, rather than ordering lots of small parts and then gluing them together in situ, your gluing is being done at a factory and then shipped to your site in a partially built state. As a result, your transport costs will be higher because you’re shipping bigger items and, in some cases, partly constructed units that are effectively full of air and so carry significant volume. And when your large jigsaw puzzle pieces arrive on site, you’ll need to put them together. To do this, you’re going to need a crane. But unlike more traditional construction methods, your on-site cranage costs will be more expensive because the things being lifted are much heavier and bulkier, which incurs additional costs.
Another challenge concerns lead times. Your bespoke panels are being built at a factory, so the work must be scheduled. If the factory has long lead times, you could incur significant finance costs while you wait for your job to be completed. You may also have to pay the factory upfront, impacting your cashflow and overall costs. Any deferred build slots could also lead to you incurring time extension penalties with your contractor, which could negate much of the cost-benefit. Also, it’s worth noting that SIP manufacturers enjoy economies of scale when they supply multiple identical units. If you’re building a dozen similar properties, the factory will make a dozen of each panel. This gives them, and therefore you, economies of scale, making each unit cheaper to build. However, if you’re building just one property, you won’t get this benefit and will be effectively paying a premium.
Not everyone will work with modular construction, so your talent pool will also be smaller when it comes to recruiting a contractor. Coordination is then required between the groundworks team and the main structure contractors, who will typically be different businesses, unlike brick and block. You’ll also be required to sign off the final design much earlier than you would with a traditional build since a great deal will be set in stone at the factory. As a result, you’ll have less flexibility to change design elements down the line, should you want to (or need to).
So, while these modern construction methods can give you a quicker build time on site, the overall timescales may not be that different once you’ve factored in the longer lead times. One of the key reasons why I suspect they’ve not been fully embraced during the many decades they’ve been around is because the savings in cost and time simply don’t materialise. It’s still generally more cost-effective and easier to build using timber frame or brick and block, plus you have a lot more design flexibility and a bigger pool of contractors from which to choose.