Why Precast Gets Top Marks In Education | Modern Methods Of Offsite Construction

With strong government backing for offsite construction methods in the education sector, and numerous  operational efficiencies, precast is perfectly positioned to take advantage.

State support for offsite construction methods has never been stronger. Two years ago, the government announced a “presumption” in favour of using modern methods of construction (MMC). And in March, the Infrastructure & Project Authority’s MMC programme director Will Varah told Construction Manager magazine that the new government would continue with this policy.

Leading the way among public clients is education. The university sector is embracing MMC, for faculty buildings and student accommodation [see project case studies, pages 5-8], while the Department for Education (DfE) announced the winners of a £3bn offsite schools framework in January.

In the schools sector, precast undoubtedly scores highly when compared to other offsite construction methods in the market.  Robust, with strong acoustic and thermal insulation properties, and quickly assembled on site, it is little surprise that schools are  drawn to precast’s many advantages.

“The use of precast as a material for schools has been increasing over recent years, with the benefits realised by both the client and end-users alike,” says Richard Wilks, technical manager at Sterling Services.

Derek Russell, head of engineering at Techrete, notes that the nature  of schools lend themselves to high levels of repeatability – which suits precast.

“A significant advantage of precast concrete in education projects is the economy of design that can be achieved when the modular nature, in terms of classroom layouts, is considered,” he explains. “With sufficient lead in time to develop the functional and aesthetical requirements, a high degree of modularisation and offsite manufacturing can be applied to education projects.

“A primary consideration for Techrete is to work with the design team to achieve this modularisation and fully realise the benefits of offsite construction, while creating efficient environments for education.”
In the hustle and bustle of the school environment, exposed concrete offers a durable and hard-wearing surface. 

“This is a significant benefit in terms of both maintenance costs for internal surfaces and energy efficiency, especially when these are extrapolated over the working life of the structure,” says Russell.
Acoustic performance - vital in the noisy corridors and classrooms of a school building – also give precast an edge over other materials.

“Due to the durability and density of C40 grade concrete used in our façade panels, excellent noise reduction properties are achieved, important for buildings located near busy main roads with heavy traffic, with precast having the added benefit of impact resistance and resilience against potential vehicle impact damage directly against the façade,” says Wilks.

The UK’s first Passivhaus-rated school in Exeter was delivered with the help of precast units – supplied by Buchan, since acquired by FP McCann – demonstrating how the product can be used to achieve strong thermal performance with minimal air leakage.

“Precast cladding provides increased thermal mass, and improved  services efficiency with minimal cold bridging,” says Steve Morgan, technical manager at Thorp Precast. “It enhances both the structural and air borne acoustic performance of the external envelope.  

Precast cladding provides equalised air tightness levels of the  external envelope.”

Thermal performance can be enhanced by adding insulation to the panels, adds Wilks.

“A layer of insulation is fixed to the rear face of the panel during the install period, with the remaining insulation being inserted within the inner skin SFS/metal stud and board system,” he explains. “This means  U values of 0.15 W/m2degk or less are achievable. 

“Excellent air tightness is achieved and each panel and panel junction  is fitted with a double seal mastic joint once the panels have been lifted and installed on the façade.”

Fire safety, a major consideration for all clients since the Grenfell tragedy, is an area where precast outperforms all its rivals. 

“Materials used, and designs employed, address the requirements of Building Regulations, and leading insurance providers,” says Morgan.  

“All materials used are classified non-combustible, A1 fire rated.  Firestops, insulation and vapour control layers can be accessed  following panel installation.”

“The panels are sealed against the individual floor slab edges during installation using a continuous fire break detail, this form of construction being ideal for multi-storey construction,” adds Wilks.
A huge range of precast units, architectural and structural, are used in school schemes. Techrete says its most commonly used units are flat wall panels, vertical and horizontal spandrels, and mullions. It delivers façades either as single skin external panels or combined as sandwich panels to create both internal and external skins as a single panel. 

“These panels can be delivered to site and erected with windows, service voids and finishes applied,” adds Russell. “We are also noticing an increase in requests for window incorporated panels. These panels are pre-installed at our factory and serve to further reduce programme time, on-site labour and overall project cost.”

This also makes precast highly suitable for remote school projects, such as Techrete’s Wick High School project on the north coast of Scotland, where it installed 511 precast units totalling 3,420 sq m.

With windows, service channels and finishes invariably taken care of in the factory, site installation of precast panels has become increasingly efficient and quick, says Morgan.

“There are no external scaffolding requirements and no wet trades required on site,” he says. “Safety is increased through reduced numbers on site, with significantly less site traffic and supervision required.  Small teams of specialist erection gangs – typically four men and a crane operator – travel to site together. Crane time and number of positive lifts are optimised.

“No site storage is required. Panels are lifted from our specially adapted delivery vehicles directly onto the building. There are minimal noise levels – extremely important in sensitive neighbourhoods. Power tools are not required to install precast panels.”

It all helps to minimise disruption for schools during construction work. 

“For school projects, the fast erection times allow construction to take place during school holiday periods, with minimal waste, noise or dust,” says Wilks.