Concrete lintels, stair flights, floor planks and structural elements can either be cast in position on site or manufactured off site and delivered ready to install. The right choice depends heavily on access, programme and how much you need the design to flex once work starts.
This decision usually gets made early, at design stage, because it affects how the whole sequence of the build is planned.
Quality and curing conditions
Precast elements are cast in a factory under controlled temperature and humidity, which gives more consistent strength development and a cleaner finish than concrete poured on a cold, wet site in winter.
In-situ concrete is entirely dependent on site conditions during the pour and cure — it can still be done well year-round, but it takes more careful protection and curing management in poor weather.
Access and lifting
Precast elements need a clear route and a crane or suitable lifting plant to get them into position, which is straightforward on an open plot but can be a genuine obstacle on a tight urban site with no crane access.
In-situ casting only needs materials to be brought to site in workable form — wet concrete, formwork panels, reinforcement bar — which suits confined sites where nothing large can be craned in.
Programme and flexibility
Precast elements are manufactured to an exact specification ahead of time, so any late design change means a delay while a new element is made, whereas in-situ work can be adjusted on site right up until the pour.
Once on site, though, precast installs fast — often in a single day for an element that would take a formwork crew a week or more to build, pour and strike in situ.
Tolerance and fit on site
Precast elements are manufactured to fixed dimensions, so the opening or bearing they land into on site needs to be built accurately to match — any error in the surrounding structure becomes a problem for the installation team to solve on the day.
In-situ concrete is cast directly against the existing structure, so it naturally takes up small irregularities in the surrounding brickwork or blockwork as it's poured, which is one reason it remains popular on older or less regular buildings.
Structural design input needed
Both routes need an engineer's design, but precast elements typically come with manufacturer's technical data and load tables that speed up the specification process once the right product is chosen.
In-situ work needs a bespoke reinforcement design and formwork drawing for each pour, since nothing is standardised — more design time up front, but total flexibility over the final shape and dimensions.
Common questions
Is precast concrete always stronger than in-situ?+
Not automatically — both can be designed to the same structural performance, but precast's factory curing conditions tend to give more consistent, predictable results batch to batch.
Can the two be mixed on the same project?+
Yes, this is common — precast lintels or stair flights alongside in-situ foundations and slabs, chosen element by element according to which route suits each part of the build.
Does precast cost more once transport is included?+
It depends on quantity and site access — a small one-off element often costs more precast due to setup charges, while larger runs of identical elements can be cheaper precast because the labour cost of formwork on site is avoided.
Get advice on your concrete build-up
We'll assess your site access and programme before recommending in-situ or precast — free site visit, written itemised quote.