Drawings and design from live projects.

The garage forms the side structure to an existing single-storey property, and the client wished to convert it to habitable space. Three boreholes and trial pits were sunk to prove the ground and expose the neighbour's existing footings, finding coarse sands and gravels — likely river terrace deposits — over which traditional foundations could be safely formed.

Because new foundations sat directly against the boundary, a standard strip footing risked undermining the neighbouring wall. A stepped cantilever foundation was designed instead, using a deeper concrete section as a counterweight to keep the structure stable. The superstructure design covered the new flat roof, masonry leaf and a steel beam over the opening, all checked to Eurocode.

Trial pits revealed a blue-grey cohesive clay with peat inclusions and a perched groundwater table entering at around 1.5 m. The clay carries a medium volume-change potential, and the plot is ringed by willow, hawthorn and leylandii — all drivers of seasonal ground movement.

Founding depths were set using the NHBC tree-and-clay tables: up to 2.4 m where leylandii sit close to the works. The workshop was given pad foundations at depth with FND2 sulphate-resisting concrete, while the residential extensions were steered away from ground-bearing slabs toward suspended floors, to accommodate long-term heave as the ground recovers from removed trees.

Bi-fold doors are unforgiving of movement, so the supporting steel was sized for a deflection limit of under 1 mm rather than strength alone. A 178 UB with a welded bottom plate was detailed, with the connection arranged to bear cleanly onto the masonry and the secondary timber lantern trimmers framing in above.

The package included the timber trimmer design for the roof lantern and the bolt, plate and weld specification for the steel — every member checked to the relevant Eurocode and issued as buildable details.

Converting the loft meant opening up an existing trussed roof and carrying the new floor and dormer over the rooms below. A grid of 203×102 UB and 152×89 UB steels in grade S275 was arranged gable-to-gable and around the stairwell, with knife-plate and welded connections detailed bolt-by-bolt for the steel fabricator.

The existing trusses were supplemented with new C24 rafters at 300 mm centres to prevent long-term sag, and the dormer was framed in studwork tied back to the masonry. The package set out every member, fixing, weld and resin anchor — from the floor joists down to the spreader plates that stop the steel crushing the timber wall plates.

The existing garage was a single-skin brick structure on shallow strip footings, set with the head of concrete some 675 mm below ground. Trial pitting exposed those footings so new Gen 3 concrete foundations could be trench-filled down to the same depth and tied back to the existing masonry, giving the converted structure a sound base before the new floor was carried over.

Above, a grid of 203×102 UB, 152×89 UB and 152×152 UC steels in grade S275 was arranged to pick up a new suspended floor of 47×175 C24 joists at 400 mm centres, with the beams bearing 300 mm into masonry or onto welded UERSA bearers. Every connection was detailed bolt-by-bolt — 10 mm end and side plates, 4 No. M16 grade 8.8 bolts and 6 mm fillet welds — and a stud buttress partition off 7.3 Newton blockwork was strapped back to the side elevation to restrain the external wall.