Conservatory Bases
Footings & slab in one pour.
Strip footings to 600mm, 100mm slab on top, all from a single ready-mix delivery. C28/35 for dwarf walls that'll never crack.
The Mix You Need
C28/35 Foundation Mix
- Mix grade
- C28/35
- Slump
- 75mm (workable)
- Aggregate
- 20mm
- Slab depth
- 100-150mm
- Dwarf wall footing
- 225 × 600mm (typical)
- Sub-base
- 150mm Type 1 MOT, compacted
Volume Guide
How much concrete for a conservatory?
Slab volumes shown separately. Add roughly 0.8-1.2 m³ for strip footings on a 4×4m base depending on ground conditions.
Small lean-to
3.0m × 3.0m
slab only, 100mm
Standard Victorian
3.5m × 3.5m
slab only, 100mm
Large P-shape
5.0m × 3.5m
slab only, 100mm
Edwardian + footings
4.0m × 4.0m
slab + footings combined
Why It Matters
Get this right and you won't redo it for 30 years
- Conservatories are governed by building regs if the base supports heavy glazing, a tiled roof, or a masonry dwarf wall, the base needs to match.
- Dwarf walls sit on 600mm-deep strip footings. Get the depth right or the wall will crack as the ground moves through winter/summer cycles.
- DPC and DPM must be continuous with the house, breaking that line is the #1 cause of damp showing up inside the finished conservatory.
- One ready-mix pour covers footings and slab in a single visit. Barrow mixers and bag mixes can't match the strength or consistency.
Step by Step
How to prepare & pour
Mark out & dig footings
Footings go 600mm below ground level (or below any made ground) and 225mm wide minimum. Excavate to solid, undisturbed subsoil, not topsoil.
Dig the slab area
Inside the footing line, dig 250mm deep for the slab (100mm slab + 150mm sub-base). Level the bottom and check for soft spots.
Compact sub-base
150mm of Type 1 MOT, whacker-plated in 50mm lifts. Run a straight-edge over the top, you're aiming for a uniform level to take the slab.
DPM & formwork
Lay 1200-gauge DPM over the sub-base and up the inside of the footings, tying into the house DPC at the wall. Set shuttering to finished slab level.
Reinforcement
A142 mesh in the slab on 50mm spacers. If your conservatory sits on reactive clay or near trees, talk to us about footing reinforcement too.
Pour footings & slab together
One ready-mix truck fills both footings and slab in one continuous pour. Tamp footings flush, screed the slab level, then float smooth. Cover with plastic for 24 hours.
FAQ
Common questions
Does a conservatory base need building regs approval?
Most conservatories are exempt if the base area is under 30m² and separated from the house by external-quality doors. But the base itself still needs to be structurally adequate. Check with your installer or local BCO.
How deep do the footings need to be?
600mm below ground level to undisturbed subsoil is the standard for a dwarf wall conservatory. On clay soil or near mature trees, the NHBC specifies deeper, sometimes 1.0-1.5m. Check your soil type first.
Can I pour footings and slab in one go?
Yes, and you should. Ordering one ready-mix truck for both saves money, gets a consistent mix throughout, and removes any cold joint between footings and slab. This is how most trade groundworkers do it.
What about the DPC connection to the house?
The conservatory DPC must tie into the house DPC with no break. The DPM under the slab wraps up behind the dwarf wall and connects to the DPC, this is critical for keeping damp out.
Do I need underfloor insulation in the base?
If the conservatory will be heated (extension-style use) you'll want 100mm PIR under the slab on the DPM, then a second DPM on top of the insulation. This is separate to the structural base pour.
How long before we can build the walls?
Wait 48 hours before you start setting blocks on the footings. The full slab will be walk-on at 24 hours, fully cured at 28 days. Most brickies start on day 3.
Ready to order?
Instant price in 60 seconds. Next-day delivery subject to availability. With volumetric, pay only for what's poured.