The part of a conservatory nobody looks at is the part that decides whether it lasts. Below the frames sits a base: foundations, a damp proof course, a floor build up and usually a dwarf wall, and if any of that is wrong the glazing above it will never sit right. Cracked plaster, doors that stop closing and a floor that feels cold underfoot almost always trace back to base and floor decisions made before a single frame arrived.
Key takeaways
- A conservatory base is a structural element requiring proper foundations, not a slab poured on topsoil.
- The damp proof course must link correctly with the house DPC or you get damp at the junction.
- A dwarf wall gives you a solid lower section, more usable wall inside and a warmer floor perimeter.
- Floor insulation is the difference between a room you use all year and one that feels cold from October.
- Ground conditions, drains and levels drive base cost.
What is actually underneath a conservatory
Working from the bottom up: an excavation to suitable bearing ground, foundations sized for the loads and the soil, then a floor build up containing insulation, a damp proof membrane linked to the house DPC, and a screed. On top of the foundation the dwarf wall is built, with its own DPC, and the frames sit on that.
Every element is doing a specific job and the sequence matters. You cannot add floor insulation afterwards without lifting the floor, and you cannot correct a damp proof course that was never linked properly without opening up the junction. This part has to be right first time.
Our conservatories page covers the styles, and the comparison in our guide to orangeries against conservatories helps if you are still choosing.
Dwarf wall or full height glazing?
A dwarf wall is the low brick wall, typically around 600mm high, that the frames sit on. It is not purely aesthetic. It gives you wall for furniture, hides radiators and sockets, insulates the floor perimeter far better than glass, and ties the conservatory into the brickwork.
Full height glazing gives more light and a stronger connection to the garden, and suits a room where the view is the point. The trade off is comfort at floor level and the loss of usable wall. On most Wirral homes we fit dwarf walls, and where a homeowner wants full height we talk through how the room will be used in the cooler months.
| Option | What it gives you | Worth considering |
|---|---|---|
| Dwarf wall base | Warmer perimeter, usable wall, matches house brickwork | Reduces glazed area, so light comes from higher up |
| Full height glazing | Maximum light and garden view | Colder at floor level and no wall for furniture or radiators |
| Insulated solid floor | A floor that is comfortable underfoot all year | Must be designed in from the start, cannot be retrofitted easily |
Damp, levels and the junction with the house
The junction with the existing house is where problems concentrate, and two things have to be right. The new damp proof course must connect with the house damp proof course to give a continuous barrier, and the internal floor level must sit sensibly relative to both the house floor and the external ground.
Get the levels wrong and you either step down awkwardly, or the external ground sits too close to the damp proof course and bridges it. Drains and manholes must be dealt with rather than built over, and a drain run crossing the footprint may need diverting or bridging with a lintel. Guidance sits with LABC.
Do you need planning permission or building regulations approval?
Many conservatories fall within permitted development, subject to limits on size, height and position relative to boundaries, and are often exempt from Building Regulations where they meet specific conditions including separation from the house by external quality doors and independent heating controls. Those conditions are precise and easy to fall outside of, particularly if you remove the doors. Our article on planning permission for a conservatory or garden room goes into it, and the Planning Portal is the authoritative source.
How we handle the base on a conservatory build
What genuinely drives the cost of a conservatory base
Ground conditions dominate, and they are the one thing nobody can quote accurately from a photograph. Founding onto firm ground at shallow depth is a very different job to digging through made ground, or working near a mature tree where foundations must go deeper. After that: whether drains need diverting, how much spoil has to leave site to reach the required floor level, the height and finish of the dwarf wall, and access. A rear garden reached only through the house is slower to work in.
This is why we survey before quoting. It is also why an unusually low base price is worth questioning, because the corners that get cut are the ones you cannot see afterwards. If your existing conservatory has a sound base, replacing just the roof is often the better investment.
Questions to ask about the base before you commit
- What foundation depth and design are you allowing for, and how was that decided?
- Have trial holes been dug, or is the price based on an assumption?
- How will the new damp proof course connect to the house damp proof course?
- Is floor insulation included, and what floor build up is specified?
- Are there drains within the footprint, and what is the plan for them?
Frequently asked questions
Can a conservatory be built on an existing patio or slab?
Why does my conservatory floor feel cold?
What is the difference between a conservatory base and an extension foundation?
Can I put a solid roof on a conservatory with an old base?
How long does the base take to build?
Is a dwarf wall better than full height glass?
Getting the part you cannot see right
The base is the least visible and least discussed part of a conservatory, and it is the part that decides whether the structure still looks right in fifteen years. We dig trial holes, locate the drains, set the levels properly and build the base as a structural element rather than a slab. If you are considering an orangery instead, the same principles apply with a heavier structure above.