Yes, a conservatory does need foundations. Foundations are essential for transmitting the building’s weight safely to the ground and ensuring the structural integrity of the conservatory. Without adequate foundations, a conservatory can sink and shift, leading to severe problems such as water leaks, structural instability, and cracked walls or floors.
While it is technically possible to build a conservatory without foundations, it is not generally recommended. Building a conservatory without foundations might seem like a tempting way to save money, but it can cause a lifetime of problems from subsidence, damp, and uneven floors.
Check With Your Local Authority
Before starting work on a conservatory, it is advisable to speak to your local authority about building regulations or use a registered installer that will do this on your behalf. Many conservatories are now built with open access to the house or with integrated heating systems, which means they fall under the same bracket as an extension for permitted development rights and building regulations.
You always check with your builder too, most good builders will advise you without necessarily carrying out the work. Pure Conservatories in Liverpool are highly recommended as a go to choice of conservatory builder with the downside is that they generally only work throughout the local area.
Concrete Foundations
Traditionally, conservatories required concrete foundations around the perimeter to provide a solid, stable base. However, foundation technology and conservatory construction has advanced. Today, there are three main foundation options to consider:
- Full Foundations
- Floating Slab
- Base Frame
Installing foundations increases initial outlay but provides a robust, long-lasting base for the conservatory. Skip foundations and you’ll reduce costs and disruption from excavation work. But the structure may be more vulnerable and less stable.
Other factors impact your choice, including:
- Type of Conservatory
- Ground Conditions
- Existing Foundations
- Building Regulations
Foundation Depth
The depth of the foundations for a conservatory can vary based on several factors, including the size of the conservatory, the type of soil, and local conditions.
Generally, conservatory footings should be at least a metre (1000mm) deep, or 1500mm for more challenging conditions such as the proximity of trees, rivers, and train lines. However, there is no legally defined minimum depth for conservatory foundations.
Below we look in detail at the pros, cons and scenarios suiting each foundation type.
Full Foundations for Conservatories
Full foundations involve digging concrete trenches around the perimeter of the planned conservatory. The trenches are filled with concrete to create a solid base. Dwarf walls are then built on top using bricks or blocks.
Constructing full foundations is the traditional method:
Pros of Full Foundations:
- Provides very strong, secure base
- Won’t subside or shift over time
- Allows for larger span conservatories
- Can support solid or glazed roofs
- Guaranteed stability for upper floors
- Often required by building regulations
- Adds value to your home
Cons of Full Foundations:
- More expensive (labour & materials)
- Increased construction time
- Significant groundwork and digging
- Disruption to gardens and patios
Laying full foundations is advisable for:
- Large conservatories (over 25-30m2)
- Conservatories with upper floors
- Areas of poor drainage
- Unstable, sandy soil
- Exposed, windy locations
- Solid tiled roofs (greater weight)
- Significant height above ground level
- Replacing old conservatory foundations
Generally, laying new foundations provides the strongest base. It may add 20-30% to the build cost but gives long-term peace of mind. If you ever extend the house above the conservatory, full foundations become essential too.
Floating Concrete Slab Foundation
A floating slab gives an alternative to full foundations. It comprises a concrete raft slab laid over the ground, edged with insulating foam to prevent frost damage.
Pros of a Floating Slab:
- Quicker, cheaper and less messy than full foundations
- Avoids excavation work
- Minimal ground disruption
- Can be laid over existing patios or slabs
- Offers good stability and support
Cons of a Floating Slab:
- Less robust than full foundations
- Potential for sinking or cracking over time
- Not suitable for larger spans or heavy roofs
- Provides minimal insulation benefits
Factors making a floating slab suitable:
- Small to medium conservatories (under 25m2)
- Lightweight polycarbonate or glass roofs
- Solid, well-draining ground conditions
- Areas with no existing foundations
- Budget build
- Quick, low-disruption project
A floating slab gives a middle ground between foundations and frame. It spreads structural loads better than a base frame alone. However, it lacks the strength and longevity of full foundations. Check guarantees carefully as many won’t permit a floating slab.
Base Frame Foundation
A base frame comprises a simple wooden frame sat on the existing ground under the conservatory:
Pros of a Base Frame:
- Lowest cost option
- Rapid construction time
- Zero groundwork or excavation
- Minimal garden disruption
- Can be directly laid on patios or existing slabs
- Easy to install and remove
Cons of a Base Frame:
- Higher risk of subsidence and cracking
- Not as stable or durable as solid foundations
- Only suitable for small, lightweight builds
- Requires precise, packed ground level
- Usually needs supporting piers
- Most guarantee warranties invalid
Base frames suit:
- Small, lean-to conservatories under 20m2
- Conservatories against house walls
- Polycarbonate roofs or glazing bars under Q6
- Firm, level garden soil
- Temporary budget builds
- Quick projects without consents
For small, basic conservatories, a base frame keeps costs low. But longevity and stability are compromised. Check guarantees carefully as few companies will warranty a frame-only build. bear in mind frames can’t easily be upgraded if you later want solid foundations.
Do You Need Foundations for a Lean-To Conservatory?
Lean-to conservatories are built against the house, often overhanging the damp proof course (DPC). Their single-pitch roof slopes downwards away from the wall.
You can install a lean-to conservatory without foundations by fixing to the house wall. The existing wall foundations provide structural support, so extra concrete footings may not be needed.
For larger lean-tos or those separate from the house, partial perimeter foundations are recommended. Digging small trenches just under the uPVC frame gives stability without the cost of full footings.
If you use an existing wall, check it can take the load, and that the height suits building regulations. Lean-tos also sometimes require planning permission if extending beyond the original house.
Do You Need Planning Permission for Conservatory Foundations?
Laying foundations normally doesn’t require planning permission. Digging work is usually classified as permitted development, exempting consent. But regulations vary across the UK. Key factors determining if you need permission include:
Location
- Conservation areas often require planning approval for foundations.
- Digging near trees subject to protection orders also needs council approval first.
Depth and Position
- Foundations under 200mm depth in your garden don’t usually need consent. Deeper trenches may require permission.
- Building foundations over or close to public drains or sewers normally needs approval to avoid damage.
- Foundations outside your property boundary require permission, eg. encroaching on a neighbour’s land.
Existing Foundations
- If the property already has foundations in place, you typically won’t need permission to renovate or rebuild on top of these.
- But if the existing foundations didn’t have approval, extending them still requires consent.
Other Factors
- Unusual soil conditions like clay may demand deeper foundations, requiring permission.
- Foundations supporting raised floors or platforms above 300mm height often require approval.
- Likewise for foundations close to trees or wildlife habitats.
When in Doubt, Check First
Due to the variables, it’s advisable to confirm with your local authority whether planning permission is necessary. Unapproved foundations potentially risk enforcement action requiring modification or removal if built illegally.
Does a Conservatory Need Foundations by Building Regulations?
UK Building Regulations aim to ensure conservatory structures are safe, stable and suitable for habitation. Whether foundations are mandated depends on the conservatory design.
Key factors determining if foundations are required under building regulations:
Height
Conservatories over 300mm above ground level normally need foundations to provide stability. The higher above ground, the greater need for footings.
Floor Area
Larger conservatories have heavier weight and spans placing more stress on foundations. Those over 30m2 typically need proper footings.
Roof
Solid roofs require stronger foundations than glazed or polycarbonate panels which are lighter.
Location
Exposed sites subject to high winds require secure footings to resist wind uplift forces.
Soil
Poor ground conditions like sandy or unstable soil demand proper foundations to prevent subsidence.
Structure
Independent conservatory buildings not attached to existing walls require full footings.
Usage
Using a conservatory as living space with heating and lighting adds loading, necessitating foundations.
Walls
conservatories with dwarf walls above 600mm high require reinforced foundations able to take the loads.
Meeting building regulations gives reassurance your conservatory is structurally sound. While technically you can install without footings, skimping on foundations risks problems further down the line.
Can I Add a Conservatory Without Foundations?
It’s technically possible to install a conservatory without foundations or with minimal groundwork. But there are drawbacks:
No Guarantees
Most quality suppliers won’t offer product guarantees on conservatories without proper foundations.
Structural Issues
Lack of footings increases risk of subsidence, cracking and collapse over time as the ground naturally settles.
Regulation Problems
Conservatories without foundations may fail building regulations, leaving you liable to enforcement action.
Insurance Issues
Insurers often insist on correct foundations to provide cover. Non-compliant builds may invalidate cover.
Resale Problems
Conservatories lacking evidence of proper foundations can put off potential buyers and down-evaluate your home.
While skipping foundations seems tempting to reduce hassle and costs, the long-term compromises often outweigh short-term savings.
Can You Add Foundations to Existing Conservatory?
If your conservatory was built without suitable foundations, it is possible to retrofit them. Typical ways to add foundations to an existing build include:
Underpinning
Digging beneath the current base and concreting new foundation trenches. The conservatory gets jacked up temporarily while work progresses.
Raft Foundations
Laying a concrete slab beneath the floor after removing floorboards and the existing base.
Peripheral Foundations
Excavating small trenches around the perimeter and filling with concrete to stabilise the edges.
Bolt Down Frame
Fixing a wooden frame to the existing base then concreting and bolting into the ground.
The most suitable technique depends on the current design. Underpinning gives full foundations but is the most disruptive. Peripheral footings offer a minimally invasive option.
Adding foundations later is worthwhile if your conservatory shows signs of subsidence or needs structural strengthening. Doing so can also validate guarantees, make extensions above easier, and boost resale value.
Design Factors Impacting Foundation Choice
Certain conservatory design factors impact whether you need foundations, and if so, what type. Key considerations include:
Size
Larger conservatories have heavier structural loads, demanding robust foundations able to resist soil movement and pressures.
Height
The taller a conservatory, the greater wind forces it faces. Elevated designs benefit from secure foundations preventing uplift.
Roof Type
Glazed polycarbonate or glass roofs have lighter weight than traditional solid tiles and slates, relaxing foundation requirements.
Frame Type
Modern uPVC and aluminium frames offer greater strength and rigidity than older timber frames, reducing foundation loads.
Wall Build
Brick or block dwarf walls require reinforced foundations. Low-level glazing or panel walls need less substantial footings.
Orientation
South-facing conservatories get greater solar gain, expansion and movement, warranting robust foundations.
The combination of factors is also key, eg. large, heavy solid roofs require more foundation support compared to a compact glazed roof.
Laying Conservatory Foundations Step-By-Step
Laying foundations for a new conservatory requires careful planning and execution. Follow these steps to ensure a solid, perfectly level base:
1. Mark Out
Mark the footprint using peg posts and string lines. Check right angles for squareness. Include room for dwarf walls.
2. Excavate
Dig trenches minimum 450mm wide and deep following the marked layout. conserve topsoil.
3. Add Sand Blinding
Cover the base of the trench with 50mm sand blinding or similar for a smooth finish.
4. Insert Damp Proof Membrane
Line the perimeter with 1000 gauge DPM, overlapping joints 100mm. Fold up trench sides.
5. Add Insulation
Optional XPS rigid foam insulation provides thermal separation.
6. Add Reinforcement
Insert looped steel rebar or mesh reinforcing and check levels.
7. Pour Concrete
Fill the trench with 200mm C20 concrete, levelling and smoothing the top.
8. Allow to Cure
Leave concrete foundations to fully set and harden for at least 7 days before building.
Correctly laying foundations ensures your dream conservatory gets off to the strongest start and will last for decades to come. Don’t compromise on the base structure.
Alternative Foundation Materials
Concrete is the typical choice for conservatory foundations but alternatives include:
Brick
Using engineering bricks rather than blocks for dwarf walls spreads foundation loads well. They can also match existing house walls.
Steel
Box section galvanised steel can replace concrete but requires more precise installation. Avoid in coastal corrosion zones.
Timber
Tanalised treated wood can be used but has shorter lifespan than concrete options when in ground contact.
Screw Piles
Steel screw piles screwed into ground offer minimal dig options in unstable soils but can be costly.
Concrete generally provides the most versatile and cost effective modern foundation solution for conservatories. Always use decent strength C20 concrete or stronger.
How Much do Conservatory Foundations Cost?
You can expect to pay in the region of £1500 – £2500 for a typical conservatory with full poured concrete foundations, including materials, labour and plant hire. Key factors impacting the cost include:
- Conservatory size – foundations for larger spans costs more
- Foundation depth and trench dimensions – deeper is more expensive
- Soil type – heavy clay or rocky soil adds to excavation costs
- Access issues – restricted sites drive plant hire rates up
- Reinforcing spec – more steel mesh or rebar costs extra
- Underground obstructions – navigating drains or cables adds hassle
- Disposal fees – removing waste soil/rubble can be pricey
Get quotes from several builders to compare foundation prices for your conservatory plan and ground conditions. Consider long-term benefits as well as upfront costs.
Do Conservatories Add Value?
Adding a conservatory can enhance enjoyment of your home and provide useful extra space. In terms of resale value, conservatories offer mixed benefits:
Pros
- Added floor area increases house size, valued by buyers
- Multi-functional room adds utility and relaxation space
- Glazed design brings coveted light and views of garden
- Modern double-glazed builds enhance thermal comfort
Cons
- Dated styles in need of refurbishment can deter buyers
- Poor quality builds with signs of structural issues or damage raise concerns
- Conservatories may not suit tastes of all potential purchasers
- Heavily glazed rooms can be hard to heat efficiently
Maximising Value
Opting for timeless rather than trendy styles that will date offers long-lasting appeal. Investing in quality materials like aluminium frames, double glazing and proper foundations provides evidence of robust construction.
Assuming it’s well-built, incorporating power and heating extends usability. Overall, a conservatory adds more value than cost to most properties.
Finding Conservatory Builders
Choosing an experienced conservatory installer is key to achieving a quality build. Look for:
- Strong portfolio of past conservatory projects
- Extensive knowledge of regulations and structural requirements
- Advice on the most suitable foundations and designs
- Offering a full service – design, planning, foundations, construction
- Option of bespoke conservatories tailored to your needs
- Supply of quality, branded construction materials and glazing
- Provision of guarantees and insurance backed warranties
- Long Standing reputation and recommendations
- Clear itemised quotes showing all costs
- Membership of professional trade associations
- Great customer service throughout the project
Take time to research and get recommendations before selecting your conservatory installation company. Upfront due diligence pays dividends in the long run.
Conclusion
Traditionally, full perimeter foundations were required for any solid conservatory build. But with better framing technology and smaller designs, today’s conservatories can sometimes forego foundations.
Yet compromising on the foundations remains a false economy. Opting for no or minimal footings may save on your initial outlay but puts long-term structural integrity at risk. Having to retrofit proper foundations later proves ultimately more disruptive and expensive.
In most cases, the wise option is still to install appropriate concrete foundations calculated to suit your conservatory’s size, height, roof type and soil conditions. This provides greatest resilience and stability, validating your guarantee.