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Planning a garden decking project starts with more than choosing the boards. The position, ground conditions, supporting frame, drainage and access all affect the materials required and how the finished deck performs.
This guide covers the main considerations when planning timber decking, estimating materials and preparing for installation, whether you are building a simple ground-level deck or a raised outdoor platform.
1. Plan the Position and Size of Your Decking
Start by deciding how the decking will be used. A dining area, seating space or access route may need a different layout and amount of usable space. Consider sunlight, shade, access from the house and how the new deck will fit with existing paths, planting and garden boundaries.
Measure the available area and sketch the proposed layout. Rectangular designs are generally easier to measure and build than layouts with multiple angles, steps or changes in level.
Before digging or installing supports, check for underground services, drainage routes and inspection covers. Avoid building over manholes or drains that may need future access.
- Measure the proposed decking area and finished height.
- Allow room for steps, access and any required handrails.
- Check drainage, ventilation and ground conditions.
- Locate underground pipes and cables before excavation.
- Check whether planning permission or other approvals may apply.
2. Check Planning Permission and Building Regulations
Some domestic decking projects can be carried out under permitted development rights, but this depends on the design, property and location. Do not assume that all decking is exempt from planning permission.
Check the current rules before work begins, particularly if the decking is raised, close to a boundary, attached to a building, or proposed at a property with specific planning restrictions.
Restrictions may apply to listed buildings, designated areas and properties where permitted development rights have been removed. The position and height of the platform can also affect the requirements.
Use the official Planning Portal for general guidance and contact your local planning authority if you are unsure about a particular project.
Planning permission and building regulations are different matters. Depending on the design and circumstances, building regulations or other safety requirements may also need to be considered. Confirm the requirements for your project before construction.
3. How to Calculate the Decking Materials Required
Once the layout is settled, calculate the area in square metres. For a rectangular deck, multiply the length by the width.
Example: Decking area
Length: 4 metres
Width: 3 metres
4 × 3 = 12m²
Allow for waste
Order additional material for cuts, trimming and the layout. The allowance depends on board lengths, the deck shape and the installation method.
For an irregular layout, split the area into manageable rectangles, calculate each section and add the results together. Measure the decking boards and check their effective coverage, accounting for the specified installation gap.
Do not calculate the boards in isolation. The supporting joists, perimeter framing, fixings and any steps or edging also need to be included in the materials list.
4. Choose Suitable Decking Boards and Timber
Choose boards that are suitable for external use and follow the manufacturer's installation instructions. Consider the required appearance, board profile, dimensions and maintenance needs.
The timber used for the supporting frame is just as important as the visible decking. Select suitable structural timber for the intended exposure and loading, and make sure the design provides adequate support across the full deck.
Decking boards
These form the walking surface. Plan board direction, joints, spacing and the position of cut ends before installation.
Subframe timber
Joists and supporting members carry the decking boards. Their size, spacing and support points should suit the span and expected loads.
Fixings
Use exterior-suitable screws or other specified fixings compatible with the timber and any treatment. Follow the board manufacturer's recommendations.
Supports and foundations
Choose a suitable support arrangement for the ground conditions, deck height and design. Raised decks may require a more substantial foundation and bracing system.
Explore Wade's landscaping range for relevant outdoor project materials. Check individual product specifications before ordering to ensure they suit your intended application.
5. Prepare the Ground and Build the Subframe
A stable, well-drained base helps support the decking and reduces problems caused by standing water or movement. The preparation required will depend on whether the deck is at ground level or raised.
Ground-level decking
Remove unsuitable vegetation and prepare the ground so water can drain away. A suitable permeable weed-control membrane may help limit weed growth beneath the deck, but it does not replace proper ground preparation or drainage.
Where appropriate for the site and design, concrete paving slabs or other suitable supports can provide bearing points for the subframe. Ensure the supports are stable, level and positioned to suit the frame layout.
Raised decking
Raised decks need a support structure designed for the height, spans and anticipated loads. Posts, foundations, bracing, connections and any stairs or handrails must be suitable for the design and ground conditions.
Do not rely on simply placing timber posts into the ground without checking that the foundation and connection details are appropriate for the project.
6. Decking Next to a House Wall
Decking installed beside a house needs particular attention to moisture management. The finished deck must not bridge the damp-proof course or obstruct existing drainage and ventilation provisions.
Check the required clearance below the damp-proof course and ensure water cannot collect against the building. The correct level and detailing depend on the property and construction, so seek suitable advice if the existing levels or damp-proof course are unclear.
Where a ledger or other structural connection to the building is proposed, use an appropriate design and fixing method. Do not assume that the wall construction is suitable for supporting the deck without checking first.
7. Decking Installation Tips
Before fixing the boards, check that the subframe is square, level where required, adequately supported and arranged to provide the specified board spans.
- Board joints: Position board ends over suitable joist support and follow the required end-joint details.
- Board gaps: Allow for drainage, ventilation and the movement characteristics of the decking material.
- Fixings: Use the recommended type, length and quantity of exterior-suitable fixings.
- Screw depth: Install fixings in accordance with the board manufacturer's instructions, avoiding protruding screw heads and damaged board surfaces.
- Ventilation: Leave suitable airflow beneath the deck and avoid trapping moisture around timber.
- Drainage: Prevent water from collecting beneath the deck or against walls and supports.
- Safety: Check edges, changes in level, steps and handrails as part of the finished installation.
Do not use a single screw length or joist spacing for every project. Board thickness, timber dimensions, spans, loading and the manufacturer's instructions all affect the correct specification.
8. Aftercare and Maintenance
Inspect the decking periodically, particularly after winter and periods of wet weather. Look for loose fixings, damaged boards, signs of decay, movement in the subframe and blocked drainage routes.
Keep the surface clear of leaves and debris that can retain moisture or make the deck slippery. Clean the boards using a method suitable for the material and any applied finish.
Where a protective treatment or finish is used, follow the product instructions for preparation, application and re-treatment. The maintenance interval will depend on the decking material, exposure and finish.
Frequently Asked Questions
Do I need planning permission for garden decking?
Not every decking project requires planning permission, but the answer depends on the platform, property and location. Check current guidance on the Planning Portal and confirm any site-specific restrictions with your local planning authority.
How do I calculate how much decking I need?
For a rectangular area, multiply the length by the width to calculate the square metres. Then use the board dimensions and specified installation gap to estimate the quantity, allowing for cuts and waste. Remember to calculate the subframe and fixings separately.
Can decking be installed directly onto grass?
Decking should not simply be laid directly onto grass. Prepare the ground and provide a suitable support system that keeps the frame stable and allows drainage and ventilation. The exact method depends on the site and deck design.
Can I attach decking directly to my house?
A deck may be designed with a connection to a building, but the wall construction, fixings, damp-proof course, drainage and structural loads must be considered. Use a suitable design and installation method rather than assuming any wall can support the deck.
What timber should I use for the decking frame?
Choose timber suitable for the intended structural use and external exposure. Joist dimensions, spans, support spacing, treatment and connections should be selected for the specific design and loading requirements.
What fixings should I use for decking boards?
Use fixings specified for the decking material and external conditions. Check the recommended screw type, length, number of fixings per board and installation details in the manufacturer's instructions.
Planning a Decking Project?
Measure the area, confirm the design and calculate the boards, subframe timber, supports and fixings before ordering. Checking these details at the planning stage can help reduce waste and avoid delays during installation.
This guide provides general planning and installation information. Project-specific planning, structural and building requirements should be checked before work begins.
