How far apart should ground screws be?
Ground screw spacing is set by the structure above, not by a fixed rule — understanding how ground screws work helps explain why. The correct spacing on any project depends on structural loads, ground conditions, screw diameter and length, the timber or steel subframe design, joist and span requirements, concentrated point loads, and the intended use of the building.
There is no universal ground screw spacing measurement suitable for every structure. A layout that works for a lightweight garden room can be entirely wrong for a modular building carrying higher loads over longer spans.
- Structural loads and how they are distributed across the footprint
- Ground conditions and the installation response at each position
- Ground screw diameter, length and helix configuration
- Timber or steel subframe design and beam layout
- Joist and span requirements for the floor or deck above
- Concentrated point loads, such as posts, stairs or heavy fixtures
- The intended use and expected life of the building
Typical ground screw spacing ranges
The ranges below are practical, commonly used starting points across common ground screw applications — not a specification. They assume reasonable ground conditions and a conventional timber subframe; every project should be checked against its own loads, spans and site.
| Application | Typical spacing (guide only) | Depends heavily on |
|---|---|---|
| Timber decking | 900mm–1,500mm centres | Joist size, span and deck loading |
| Garden room perimeter | 1,000mm–1,800mm centres | Frame type, corners and openings |
| Garden room intermediate supports | Set by beam layout, not a fixed grid | Point loads and internal spans |
| Modular building perimeter | Engineer-specified | Building loads, which are typically higher |
These figures are indicative examples only. Final spacing should be confirmed against the actual structural design.
Ground screw spacing for decking
Decking spacing is driven by the beam layout, timber dimensions, joist spans and expected deck loading. Wider joist spans generally call for closer screw centres beneath the supporting beam, while shorter spans and stiffer sections can allow wider spacing.
Ground conditions still matter at deck scale. A soft or variable area under part of the deck can call for a revised layout even where the structural calculation looks straightforward on paper.
Ground screw spacing for garden rooms
Garden rooms and other SIP or timber-frame garden buildings typically need a perimeter of ground screws around the base, with intermediate support introduced where spans, openings or point loads require it.
Corners, either side of doors and windows, and any concentrated load — such as a structural post or a heavier roof section — usually need their own support rather than relying on the nearest point in a generic grid.
Ground screw spacing for modular buildings
Modular and prefabricated buildings generally carry higher loads over larger spans than a typical garden room, which usually means a closer, engineer-specified layout rather than a standard residential spacing pattern.
See the dedicated guide to ground screws for modular buildings for how layout, ground conditions and testing are approached for this application.
What determines the number of ground screws?
Screw quantity follows from the layout, not the other way around. Because a screw foundation supports point loads rather than a continuous strip — unlike ground screws vs concrete foundations — the number and position of screws matters more than it would for a continuous footing.
- Overall building dimensions and footprint
- Total structural weight and imposed (live) loads
- Ground conditions and screw capacity at each position
- Beam spans and how loads are shared between supports
- Openings, cantilevers and unsupported edges
- Heavy fixed equipment or plant loads
- Concentrated point loads from posts, stairs or partitions
There isn't one correct ground screw spacing
Every project is different, which is why we built this into something you can explore rather than a single number. Choose a structure type and adjust the ground and loading conditions below to see how a considered layout typically responds — more support where the ground is harder to read or the loads are higher, less where conditions are straightforward.
This is a simplified, illustrative model to show the idea. It is not a structural design, a quote or an exact calculator, and it does not replace project-specific engineering.
What actually determines the spacing
Behind the tool above, a real layout is set by five things working together:
- Structural loads — how much weight the foundation carries, and how evenly it's distributed
- Ground conditions — how firm and consistent the ground is at each position
- Screw capacity — the diameter, length and helix configuration selected for the site
- Frame spans — the timber or steel subframe's beam layout and span between supports
- Point loads — concentrated loads such as posts, stairs or corners that need their own support
Want us to work yours out?
Send us your dimensions or plans and we'll suggest a likely layout for your project.
Send us your plansCan ground screws be too far apart?
Yes. Spacing screws further apart than the structure allows can lead to excessive beam deflection, bouncy or springy floors, and higher loads being carried by fewer screws than the design intended.
- Excessive beam deflection between supports
- Bouncy or springy floors underfoot
- Higher loads carried by individual screws than intended
- Overloading individual ground screws beyond their safe capacity
- Poor load distribution across the foundation as a whole
Do all ground screws carry the same load?
Not necessarily. Screws nearer corners, openings, posts or other concentrated loads can carry more than screws along a lightly loaded straight run, even within the same building.
This is why installation torque, ground response and — where the project calls for it — pull and load testing matter alongside the spacing itself, guided by the same principles covered in our testing and verification guide. A considered layout and appropriate verification work together; neither replaces the other.
Frequently asked questions
How far apart should ground screws be?
It depends on the structure, ground conditions, screw size and loads involved. Typical residential ranges are commonly between 900mm and 1,800mm centres, but the correct spacing for any project should be confirmed against its actual design.
How many ground screws do I need?
The number follows from the layout: building dimensions, structural loads, beam spans, openings and point loads all determine how many support positions are needed once the spacing is set.
What spacing should I use for decking?
Decking spacing is usually driven by joist size, span and deck loading, with common ranges around 900mm to 1,500mm centres — narrower spans and lighter loads can sometimes allow wider spacing.
What spacing should I use for a garden room?
Garden rooms typically need a perimeter of ground screws with intermediate support at corners, openings and concentrated loads, commonly in the range of 1,000mm to 1,800mm centres depending on the frame design.
Can ground screws be spaced 2 metres apart?
Sometimes, for lightly loaded structures with a suitably stiff subframe and good ground conditions — but wider spacing increases the demand on the beams and screws either side, so it should be checked rather than assumed.
Do larger ground screws allow wider spacing?
A larger diameter or longer ground screw can offer greater capacity, which may support wider spacing in suitable ground — but capacity, ground response and the structural design all need to be assessed together, not the screw size alone.
Does soil type affect ground screw spacing?
Yes. Ground conditions affect how much load a screw can safely carry at a given position, which in turn affects how many screws — and how closely spaced — a layout needs.
Do ground screw foundations need structural calculations?
For anything beyond the smallest, lightest structures, yes — appropriate structural design is the responsible way to confirm spacing, screw selection and layout rather than relying on indicative guidance alone.
Indicative online quantities and the spacing ranges above are not a structural design. Appropriate structural engineering may be required before installation.