Published 15 April 2026 · Sussex Oak Structures
Planning permission is almost always the first question clients ask when they get in touch about an oak framed annexe. The rules can feel confusing because they sit across three different regimes — planning, building regulations and council tax — and each has its own quirks. Here’s a plain-English 2026 guide based on the applications we run through Sussex, Surrey and Kent councils every month.
What Counts as an “Annexe”?
Planning authorities generally treat an annexe as self-contained accommodation that is ancillary to a main dwelling. If it has its own kitchen, bathroom, sleeping area and separate access, it is almost always classed as an annexe — and will almost always need planning permission.
A building used purely as a garden office, gym or hobby room is not an annexe in planning terms. Those structures often fall under permitted development as outbuildings, provided they meet the size and height limits.
Three Planning Routes for an Oak Framed Annexe
Route 1: Full Householder Planning Application
This is the most common route for genuine annexes. You submit a householder application to your local planning authority with drawings and a design & access statement. Typical timeline is 8–10 weeks. Most well-designed oak framed annexes in Sussex get approved first time, especially if the design respects the proportions and materials of the existing house.
Route 2: Permitted Development (Outbuilding)
If the building is genuinely incidental to the main house — so no self-contained living, no kitchen, no bedroom used independently — it can be built under permitted development, provided:
- It is single storey
- Eaves height does not exceed 2.5m
- Ridge height does not exceed 4m (dual pitch) or 3m (other roofs)
- It is at least 2m from any boundary for 2.5m height
- Total outbuildings do not exceed 50% of the curtilage
- You are not in a conservation area, AONB or national park
Route 3: The Caravan Act
The Caravan Sites and Control of Development Act 1960 is a little-known but extremely useful route for granny annexes. If an annexe is built to caravan legal dimensions (20m × 6.8m × 3.05m internal, in no more than two sections), it can be stationed on a residential plot without planning permission for use by a dependent relative. Many of our oak framed “mobile” annexes are designed specifically to fall within these limits.
Council Tax & Annexes
This is where a lot of families get a nasty surprise. By default, a self-contained annexe gets its own Council Tax band from the Valuation Office Agency. However there are two key reliefs:
- Full exemption — available where the annexe is joined to the main home and occupied by a disabled or elderly dependent relative.
- 50% discount — available where the annexe is used by the occupier of the main house as part of the main dwelling (for example, as a home office or guest suite).
Our planning partners will flag the route most likely to qualify for relief at the design stage.
Building Regulations — the Other Half of the Equation
Even if you secure planning permission, an annexe will also need to meet current building regulations. For oak framed annexes this includes:
- Structural calculations for the oak frame and foundations
- Thermal performance (we use Kingspan TEK SIP encapsulation to comfortably meet Part L)
- Ventilation, drainage and Part P electrical certification
- Fire separation from the main house where attached
All Sussex Oak Structures projects are signed off under building control as standard, so you have full documentation when you eventually sell the house.
Designing an Annexe That Gets Approved
In our experience, oak framed annexes that get approved on the first planning submission share five traits:
- Modest footprint relative to the main house
- Matching or sympathetic materials (oak, clay tiles, brick plinth)
- Roof proportions that echo the main house
- Set well back from neighbouring boundaries
- Clear evidence of genuine family need, ideally a letter from a GP for elderly or disabled relatives
Next Steps
If you’re considering an oak framed annexe, we recommend starting with a pre-application enquiry with your local planning authority and a free consultation with our design team. We’ll come out to your property, take measurements, and advise on the most realistic planning route for your site.
Learn more:
Frequently Asked Questions
Do you need planning permission for a wooden annexe?
Yes, in most cases — self-contained annexes almost always require full planning consent. Incidental outbuildings may fall under permitted development.
What is the Caravan Act and can I use it for an oak annexe?
The 1960 Caravan Act allows annexes within strict size limits (20m × 6.8m × 3.05m, two sections max) to be stationed on a residential plot for a dependent relative without planning permission.
How do I avoid council tax on an oak framed annexe?
Full exemption is possible when the annexe is joined to the main home and occupied by a disabled or elderly dependent relative; a 50% discount applies when used as part of the main dwelling.
Can I build a granny annexe on permitted development?
Only if the building is strictly incidental to the main house. Fully self-contained granny annexes usually require a full planning application.
How big can an oak framed annexe be without planning permission?
Under outbuilding PD rights, generally up to 2.5m eaves and 4m ridge if 2m+ from the boundary, and no more than 50% of garden coverage — but annexe use typically still needs consent.
