Short answer: in England a solid fuel stove usually needs a constructional hearth of solid non-combustible material at least 125 mm thick, measuring at least 840 mm by 840 mm if the stove stands free in the room. A thin 12 mm hearth is allowed only for an appliance outside a recess that has been tested to keep the hearth surface below 100 °C. Separately from the hearth itself, the surface around the stove must be clear of combustible material by 225 mm at the front and 150 mm to the sides.
Those two requirements get confused constantly, because they are drawn on the same plan. The hearth is what the stove stands on. The clear surface is what nobody may put a rug on. This guide separates them, then shows both to scale.
Which hearth do you need?
Approved Document J paragraph 2.23 gives two ways to satisfy the requirement, and only one of them is usually available.
The 12 mm option (2.23a, Diagram 27a) is non-combustible board, sheet or tile at least 12 mm thick. It applies only when both of these are true:
- the appliance does not stand in a fireplace recess, and
- the appliance has been tested to an applicable standard showing it cannot raise the upper surface of the hearth above 100 °C.
That test result comes from the manufacturer’s documentation. If the paperwork does not say it, you do not have it, and the answer is the other option.
The constructional hearth (2.23b, 2.24) is solid non-combustible material such as concrete or masonry, at least 125 mm thick. That thickness includes any non-combustible floor and any decorative surface on top, so a 100 mm slab with 25 mm of stone tiles on it counts, and a 50 mm screed with a 20 mm slate hearth on top does not.
The plan dimensions
The constructional hearth’s footprint depends on where the appliance stands (Diagram 24).
| Where the appliance stands | Minimum constructional hearth in plan |
|---|---|
| Free standing in the room | 840 mm × 840 mm |
| In a fireplace recess | Projects at least 500 mm in front of the jamb, and extends at least 150 mm beyond each side of the opening |
So for a recess with a 700 mm wide opening, the hearth is at least 700 + 150 + 150 = 1,000 mm wide and projects 500 mm forward of the jamb.
The clear surface is a different rule
Diagram 26 asks for a surface free of combustible material around the appliance, whatever hearth it stands on:
- 225 mm in front of a closed appliance, or 300 mm in front of an open appliance, or a closed one that can properly be used with its front open;
- 150 mm to each side, and also 150 mm behind if the appliance stands free rather than in a recess, unless it backs onto a suitably heat-resistant wall.
Paragraph 2.26 adds that the boundary of that surface must be visually apparent — a change in level is the example the document gives. The point is that a person laying a rug or stacking kindling can see where the safe zone ends.
Does a 840 × 840 hearth actually fit your stove?
Not automatically. Work the clear surface outwards from the appliance footprint and compare. For a stove 500 mm wide and 400 mm deep, closed-fronted:
- width needed: 150 + 500 + 150 = 800 mm, inside the 840 mm hearth
- depth needed: 150 behind + 400 + 225 in front = 775 mm, inside the 840 mm hearth
A wider stove, or one used with its front open, can easily need a hearth larger than the 840 mm minimum. Stove Toolkit draws this plan for your actual appliance size and tells you which dimension is driving it.
What goes underneath
Paragraph 2.25 deals with the floor below. There should be no combustible material beneath a constructional hearth unless either:
- there is an air space of at least 50 mm under the hearth, or
- the combustible material is at least 250 mm below the top of the hearth.
That is the rule that catches suspended timber floors. On the surface, paragraph 2.28 allows combustible material on or beside the constructional hearth to run under a superimposed hearth by at most 25 mm, and never closer than 150 mm horizontally to the appliance.
The hearth also has to carry the load: paragraph 2.22 says it must be able to support the appliance and, where it is not independently supported, its chimney.
The wall behind
Diagram 30 protects walls near the hearth with solid non-combustible material:
| Situation | Wall protection |
|---|---|
| Hearth abuts the wall, appliance not more than 50 mm from it | 200 mm thick, at least 300 mm above the appliance and 1.2 m above the hearth |
| Hearth abuts the wall, appliance 50 mm to 300 mm from it | 75 mm thick, at least 300 mm above the appliance and 1.2 m above the hearth |
| Hearth does not abut the wall and is not more than 150 mm from it | 75 mm thick, at least 1.2 m above the hearth |
| Hearth more than 150 mm from the wall | None required (Diagram 30 note 1) |
There is no row for a hearth that abuts the wall with the appliance more than 300 mm away. In that case the document gives you nothing, and the manufacturer’s clearances are what you work to.
Where the manufacturer overrides all of this
Two paragraphs hand the decision back to the appliance maker, and they matter:
- 2.27: the Diagram 26 clear-surface dimensions may be reduced to the manufacturer’s recommendations for appliances whose surface temperature does not exceed 85 °C in normal use, with no risk of fuel or ash spillage.
- 2.33: the Diagram 30 wall clearances may likewise be reduced for appliances not exceeding 85 °C.
Note the direction of travel. Manufacturer’s instructions can reduce these particular figures only under those conditions, and can require more at any time. They cannot reduce the hearth thickness or the constructional hearth footprint.
Scope
This is the England edition of Approved Document J, 2010 edition incorporating the 2010, 2013 and 2022 amendments, Section 2, solid fuel appliances up to 50 kW. Wales publishes its own version; Scotland and Northern Ireland use different standards. Installing a solid fuel appliance is building work: it must be done by a competent person, such as a HETAS registered installer, or notified to building control before it starts.
Read the source at Approved Document J on gov.uk. If you also need the air vent, our guide to log burner ventilation works through Table 1.
Figures checked against the gov.uk PDF of Approved Document J on 10 September 2026. Contains public sector information licensed under the Open Government Licence v3.0. Plan CD is not affiliated with HETAS, DEFRA or any manufacturer.