Fire safety of wooden houses: how timber behaves in a fire and how it is designed for it
Wood burns — and timber buildings are still designed to resist fire for a set time, by calculation. The reason is charring: a burning timber section forms an insulating layer of char that slows the fire down, at a rate that is predictable enough to design with.
Geoniks works with wooden houses only — log, timber frame and CLT homes, cabins and villas. We can’t help with concrete, steel, apartment or office buildings.
Charring: predictable, slow and self-protecting
When a timber member is exposed to fire, its surface turns to char. The char layer insulates the wood behind it, which stays cool and keeps its strength a short distance below the char line. EN 1995-1-2, the fire part of Eurocode 5, gives a design charring rate of about 0.65 mm per minute for softwood and glulam.
In 30 minutes a softwood beam therefore loses about 20 mm on each exposed side. The engineer removes that char depth plus a thin zero-strength layer (7 mm in the reduced cross-section method) from the section and checks that what is left still carries the load. Large sections — thick logs, glulam beams, CLT panels — keep a large residual section.
Two different classifications
- Reaction to fire (EN 13501-1, Euroclasses A1 to F) describes how a surface material contributes to a fire. Untreated solid wood is typically D-s2, d0; fire-retardant treatment can bring wood products to class B or C.
- Fire resistance (REI) describes how long a building part keeps its load-bearing capacity (R), integrity (E) and insulation (I): REI 30, REI 60 and so on, in minutes. A timber wall or floor reaches its REI class by section size, charring and protective boards.
What protects a wooden house
The requirements themselves are set by national building rules, depending on the use, size and number of storeys of the building; a manufacturer or engineer confirms them for your project.
- Gypsum fire boards on walls and ceilings delay the start of charring of the structure behind them.
- Larger sections and solid panels, which keep a load-bearing core.
- Fire stops in cavities and around service penetrations, so fire cannot spread inside the walls.
- Smoke alarms and, in larger buildings, sprinklers — the most effective protection for people in any type of building.
- Distance to the boundary and fire-rated external walls where local rules require them.
With Geoniks: Planning a larger timber building — a lodge, a guest house or a multi-storey home? Send the architect plans and get prices from manufacturers who build such projects.
Large wooden house projects →Frequently asked questions
Are wooden houses more dangerous in a fire?
Timber buildings are designed to the same fire resistance requirements as other buildings. Large timber sections char slowly (about 0.65 mm per minute for softwood) and keep a load-bearing core, and boards, fire stops and smoke alarms do the rest.
How fast does wood burn?
EN 1995-1-2 gives a design charring rate of about 0.65 mm per minute for softwood and glulam — about 20 mm in 30 minutes on each exposed side.
Is CLT fire-safe?
CLT panels are designed for fire like other timber: by charring rate and residual section, often with gypsum boards. National rules decide the class needed for a building of a given use and height.
What fire class is untreated wood?
Untreated solid wood is usually Euroclass D-s2, d0 for reaction to fire. Fire-retardant treatment can raise wood products to class B or C.