The height of chimneys: regulations and examples (2026 guide)
In this article
By Pau Martínez (COAC registration no. 55,403), architect · Published on 16 March 2020 · Updated on 5 November 2026
The height of chimneys is not decided by eye. A flue outlet that is too low or badly placed sends smoke, odours or combustion gases back towards the windows, terraces and air intakes of the building itself and its neighbours. That is why the regulations set minimum heights and distances, which change depending on what comes out of the duct: ventilation air from a home, gases from soil stacks, fumes from a boiler or a wood-burning fireplace, or those from a restaurant kitchen.
In this guide we summarise what each regulation in force in 2026 says (the Spanish Building Code (CTE), the RITE regulations on thermal installations, the UNE 123001 standard and municipal ordinances), with tables and figures, the mistakes we see most often in our inspections and a real case of kitchen extraction for a bar-restaurant.
1. Why chimney height matters
Wind hitting a building creates eddies next to façades, ridges and rooftop volumes. If the chimney outlet sits inside that zone, the smoke does not disperse: it comes back down, enters through windows or flows back down the duct itself. Figure 1 shows the two most common cases.
Figure 1. Two common mistakes. Left: the chimney is lower than the neighbouring building and the wind pushes the smoke back down. Right: the outlet sits close to the roof slope and the wind creates turbulence that prevents the draught.
Many older buildings do not meet today’s heights. That is not always an infringement: when they were built, the regulations did not exist or were less demanding. But as soon as there is new construction, a renovation, a change of use or a new business, the project must comply with the regulations in force.
2. Which regulations apply to each outlet
There is no single regulation on chimneys. The one that applies depends on what the duct carries:
| What the duct carries | Regulation | Minimum height above the roof | Other conditions |
|---|---|---|---|
| Soil stack gases (primary drainage ventilation) | CTE DB HS 5 | 1.30 m; 2.00 m on accessible roofs | 6 m from any air intake and above it; 50 cm above openings of habitable rooms within 6 m |
| Home ventilation air (hybrid ventilation) | CTE DB HS 3 | 1 m; 2 m on accessible roofs | Clear obstacles 2–10 m away and 1.3 times the height of those 2 m away or less; 3 m from any air inlet |
| Domestic kitchen hood fumes | CTE DB HS 3 | According to the conditions for exhaust outlets | Mechanical extraction of 50 l/s through an independent duct |
| Fumes from boilers, stoves and wood or pellet fireplaces | RITE and UNE 123001 | 1 m above the ridge or flat roof within 10 m | Clear nearby openings and rooftop obstacles; rules depending on roof pitch |
| Bar or restaurant kitchen fumes | CTE DB SI and DB HS, UNE-EN 16282 and municipal ordinance | Up to the roof, at the height set by the ordinance | Independent, inspectable duct, EI 30 where applicable, automatic suppression depending on power |
If several regulations apply to the same duct, the most demanding condition prevails. And municipal ordinances may add requirements to all of them.
3. Home ventilation and kitchen hoods (CTE DB HS 3)
Basic document HS 3 of the Building Code, Indoor air quality, regulates ventilation in buildings. Stale air from homes (bathrooms, kitchens and wet rooms in general) is expelled outside through exhaust outlets which, as a general rule, must be on the roof and at least 3 m away from any ventilation air inlet, so that the exhaust air does not come back in.
Hybrid ventilation
When ventilation is hybrid (it works by natural draught and, when that is not enough, a fan switches on), the exhaust outlet must be:
- at least 1 m above the roof;
- above any obstacle at a distance of 2 to 10 m;
- at 1.3 times the height of any obstacle 2 m away or less;
- 2 m above the floor on accessible roofs.
Figure 2. Height of the exhaust outlet in hybrid ventilation according to CTE DB HS 3: above obstacles 2 to 10 m away (left) and 1.3 times the height of those 2 m away or less (right).
The kitchen hood
In addition to general ventilation, a home kitchen must have a dedicated mechanical extraction system for cooking fumes and vapours, with a minimum flow of 50 l/s. The hood connects to a duct independent from the general ventilation ducts, which cannot be used to extract air from other rooms, and which must end in an exhaust outlet meeting the conditions of HS 3 itself.
4. Boilers, stoves and wood-burning fireplaces (RITE and UNE 123001)
Chimneys from heat generators (boilers, stoves and wood or pellet fireplaces) are regulated by the Regulation on Thermal Installations in Buildings (RITE), approved by Royal Decree 1027/2007 and amended several times since, most significantly by Royal Decree 178/2021. As a general rule, the RITE requires combustion products to be discharged through the roof of the building, and only allows discharge through the façade in specific cases, such as replacing individual boilers in existing buildings with low-emission room-sealed appliances. For chimney design it refers to the UNE 123001 standard, Calculation, design and installation of system chimneys.
If other sources refer to «ITE 02.14», that comes from the 1998 RITE, repealed in 2007. Today the reference is technical instruction IT 1.3.4.1.3 of the current RITE.
UNE 123001 is stricter than the Building Code, because combustion fumes are more harmful than ventilation air. It sets conditions for four situations.
Façades, ridges and nearby openings
- If the chimney is 10 m or less from a ridge or the edge of a flat roof, it must rise at least 1 m above it.
- If there are windows or openings of a nearby building 10 to 20 m away, the outlet must be above the top edge of the highest opening.
Figure 3. UNE 123001: the chimney must rise 1 m above a ridge or flat roof within 10 m, and above the highest opening of a building 10 to 20 m away.
Obstacles on the same roof
Stair housings, plant rooms, parapets and other chimneys also count. If the chimney is closer than twice the height (2h) of the obstacle, it must rise at least 1 m above its highest point. If it is further away, the obstacle no longer affects its height.
For example, with a 2.5 m high stair housing, any chimney less than 5 m away must exceed it by 1 m, in other words reach 3.5 m above the roof. Under the Building Code, by contrast, a home ventilation outlet more than 2 m away would only need to clear the 2.5 m of the housing.
Figure 4. UNE 123001: within 2h of an obstacle of height h, the chimney must rise 1 m above its highest point.
Windows on the roof slope and on the façade
If there is a window on the roof slope itself, such as a rooflight, the chimney must be more than 1 m from it if it is above or to the side, and more than 2 m if it is below; in that case, its outlet must also rise more than 1 m above the top edge of the window. On a façade, the duct must be at least 1 m horizontally from any window.
Figure 5. UNE 123001: distances to windows on the roof slope (more than 1 m above, more than 2 m below) and to windows on the façade (more than 1 m horizontally).
Roof pitch
- On roofs pitched at more than 20°, the chimney must rise at least 1 m above the ridge if it is less than 2.5 m from it. If it is further away, it may sit below the ridge, as long as the outlet stays outside the turbulence zone of the slope shown in figure 6.
- On roofs pitched at less than 20°, the chimney must rise at least 1 m above the ridge.
Figure 6. UNE 123001, roofs pitched at more than 20°: within 2.5 m of the ridge, the chimney must rise 1 m above it.
Figure 7. UNE 123001, roofs pitched at less than 20°: the chimney must rise 1 m above the ridge.
5. Soil stack ventilation (CTE DB HS 5)
Wastewater soil stacks are ventilated by extending them above the roof (primary ventilation). Section 3.3.3.1 of basic document HS 5, Water drainage, requires the outlet to:
- project at least 1.30 m above the roof if it is not accessible, and 2.00 m above the floor if it is;
- be at least 6 m from any outdoor air intake for air conditioning or ventilation, and above it;
- be at least 50 cm above the highest point of the openings of habitable rooms within 6 m;
- not end under canopies or terraces, and be protected against foreign objects.
These are the vents that cause the most odour problems when placed next to a terrace or a window.
6. Bar and restaurant kitchens
The kitchen extraction of a commercial kitchen is the factor that most often determines whether a bar or restaurant can open. On top of the rules above:
- Fire safety (CTE DB SI 1). A kitchen with more than 20 kW of installed power is a special-risk area, unless its appliances are protected by an automatic suppression system. In any case, its extraction ducts must be independent from any other extraction or ventilation and exclusive to each kitchen, have access points for inspection and cleaning, and an EI 30 rating where they run inside the building, or on the façade within 1.50 m of areas that are not at least EI 30 or of balconies, terraces or opening windows.
- Automatic suppression (CTE DB SI 4). Hoods in kitchens over 50 kW must have an automatic suppression system (over 20 kW in hospital or public residential use).
- Ventilation equipment (UNE-EN 16282). This series of standards covers hoods, filters, ducts and other ventilation components of commercial kitchens.
- Municipal ordinance. It usually sets where the fumes can be discharged, at what height and whether filters or treatment systems are needed.
So before renting premises for a bar or restaurant, the first thing is to check that there is a possible route for the duct up to the roof. We explain it on our commercial premises, bar and restaurant renovation page.
7. Municipal ordinances: the case of Barcelona
Councils can require more than the Building Code and the RITE. In Barcelona, the former General Ordinance on the Urban Environment (1999) banned discharging fumes through façades and courtyards, and classified the chimneys of combustion installations into categories, by fuel and power, with a minimum height above the surrounding buildings:
| Category | Minimum height above buildings | Radius considered |
|---|---|---|
| 0 | 1 m | 10 m |
| 1st | 2 m | 20 m |
| 2nd | 3 m | 40 m |
| 3rd | 5 m | 80 m |
Category 0 covered, for example, gaseous-fuel installations of moderate power; the higher categories, fuels with more sulphur or greater power. The same ordinance required a lightning conductor on chimneys more than 10 m higher than the buildings within a 50 m radius.
Important: that ordinance was replaced by the Barcelona Environment Ordinance of 2011, and each municipality has its own. Before designing a flue outlet we always check the ordinance in force in the municipality and, if necessary, consult the council’s technical services.
8. Common mistakes
- Chimneys that are too low next to a taller building: the smoke comes down and enters the neighbours’ windows.
- Outlets next to the ridge but below it, right in the turbulence zone.
- The kitchen hood connected to the general ventilation duct of the bathroom or kitchen.
- Fume outlets onto the façade or into a courtyard from commercial premises, which almost no ordinance allows.
- Ducts without access points for cleaning, where grease builds up, with a fire risk.
- Soil stack vents near terraces or windows, which cause bad odours.
We see these often in our construction inspections and in technical building inspections (ITE).
9. Case study: two ducts up the façade in Montesquiu
In a bar-restaurant project on the ground floor of a 1930 building in Montesquiu, the premises had no inner courtyards, and taking the fumes up through the inside would have taken space from the flats above. The solution was to run two exposed ducts up the façade to the roof, from a commercial hood with an automatic suppression system. The ducts are non-combustible, with EI 30 protection along the interior section, and discharge 1 m above the ridge and above any opening within 15 m.
Current state of the façade, before the renovation of the premises.
Photomontage of the project: the two extraction ducts rise, exposed, up the façade to the roof.
We chose to leave them exposed, as one more element of the façade, rather than hide them in a built-up casing. The project is going through permitting; you can see the floor plan, the regulations applied and the other decisions on the Montesquiu project page.
10. How we can help
We design flue and extraction outlets in new builds, renovations, changes of use and bar and restaurant openings, and review existing ones when they cause problems:
- Commercial premises, bar and restaurant renovation: feasibility study, building and activity project, licence and site management.
- Change of use from commercial premises to home, where ventilation and kitchen extraction are key.
- Full renovations of homes and buildings.
- Construction inspection, if an existing chimney is causing problems.
Frequently asked questions about chimney height
Regulations cited: Spanish Building Code (CTE) (DB HS 3 Indoor air quality, DB HS 5 Water drainage, DB SI Fire safety) · Royal Decree 1027/2007, Regulation on Thermal Installations in Buildings (RITE), consolidated text · UNE 123001:2012, Calculation, design and installation of system chimneys · UNE-EN 16282 series, Equipment for commercial kitchens · Barcelona Environment Ordinance (2011).
