The short answer: how high a chimney must be
| Where the chimney is | Requirement |
|---|---|
| Closer than 1.5 m to the ridge (horizontally) | at least 0.5 m higher than the ridge |
| From 1.5 m to 3 m from the ridge | not lower than the ridge |
| Further than 3 m from the ridge | not lower than a line drawn down from the ridge at an angle of 10° to the horizontal |
| Anywhere, including on a flat roof | the top not lower than 0.5 m above the roof covering |
Both requirements must be met at the same time: the requirement relative to the ridge and 0.5 m above the roof covering. The distance to the ridge is measured horizontally from the chimney to the ridge line, not along the slope of the roof. The total height of the chimney from the grate to the top must be at least 5 m, otherwise the draught will be weak.
LBN 231-15 “Heating and Ventilation” (Cabinet Regulation No. 310 of 16.06.2015), point 61. Under 61.1, a chimney closer than 1.5 m to the roof ridge must be 0.5 m higher than the ridge. Under 61.2, at 1.5 to 3 m from the ridge it must not be lower than the ridge. Under 61.3, further than 3 m away it must not be lower than a straight line from the ridge at 10° to the horizontal. Point 62: the chimney top is not lower than 0.5 m above the roof covering (flat roofs too). Point 63: the total height from the grate to the outlet is at least 5 m. Source: likumi.lv, checked 04.11.2026.
Example: a chimney further than 3 m from the ridge
The ten-degree line from the ridge drops by roughly 0.18 m for every horizontal metre. So for a chimney 5 m from the ridge, the top may be no more than roughly 0.88 m below the ridge. For a chimney 8 m from the ridge, it may be roughly 1.41 m below the ridge.
On a shallow roof this line can be closer to the roof than 0.5 m. Then the second requirement decides, and the chimney must reach at least 0.5 m above the roof covering. On a steep roof, where the roof drops from the ridge more sharply than 10°, the 10° line usually decides, and the chimney must rise well over 0.5 m above the roof.
| Distance to the ridge | Top not lower than |
|---|---|
| 1 m | 0.5 m above the ridge |
| 2 m | ridge level |
| 4 m | 0.71 m below the ridge |
| 5 m | 0.88 m below the ridge |
| 6 m | 1.06 m below the ridge |
| 8 m | 1.41 m below the ridge |
In all cases the chimney must also be at least 0.5 m above the roof covering at the point where it passes through the roof.
Why height affects draught
As wind flows over the ridge, it creates eddies and a pressure zone behind it. If the top of the chimney is in this zone, the wind pushes air back down the flue channel, and smoke comes into the room. This is a common reason why a stove smokes only in windy weather or only with the wind from a certain direction. A taller chimney carries the flue gases above this zone.
Taller trees and neighbouring buildings cause similar problems. For new and rebuilt buildings next to a taller building, the building code requires a chimney height that keeps flue gases from being carried into the neighbour's windows and ventilation. If the draught problem also occurs in calm weather, the cause is often something else: chimney has no draught.
LBN 231-15, point 60.1: in new or rebuilt buildings next to a taller building, the chimney height is set so that pollution is not carried into the windows and ventilation openings of the neighbouring building. Source: likumi.lv, checked 04.11.2026.
What to do if the chimney is too low
- A brick chimney is raised by rebuilding the head with extra courses. The best moment is when the head needs repairing anyway: chimney head rebuilding.
- In a lined chimney the liner can be extended above the head, but a long, free-standing end of the liner must be secured against the wind.
- A metal chimney is extended with sections and fixings from the same manufacturer.
- A deflector can help in a windy spot, but it does not replace the height the building code requires: chimney cap installation.
The building code allows chimney caps and deflectors to be fitted on a chimney if they do not interfere with the appliance or with cleaning.
LBN 231-15, point 65: chimney caps and other covers, including deflectors, may be fitted on chimneys if they do not interfere with the operation of the heating device or with chimney cleaning. Source: likumi.lv, checked 04.11.2026.
Height in the technical condition inspection
In a technical condition inspection the chimney sweep assesses whether the flue complies with the construction and operation regulations, and records any non-compliance in the notes of the certificate. A chimney that is too low can be one such note. This inspection is done for solid-fuel and liquid-fuel appliances and flues once every five years and when the heating appliance is replaced: chimney sweep's condition report.
Cabinet Regulation No. 238 of 19.04.2016 “Fire Safety Regulations”, point 73: the technical condition inspection establishes compliance with the laws governing construction and operation and with the manufacturer's requirements. Point 74: inspection of solid-fuel and liquid-fuel appliances and flues once every five years. Point 78: non-compliances are stated in the “Notes” section of the certificate. Point 79: inspection when the heating appliance is replaced. Regulations checked 04.11.2026; from 2 January 2027 they will be replaced by new fire safety regulations, which we will check as soon as they are adopted. Source: likumi.lv, checked 04.11.2026.
Sources
- Height relative to the ridge (LBN 231-15, 61.1–61.3), ≥0.5 m above the roof covering also for a flat roof (62), total height ≥5 m (63), neighbouring building (60.1), caps and deflectors (65) checked 4 November 2026
- Technical condition inspection: compliance with regulations (Cabinet Regulation No. 238, 73), once every 5 years (74), non-compliances in the notes (78), replacing an appliance (79); Cabinet Regulation No. 238 loses force on 02.01.2027 checked 4 November 2026