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Norway Minimum Roof Fall (TEK17 §13-12): The 1:40 Rule

TEK17 §13-12 doesn't fix a roof-pitch number itself — it's a functional 'sufficient fall' clause. DiBK's own guidance beneath it gives one hard figure: 1:40 for membrane roofing. Tile and metal aren't numerically fixed here.

TEK17 §13-12 (2017, as amended) Clause NO TEK17 §13-12

The requirement

For membrane roofing, Norway’s minimum fall is 1:40 (about 2.5%, or 1.4 degrees). That number sits in DiBK’s guidance under TEK17 §13-12, not in the rule itself. The clause only asks for “tilstrekkelig fall”, meaning sufficient fall. Tile and metal get no number here.

Roof fall is how steep a roof is. Lay it too flat and water sits on the roof instead of running off. TEK17 §13-12 “Nedbør” (precipitation) covers this. It is a performance rule. The roof must have enough fall so rain and meltwater drain away. Water must not pool or work back under the roofing. How much fall counts as “sufficient” sits in the guidance below the clause.

Membrane roofs get the one hard number. Direktoratet for byggkvalitet (DiBK) writes veiledning under §13-12. Veiledning is deemed-to-satisfy guidance. It sets one minimum fall.

Roofing typeMinimum fall (DiBK veiledning, §13-12)
Asphalt roofing felt / membrane roofs1:40 (≈ 2.5%, ≈ 1.4°)

The figure covers asphalt roofing felt and membrane roofs. It is the only pitch number confirmed straight from DiBK’s published guidance for this clause. Read it as 1 unit of rise for every 40 units of run.

40 m1 m1:40
TEK17 · §13-12

Tile and metal roofs get no number here. §13-12 and its guidance set no minimum pitch for tile or profiled-metal roofing. Those roofs shed water very differently to a welded membrane. And TEK17 has no per-material pitch table, the way some other national codes do. In practice the pitch comes from the roofing product’s own standard and fixing instructions. Byggforskserien helps too. That is SINTEF Community’s set of paid technical detail sheets. Trades treat those sheets as best practice, not law. This page ships only the 1:40 membrane figure. That is the one confirmed straight from DiBK’s own text. It does not invent a tile or metal number to fill the gap.

Worked example

You are detailing a membrane roof. Think asphalt felt over a garage or an extension. The minimum is a climb of 1 m over a 40 m run. On a normal house roof that is a small number, and easy to lose. So scale it down:

  1. Set the ratio. 1:40 means 1 unit of rise for every 40 units of run.
  2. Scale it to your roof. Say your membrane roof runs 4 m front to back. It needs at least 4 ÷ 40 = 0.1 m (100 mm) of fall over that run.
  3. Check it in your own units. 1:40 is about 2.5%, or roughly 1.4 degrees. Convert it if your level or laser reads in degrees or percent. The roof-pitch calculator swaps between rise-and-run, ratio, percent and degrees.

Laying tile or metal instead? This 1:40 figure does not apply. Get the pitch from the product’s own fixing instructions.

Sources

  • TEK17 (Byggteknisk forskrift), §13-12 “Nedbør” — the statutory functional requirement (“tilstrekkelig fall”) with no number in the regulation text itself. Read it at dibk.no.
  • DiBK’s veiledning (deemed-to-satisfy guidance) beneath §13-12 — the source of the 1:40 minimum fall for asphalt roofing felt/membrane roofs. Confirmed by direct fetch of the current guidance page at dibk.no.

Read this first. TEK17 is amended section by section on its own schedule — check the “Endringshistorikk” on the dibk.no page for the current wording before you rely on this figure. And remember the scope: 1:40 is confirmed for membrane roofing only. Tile and metal roof-pitch minima are not numerically fixed in this clause — they come from the product standard, Byggforskserien and the manufacturer’s own fixing instructions, which this page doesn’t reproduce.

Related building rules

Frequently asked questions

Does TEK17 set a numeric minimum roof pitch?
Not directly. TEK17 §13-12 (Nedbør, meaning precipitation) only asks for 'tilstrekkelig fall', or sufficient fall, so rain and meltwater run off. That is a performance rule, not a number. The one hard figure sits in guidance from Direktoratet for byggkvalitet (DiBK), and it covers membrane roofing only.
What is the 1:40 rule for Norwegian roofs?
DiBK's guidance under §13-12 sets a minimum fall of 1:40 for asphalt roofing felt and membrane roofs. That is about 2.5%, or roughly 1.4 degrees. It is deemed-to-satisfy guidance, and it is the one figure confirmed straight from DiBK's own published text.
Does TEK17 fix a minimum pitch for tile or metal roofing?
Not in §13-12. That clause and its guidance give a numeric minimum for membrane roofing only. Tile and metal sheet roofing get no number in this section. Their pitch comes from product and NS standards, plus the maker's own installation instructions, not from a number written into TEK17 itself.
Where do tile and metal roof-pitch numbers actually come from in Norway?
From the roofing product's own standard and fixing instructions, and from Byggforskserien, SINTEF Community's paid technical detail sheets. Trades treat those sheets as best practice, not law. TEK17 does not reproduce those figures, so this page does not invent a tile or metal number that the regulation does not confirm.
Is 1:40 a steep roof or a nearly flat one?
Nearly flat. A 1:40 fall climbs 1 unit for every 40 units of run. That is about 2.5%, or roughly 1.4 degrees. It is the minimum DiBK allows for a membrane roof to still shed water. Tiled and metal-sheet roofs need much more fall than that.