# Loft floor area and knee walls: Norway's 1.90 m rule explained

> Which parts of a sloping loft count as floor area in Norway? A worked example of the 1.90 m height line, 60 cm allowance and knee-wall geometry.

- Type: Guide
- Published: 2026-11-06
- Updated: 2026-11-06
- Author: House Madness
- Web page: https://housemadness.app/en/articles/loft-floor-area-and-knee-walls/
- Topics: loft conversion, knee wall, floor area, Norway, TEK17

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**Short answer:** In Norway, a loft qualifies for floor-area measurement when it has **at least 1.90 m clear height over a width of at least 0.60 m**. Under a sloping roof, the measured area includes a further **0.60 m horizontally beyond the 1.90 m height line**, up to the wall. A higher knee wall or steeper roof brings that line closer to the side of the room. Floor area and approval as living space are separate questions.

Try the [loft floor-area calculator](https://housemadness.app/en/calculators/loft-floor-area/) with your knee-wall height, roof pitch and room dimensions. This article explains the **Norwegian** measurement rule; English is the language of the guide, not a claim that the same rule applies in the UK, US or elsewhere.

## The three measurements you need

| Measurement | What to record | Why it matters |
|---|---|---|
| Knee-wall height | Vertical height from the loft floor to the underside of the sloping ceiling at the room's side | Sets the starting height |
| Roof pitch | Angle of the sloping ceiling above horizontal | Determines how quickly height increases towards the ridge |
| Internal width and length | Dimensions inside the room's enclosing walls | Sets the available footprint |

Measure the space that will actually exist after the conversion. Insulation, linings and a new floor build-up can change the usable geometry. An old drawing is a useful starting point; check its dimensions against the house.

For planning floor area under TEK17 § 5-4, DiBK's current guidance still refers to **NS 3940:2012**. Qualifying unfinished loft space can count even without windows, insulation or an installed floor. Do not substitute an estate agent's sales-area figure for a project-specific measurement. Check the measurement basis with the person preparing your application.

## A worked example: 8 m wide, 10 m long, 40° roof

Assume a simple, symmetrical roof with no dormers or openings:

- Width inside the two knee walls: **8.00 m**.
- Length: **10.00 m**.
- Knee-wall height: **1.00 m** on both sides.
- Roof pitch: **40°**.

The ceiling must rise another 0.90 m to reach 1.90 m. For a straight roof slope, the horizontal distance from each knee wall to that height line is:

**Distance = (1.90 − 1.00) ÷ tan(40°) = 1.073 m.**

The area boundary lies 0.60 m farther out towards the knee wall. It is therefore **0.473 m** from each side. The qualifying central width comfortably exceeds 0.60 m.

**Measured width = 8.00 − 2 × 0.473 = 7.055 m.**

**Area within those boundaries = 7.055 × 10.00 = about 70.5 m².**

For comparison, only about **58.5 m²** of this rectangular room has a height of at least 1.90 m. The difference is the strip included on each side by the measurement rule. It is useful floor space for low furniture, but it is not standing-height space.

This is a geometry example for an empty rectangular loft. A formal BRA calculation must also handle the actual enclosing construction, internal walls, stairs and openings under the applicable measurement standard.

## What happens when the roof pitch changes?

Keeping the knee wall at **1.00 m**, these distances apply on each side of a straight roof:

| Roof pitch | Knee wall to 1.90 m height line | Knee wall to outer area boundary |
|---|---:|---:|
| 30° | 1.56 m | 0.96 m |
| 35° | 1.29 m | 0.69 m |
| 40° | 1.07 m | 0.47 m |
| 45° | 0.90 m | 0.30 m |

The last column cannot become negative: the boundary stops at the wall. If the knee wall itself is already at least 1.90 m high, this simple roof geometry does not create a low strip to exclude. Dormers, uneven slopes and changes in floor level need their own sections.

## Does the loft also meet the room-height rules?

Norway's TEK17 § 12-7 distinguishes different situations:

| Project | Starting point for room height |
|---|---|
| New room for permanent occupancy | 2.40 m |
| Change from ancillary space to main space within an existing dwelling | 2.20 m under the applicable guidance |
| Eligible change of use in a dwelling applied for before 1 July 2011 | A reduced 2.00 m route may apply |

Sloping portions can be lower where the room's intended function still works. The older-home route has additional conditions; it does not cover every old attic. DiBK describes, among other things, a room within the dwelling that adjoins existing living space. The **1.90 m area threshold does not replace these requirements**.

Check daylight, ventilation, escape, access and the existing floor's structural capacity separately. A generous measured area cannot resolve a missing escape route or an unsuitable structure.

## Do you need a building application in Norway?

Turning approved storage space into a bedroom is a **change of use** and requires an application. Some qualifying conversions within an existing dwelling can be applied for by the owner. Confirm eligibility and the approved use with the municipality before relying on that route.

Structural roof changes, such as a dormer or raising the roof, generally require an application and assessment against the relevant TEK17 requirements. Plan the roof, stair opening and supporting structure together. The [stair-rules guide](https://housemadness.app/en/articles/stair-rules-norway-sweden-denmark-germany/) explains why a stair that fits in plan can still lack headroom.

## Try the shape before commissioning the work

**We make House Madness.** In the app, you can create the loft from the floor below, set the knee walls and roof pitch, and compare the plan with the 3D model. Use the [loft tutorial](https://housemadness.app/en/help/lofts-and-knee-walls/) and [dormer and roof-window tutorial](https://housemadness.app/en/help/dormers-and-roof-windows/) to test alternatives. Drawings and area estimates help explain the proposal; the project still needs the appropriate measurements, design and approvals.

Start with the [calculator](https://housemadness.app/en/calculators/loft-floor-area/), then [draw your house](https://housemadness.app/app/). Save a section showing the knee-wall height, roof pitch and height lines so the assumptions are easy to review.

## Frequently asked questions

### What is Norway's 1.90 m rule for loft floor area?

A loft needs at least 1.90 m clear height over a width of at least 0.60 m to qualify for measurement. Under a sloping roof, the measured area extends another 0.60 m horizontally beyond the 1.90 m height line, stopping at the enclosing wall. This is an area rule, not permission to use the loft as a bedroom.

### What is a knee wall?

A knee wall is the low wall where the sloping ceiling meets the side of the loft room. Its height and the roof pitch determine how far into the room you must move to reach standing height.

### Does a 1.90 m ceiling make a loft suitable as living space?

No. Floor-area measurement and approval as living space are separate questions. Norway's room-height, daylight, ventilation, escape and structural requirements must also be assessed for the particular conversion.

### Do the Norwegian loft area rules apply in other countries?

No. This guide explains Norwegian rules. Choose the appropriate country in the calculator and check the local measurement and building rules before using the result elsewhere.

## Sources

1. [DiBK: TEK17 § 5-4, floor area and measurement guidance (Norwegian)](https://www.dibk.no/regelverk/byggteknisk-forskrift-tek17/5/5-4)
2. [DiBK: TEK17 § 12-7, room height (Norwegian)](https://www.dibk.no/regelverk/byggteknisk-forskrift-tek17/12/ii/12-7)
3. [DiBK: Change of use in older homes (Norwegian)](https://www.dibk.no/bygge-eller-endre/bruksendring-i-eldre-boliger)
4. [DiBK: Work on load-bearing structures (Norwegian)](https://www.dibk.no/bygge-eller-endre/arbeid-pa-eksisterende-bygg/barende-konstruksjoner)

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