Building an earthquake-safe home in Nepal: what the building code requires
What Nepal's National Building Code means for an ordinary family home, from column sizes and steel detailing to building shape, with the common shortcuts that make houses unsafe.
Kathmandu Valley sits in one of the most active earthquake zones in the world. After 2015, most families know a house has to be built to resist shaking. Fewer know what that actually means on site, or that the government has written it down in detail.
For ordinary homes, the key document is NBC 205:2024, the ready-to-use detailing guideline for low-rise reinforced concrete buildings. It replaced the 1994 “mandatory rules of thumb” and is based on the current seismic design code, NBC 105:2020. It gives ready-made sizes and steel details for columns, beams, slabs and footings, so a two- or three-storey house can be built safely without a full structural analysis.
In short: if your house fits the limits below, NBC 205 tells you exactly what to build. If it doesn’t, the house must be designed by a professional structural engineer.
Does your house fit NBC 205?
The guideline covers ordinary residential RC frame houses only, and only if every one of these is true:
| Limit | NBC 205:2024 requirement |
|---|---|
| Use | Normal residential only |
| Height | Up to 3 storeys or 12 m, whichever is less (plus a small stair cover or penthouse of up to 25% of a typical floor, no taller than 2.4 m) |
| Storey height | No more than 3.2 m, and no upper storey taller than the one below |
| Grid | 2 to 6 bays each way, each bay 2.1–4.5 m, panels no larger than 13.5 m² |
| Size | No side longer than 25 m, and ground coverage no more than 1,000 sq ft |
| Shape | Rectangular, length no more than 3 times the width, with only small wings |
| Columns | Vertical and continuous on the same line down to the foundation |
| Cantilevers | No more than 1 m, with nothing but a parapet built on them |
| Foundation | At one uniform level |
| Site | Not water-logged, filled, landslide-prone, on a river bed or on a slope that needs a step-back building |
Bigger houses, commercial buildings and anything with an irregular shape need a site-specific design by an engineer to NBC 105:2020.
Shape matters as much as steel
Plenty of steel can’t save a house with the wrong shape. NBC 205 rules out the common culprits:
- Soft storeys. A ground floor left open for shops or parking, with solid walls above, is much weaker than the floors over it. The code defines a soft storey as one with less than 70% of the stiffness of the storey above, and NBC 205 doesn’t allow any irregularity.
- Floating columns. A column that starts on a beam instead of running down to the foundation can’t carry earthquake forces safely.
- Heavy cantilevers. Rooms built out over a cantilevered slab add weight exactly where the structure is weakest. Keep projections to 1 m with only a parapet on them.
- Odd shapes. L, T and U-shaped plans twist during an earthquake. NBC 205 only covers rectangular plans with small wings.
- Extra floors later. Adding a storey the frame wasn’t designed for is one of the most dangerous things you can do to a house.
Member sizes: bigger than you might expect
The minimum sizes in NBC 205:2024 are a big step up from older habits:
| Element | NBC 205:2024 |
|---|---|
| Columns | 350 × 350 mm, or 400 × 400 mm depending on storeys, soil and seismic zone |
| Plinth beam | 250 mm wide × 355 mm deep |
| Floor beams | 250–300 mm wide × 355–380 mm deep including the slab |
| Slabs | 125 mm (5 inch) |
| Stair waist slab | 150 mm (6 inch) |
| Isolated footings | 350–400 mm thick, sized to the soil from the code’s tables |
| Plinth level | No more than 450 mm above ground |
The old 9 × 9 inch (230 mm) column falls far short of a 350 mm column. If someone suggests it for a new house, ask which code they are using.
The guideline also sorts sites by soil. Kathmandu, Lalitpur, Bhaktapur, Madhyapur Thimi, Kageshwori Manahara and Tokha are all treated as soft-soil sites (site type D). The code’s tables give their footing sizes and column steel separately from firmer sites, so make sure your engineer uses the right ones.
Steel and concrete
- Concrete: at least M20, a 1 : 1.5 : 3 mix that reaches 20 N/mm² at 28 days on a 150 mm cube, for every footing, column, beam and slab.
- Steel: Fe500 TMT bars to Nepal Standard NS 191, preferably Fe500D, with elongation above 15%. Fe415 is allowed only for sill and lintel bands.
- Bars must be clean: no loose rust, mill scale, paint or oil that would weaken the bond with concrete.
The details that save lives
These are the details we see missed most often on Nepali sites, and the ones inspectors look for:
- 135° hooks on every tie. Column ties and beam stirrups must end in a 135° hook that bends back into the core, with a tail at least 6 bar diameters long (and never less than 65 mm). A 90° hook can open up in an earthquake and let the column burst.
- Closer ties near joints. In the code’s column details, ties are 8 mm bars at 75 mm spacing near the top and bottom of each storey, opening to 125 mm only in the middle. Joints are where columns fail, so this is not the place to save steel.
- Laps in the right place. Column bars may only be joined in the zone shown in the code, never at a beam-column joint. No more than half the bars may be lapped at the same level, and each lap must be at least 57 bar diameters long.
- Enough cover. Keep 40 mm of concrete outside the ties in columns, and 50–75 mm in footings, so the steel can’t rust.
- Proper footings. Dig at least two test pits to 1.5 m to see the soil before deciding the footing size. All plinth beams sit on a toe wall, and eccentric footings at the boundary need a strap beam.
Walls and masonry
- Bricks with a crushing strength of at least 3.5 N/mm², ideally the standard 230 × 115 × 57 mm size
- Half-brick walls in 1 : 4 cement-sand mortar, full-brick walls in 1 : 6
- Bricks soaked before laying and every joint fully filled
- Plaster no leaner than 1 : 6
What to ask your builder
- Which NBC 205 tables are your column, beam and footing details taken from?
- Is this site treated as soil type D, and for which seismic zone?
- Will every tie have 135° hooks, and where will the column bars be lapped?
- What concrete grade and steel grade are you using, and can I see the NS mark and test certificates?
- Who will check the steel before each pour?
A good engineer or contractor will answer all five without hesitation.
Sources
- NBC 205:2024 Ready-to-Use Detailing Guideline for Low Rise Reinforced Concrete Buildings without Masonry Infill, Department of Urban Development and Building Construction (DUDBC). Every limit, size and detail above comes from this guideline; a full copy is also published by Koshi Province.
- NBC 105:2020 Seismic Design of Buildings in Nepal, DUDBC
- Building Act, 2055 (1998), Ministry of Urban Development
This article explains the code for homeowners. It is not a structural design. Your engineer must choose the exact sizes and steel from the code’s tables for your site.