Building an earthquake-safer house

General information, not engineering or legal advice. Every building needs a design by a qualified engineer who has seen the site. Codes and municipal rules change, so confirm current requirements with your engineer and municipality.

Nepal sits in one of the world's most active earthquake zones. Most deaths in earthquakes come from buildings that collapse, and most collapses are preventable with sound design, good materials and careful construction. You don't need to be an engineer to insist on these things, but you do need to know what to ask.

The codes that apply

Nepal's National Building Code (NBC) sets the rules. The most important documents for houses are:

• NBC 105:2025, Seismic Design of Buildings in Nepal (second revision). It replaced the 2020 edition after approval by the Council of Ministers in 2082 BS. Its Annex C gives a seismic zone factor for every local unit; Kathmandu, Lalitpur and Pokhara metropolitan cities, for example, are at 0.35. It also lists Kathmandu Valley wards treated as soft soil (type D) unless tests show otherwise, which increases the design forces.
• NBC 205:2024, Ready-to-Use Detailing Guideline for Low-Rise RC Buildings without Masonry Infill. It is mandatory for the small, ordinary reinforced-concrete houses it covers: up to three storeys or 12 m, with a footprint of up to 1,000 sq ft. Anything larger or irregular needs a full structural design.
• Other parts cover masonry, earthen buildings, loads and construction safety. See DUDBC's list of NBC documents.

The Building Act 2055 requires everyone to build to the code, and municipalities check designs against it before issuing a permit.

Principles of an earthquake-safer house

1. Keep the shape simple and regular. NBC 205 requires a rectangular plan, with the length no more than three times the width, only small projecting wings, and no irregularity. L, T and U shapes, big setbacks and split levels twist and crack in an earthquake unless specially designed.

2. Columns go straight down to the foundation. Every column that resists earthquake loads must continue on the same line to the foundation. Avoid columns that start on a beam ("floating" columns).

3. Avoid a soft storey. A ground floor left open for parking or shops, with heavy walls above, is a common cause of collapse. If you need an open ground floor, your engineer must design for it.

4. Keep storeys even. NBC 205 limits each storey to 3.2 m and says an upper storey should not be taller than the one below.

5. Limit cantilevers. NBC 205 limits cantilever projections to 1 m and allows no walls (other than a parapet) on a cantilevered slab unless it is framed with beams.

6. Build on good ground. NBC 205 excludes waterlogged sites, filled ground, riverbeds and sites prone to landslides or rockfall, and steep slopes that need stepped buildings; these need a specific design and usually a soil investigation. Foundations should be at one level.

7. Size members properly. For the houses it covers, NBC 205 recommends columns of 350 mm or 400 mm square, plinth beams of 250 × 355 mm, floor slabs 125 mm thick, and footings 350 to 400 mm thick, with reinforcement from its tables. Smaller "9-inch" columns, still seen on many sites, are well below these sizes.

8. Detail the reinforcement for earthquakes. NBC 205 calls for:

• Closed stirrups with 135° hooks (hook length at least 65 mm), not 90° bends that open up in shaking
• Stirrups closer together near the ends of beams and columns, where damage concentrates
• Laps staggered, so no more than half the bars are spliced at one section, with adequate lap length
• M20 concrete (1:1.5:3) and Fe500 bars, preferably Fe500D

9. Use good materials and workmanship. Fresh cement, clean sand and aggregate, bricks of at least 3.5 N/mm², proper mortar, compacted concrete and proper curing. See Choosing cement, rebar, bricks and sand.

10. Don't add floors without a check. Adding a storey to a building not designed for it is one of the most dangerous things owners do. Get a structural assessment and a permit first.

11. Secure what can fall. Anchor rooftop water tanks and solar frames, keep parapets low and reinforced, fix tall cupboards to walls and secure gas cylinders.

Questions to ask your engineer

1. Which code documents is the design based on? Is it designed to NBC 105:2025, or does it use NBC 205:2024?
2. Which seismic zone factor and soil type did you use? Do we need a soil investigation?
3. Is the building regular? Any soft storey, floating columns or large cantilevers?
4. What are the column and beam sizes and the reinforcement? Is Fe500D specified?
5. Have you allowed for the water tank and any future floor? If future floors are not allowed, please put that in writing.
6. Will you inspect reinforcement before every pour? Will concrete cube tests be done?
7. Can I have the full structural drawings and design report for my records?

During construction

The municipality inspects at set stages, and DUDBC's Building Construction Guidance 2082 requires owners to attend an orientation on earthquake-resistant construction and expects masons and contractors to be trained in it. Ask your mason and contractor for their training certificates. Between municipal visits, your own engineer should check:

• reinforcement against the drawings (bar sizes, numbers, stirrup spacing and hooks, laps) before every pour
• concrete mix, compaction and curing
• that columns are vertical and in line from floor to floor

Take photos of reinforcement before it is covered and keep them with your drawings.

Existing buildings

If you are buying or living in an older house, look for warning signs: diagonal cracks around doors and windows, cracks at beam-column joints, exposed rusting bars, sagging slabs, or floors added later. An engineer can assess the building and advise whether retrofitting (strengthening) is possible and worthwhile.

Quick checklist

• Design by a registered engineer to the current NBC (NBC 105:2025; NBC 205:2024 for small RC houses)
• Simple, regular plan; columns continuous to the foundation; no soft storey
• Cantilevers no more than 1 m; storeys even
• Good ground, soil investigation where needed
• Adequate column sizes and earthquake detailing (135° hooks, close stirrups at ends, staggered laps)
• M20 concrete, Fe500D bars, good bricks and curing
• Reinforcement inspected before every pour; no unplanned extra floors