“As per IS code” turns up in a lot of BOQ lines for expansion joints. It is meant as a guarantee, and it reads like one, but it points at three different documents written for three different purposes, and none of them describes the product being bought. This piece sets out what each code is for, what it asks of a building joint, and the half of the joint that has to be written into the specification because no code covers it.

Check the edition in forceClause numbers and figures here are a working reference from the editions cited. Confirm them against the current editions before they go into a drawing or a specification. Where the joint goes and how wide it is are decisions for the structural engineer of record; a joint supplier checks a system against them and never originates them.
Which code covers which part of a building expansion joint Two blocks of a building, a low podium on the left and a taller tower on the right, separated by a full-height gap. IS 456 governs whether and where a joint is needed in the concrete frame. IS 1893 sets the width of the separation between the blocks. IS 3414 covers the design and installation of joints in buildings. The cover over the gap, with its movement class, traffic rating, membrane and fire barrier, is set by the project specification; no code specifies it. IS 456 whether and where a joint is needed IS 1893the separation width Your specification the cover: movement class, traffic, membrane, fire barrier IS 3414 the joint in the building Podium Tower
Which code covers which part of the joint. Schematic, not to scale.

The three codes, and what each is for

  • IS 456:2000, plain and reinforced concrete. The concrete design code. It decides when a frame needs to be broken by a joint.
  • IS 3414, joints in buildings. The code of practice for the design and installation of joints in buildings, and the document IS 456 refers the joint itself to.
  • IS 1893 (Part 1):2016, earthquake-resistant design of buildings. It sets the seismic separation between adjacent blocks, which in the higher zones usually decides the width of the gap.

What IS 456 asks

IS 456 deals with expansion joints in its clause 27. It looks at two situations. One is a structure whose plan changes abruptly: an L, a T or a U, or a long block meeting a short one, where the parts move in different directions and the corner takes the strain. The other is length. Practice in India has settled on a joint roughly every 45 m of continuous reinforced concrete, and IS 456 leaves the joint’s design to IS 3414.

The same code supplies two of the numbers that size a thermal joint. It gives the coefficient of thermal expansion of concrete as a range that depends on the aggregate, with 10 × 10−6 per °C the value normally used, and it takes a total drying shrinkage strain of the order of 0.0003 for design. On a 45 m bay those come to about 20 mm of thermal movement in Delhi NCR and about 13 mm of shrinkage over the life of the frame.

Read 45 m as a default to be checked. An exposed deck, a car park or a roof sees a wider temperature range than a shaded internal frame and wants joints closer together; a short building with an awkward plan may need one at a corner well inside 45 m. How far apart expansion joints should be goes through the four things that override the default, and how to calculate the gap works the arithmetic.

What IS 3414 covers

IS 3414 is the code of practice for the design and installation of joints in buildings. Where IS 456 says a joint is needed, this is the code it points to for how that joint is formed and closed.

We name it here and do not paraphrase its clauses. We quote only what we hold, and the clause-by-clause reading belongs with the edition on the structural engineer’s desk. A specification that cites “IS 3414” should still say, in its own words, what the joint must do. The code’s number alone does not tell a supplier the gap, the movement or the traffic.

IS 1893 and the seismic separation

IS 1893 (Part 1) divides India into four seismic zones, with zone factors of 0.10 for Zone II, 0.16 for Zone III, 0.24 for Zone IV and 0.36 for Zone V. For two adjacent blocks it sets the separation from their calculated displacements, multiplied by the response reduction factor R, so that the blocks cannot hit each other as they sway out of phase.

The multiplication is what makes the seismic gap large. For two 15-storey blocks in Zone IV, each with a calculated roof displacement of about 40 mm and R of 5, the separation is 5 × (40 + 40) = 400 mm, against about 20 mm of thermal movement for a 45 m bay in the same city. Once the seismic case applies, it sizes the gap and the thermal figure becomes a check. What the seismic zone changes works through it zone by zone.

What no code specifies: the cover

Between them, the three codes decide where the gap is and how wide it is. None of them says what goes over it. Six things about the cover have to be stated in the specification, because otherwise the cheapest product that fills the gap will meet “as per IS code” as well as the right one:

  1. The movement it must take, in millimetres, at each location, and that it has been cycled to prove it. ASTM E-1399 is the usual test: Class I for thermal movement, Class II for wind and Class III for seismic.
  2. The traffic over it, from people to trolleys, beds and cars. Data sheets give a rating per day for each kind of traffic.
  3. The finish height, so the joint sits flush with the floor and not proud of it or sunk below it.
  4. The membrane under floor and roof joints, and who laps it onto the waterproofing on each side.
  5. A fire barrier where the joint crosses a fire compartment line. We supply one on request, its rating confirmed per job.
  6. The fixing and the method statement: how the frame is bedded and anchored, and who installs it.

A BOQ line that meets the codes and the site

Keep the code references, then add a line per location that fills those six gaps. For a CPWD tender, the DSR items 5.44, 5.45 and 5.46 cover floor, wall and roof joints, and the DSR page shows what each item asks for and what it leaves out. For any other tender, the performance clause on each product page, and the one on expansion joint details and specification, turns the six points into requirements a substitute has to meet. For the whole subject in one place, see expansion joints in buildings.

Send us the drawingsWe return a joint schedule with every joint located, its gap, its calculated movement and the system that meets it, ready to sit under the code references in the tender. Get a joint schedule, or send the BOQ for a quote.
IS 456IS 3414IS 1893Expansion joint as per IS codeDesign stageSpecification