Superimposed dead load, or SDL, is the permanent weight a structure carries on top of its own self weight: floor finishes, screed, ceilings, services, cladding and fixed partitions. It is dead load, but it is listed separately because it comes from the fit-out, not the structure. Added to the slab self weight, it gives the total floor dead load you enter into a takedown. StructLoads carries the combined dead load down once you set it.
Self weight versus superimposed
Dead load splits into two parts. Self weight is the structure carrying itself, the slab, beams and columns, computed from geometry and material density, as in concrete slab self-weight calculation. Superimposed dead load is everything permanent added on top. They are separated because self weight follows the structural design while SDL follows the architectural fit-out, so the two are estimated and revised independently.
What counts as SDL
SDL is the permanent, non-structural weight on a floor.
| Item | Typical contribution |
|---|---|
| Floor finish and screed | 0.5 to 1.2 kPa |
| Suspended ceiling | 0.1 to 0.3 kPa |
| Services (M and E) | 0.2 to 0.5 kPa |
| Fixed partitions allowance | 0.5 to 1.0 kPa |
Finishes and screed usually dominate. A heavy stone finish or a thick sand-cement screed pushes the SDL up quickly, while a thin carpet-on-slab build-up keeps it low. Ceiling and service allowances are smaller but add up. The way to pin the number down is layer by layer: Structural Basics’ dead load walkthrough sums a real build-up of 200 mm slab, insulation, perlite screed and floor finish to 7.16 kN per square metre, of which almost 2.5 is the superimposed layers sitting on the 4.7 of slab.
Typical values
A typical floor SDL lands around 1.0 to 2.0 kPa once finishes, a ceiling, services and a partition allowance are included. That is meaningful next to a slab self weight of around 3.75 kPa for a 150 mm slab, so the total floor dead load often reaches 4.5 to 5.5 kPa. The exact figure depends on the build-up and the material densities, which you can confirm from published concrete properties and finish weights.
Partitions: SDL or live
A fixed, permanent partition is SDL, counted by its real weight, for example a drywall partition at its known mass per square metre of wall. A movable or relocatable partition is usually covered by a live load allowance instead, because its future position is unknown. So the same physical wall can be SDL or live depending on whether it is permanent, a distinction also drawn in dead load vs live load.
How it enters the takedown
SDL is added to self weight to give the total floor dead load, a single pressure you apply across the floor. Over a 30 square metre interior column tributary area, a 1.5 kPa SDL adds 45 kN of dead load per floor on top of the slab self weight. That combined dead load then accumulates down the building and is factored. Keeping SDL in mind matters because it is easy to model the slab and forget the finishes, which under-loads every member.
Key takeaways: superimposed dead load
SDL is the permanent weight on top of the structure: finishes, screed, ceilings, services and fixed partitions, typically 1.0 to 2.0 kPa for a floor. It is dead load, separated from self weight because it follows the fit-out. Add it to self weight for the total floor dead load before the takedown. StructLoads carries the combined dead load as a preliminary figure a qualified engineer confirms.
Quick answers
What is superimposed dead load?
Superimposed dead load, or SDL, is the permanent weight added on top of the structure’s own self weight: floor finishes, screed, ceilings, services, cladding and fixed partitions. It is dead load, but it is listed separately from self weight because it comes from the fit-out rather than the structure. A typical floor SDL is around 1.0 to 2.0 kPa.
What is the difference between self weight and superimposed dead load?
Self weight is the weight of the structure itself, the slab, beams and columns, computed from geometry and material density. Superimposed dead load is the permanent weight added on top of it, finishes, services, ceilings and fixed partitions. Both are dead load; they are separated because self weight follows the structure and SDL follows the fit-out.
What are typical superimposed dead load values?
A typical floor SDL is around 1.0 to 2.0 kPa, covering finishes, a screed, a suspended ceiling and services, plus a fixed-partition allowance where applicable. The exact value depends on the build-up: a heavy stone finish or a thick screed pushes it up. Add the SDL to the slab self weight for the total floor dead load.
Is a partition a superimposed dead load or a live load?
A fixed, permanent partition is a superimposed dead load, counted by its real weight in the SDL. A movable or relocatable partition is usually covered by a live load allowance instead, because its position is not known in advance. So whether a partition is SDL or live depends on whether it is permanent or movable.