ᐅ From structural dimensions to clear ceiling height

Hello Forum,

this topic has been partially discussed in some posts, but I haven’t gained complete clarity yet, so here is my question again in my own words:


How do you correctly calculate from the shell dimension to the clear ceiling height?


Shell dimension:
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The construction module is 12.5cm (5 inches) = half a brick layer, so one brick layer in shell construction is 25.0cm (10 inches).

Accordingly, the shell dimension is
- for a current “standard” living room height 10.5 layers = 262.5cm (103.5 inches)
- for a current basement room height 10.0 layers = 250.0cm (98.5 inches)


Clear ceiling height:
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Clear ceiling height = shell dimension – ceiling – floor

Ceiling:
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The ceiling = raw ceiling slab + ceiling plaster + ceiling cladding (e.g. wooden ceiling)

From what I have read so far, you can roughly estimate:
Raw ceiling slab = 20.0cm (8 inches) (concrete ceiling)
Ceiling plaster = 1.5cm (0.6 inches)
Ceiling cladding = 3.0cm (1.2 inches)
That means:
- in living areas you need about 21.5 to 24.5cm (8.5 to 9.5 inches) for the ceiling
- in basements the ceiling is usually left unfinished (20cm / 8 inches)

But what if a central ventilation system is installed in the house?
The necessary ducts are usually routed inside the ceiling in new builds, which makes sense. From what I have read, spiral ducts offer the cleanest solution but have a diameter of 16.0cm (6.3 inches).

1. Does the concrete ceiling slab then need to be correspondingly thicker for structural stability: instead of 20.0cm (8 inches) then 36.0cm (14 inches)?


Floor:
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For the floor, it depends on whether there is underfloor heating or not:

* Floor without underfloor heating:
Floor = screed + impact sound insulation + floor covering

From what I have read, you can roughly estimate:
Screed: 5.5cm (2.2 inches)
Impact sound insulation = 2.5cm (1 inch)
Floor covering = 3.0cm (1.2 inches)
That means:
- in living areas the floor is 11.0cm (4.3 inches)
- in basements no impact sound insulation is needed, so it remains 8.5cm (3.3 inches)

* Floor with underfloor heating:
For the floor with no underfloor heating add the insulation layer with pipes for the underfloor heating = +6.0cm (2.4 inches)
That means:
- in living areas the floor is 17.0cm (6.7 inches)
- in basements no impact sound insulation is needed, so it remains 14.5cm (5.7 inches)


The clear ceiling height would then be
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* without underfloor heating and without central ventilation:
Shell height (living room) = 262.5cm (103.5 inches)
- Ceiling = 24.5cm (9.5 inches)
- Floor = 11.0cm (4.3 inches)
= Clear ceiling height = 227.0cm (89.4 inches)

* with underfloor heating and central ventilation:
Shell height (living room) = 262.5cm (103.5 inches)
- Ceiling = 24.5 + 16.0cm (9.5 + 6.3 inches)
- Floor = 11.0 + 6.0cm (4.3 + 2.4 inches)
= Clear ceiling height = 205.0cm (80.7 inches)


I’m not sure if this is correct …

2. Where am I mistaken, or is this actually correct in the end?
(If it is correct, I would have to increase the shell height to 302.5cm (119 inches) to achieve a clear ceiling height of about 250cm (98 inches))


Thanks and best regards

I believe your mistake is with the ceiling: when you say the ceiling = raw ceiling + ceiling plaster + ceiling cladding (e.g., wooden ceiling), you mean the total ceiling "thickness."

However, you cannot subtract this entire amount from the ceiling height, but only the plaster and the cladding. Otherwise, it would mean that you are building the ceiling downwards from the top edge of the masonry, which is not correct. The precast (concrete) ceilings rest on the brick courses. From that point on, your zero reference applies, and you would need to subtract a) the floor construction and b) the ceiling plaster and cladding from the shell construction height to get the correct measurement.

Your calculations are individual. For example, we have a total floor construction of 20cm (8 inches)! The ventilation ducts installed in the ceiling are not 16cm (6.3 inches) but only 7.5cm (3 inches) in our case.

On the ground floor, the raw structural height is 2.80m (9 ft 2 in), minus ceiling plaster and floor construction, leaving just under 2.60m (8 ft 6 in) of actual usable room height.