Ceilings & suspended ceilings

Ceiling insulation with a suspended ceiling: thermal insulation, EI fire resistance and sound insulation in the cavity

Last updated: 15 October 2026

It starts by setting out the performance we require and shows where the insulation goes, where the vapour barrier goes, and why spotlights and roller blinds mou

The system at a glance

Solutions & Applications · Roof Insulation

The cavity above a suspended ceiling is usually filled with air — and air does not insulate, does not stop fire and does not block noise. With stone wool in the cavity and the correct boarding, the same construction provides thermal insulation, fire resistance up to EI 120 and sound insulation towards the upper floor all at once. The question is not whether to install insulation, but which of the three performance characteristics we require — because each one alters the composition.

What performance are we looking for?

Performance	When does it make sense?	What determines it
Thermal insulation	The roof separates heated from unheated spaces: beneath a flat roof or pitched roof, above a porch, beneath a loft	Thickness and l of stone wool, continuous without gaps, vapour barrier on the warm side
Fire resistance	Fire protection design, escape routes, protection of the load-bearing structure	Certified layout: type and layers of boarding, frame spacing, insulation density, penetrations
Sound insulation	Intermediate floor, noise from above or towards the upper storey	Board mass, void filling, elastic suspension, perimeter tape

On a mezzanine floor with heated spaces above and below, stone wool is installed for sound insulation and fire resistance — not for thermal insulation. The choice of material and thickness starts here.

Fixed or accessible roof

	Closed plasterboard	Viewable 60×60
Surface	Seamless, with no visible joints — can be painted	Visible battens
Fire resistance	Up to EI 120 with a certified system	Limited — depends on the specific system
Upward sound insulation	High-density boards and sealed joints	Fair — the joints between the slabs allow water to leak through
Access to the vacancy	Access via service hatches only	Complete, in every detail
Where is the insulation installed?	Above the plank, between the guides	Fixed to the concrete slab or self-supporting above the battens

Where there are valves, air-conditioning units or electrical connections above the ceiling that will require maintenance, a suspended ceiling requires carefully planned access hatches — designed from the outset, not cut out afterwards.

Insulation above an accessible suspended ceiling

This is the scenario that is most often dealt with in a slapdash manner: rolls of stone wool laid on top of mineral fibre boards. It works from a thermal point of view, but creates three problems:

Load: the slabs and the grid were designed to support their own weight, not an insulation layer laid on top.
Access: every time a slab is lifted, the insulation shifts and does not settle back into place correctly — the gaps increase with every maintenance operation.
Fibres and dust: the opening slab discharges material into the space below.

There are two correct solutions: the insulation is fixed to the concrete slab, leaving the cavity free for the services, or self-supporting slabs are used on an independent framework above the battens, which do not rest on the roof slabs.

The composition of the closed insulated roof

No.	Item	Point to note
1	Plasterboard — A, H2, DF, DFH2 or DFIR	The type defines the performance; for EI systems, the number of layers is also specified
2 · 3	CD 60×27 guides — primary and secondary	The step is determined by the load and the certified system, not by convention
4	Foam soundproofing tape	Beneath the perimeter profiles — breaks the thermal bridge to the masonry
5 · 6	Joint tape & joint filler	Complete filling in layers; the joint is the weakest point
7	TN screws	The length varies per layer of boarding
8	Anchor plug for concrete slabs	The type is selected based on the substrate — concrete, aerated concrete, composite
9	LB / LN sheet metal screws	Connecting metal components to one another
10	Direct-fix P, fastener, screw	The choice depends on the height of the gap
11	Stone wool	Complete coverage with no gaps; A1 non-combustible
12	Vapour barrier	Only where there is a temperature difference — always on the warm side

ARGYNET Note

In a certified EI system, the steps are not merely indicative. They form part of the test.

The fire resistance of a suspended ceiling is determined by testing the entire assembly: type and thickness of board, number of layers, stud spacing, suspension spacing, density and thickness of stone wool, and method of jointing. If the battens are spaced further apart to save money, the certification becomes invalid — and this fact is not apparent anywhere until the inspection takes place.

The same applies to penetrations: any light fitting, loudspeaker, vent or recessed spotlight that creates a hole in the fire-rated surface requires a correspondingly certified solution. An EI 120 ceiling with twelve recessed spotlights without protection is not EI 120.

Thermal insulation: continuity and water vapour

Stone wool only performs effectively when it provides full coverage: slabs in contact with one another, with no gaps around the fixings and without being ‘compressed’ by pipework. A gap of just a few centimetres around the entire perimeter negates a significant portion of its performance — and creates a cold zone where condensation forms.

Where there is a temperature difference — beneath a flat roof or above a porch — a vapour barrier should be considered. It must always be positioned on the warm side, that is, between the boarding and the insulation, towards the heated space. If positioned incorrectly, it traps moisture within the insulation.

Fire resistance: protection of the slab from below

The suspended ceiling protects the slab and the load-bearing structure from below. The combination of fire-rated boarding with non-combustible A1 stone wool delays the transfer of heat to the concrete — and the concrete, when heated rapidly, peels away and exposes the reinforcement.

Sound insulation: a distinction that is often misunderstood

Sound insulation to the floor above — airborne and, in part, impact sound. This is improved by the mass of the boards, filling the void and decoupling the framework from the slab using elastic hangers.
Sound absorption within a space — smooth plasterboard does not absorb sound. Where reverberation control is also required, perforated boards with a sound-absorbing backing are used.

And the one thing that ruins the whole job: the perimeter sound-insulating tape beneath the profiles. Without it, sound passes through the joint with the masonry, no matter how well the gap is filled.

The post covers everything

The weight of a double plasterboard cladding with stone wool is not negligible. The suspension system is selected based on the height of the void — direct P-type suspension for low heights, and quick-adjustment hangers or brackets for greater heights — and the fixing to the substrate. On composite floors and old concrete, the pull-out strength is checked on site.

Heavy light fittings, spotlights, loudspeakers and screens are suspended independently of the concrete slab, not from the framework. A load suspended from the beam deforms the surface and causes cracks in the joints.

ARGYNET Note

Roof insulation is installed only once. Once the roof is closed, any gaps, any unsealed penetrations and any incorrect positioning of the vapour barrier remain hidden until they manifest as mould, noise or a failure in the fire safety inspection. That is why the inspection is carried out before the last board is screwed into place.

At ARGYNET, we specify the system with its exact composition — boarding, framework, suspension, insulation and vapour barrier — and calculate materials per m².