Wood was the most widely-used material for ceilings and floors until the early 20th century. The ends of the joists, laid with a 12-15 centimetre bearing, must be protected from water, so there is no direct contact with the rest of the structure. A 2-3 centimetre air gap is kept at the end of the beam, under which a supporting sill or insulation board is placed. The ceiling material also requires fungicide and insect-proofing. These structures have a high fire-risk rating, and a further disadvantage is their low sound insulation performance. However, they are characterised by low dead weight and quick assembly work due to the prefabricated elements. Another advantage is the favourable thermal performance.
I.Traditional timber joist ceiling
1. Timber joist ceiling with densely-spaced joists (Timber ceiling with pegged log joists)
The beams, split and trimmed from whole logs, are placed directly adjacent and connected by hardwood dowel pins or wedges every 1.5 (1.5!) to 2 metres, creating a slab with an extremely heavy load-bearing capacity. There was no need to trim the upper part of the beams, which remained circular. Above this, an earth filling and a subfloor could have been made.
2. Timber joist ceiling with sparsely-spaced joists
a) Exposed timber joist ceiling and floor system
When making an exposed timber joist ceiling system, the beams are placed with an 80-100 centimetre axial span at the top of the wall. A double layer of decking is laid on the surface of the beams, often filled and clay-plastered.
b) Cladded joist ceiling and floor system
- The cladded joist ceiling system is an improved version of the exposed timber joist ceiling system. Here, the bottom surface is also decked.
- In a special cladded joist ceiling system, the flooring layers are drawn into the space between the joists to reduce the ceiling thickness. To do this, longitudinal lathing is done on both sides of the joists, and the decking supporting the floor is laid on top of this.
- The planked ceiling is a material-saving solution to the cladded joist ceiling system. The planks are placed more densely, at 40-50 centimetre intervals and are braced transversely with diagonal battens. The upper planking is made on the surface parallel to the beams.
In every case above, earth filling and a subfloor are made for the parquet above the upper decking. The mud plaster is applied and reinforced with a reed mat on the lower surface.
II. Modern wooden ceiling joists
Modern wooden ceilings are timber joist ceilings with sparsely spaced joists. The cross-section of the joists can be varied and typically assembled from laminated glued elements bonded together. Joist spacing depends mainly on the span and size of the joists' cross-section: it varies from 40-50 centimetres to 80-100 centimetres axis spacing, considering the level of use.
The attachment method can include anchor studs, steel pockets, or anchor rails combined with angle bars. In all cases, the receiving elements must be carefully positioned and adjusted before the reinforced ring beam is poured. The ends of the wooden joists must have at least 15 centimetres of bearing width and be protected against moisture with insulating boards.
