The service cavity lining is the last layer of a wall or roof on the room side. It protects the airtight layer from holes, carries the services and decides how the wall “breathes”. It can be plasterboard — or a wood fibre board finished with lime or clay.
What the service cavity lining does
In a timber house or an attic room the layers from inside out are: lining, batten layer, airtight layer, insulation between the studs or rafters, and an outer board. The batten layer between the lining and the airtight layer is the service cavity — in German Installationsebene.
- It protects the airtight layer. Cables, electrical boxes, pipes and shelf plugs go into the cavity between the battens and do not pierce the layer behind it.
- It carries the lining. Battens of 30–50 mm at about 40 cm centres, with the lining screwed to them.
- It shapes the indoor climate. The lining is the first thing room moisture reaches. Plasterboard lets it through but hardly stores it. Lime, clay and wood fibre take it up and release it again.
A naturheld board instead of plasterboard
Instead of plasterboard, a wood fibre board naturheld 220, 22 mm, n+f, can be screwed to the battens. It is finished with a reinforcing mesh and a lime or clay skim — for example a few millimetres of FIRNA lime skim — and a lime paint.
- It adds insulation. 22 mm of wood fibre at λ 0.047 W/mK is an extra layer that plasterboard does not give. You can compare both linings for your wall in the construction generator.
- It buffers humidity. Lime, clay and wood fibre take moisture from the air when there is a lot of it and give it back when the air dries.
- A heavier wall. The board is heavier than plasterboard, which helps sound insulation.
- No gypsum. The whole construction stays timber, wood fibre and mineral plaster, and remains vapour-open.
Airtight inside — but with a way out for moisture in both directions
Two things must hold at the same time. First, the construction must be airtight on the inside: warm room air carries a lot of moisture, and if it gets into the insulation through a gap, the moisture condenses where it gets cold. Second, the construction must be able to dry: the little moisture that does get in has to get out — to the outside in winter and, in summer, when it is warm outside and the sun heats the wall or roof, back to the inside.
That is why we recommend one of these three options on the inner side of the service cavity:
| Inner layer | Vapour resistance | How it becomes airtight |
|---|---|---|
| ELKA esb Plus, 15 mm, n+f | Moderate: sd ≈ 0.6–1.2 m (µ 40–80) | Joints and penetrations are taped |
| Membrane Isocell AIRSTOP DIVA | Variable: sd 0.5–30 m — tight in dry winter air, open in humid summer air | Overlaps and junctions are taped with AIRSTOP tape |
| A naturheld board only, n+f | Low — the board is vapour-open | Every joint, junction and penetration is sealed |
With all three, vapour can move in both directions. ESB and DIVA slow it down enough in winter but do not close the construction. When the airtight layer is the naturheld board alone, it must be n+f, and every joint, every junction with a wall, window or ceiling and every penetration for a cable or pipe must be sealed. The construction must then also be vapour-open on the outside — with an outer wood fibre board — and it is worth checking it for condensation in the generator or writing to us.
Why we do not rely on a vapour-closed system
A vapour-closed construction has a foil on the inside that stops vapour almost completely (for example PE foil, sd 100 m and more), and often another tight layer on the outside — OSB or a bituminous membrane. On paper almost no moisture passes through such a foil. In practice the problem is not the vapour that passes through the foil, but the air that passes around it.
- The membrane often gets pierced. Staples, cables, boxes, a torn overlap, a shelf fixed later — however careful the installers are.
- Far more moisture comes in through a hole than through the membrane. Research by Fraunhofer IBP shows that moisture carried in by air through leaks is the main risk even in carefully sealed timber constructions. That is why DIN 68800-2 requires lightweight timber constructions to have an extra drying reserve of 250 g/m² — precisely for moisture from leaks.
- In a closed construction this moisture stays. A foil that keeps vapour from getting in also keeps the moisture from drying towards the room in summer. If there is a tight layer outside too, the moisture builds up in the insulation and the timber — mould, rot, lost insulation.
- In an open construction it dries out. With ESB or DIVA inside and a wood fibre board outside (sd about 0.2–0.5 m), moisture from a hole dries to the outside in winter and to the inside in summer. A workmanship error does not become damage.
Fraunhofer IBP’s recommendation is short: build timber constructions as vapour-tight as necessary and as vapour-open as possible. That is why we offer ESB or DIVA rather than PE foil.
How it is built
- Airtight layer. ESB Plus with taped joints or a DIVA membrane with taped overlaps, also taped to the adjoining walls, floor, ceiling and windows.
- Batten layer. Battens 30×50 mm at about 40 cm centres. Cables and boxes run in the cavity.
- naturheld 220 board, 22 mm. Screwed to the battens with wide-head screws, n+f, with staggered joints.
- Plaster. Reinforcing mesh and a lime or clay skim, then lime or clay paint. No dense paints, wallpaper or vinyl that would seal the surface.
Quantities for a wall or roof with this lining come out of the construction generator, and prices are in the price list. If you would like help with your construction, write to us.
Questions
What is a service cavity lining?
A batten layer, usually 30–50 mm, fixed on the room side of the airtight layer, with a lining in front of it. Cables, boxes and pipes run in the cavity between the battens without piercing the layer that stops the room air.
Can plasterboard be replaced with a wood fibre board?
Yes. A naturheld 220 board (22 mm, n+f) is screwed to the battens and finished with lime or clay plaster on a mesh. It adds a little insulation, takes up and releases moisture, makes a heavier wall with better sound insulation, and contains no gypsum.
Do I need a vapour barrier in the service cavity?
You need an airtight layer that also slows vapour down, but not completely. We recommend ELKA esb Plus with taped joints or the moisture-adaptive Isocell AIRSTOP DIVA membrane (sd 0.5–30 m). If the lining is only a naturheld board, it must be n+f and every joint and penetration must be sealed.
Why not a PE foil that stops vapour completely?
Because in practice the membrane often gets pierced — by staples, cables, shelves and later repairs. Humid air gets in through the hole. If the construction is closed to vapour, that moisture stays inside. If it is open, it dries out to the outside or the inside.