Internal partition wall

Partition joints between adjoining buildings (e.g. semi-detached, terraced or block-of-flats) were rarely insulated until the 1960s; however, this is still commonly the case in buildings constructed in later years. Insulation improves both thermal and acoustic insulation in equal measure.
To reduce sound transmission, the partition walls separating neighbouring properties were often constructed with an air gap up to 10 cm thick even back then. However, draughts flowing through the joints and cracks, as well as air movement within the joint, lead to additional heat loss. Contrary to the assumptions made in many energy performance certificates, these are not ‘semi-detached’ or ‘terraced’ houses, each with only two thermally effective walls, but rather closely adjacent individual buildings with four walls that radiate heat.

Such houses are neither terraced nor semi-detached, but ‘detached’ individual buildings, as the air gap between them and the adjacent house is always subject to strong wind flow. This air gap can be easily eliminated entirely using blow-in insulation made of fibrous material.

How can I find out if my building has a building separation joint? All you need to do is look under the cover strip, which you can access by removing it.

How is it insulated?

1. The cover panel is removed.

2. An injection hose is inserted into the cavity and the cavity is completely filled with fibrous blow-in insulation.

3. Once the blow-in insulation has been installed, a cover is refitted and the joint is visually sealed on the outside. As air cannot pass through the joint at all, the cover does not need to be airtight.

Which insulation materials are suitable?

The products used must have the following properties:

for fire safety reasons: non-combustible/mineral-based
For moisture reasons: hydrophobic
to ensure the cavity does not eventually empty: non-free-flowing

This means that only fibrous blow-in insulation materials made from glass wool or rock wool are used.

Insulation thickness

The thickness of the insulation depends on the width of the partition wall joint. It is usually between 3 and 15 cm.

All the benefits at a glance

Improved thermal insulation: If the so-called heat transfer coefficient (U-value) of the wall separating the property from the neighbour’s was previously approx. 1.2 W/(m²K) (watts per square metre and kelvin), it is reduced to 0 once the partition joint has been insulated. This means that no heating energy is lost through the partition wall. From an energy efficiency perspective, two external walls become two internal walls.

This effect applies to both buildings! In other words, a single insulation measure simultaneously improves the energy efficiency of two walls and the adjoining living space.

What needs to be taken into account during the planning stage? The neighbour must be consulted before work begins and must give their consent – preferably in writing. As both parties benefit, it makes sense to commission and pay for these measures jointly.

Lower heating costs: The heating costs for both buildings are reduced by up to approximately 10 per cent each, depending on the proportion of the building’s surface area accounted for by the partition walls and the size of the air gap.

Further benefits:

Living comfort is enhanced due to higher temperatures on the inner surfaces of the external walls
Mould growth is prevented, as the inner surfaces of the external walls are warmer, thereby preventing condensation from forming in these areas
CO₂ emissions are reduced
Sound insulation from the neighbouring building is improved

Costs:

Depending on the size of the property and the complexity of the cover panel to be installed, the total cost of this individual measure can amount to up to €2,000. A major advantage here is that neighbours can share the cost of insulating the party wall between two houses.

Funding: The insulation of building partition joints is subsidised by the government by up to 20 per cent.

Can I install the insulation myself? No, blow-in insulation can only be installed by a specialist contractor. Simply ask your specialist contractor!

Download document:

Fördermittel - Bundesförderung effiziente Gebäude .pdf