How should you approach insulating a flat in a tenement building from the inside?

It is worth preparing a simple description of the planned works with the location of the room and the layers. This will make the conversation with the designer and the building manager easier. If decorative mouldings or joinery need to be retained, this should be accounted for in the technical solution rather than relying on a chance fit after the insulation has been installed.

Old brick, various mortars and bricked-up openings make the building element less homogeneous than a new wall. Traces of former leaks may be present under the plaster. The ground-floor area, the wall below the cornice and the section next to the chimney require separate inspection. The whole flat should not be assessed on the basis of a single dry sample.

Before covering, the condition of the substrate, the moisture content and the sources of water ingress are established. Weak plaster may need to be removed or repaired. A tight layer on the interior side will change the drying behaviour of the wall, so the absence of visible mould alone does not confirm that the chosen system will be suitable.

In some tenement buildings the floor beams are embedded in the external wall. After internal insulation, the areas around their bearings may have different thermal and moisture conditions. This is an important detail that a calculator for a flat wall does not describe. An investigation of the structure and an assessment of its condition are needed.

Such places should not be covered without inspection. A more detailed analysis of heat and moisture flow may be needed, along with a solution tailored to the specific floor structure. Thicker insulation on the wall is not automatically more favourable for a timber element concealed in the wall.

Low thermal conductivity can help preserve the floor area of a small room. However, a board with an aluminium facing creates a system with high vapour resistance and requires airtight joints. The solution should follow from an assessment of the whole building element, not from the assumption that every old wall needs the same barrier.

Other modernisation methods can also be compared if the condition of the building requires it. The choice should take into account rain driving against the façade, moisture in the wall and the ability to dry out. The aim is to improve comfort without hiding the problem in an area that will be inaccessible after renovation.

In a tall room with wide window surrounds, insulation changes the proportions of the reveal. It is necessary to establish how it will connect with the frame, the sill and the internal cornice. Leaving a decorative band without thermal assessment can preserve a cold section, even though the whole wall will be new.

Before the work, measure the opening of the sashes and the position of the radiator. Also check the route of installations in thick plaster. A well-prepared detail allows the dismantling and reinstallation of equipment to be planned. Ad-hoc cutting of insulation around each retained element makes its continuity difficult.

Work in a flat is often carried out room by room. It is worth providing space for dry material and preparing a board layout that limits narrow offcuts. A format that is easy to carry up the stairs may prove more practical than a large element requiring cutting before entry into the premises.

The most important inspection takes place before the joints are covered. The perimeter of the wall, the reveals and the installation penetrations are checked in accordance with the design. Photographs together with a description of the materials used will help with later work. Heavy shelves should not be fixed solely to the insulation.

Replacing windows and new insulation can change the existing airflow. Ventilation must also function with the windows closed. In a flat with a kitchen and bathroom, vapour should not seek a path behind the boards through leaky sockets or ceiling terminations.

After renovation, observe the reveals, corners and places of previous damage. It is worth comparing humidity under normal conditions of use. The success of the work is evidenced not only by a more pleasant temperature at the armchair, but also by the absence of increasing dampness in critical details.