Quality assurance measures during (serial) renovation

Auther: Tanja Schulz

The thermally insulated and airtight building envelope must be designed with as few gaps as possible. With regard to the position of the insulation layer, there are several options in old buildings, which must be evaluated differently with regard to thermal bridge effects.

• Course of the insulation layer in the area of the cold cellar
• Course of the insulation layer in the area of the upper building closure: top storey ceiling or roof
• Dealing with the heated staircase in the area of the cold cellar and the unheated roof space

For the position of the airtightness layer, see the separate airtightness checklist.

• at the perimeter in combination with the basement ceiling
• at verge and eaves,
• at the transition of the façade element ─ to the top storey ceiling. Only provide fire protection plates in the rear ventilation space of the outer skin. They must not pass through the insulation level.

• Position of the supporting elements (timber frame) in the area of joints and transitions
• Optimization of the window installation (with and without external venetian blind box)
• Position and construction of the anchors
• Minimization of the weight of the refurbishment modules (timber content, clinker brick slips instead of clinker brick facing shell) to minimize anchorages
• The elements must be constructed in such a way that no gap remains between the existing wall and the element. This prevents convection in the gap and sound transmission.
• The windows should be connected to the façade element. This prevents sound and odour transmission. This applies regardless of where the airtight layer runs.
• Façade elements that already have the outer skin integrated as far as possible are advantageous. Scaffolding downtimes for completing the façade can thus be shortened or the scaffolding can be dispensed with altogether.

• Advice on insulating the heat distribution pipes in the ground
• Advice on the insulation and position of the heat distribution pipes within the façade elements (backpackers)
• Insulation and airtightness of external riser shafts (backpacker)

Smaller ventilation units with heat recovery can be easily integrated into the façade elements (backpackers). This allows them to be arranged outside the apartment to save space. From there, only ventilation ducts need to be routed into the apartments. Nevertheless, detailed planning must be carried out in advance for this air distribution ducts:

• The air distribution ducts must be planned in detail and, if necessary, in several variants for different apartment layouts so that the installation in the individual apartments can be carried out quickly and with as little inconvenience to the tenants as possible.
• It must be expected that tenants will have individual built-in furniture in their apartments, which must be taken into account when routing the air ducts. Tenants may be able to refuse the installation of ventilation. This can then only be done when the next tenant moves in. However, this is not detrimental to the concept because the ventilation units will simply not be in operation until then.
• The connections of exhaust air ducts from the bathroom, toilets and kitchen must be planned in detail. Silencers must be provided in the exhaust air ducts. Space in the bathroom and kitchen may be very limited in small apartments. Detailed planning is therefore particularly important.
• The supply air ducts are best routed directly from the appliance to the hallway of the apartments. In the hallway, the air ducts can be concealed behind a suspended ceiling if necessary. Sufficient silencers must be provided in the supply air ducts. Openings from the corridor into all living rooms and bedrooms must be defined in the planning. Only supply air valves from the corridor must be placed in the living rooms. No further ventilation ducts are required in the living rooms.
• Alternatively, the supply air and exhaust air ducts can also be routed on the outside wall in the newly installed wall elements during serial refurbishment. This means that air ducts in the apartments can be largely avoided. The air ducts run along the outer wall and each living space is equipped with a supply air or exhaust air element.
• However, the arrangement of the ventilation units and the ducts in the façade elements must be planned with particular care.
• The length of the warm supply air and exhaust air ducts in the outside wall elements must be kept as short as possible to minimize heat loss. This is because covering the air ducts with around 20 cm of thermal insulation is good. However, the remaining heat losses are noticeable and may significantly reduce the heat recovery rate.
• Even if the ducts are routed outside, individual flats may not remain connected for the time being: the ducts are laid and sealed at both ends. The pipes are only connected to the central ventilation units and the rooms when new tenants move in.

The experiences from some real construction projects are briefly presented here so that those problems mentioned can be avoided as far as possible in the future:

• The anchors of the façade elements are usually attached to the external wall in the area of the basement ceiling without much covering by thermal insulation. The thermal bridge optimization showed that the horizontal leg of the support angle should reach no further than the middle of the insulation level. Penetration of the insulation level with steel should therefore be avoided as far as possible.
• According to the original planning, the window was to be installed without over-insulating the frame and without a thermal break between the shutter box and the frame. With the help of thermal bridge calculations, it could be shown that this would have been unfavorable and that a significantly improved installation situation is possible and feasible. So just do it accordingly!
• Advice on window installation: If possible, the windows should be installed in the insulation level and not in the old position in the existing wall. The window frame should be additionally insulated to minimize the thermal bridge effect resulting from installation of the window.

If the planning has been optimized well, QA in the factory should be easy. Here it should be checked whether

• the windows or other openings are connected airtight (foil bonding, preferably no compression tapes), and
• the compartments of the prefab elements are completely filled with insulation material

Quality assurance on site is also required for prefabricated and quality-assured planned elements.

• The connections of the façade element to the base and verge or eaves should be checked carefully. If airtightness is achieved using adhesive tapes, care must be taken here to ensure careful processing. Particular attention must be paid to the correct preparation of the substrates and these must be checked.
• If the airtight layer is the existing plaster, the airtight connection of the window frames to the existing reveal must be ensured. This also applies if the airtight layer runs inside the element. The main reasons for this are sound insulation and the prevention of odor transmission from one apartment to another adjacent.
• When installing the elements, care must be taken to ensure that the airtight layer is realized without gaps. If necessary, repairs must be carried out immediately before the joints are no longer accessible.
• Probable cavities between the existing wall and the prefabricated modules must be completely filled with insulation. A layer of flexible mineral wool, which is already fitted to the element, has proven to be practical because it can flexibly compensate for the unevenness of the existing wall during installation.
• In the case of trade interfaces, it is important to provide temporary covers or protective measures, for example against rain during the construction period.

There must be given sufficient time for optimization between planning and execution. Subsequent changes to the planning during the production of the elements are particularly costly and time-consuming. When refurbishing several buildings or an entire quarter consisting of identical or similar buildings, it is desirable to carry out a single “pilot project” to test the functioning of the refurbishment concept before starting series production of elements for further refurbishment projects. It is desirable to check the geometrical measurements of the existing façade and the allocation of the later prefab elements several times. Even measurements created automatically (laser scan) can have logical errors and incorrect assignments that may not be recognized by the software. Practical experience has shown that façade elements were faulty and unusable (e.g. incorrect window position).

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