LPH 5 in heritage protection: Why detailed design in existing buildings is a prerequisite, not a luxury
The design shows where a project is meant to lead. Whether it will actually work in the long term, however, is often decided only in the detailed design. In heritage protection in particular, LPH 5, the fifth service phase of the German fee scale for architects (HOAI), is therefore not a nice-to-have but a central prerequisite for quality, construction process and cost control.
In existing buildings, after all, almost nothing is truly standard. Junctions between old and new, irregular geometries, varying wall build-ups and sensitive historic building components cannot be addressed with blanket solutions. Anything that has not been properly thought through in planning is decided later on the building site, usually under time pressure, with makeshift solutions and often at considerably higher cost. As an architecture practice in Wiesbaden specialising in heritage protection, fbnSTUDIO knows from experience: in existing buildings, detailed design is the economically most important phase of the entire project.
What is detailed design (LPH 5) and why is it so important in existing buildings?
Detailed design translates the approved design into concrete, buildable solutions. It comprises detail drawings at large scales, material specifications, construction details and the coordination of all technical trades. In new builds, many details can be derived from recurring standards. In existing buildings, and especially in listed buildings, that is different. Here, new requirements meet existing fabric that is often neither square nor uniform and cannot be planned for in full.
That is exactly why detailed design is so important. It answers the questions the design leaves open: how do new building components connect to historic structures? How are transitions formed without causing damage, thermal bridges or unnecessary interventions? How can technical requirements be integrated without burdening the fabric more than necessary? The earlier these questions are answered properly, the lower the likelihood that decisions will later be improvised on the building site.
Why is quality in listed buildings decided in the detail?
In heritage protection in particular, the quality of a project is rarely evident in the broad lines alone. It shows where materials, constructions and requirements meet. A junction that remains open on the drawings is no minor matter on the building site. It becomes a question of cost, a question of time and, in case of doubt, also a question of whether the building will function without damage in the long term.
This concerns not only visible details, but also interrelationships in building physics, technical systems and fire protection. Good detailed design therefore means not postponing these interfaces, but planning them in advance so that execution and the existing building fit together. The details fixed in LPH 5 determine the quality of the finished building for decades.
Which detail traps occur most often in existing buildings?
Many problems in old buildings and in heritage protection arise at similar places again and again. Anyone who knows these typical traps can defuse them in a targeted way in the detailed design.
Internal insulation: Building physics decides between success and damage
A classic issue is internal insulation. It can make sense, but it works in the long term only if junctions, transitions and building physics relationships are properly taken into account. Without precise planning, the risk of moisture damage and later defects rises considerably. Particularly critical are the beam ends of timber joist floors, window reveals and internal walls that tie into the external wall. These details must be resolved in the detailed design, both in drawings and in terms of building physics, before the tender begins. You can read more about the risks in our article on energy-efficient refurbishment of listed buildings.
Windows: The installation decides, not just the component
Windows are similarly sensitive. It is not the component alone that decides, but its installation. Without a clear installation concept for airtightness, junction details and the handling of thermal bridges, weak points quickly arise that can only be corrected later at great expense. Especially with upgraded historic windows or box-type window solutions, the detailed planning of the installation is decisive for long-term function.
Bathrooms and kitchens: The service routing strategy is decisive
Bathrooms and kitchens, too, are often underestimated in existing buildings. It is not enough here to specify taps and sanitary fixtures. What is decisive is the service routing strategy. Where do the installations run? How can they be integrated without needlessly damaging historic fabric? And how can interventions be planned so that use and the existing building come together? Well-thought-out service routing makes use of existing shafts and installation zones and minimises interventions in building components of heritage value.
Fire protection: Planning too late gets expensive
Another typical point is fire protection. If it is taken seriously too late in the detailed planning, costly retrofits, elaborate redesigns or compromises that could actually have been avoided often follow. In listed buildings, fire protection is particularly demanding because standard solutions such as full-surface cladding often conflict with the heritage value. The detailed design must develop building-specific solutions here that combine safety with the preservation of the fabric.
How does detailed design reduce conflicts on the building site?
The more precisely planning is done in advance, the less has to be decided on site under pressure. In existing buildings in particular, this is a great advantage. After all, building sites in heritage protection are rarely as predictable as a standard new build. Surprises cannot be avoided entirely, but their extent can be reduced considerably.
Good detailed design provides the basis for this. It ensures clearer details, more comparable tenders, more reliable bids and a more logical construction schedule. When it is clear how junctions, transitions and technical integration are to be resolved, the number of queries, improvised solutions and change orders falls. For clients, this means above all more overview. Not because everything in an existing building suddenly becomes certain, but because risks become visible earlier and easier to manage.
How are detailed design and tendering connected?
The quality of the detailed design directly determines the quality of the tender. Only when details, materials and constructions are precisely specified can bills of quantities be drawn up that reflect the actual effort involved. Unclear or incomplete detailed design leads to bills of quantities with room for interpretation, and on the building site that room is almost always resolved at the client's expense.
In existing buildings, the contractors carrying out the work must also understand the particularities of the building from the documents. Detailed design that documents the existing building precisely and shows the transitions between old and new unambiguously enables contractors to price realistically. The result is more reliable bids, fewer speculative surcharges and a considerably lower rate of change orders during the construction phase.
What do clients actually gain from good detailed design?
In existing buildings in particular, the value of detailed design is often underestimated because, at first glance, it is less visible than the design or the fit-out. In fact, it is one of the economically most important phases of the project. The advantages can be named specifically:
- Fewer change orders, because more decisions are made in advance and the contractors carrying out the work price on a clear basis
- More comparable bids, because the works are described precisely and not every contractor has to make its own assumptions
- A better construction process, because the dependencies and sequences of the trades have been prepared
- Fewer conflicts on the building site, because fewer decisions have to be made under uncertainty
In this way, good detailed design does not only avoid problems during execution, but often saves money before it has even been spent. The investment in a precise LPH 5 generally pays for itself through the change orders avoided.
Why is experience in LPH 5 especially important?
It is in detailed design in particular that the value of experience in dealing with existing buildings and heritage protection becomes apparent. Anyone who regularly accompanies such projects recognises early where details become critical and where seemingly small decisions have major consequences for costs, construction process and quality.
At fbnSTUDIO, we bring many years of experience to this. We know that good detailed design in listed buildings does not consist of transferring standard details, but of developing suitable solutions for the specific building. That is why we start early at the right levers: the junctions between old and new, areas that are sensitive in terms of building physics, service routing, fire protection and the coordination of all the trades involved. In this way, many problems can be identified before they become expensive on the building site. Projects such as the refurbishment of the cultural monument V12 in Wiesbaden show how precise detailed design works in practice in listed buildings.
Detailed design in heritage protection: A prerequisite, not a luxury
In heritage protection, detailed design is not a luxury but a prerequisite for a project that works. LPH 5 is the phase in which a good design is turned into buildable, durable and coordinated solutions. Good detailed design saves money before it is spent and reduces change orders, conflicts and improvisation, especially in old buildings, conversion and heritage protection.
Arrange an initial consultation with fbnSTUDIO. We prepare the detailed design for your existing-building or heritage protection project in Wiesbaden and the Rhine-Main region and ensure that your project is convincing in its details as well.
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