ᐅ HOAI Service Phases for Structural Engineering in Single-Family Home Construction

How strictly are the content requirements of the HOAI service phases followed in the structural engineering area for a single-family house? And to what extent does the structural engineer typically coordinate with the architect?

Background: For our construction project, I have received several structural engineering quotes – ranging from fixed lump sums to a full HOAI offer (€4,500–12,000 gross). Some structural engineers described service phase 5 for a single-family house as unusual and did not initially refer to HOAI. They only wanted to know some key basic information (construction method, foundation, number of floors, etc., rather superficially) and sent a fixed-price offer after a short time. However, our architect insists on structural engineering service phases 3/4/5 and is pushing for the appointment of his preferred firm according to HOAI. This makes me suspicious; I unfortunately get the impression that he is acting more in favor of the structural engineer and trying to secure him a contract.

What is the common practice in this regard?

The question is, how "complex" is your house? Special foundations, cantilevered ceilings without supports, and so on.
In such cases, the architect’s request is understandable. However, for a standard single-family house without any special features, I would be surprised and would simply accept a fixed-price offer.

The house is single-story with an open roof structure and will be built on stilts on a slight slope. However, none of the structural engineers considered this particularly challenging. Especially not the most affordable one, who has already handled several similar projects.
I am unable to assess how this normally works. The architect is heavily involved in securing the structural engineer, and since there are some conflicting statements about which service phases are actually required and which are not, I would be interested in your opinion.

Leiterwagen schrieb:

How strictly are the content requirements of the HOAI service phases followed in the area of structural engineering for a single-family house? And to what extent does the structural engineer typically coordinate with the architect? [...] What practice is common here?

The structural engineer is responsible for planning the stability of the building and its structural components. He guarantees—legally liable for his diligence—that the house will not collapse based on his calculations. His professional liability insurance becomes more affordable the more often “his” buildings actually do not fail. The better the coordination between architect and structural engineer, the more reasonably the house can be constructed. There are basically two common approaches here; I prefer Plan A: The architect and structural engineer engage in an exchange where they learn from each other, the architect designs realistic construction methods, and the structural engineer rarely has to say “no!” or “ouch, that’s going to be expensive.” The architect can gauge how challenging his design is for the engineer’s calculations. Plan B works so that the structural engineer applies higher safety margins as a precaution: the homeowner then pays with reduced ceiling heights due to thicker slabs, increased steel reinforcement, and consequently higher demands for concrete, steel, and the like. In other words, less intellectual input requires appropriate additional material usage.

Leiterwagen schrieb:

Some structural engineers considered service phase 5 for a single-family house unusual and did not even refer to the HOAI on their own initiative. They only wanted some core data (construction method, foundation, number of stories, etc., rather superficially) and sent a fixed-price offer after a short time. Our architect insists on structural engineering service phases 3/4/5 and pressures to commission his preferred office according to HOAI.

The work of the structural engineer typically covers service phases 3 to 5, whether they bill in detailed accordance with the official guideline or on a lump-sum basis. Of course, there are also discount providers among structural engineers who assume in their calculations that during service phase 3 they will be loosely involved—especially with architects who do not regularly cooperate with them—and in service phase 4 receive impractical dimensioning proposals from the architect, which they have to counter with the mentioned Plan B. To me, service phase 5 implies detailed formwork plans down to the exact quality of the tie wires for steel and fiberglass reinforcements—so I agree that for a standard single-family house, reinventing the wheel usually does not occur.

With a price range from 4,500 to 12,000 Euros (4,500 to 12,000), it may be that the “most expensive” engineer is a nitpicking perfectionist and will not save you the entire 7,500 difference in material costs. But whether the truth truly lies in the middle: 7,000?
The only well-established fact is: the less smooth the coordination between architect and structural engineer, the thicker the support columns become and the more likely it is that the construction inspector will struggle on site, as the site managers tend to dismiss the structural engineer’s plans as exaggerated. Good cooperation here is ultimately also beneficial for the client.

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11ant schrieb:

Good cooperation here is ultimately also beneficial for the client.

That is the key argument, thank you (also for the rest of the detailed response).