Cost comparison between a duplex and a single-family house realistic?

Hello dear forum members,

we are currently in talks with a developer for a single-family house. Friends of ours are building a semi-detached house together with another couple with this developer. They showed us their offer, which is 30,000 euros below our offer, which surprises me a lot since our house is smaller (8.356 x 10.5) than their house (11 x 9 m) and they even have an extra attic with knee walls of 75 cm, which of course means more enclosed space, windows, extra stairs, etc. We only have a small attic with a pull-down ladder due to the 22-degree gable roof.

When I mentioned the big price difference to the developer, he made a comparison, where I think the listed costs for one side of the house are already set way too high, because other developers told me that the cost difference between a single-family house and a semi-detached house is negligible. By the way, the number of windows is the same in total for both houses, I checked, so the 3,300 EUR are also not correct.

Here is his breakdown of additional costs:

Design and approval planning already available for the Müller family €4,500.00
Working planning for semi-detached house ProHaus less effort (synergy effect) €2,000.00
Higher construction site setup costs for single-family house (crane, WC, tools, travel costs) €3,500.00
this can be divided between two houses for the semi-detached house
For the semi-detached house, one gable side with exterior plaster, painting, reinforcement, scaffolding is omitted €4,200.00
For the semi-detached house, the roof finish on one gable: verge, flashing, €980.00
visible boarding is omitted
For the semi-detached house, windows on one gable side, approx. 3 pieces, incl. roller shutters, window sills inside, outside, roller shutter box are omitted €3,300.00
For the semi-detached house, excavation at one gable is omitted, the construction pit must be larger than the house to work. Plus backfilling of the pit again as extra effort on one gable wall €950.00
Lower thermal insulation of a basement outer wall (between semi-detached houses) €970.00
and the lower thickness is divided between two houses.
Load-bearing interior walls mostly 24 cm instead of 17.5 cm €3,600.00
as well as non-load-bearing in 17.5 instead of 11.5 cm.

What do you think about the listed costs? Is this realistic or exaggerated?

Thank you very much and best regards

Sony1970

Apart from the fact that the items are understandable even to a layperson and do not seem exaggerated in my opinion, the GÜ is not at all obliged to give an account of how he calculates the individual items. It is fair and transparent to receive such a breakdown, even if it is not 100% accurate or calculable.

However, it is somewhat naive to compare two different contracts without background knowledge. It may be that your construction service descriptions are not identical and the contract for work contains different conditions. Apart from that, items may have been subtracted or the equipment may be different. Ultimately, a house price can also be negotiated. So if your friends pushed the price down, they save at the bottom right of the invoice, but it may also be that savings in the sample selection are added back on.

Best regards in brief

Well, I do know what they have inside, it’s only about the estimated costs for one side of the house, whether that is realistic, it’s almost 23,000 EUR!!

Well, first of all, thank you for the feedback. I do know the content of the other house. This is only about the specified costs for the one wall, since that amounts to a total of 23,000 EUR.

It doesn't really matter, if the offer is too expensive for you, just get another one. What is your intention with the comparison?

I do not find the arrangement of the positions either sequentially or in terms of height inconsistent.