ᐅ Concrete slab, foundations, earthworks – is the quotation acceptable?

Hello dear forum,

we are building a bungalow without a basement, measuring 9.5 x 12 m (31 x 39 ft). It is not yet decided whether to use a timber frame or masonry construction. The plot is a slight hillside site.
We have received quotes for the slab foundation, footings, and earthworks from two local companies, and they are quite close, around €32,500. That really surprised me at first.
I would like to ask you to take a look at this.
Especially the major items slab foundation and footings. Does it have to be this complex/expensive, where can costs be reduced, can it be approached differently and possibly done much cheaper?
Thank you for that!!
Prices are all net.

Earthworks total €6,650:
350 sqm (3,767 sq ft) topsoil stripping, stored on-site €437
150 cubic meters (5,295 cubic feet) excavation of building pit, stored on-site €465
50 cubic meters (1,765 cubic feet) backfill €210
145 cubic meters (5,117 cubic feet) wall gravel as backfill material, placement + compaction €3,842
130 sqm (1,399 sq ft) leveling building pit bottom €235
250 sqm (2,691 sq ft) rough grading €350
100 cubic meters (3,531 cubic feet) excavation disposal €1,110

Sewer works total €1,509.00:
15 cubic meters (530 cubic feet) trench excavation for pipes + reinstatement €615
50 meters (164 ft) laying KG pipes €750
Connection chambers €140

Concrete/Reinforced concrete works total €24,600:
150 sqm (1,615 sq ft) PE foil under slab €267
120 sqm (1,292 sq ft) slab foundation C25/30, 32 mm (1.26 in) reinforcement, 25 cm (10 in) thick incl. edge formwork €3,996
25 cubic meters (883 cubic feet) individual + strip footings C15/20 incl. formwork €5,125
5 cubic meters (176 cubic feet) individual + strip footings C20/25 incl. formwork €1,040
50 meters (164 ft) equipotential bonding €360
4.3 tons (4.7 US tons) reinforcing steel installation €5,550
400 kg (880 lbs) professional steel S235JR for columns/beams €1,840
23 sqm (248 sq ft) perimeter insulation 100 mm (4 in) + installation €455
125 sqm (1,345 sq ft) XPS insulation panels 100 mm (4 in) under slab €2,537
4 cubic meters (141 cubic feet) reinforced concrete for ring beam €2,080
15 meters (49 ft) vertical meters stirrups for columns 25/25 cm (10 x 10 inches) €1,350

Broadly speaking, I can’t find any obvious errors, but I’m not 100% well at the moment. The prices are as I know them. Civil engineering work is expensive.

1. If you don’t yet know which house will be built, you won’t know the structural load. This affects the amounts of steel and concrete needed. Do you already have a soil report? With specifications for the gravel layers? Or how is the amount of gravel/grit determined?

2. What about the foundations concerning the slope of the site?

3. The sewer work appears to be fairly estimated. However, I notice the often required inspection chamber is missing here. This typically costs around 1,500 plus installation. This is an approximate figure.

I would wait with everything until it’s clear exactly which house will be built.

You already have a rough estimate. Maybe it can still become more affordable.

Kind regards
Thorsten

Hello Thorsten,

Thank you.
After consulting with the planner, he told me that the measurements were initially only roughly estimated and are probably on the high side. Once the construction drawings are available, there will be a more detailed and precise offer. Now it is clear that it will be a wooden house, and then we can calculate everything more accurately.
In any case, thank you for your efforts.

You’re welcome.

The earthworks sound affordable..

But how do you store 500 m3 (650 cubic yards) of soil to the side? What happens to the soil? When will it be disposed of?

I don’t see anything about drainage?
Insulation under the slab?
Working hours?
Machinery, etc.

PS. 32k could be realistic, but it sounds cheap and is probably regionally dependent.

As mentioned, this is a rough overview for now, more details will follow.

I found something during my research today:

Elevated Slab-on-Grade
One way to reduce foundation costs is by elevating the slab-on-grade. Elevating means raising the slab (on which the house is built) so that it sits above the ground surface.

With this method, excavating a foundation pit is avoided. Only frost-resistant strip or pad foundations are required to support the slab. There is no need to prepare a stable subgrade for the slab, and no waterproofing or drainage is necessary. The underside insulation of the slab is not subject to load, so there are no compressive strength requirements for the insulation material....
This approach is particularly worthwhile on challenging ground conditions......
....the elevated slab does not come into contact with the soil. Therefore, this design is also interesting for wooden houses with wooden floors... The thermal insulation requirements for the slab are higher than for slabs that are in contact with the ground....

Has anyone had experience with this or can share insights?