ᐅ Is the price for the concrete slab justified?

Hello everyone,

I have received a quote for a concrete slab. From your perspective, is the price reasonable, or should I get additional quotes? The building site is in rural eastern Germany.

The size of the garage is about 56 m² (600 ft²). The quote includes soil replacement of approximately 90 cm (35 inches) with mineral aggregate but without disposal, strip foundations, and the concrete slab. The price for the groundworks is around 4,000 euros net, and the concrete works (strip foundation and slab) are about 10,000 euros. The total gross price is therefore approximately 17,000 euros.

Best regards

I can only assess the earthworks. It’s about right. In the end, I had 1 meter (3.3 feet) deep excavation and new material 1.2 meters (4 feet) high for 8,000 euros, but for a 100 m² (1,076 sq ft) floor area.

The foundation slab depends heavily on the exact specifications (thickness, type of concrete, amount of reinforcement).

Tolentino schrieb:

I can only assess the earthworks. It’s about right. I ended up with an excavation depth of 1 meter (3.3 feet) and 1.2 meters (4 feet) of new material on top for 8,000 EUR, but that was for a 100 m² (1,076 sq ft) area.

The concrete slab depends heavily on the exact specifications (thickness, type of concrete, amount of reinforcement).

Here are some details:

12.5 m³ (441 cubic feet) strip foundation
5 cm (2 inches) concrete blinding layer
1,200 kg (2,645 lbs) reinforcement
C25/30 concrete, 15 cm (6 inches) thickness

I am wondering whether a 90 cm (35 inch) soil replacement combined with strip footings is really necessary. Without knowing the exact ground conditions at your site, a 90 cm (35 inch) base layer should be structurally sufficient for the foundation of a garage. The wall loads are not likely to be very high, unless you plan to build multiple floors on top.

If you use an F1 (frost protection) mineral mixture, you also ensure frost resistance at the same time. This way, you can save on concrete and steel for strip footings as well as the related labor.

Of course, if the garage builder insists on this approach, there is nothing you can do.

LukPfaffendorf schrieb:

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I’m not sure if this helps, but it might serve as a reference: The concrete slab for our garage is smaller, and part of the earthworks (?) was already carried out in connection with the house construction due to the crane setup area. Attached are photos of our quote, anonymized. We are building/living in the Leipzig district, postal code 0457x.

Also attached is a photo of the requirements for our garage’s concrete slab.

Cronos86 schrieb:

I’m more wondering whether a 90cm (35 inch) soil replacement along with strip foundations makes sense at all. Without knowing the exact soil conditions on your site, a 90cm (35 inch) base layer should be structurally sufficient for a garage foundation. The wall loads can’t be that high, unless you plan to build several floors on top.

If you use an F1 mineral mixture (frost protection material), you automatically achieve frost resistance. This saves concrete and steel for strip foundations, as well as the labor involved.

However, if the garage builder insists on it, there’s nothing you can do.

I also question whether this is necessary and reasonable. A soil investigation was carried out for the adjacent house (80–90cm (31–35 inch) are soil group OH topsoil).

For the house foundation, these were the recommended measures in the report (removal of topsoil and strip foundations). I can’t judge whether this is necessary for a garage. We plan to build the garage ourselves and intended to have the concrete slab done by the main contractor at the same time. There are no requirements from a garage manufacturer.