Strip foundation what costs do you have to calculate?
Many smaller garages can easily be built on a strip foundation. At first glance, this looks cheaper than a continuous foundation plate - but in most cases this is deceptive. The cost check expert reveals in detail in an interview what strip foundations really cost.
Question: Where are strip foundations used everywhere - and are they really a cost-saving alternative?
Cost check expert: Strip foundations can be found in almost all types of buildings - but they are usually used where there is not a lot of weight: this is the case with small prefabricated garages or simple garden sheds, for example. However, they can also be found under larger buildings, where they are usually installed directly below the load-bearing walls.
It doesn't sound logical at first, but the more cost-effective alternative is usually the continuous concrete foundation slabs. Although a strip foundation usually takes up less space, the effort for the construction - and thus the price - can be significantly higher than with continuous foundations.
There is also the other alternative: strip foundations connected by a simple, thin concrete slab. In any case, of course, that is more expensive than a continuous, stable plate. "
Question: What does a strip foundation generally cost?
Cost check expert: You simply cannot say that across the board . The requirements for foundation strips can vary completely from building to building, and of course the foundations are also of different sizes and depths and are reinforced differently depending on the requirements.
In addition, the excavation work can sometimes cause a very different effort.
Extrapolated to the area, everything is possible with strip foundations between EUR 90 per m2 and EUR 300 per m2.
To illustrate the effort, a small cost example from practice:
A (unreinforced) strip foundation should be created for a prefabricated garage. The single foundation strip is 90 cm deep and 70 cm wide - the length is 6 m. Two parallel strips are created. So 7.5 m3 of concrete are required.
|Measuring and setting up - working hours||EUR 87|
|Formwork (in our case 21.60 m2)||210 EUR|
|Working time formwork||625 EUR|
|Concrete - material costs||EUR 820|
|Concrete - working hours||260 EUR|
|Small equipment and additional costs||50 EUR|
|Other work afterwards||175 EUR|
|total cost||EUR 2,227|
Of course, this is just a single example. Other strip foundations in other locations can be significantly more expensive or cheaper.
In our example, the costs for excavation work have not yet been taken into account, as they have already been done by another company. Otherwise you would have to calculate an additional EUR 1,000 for this work. There are also the costs of filling and compacting.
In our example, we come to the area, i.e. a price per square meter of approx. EUR 265 per m2.
Question: What does the cost of a strip foundation generally depend on?
Cost check expert: Several factors play a role here, each factor in itself can be highly price-determining:
- the dimensions of the foundation
- the type of reinforcement
- the type of concrete used
- the backfilling and compaction and of course
- the cost of excavation
This already shows why each strip foundation has completely different requirements and, depending on the foundation plan and local conditions, very different costs can arise.
Question: To what extent do the dimensions of the foundation matter?
Cost check expert: Well - foundation strips differ from each other both in length and in width. The depth is variable and depends on the one hand on the load-bearing capacity and on the other hand on the location of the property
The respective depth for the frost-free area can vary widely from region to region - in most areas of Germany it is between 60 and 80 cm, in areas with a lot of frost and severe winters, the frost-free zone can only be around 150 cm. Of course, this clearly determines the costs.
The overall dimensions of the foundation then again influence the costs for the formwork and for the concrete, since with larger or deeper strips more concrete is also used and more formwork has to be created.
Question: Strip foundations always consist of individual, separate foundation strips, is that correct?
Cost check expert: No. In quite a few cases, the individual strips are then connected to one another by a very thin, cast plate.
Here it also becomes clear why the cost of strip foundations is generally significantly higher than that of continuously cast floor slabs - as here . The effort is simply much higher, the formwork more complex, and if both strips also have to be connected, as is often the case, the costs increase because of the complexity of the construction.
Question: How does reinforcement play a role in the cost?
Cost check expert: As in our example, many strip foundations are completely unreinforced. This means that there are no costs for reinforcement or installation.
Depending on the type of reinforcement mesh used, you will have to calculate around EUR 70 to EUR 200 per reinforcement element in other cases. These costs add to the other costs (as shown in our example).
Question: What prices have to be expected for the concrete and why can they be different?
Cost check expert: Concrete can have different strengths and load capacities. As a rule, at least class C25 concrete is used for foundations, but in many cases higher concrete qualities are also required.
Then there are any additives that have to be added to the concrete:
- flow improvers
- Retarder (to delay hardening and keep the concrete workable for a little longer)
- Means for easier processing
So concrete is not just concrete, but can have very different properties.
Specialist companies usually use the concrete directly from the mixer for smaller strip foundations. This is usually an inexpensive solution. In other cases, ready-mixed concrete is used, which is delivered mixed in the mixing wagon and pumped directly into the formwork.
In general, you have to expect costs for the concrete of around EUR 110 per m3 to around EUR 160 per m3.
A special case is steel fiber concrete. Here special steel fibers are added to the concrete (already in the concrete plant) to reinforce it. In many cases, this can make additional reinforcement superfluous.
This solution is quite interesting in terms of costs, because the steel fiber surcharge often only incurs around 5 - 6 EUR per m3 of additional costs for the concrete - this is significantly cheaper than classic reinforcement, which then also has to be installed.
Question: What is backfilling and compaction?
Cost check expert: A foundation is dug quite deep, but not everything is made of concrete. Even the foundation pit must be carefully compacted at the bottom of the pit - the so-called pit base.
Gravel or other base layers are often planned on top of this, which must also be compacted after installation. The structure can be different in individual cases.
As a rule, backfilling and compaction are carried out together with the excavation work.
Question: That brings us straight to the next question: Why does even simple excavation work always appear so disproportionately expensive?
Cost check expert: This work is not always that easy - and it means a considerable amount of work for the executing company.
In general, the costs consist of three main points:
- a price for the excavation per m3
- a price for the machine use and
- the price of storage or disposal of the soil
The so-called soil class plays a role in the effort. The standard case is soil classes between 3 and 5, such a mixed soil occurs on most properties. The excavation price for such soils is usually between 8 and 12 EUR per m3.
Soil class 6 then designates a soil that is slightly rocky, but the rocks are easily detachable. This increases the costs considerably because of the higher effort. In classes 6 and 7, the prices for the excavation can already rise to around EUR 60 per m3 to EUR 70 per m3, in Class 7 (rocks that are difficult to remove) this can reach up to EUR 100 per m3.
When using machines, it always depends on which devices are used. As a rule, only small excavators can be used for strip foundations anyway - here you will generally have to expect around EUR 80 per hour to EUR 90 per hour.
Question: Are there also costs for storing and disposing of the soil?
Cost check expert: Yes - the excavated soil has to be stored somewhere. If this is done right next to the excavation pit on the side, it is always the cheapest solution.
Since it is not a large amount, this earth can often be easily distributed on the property or used to pour or straighten the property (but be careful: if you commission this work from a GaLa farmer, this can result in considerable costs attack).
On the other hand, loading onto the truck and transporting it to the landfill instead of storing it on the property are an expensive solution. Larger excavation quantities usually charge EUR 8 per m3 to EUR 12 per m3 for loading a truck and transporting it to the landfill. At the landfill itself, around EUR 2 per m3 to EUR 5 per m3 can then be added for disposal. For smaller quantities, companies often calculate differently.
Tips & Tricks
The production of strip foundations is complicated and time-consuming - you generally have no chance of building it yourself if it is not exactly a foundation for a very small garden shed or similar small tasks.
It is best to always leave the foundation production to a specialist - even minor errors can have a massive impact on the foundation quality and load-bearing capacity.