Cracks in prefabricated garages: What you need to know
You discovered cracks in your prefabricated garage und ask yourself if that’s a problem?
First, to reassure you: Reinforced concrete is a building material that cracks due to its construction – and that is even desirable when done properbly. In this guidebook we will explain why cracks occur, when a defect according to DIN EN 13978-1 actually exists, and what you can do about cracks in your prefabricated garage.
Why do cracks occur in prefabricated garages
There are several causes for cracking in prefabricated garages, all of which are related to the manufacturing process and the physical properties of reinforced concrete. To understand why fine cracks are completely normal, it’s worth taking a look at the production process.
The bell casting process
Prefabricated garage are made in the so called bell casting process. In this process, a formwork mold is completely filled with concrete, creating a monolithic – i.e. jointless – garage structure. The advantage of this process lies in its fast and economical production and the avoidance of joints, which can sometimes be disadvantageous from a technical point of view.
Temperature fluctuations and shrinkage
Concrete changes its volume when exposed to temperature fluctuations and during the hardening process (hydration). As it hardens, concrete releases water and shrinks, meaning that its volume decreases. Since the garage is a monolithic structure, it cannot compensate for these movements via joints, resulting in internal stresses. These stresses are released through fine cracks—a completely natural physical process.
Influence of wall thickness
Wall thickness also plays a role in crack formation. For weight and transport reasons, prefabricated garages typically have wall thicknesses of 6 to 8 centimeters for freestanding garages. However, increasing the wall thickness is hardly possible for practical reasons: a standard prefabricated garage (3 x 6 m) already weighs between 14 and 20 tons. Thicker walls would not only increase the weight significantly, but also reduce the usable interior space. In addition, the increased weight would often require a crane for assembly, making transport and feasibility more difficult and increasing costs.
Why cracks in reinforced concrete are actually desirable
What many people don’t know is that controlled cracking is deliberately sought in reinforced concrete construction. This may sound paradoxical at first, but there is an important structural reason for it.
The interplay between concrete and reinforcing steel
The reinforcement designed to limit crack width ensures that many small, harmless cracks form instead of one large crack. These fine hairline cracks are barely visible and do not affect the structural integrity or impermeability of the component. The reinforcement distributes the cracks so that they remain within harmless widths.
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The role of reinforcement
The reinforcement designed to limit crack width ensures that many small, harmless cracks form instead of one large crack. These fine hairline cracks are barely visible and do not affect the structural integrity or impermeability of the component. The reinforcement distributes the cracks so that they remain within harmless widths.
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When does a crack become a defect? DIN EN 13978-1
There are clear rules governing whether a crack constitutes a structural defect. The relevant standard is DIN EN 13978-1 Precast concrete products – Prefabricated garages, Part 1: Requirements for monolithic reinforced concrete garages or garages consisting of room-sized individual parts.
Section 4.3.7 (Durability) clearly defines this:
The crack width must not exceed 0.4 mm.
Specifically, this means:
| Crack width | Assessment according to DIN EN 13978-1 |
| Up to 0.4 mm | Compliant with standards – no defect, acceptable |
| Over 0.4 mm | Defect – entitlement to rectification |
| Water-bearing (from inside to outside) | Defect – regardless of width |
Important: Even cracks wider than 0.4 mm do not pose a risk to stability. The garage will not collapse and can continue to be used without concern. This is a warranty case that must be remedied by the manufacturer.
Special case: Water-bearing cracks
DIN EN 13978 – 1 additionally stipulates in section 4.3.8.2.1: All parts of a garage must be designed in such a way that dripping from water ingress on the inside of the garage is prevented.
This means that if water penetrates through a crack – whether dripping from the ceiling or running down a wall – this constitutes a defect, regardless of the width of the crack. A distinction must be made between:
Moisture in the crack: Often repairable as a gesture of goodwill (often this is only non-critical condensation)
Actively dripping water: Clear defect with a claim for rectification
Note: The water that enters the garage via a wet or snow-covered vehicle is usually significantly more than what could penetrate through a fine crack. Ventilation of the garage is therefore more important than avoiding damp spots on non-critical cracks.
How to measure crack width correctly
To determine whether a crack is within the norm, you need a crack width card. These practical measuring aids are inexpensive and allow you to easily determine the crack width on site.
Here’s how to proceed:
- Hold the crack width card directly against the crack
- Compare the lines on the card with the actual crack width
- Take a photo of the crack with the card as a reference
- Also document the entire course of the crack with overview photos
Tip: Small adhesive marks along the course of the crack help with documentation and clearly show both the location and the course of the crack.
Repairing cracks in prefabricated garages
If there is a defect or you want to remove cracks for aesthetic reasons, there are various repair options available. Depending on the location and type of crack, the method of repair is at the discretion of the technician:
Professional Closing
In professional crack repair, the crack is opened close to the surface (maximum depth 1-2cm) using a cut-off grinder. Cuts are then made across the crack for stainless steel connectors, which serve as clamps. After removing the concrete dust, expoxy resin is filled evenly into the crack, pressed in, and sprinkled with quartz sand. The result is a permanent seal.
Crack-bridging coating
In the case of many fine hairline cracks, a special crack-bridging coating is often the more economical solution. These elastic coatings can compensate for small movements in the material and prevent cracks from becoming visible.
Filling/ Grouting
In the case of purely superficial hairline cracks, a new coat of paint or plaster is often sufficient to improve the visiual appearance. This is the simplest and most cost-effective option.
Conclusion: Correctly classifying cracks in prefabricated garages
Fine cracks in prefabricated garages are completely normal and harmless in most cases. They are caused by the manufacturing process and the natural properties of reinforced concrete – and are even a sign that the material is working properly.
The most important points summarized:
– Cracks up to 0.4 mm are compliant with DIN EN 13978-1 and do not constitute a defect
– Cracks larger than 0.4 mm or water-bearing cracks are defects that must be repaired
– Stability is not compromised even in the case of larger cracks
– Cracking in reinforced concrete is intentional from a structual engineering perspective and is part of the load-bearing behaviour
– Professional renovation is possible any time
Do you have questions about cracks in your prefabricated garage?
ZAPF specializes in the moderinziation and renovation of prefabricated garages. Our experts will be happy to advise you and ensure that your garage is professionally repaired. Contact us for a no-obligation consultation.
Sources and further information
– DIN EN 13978-1: Precast concrete products – Prefabricated garages, Part 1
– DIN EN 1992-1-1: Eurocode 2 – Design and construction of reinforced concrete and prestressed concrete structures
– Fachvereinigung Betonfetiggaragen e.V. (Professional Associaton for Prefabricated Garages)
– beton.wiki – Technical dictionary of the concrete industry
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