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Wood, WPC, or aluminum: Which substructure is suitable for which decking board?
The substructure supports the decking, transfers loads to the ground via the supports, and forms the base for fastening the boards. Therefore, which substructure is suitable for decking boards does not depend on the material alone. The decisive factor is the interplay between the decking board, substructure, fastening system, sub-surface, installation height, and drainage.
Wood, WPC, and aluminum differ primarily in their movement behavior as well as their requirements for support and fastening. This article provides an initial overview of which material for a deck substructure is suitable for which type of construction. You can find specific installation instructions, spacing, and execution details in the respective installation guidelines.
You can find an overview of available substructures for wood, WPC, and aluminum decking boards directly in our product range.
Why the decking board is a key factor in choosing the substructure
The decking board dictates essential requirements for the substructure. These include, in particular, the permissible spacing of the substructure profiles, the type of fastening, and the material movements that must be taken into account in the construction.
Decking boards and substructures do not necessarily have to be made of the same material. Depending on the wood species and fastening system, wood decking boards can be installed on suitable wood or aluminum substructures. WPC or aluminum substructures are intended for Gunreben WPC decking boards.
The deciding factor is therefore not whether both components consist of the same material, but whether the board, substructure, and fastening system are technically coordinated with each other.
Wood, WPC, and aluminum in direct comparison
The following overview shows the essential differences between the three materials. Specific spacing, fastening details, and construction requirements are always based on the respective product or system.
| Material | Typical movement behavior | Practical properties during processing | Important planning points | Possible application scenarios |
|---|---|---|---|---|
| Wood | Swelling and shrinking primarily depending on wood moisture; temperature-related dimensional changes play a significantly smaller role in comparison. | Processing possible with standard woodworking tools; requirements for drilling and screwing depend on the wood species, among other things. | Consider wood species and cross-section, structural wood protection, ventilation, drainage, and fastening. | Primarily as a substructure for wood decking boards; the wood species must be coordinated with the surface and construction. |
| WPC | Temperature-dependent length change; the specific behavior depends on the formulation and profile design, among other things. | Processing possible by sawing and drilling; observe profile geometry and fastening areas. | Consider system specifications, support, profile spacing, expansion gaps, and fastening. | As a substructure for Gunreben WPC decking boards within the intended deck system. |
| Aluminum | Temperature-dependent length change; no moisture-related swelling and shrinking movements like with wood. | Processing with suitable tools; fastening and connection must match the profile used. | Consider profile cross-section, support, profile joints, fastening, and temperature-related length changes. | Can be used under wood and WPC decking boards, depending on the system. |
Wood substructures
A wood substructure for a deck can be processed with the tools standard in timber construction. Different types of wood are suitable depending on the structure. In deck construction, for example, Angelim Pedra, Douglas fir, and larch are used as substructure timber.
The wood species differ in terms of their density, workability, and properties in outdoor areas. The selection should therefore be coordinated with the board material, fastening, and structural design.
For the movement behavior of wood, the wood moisture is the decisive factor. If wood absorbs moisture, it swells; if it releases moisture, it shrinks. Temperature-related dimensional changes play a significantly smaller role compared to this moisture-related behavior in deck construction.
Structural wood protection is therefore correspondingly important. Water should be able to drain from the structure, and the wooden components should be able to dry out after getting wet. Direct contact with the ground and areas where moisture collects for longer periods should therefore be avoided.
The fastening must also be coordinated with the wood species, decking board, and substructure. Details on support, spacing, screwing, and structural execution can be found in our installation tips for wood decks.
For material selection: In our selection of deck substructures, you will find substructure timbers as well as alternative systems for deck construction.
WPC substructures
A WPC substructure for a deck is part of a coordinated deck system. It is not possible to derive which spacing, supports, or fasteners are intended for a specific profile from the material alone.
WPC reacts to temperature changes with changes in length. The extent of these changes depends on the formulation and profile geometry, among other factors. Expansion gaps and fastening must therefore be planned according to the respective deck system.
Two types of spacing must be distinguished: the spacing of the substructure profiles under the decking board and the required support for the substructure itself. Both are determined by the system being used.
WPC substructure profiles must be supported in accordance with system specifications. They are not intended for self-supporting or spanned constructions.
Specific requirements for the substructure, fastening, spacing, and expansion gaps can be found in the Gunreben installation tips for WPC decks.
Suitable profiles: You can find our WPC substructures for decking boards with the corresponding product information directly in the shop.
Aluminum substructures
For an aluminum substructure for decking boards, the respective profile is decisive. Profile height and width alone are not sufficient to evaluate the structural properties. Profile design, support, and connecting elements also play a role.
Depending on the deck system, aluminum substructures can be used under both wood and WPC decking boards. They are particularly suitable when only a low installation height is available or the intended fastening system requires an aluminum substructure. The possible support spacing depends on the respective profile and construction.
Aluminum does not show moisture-related swelling and shrinking movements like wood, but its length changes with temperature. For longer profiles, profile joints, and fastening points, this behavior must be taken into account in accordance with system specifications.
Even with an aluminum substructure, the movement behavior of the decking surface remains: wood continues to work depending on moisture, while WPC continues to react to temperature changes.
Selecting an aluminum substructure: Suitable aluminum substructures for decking boards as well as coordinated connecting elements and fasteners can be found in the corresponding collection.
Selection based on installation height, sub-surface, and fastening system
Anyone wanting to clarify which substructure is suitable for decking boards should not consider wood, WPC, and aluminum in isolation. For work preparation, the following inspection sequence is recommended:
- Determine the decking board and potential substructures: The board material, profile, and intended fastening system determine which combinations are possible.
- Check the sub-surface: Load-bearing capacity, flatness, drainage, and the method of load transfer must be suitable for the planned construction.
- Determine installation height: Consider the board thickness, substructure, support, and connection heights together.
- Define profile cross-section and spacing: The spacing of the substructure depends on the decking board, and the required support additionally depends on the respective substructure profile.
- Coordinate fastening: Visible screws, hidden fasteners, and clip systems place different requirements on the substructure.
- Consider drainage and ventilation: Water must be able to drain from the structure; in the case of wood, the drying of the components is also particularly important.
The exact structural execution, including spacing, fastening, and detail connections, should subsequently be determined based on the respective Gunreben installation instructions. For structures with height adjustment, suitable deck supports for the substructure can also be included in the planning.
Typical mistakes in material combination
Selection based solely on material price:
A cheaper substructure does not necessarily lead to a lower overall cost. Depending on the profile, additional supports, different fasteners, or other components may be required.
Lack of system compatibility:
Decking board, substructure, and fastening must technically fit together. This must be observed particularly with grooved WPC boards and hidden fastening systems.
Incorrect spacing:
The spacing between the substructure profiles and the required support of the substructure are different planning parameters. Both must be determined based on the system used.
Profile joints without considering system specifications:
Joints and longitudinal connections are executed differently depending on the substructure material and profile. Therefore, the respective installation and product specifications are decisive.
Inadequate moisture protection for wood:
Wood substructures should be designed in such a way that water can drain away and the drying of the components is not hindered.
Equating profile height with load-bearing capacity:
The height of a substructure profile alone does not indicate which support spacing or loads are permissible. The profile design and the respective system specifications are the deciding factors.
Conclusion: The entire deck system is what matters
Which substructure is suitable for decking boards is not decided solely by choosing between wood, WPC, and aluminum. Decking board, sub-surface, installation height, fastening, and material movement must be considered together.
In deck construction, wood primarily reacts to changes in moisture, WPC shows temperature-dependent movement behavior that depends on the formulation and profile, and aluminum also changes its length depending on temperature. These differences must be taken into account when planning the respective deck construction.
This article provides an initial orientation for material selection. The concrete execution should subsequently be planned based on the respective installation tips for wood decks or installation tips for WPC decks.
Select a suitable substructure: Compare our substructures made of wood, WPC, and aluminum and choose the material, profile, and accessories that match your deck construction.
