How to lay decking boards correctly

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If you want to install decking correctly, you must pay a lot of attention. Wooden decks consist of a foundation, a substructure of stringers and the actual decking, the decking itself. Similar to railroad tracks, the foundation stones lie in a ballast bed and carry the wooden beams on which you screwed the decking. For the installation of decking, different types of wood or WPC come into question. With the most important thing: water must go!

The main features of wooden decking

Wood works as a natural material - it will swell or contract depending on the water absorption or release. However, this only in the width and thickness, not in the longitudinal direction. As the seasons change, the dimensions of the decking can vary by up to five percent. In practice, this means that you should not lay the decking close together, otherwise they push each other up.
The wood used for decking is constantly exposed to the weather and turns gray over time. Sunlight fades over the years as well. Durability suffers - with the right choice - but not among them. Who wants to preserve the wood color as long as possible, should oil the planks at least once a year.
Wood does not tolerate moisture - rot threatens. It is important to avoid any contact with the ground and to lay the substructure and the decking boards in such a way that nowhere does water accumulate and the wood can dry as quickly as possible after a rain. You achieve this by a one to two percent slope of the entire terrace and a gravel surface and ideally spacers between decking boards and stringers. If the decking boards are directly on the support beams, the relatively large contact area becomes susceptible to moisture. This can be prevented with support pads or spacer strips made of plastic.

Which materials can be laid as decking?

Wood is by far the most popular material for decking. You have the choice between tropical or local woods, between treated and untreated wood composites (WPC). It is a mix of plastic and wood fibers. WPC stands for Wood Plastic Composite. The planks combine the best of wood and plastic, do not swell when wet and are easy to clean. But they are very hot in direct sunlight.

Terrace made of WPC planks

WPC planks are becoming increasingly popular as terrace flooring. In addition to products in typical wood decor as here, there are now many models that deliberately detach from the wood look and thus expand the architectural possibilities

Tropical wood and local woods

Tropical Bangkirai from Asia is in high demand. Because like Massaranduba, Garapa, Teak and other tropical hardwoods, Bangkirai is heavy, massive and absolutely "outdoor-fit": it naturally contains a wood preservative in the form of essential oils. If you choose tropical hardwoods for your decking, pay attention to the FSC sign. The seal of the Forest Stewartship Council certifies the plantation rearing of the wood. However, the seal (because of possible counterfeits) does not guarantee 100% security. If you want to be on the safe side, take better local Douglas fir, Robinie or softwoods like larch. However, these are not quite as long lasting.


Other woods such as ash, alder or beech are increasingly being offered as so-called thermo wood. It is also known as TMT (Thermally Modified Timber). The heat treatment, in which the wood is heated to over 200 degrees Celsius under exclusion of oxygen, significantly reduces the water absorption capacity of the wood. This makes it more durable and durable - but also more brittle and darker.
Important: Each type of wood has its own swelling and shrinkage behavior, so you should always use only one type of wood for your patio.

How are decking boards fastened?

Decking boards are bolted with stainless steel screws labeled "A2". For very tannic acid-containing wood, special screws are required, which are labeled "A4" for absolute acid and water resistance. Sometimes you can also find the older names "V2A" and "V4A". The screws should be about two and a half times as long as the decking boards are thick. Ideal are screws with star-shaped Torx profile. In contrast to slotted or Phillips screws, Torx screws remove the high torques of the cordless screwdriver very well and the screw head does not tear off.
For hardwood decking, you should pre-drill the holes for the screws in the board. The drill should be just under a millimeter thicker than the screw so that the wood can still work.

Pre-drill wood

Important: Only drill the deck board and not the support beam, otherwise the screw will not have enough hold at the end

Concealed and visible screw connection

You can concealed or visible screwed decking. The classic method is the visible screw connection - it goes faster. You simply screw the planks from above onto the support beams and the screw heads remain visible.
The concealed screw connection is more expensive, but the screws remain invisible. This is made possible by special mounting clips or plank holders, which are screwed onto the planks and the support beams. Laying works then similar to clicking laminate. In terms of stability, the variants do not differ.

Before laying decking, some planning is needed

The actual laying of decking is not that difficult - calculating the necessary material is often more difficult. To determine the exact material requirements, it is best to draw up a sketch. This additional work pays off later. This should be considered in the planning:

  • Will the decking be laid longitudinally or transversely?
  • The terrace size decides whether the decking can be laid in one or whether shocks are necessary. If possible, plan that you do not have to saw off planks.
  • How is the underground? What kind of foundation is needed?
  • The terraces should have a slope of one percent, so that rainwater can drain. The gradient ideally coincides with the direction of the grooves on the planks.

How many decking boards are needed?

The most important data are the planned terrace area and the dimensions of the floorboards you want to lay:
First, cut off the surface with a string and pegs and take the measurements. Usual decking is often 14.5 inches wide, 245 or 397 inches long and 2.5 inches thick. If the terrace is bigger, you have to piece it. In this case, use shorter planks so that the bumps are more in the middle and not on the edge of the terrace - otherwise it will look like a patchwork quilt.
Think of the joints between the decking and plan for a width of five millimeters so that water can drain and the boards will not bulge when laid too close. If you disturb the joints, you can laminate them with expansive joint tapes. Then no small parts fall between the joints, to which one can no longer approach.

The substructure

The substrate must be stable but permeable to water. The more carefully you prepare it, the longer the decking will last. Spent sidewalks are a popular and inexpensive foundation for the girders. But only if the subsoil is well compacted and completely level. On the 20 centimeters thick gravel layer should still be a chippings, in which you can align the plates horizontally. Otherwise, you need a point foundation: with a hand-operated excavator, you can lift 50-centimeter-deep holes and fill in concrete.
The support beams are always laid across the decking. The distance between the support beams and thus the foundations to each other depends on the thickness of the board: the number of fist counts 20 times the board thickness. If the distance is too large, the planks hang through, too narrow a distance means unnecessary extra work and costs.
Important: The construction becomes trickier on large terraces because the decking is too short for the entire terrace length. So you have to piece the pieces; Butt joints are inevitable. You should already plan this with the support beams, because planks can not share a beam. At the joints place two support beams three to four centimeters apart next to each other on the foundation stone. For a harmonious picture, lay each new row of boards alternately with a longer and a shorter board, so that the joints are always offset from each other.

Wooden terrace construction cross section

Example construction of a wooden terrace: 1 foundation (about 20x20x40 cm), 2 filling sand (about 10-15 cm), 3 plastic fleece, 4 gravel layer (5 cm), 5 concrete stone (gutter stone, 14x14x15 cm), 6 pond liner, 7 Wooden beams (4.5x9 cm), 8 wooden planks (12.5x2.5 cm), 9 wooden blocks as spacers, fixed on both sides with metal brackets, 10 wooden planks as a screen

Tips for laying decking

Some decking boards are slightly curved. You can shape them with screw clamps or straps and then tighten them. The first decking should be as straight as possible, as all others are oriented to it. Align this board exactly at right angles to the beam of the substructure and keep the recommended distance of five millimeters to the wall of the house. Important are two screws per beam, one in front and one in the back, so that the decking does not bulge in itself.
When screwing you should proceed with care: Clamp a mason cord, so that the screws are also on a line. Spacers guarantee the correct gap between joints. The wooden or plastic tiles clamp in front, in the middle and at the end between the decking boards and then pull out with pliers again.

Video Board: How to Install Deck Boards Properly.

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