Wood and bare earth don’t get along because the earth’s moisture makes the wood rot. So you need to prepare the subfloor before you put down the decking. For example, a substructure made of wood always works when building a foundation.
On top of this, you put spacers made of wood that can hold weight, and only on these do you lay decking boards.
However, substructures can also be made of metal. The respective manufacturer of the various products will give you tips on terrace construction – and we will answer your questions in advance.
Why should decking boards not lie on the subsurface?
Wooden decking boards respond to water like any other wood: they soak it up, swell, and rot.
Even if you apply a liquid plastic coating to wood, it will never be completely waterproof, no matter what you do. Without a substructure, your wooden terrace will fall apart in a few months.
The substructure is the frame that your deck boards sit on. When it comes to the substructure, there are several choices:
- Foundation of several layers
- moisture-insulating layer and simple substructure
- simple substructure with high spacers
All of your choices have pros and cons that you should compare. This kind of guide will help you figure out what to do.
A common mistake with the wood decking substructure
Putting up wooden decks, substructures, and floorboards is not magic. But you should know before laying out that mistakes can’t be fixed.
When building the base and the wooden terrace, some of these are often done:
- The decking boards are laid on a wavy base, making the terrace’s surface uneven.
- The foundation is too weak to support the beams of the substructure. The terrace sags on one side.
- The substructure has too few support beams, so the wooden floorboards will eventually sag.
- The boards of the deck are in contact with either water or dirt. They go bad.
- There is no space between the boards, so they will buckle or push up against each other.
- The screws have been put in wrong, which has caused the planks to crack and turn black near the screws or bulge along their length.
Step-by-step instructions for the wooden deck substructure
Various Youtube videos, online house-building guides, and relevant magazines and forums provide such instructions. Here is a summary for a rough guide:
- Mark the intended area at the corners with metal rods, and mark the height of the support beams with a cord running around.
- Excavate the surface; use filling sand.
- Dig foundation holes, fill with semi-dry concrete, and compact.
- Place synthetic fleece over the foundations to prevent weed growth, and place base stones on the foundation.
- Bring base stones or basement stones to the exact height.
- Check the slope and adjust the basalt stones again if necessary.
- Apply gravel fill.
- Put on the support beam.
- Lay the floorboards on and screw them together.
- Last step: check everything, sand down corners and edges, and clean with a broom.
Why is the substructure so important for the wooden deck?
The substructure is important for several reasons:
- Wooden floorboards should not come into contact with damp soil or water; otherwise, they will rot.
- The wooden deck needs an even slope so that rainwater runs off.
- The subfloor must be level to lay the decking boards with an even surface. If the surface is not level, you can injure yourself while walking, boards and furniture warp, and you do not stand well.
- The surface of your wooden terrace has to look like your balcony: slightly sloping so that rainwater can run off, and above all, even.
Which wood do I use for the wood deck?
Many types of wood are suitable for the terrace. Local woods are inexpensive and ecologically harmless. Depending on the exact type of wood, you can use the wood without chemical wood preservatives. The durability class says how long this goes well:
- Douglas fir corresponds to class 3-4 and is moderate to slightly durable.
- Oak is durable with durability class 2.
- Spruce and pine correspond to durability class 4 and are not very durable.
- Larch also belongs to durability class 3-4.
- Robinia, or false acacia, corresponds to class 1-2 and is very durable to durable.
- In addition, thermowood comes into question, which is also made from local wood and is particularly water-repellent and resistant to rot.
Tropical woods are considered unbeatable when it comes to outdoor areas. However, you should ensure that the wood is FSC certified and has been legally felled.
In the socially responsible area, you must calculate three to four times the amount of domestic wood for tropical wood.
How do I waterproof the wood deck?
Why are wooden decks not waterproof? Because water gets through every knothole, adhesion, spider crack, and other flaws, so water will always get in a little bit.
The question is whether the water can drain away without hurting the wood. Chemical wood preservatives and other products can help with this.
Compared to wood that hasn’t been treated, thermowood is also waterproof and won’t rot. The terrace’s surface must have a slope so that water runs off when it rains and doesn’t pool.
How much slope should the patio cover have?
Your wooden deck should have a slope of at least 1% so that water can flow off without getting stuck.
It can be a little more sloped, but you should ensure it works with the furniture you want to put there. If the slope is too steep, tall furniture won’t be able to stand very well.
The slope is made by laying and screwing the floorboards and is the first step in building the foundation.