Build a wooden deck yourself: how to proceed

A wooden terrace is not only chic, but also brings comfort to the garden. Learn how to build a wooden deck yourself with this practical guide.

Wooden terrace

A homely wooden terrace can be built by yourself with a little skill

  • The right wood
  • The right dimensions
  • Screws and fittings
  • Costs
  • The right height
  • Substructure
  • Foundations and base stones
  • Gravel fill and support beams
  • Laying a wooden terrace
  • The right wood
  • The correct dimensions
  • Screws and fittings
  • Cost
  • The right height
  • Substructure
  • Foundations and plinths
  • Gravel fill and support beams
  • Laying wooden terrace

Wooden terraces in the garden have enjoyed great popularity for many years – and if you have some manual skills, you can even build a wooden terrace yourself. However, serious mistakes often creep in when you build it yourself, which limit the life of the wooden decking. With a little help you can plan and build your own terrace in detail. We have a step-by-step guide on what you need to do to make the construction of a wooden terrace a success.

First of all: take your time and make a detailed drawing of your project before you start building – it is worth it! Measure the area intended for the terrace exactly and draw a scaled plan view with pencil and ruler. This should take into account each individual plank, the substructure for the wooden terrace and the distances between the boards. You can then calculate exactly how many wooden planks, support beams and screws you will need. You may even save some money on the construction of the terrace. Important: Plan the size of your wooden terrace in such a way that you do not have to saw through any planks lengthwise if possible. If you can’t avoid it, be sure to saw through this plank with a table saw with a guide rail, or have it cut to size at the hardware store.

The right wood for the terrace

The most popular wood for wooden decking is Bangkirai, a tropical wood from Southeast Asia. It is very heavy, weather-resistant and has a reddish-brown hue. There are also a number of other tropical wood species with comparable properties but different color tones, such as massaranduba, garapa or teak. A fundamental problem with tropical woods – despite all the constructive advantages – is the overexploitation of tropical rainforests. If you decide to use tropical wood, then be sure to buy FSC-certified wood. FSC stands for Forest Stewardship Council – an international organization that promotes sustainable forestry worldwide. However, this seal does not offer one hundred percent security, as it is often falsified, especially in the case of highly sought-after wood species such as Bangkirai.

Bankirai decking boards

Very popular are terrace boards made of Bangkirai. Tropical wood has an attractive color and is very durable. But buy the wood only if it bears an FSC label

Native wood species

If you want to be on the safe side, buy wood from domestic forestry. Relatively durable and about 40 percent cheaper than Bangkirai are, for example, terrace boards made of Douglas fir or larch. Robinia wood is even more durable, but also more expensive and more difficult to obtain. For some years in addition so-called thermo-wood is offered. A special temperature treatment gives beech or pine wood the same durability as teak wood. Going one step further, decking made of Wood-Plastic-Composites (WPC). This is a composite material of wood and plastic, which is also very resistant to weathering and rotting.

The right dimensions

Terrace boards are usually offered in 14.5 centimeters width and 2.1 to 3 centimeters thickness. The length varies between 245 and 397 centimeters, depending on the provider. Tip: If your terrace is wider and you have to lay two planks butt to butt in each lane anyway, it is best to buy shorter planks. They are easier to transport and process, and the joint is then not too close to the outer edge of the wooden deck, which is always a little "patched" looks.

The support beams for the wooden planks should have a minimum thickness of 4.5 x 6.5 centimeters. The distance between the bars should not exceed 60 centimeters. The projection from the beam to the edge of the terrace should not exceed 2.5 times the beam thickness – in this case a good 16 centimeters. This formula also applies to the plank overhang. It should not significantly exceed 6 centimeters for 2.5 centimeter thick planks.

Wooden terrace from thermo-ash

The right covering for the wooden terrace

Substructure for a wooden terrace

The right substructure for the wooden terrace

Wooden terrace

Cleaning and maintenance of wooden terraces

Terrace made of WPC boards

How to lay decking boards correctly

Terrace made of WPC boards

In trend: WPC decking boards

Wooden terrace

Laying decking boards: The 5 most common mistakes

Screws and fittings for wooden terraces

All visible screws and metal parts used in the construction of your wooden terrace must be made of stainless steel. Reason: normal wood screws corrode due to moisture and the wood gets ugly black-brown spots at the screw joints. A screw size of 5 x 50 millimeters is optimal for the mentioned plank size. Longer screws require more effort and do not make the construction much more stable. It is best to buy countersunk stainless steel screws with partial threads. Screws specially designed for wooden terraces are available in specialized stores. They have a drill point, which penetrates the wood particularly easily, and are screwed in with a multi-tooth hexagon socket. Such screws are also known under the trade name Torx. Torx screws withstand greater torque than normal Phillips screws. Therefore, when screwing them in, they do not easily form sharp-edged burrs on which one could injure oneself.

Terrace edge

If you want to build the wooden terrace at ground level and finish it off with a stone edge, you need to excavate the subsoil deep enough

This is how much a wooden terrace costs

The cost of materials for a wooden terrace depends mainly on the chosen type of wood and the desired substructure.

The cheapest tropical woods are Bangkirai and Garapa. European larch wood as well as Douglas fir wood are not quite as durable, but they are also significantly cheaper. One of the most expensive variants is Ipe, a very durable, heavy tropical wood. You can assume the following indicative prices:

  • Ipe terrace boards (21 x 145 mm): 75-85 Euro/m2
  • Terrace boards from Bangkirai (21 x 145 mm): 45-55 Euro/m2
  • Larch terrace boards (27 x 145 mm): 17-25 euros/m2
  • Terrace boards made of Douglas fir (26 x 120 mm): 15-20 Euro/m2

The purlins for the substructure of the wooden terrace should always be made of the same type of wood as the planks, so that both last the same length of time. Alternatively, you can choose a type of wood with longer durability for the foundation. Important: Use only planed wood. Depending on the thickness and type of wood, you can calculate the following costs:

  • Ipe construction timber (70×70 mm): 13-15 euros per linear meter
  • Construction timber from Bangkirai (42×65 mm): 9-11 Euro per running meter
  • Larch construction timber (45×70 mm): 3,50-4,50 Euro per running meter
  • Construction timber made of Douglas fir (40×68 mm): 3-4 euros per running meter

With the purchase of wood is already covered by far the largest part of the costs. For the rest of the required material, there are still the following costs:

  • Terrace screws made of V2A steel (5,0×50 mm): ca. 20 Euro/100 pieces
  • gutter stones (16x16x12 mm): ca. 1 Euro per piece
  • Dry concrete for foundations (z. B. "quick-mix"): ca. 7 Euro per foundation
  • Filling sand: ca. 6-10 euros per cubic meter
  • Pond liner (EPDM, 1mm thick): 11-14 euros per square meter
  • Weed fleece (90 g/m2): ca. 2-3 Euro per square meter

If you build the wooden terrace yourself, you should possibly include rental fees for powerful cordless drills and screwdrivers with interchangeable batteries. The investment is worthwhile, because experience shows that simple DIY equipment quickly breaks down, especially when processing heavy tropical timber.

If you have your wooden terrace built by a professional, there will of course be craftsmen’s costs in addition to the material. Calculate for an average size wooden terrace (approx. 15 to 20 square meters) about 40 working hours of 50 to 60 euros each.

The height of the wooden terrace

Measure your wooden terrace very carefully, especially in height. Especially for wooden terraces on the house, you usually have predetermined heights, such as the threshold of the patio door. It should be at the level of the decking so that there are no dangerous trip hazards. Rule of thumb for planning: either an exact height connection or a clearly visible step. Also light wells for basement rooms, of course, should not be built over with the wooden terrace. For wooden terraces at ground level in the garden, the subsoil must be excavated correspondingly deeper than for wooden terraces that protrude above the ground surface and end with a skirting board. And also the transition from the terrace to the garden should be planned in.

If the wooden terrace is not covered, you should install a small slope of about one percent along the wooden planks (one centimeter per meter). This allows rainwater to drain off well along the longitudinal grooves. This is especially important in shaded areas, where the terrace does not dry out so quickly. The longer the moisture can stay on the wood, the shorter the life of the patio decking. In addition, algae can grow over time and make the decking very slippery.

Distance of the wooden terrace from the house wall

In many building instructions it is recommended to screw the first support beam directly to the house wall. We advise against this for two reasons: Firstly, dirt and rainwater collect in the groove between the wall and the wood – an ideal breeding ground for wood-destroying fungi. On the other hand, the wood works and expands in the presence of moisture. A tight connection with the house wall can cause stresses in the wood, which can lead to cracking or bulging. The same applies to the wooden planks: They should therefore be laid at a distance of at least five millimeters from the house wall – especially if they are parallel to the wall.

The substructure of the wooden terrace

The most difficult step in the construction of a wooden terrace is the supporting structure. There are different methods of construction, from a simple concrete block substructure to point foundations with beam supports. We recommend a substructure with concrete blocks on small foundations. This is inexpensive and not so rigid. For the beams rest on the stone without further fastening, so that the wood can work. Before you start, you should mark out the intended area for the wooden terrace at the corners with metal rods. Mark the height of the top edge of the supporting beam with a circumferential string, taking into account the required gradient. The height is equal to the final height of the terrace minus the thickness of the decking boards.

Terrace cross section

Exemplary construction of a wooden terrace: (1) Foundation (ca. 20 x 20 x 40 centimeters), (2) filling sand (about 10 to 15 centimeters), (3) weed fleece, (4) gravel layer (about five centimeters), (5) concrete stone (gutter stone, 16 x 16 x 12 centimeters), (6) pond liner, (7) wooden beams (45 x 70 millimeters), (8) wooden planks (145 x 21 millimeters), (9) wooden block as spacer, fixed on both sides with metal angle, (10) wooden plank as screen

The next step is to excavate the entire area and replace the topsoil with about 10 to 15 centimeters of fill sand. The floor height after preparing the subfloor depends on the desired terrace height: If the terrace decking is to be above the floor level, as in our example, including the side screen, the prepared subfloor must be about ten centimeters lower than the floor surface.

Set foundations and plinth stones

Now dig foundation holes for the substructure according to your drawing along the upper closing edge at a distance of no more than one meter from hole center to hole center. It should be around 20 x 20 centimeters in size and 40 centimeters deep. If you want to make the work a little easier, you can also use a soil auger for this purpose. The equipment can be borrowed from the hardware store.

Fill the foundation holes in rows with earth-moist concrete and compact it thoroughly. After that, lay a plastic fleece over the finished foundations as protection against weed growth. Place on it one concrete base stone for each foundation. Square gutter stones measuring 16 x 16 x 12 centimeters are best suited for this purpose. They are also known as basement stones and are used in road construction to pave the side drains next to the sidewalk. Tension a second string that runs at the height of the lower edge of the later support beam. Align the base stones in rows exactly to this height. To do this, you need to either underpin it with additional concrete or knock it down a little with a rubber mallet. Also use a spirit level to check that each pedestal stone is level. Use this principle to lay the foundation rows for the other supporting beams of the terrace at a maximum distance of sixty centimeters from each other.

Substructure for a wooden terrace

The correct substructure for the wooden terrace

Apply gravel fill and lay supporting beams

When the concrete has hardened, cover the entire surface with a layer of gravel about five centimeters high. This so-called clean layer under the terrace ensures that rainwater quickly seeps into the ground and humidity does not become too high. This increases the service life of the decking material. Then place the support beams at an exact distance from each other, after you have cut them to the correct length with a saw. Between the beams and the base stone you should place a piece of pond liner measuring around 16 x 16 centimeters with a smooth surface. It ensures that moisture does not penetrate into the stone. If necessary, you can also compensate for slight height tolerances with several layers of pond liner.

Tip: If you need to lay two support beams butt to butt because their length is not enough, you should connect them together. It is best to use perforated plates made of stainless steel, which you screw on both sides. The joint should rest on a base stone for static reasons.

Pre-drill the wood

Important: Pre-drill only the decking board and not the support beam, otherwise the screw will not have enough grip at the end

Lay the planks of the wooden terrace

Now it is time to build the actual terrace. Start laying the decking boards at one end and choose one that is as straight as possible. Place them on the supporting structure and align them exactly at right angles and, if necessary, with the recommended distance from the house wall. If the planks were not cut cleanly and squarely at the sawmill, you should re-cut one end with a chop saw before installation. Then fasten the plank to each support beam with one screw at the front and one at the back. This prevents the wood from arching up in the event of moisture.

Be careful when screwing them to the supporting beams: for optical reasons, all screws should be exactly in one line. A taut mason’s cord is very helpful as a guide. You should pre-drill the screw holes in each deck board, at least for hard tropical woods. The drill must be one millimeter larger than the screw so that the wooden planks can work and are not under too much tension.

Attach a special countersink to the drill with a clamping screw. This is how the recess for the screw head is also milled out in one operation. Some screw manufacturers include a suitable drill bit with countersink in the screw package. For screwing in the screws, it is best to use a powerful cordless screwdriver with a suitable Torx attachment and interchangeable battery pack. Experience has shown that the current storage capacity of tropical woods in particular is quickly exhausted. By the way, the screws can be screwed in more easily if you dip them briefly in vegetable oil beforehand.

Terrace made of WPC boards

How to lay decking boards correctly

To maintain an exact plank spacing of five millimeters everywhere, you should work with hardwood or plastic spacers. They are inserted into the joint at the front, middle and back before screwing on the plank. If the blank space varies because a decking board is not perfectly straight, use a lever clamp or tensioning strap. This way you can easily press the board into the right position. After screwing, you can usually only get the spacers out again with a pair of pliers.

For reasons of structural wood protection, experts recommend inserting a three-millimeter-thick plastic washer made of polyamide at every screw connection between the plank and the support beam. This has the advantage that the planks and support beams do not have any contact surfaces and dry off more quickly after rainfall. However, this technique is rarely practiced nowadays, even by professional companies, due to time constraints.

Straight finishing edge

To get a straight edge at the end of the terrace, it has proven useful to let the planks protrude a little at one end first. Only at the end they are brought to a uniform length with a hand-held circular saw. Before sawing, fix a guide rail using screw clamps so that the edge is exactly straight. You must of course measure the guide rail so that the planks protrude beyond the support beams by the desired length.

Terrace boards

View of a wooden terrace with professionally installed decking boards

Large wood decking: Lay planks butt to butt

With large wooden terraces, the construction becomes a bit trickier because the planks are not long enough to cover the entire terrace. In order to still achieve an attractive overall appearance, you must take this into account when building the substructure: At points where a new plank is to be placed, lay two support beams next to each other on the plinth with a gap of about three to four centimeters. Now start each new row alternately with a longer and a shorter plank, so that you have two offset butt joint rows. Make sure that the joints are at least five millimeters wide and that the screws are exactly in line. For optical and constructional reasons, you should also screw the continuous planks to both adjacent support beams.

Depending on the construction, you can either border the wooden terrace at the end with a paving edge or – in the case of somewhat elevated seating – add a plinth trim so that the substructure is not visible. The skirting board must be below the decking boards so that water drainage is not impaired. Also use decking boards for the fascia and cut them to the correct length. They are then fixed to the side of the support beams with stainless steel screws. Ideally, the fascia board should end with the edge of the terrace without any offset. If the distance from the longitudinal beam to the edge of the terrace is too large, you can, for example, insert suitable wooden blocks as spacers and fix them with stainless steel angles.

Remaining work

Finally, check all the screws of the wooden terrace once again and tighten them slightly if necessary so that the screw heads do not protrude. Then sand all corners and edges with sandpaper and sanding block or orbital sander. This is important so that you can also walk on the terrace barefoot without injuring yourself on wood splinters. Finally, you only need to clean the surface from wood and metal chips with a broom.

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