What weight can a wooden terrace withstand?

Installing a Jacuzzi, or Spa allows you to create a real relaxation area in your garden. Combining a spa with a composite wood deck provides an optimal aesthetic appearance. However, some technical constraints must be taken into account to ensure that your installation is durable. Here’s all you need to know before you put a spa on a composite deck.

Place a spa directly on the terrace

The installation of your jacuzzi directly on a composite terrace is possible but strongly not recommended. Indeed, the weight of the spa added to that of the water and users can greatly impact the life of your terrace and accelerate its deterioration. Composite wood blades, although resistant, are not made to withstand such a daily load and may break prematurely.

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For the bravest who still want to install their spa directly on a composite deck, only one tip: pay very attention to the weight!

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Spa on terrace: calculate the required load

Before placing a Jacuzzi or spa directly on your composite deck, you need to make sure that it can withstand such a weight. To find out the total weight of the spa, you need to add:

  • The empty weight of the spa;
  • The weight of water;
  • And the weight of users.

Example: vacuum spa (290 kg) capacity of 900 L (900 kg) 3 users of 70 kg (210 kg) = 1,400 kg.

Then it is worth knowing the weight of the spa per square meter. For this, it is necessary to divide the weight of the spa by its surface.

Example: 1,400 kg /3.78 m2 (spa 1.8 m wide and 2.1 m long) = 370 kg/m2.

In this example, the terrace would have to be able to withstand a load of at least 370 kg/m2 to receive the spa.

What support for the spa ?

Although the installation of the spa on composite decking is strongly not recommended, it is better to opt for a terrace placed on an aluminum structure that rests on a waterproof floor (concrete slab or tile). This will provide greater strength and stability to your terrace.

To minimize the risk of breakage of your composite blades, the best solution is to opt for full-profile blades from Neowood’s Extreme range. Ideally, the blades should be based on an aluminum structure such as the Trocosto® structure which has a mechanical strength of 500 kg/m2. Like composite blades, this structure is rot-proof, and can be exposed to water without problems.

Although solutions exist to try to extend the life of your terrace with a jacuzzi, we strongly advise you to opt for another solution: the buried or semi-buried spa.

Buried Spa or semi-buried and composite decking

As if it were an above ground pool, the semi-buried or buried spa is an ideal aesthetic and much safer solution than direct spa placement on the composite deck. In this case, either the spa arrives at ground level (buried spa) or it protrudes from the ground (semi-buried spa). Of course, the terrace must be installed after laying the spa, which requires additional cutouts. A square or rectangular model will be easier to integrate than a round model. If you want a buried (or recessed) spa, two solutions are available to you.

  • Dig the floor, and make a concrete tank in which your spa will be recessed. This method of laying requires substantial work, and the intervention of a professional.
  • Raise the composite deck, to put it at the height of the spa, giving the impression that it is buried. This solution is much simpler to set up, if only to pass cables and pipes without having to dig trenches. However, steps will need to be provided to access the terrace.

Jacuzzi on composite deck: prepare the floor

Whether buried or semi-buried, your spa should be placed on a perfectly clean and flat floor. A 15 cm concrete slab is therefore required to receive the spa. Here are the stages of pouring a concrete slab.

  • Mark the location of the slab to the floor. Make sure that it protrudes at least 70 cm on each side of the spa.
  • Dig the soil to a depth of 20-25 cm.
  • Lay a layer of gravel about 15 cm.
  • Lay a polyane cloth to protect the slab from rising moisture.
  • Make a formwork with 25 mm boards that will contain the concrete, attached to pegs planted at the four corners of the slab. Brush the boards with deformwork oil.
  • Lay the reinforcement to ensure that it is fully coated in the concrete. You will need to raise it with wedges, so that it is not in contact with the ground.
  • Spoil concrete dosed at 450 kg/m2.
  • Pour the concrete as you go and pull to the mason ruler, then float the surface.
  • Wait 2 days before removing the formwork boards, and 10 days to lay the spa on the tile.

Lay the composite deck around the spa

Raising a composite deck is relatively simple to implement to enjoy a semi-buried or buried spa. Depending on the necessary elevation, there are several solutions:

  • Lay concrete studs on which the slings of the terrace will rest;
  • Lay fixed pads or adjustable, then pine or aluminum lambings;
  • For a higher elevation (recessed spa), the terrace will be laid on stilts (it will be necessary to provide concrete foundation for stilts) with adjustable pole legs.

Remember that a building permit is required for a terrace elevation of more than 60 cm and an area of more than 20 m2. If the area is less than 20 m2, you must file a prior declaration of work.

Allow a 50 to 80 cm technical space around the spa, to access the machinery and carry out maintenance operations. At the immediate outskirts of the spa, the deck blades must be removable in order to access this space.

Reminder of the rules concerning the laying of slurries:

  • Observe a maximum distance between the lambourdes;
  • Keep a 5mm gap between each end of a slurp
  • ; Double the cutters at the end of the cutting of two blades in the length, but the lambors are in contact with each other.

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