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  • Writer's pictureLeigh Julier

From the Ground Up

One of the most common questions asked is what prep needs to be done in preparation to install Grad.

Pedestal systems have mostly been associated with rooftop terraces and balconies; however, Grad can be used much more widely than that. Applications can range from pontoons and boardwalks to holiday lodges, temporary and permanent structures, and general commercial and residential decking. Understanding the project requirements is a must.

Let’s go through each type.


1.      Stabilised Ground

The idea of putting pedestals on soil is and always will be a contentious subject in the industry. Even I struggled to understand it before seeing it done. I am going to tell you that, yes, you can use pedestals on soil, but you need to ensure that it is stable.

What does stable mean? Well, this means the surface needs to be able to withstand 2KN of pressure before you can place pedestals directly onto it. With soils, it is very important to consider the soil type. The stability of sandy soil is going to be vastly different from clay. This is due to the ability of water to drain. All landscapers, groundworkers, builders and fencers, unless you’re really lucky, know that clay is a colossal pain to work in. When soil is compressed, the loose soil on top will give as water escapes from the compressed area. In this case, directly beneath the pedestals. Clay disperses water slower, whereas sandy soil will disperse much quicker. To combat this, you will need to dig out around 100mm (4 inches) to find stable soil, although it’s always going to be worth getting this checked by out by an engineer, to be certain.

This dig out ensures that the ground will be less likely to compress and settle once the weight of the deck is added.

Now, I personally recommend that you consider spreading the load across the soil, similar to a building foundation, to help stability. This can be a Type 1 sub-base, Grano-dust, or solid reinforced concrete, which is the best option. You should always consider drainage at this stage. With a non-porous base like concrete, you will need to incorporate a drainage system.

A great alternative is to use ground screws to support the structure. Our PR56 rails can span up to a maximum of 1200mm, requiring fewer screws. Suitable fixings are required, as well as a barrier between the aluminium and steel. Alternatively, these can again be fixed to a timber frame with a flat rail fastened.

For areas of concern, high-traffic areas, or heavier furniture, the density of the pedestals can be increased as needed to further support the deck.


2.     Solid/Hard Ground

Ok, so you’ve got an existing patio or concrete slab that needs to look better. Much better, perfect for using our system. Hard ground is arguably the best way to install our system, but again, a few things need to be considered before you get started.

Firstly, you need to ensure enough space to use the rails. As a minimum requirement, you must ensure that you have the depth for the rail, clip and boards. Our Flat Rail is the smallest profile(12mm), with the rubber strip (2/4mm), clip (6mm) and board (normally 21mm). The minimum gap required is 41mm. This method allows you to fix straight into the patio/concrete without pedestals. That said, pedestals are better for allowing for better airflow around the board, which helps to improve the deck's longevity.  With the pedestal, you have a minimum requirement of 86mm consisting of pedestal (35mm), PR24 rail (24mm), clip (6mm) and board (21mm). Maximum deck height is 408mm with the right accessories.


3.     Unstable Ground/Elevated Decks

Let’s be fair: We’re in the UK. Most of the ground here falls into this category, and we have an abundance of slopes and hills (I grew up in Devon; push-biking everywhere was tiring). As we are not fortunate enough to be flat like Belgium and Holland, our industry always needs to get around this situation.

By all means, the best method is to tier the garden, create flat levels with adequate drainage, and stabilise the ground using one previously mentioned method. However, this may not be suitable for multiple reasons: there isn’t always the budget, time constraints, or digger access, and let’s be fair, digging it out by hand is a mad concept.

When dealing with unstable grounds or raised decks, the best solution is to use timber or steel to create a sturdy structure to support our rails. Although these methods have some drawbacks, they have been tested and proven to work. This is where material choice comes into play, and it's far too easy to be swayed by cost. Cheaper is definitely not the choice here, and the right materials will ensure the structure lasts. To ensure the structure lasts, use

UC4-treated timber and C24 stress grading. Use quality fixings and always cover joists with deck tape to prevent water from seeping in. While these considerations are essential, there isn't time to go into detail, and I recommend signing up for TASK Academy and training with Karl Harrison to learn more.


Once the frame is in place, the rails can be screwed or bolted to it using our innovative clip system. This system offers many advantages, such as reducing warping and eliminating the need for visible screws or nails. It also makes the installation process more efficient and profitable for installers. However, that's a discussion for another time."





4.      Waterproof Membranes/Balconies/Roof Terraces

Our system excels in installations like these (and most people assume this is what our system is designed for). Pedestals won't puncture the membrane and allow water into the building. At the same time, the usable area needs to be strong and stable. Our clips have excellent pull-out resistance, making them a perfect solution.

 These installations are similar to those on hard ground, making them simple and long-lasting.

However, various building standards, including fire ratings, balustrade height, and material constraints, must be considered. We recommend consulting with an engineer to ensure these standards are adhered to. 

Weight can be a concern when it comes to waterproof membranes. However, our Grad system, made of lightweight aluminium rails and plastic, provides the necessary strength while minimising the load. Compared to other options, such as pressure-treated timber or steel, Grad is a superior choice for these installations.

All installations will relate to one of these main ground types. The scope of using Grad for decking is only limited to your imagination. Its versatility allows for limitless design possibilities, and it has been used to create beautiful and unique installations worldwide.

If you have any questions or want to learn more about our Grad system, please get in touch with us here at Grad System UK.

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