When and how to construct a rooftop pool: helpful advices, construction types, and load distribution techniques
A swimming pool project is perhaps a dream for many of your clients althought a suitable project space isn’t always available. Constructing a rooftop pool might offer the solution for enjoying outdoor relaxation even in urban settings! Let’s explore when it’s feasible to design a rooftop pool without damaging the existing structure, the recommended structural analysis software to use, along with costs and precautions to consider.
Feasibility of Rooftop Pool Construction
Before planning a rooftop pool on a terrace, understanding factors like construction systems, materials, and costs, it’s crucial to assess feasibility regarding installation and load-bearing capacity.
The feasibility of a rooftop pool largely depends on the existing building’s structural characteristics. Assessing the structural elements’ strength using a structural analysis software is always recommended. This process provides precise insights into the additional load on the roof and any required reinforcements. Crucial considerations include the weight of the new structure, water, building age, flooring type, and maximum resistance. Only after structural calculations, load considerations, and stress transmitted to the floor can the maximum pool size be determined, considering measurements, especially depth. Additionally, consulting local regulations and national standards before starting the project is advisable to assess permits, constraints, and current regulations.
Let’s delve into evaluating a rooftop pool’s impact on floor stresses.
Assessing Increased Floor Stresses
The inception of a rooftop pool involves a critical phase: structural calculation. A detailed study of the building structure hosting the pool is essential since pool installation significantly increases the load on the existing structure. Choosing the installation site involves considering several factors, including soil strength, existing foundations, and building orientation, all playing crucial roles.
The first step is understanding the additional loads a pool requires on the terrace. Using water’s specific weight, at 1000 kg/mc, one can assess the load per square meter transmitted by the pool, making it comparable to accidental project loads used for floor calculations.
For every 10 cm of water height, the floor load increases by 100 kg/sqm. Thus, for water heights of:
- 20 cm, the load will be 200 kg/sqm;
- 50 cm, the load will be 500 kg/sqm;
- 100 cm, the load will be 1000 kg/sqm.
Once the load per square meter transmitted by the pool is determined, an initial assessment comparing it to accidental project loads for floors can be made. If the water height exceeds 20 cm, the accidental project load (usually estimated at 200 kg/sqm) might be surpassed. However, note that the accidental project load is generally assumed to be distributed across the entire floor surface, while the pool’s load is localized to a specific area of the roof.
Some designers might consider an accidental load of 400 kg/sqm for terraces, assuming them to be potentially crowded areas to enhance safety. However, this isn’t a universal rule. In the absence of specific documentation, as a precaution, it can be assumed that the terrace floor was designed to support an accidental load of 200 kg/sqm.
Apart from water weight, considering the pool structure’s weight is crucial. While inflatable pools may neglect this weight, fixed-structure pools like those with hydro massage systems can range around 100 kg/sqm, added to the water weight.
Floor stress increment also depends on the pool’s surface and its position concerning the structure’s beams and pillars. The linear load transmitted from the pool to the floor also relies on the pool’s plan shape. In the case of a rectangular pool, the load per unit length acting on the calculation’s floor strip will be constant. For a circular pool, the linear load will vary.
Furthermore, the pool’s placement on the terrace affects stress increment. Placing the pool in different terrace positions leads to varying stress levels on the floor. For instance, pool positioning:
- at the midpoint leads to a +34.2% increase in bending moment at the midpoint of the span;
- adjacent to the perimeter beam results in a +45.0% increase in bending moment within the span;
- on a beam or load-bearing wall’s edge maximizes the negative moment at the support. In this case, the increase in negative bending moment is 11.1%;
- centered on a pillar or at the intersection of load-bearing walls, the effect on floor stress is similar to the previous case. However, stress increase on the beam will be minimal, as the pillar or wall intersection will absorb the pool’s weight.
Once the floor’s stress increment due to the pool’s presence is determined, it’s the structural engineer’s responsibility to verify the existing floor’s strength and deformability. This requires information about floor material characteristics like concrete and steel, section dimensions, and reinforcement characteristics.
Such details can be inferred from investigations and tests on the existing floor or the original project’s analysis, if available. Depending on available information, the level of knowledge regarding the existing structure will be established.
If strength verifications fail, designing specific floor reinforcement interventions, such as laminating or using FRP, becomes necessary to adapt the floor to required safety levels.
Weight distribution for rooftop pool construction is essential to evenly spread the new load on existing structural elements. The most common intervention involves using grids made of hot-dip galvanized steel beams of various sizes and thicknesses (variable based on the load) alongside special aluminum panels.
During design, specific calculations are necessary to distribute the pool’s weight, considering both the structure’s total weight and its placement on the terrace or attic. This phase is vital to ensure building stability. The goal is to minimize the pool’s weight and strategically distribute it.
Usually, beams are positioned flatly and laterally fixed to poles or beams without damaging the floor, enabling compensation and beam flexion based on the load they support. Beams typically have an average thickness of 10-20 cm.
An essential aspect is the use of aluminum panels composed of an internally honeycombed structure, extremely rigid and lightweight simultaneously. These panels support high loads with minimal thickness, allowing for maximum pool height without surpassing the existing parapet. These panels possess various technical features like lightweight, stiffness, weather resistance, and the ability to withstand static loads.
Furthermore, during pool construction, a focused approach to weight optimization is crucial. For instance, adapting standard pools to reduce overall weight by rounding corners, using lightweight materials like sintered EPS for stairs, benches, and relaxation areas, alternative filtration systems, and reinforced liner instead of mosaic. These choices significantly reduce pool weight, saving structural load without compromising quality. To execute calculations, evaluate loads, and structural element resistance while ensuring compliance with current technical regulations, using a structural analysis software is advisable. Designing safely is always the best choice and shields against potential issues, risks, and liabilities.
Rooftop Pool Types
Once the intervention’s feasibility is evaluated, choosing the pool type comes next.
The selection depends on various variables related to structure, external finishes, and accessories. Choices range from those lined with impregnated pine wood to those with shaped and textured edges or infinity pools, etc. There are also pools with non-slip edges and ladders besides plastic or fiberglass pools easy to assemble and maintain. For swimming enthusiasts, there are counter-current pools with a motor generating adjustable intensity waves based on individual needs and training requirements. Additionally, temperature control devices, spa-style hydro massage, and more options are available.
Determining the pool type relies on available space dimensions, budget, and project area climate conditions. Material quality also dictates the pool’s lifespan.
Fiberglass pools, for example, can be installed quickly and at reasonable costs. However, being a prefabricated structure in a single or double block, it offers limited design freedom. Moreover, its surface layer tends to degrade faster than other materials.
Steel structures are easy to install, known for their lightweight and elasticity. They offer more design freedom in terms of shape and size, but limited choices in lining, usually limited to PVC liners.
In general, among the most commonly used materials for panoramic pool construction, we find polyester, stainless steel, and shotcrete (sprayed concrete). Each option has its characteristics: fiberglass-reinforced polyester is quick to install but demands more maintenance, stainless steel offers greater strength and design freedom with less maintenance, while sprayed concrete allows adherent and resistant construction on any surface and shape.
For rooftop pools, it’s important to consider a double-glass structure, an upper container for water, and a lower layer to prevent leaks. Coatings can be made with porcelain stoneware, mosaic, or liner, ensuring reliable sealing.
Innovative Systems: The Retractable Pool
For those desiring a pool but needing to utilize terrace space, an innovative and practical solution exists: the retractable deck.
It’s an automatic system employing a gear mechanism enabling automatic (via remote) or manual pool covering and uncovering, in more economical versions. When the deck covers the pool, the area becomes usable for other purposes, furnished with tables and chairs, for instance. Even when closed, the pool space has a system allowing air circulation, preventing humidity and material degradation. Here are the advantages:
- Space utilization – when the pool is covered, the area can be used for other functions and furnished, for example, with tables and chairs;
- Safety – children and pets are prevented from falling into the water unsupervised;
- Dirt prevention – when the pool is covered, water isn’t dirtied by leaves and dust;
- Aesthetics – unlike traditional pool covers, the retractable deck doesn’t disrupt terrace harmony. It’s available in various wood shades or even artificial grass.
For more design ideas, read “How to Design a Swimming Pool, the Complete Guide“.
Rooftop Pool Costs
In terms of prices, the cost for a rooftop pool can vary considerably, starting from about €10,000-15,000 for a basic size of 3×3 meters and 80 cm depth. Price differences compared to traditional pools are mainly due to required structural reinforcements, specific installation site conditions, materials, and optional items like purification devices or lighting.
Apart from installation costs, evaluating maintenance expenses is necessary. Fixed costs include:
- Water – the pool needs to be emptied and refilled about once a year. Also, consider that water levels decrease by about half a centimeter per day due to evaporation, requiring periodic refilling. Water is also used for filter washing, removing silt, insects, hair, and debris. Considering an average tariff of 2 euros per cubic meter, for a small-sized pool, the cost is around 50/70 euros per season;
- Energy consumption – a rooftop pool also incurs costs on the electricity bill. The main expense is represented by the circulation pump, with potentially lesser expenses for nighttime lighting. The cost is approximately 50-70 euros per season (June/September). Costs increase if the pool is equipped with heating, whirlpool, or counter-current swimming;
- Water sterilization products – an essential operation to maintain pool hygiene and prevent the proliferation of bacteria and algae is the use of specific products. In most cases, sterilization occurs through the use of chlorine, although in recent years, other types of products like salt and magnesium have gained popularity. Generally, this item costs around 40-50 euros per season;
- Emptying and cleaning, system and control unit tests – if these operations are entrusted to a specialized company, the expense is approximately 200-250 euros per year.
It’s always advisable for the client to have a clear idea of the management and maintenance costs of a pool before initiating the design process. However, it’s also necessary to know that after the construction of a rooftop pool, a property can experience an increase in its market value by 20 to 30%.