New Part L Regulations for Swimming Pools and What it Means

The Government have proposed that swimming pools be included in the Part ’L’ of the building regulations bringing them in line with the same insulation requirements of that which appertain to domestic and, if applicable, commercial properties.

The regulation states that: “Where a swimming pool is being provided in a building, the U-value of the basin (walls & floor) should not be worse than 0.25W/m2/K as calculated according to BS EN ISO 13370.”

This regulation will require the swimming pool basin (walls & floor) to be insulated so that the Thermal Transmission (heat loss) through the basin is reduced to 0.25W/m2/0C, which approximately equates to a pool at 28C and the ground at say 10C losing 4.5W/m2 into the surrounding ground. In comparison an un-insulated concrete pool at the same temperature will loose 100W/m2. There are of course a number of variables that could change this figure but it gives an idea of what insulating a pool shell can achieve.

From October 2010 the pool builder will have to produce calculations to the Local Authority together with drawings showing how the construction method proposed to build the pool will comply with the new Part L regulation.

So how do we do it?

There are four standard methods of producing a swimming pool shell.


Reinforced shell using poured concrete in forms to produce the required shape.
Gunite or Shotcrete where concrete is blown on to the steel reinforced walls and floor to form the required shape.


Concrete blocks are laid on a foundation or reinforced concrete slab and laid to form the required shape. The blocks are either solid block laid on their flat to form a wall 225mm thick or hollow blocks 225mm in width which are laid and filled with concrete. The hollow blocks can be reinforced with steel.


Made from: Polymer or Steel or purpose made Insulated Panels, are laid on a concrete slab or foundation and bolted or locked together to form the required shape.


A preformed shell is delivered to site and installed in a one piece operation.

There are also two types of lining for Nos. 1-2; Tiled or a PVC type of liner which produce the waterproof membrane in the swimming pool.

No. 3 always uses a PVC liner to form the waterproof membrane with the exception of some insulated panels which can receive a tiled finish.

No. 4 does not require any form of waterproof membrane being a seamless structure of fibre glass or polymer material.

An insulating product can be fixed to the pool shell and floor on either the outside or inside of the pool with the exception of the preformed shell where practicality and the nature of the construction mean that the insulation has to be fixed to the outside. The use of insulated panels however has the added benefit of not requiring any additional insulation to the pool walls.

There are a number of insulation materials that can be used to give the required U Value to the pool walls and floor. The practicality of each has to be considered and to whether its use is suitable for structural reasons or ground conditions. Various loadings or fixings that are applied to the pool shell could possibly exclude some forms of insulation applied to the inside of the pool. The design of the shell has to be taken it into account on these occasions. Loads or fixings to the top of the pool are an example of this where the insulation will not take a load or fixing. A high water table will also exclude some products fixed to the outside, where dry conditions will not.

Expanded polystyrene is an example of this due to its water absorption properties. It should not be used in wet areas but is perfectly suitable in absolute dry conditions. Extruded Polystyrene however can be used in either condition. Although certain Extruded Polystyrene and Polyurethanes absorb water their absorption rates are so low that it can be ignored.

It is quite apparent that although there are a number of products that will achieve the required U value. The type of insulation or product cannot be included in any requirement of the regulation and it will be up to the contractor or Architect /Consulting Engineers to specify the product that will give the required level of insulation under Part ‘L’ regulations.

U-value 0.18
The performance of individual products is available from different manufacturers in their technical guides to assist in the choice of product to use. It has been proven that insulation applied to the inside of a pool is more efficient than on the outside and this has to be taken into account when choosing which product to use. The thickness of the insulation depends on the type that is used and a typical type such as extruded polystyrene will be 75mm-100mm thick so the builder should allow for this in the overall dig size.

Swimming pools are constructed in varying soil conditions and in some instances out of the ground. The heat loss through the shell of the pool is therefore dependant upon the ground conditions that surround the pool.

If a pool was constructed in dry ground with the insulation on the outside, then it would require less insulation than if it were constructed in heat absorbing wet ground. On the other hand if the insulation was on the inside then there is no difference and the insulation thickness is only that which will give the required heat retention in the pool.

When pools are constructed with insulated panels it is irrelevant whether the ground is dry or wet as the pool wall is the insulation as well as being its structural component. In this case the only decision to be made is whether to put the floor insulation on the inside or under the floor slab. If it is on the inside then there are no thermal bridging problems. If it is put on the outside then it should be placed in a manner that prevents thermal bridging.

There are standard methods within the building regulations for building and insulating basements that are very similar to that of a swimming pool and the methods of insulating these structures can be used to insulate swimming pools.

The calculations to prove the construction will have to be laid out according to: Thermal Performance of buildings- Heat Transfer via the ground – Calculation Methods BS EN ISO 13370. The pool builder will have to submit these calculations for the approval of the Local Authority direct or through an Architect or a suitably qualified person or persons.

If the pool builder is going to use concrete blocks or using sprayed concrete or poured concrete into shutters to build the pool he will have to produce the calculations for heat loss relating to the type of insulation he/she intends to use. However if the pool is built from manufactured insulated panels or other pool kits then the manufacturer should produce the necessary calculations for the builder to submit proving that the panels and floor construction meet required U value (level of heat loss) through the pool basin.

If an existing pool is renovated then insulating that pool to modern standards would become compulsory under the proposed regulations. The regulations propose that if 50% of any part of the pool including the rendering is removed and replaced then this will be deemed to be a renovation not a repair and the pool will be subject to Part L regulations. In this case insulating the floor by putting the insulation on the outside would not be practical and the insulation would have to be placed on the inside. This would not be a problem for a liner pool but a tiled pool however would have to use a product that could be tiled upon and there are a limited number of products available for this purpose.

There are two situations where a swimming pool is sited, INDOOR & OUTDOOR. Each has a different rate of heat loss associated to it. The outdoor pool has a greater heat loss than an indoor pool due to it being subjected to outdoor elements such as wind and rain. However both pools if sited in the same ground conditions loose the same amount of heat into the ground.

Evaporation has a more significant effect on outdoor pools than indoor. The outdoor pool is subjected to wind and at most times a lower air temperature so heat is lost through the surface of the pool.

In an indoor pool the air temperature is higher and normally 1C higher than the water. This reduces the evaporation rate and the air handling units normally recover the latent heat of vaporisation which is then put back into the air or pool water. Most of the heat loss is therefore through the walls and floor.

Common sense therefore dictates that the U values for the walls and floor of a pool should be reduced to save energy which is where the new Part ’L’ regulations for walls and floors come in. Although the walls and floor of an outdoor pool have a lower percentage of the overall total heat loss, the heat loss through them is the same as an indoor pool so should have the same U value in their construction. However the regulation to insulate an outdoor pool will not come into effect until 2013 but the savings in running costs are nevertheless real and should be brought to the attention of the customer requiring an outdoor pool so they could be given the choice and opportunity to insulate or not.

The use of Pool Covers should be highly recommended but practicality dictated that their use could not be included in the Part ’L’ regulations due to the comparative short longevity of the product.

The amount of energy used on swimming pools is significant and the Government’s policy of reducing carbon levels made it a target for regulation and inclusion of swimming pools into the Part ‘L’ Regulations was without doubt inevitable.


PREFORMED GLASS FIBRE OR POLYMER ALL IN ONE SHELLS. A preformed shell is delivered to site and installed in a one piece operation.