HA Acoustics are specialist acoustic consultants covering the UK

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Water Efficiency Calculations

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What Are Water Efficiency Calculations?

Water efficiency calculations predict the water consumption of a proposed new-build and conversion property. The UK Government is focused on delivering a sustainable residential development programme, encouraging improved water efficiency in the built environment.

The Code for Sustainable Homes was introduced in 2007 and The Building Regulations update from April 2010, requirement Part G.2 states that any new build or conversion dwelling must have a water efficiency calculation completed on it.

The Regs state that ‘reasonable provision must be made by the installation of fittings and fixed appliances that use water efficiently for the prevention of undue consumption of water’.

The regulations allow for a maximum of 125 litres of water use per person per day. This figure breaks down to mean internal water use of 120 litres (per person per day) plus an allowance of 5 litres per person per day for outdoor water use. Though it should be noted, that individual local authorities may choose to set a lower target. This is especially true in the south of England, where water shortages are more frequent.

Non-compliance with the above may adversely affect the Standard Assessment Procedure (SAP) calculation and therefore could result in a lower Energy Performance Certificate (EPC) rating. Thus making it harder to rent or sell the property.

When do you need to get a Water Efficiency Calculation?

If you are planning a new build or conversion to residential development the talk to HA. Our advice is to get the calculations undertaken at building design stage, as the final figures may well dictate the number of wet rooms/layout of water useage facilities and the make/model of appliances proposed.


Water Efficiency Calculations

We have found it is far easier for clients to obtain a Pass if the water efficiency calculations concentrate on the products, which use the highest use factor. When calculating the use factor we look at the capacity flow rate of the fittings and multiple these with how often they will be likely to be used. We can advise on such matters as the importance of including certain water use appliances, such as a shower which in the UK is used a lot more than a bath, therefore permitting a bath, which can be used for occasional use.

Why you need to get a Water Efficiency Calculation

The building regulations require a water efficiency calculation to be undertaken and provided they pass a Certificate to be issued in order for the Building Control Officer to sign-off on the residential development. Other important reasons include the importance of us all considering the impact to environment. There is also the importance of cost saving. Using fittings with low-flow rates and capacities will enable water bill savings, as majority of water supplies are now on a meter.

Which domestic appliances are affected?

  • WC’s – The majority of modern toilets have either a single-flush or a dual flush mechanism. The manufacturer provides the flush capacity of both single and dual flush in litres.
  • Taps –The manufacturer will provide the flow rate of the kitchen and bathroom taps, this is measured in litres per minute. If you can’t find this information don’t despair, we have a database of such appliances and so provided you can tell us the make/model, we can look up the relevant information.
  • Baths – another water useage appliance, information needed to be known for baths is the total capacity of the bath, to the overflow, again the volume is given in litres.
  • Showers – The make/model information will provide us with the litres of flow rate.
  • Dishwashers – Measured in litres of water, HA use the ‘per place setting’, information usually being provided in the manufacturers literature. The ‘per place setting’ means the number of litres used in a standard cycle, divided by the number of place settings that the dishwasher can hold.
  • Washing Machines – Similar to washing machines, these are measured as ‘litres per kilogram of dry load’, that means the litres of water used in a standard cycle of wash which is then divided by the capacity of the dry clothes that the drum of the washing machine can take.

What we’ll need to undertake your Water Calculations

To undertake your water efficiency calculations we’ll need from you or your architect a complete set of floor plans showing the number of ‘wet rooms’. Wet rooms include the kitchen, bathrooms, ensuite, utility rooms. In addition, the plans will need to show the number of facilities which will use water such as the showers, WC;s, sinks, dishwashers and washing machines. If this information is not on the plans, it’ll need to be provided separately.

Our water flow rate assessors cover nationwide. As a remote service, we’ll also send you a questionnaire so as to obtain information on each rooms make/model of water useage appliances.

Using the information provided, HA will calculate the projected water consumption levels of the dwelling. Generally, we’ll do the water efficiency calculations at design stage and usually as part of your SAP calculations. However, it’s not unusual for HA to be asked to do the water efficiency calculations when the development is in the process of build or has been built.

We understand that this information is required urgently and therefore we offer a fast turnaround on water efficacy calculations.

How HA can assist

At HA we undertake a number of building compliance services including Standard Assessment Procedure (SAP), air tightness testing, sound insulation testing and ventilation testing. Therefore, HA are well placed to also undertake your Water Efficiency Calculations, enabling you to deal with one friendly, professional company for all your building compliance needs, and thus enabling a cost competitive service.