SAP Calculations assess the energy efficiency of any property that is new build, or converted from an existing building into residential dwellings, It ensures that all residential dwellings comply with Building Regulations Approved Document Part L1a (New Build) or Approved Document Part L1b for conversion projects,
SAP (Standard Assessment Procedure) is the calculation method to determine the dwellings C02 emissions, Fabric efficiency and energy usage costs. Below outline how the SAP Calculations process works
The first step in the SAP calculations process, is to calculate the dimensions of the property, this is done by using architectural drawings that are to scale. measurements are taken for floor areas, wall areas, roof areas as well as glazing areas and door areas. this step is completed to model the dwelling to scale and account for all of the thermal elements within the dwelling of which heat will be lost through.
Once an accurate representation has been calculated of the dwelling in the form of ‘exposed thermal elements’ as above, The next step would be to calculate how thermally efficient these elements are. in order to calculate how thermally efficient a wall/floor/roof element is, a U-Value calculation must be carried out. A U-Value calculation will show how well the element will retain heat.
U-Values are completed by modelling the construction of each element along with the lamba values for each element. Lamba values can be found on product technical data sheets or from the product manufacturer and are displayed in W/m2K. An example construction may look like the below
Example Wall Build up
-105mm Facing Brickwork
– 100mm PIR Insulation in cavity
– 100mm lightweight blockwork
– 12.5mm Plasterboard, Dot and dabbed to blockwork
– 3mm Lightweight plaster
Once the U-Value calculations of the thermal elements are complete, we are starting to build a representation of how the building as a shell will retain heat.
Once the calculations & U-values are complete, the ‘openings’ must not be inputted into the model that is being created of the dwelling, Openings are windows and doors that are within the thermal elements. Windows and doors are classed as ‘weak points’ in the structure as the U-Values are higher than that of walls/floors/roofs (Note: The lower the U-Value figure, the better thermal values the element has!) an example of this would be that a wall could have a U-value of 0.28W/m2K, where are windows in a dwelling may have a U-Value of 1.6W/m2K.
All of the windows, roof lights and doors will be inputted into the calculations along with the U-values for these elements, Again, these can be found in product data sheets or from the product manufacturer.
Now that the model we are creating of the dwelling has wall, floor, roof, windows and doors all with U-values, the next step would be to assess the Ventilation, Heating and Heating controls of the dwelling and water heating elements, The efficiency of the heating system plays a big part in achieving compliance, however the heating controls are equally if not even more important. At this stage the heating system and controls as well as any ventilation systems would be inputted into the calculations, we can now see how the dwelling contains heat as well as how efficiently is heats and controls the heat within the dwelling.
A key element of ensuring that the efficiency of a dwelling is maintained is the air permeability of the dwelling, also know as the air tightness, the air tightness of the dwelling plays a key part in ensuring that heat can be retained, if the U-values of the thermal elements and opening are performing to a high standard but the dwelling is not air tight, then the dwelling will leak heat. at a design stage, an air permeability target will be set, once the dwelling is complete, an air tightness test will be carried out to determine the result of the air test and this can then be inputted into the calculations at an ‘as-built’ stage, when looking to set and maintain an air tightness level, it is always important to consider the ventilation of the property at the same time, lack of ventilation can cause damp.
Once all of the above are complete, some final elements are added to the assessments, this includes the use of any renewable energy sources such as solar PV systems, or air or ground source heat pumps. Renewable energy can dramatically improve the energy efficiency of the overall dwelling.
Other elements considered are Low energy lighting, building type and orientation.
The above outline the process that will be taken when carrying out SAP Calculations on a new build dwelling, if you have any questions or would like to know more regarding how the process works or how to ensure compliance, visit www.vision-energy.co.uk or contact one of our technical team on 01625 315040