Sap Calculations for New Build

New Build SAP Energy Estimator

Use this calculator to get a simplified estimate of the annual energy demand and CO2 emissions for a new build dwelling, based on key SAP (Standard Assessment Procedure) factors. This tool provides a basic indication and is not a substitute for a full, official SAP calculation.

Dwelling Floor Area (m²):

Average Ceiling Height (m):

External Wall Area (m²):

Roof Area (m²):

Window Area (m²):

Door Area (m²):

Wall U-value (W/m²K):

Roof U-value (W/m²K):

Floor U-value (W/m²K):

Window U-value (W/m²K):

Door U-value (W/m²K):

Air Permeability (m³/(h.m²) @ 50 Pa):

Main Heating System Efficiency (%):

Hot Water System Efficiency (%):

Number of Occupants:

Solar PV Annual Generation (kWh/year):

Estimated Results:

Enter values and click 'Calculate' to see your estimate.

function calculateSapEstimate() { // Constants for simplified calculation var heatingDegreeDays = 2200; // Typical for UK climate var hotWaterDemandPerPerson = 45; // kWh/person/year var co2FactorGas = 0.21; // kgCO2/kWh (assuming natural gas for heating/HW) // Get input values var dwellingFloorArea = parseFloat(document.getElementById("dwellingFloorArea").value); var ceilingHeight = parseFloat(document.getElementById("ceilingHeight").value); var externalWallArea = parseFloat(document.getElementById("externalWallArea").value); var roofArea = parseFloat(document.getElementById("roofArea").value); var windowArea = parseFloat(document.getElementById("windowArea").value); var doorArea = parseFloat(document.getElementById("doorArea").value); var wallUValue = parseFloat(document.getElementById("wallUValue").value); var roofUValue = parseFloat(document.getElementById("roofUValue").value); var floorUValue = parseFloat(document.getElementById("floorUValue").value); var windowUValue = parseFloat(document.getElementById("windowUValue").value); var doorUValue = parseFloat(document.getElementById("doorUValue").value); var airPermeability = parseFloat(document.getElementById("airPermeability").value); var heatingEfficiency = parseFloat(document.getElementById("heatingEfficiency").value); var hotWaterEfficiency = parseFloat(document.getElementById("hotWaterEfficiency").value); var numOccupants = parseFloat(document.getElementById("numOccupants").value); var solarPVGeneration = parseFloat(document.getElementById("solarPVGeneration").value); // Validate inputs if (isNaN(dwellingFloorArea) || dwellingFloorArea <= 0 || isNaN(ceilingHeight) || ceilingHeight <= 0 || isNaN(externalWallArea) || externalWallArea < 0 || isNaN(roofArea) || roofArea < 0 || isNaN(windowArea) || windowArea < 0 || isNaN(doorArea) || doorArea < 0 || isNaN(wallUValue) || wallUValue <= 0 || isNaN(roofUValue) || roofUValue <= 0 || isNaN(floorUValue) || floorUValue <= 0 || isNaN(windowUValue) || windowUValue <= 0 || isNaN(doorUValue) || doorUValue <= 0 || isNaN(airPermeability) || airPermeability <= 0 || isNaN(heatingEfficiency) || heatingEfficiency 100 || isNaN(hotWaterEfficiency) || hotWaterEfficiency 100 || isNaN(numOccupants) || numOccupants <= 0 || isNaN(solarPVGeneration) || solarPVGeneration < 0) { document.getElementById("result").innerHTML = "Please enter valid positive numbers for all fields."; return; } // 1. Calculate Dwelling Volume var dwellingVolume = dwellingFloorArea * ceilingHeight; // 2. Calculate Total Fabric Heat Loss Coefficient (W/K) var totalFabricUValueArea = (externalWallArea * wallUValue) + (roofArea * roofUValue) + (dwellingFloorArea * floorUValue) + // Floor heat loss often based on floor area (windowArea * windowUValue) + (doorArea * doorUValue); // 3. Calculate Ventilation Heat Loss Coefficient (W/K) // Simplified conversion from m³/(h.m²) @ 50 Pa to Air Changes Per Hour (ACH) // A very rough estimate: 1 ACH ~ 25 m³/(h.m²) @ 50 Pa for a typical dwelling var ventilationRateACH = airPermeability / 25; var ventilationHeatLossCoefficient = 0.33 * dwellingVolume * ventilationRateACH; // 0.33 is specific heat capacity of air * density // 4. Total Heat Loss Coefficient (W/K) var totalHeatLossCoefficient = totalFabricUValueArea + ventilationHeatLossCoefficient; // 5. Gross Space Heating Demand (kWh/year) // Formula: (Total Heat Loss Coefficient * Heating Degree Days * 24 hours/day) / 1000 W to kW var grossSpaceHeatingDemand = (totalHeatLossCoefficient * heatingDegreeDays * 24) / 1000; // 6. Gross Hot Water Demand (kWh/year) var grossHotWaterDemand = numOccupants * hotWaterDemandPerPerson; // 7. Net Energy Demand (considering system efficiencies) var netSpaceHeatingDemand = grossSpaceHeatingDemand / (heatingEfficiency / 100); var netHotWaterDemand = grossHotWaterDemand / (hotWaterEfficiency / 100); var totalNetEnergyDemandBeforePV = netSpaceHeatingDemand + netHotWaterDemand; // 8. Energy Demand After Solar PV Contribution var energyAfterPV = Math.max(0, totalNetEnergyDemandBeforePV – solarPVGeneration); // 9. Estimated Annual CO2 Emissions var annualCO2Emissions = energyAfterPV * co2FactorGas; // Display results var resultsHtml = "

Energy Performance Summary:

"; resultsHtml += "Estimated Gross Space Heating Demand: " + grossSpaceHeatingDemand.toFixed(0) + " kWh/year"; resultsHtml += "Estimated Gross Hot Water Demand: " + grossHotWaterDemand.toFixed(0) + " kWh/year"; resultsHtml += "Total Estimated Net Energy Demand (before PV): " + totalNetEnergyDemandBeforePV.toFixed(0) + " kWh/year"; resultsHtml += "Energy Demand After Solar PV Contribution: " + energyAfterPV.toFixed(0) + " kWh/year"; resultsHtml += "Estimated Annual CO2 Emissions: " + annualCO2Emissions.toFixed(0) + " kg/year"; resultsHtml += "Note: This is a simplified estimate. Official SAP calculations are more detailed and required for Building Regulations compliance."; document.getElementById("result").innerHTML = resultsHtml; } .sap-calculator-container { font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; max-width: 700px; margin: 20px auto; padding: 25px; background: #f9f9f9; border-radius: 10px; box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1); border: 1px solid #e0e0e0; } .sap-calculator-container h2 { color: #2c3e50; text-align: center; margin-bottom: 20px; font-size: 1.8em; } .sap-calculator-container h3 { color: #34495e; margin-top: 25px; margin-bottom: 15px; font-size: 1.4em; border-bottom: 2px solid #e0e0e0; padding-bottom: 5px; } .sap-calculator-container p { color: #555; line-height: 1.6; margin-bottom: 10px; } .calculator-inputs { display: grid; grid-template-columns: 1fr 1fr; gap: 15px; margin-bottom: 20px; } .input-group { display: flex; flex-direction: column; } .input-group label { margin-bottom: 5px; color: #34495e; font-size: 0.95em; font-weight: bold; } .input-group input[type="number"] { padding: 10px; border: 1px solid #ccc; border-radius: 5px; font-size: 1em; width: 100%; box-sizing: border-box; } .input-group input[type="number"]:focus { border-color: #007bff; box-shadow: 0 0 5px rgba(0, 123, 255, 0.3); outline: none; } .sap-calculator-container button { grid-column: 1 / -1; padding: 12px 25px; background-color: #28a745; color: white; border: none; border-radius: 5px; font-size: 1.1em; cursor: pointer; transition: background-color 0.3s ease; margin-top: 15px; } .sap-calculator-container button:hover { background-color: #218838; } .calculator-results { background: #e9f7ef; border: 1px solid #d4edda; border-radius: 8px; padding: 20px; margin-top: 20px; } .calculator-results p { font-size: 1.1em; color: #155724; margin-bottom: 8px; } .calculator-results p strong { color: #0a3622; } .calculator-results .disclaimer { font-size: 0.85em; color: #6c757d; margin-top: 15px; border-top: 1px dashed #c3e6cb; padding-top: 10px; } @media (max-width: 600px) { .calculator-inputs { grid-template-columns: 1fr; } }

Understanding SAP Calculations for New Builds

The Standard Assessment Procedure (SAP) is the UK government's methodology for assessing and comparing the energy and environmental performance of dwellings. It is a crucial part of the Building Regulations (Part L) for new constructions and conversions, ensuring that new homes meet minimum energy efficiency standards.

Why are SAP Calculations Important?

Building Regulations Compliance: All new dwellings in the UK must demonstrate compliance with Part L of the Building Regulations, which sets targets for energy performance and carbon emissions. SAP calculations are the primary method for proving this compliance.
Energy Performance Certificates (EPCs): A SAP calculation generates the data required for an Energy Performance Certificate (EPC). An EPC provides an energy efficiency rating (from A to G, with A being the most efficient) and is legally required when a property is built, sold, or rented.
Informing Design Decisions: By modelling the energy performance of a dwelling, SAP calculations help architects, developers, and builders make informed decisions about insulation levels, heating systems, ventilation strategies, and renewable energy technologies.
Predicting Running Costs: SAP provides an estimate of a dwelling's annual energy costs for heating, hot water, lighting, and ventilation, giving future occupants an idea of their potential utility bills.

Key Factors Influencing SAP Ratings

A comprehensive SAP calculation considers a wide array of factors. Our simplified calculator focuses on some of the most impactful:

Dwelling Dimensions: The size and shape of the building affect heat loss.
Fabric U-values: These measure how effectively building elements (walls, roof, floor, windows, doors) prevent heat from escaping. Lower U-values indicate better insulation and less heat loss.
Air Permeability (Air Tightness): This measures how much uncontrolled air leaks in and out of the building. A tighter building (lower air permeability) reduces heat loss through draughts.
Heating and Hot Water Systems: The efficiency of the primary heating system (e.g., gas boiler, heat pump) and the hot water system significantly impacts energy consumption.
Renewable Energy Technologies: Systems like solar photovoltaic (PV) panels or solar thermal water heating can offset energy demand and improve a dwelling's SAP rating.
Ventilation Strategy: While essential for indoor air quality, poorly designed ventilation can lead to heat loss. SAP considers natural, mechanical, and heat recovery ventilation systems.
Thermal Bridging: These are areas in the building fabric where insulation is discontinuous, leading to localised heat loss.

How This Calculator Works (Simplified Model)

Our "New Build SAP Energy Estimator" provides a simplified approximation of a dwelling's energy performance. It uses common engineering principles to estimate:

Heat Loss through Fabric: Based on the area and U-value of each building element (walls, roof, floor, windows, doors).
Heat Loss through Ventilation: Estimated from the dwelling's volume and air permeability.
Hot Water Demand: Based on the number of occupants.
System Efficiencies: Accounts for the efficiency of your chosen heating and hot water systems.
Renewable Contribution: Deducts energy generated by solar PV from the total demand.

Assumptions made by this calculator include:

A typical UK heating season with 2200 Heating Degree Days.
A simplified conversion from air permeability to air changes per hour.
Standard hot water demand per person.
Natural gas as the primary fuel for heating and hot water, with a fixed CO2 emission factor.

Due to these simplifications, the results should be used for indicative purposes only. A full SAP calculation involves much more detailed data, including orientation, shading, thermal mass, lighting, and more precise climate data.

Interpreting Your Results

Gross Space Heating/Hot Water Demand: This is the raw energy required before accounting for system efficiencies.
Net Energy Demand (before PV): This is the energy you would need to purchase from your energy supplier, considering your heating and hot water system efficiencies.
Energy Demand After Solar PV: This shows the net energy demand after any on-site renewable generation has been subtracted. A lower number here means lower running costs and environmental impact.
Annual CO2 Emissions: This estimates the carbon footprint of your dwelling based on its energy consumption. Lower emissions are better for the environment.

Tips for Improving Your New Build's SAP Rating

Enhance Insulation: Specify U-values that are significantly better than the minimum Building Regulation requirements for walls, roofs, floors, windows, and doors.
Improve Air Tightness: Aim for a very low air permeability score (e.g., 3 m³/(h.m²) @ 50 Pa or less) through careful design and construction detailing.
Choose Efficient Heating Systems: Opt for highly efficient boilers, heat pumps (air source or ground source), or district heating connections.
Consider Renewable Technologies: Integrate solar PV, solar thermal, or biomass systems to reduce reliance on fossil fuels.
Optimise Hot Water: Use efficient hot water cylinders, point-of-use heaters, or solar thermal to reduce hot water energy demand.
Minimise Thermal Bridging: Pay attention to junctions between building elements to avoid cold spots and heat loss.
Consider Mechanical Ventilation with Heat Recovery (MVHR): For very airtight homes, MVHR systems provide fresh air while recovering heat from outgoing stale air, improving both comfort and efficiency.

Working with an accredited SAP assessor early in the design process is highly recommended to ensure your new build achieves its desired energy performance and complies with all regulations.