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Thermcalc Limited

(Accredited On Construction Energy Assessor)


Thermcalc Limited




Thermcalc will only produce calculations for new build dwellings Calculations will not be carried out for 
commercial buildings or house extensions. 

Modern House

Thermcalc Limited

Design Stage SAP Calculations

A SAP Data form will need to be completed showing the proposed design specifications for each dwelling and along with a set of plan, section & elevation drawings in PDF format. These can then be e-mailed to

Final As Built SAP Calculation and EPC
A completed final SAP and EPC checklist or signed & dated design stage letter confirming the as built specifications & noting any changes. Invoices or photographic evidence is also required showing proof of materials, glazing & gheating system in order to provide the final as built SAP calculation and EPC this imformation can be e-mailed  to
Information required on the checklist plus additional documentation is as follows:

1. Design stage job ref no. J_____
2. Royal Mail post addresses and to which plot that they apply.
3. Make, model of boiler, heat pump etc and hot water storage tank size if applicable.
4. Confirm kilowatt rating of any photovoltaic arrays, size and make of evacuated tube or flat
plate collectors.
5. Please supply MCS certificates for renewable energies, proof of glazing U-Values and an
air pressure test certificate if applicable.
6. Any changes to the original design stage SAP calculation if applicable.
7. Sign, date and supply e-mail address at the bottom of the form.

Provision of photographic evidence / documented proof of construction elements. SAP 2021

Architects should be aware that when drawing up specifications for dwellings, every dwelling will need to be air tested (rather than a test sample in a development), and onsite evidence of installation will be required – a Building Regulations England Part L (BREL) report and photographic evidence / documented evidence is required.


Alongside the usual data that is required to complete SAP Calculations, photographic evidence of the following will be needed:

  • Image of each thermal junction type

  • Insulation levels & type

  • Ventilation systems

  • Main & secondary heating and control

  • Low and zero carbon (LZC) technologies

Wooden Blocks with the text: Fees.jpg

Fees (From 1st January 2021)
Prices are valid at the date of the quote but maybe subject to change due to future price increases.

Total Floor Area up to 300m2 the fee will be £125.00 + VAT
Total Floor Area over 300m2 the fee will be £180.00 + VAT
Final As Built Calculations including EPC document the fee will be £80.00 + VAT
(Please Note that the final SAP & EPC fee is for design stage work was previously carried by Thermcalc Limited. If not

the design stage calculation fee will be payable in addition to this)
Duplicate dwelling calculations £60.00 + VAT
Amendments the fee will be £70.00 + VAT

U-Value calculations £15.00 + VAT
All SAP calculations and EPC´s will be E-mailed to
clients in PDF format only.
Please note that due to new Government legislation, final SAP calculations & EPCs can only be provided once the EPC checklist & relevant other documentation such as air test certificates & MCS certificates are received.

Modern House
L1A Regulations - SAP 2012

Most of the changes in Part L 2013 focus on residential new build, which makes
sense considering that the zero carbon target is only 2 years away. There is 6%
uplift in the Target Emissions Rating (TER) on 2010 levels. This is slightly lower
than the 8% target originally put forward as the Government’s preferred option
when it consulted in 2012, the reasoning being that “it was difficult for detached
houses to achieve the 8% target through fabric measures only, on basis of cost
effectiveness and consistency of construction.”
The most significant difference between 2010 and 2013 Building Regulations is
the introduction of Target Fabric Energy Efficiency (TFEE) and Dwelling Fabric
Energy Efficiency (DFEE). These are measured in kWh/m2/yr and practitioners
will need to learn to use them a lot in the short-term future. For a dwelling to
comply with Criterion 1, the DER must be less than the TER and the DFEE less
than the TFEE. So, what is the TFEE and how is this calculated? The TFEE is
approximately equal to the Interim FEES (Fabric Energy Efficiency Scheme) level,
as defined by Zero Carbon Hub a couple of years ago.
Another new element within Part L 2013 is the introduction of the Elemental
Recipe. This recipe includes a performance specification for the building fabric
and services, which is compliant with Criterion 2 and if it is followed by the design
team should achieve compliance in almost all dwellings for Criterion 1. [1] This
recipe will give a compliant DER and a compliant DFEE (as the TFEE is
calculated by increasing the kWh/m2/yr of the elemental recipe by 15%). This
doesn’t mean that all buildings need to be designed in line with the recipe.
Developers and the design team can always decide to follow a different
specification if their approach still meets the TER and TFEE.

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General Information

Please note to meet compliance with the new SAP 2021 L1A regulations. Using an air source heat pump the option for your primary heating system.  
Low U-Values with a low air pressure test result will all assist you getting a pass for your SAP calculations. (See design example below). 

Example of Low U-Values for Guidance Only
Floor = 0.10
Walls = 0.16

Cold Roof = 0.10
Sloping & Flat Roofs = 0.13
Thermal Bridging - Use Government Approved Accredited Construction Details. (On Planning Portal)

Part O calculations should be carried out prior to your SAP calculations as the results may affect opening sizes. You can use the simplified Part O method for this. (See link below)


Primary Heating - Air Source Heat Pump
Primary Heating Controls - Use time temperature zone control.
Secondary heating such as a HETAS approved log burner or open fire

Party walls The following u-values are specified in the SAP calculation:
Solid. Wall u-value = 0.0
Unfilled cavity with no effective edge sealing. Wall U-value = 0.5.
Unfilled cavity with effective sealing around all exposed edges and in line with insulation layers in abutting elements. Wall U-Value = 0.2.

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L1A New SAP 2021 Construction Examples 

(SAP & EPC Forms Download at The Bottom of The Page)

For Guidance Purposes Only

For Primary Heating -  An air source heat Pump such as a MIitsubishi Ecodan is your best option.

If a gas boiler or oil is used a reasonably large PV solar array will be required.  The size of your roof area

will also need to be able to accept the size of array.

Final SAP & EPC Requirements - Photographic evidence of stages of the build will be required as

proof of insulation type & thickness used. Heating system & external doors & windows.


Air Test Results of 4.0 to 5.0 will be required to achieve a pass in the SAP.

Thermal Bridging Used in SAP will be The Government Approved Table K1 Default.

Ground Floor

1. Solid Slab/165mm Celotex XR4000/Screed. P/A 0.35 U-Value = 0.10

2. Beam/Medium Dense Block/165mm Celotex XR4000/Screed. P/A 0.35 U-Value = 0.11

3. Suspended Timber With 200mm Celotex XR4000 Between Joists. P/A 0.35 U-Value = 0.13

(Note: Ground Floor U-Values Vary Dependant on The Perimeter over Area Value. P/A)
Sheltered Floors
e.g. floor between dwelling & garage > (200mm Celotex laid between joists). U-Value = 0.13
Block Type
Aircrete blocks e.g Celcon, Thermalite and Durox. These blocks give an improved Thermal
Mass Parameter (TMP) in your calculations which improves the SAP rating.

Party Wall - Solid Wall/Dry Lined. U-Value = 0.00

Party Wall - Filled + Filled Cavity Wall/Dry Lined. U-Value = 0.00

Party Wall - Double Insulated Timber Stud Wall .U-Value = 0.00
Walls Fully Filled Cavity
1. Brick/125mm Xtratherm Full Fill CavityTherm CT/PIR (includes 5mm unvented airspace) /100mm
Celcon Standard/12.5mm P´bd52.5 Celotex PL400 on dabs. U-Value = 0.15
2. Brick/125mm Dritherm 32/100mm Celcon Standard/37.5mm Celotex PL4000. U-Value = 0.16

3. Brick/10mm Residual Cavity/90mm Kingspan K106/100mm Celcon Standard/12.5mm P'bd on dabs. U-Value = 0.16

Timber Frame Wall

Weatherboard/Battens/140mm Timber Frame Insulated With 120mm Celotex XR4000/52.5mm Celotex PL4000. U-Value = 0.15

Timber Frame wall With Masonry Outer Leaf

Brick/50mm Cavity/140mm Timber Frame Insulated With 120mm Celotex XR4000/37.5 Celotex PL4000

U-Value = 0.16

Walls Partially Filled Cavity

Brick/50mm Low-E Cavity/85mm Celotex CW4000/100 Celcon Std/12.5 P'bd on dads. U-Value = 0.18

Cold Roof

400mm Mineral Wool (K=0.04) Cross Laid . U-Value = 0.10

Sloping Roof - Unvented With Breather Membrane

120mm Celotex XR4000 Between Rafters/72.5mm Celotex PL4000 Under Rafters. U-Value = 0.13

Sloping Roof - Ventilated

120mm Celotex XR4000 Between Rafters/65mm Celotex GA4000 Under Rafters. U-Value = 0.13

Sloping Roof - Warm 

120mm Celotex GA4000 Between Rafters/65mm Celotex GA4000 Over Rafters. U-Value = 0.13

Flat Roof - Warm

165mm Celotex XR4000 Over Joists. U-Value = 0.13

Flat Roof -Cold

140mm Celotex XR4000 Over Joists/72.5mm Celotex PL4000 Under Rafters. U-Value = 0.13

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Useful Links

Insulation Products

Client 4


Insulation Products

Client 1


Insulation Products

Client 7


Insulation Products

Client 8


Insulation Products

Client 2

Clarendon Testing

Air Testing & Water Calulations. SE Area

Client 3

Falcon Energy Limited

Energy Calculations Inc SBEM

Client 5

Award Energy Consultants

Energy Calculations inc SBEM

Client 6

Greenfish Consulting

Energy Consultant + L1 & L2 EPC Work

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Countrywide Coverage - Air Testing, Sound Testing,Water Calculations, SBEM

Useful Links Continued

Client 4

Planning Portal

Client 1

Recticel Insulation

Insulation Products

Client 7

H + H UK Ltd

Aircrete Blocks (Celcon)

Client 8


Aircrete Blocks (Thermalite)

Client 2

Xella (Ytong Blocks)

Aircrete Blocks

Client 3

Energy Saving Trust

PV Solar Panels

Client 5

Energy Saving Trust

Air Source Heat Pumps

Client 6


Standard Assessment Procedure (SAP)

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Contact Us

1 The Landway, Borough Green, Sevenoaks

TN15 8RG, UK

Thermcalc Limited

Telephone: 07958 661176

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