AECB Silver Performance Standard

Background to the Silver Standard

Whilst in the UK, a prescriptive standard might still be the best introduction to the approach needed, a lack of suitable UK funding has meant that a sufficiently robust prescriptive standard cannot currently be developed to allow widespread adoption of, and support for, the Prescriptive Standard Route. The original hope was that pre-approved combinations would be issued by the CarbonLite Programme designed to satisfy the requirement of the standard for different types of small building; e.g., detached bungalows, semi-detached houses and flats, without the designer doing any significant further calculations. Practitioner experience has shown that it is very easy for architects to design in energy inefficiency e.g., by a combination of poor glazing orientation, shading elements created by the building form etc. such that it is difficult to meet 40kWh/(m².a) despite PH components and U values.

Certification

Independent certification has been considered and could, in principal, be provided by Passivhaus Certifiers. However there are a number of problems with this route:

  1. Cost – re-entering a building into PHPP can be very time consuming as can obtaining and verifying all the information required. There is no reason why Silver Certification would cost any less than Passivhaus.
  2. Quality Assurance (QA) – whilst certification independent of the project’s design and energy consultants helps avoid the propagation of mistakes, there is a limit as to what the certifier can check at a distance.
  3. If the AECB is to use non-Passivhaus Institute approved certifiers then this would introduce a very onerous level of quality assurance for the AECB.
  4. Potential conflict with Passivhaus standard(s) has been raised as a possible concern.

Thus a self certification route has been developed whereby the self certifier (typically the building’s energy consultant) takes responsibility for certification and for underwriting the Silver Standard claim.The AECB has provided a form of declaration for completion by the certifying consultant but will deliberately not audit or take responsibility for the certification.

The AECB self certification process is designed to make explicit the project’s claim to be a low energy design and to provide the consumer with a degree of protection under trading standards – without the AECB having to get involved in quality control and legal matters.

This approach puts the responsibility for performance claims clearly with the person signing the certificate and a duty of care on the client to ensure that the consultant is competent and suitably insured.

AECB Silver Standard certification costs

All prices are plus VAT and are for guidance only as each project will be individually assessed.

Guide prices for domestic buildings (per unit or terrace block):

AECB Members
up to 250m2 £50
251 – 1500m2 £150
1501m2 and < 3000m2 £180
3001m2 and above £250
Non Members
up to 250m2 £250
251 – 1500m2 £750
1501m2 and < 3000m2 £900
3001m2 and above £1250

Charges for non domestic buildings will be based on the above prices, based on floor area with an additional cost of up to 50%, the final cost to be advised on application to cover the relevant complexity of the project.

AECB Silver Standard criteria

The AECB Silver Standard can be said to be achieved where a building that is designed and modelled using PHPP1 in accordance with current Passivhaus methodology meets the following requirements:

Parameter Target Notes
Delivered Heat and cooling ≤ 40kWh/(m².a) According to PHPP * and Passivhaus methodology.
Primary Energy demand 120 Wh/(m².a) ditto
Air tightness (n50) ≤ 1.5 h-1 (≤ 3 h-1) With MVHR (with MEV) **
Thermal Bridges *** Psiexternal <0.01 W/m Calculated if > 0.01 W/m
Summer overheating <10% <5% recommended


* Passive House Planning Package.
**  it may not be possible to meet the heat demand target without MVHR for some buildings.
*** Standard Passivhaus methodology is used. If no calculation is submitted, then the decision as to whether a detail is thermal bridge free may be queried at the discretion of the AECB.

Notes on compliance

AECB Silver compliance cannot be assumed unless the building has been modelled in PHPP and construction quality has been verified:

  • Providing a PDF copy of the PHPP Verification sheet can be accepted as confirmation that the building has been designed in PHPP
  • A set of key construction details (drawn details and their photographic equivalent) will be required from all self-certified projects to provide evidence of construction quality please use the construction detail checklist provided.

Both of these elements of verification are important as it is possible to design a building that uses Passivhaus Approved components and typical Passivhaus U values but that fails to meet the AECB Silver Standard because of poor form or fenestration.

Energy Performance

  • Specific heat demand according to PHPP ≤40kWh/(m².a)
  • Specific primary energy demand according to PHPP ≤120kWh/(m².a)
  • Air leakage (n50) ≤1.5 h-1 if balanced ventilation with heat recovery used or ≤3 h-1 if mechanical extract ventilation is used3.

Thermal Bridges

The Passivhaus approach of designing out thermal bridges and using external dimensions simplifies modelling and guards against problems such as mould and condensation. For these reasons it is recommended that where possible designs are thermal bridge free according to the Passivhaus definition. Where it is not practical or economical to achieve a thermal bridge free junction, the additional heat loss must be determined. If no calculation is submitted, then the decision as to whether a detail is thermal bridge free may be queried at the AECB’s discretion.

Comfort Requirements

Whilst the Passivhaus approach simplifies the achievement of winter comfort conditions by requiring surface temperatures including glazing to be greater than 17°C, this is unlikely to be achieved with all Silver Standard buildings, which are likely to have higher window U values than required for Passivhaus. To prevent user dissatisfaction the designer will need to consider comfort, for example limiting glazing areas and careful positioning of heat emitters as well as heat distribution within rooms and the building as a whole.

Passivhaus Certification requires summer overheating according to PHPP to be <10% (hours exceeding 25°C) but 5% or less is recommended.

Responsibility

Responsibility for claims made about the building performance lie with the energy consultant or building designer making that claim. Whilst actual energy consumption for any building will vary due to a wide range of factors including annual weather variation, occupant behaviour and normal building tolerances, the claim that a building is designed to the AECB Silver standard can be independently verified.

Where a certificate is provided by the AECB, the responsibility for certification still rests with the professional signing this certificate and not with the AECB however the AECB reserve the right to recall the certificate in the case of proven malpractice or false claims.

The AECB will retain electronic copies of such details as are required to verify that the building meets the AECB Silver standard but does not necessarily check for compliance.

Supporting evidence requirements

Drawing & Photographic Record Drawings. Pdf A4 format Photographs jpeg format.
1 All elevations of completed building One elevation per page. Scale bar to be included. one photo. for each elevation
2 Floor to wall junction – continuity of insulation visible
3 Floor to wall junction – airtightness measures visible
4 Intermediate floor to wall junction – airtightness measures visible
5 Roof to wall junction – continuity of insulation visible
6 Roof to wall junction – airtightness measures visible
7 Typical window in wall detail – jamb with wall insulation measures visible
8 Typical window in wall detail – jamb with airtightness measures visible
9 Typical treatment of services penetration in fabric – with airtightness measures in place
10 Typical MEV or MVHR installation showing ducts & duct insulation
11 Hotwater storage and pipework – showing tank and pipe insulation
12 Windows/doors – showing opening light with seals and glazing spacer bars
Other
13 Air pressure test certificate (pressurisation and depressurisation results)
14 PHPP verification sheet as pdf
15 Copy of building users manual

Support and further information

Silver Standard Certification is handled at the Low Energy Building website and you will be required to either create an account or log in to process certification.

If you require technical assistance or further information about AECB Silver certification please contact us at silvercertification@aecb.net.

AECB members can access compliance tools, valuable design and construction guidance and training:

You or your consultant will need to use PHPP.

Members only, Design & Construction guidance to help you design to AECB Silver or Passivhaus can be found here and here

A non member taster can be found here

If you need to undertake training in the design of low energy buildings or just the use of PHPP click here.

If you are applying the Silver Standard to a retrofit project you may need training in delivering moisture-robust energy efficiency measures, click here.

You may wish to incorporate environmental condition monitoring into your project (especially if it is a retrofit). Click here for more details.

To browse projects aiming at or certified to AECB Silver click here

To browse projects aiming at or certified to Passivhaus click here

To browse projects aiming at or certified to EnerPHit click here

Non members – join us now

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