CONSULTANCY

Andy provides consultancy services to domestic clients, other Architects & designers, contractors, timber frame designers, and other industry professionals. This includes:

Technical Advice
- Reviews of other Architects/designers' detail drawings when using natural building materials;
- Assistance complying with Building Control;
- PHPP Modelling to predict a building's energy use (even if not targetting a performance standard such as Passivhaus/AECB CarbonLite);
- Assistance with developing contractor/timber frame supplier's standard details;
U-Value Calculations & typical construction build-ups;
- Modeling U-values using the BRE U-Value Calculator;
- Standard construction build-ups (e.g. wall/roof/floor constructions), for small projects using natural materials;
Thermal Bridge Calculations;
AECB CarbonLite Modelling & Certification;
Passivhaus Design;
PHPP Modelling - including when not aiming for Passivhaus/CarbonLite.

Thermal Bridge Calculations

Wall/roof junction (eaves) thermal bridge calcualtion.

What is a Thermal Bridge?

Thermal Bridges are points in building fabric where more heat is lost than is calculated in U-value calculations, this can be due to the geometry of the building, such as a wall corner or wall/roof join, or because of a junction between two elements (e.g. around a window opening), or interruption in an otherwise continuous thermal element (e.g. where a balcony fixes into a wall);
U-values are a measurement of heat lost per square metre of building fabric (e.g. wall/roof/floor) per degree of temperature difference from inside to outside assuming a constant temperature difference, so thermal bridge calculations are essentially a correction to U-values and therefore need to be specific to a build-up and U-value;
Thermal bridges can be repeating, (e.g. timber wall, roof rafters, or cavity wall ties in masonry) in which case they can be included in a U-value calculation, or linear / point thermal bridges, which need to be calculated and accounted for separately.

When do you need thermal bridge calculations?

If you need to look at the risk of condensation at a junction;
If targeting Passivhaus, EnerPHit, or AECB CarbonLite, you may need thermal bridge calcualtions to enter into PHPP for some, or all, of the junctions;
To comply with Building regulations Part L. New buildings generally need to have Thermal Bridge calculations to enter into SAP for all major junctions:
- If using a standard construction or manufacturer's details, you may be able to use their standard calculations, however if you vary from these details, you may need bespoke thermal bridge calcualtions;
- Building Control used to allow Accredited Details and their accompanying thermal bridge calculations to be used;
- The Accreddited details have now been withdrawn, so you will either need to use a manufacturer's standard construction & details if they already have calculations, or you will need to get bespoke calculations done.

Intermediate Floor junction thermal bridge calculation

Wall/intermediate floor junction thermal bridge calcualtion.

Wall/floor junction thermal bridge calcualtion.

How can Andy Hales help?

Using Flixo, Andy can model thermal bridges in 2D for all junctions and around window/door openings to provide thermal bridge calculations required for SAP/PHPP;
Provide fRsi figures for condensation risk assessment.
Andy can:
- Either model thermal bridges based on the details specific to your project;
- Or model a supplier/contractor's standard details with a range of build-ups and options to cover most situations to satisfy building control and Passivhaus requirements.

AECB CarbonLite

Services

Andy is an AECB CarbonLite Approved Certifier & Modeller, and can:

Model your building in PHPP and use the CarbonLite spreadsheet to check your project is on target to meet the standard;
Provide design and detailing advice to help meet the standard;
Calculate thermal bridges and condensation risk (fRsi) as required;
Provide site assistance during construction;
Assist you in preparing the information required for certification during and after construction;
Collate the information required and certify the project;
Register the project on the AECB Low Energy Building Database.

AECB CarbonLite Key Criteria

Air Permeability (measured to TM23 AP50 average of Pressurisation & Depressurisation tests):

New-Build: ≤ 1.5 m3/(m2.hr)

Retrofit: ≤ 2.0 m3/(m2.hr)

Step-by step: ≤ 5.0 m3/(m2.hr) at step 1

Space Heating Demand:

New-Build: ≤ 40 kWh/(m².yr)

Retrofit: ≤ 50 kWh/(m².yr) (or ≤ 100 kWh/(m².yr) with approved exemption)

Either Primary Energy (PE):

New-Build: ≤ 85 kWh/(m².yr)

Retrofit/Step-by-step: report result

OR Primary Energy Renewable (renewable energy needed to meet building energy demand):

New-Build: ≤ 75 kWh/(m².yr)

Retrofit/Step-by-step: report result

Summer Overheating:

≤ 10% exceeding 25°C (best practice: ≤ 3%)

Thermal Bridges & Surface Condensation (fRsi) risk:

New-Build: either design out TBs to < 0.01 W/(mK) or fRsi ≥ 0.75 and limit in PHPP

Retrofit: either calculate all TBs or use 15% of fabric losses then use worst TTB and ensure fRsi ≥ 0.75 and limit in PHPP

Step-by-step: N/A. If significant fabric measures are being installed estimate TB within 0-15% of fabric losses

Ventilation:

Continuous or Demand Controlled MEV, or MVHR

Heating & Hot Water (if Heat Pump required flow temperature ≤ 50°C (best practice ≤ 45°C):

New-Build: non fossil fuel system (usually a Heat Pump) or low carbon district heating

Retrofit: Existing system may be retained with practical plan for future low carbon heating supply in place

Step-by-step: Heat Pump required

About

Many projects claim to be built, "using Passivhaus Principles" or, "close to Passivhaus standard, but not certified". The problem with this approach is that it misses out on some of the key aspects of the Passivhaus and EnerPHit standards, the rigour and oversight that comes from achieving certification, and is likely to lead to buildings that do not perform as well as expected, the so-called "performance gap" between design and reality (see 'Nearly Passivhaus' is a false economy). For example, if you are not actually trying to achieve certification, the additional time and effort required to eliminate, or calculate and minimise, thermal bridges at design stage and on site is harder to justify, so is less likely to happen, and without the requirement for detailed photo records of the construction process as evidence, it is far easier for things to change on site without being accounted for..

The AECB (The AECB (Association for Environment Conscious Building) is a network of individuals and companies with a common aim of promoting sustainable building. The AECB has created a series of building standards to promote the creation of low carbon, energy efficient buildings that are comfortable and healthy. There are AECB CarbonLite standards for New Build and Retrofit, with several options for how to achieve the retrofit standard, including step-by-step.

The AECB CarbonLite Standards are actually based on Passivhaus Principles, and use the same "whole house" approach where the entire building is modelled in PHPP (the Passivhaus software) taking into account the specific site location, climate, and shading, the building shape, orientation, and detailed construction specification to accurately predict how a building will perform.

The standard is not as strict in terms of performance targets as Passivhaus or EnerPHit, it has slightly lower energy and airtightness criteria, but still requires a high level of airtightness, a properly designed and efficient ventilation system, minimised thermal bridging, good attention to detail (including on site), and thorough recording of information to demonstrate compliance.

Having a standard to target beyond Building Regulations compliance gives clearly defined targets to achieve, and a standard to be measured against, resulting in low-carbon buildings which are far closer in reality to their theoretical design performance than typical in the UK.