Part of the
Documents
Download our U-Values brochure which contains 100's of examples of wall and floor constructions to meet specific u-value targets using our range of blocks
External
For a comprehensive suite of
modelled thermal bridging junctions and psi-values for our range of blocks, please visit the RCD Website
Our wide range of block types and thermal conductivities give the builder multiple options for finding the most practical and economical solution for meeting target u-values. Furthermore, exceptionally low u-values can be achieved resulting in improved SAP ratings with the possibility of reducing the amount of additional and expensive energy saving measures.
The table below summarises the key technical properties of our block range including their thermal conductivity values.
Part L 2021 of the Building Regulations came into force in June 2022 as a stepping-stone to another round of significant changes in 2025 when the ‘Future Homes Standard’ takes effect.
The Future Homes Standard aims to significantly reduce carbon emissions from dwellings by focusing on, among other things, getting the fabric energy efficiency of the building as good as possible before relying on other technologies.
The transitional arrangements for Part L 2021 only apply to homes where building work has commenced on each individual plot before 15th June 2023.
This is significant as previous Part L changes could be avoided if work had already started on a site. With Part L 2021 the new regulations apply to any plots that have not yet started.
There are now four separate targets for Part L 2021 supported by the new SAP 10 method of assessment:
1. Primary energy target
2. CO2 emission rate
3. Fabric Energy Efficiency Standard (FEES)
4. Minimum standards for fabric and fixed building services
Fabric Energy Efficiency Standard (FEES)
The FEES requirement is where our masonry wall and floor solutions can make a difference. Getting the fabric of the building right at the design stage will make achieving compliance easier. There are two u-value categories to be taken into account:
1. Notional u-values (aka Nominal u-values)
2. Limiting u-values (aka Backstop u-values)
The new SAP 10 method of assessment software creates a ‘notional’ dwelling based on the inputted information and calculates how much energy the proposed construction will use. By achieving the notional u-values, your dwelling should meet the requirements for CO2 emissions and comply with the requirements.
In cases where notional building element u-values values cannot be achieved, the limiting / backstop u-values can be used. This will however make compliance more difficult to achieve and must be offset elsewhere in the dwelling thereby adding cost and complexity to the overall design.
Notes: Party wall compliance is achieved by fully-filling the cavity and ensuring effective edge-sealing.
Air permeability testing must be carried out on each and every dwelling. A sampling approach is no longer allowed.
The Future Homes Standard (FHS) indicative specification is based on current guidance from the Department for Levelling Up, Housing and Communities but is subject to change.
There are no backstop values for
existing buildings / extensions and
the limiting values shown in this
table must be met!
Robust Detail Party Walls as approved for use with Thomas Armstrong’s range of blocks have been updated to include fully-filled options and therefore allow a party wall u-value of 0.00 W/m2K to be applied.
Furthermore, solid wall options (traditional blocks laid flat or solid Airtec blocks) allow a u-value of 0.00 W/m2K to be applied.
The limiting value for air permeability has been set at 8 m³/hr/m² tested at 50 pascals, and the requirements for on-site air permeability testing has been increased over previous regulations so that every property now requires testing. In reality, air permeability figures approaching 5 m³/hr/m² will be required to help achieve SAP compliance.
Masonry block walls using any type of Thomas Armstrong Concrete Block have been shown to easily achieve these figures provided that good workmanship is employed. Figures of around 5 m³/hr/m² are commonplace and are desirable.
A parge coat on the internal wall faces can contribute to exceptionally low air permeability figures of 2 or less which help to
achieve Passivhaus and Code Level 4 requirement
Table: Air Permeability of Thomas Armstrong Concrete Blocks
However, the designer has to be aware that air quality might suffer, and mechanical ventilation systems may have to be installed to avoid condensation and related health issues for the residents.
Higher thermal performance and airtightness of the building fabric has increased the significance of heat loss at junctions and must be accounted for in SAP calculations.
Simply put, the detail of each junction between each building element throughout the property (e.g. wall/window, floor/wall junctions) must be assessed individually to give a ψ “psi” value for that junction. The psi values are then added together to give an overall Linear Thermal Bridging figure for the property; its “y-value”. There are currently 3 options for determining the overall y-value of a building:
Current Status:
For aggregate and Airtec blocks, option 3 can be used. As part of the CBA and the APA we have a comprehensive range of modelled thermal bridging details resulting in significant improvements over the options 1 & 2 described below.
All models are available as Construction Details here.
At Thomas Armstrong (Concrete Blocks) Ltd we pride ourselves on our high level of customer service across the company. Our friendly staff will be more than happy to help answer any questions you have relating to sales and our products as well as any technical advice you have. Please contact our local office (see offices) near you today!