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What is a G-Value?

What is a G-Value?

Solar Gain Coefficient (g-value)

In the context of windows and glazing, the g-value, also known as the solar heat gain coefficient (SHGC), represents the fraction of solar radiation (both directly transmitted and absorbed and then reradiated) that enters a building through a window or glazed surface. It is expressed as a number between 0 and 1, with higher values indicating a greater ability to transmit solar heat into a building.

The Importance in SAP

The more solar energy that enters a building, the less space heating that is required in the winter. But, in the summer this can lead to overheating.

Like everything in energy modelling, there needs to be a balance. That is why overheating needs to be assessed at planning stage and a full design is carried out to avoid issues further down the building process.

Other Considerations

  • Acoustic Attenuation
  • U-values
  • Off-set/ Thermal bridging
  • Passive Ventilation
  • Purge Ventilation
  • Means of Escape
A New Net-Zero Agenda

A New Net-Zero Agenda

The UK’s Government Net Zero Agenda Press Release
20 September 2023

A change of pace, not direction

What’s Happening?

The purpose of this announcement is twofold: firstly, to reassure the public of the government’s unwavering commitment to achieving Net Zero by 2050; and secondly, to alleviate the financial burden on individuals, given that the UK is currently surpassing earlier projections regarding the path to Net Zero.

What is Net-Zero?

Understanding Net Zero “Net zero” signifies a state where the emissions of greenhouse gases (GHGs) into the atmosphere are balanced by the removal or offset of GHGs, resulting in no net increase in atmospheric GHG levels. In simpler terms, the amount of GHGs added is equaled by what is removed or offset, making it a crucial target in the battle against climate change. Achieving net zero helps limit global warming and mitigates the impacts of climate change.

What’s Changing?

Here are the key alterations:

  • Streamlining Regulations: The government is eliminating unnecessary and heavy-handed measures. This includes discarding proposals for taxing meat and flights, revising residential waste management policies, and reevaluating vehicle passenger regulations.
  • Transition Deadlines: Deadlines for transitioning to clean energy are being adjusted. For instance, the ban on the sale of fossil-fueled cars is now postponed until 2035, and the ban on gas boilers is also being delayed.


What’s the impact on the Property Sector?

These changes may not significantly affect the property sector. The deadline for achieving net-zero status (with a SAP rating of A) by 2050 remains intact. For now, gas boiler installations are likely to continue, given their typical lifespan of 15-25 years. It’s imperative to recognize that time is ticking. Managing and sequencing structural improvements within this timeframe, via planned maintenance plans, is vital. This ensures that when the 25-year mark arrives, buildings are primed for low-energy or zero-carbon technologies like Air Source Heat Pumps (ASHP).

In fact, there is now a stronger incentive to shift towards low-energy and zero-carbon heating. The grant for boiler upgrades has been augmented to £7,500, a sum that can potentially fully fund a new installation of an Air-Source Heat Pump

In Summary

The United Kingdom is evolving with the end goal of becoming Net Zero. The pace of change, along with associated reductions in cost, has happened more rapidly than previously anticipated. This grants us the breathing room to meticulously work towards achieving Net Zero by 2050.

Simply put, the agenda has not changed. It is not a change of direction, merely a change of pace.

U-values and New Targets

U-values and New Targets

A “U-value” is a measure of the rate of heat flow through an element.

It is expressed in W/m2k, and shows the amount of heat lost in watts (W) per square metre of material (for example wall,
roof, floor etc.) When the temperature (k) outside is at least one degree lower.

Lower U-values indicate better thermal insulation, i.e. an element with a U-value of 0.3 W/m2K loses heat at half the rate of an element with U-value of 0.6 W/m2K.

Building elements are normally built up from a number of layers, so U-values must take into account the performance of each layer.

We set out below the minimum U-values for the key building elements in existing dwellings, as
set out in Approved Document L of the Building Regulations – Conservation of fuel and power,
Volume 1: Dwellings.

Table 4.2 Limiting u-value for new fabric elements in existing dwellings
Element type Minimum U-Value W/(M2K)
Roof 0.15
Wall 0.18
Floor 0.18
Window 1.4 or Window Energy Rating B
Roof light 2.2
Doors with >60% of internal face glazed 1.4 or Window Energy Rating B
Other doors 1.4 or Window Energy Rating B

For new buildings however, targets are tighter

  • Walls  0.18 – this can be achieved with a full-filled 150mm cavity and thermal blocks on the inner-leaf
  • Floors 0.13 – this can be achieved with a PIR insulation of at least 150mm insulation
  • Cold Roof 0.11 – this can be achieved by insulating between joists and above with at least 400mm total thickness
  • Warm Roof 0.11 – this can be achieved by insulating between the rafters and at least 150mm of rigid board insulation over top.

In addition air-tightness, thermal bridging and heating efficiencies have been uprated:

  • Airtightness – typical maximum result of 5.0
  • Thermal bridging – all bridges require measuring however defaults are available (target Y-value of 0.05)
  • Heating – if mains gas is to be used, a 92% ErP is required with interlock and compensator.


Offer considerations include:

  • Holistic fabric-first approach to becoming net-zero by 2050 (by the implementation of low/zero carbon technologies and onsite generation)
  • Appropriate ventilation strategies
  • Internal comfort: overheating analysis and background noise levels
  • Water useage
  • Lighting designs

For more information give us a call on 01621 493594 or email

How can air tightness and ventilation prevent condensation and mould

How can air tightness and ventilation prevent condensation and mould

Air tightness and ventilation play essential roles in preventing damp and mould in buildings by controlling moisture levels and air circulation. Here’s how they work together to address this issue:

  1. Air Tightness:
    • Reduced Moisture Infiltration: An airtight building envelope prevents outdoor moisture from entering the structure through gaps, cracks, and openings in walls, roofs, and windows. This is especially crucial in humid or rainy climates.
    • Condensation Control: Air tightness minimizes the risk of warm, indoor air coming into contact with cold surfaces, which can lead to condensation. Condensation can create ideal conditions for mould growth on walls, ceilings, and windows.
  2. Ventilation:
    • Moisture Removal: Ventilation systems, such as mechanical ventilation or natural airflow, help remove excess moisture from indoor spaces. This includes moisture generated from activities like cooking, showering, and breathing. Proper ventilation ensures that humidity levels remain within a healthy range, reducing the potential for dampness and mould growth.
    • Air Circulation: Ventilation promotes air circulation within the building, preventing pockets of stagnant, moist air from forming. Stagnant air can lead to localized moisture problems, which are conducive to mould development.
  3. Balancing Air Tightness and Ventilation:
    • It’s crucial to strike a balance between air tightness and ventilation. While air tightness prevents uncontrolled moisture infiltration, it’s equally important not to create an overly sealed environment that can trap moisture indoors.
    • Mechanical ventilation systems, like heat recovery ventilation (HRV) or energy recovery ventilation (ERV), provide controlled and efficient ventilation while maintaining air tightness. These systems exchange indoor and outdoor air, recovering heat or cooling energy in the process, which helps save energy.
    • Natural ventilation strategies, such as strategically placed windows and vents, can be employed to encourage cross-ventilation and airflow, especially during periods of lower humidity.
  4. Insulation and Thermal Bridging:
    • Proper insulation and the mitigation of thermal bridging (areas where heat escapes more readily) can prevent cold spots on interior surfaces. Cold spots can lead to condensation, so adequate insulation helps maintain consistent indoor temperatures and reduces the risk of moisture-related problems.

In summary, air tightness and ventilation work together to control moisture levels in buildings. A well-balanced approach ensures that the building envelope is sufficiently sealed to prevent unwanted moisture infiltration while providing controlled ventilation to remove excess moisture from indoor spaces. This combination helps create a healthy indoor environment, minimizing the risk of dampness and mold growth.

Why did my Sound Insulation Test Fail?

Why did my Sound Insulation Test Fail?

Part E of the Building Regulations in the United Kingdom addresses sound insulation and requires sound insulation testing for new residential and commercial buildings.


Failing sound insulation testing can be attributed to several factors, including:

  1. Poor Construction Quality: One of the primary reasons for failing sound insulation testing is subpar construction quality. If walls, floors, or ceilings are not constructed to the specified standards, gaps, cracks, or weak points can allow sound to pass through easily.
  2. Inadequate Soundproofing Materials: Using insufficient or inappropriate soundproofing materials can lead to test failure. These materials include insulation, acoustic membranes, and seals. If these materials do not meet the required standards or are not installed correctly, sound can transmit through the building elements.
  3. Airborne Sound Leakage: Sound insulation tests measure both airborne and impact sound insulation. Failing the test may be due to airborne sound leakage, where sound travels through walls or ceilings due to inadequately sealed joints, holes, or penetrations.
  4. Impact Noise: Impact noise, such as footsteps or objects dropping on floors, can result in test failure. If the floor structure is not designed or constructed to dampen impact noise adequately, it can easily transmit to adjacent spaces.
  5. Incomplete or Incorrect Documentation: Insufficient or inaccurate documentation related to building design and construction can lead to test failure. It’s essential to ensure that the design and construction align with the specified acoustic requirements.
  6. Inadequate Isolation: Lack of proper isolation between building elements, such as separating walls or floors, can cause sound to transfer easily from one space to another. This is especially important in multi-unit residential buildings.
  7. Variability in Construction: Differences in construction quality between units or rooms within the same building can lead to uneven sound insulation performance, resulting in test failure in specific areas.
  8. Deficient Windows and Doors: Windows and doors are potential weak points for sound insulation. If they are not constructed with suitable acoustic properties or are not installed correctly, they can allow sound to pass through.
  9. Improper Installation: Even with the right materials, if they are not installed correctly, they may not provide the intended sound insulation. Proper installation techniques are crucial for achieving the desired acoustic performance.
  10. Lack of Testing and Quality Control: Failing to conduct intermediate acoustic tests during construction or ensuring quality control measures are in place can lead to issues being discovered only during the final sound insulation test, potentially resulting in failure.

To avoid failing Part E sound insulation testing, it’s crucial to work closely with architects, engineers, and acoustic consultants from the early design stages. This collaboration ensures that the building is designed and constructed to meet the necessary acoustic requirements, and testing can confirm compliance before occupancy.

Build Tight, Ventilate Right

Build Tight, Ventilate Right

Build Tight, Ventilate Right!

Why is everyone banging on about Building Airtight Homes, but ensuring the Ventilation Strategy is compatible?

Build tight, ventilate right is a fundamental principle in building design and construction that emphasizes creating a well-sealed building envelope to improve energy efficiency, indoor air quality, and overall occupant comfort. This concept underpins the importance of balancing airtightness with adequate ventilation.

Here are some key reasons why “build tight, ventilate right” is crucial:


Energy Efficiency: A well-sealed building envelope reduces the infiltration of outdoor air, which can decrease heating and cooling energy consumption. This can lead to substantial energy cost savings over the life of a building.

Indoor Air Quality (IAQ): Building tightness helps prevent the entry of pollutants, allergens, and outdoor contaminants into the indoor environment, which can improve IAQ and promote occupant health.

Comfort: Airtight buildings are more comfortable because they have fewer drafts and temperature variations. This contributes to a consistent and pleasant indoor environment.

Moisture Control: Proper sealing of a building envelope can prevent moisture infiltration, reducing the risk of mould growth, rot, and structural damage, which can improve the durability of the building.

Radon Mitigation: Building tightness can help prevent the entry of radon gas, a naturally occurring radioactive gas that can be harmful when it accumulates in indoor spaces. This is particularly important in areas with high radon levels. To learn more about Radon and its risks visit:

Controllability: When a building is tightly sealed, ventilation can be controlled and managed more effectively. This allows for the introduction of fresh outdoor air when needed and reduces the reliance on passive, uncontrolled ventilation, such as through leaks and gaps.

Part L and F Building Regulation Compliance: Energy efficiency standards require airtightness testing to ensure that new construction meets specific performance criteria. Compliance with these standards may be necessary for legal and regulatory reasons.

Sustainability: Improving the energy efficiency of buildings is essential for reducing greenhouse gas emissions and combatting climate change. “Build tight, ventilate right” is aligned with sustainability goals by reducing a building’s carbon footprint. All residential homes are required to be net-zero by 2050!

Cost Savings: Building tightness, when combined with efficient ventilation systems, can lead to long-term cost savings in terms of reduced energy bills, maintenance, and repairs.

Resilience: Airtight construction can make a building more resilient to extreme weather events, such as hurricanes and wildfires, by reducing the potential for wind-driven rain or embers to penetrate the building envelope.

In summary, “build tight, ventilate right” is a critical principle in modern building design and construction because it addresses energy efficiency, indoor air quality, occupant comfort, durability, health, and environmental sustainability. Balancing airtightness with effective ventilation ensures that buildings perform optimally and provide a safe and comfortable indoor environment for occupants.


So how can we help at Building Compliance Testing?

Air Permeability Testing: This test measures the air leakage rate of the building envelope and identifies areas that need improvement. It helps ensure that the building is adequately sealed. To learn more about our Air Tightness Services visit our services page.

Ventilation Design, Inspection, Commissioning and Air-flow Testing: This way we can design an efficient ventilation system that meets the specific needs of the building and its occupants. To learn more about our Ventilation Services visit our services page.

Alternatively to learn more:


phone: 01621 493594

Passivhaus Air Tightness Testing

We have been lucky enough to work with the guys at Assets For Life.

On their recent Passivhaus project we got the chance to have a quick catch up with Jay to talk Passivhaus Air Tightness Testing.

“Don’t panic, ensure an air barrier is embedded into the design, and if in doubt, get in touch with the specialists”

George Booth – Building Compliance Testing

Check it out on Youtube:
Learn more about Passivhaus:

Find Assets For Life at:

We are registered with ATTMA to carry out Passivhaus TSL4 Air Tightness Testing. We have nearly 10 years experience. We cover London, Home Counties and East Anglia.

Get in touch.

01621 493594

Please check us out on the socials too @build_comply

New Venture! Introducing Building Energy Efficient Homes

New Venture! Introducing Building Energy Efficient Homes

The UK Government has set a target of net zero by 2050. However did you know up to 35% of all the energy consumed in the UK is by the existing housing stock!

bee homes, building energy efficient homes

Trading as BEE Homes, the new venture exists to serve the domestic market, dealing with common homeowner concerns such as:

  • Noisy Neighbours – we can provide acoustic testing, advice and mitigation measures
  • Mould and Condensation – we can provide ventilation surveys and mitigation measures
  • Draught-proof – we can provide air leakage testing, advice and mitigation measures

With these services, we are able to provide more extensive assessments including occupancy, heat loss, heat pump feasibility to full PAS2035 Retrofit Assessments and Energy Performance Certificates.

We aim to provide our clients plain english advise, to a) reduce household running costs; but to us more importantly b) ensure the UK can get to netzero by providing cost effective measures to improve every UK home’s energy efficiency.

To celebrate this we are offering FREE ENERGY EFFICIENCY AUDITS* to anyone within a 15 mile radius of Maldon, Essex.

For more information please do not hesitate to give us a call: 01621 4932594

bee homes , building energy efficient homes

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Building Energy Efficient Homes.


*For December 2021 only. Visit come first served basis. Can be cancelled anytime.