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Ventilation is a fundamental component of modern building design, particularly in new build homes. It plays a pivotal role in creating a healthy and comfortable living environment. Adequate ventilation is key to maintaining good indoor air quality, regulating moisture levels, and preventing the buildup of pollutants and allergens. In new homes, where construction techniques often focus on energy efficiency and airtightness, a well-designed ventilation system is essential to balance these factors.

This page explores various aspects of ventilation in new build homes, focusing on grilles, door undercuts, flexi duct use, trickle vents, terminals, and different types of mechanical ventilation systems. It provides homeowners with insights into the importance, challenges, and best practices related to each element of their home’s ventilation system. By understanding these components, homeowners can ensure their new build home not only conserves energy but also provides a healthy and comfortable living space.



Ventilation is a crucial aspect of new build homes, ensuring good air quality and preventing dampness. Grilles play a significant role in this process. However, certain common issues with ventilation grilles can hinder their effectiveness. Here’s what homeowners need to know about grilles in ventilation systems:

Size and Cleaning of Ventilation Grilles

A frequent issue is the use of undersized ventilation grilles that are not cleaned out properly. This can lead to inadequate ventilation, affecting indoor air quality. It’s important to ensure that grilles are of the appropriate size for the space they are ventilating and that they are maintained regularly to prevent blockages.

Avoidance of Blockages

Often, grille openings can be unintentionally blocked with mortar during construction. This severely restricts airflow, negating the purpose of the grille. Regular checks during and after construction are essential to ensure that all ventilation openings are clear and unobstructed.

Ensuring Adequate Free Area

The terminal of the ventilation system should have a large enough free area to allow for effective air exchange. This often requires a double grille or two airbricks, although some airbricks are designed to achieve the necessary free area with just one brick.

Compatibility with MVHR Systems

For homes with Mechanical Ventilation with Heat Recovery (MVHR) systems, it is usually necessary to have a double air brick. This helps reduce pressure drop and inefficiency of the fan, ensuring that the MVHR system operates effectively.

Selecting the Right Air Bricks

When choosing air bricks, it’s important to select ones that provide enough free area for air to flow. Not all clay air bricks offer sufficient free area, so selecting the right type is critical for effective ventilation.

Correct Discharge Opening

The grille discharge opening should match the correct free area needed for the specific ventilation requirements of the home. This ensures that the ventilation system can perform its function efficiently and effectively.

By paying attention to these aspects of ventilation grilles, homeowners can significantly enhance the air quality and overall comfort of their new build home.


Door Undercuts

Proper ventilation in new build homes is vital for maintaining good air quality and comfort. An often-overlooked aspect of this is the undercut of interior doors, which plays a crucial role in air circulation. Here’s what homeowners need to know about door undercuts for effective ventilation:

Importance of Door Undercuts

The absence of a door undercut can prevent the transfer of air between rooms, leading to stuffy air in certain areas of the home. Undercuts allow for air to move freely under doors, facilitating better ventilation throughout the house.

Correct Sizing of Undercuts

It’s recommended to trim all doors to achieve a clear gap of 10mm at the bottom. This gap should be maintained even when finishes like carpets or tiles are fitted. A minimum of 25mm without finishes is advisable to ensure adequate airflow.

Complementing Other Ventilation Methods

Door undercuts work in conjunction with other ventilation methods, such as background ventilation through trickle vents and extraction systems in wet rooms. The combination of these elements ensures a holistic approach to maintaining good indoor air quality.

Avoiding Blocked Airflow

Without proper undercuts, certain rooms can become isolated in terms of airflow, potentially leading to issues like dampness, mould, or poor air quality. Ensuring that each door has an appropriate undercut is a simple yet effective way to enhance the overall ventilation strategy of the home.

Practical Implementation

When fitting or adjusting doors, it’s important to consider the ventilation needs of the home. This might involve planning for undercuts during the door installation process and ensuring that any finishes or floor coverings do not impede the necessary air gap.

By understanding the significance of door undercuts in home ventilation, homeowners can take proactive steps to ensure that their new build home remains fresh, comfortable, and healthy.


Flexi Duct Use

Flexi ducts are commonly used in ventilation systems of new build homes, but their improper installation can lead to reduced airflow, inefficiency, and increased noise. Understanding the correct use of flexi ducts is crucial for maintaining an effective ventilation system. Here’s a guide for homeowners:

Limiting Length of Flexi Ducts

Ensure that all ducting is rigid apart from the last 300mm approaching the duct or terminal. Excessive use of flexi ducts, especially lengths over 300mm, can significantly reduce airflow. The restricted flow can lead to inefficiency and potentially cause the ventilation system to be noisier.

Keeping Duct Work Short and Straight

The duct work should be kept as short and straight as possible. Long, convoluted duct runs, especially with flexi ducts, can create resistance and reduce the efficiency of air movement. Straight, rigid duct runs are more effective in maintaining good airflow.

Sealing Joints Properly

All joints in the duct work, including those involving flexi ducts, should be properly sealed. This prevents air leakage, ensuring that the maximum amount of air is delivered to the intended areas.

Avoiding Tight Bends

If flexi ducts are used, ensure that bends have as large a radius as possible to keep the duct width free and unobstructed. Tight bends can restrict airflow and reduce the efficiency of the system.

Positioning of Fans

Fans should be positioned to minimise the length of ductwork. Where possible, installing fans through the wall can significantly reduce the need for long duct runs, thereby enhancing the system’s efficiency.

Installation of Condensate Traps

In vertical sections of the duct work, particularly in areas with high humidity, install condensate traps. This helps in preventing moisture buildup within the ducts, which can lead to blockages or reduced airflow.

By following these guidelines, homeowners can ensure their home’s ventilation system operates efficiently, quietly, and effectively, providing a comfortable living environment.


Trickle Vents

Trickle vents are an essential component of a home’s ventilation strategy, providing background ventilation and helping to maintain indoor air quality. In new build homes, it’s important to ensure that these vents are correctly sized and used effectively. Here’s a guide for homeowners on the proper use of trickle vents:

Avoiding Ventilation Short Circuits

One common issue with trickle vents is the potential for ventilation short circuits. This occurs when air enters and exits a space too quickly, without properly ventilating the room. Correct placement and sizing of trickle vents are crucial to avoid this problem.

Checking Window Schedule for Trickle Vents

When planning or reviewing your home’s construction, check the window schedule and window order to ensure that trickle vents are included. This step is key in ensuring that each room will have adequate background ventilation.

Protecting Trickle Vents During Construction

To prevent dust and debris from clogging the vents, tape up the trickle vents during the construction phase. This helps to maintain their effectiveness and longevity.

Educating Occupants on Trickle Vent Use

It’s important for occupants to understand the use of trickle vents. These vents should generally be kept open to ensure adequate ventilation, especially in rooms that are prone to dampness, like kitchens and bathrooms. Explaining their function and importance can help ensure that they are used effectively.

Sizing of Trickle Vents

Ensure that the trickle vents installed are of the correct size for the space they are ventilating. Inadequate sizing can lead to insufficient ventilation, contributing to issues like condensation and poor air quality.

No Trickle Vents in Wet Rooms

Typically, wet rooms such as bathrooms and kitchens should not rely solely on trickle vents for ventilation. These rooms usually require more active forms of ventilation, like extract fans, due to higher levels of humidity.

By ensuring the correct implementation and use of trickle vents, homeowners can significantly improve the air quality and overall comfort of their new build home.



Terminals, the points where ventilation systems interact with the outside environment, are critical for ensuring efficient and effective ventilation in new build homes. However, there are common problems associated with ventilation terminals that homeowners should be aware of. Here’s a guide on how to address these issues:

Securing Terminals in Position

One of the main issues is terminals not being fixed in position, often lacking locking nuts. This can lead to them being easily altered or moved, which can disrupt the balance of the ventilation system. After commissioning the system, it’s important to secure the terminals with locking nuts to prevent any unintended alterations.

Balancing the System

Ensuring the system is balanced, with neither too much nor too little free area at the terminal, is crucial. An unbalanced system can lead to inefficient ventilation, either pulling in too much outside air or not enough, which can affect the air quality and energy efficiency of your home.

Maintaining Free Area at Terminals

There should be enough free area at the terminals, approximately a finger width gap, depending on the ductwork and fan. This space is necessary to allow for adequate airflow without causing noise issues or inefficiencies in the Mechanical Ventilation with Heat Recovery (MVHR) system.

Avoiding Noisy MVHR Systems

Improperly installed or unbalanced terminals can contribute to a noisy MVHR system. Ensuring that the terminals are correctly installed and the system is well-balanced helps maintain a quiet and efficient MVHR system.

Choosing the Right Ventilation Terminal

In some cases, alternative ventilation terminals may be required to suit specific building designs or to improve performance. Homeowners should consult with their ventilation system installer to determine the best type of terminal for their specific needs.

By focusing on these aspects of ventilation terminals, homeowners can enhance the effectiveness of their home’s ventilation system, ensuring it operates quietly, efficiently, and effectively.


Mechanical Ventilation with Heat Recovery (MVHR)

Mechanical Ventilation with Heat Recovery (MVHR) systems are an effective and energy-efficient way to provide fresh air and improve indoor air quality in new build homes. However, there are specific installation and maintenance considerations to ensure their optimal performance. Here’s a guide for homeowners on MVHR systems:

Insulation of Intake/Exhaust Ducts

A common problem with MVHR systems is the lack of insulation on intake and exhaust ducts. These ducts, especially when they pass through unheated spaces like lofts, should be properly insulated to prevent heat loss and condensation. Use proprietary insulated ductwork for all ducts connected to the outside.

Location of MVHR Unit

Ideally, the MVHR unit should be installed inside a heated and easily accessible space. Installing the unit in a loft can create problems of heat loss and access for maintenance. Placing the unit within a heated area of the home ensures better efficiency and easier maintenance.

Proximity to the Outside Wall

For efficient operation, the MVHR unit should be installed within 1.5 meters of an outside wall. This reduces the length of ductwork to the outside, minimising heat loss and improving the overall efficiency of the system.

Proper Installation and Commissioning

Ensure that the MVHR system is installed and commissioned by qualified professionals. This includes correct sizing of the unit for your home, proper balancing of airflows, and ensuring that all components, such as filters and heat exchangers, are accessible for regular maintenance.

Regular Maintenance

To keep the MVHR system running efficiently, regular maintenance is crucial. This includes cleaning or replacing filters, checking and cleaning heat exchangers, and inspecting ductwork for any blockages or leaks.

By addressing these key aspects of MVHR systems, homeowners can significantly enhance the comfort, air quality, and energy efficiency of their new build home.


Mechanical Extract Ventilation (MEV) / Mechanical Ventilation with Heat Recovery (MVHR)

Mechanical Extract Ventilation (MEV) and Mechanical Ventilation with Heat Recovery (MVHR) are crucial for maintaining good air quality in modern homes. However, their effectiveness can be compromised by poor installation and maintenance practices. Here’s a guide for homeowners on what to consider for MEV/MVHR systems:

Proper Installation of Ductwork

Poorly installed ductwork with multiple bends can prevent airflow and create noise. The ductwork should be connected to the unit with minimal bends and positively fixed with proprietary clips or collars. Avoid twisting ducts around each other as this can lead to airflow restrictions and increased noise.

Access for Maintenance

Ensure there is easy access for cleaning and maintenance, especially for filters. Difficult access can lead to neglect of regular maintenance, reducing the efficiency of the system. For example, cupboard doors should not prevent access to filters.

Avoiding Crushed or Kinked Ducts

The flexible connection to the terminal should not be crushed or kinked. This can restrict airflow and reduce the efficiency of the ventilation system.

Tidy and Sealed Duct Penetrations

When installing ducts, especially in ceilings, use an MDF template to create holes for duct penetration. This approach ensures a tidy and sealed finish, which is crucial for maintaining the integrity of the building envelope.

Mounting of MVHR/MEV Units

Install MVHR/MEV units with mounting brackets on masonry walls, or use a suitable pattress for stud walls, such as 18mm ply. This helps to reduce noise and vibration from the units, contributing to a quieter home environment.

Clear Information for Homeowners

Provide clear and simple information about filters and maintenance to the homeowner. Understanding how to maintain and manage their ventilation system is key for homeowners to ensure its long-term efficiency and effectiveness.

Efficient Duct Connections

Ensure duct connections are efficient and well-sealed. This maximises airflow and the overall efficiency of the ventilation system, ensuring that fresh air is effectively distributed throughout the home.

By focusing on these aspects of MEV/MVHR systems, homeowners can significantly enhance the air quality and comfort of their new build home.


Operation and Maintenance

Effective operation and maintenance of ventilation systems are crucial in ensuring good indoor air quality in new build homes. However, common issues can arise if these systems are not properly maintained. Here’s a guide for homeowners on operation and maintenance of ventilation systems:

Comprehensive Home Occupier Handover

A common problem is insufficient handover to the home occupier regarding the ventilation system. Homeowners should receive a thorough explanation of how the system works, its maintenance requirements, and what to do in case of issues.

Regular Cleaning of Filters, Ducts, and Heat Exchangers

Dirty filters, ducts, and heat exchangers can significantly restrict airflow, leading to poor indoor air quality, condensation, and mould. Filters should be replaced every year, and other maintenance tasks, like cleaning ductwork, should be carried out by a qualified person. It’s recommended to clean ductwork every five years.

Commissioning of the System

All systems should be commissioned upon completion. This involves using an airflow hood to measure normal and boost flow rates, as per BSRIA BG/2013 guidelines. The completed commissioning sheets should be provided to the site manager and Building Control.

Simple Home User Guide

Provide homeowners with a simple guide explaining the maintenance of the ventilation system. This guide should include easy-to-understand instructions and images, and it could also be made available online for easy access.

Labelling of Ventilation Units

Label the ventilation units clearly to demonstrate maintenance procedures. This helps in ensuring that maintenance tasks are carried out correctly and at the right intervals.

Testing with Air Flow Hood

Use an air flow hood for testing as part of the commissioning process. This ensures that the system is operating at the correct flow rates and is effectively ventilating the home.

Routine Maintenance Schedule

Homeowners should be aware of and adhere to a routine maintenance schedule. This includes regular cleaning and replacement of filters and periodic checks of the entire system to ensure it remains in good working order.

By following these guidelines, homeowners can ensure their ventilation system operates efficiently, maintaining good indoor air quality and preventing issues like mould and dampness.