The government’s goal is to reduce carbon emissions to net zero by 2050, which will have a major impact on the way houses and other buildings are built. As legislation develops, it will be critical to ensure that the roof provides protection while allowing effective ventilation to ensure a comfortable indoor environment.

This CPD will focus on the subject of pitched roof cushions and how to specify them to meet building codes and standards to ensure the integrity of the building, while also covering roof ventilation requirements that are closely related to membrane selection.

Specifying pitched roof underlays for new construction or renovation projects is often a confusing subject. There are so many options on the market to choose from, and each option offers various technical attributes and performance certificates.

Almost all tile and slab-sloping roof structures need padding, which should be designed as a real hidden protective layer as a secondary line of defense for roof tiles, providing weather defense against wind, rain, and snow, and resistance to wind uplift of the load According to BS 5534, Code of Practice for Slate and Ceramic Tile, the pressure applied to the structure.

The liner also has a requirement to absorb part of the wind load acting on the roof without swelling and touching the underside of the roof covering. The use of some modern liners in this country is strictly restricted, and some liners imported from Europe are generally not suitable for UK conditions.

However, because roof liners are usually specified individually, it is easy to overlook the overall connection between the specified membrane type and the need for controlled ventilation strategies to manage condensation risk.

Roof liner and ventilation must work at the same time to provide a complete solution, provide a waterproof structure and avoid the accumulation of condensation in the roof space, which ultimately leads to a healthy indoor living environment.

Any choice of padding for pitched roofs will affect the amount of ventilation required to eliminate the risk of harmful condensation and create better buildings and healthy homes. This means that choosing a manufacturer proficient in providing appropriate guidance and a range of solutions is crucial. Choice is the most important factor here, not a one-size-fits-all approach, the membrane is an integral part of the overall solution.

Even if the entire roof pack has cost constraints, using the cheapest membrane without considering additional ventilation requirements may cause future problems and expensive structural repairs. Doing it right once means that the house is future-oriented, can maintain its property value and ensure that maintenance costs are reduced.

The need for controlled ventilation in houses has never been more important. With the onset of climate change and the continued commitment of the British government to net all greenhouse gas emissions to zero by 2050, reducing at least 80% from the 1990 level compared with the previous target, energy efficiency has become a top priority on the agenda Heavy.

At the same time, by lowering the nominal U value target, building regulations will become more onerous. In addition to the update of Part L (fuel and electricity saving) and Part F (ventilation) of the building code approval document, the government recently announced the update after the initial consultation process, and it is expected to be changed to BS 5250 this year, which is the code of practice for controlling buildings Condensation in the material.

Improvements to these regulations in 2021 will facilitate the transition to future residential standards, which will greatly improve the energy efficiency of newly built properties that will be introduced in 2025. In addition, the government recently introduced a new constitution for social housing residents that promises to review decent housing standards to support the decarbonization of social housing.

Since these stricter goals mean that the design of the house uses a fabric-first approach to increase air tightness, it is important to balance this with the correct ventilation strategy to prevent excessive accumulation of moisture and pollutants. This includes roofs. The key is to have proper ventilation to meet the specified roof liner type, especially if the attic is a livable space.

So, while ensuring that the importance of providing ventilation to the residence is unquestionable, what are the different types of membranes available and how do these affect the ventilation requirements of each type of membrane? Whether the building is a cold roof (insulation material is located directly above or between the ceiling joists) or a warm roof (insulation material is placed on the rafter line or above or between the rafters) how does it affect this structure?

The two main categories are low-resistance (LR) products, which are permeable to steam, and high-resistance (HR) products, which are not permeable to steam. Starting with LR products, there are two main types of such gaskets on the market today.

Traditional LR products are sealed, but allow water vapor to diffuse into the atmosphere. For residential-sized cold roof solutions, BS 5250 recommends combining a breathable, air-tight bottom layer with a high level of ventilation of 5,000 mm2/m through tiles or ridge vents, whether it is a well-sealed or ordinary ceiling area.

Or, if the ceiling is well sealed, it is only necessary to provide ventilation of 3,000 mm2/m at the lower level (for example, through the eaves)-although for reroofing projects that may have normal ceilings and wells-a sealed ceiling cannot be achieved, and low-level ventilation should Increase to 7,000mm²/m.

In a warm roof building, the attic area is designed as a habitable space, so the insulation layer is laid at the level of the rafters. The use of airtight and steam-permeable LR roof liners will not require any additional ventilation and is subject to a well-sealed The ceiling and an air and steam control layer (AVCL) are installed on the warm side of the insulation.

If there is any doubt about the ability to provide an effective sealing ceiling and AVCL during the specification stage, further ventilation should be planned in the design; the selected manufacturer should provide appropriate guidance.

The second type of LR liner is both breathable and vapor permeable, and the ventilation can be delivered to the roof space through a special melt blown technology built into the membrane core. This ensures that airflow passes through the material and allows steam to escape, which helps control the risk of condensation.

For these product types, specifications should be made for the bottom layer that has also been hydrophobically treated to waterproof to provide additional protection. Although the breathable cushion may involve higher initial material costs, this can be offset by not requiring additional ventilation, thereby saving installation time and labor costs.

Whether it is a cold roof or a warm roof, the air and steam permeable membrane can be used without additional ventilation. NHBC accepted this in its R3 document of technical requirements related to cold roof construction.

The only exception is when the liner is installed on the bottom plate of a closed connection, or the use of air-tight roof coverings, such as metal tiles or fiber cement boards. In this case, it is necessary to use 25 mm counter slats to ventilate the slat space. The selected manufacturer should always recommend a well-sealed ceiling and use a separate AVCL when feasible.

Another major category of pitched roof liners is high-resistance (HR) membranes, which are both air-tight and prevent water vapor from diffusing through the material. In order to overcome the shortcomings of traditional 1F felts, air-impermeable HR membranes are usually the most cost-effective in terms of purchasing membranes separately.

However, this must be balanced with the additional high and low levels of ventilation requirements for cold roofs and warm roofs. This additional ventilation measure is necessary to avoid the risk of condensation forming a gap on the underside of the liner.

For example, for a residential-sized cold roof with a slope of more than 15°, the lower level requires at least 10,000 mm2/m of ventilation, and the upper level requires at least 5,000 mm2/m. For pitches exceeding 35° or spans exceeding 10m, additional 5000mm2/m ventilation is required. For warm roofs using HR padding, high and low levels of ventilation are also required. The selected manufacturer shall provide relevant ventilation guidance according to the specific conditions of the project.

There is no doubt that the correct choice of roof liner materials and the use of appropriate ventilation strategies can achieve synergistic effects, and it is essential that the selected manufacturer can advise on a complete solution to ensure that the roof faces the future and contributes to health Resident's home.