When installing roofing membrane products, it’s important that steps are taken to ensure the process is safe and efficient, and ultimately guarantees long-lasting performance of the roof materials installed. At Klober, we champion raising the standard of roofing components, and membranes are one key area that can often get overlooked both in terms of specification and installation.
Here we have compiled seven top tips to think about before you get started with pitched roofing membranes.
Firstly, there is a huge difference in quality of membranes across the market. Over the years designs have become more advanced meaning there is more to understand from a technical perspective, particularly when referring to ventilation properties and benefits of a membrane. For pitched roofing, the most common types of membranes fall into two types, often referred to as breathable and non-breathable membranes. The former is the most popular and can also be known as vapour permeable membrane, roof tile underlay, or roof breather membrane and felts. These can help with the ventilation process and may reduce or in some cases negate the amount of additional ventilation required.
The UK’s diverse building stock means complex roof structures are more common. These are often found on apartment buildings or those with breaks in the roofline (including dormers windows or rooflights). In these circumstances, roofers are encouraged to install a superior breathable membrane product, such as Klober’s Permo Air membrane. These can be useful during the drying out phase of new build properties, as the breathability helps when air movement is limited.
For a low pitch roof, which can vary depending on the minimum pitch of the selected roof covering, a high-quality membrane solution is the key to safeguarding the roofing investment. Klober’s Permo Extreme, for example, is designed specifically for this purpose and is also much stronger than the average underlay on the market. This greatly reduces the risk of ripping and tearing whilst installation takes place. Pitched roof waterproofing and pitched roof membrane types should also be carefully considered for pitched roofs. You can read more about the full range here.
It is important that the roofer pays close attention to the manufacturer’s recommended installation process. For example, when installing Permo Extreme, the adhesive strip on the underside needs to be fixed to the underlay support tray in the first run.
Then with each run of Extreme, ensure the underside adhesive strip fix’s down to the adhesive strip on the top side of the run below. This will create a head lap of 100mm. You can also find more information on this stage in our installation tips video on YouTube here.
In order to allow any moisture to run to the eaves and into the guttering, the membrane needs to be laid creating a drape between rafters. The ideal measurement of this will sit between a minimum of 10mm and a maximum 15mm. If the membrane is taught, there is risk of tearing and the water could become trapped behind the tiling batten. Water may also track its way into the nail holes, ultimately infiltrating the roof space.
To create a more airtight roof and minimise air leakage, the use of a tape should be considered, often known as breather membrane tape. Alternatively, membranes fitted with integral tape, such as Klober’s Permo Forte with adhesive tape, provides exceptional water tightness and protection against winds. While integral tapes can help to protect against strong winds, it is important to also check the zonal performance of the membrane itself. However, membranes with integral tape tend to offer an enhanced zonal performance.
Allowing the membrane to sag down into the guttering is a common mistake but is easily avoided. Simply stop short of the gutter and allow the underlay support tray to ensure safe passage of water to the gutter. Exposure like this should be avoided because modern day membranes are not permanently UV stable.
Inadequate product installation could allow water ingress from rain and snow to affect the eaves, particularly in colder weather with repeated freezing and thawing. Over time this will corrupt the roofing system and could lead to water damage.
Roofing membrane types known as vapour permeable underlay or breathable roofing felt, may allow water vapour to exit freely without the need for separate ventilation above the roofing insulation. It should be remembered that approval is required to prove that any breathable roof membrane products used do not require additional forms of ventilation. For example, the National House Building Council (NHBC) recognises Klober’s Permo Air membrane as being air open as well as vapour permeable because it is a British Board of Agrément (BBA) approved membrane. Vapour permeable membranes that are not air open will normally require some form of additional ventilation, especially for new build properties.
Selecting a vapour permeable membrane with a reinforced grid helps to provide superior strength and added safety benefits. This has advantages across all project types, but is especially pertinent for re-roofing projects, where there may be access and space limitations due to the nature of refurbishments. In these scenarios, having the grid helps to provide extra grip and reassurance during the installation process.
It is also a common misconception that the thicker the membrane, the better the strength. In actual fact, a very thick membrane on its own, may not be as strong as a membrane combined with a reinforced grid.
It must be remembered that while a strong membrane with a reinforced grid can be extremely beneficial to maximising safety, it is not a replacement for primary on-site safety procedures. It is vital that all guidance and regulations, such as HSE’s Health and safety in roof work, is followed when working at height.
Klober’s product range spans low pitch roof felts, pitched roof felts, non-permeable membranes and both cold and warm roof vapour barriers. To find the right roofing membrane, UK roofers can view the full range of membranes and barriers HERE.
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