Onduline explains making the most of loft conversions

Onduline explains making the most of loft conversions

Ardit Strica, Technical Manager at Onduline Building Products talks about loft conversions and how installers can make the most of them.

There are several ways to undertake a loft conversion, the most popular being a rooflight conversion. This is because it’s the simplest and most affordable option. A rooflight conversion involves installing a raised skylight or roof window to create a light and airy space. This is a great option for a customer if they want to add extra light, and potentially some extra space, without making any major changes to the home. 

If a customer is looking to gain more space than a rooflight conversion can offer, a dormer conversion may be the right option. This involves adding a small box shaped structure onto a pitched roof, creating walls that sit at a 90-degree angle to the floor. This helps to expand not only headspace, but floorspace too. Dormers can be either gabled or hipped, and they come in a variety of shapes and sizes.

Alternatively, a full loft conversion can be undertaken, with several options including hip-to-gable conversions, mansard conversions, and L-shaped, all of which would be dependent on the type of property a customer owns and planning regulations within the area. These full conversions will generally involve the removal, addition, or modification of parts of the roof structure to gain additional living space.

Roof pitch

Undertaking a loft conversion project in most cases means creating a new roof structure, and, the lower the roof pitch, the larger the living area there will be available underneath the roof.

A loft conversion is a great way to upgrade a roof and to re-design it to be more thermally efficient by adding insulation and creating a warm roof, especially with an older property that more than likely has a cold roof loft. However, constructing a new roof structure as part of a loft conversion usually involves creating various roof pitches, some of which may be very low. With low pitched roofs there are fewer tiling options and sometimes, depending on pitch, there might be no tiling options at all. This is where a sub-roof’ can come into play.


Sub-roof systems have seen a rise in popularity within the market over the last few years, allowing contractors more freedom when it comes to roofing projects. A sub-roof is an additional protective layer within the roof structure which acts as the primary waterproofing layer under the tiles when the minimum tile pitch cannot be met.

Tighter restrictions when it comes to roofing came into force with the launch of BS 5534, with amendments in 2015 and 2018 in relation to extreme weather changes and a need to align with European Standards. However, BS 5534 recognises that there are situations where it would be difficult to avoid using a roofing product at less than the recommended roof pitch. It highlights that a roof that is designed below the recommended minimum roof pitches should have a functional weatherproof sub-roof system to remove any rainwater ingress safely to the eaves gutter.

With a suitable sub-roof, all tiles can be used at a low pitch, allowing greater scope when it comes to making modifications to a home. This includes loft conversions, allowing lower pitches and the ability to use either existing tiles, which can save a homeowner money, or new tiles that they would like to fit in due to aesthetics.

All concrete, slate and clay roof tiles can be installed on a roof pitch as low as 10º by integrating a suitable sub-roof, making a huge difference to contractors when it comes to designing and completing roofing projects.


Onduline has recently launched its new and unique sub- roof system, ISOLINE LOW LINEthe only system in the UK to be BRE tested and BBA Accredited to as low as 10°.

Designed to be used with all roof tiles, new or existing; ISOLINE LOW LINE, lightweight bituminous sub-roof is fixed below the primary tile or slate roof covering, acting as the primary waterproofing layer of a roof, making roof tiles a secondary aesthetical line of defence.

To find out more about ISOLINE LOW LINE and Onduline’s other lightweight, and durable waterproofing solutions, visit ISOLINE professionals | Onduline.

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