General Overview

BRE tested and BBA Accredited to as low as 10 degrees
ISOLINE LOW LINE sheet dimensions
ISOLINE LOW LINE increased ventilation and airflow
ISOLINE LOW LINE worldwide leading waterproofing
ISOLINE LOW LINE worldwide leading waterproofing
ISOLINE LOW LINE worldwide leading waterproofing
ISOLINE LOW LINE worldwide leading waterproofing
ISOLINE LOW LINE worldwide leading waterproofing


Product Benefits

Suitable for any type of roof tile
Eco friendly: made from 50% recycled content
BRE tested with BBA Accreditation
Low pitches maximise living space
Pitch can be as low as 10 degrees
Adapts easily to each roof structure: adaptable to roof shape, ideal for renovation
Ideal for house extensions, greatly enhancing the aesthetic quality of a property
Increased ventilation and airflow due to the corrugations
Quick weatherproofing
30-year warranty
BBA Accredited

ISOLINE LOW LINE: Sustainable sub-roof system for any roof tile


A sub-roof is an additional protective layer within the roof structure. The ISOLINE® LOW LINE sub-roof is ideal for:

  • Heritage sites: the existing roof tiles can be re-used, as the ISOLINE® sub-roof becomes the main waterproofing element, helping to conserve the original aesthetics of a building.
  • Extra guarantee / protection: the ISOLINE® sub roof is forgiving, meaning any issues with the roof tiles are taken care of by the 'roof beneath the tiled roof'.
  • Low pitch roofs: the pitch of a roof can be limited to the roof tiles used, by integrating the ISOLINE® sub-roof, all roof tiles can go down to 10 degrees, allowing lower pitched roofing, in some cases this could mean an additional floor


The most reliable waterproofing solution for very low pitched roofs
The low profile configuration of ISOLINE LOW LINE, makes it the perfect underlay solution for a reduced roof section making it ideal for projects on which the height restriction or the aesthetic appearance of the roof line is of prime importance.

Engineered to be 100% leak free, ISOLINE LOW LINE roofing underlays deliver long-lasting waterproofing to any building, offering complete peace of mind to professionals and homeowners. ISOLINE LOW LINE acts as a roof under the roof. 

ISOLINE LOW LINE roofing underlay sheets work with any type of roof tile
ISOLINE LOW LINE compliments and enhances the performance and reliability of traditional tile or slate roofs. The ISOLINE LOW LINE underlay system can be used in both new constructions and renovation to keep the aesthetics of the original heritage of a building, whilst acting as the primary waterproofing material and protection for the building.

With a corrugation height of just 24mm, ISOLINE® LOW LINE is fixed below the primary tile or slate roof covering, acting as the primary waterproofing layer of a roof. Thus, making roof tiles a secondary line of defence enabling the pitch of the roof to be much lower than the minimum as recommended by the tile manufacturer.


Support battens and full deck installation

ISOLINE LOW LINE BBA underlay system


Ridge detail 

ISOLINE LOW LINE BBA underlay system


Innovation of ISOLINE LOW LINE 

The innovation of ISOLINE LOW LINE has provided opportunities to allow roofing tiles and slates to be laid below the manufacturers minimum recommended roof pitch with confidence. With this type of underlay technology, roofs can be designed with lower pitches, allowing you to use any type of tile or to deliver more usable floor area. 



As light weight roofing systems and waterproofing specialists, Onduline's ISOLINE® sub-roof systems provide long-term protection against any potential water ingress that may happen over time through a breach in the primary roof covering, as well as being: 

  • Easy to install: easy to carry, handle and fix due to the light weight of the system, and vertical overlaps embossed in to the sheet for ease of cutting.
  • Ideal for retrofit or new roofing projects: existing tiles can be re-used.
  • Ventilated: allows increased ventilation to minimise condensation and maintain excellent moisture control within the cavity, preventing mould build up.
  • Sustainable: the sub-roof is made up of 50% recycled cellulose fibres, contains no asbestos and does not release any hazardous substances.
  • Suitable for use with all major roof tiles.
  • Suitable for roof pitches as low as 10 degrees, which could mean an additional floor.
  • Tried and tested: BRE tested and BBA accredited.
  • Guaranteed with a 30-year waterproofing guarantee.



ISOLINE roofing underlay sheets are provided with a 30-year waterproofing warranty going along with the respect of our installation guidelines and the use of ONDULINE accessories.

For additional ventilation, use ONDUTISS AIR permeable membrane.


We have a select few ISOLINE LOW LINE distributors in the UK.
If you would like to purchase ISOLINE LOW LINE, you can go direct to one of the following stockists, or speak to us directly.


SOUTHERN SHEETING SUPPLIES LTD Hill Place Farm, Turners Hill Rd, East Grinstead RH19 4LX 01342 590122
ICB WATERPROOFING LTD. (SCOTLAND) 85 Calder St, Coatbridge ML5 4EY 01202 785200
MKM BUILDING SUPPLIES (GRIMSBY) Eleanor St, Grimsby DN32 8AL 01472 242111
To become a stockist of the ISOLINE LOW LINE system, please get in touch at [email protected] or call the office on +44(0)207 727 0533
Do you have questions about ISOLINE?