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Roof substructure

When using a sunroof, Robisol assumes a condensation foil with water tightness class 1. This ensures that your roof is always protected against condensation and moisture that may occur under the sunroof. In addition, we recommend that you choose a condensation foil with fire class B. With modern photovoltaic systems that are properly installed, the risk of an electric arc is zero, but still present. The condensation foil is the construction material that can most easily be ignited. You can read more about this on our (fire) safety page. If necessary, contact your insurer to ensure that no additional requirements are imposed. Your PV system is of course installed for you fully in accordance with the Scope 12 guidelines.

Primary skin

Robisol solar roofs offer a safe roof construction that more than meets the strength requirements for roof coverings and solar panels. The materials used are durable and the systems are maintenance-friendly. However, the solar panels and aluminium profiles can become damp through condensation. It is therefore important that the system is used in combination with the right roof system components that have been processed correctly. For this reason, we provide information here on how a roof is constructed.

As with roof tiles, our solar panel systems form the primary waterproofing layer. It protects the underlying structure from various weather influences such as precipitation, UV rays and wind. Also roof tiles and slates are never 100% waterproof. In Robisol's systems the Kyroof System is slightly denser than roof tiles, while the BiTile System is slightly more open than roof tiles. This has advantages and disadvantages. With the Kyroof System a ventilated cavity between the system and the roof boarding must be taken into account. A possible air leak through which humidity escapes (as occasionally happens with a skylight) can be annoying with this system. It is therefore important that the under-roof is constructed properly. The BiTile, on the other hand, ensures excellent ventilation of the under-roof. Besides cooling the solar panels, there is no risk of internal condensation. However, we do have to take extreme wind in combination with drifting snow into account. The secondary skin is important in order to guarantee a good watertightness even in this situation.

Robisol solar roofs are rainproof, which means that virtually all precipitation is drained via the system. We therefore take into account that a small amount of precipitation can penetrate the primary skin and must be drained away through the sub-roof to outside the structure. In principle, this is not much different than with roof tiles, but it is important that the under-roof is designed to fulfil the function of a secondary water-retaining layer.

Secondary skin

The under-roof performs the following functions:

  • Ensuring the rain tightness of the roof and draining the water into the gutter:
    • During the construction of the roof, pending the installation of the solar roof
    • In the event of breakage or storm damage to solar panels
    • In the event of severe weather conditions resulting in water infiltration
    • In the event of drifting snow
  • Improve the storm tightness of the mounting system
  • Improve the dust-tightness of the roof
  • Finishing the roof insulation windproof (improvement of energy performance)
  • To reduce or prevent the dripping of condensation water

It is recommended to install a subroof in accordance with the processing instructions of the roof liner or roof panel manufacturer. In order to guarantee the function of the under-roof Robisol uses class W1 (watertight) and vapour-permeable condensation foil with Fire class B. Robisol supplies this foil and applies it in many projects. This can prevent unpleasant problems. However, it is still important that there are no interruptions in the roof surface (as is often the case with flashing), that any required gutter sets are fitted (at roof windows, dormer windows or next to fascias) and that the roof is made airtight (around roof penetrations and interruptions).

Residential moisture

A pitched roof construction is generally vapour permeable. Especially in winter, when the temperature difference between inside and outside is big, there is a vapour pressure which causes vapour transport from the inside to the outside. If a pitched roof construction is built up properly, the layers used from the inside to the outside therefore have increasingly higher vapour permeability. This allows vapour to escape without resistance. This is also the reason why you should not apply a thin layer of insulation on a roof boarding. In that case internal condensation can occur on the roof boarding. So it is also essential that the under-roof foil has a high vapour permeability.

Minimum roof pitch

The BiTile System is designed for a minimum roof pitch of 25 degrees. If your roof is steeper than or equal to this, it falls within the criteria of a "normal roof". You can use this roof category when selecting the roof system components. Provided that the influence factors fall within the standard criteria, a "standard roof" is sufficient for a roof pitch of 25 degrees or more.

Influencing factors

To determine the requirements for the substructure, the severity of the conditions to which a roof is exposed must also be considered. The roof length, ridge height, wind area and roof shape are important influencing factors for the severity of the conditions a roof is exposed to. A "standard shelter" is likely to set criteria such as:

  • Maximum roof length 20 m1
  • Ridge height maximum 15 m1
  • The project is not located in the coastal zone or on one of the Wadden Islands
  • Only simple roof shapes such as gable roof, mansard roof, pyramid roof or pent roof.
  • Design and construction requirements

Roof liner Robisol

A good under-roof is designed according to the requirements of the under-roof. When choosing a roof liner it is a question of vapour permeability, strength and water tightness. Because we like to offer you a carefree total product, Robisol is pleased to supply a good roof liner that we deliver and install together with battens. Our foil is vapour permeable, waterproof, windproof, UV-resistant and fireproof. To install the foil it is desirable that no tiles and battens have been fitted to the roof. The foil can be applied over existing battens. Naturally, you should ensure that there are no underbrushings (such as a sloping gutter board and a condensation drain above the skylight) and you should apply the usual provisions as you do for tiles (concealed gutters, cuffs and seals). For roofs with a pitch of 25 degrees or more, we can then always guarantee good watertightness. For roofs with a pitch of less than 25 degrees, solutions are always possible, but we will determine the most suitable solution in consultation.

Roof panels and detailing

Robisol has close contacts with various roofing sheet suppliers such as Unilin and Kingspan. This shows that we can install solar roofs on virtually any roofing plate. However, you should bear in mind that some roofing sheets offer better fire safety than others. With our safety features in plugs, controls and arc detection, a solar roof poses no immediate danger. We work safer than ever and have never experienced a fire in hundreds of homes already installed. Even if it does happen, a fire on your roof is not an immediate threat to your safety. The fire will escape and our systems are well-ventilated, which means they can be easily extinguished. It is true, however, that some insurers make additional demands on your insulation material. This is not always rational, but it is part of the current market. Please contact your insurer to find out if there are any additional requirements for your insulation material. If you wish, we will be happy to help you choose a reliable solution for all parties concerned that is supported by us as well as by the roofing sheet supplier and insurer.


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