Skylights, or rooflights, have become a popular design choice for those looking to convert their basement or cellar. Typically, skylights can admit up to 40% more light into a roof space than a standard window, but create only minimal visual impact from outside and typically overlook the sky. As such they do not usually require planning permission. However, there are a number of potential issues to be aware of.
In England and Wales, you are unlikely to require planning permission for skylights unless:
- The skylight projects beyond the existing roof plane by more than 150mm
- The proposed skylight installation occupies a large area of your roof beyond what is considered a “reasonable” size
- You live in a Listed Building or in a designated Conservation Area
- A so-called “Article 4 Direction” or other planning condition is in place for the area in which you live
Even if planning permission for a new roof window is not required, building regulations cannot be ignored. By law, any building or structural modification work must comply with building controls which stipulate minimum standards for design and safety.
There are two sets of building regulations for roofs; work on an existing roof and the construction of a new roof, e.g. for an extension.
Be sure to pay particular attention to Parts J and L of Building Regulations; these deal with energy efficiency, thermal insulation and the protection of buildings against the threat of fire.
Approval under the Building Regulations will generally be needed for the installation of a new rooflight because:
- The roof structure will often need to be altered to create the opening
- The roof will need to carry the weight of the new skylight, which might require roof strengthening prior to installation
- If a skylight is in close proximity to a boundary, fire performance must also be taken into consideration
- Any rooflight installed must prove to have sufficient insulation against heat loss with effective energy performance
According to skylight manufacturers Sunsquare, limiting heat loss is crucial. Aluminium, which most skylights are manufactured from, transmits heat/cold very efficiently. If the external temperature manipulates the skylight frame, it not only creates a skylight that acts as a huge heat loss area for a property but also opens up the possibility of serious condensation issues.
For a skylight to achieve true thermal performance according to today’s standards you should expect to see polyamide sections dividing all materials that sit across the internal to external parts of your building. This is the only effective way of maintaining insulation and, therefore, the climatic control of your home.