How are flat roofs defined?
In BS 6229, a roof is defined as flat if it has an overall pitch of 10 degrees or less.
The two variations of flat roof
Usually, flat roof constructions are defined as either ‘Cold’ or ‘Warm’, depending on how the thermal insulation is positioned in the construction.
Cold flat roofs are found in many homes around the UK, though they are not recommended these days and are actually banned in Scotland.
Cold roofs involve the thermal installation being installed between the joists and below the structural deck. Because the insulation doesn’t bear any load, quilts and other forms of loose fill material can be used instead of rigid insulation. Ventilation is a requirement in order to prevent moisture build-up in the roof void.
The downside of cold roof construction is that the heat rays of the sun hit the structure unprotected, and thermal movement can have a negative result.
In warm deck roofs, however, the insulation is positioned above the structural deck, and no ventilation is necessary as a result.
The roof deck is kept at a temperature similar to the inside of the building throughout the year and this protects the roof structure from the hot and cold extremes, cutting down the thermal movement.
Warm deck roofs also help reduce the risk of condensation build-up, with any water vapour entering the roof having no cold surface on which to settle.
What are the requirements for a flat roof?
Flat roofs should be tough, stable and durable. Needless to say, it must provide adequate protection against external elements, keep the building’s interior dry and – of course – playing its part in the stability of the building.
I’ve heard that flat roofs can fail early, is this the case?
Not anymore! In previous years, flat roofs had earned a reputation for simply not lasting as long. However, ongoing improvements to materials and design have seen them improve in every aspect, including:
- Weather resistance
Do I need planning permission when adjusting a flat roof?
Typically, the answer is no. If you’re planning to carry out repairs on or re-covering less than 25 per cent of the roof, then you won’t need planning permission.
When will I need it?
You will have to obtain planning permission if:
- You’re carrying out structural alterations.
- The performance of the new covering is going to be significantly different to the old one in the event of a fire.
- You’re replacing more than 25 per cent of the roof area, which typically means that the roof thermal insulation will normally need to be improved at the same time.
Note: Don’t forget that we have a detailed guide to the ins and outs of planning permission for roof windows.
Sign up for our whitepaper on building regulations
Written to help architects, surveyors and home improvers alike understand every UK building regulations.
Give us a call
If you’re at all unsure about how your roof will be affected by the installation of a flat roof skylight or new window, give Sunsquare’s friendly team a call on 01284 846551. We have years of experience in this as market leaders and can assist you more once we understand your situation.