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Great Home

Independent Advice On Improving Your Home

Flat Roof Construction – Part 4

January 6, 2016 by Jon Davies 2 Comments

This is Part 4 of our Guide To Roof Construction. It covers flat roof materials and flat roof construction of warm and cold roofs.

Also See:
Part 1 – A Guide To Roof Construction: covers an overview of flat and pitched roofs.
Part 2 – Pitched Roof Construction: covers pitched roof materials, basic pitched roof designs, cold and warm pitched roofs and pitched roof construction.
Part 3 – Pitched Roof Detail: covers pitched roof detail: roof ridges and ridge tiles, roof hips and hip tiles, roof valleys, roof verges and lead flashings.

A flat roof is generally defined as having a pitch not greater than 15° to the horizontal. A truly flat roof would not allow rainwater to drain away so most flat roofs have a fall on them so that the rainwater naturally flows to collection points.

Whilst you can have tiled roofs of  10-15° these are really flat roof construction with a cosmetic covering of tiles.
Flat Roof Materials: Waterproofing Layer

Examples Of Flat Roofs
Examples Of Flat Roofs

There are different types of roofing material used in the waterproofing layer of a flat roof construction:

  • EPDM is a type of rubber which comes in continuous sheets. (EPDM stands for ethylene propylene diene monomer if you are desperate to know)
  • Roofing felt is a bitumen coated sheet with a mineral coated surface to add colour and provide the bitumen with protection from the sun
  • Fibre glass is a rigid material 

Flat Roof Construction

Flat Roof Construction Diagram - Warm Roof
Flat Roof Construction Diagram – Warm Roof


Above is a typical construction of a warm flat roof. It consists of six basic elements

  1. A Waterproof layer which resists water.
  2. Thermal insulation which retains heat within the building rather than allowing it to escape through the roof.
  3. A vapour barrier to prevent moisture escaping
  4. A timber deck, often of plywood sheeting, which allows the roof to support a load such as someone walking on it
  5. Wooden roof joists which are supported by the walls
  6. Plasterboard ceiling
Flat Roof Construction Diagram - Cold Roof
Flat Roof Construction Diagram – Cold Roof

A cold flat roof consists of the same elements mentioned above but in a different order. New installs of cold roofs are generally discouraged and in Scotland are banned. with the Technical Guidance for Building Regulations in Scotland stating: “There is evidence to suggest that condensation in cold deck flat roofs can cause problems and these type of roofs should be avoided“.

Filed Under: Roof construction, Roofing

Comments

  1. Victoria Morgon says

    May 10, 2018 at 6:27 am

    Roofing felt is bitumen coated sheet with a mineral coated surface to add colour and provide the bitumen with protection . epdm liquid rubber roofing is better to get long lasting results in roofing.

    Reply
  2. Jessica Laurent says

    September 8, 2017 at 6:28 am

    Warm roof is truly beneficial in cold climate. A good heat insulator and reduce glare as nobody wants to face the harsh and dazzling light.

    Reply

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Jon Davies

Hi I'm Jon. This website seeks to help those searching for the basics about improving their home. It offers an independent view, trying to balance the interests of … read more

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