An essential part of installing a durable flat roof is the use of high quality materials.  It’s a widely-known fact that many contractors use substandard roofing materials in an effort to save costs, leading to roofs that leak after a short period or suffer sun damage etc.  Flat Roofing Cambridge ensure that by using felt from the ICOPAL SBS range, that 10, 15 and 20 year insurance-backed guarantees can be offered without concern for the lifespan of the roof.

Having safely stripped the old roof covering, we will then lay down roofing surface with nothing but premium quality 18mm structurally engineered decking.

Having survived the most rigorous of testing, with full BBA approval, Flat Roofing Cambridge’s choice of ICOPAL flat roofing provide superior durability and strength.  With 3mm underlay and 4mm capping layers that are well above industry standard thicknesses (1.5mm and 2mm), these correctly-installed ICOPAL Flat roof coverings will last for decades.

Laying Felt

There are two different methods for laying felt depending on the kind of felt that is being used. Some membranes are specifically designed to be torched on, others to be rolled over hot bitumen. Despite this, there are some features that both methods have in common:

  1. They must all make use of a vapour control layer. This layer is placed beneath the roof insulation and should act to prevent damp.
  2. If the roof has any camber, the sheets should be laid starting from the bottom with each subsequent sheet overlapping the one before. This is so that any water run off will get between the sheets.
  3. The side lap of each sheet should be at least 50 mm and the end laps should be at least 75 mm.
  4. The joins should always be staggered.

The potential benefits of a partially bonded waterproofing base layer.

Both the torch on and ‘pour and roll’ methods of felt application will result in the base layer being fully bonded to the substrate.  This offers very positive resistance to wind uplift and can help to prevent water from becoming trapped between the felt and the substrate causing blistering.  The rigidity of this format provides little room for thermal movement however and, over time, this can cause the membrane to split or crack.

In order to overcome this difficulty the first waterproofing layer may be only partially bonded.  The benefit of this is that the cracking can be avoided but it could open the door to wind lift.  There are three different ways to achieve this:

  • By providing a perforated felt under layer.  Membrane type 3G may be laid straight over decking or insulation boards and the bituminous membranes then laid on top of it.
  • Instead of pouring an even layer of bitumen over the substrate, it could be poured out in a series of strips.
  • Fixing the first layer of membrane to the substrate with 20 mm galvanised clout nails 150 mm apart in both directions rather than forming a bond with bitumen. This is considered the standard where the substrate is made of timber boards.