Falls were usually created in the timber structure beneath by using tapered ‘firring pieces’ and these is usually suitable for re-use without adjustment. If you come across it, it should be replaced. Falls are usually created in the timber structure beneath the deck by using tapered ‘firring pieces’.Ĭhipboard – Although used in the past, chipboard is not considered suitable for use as a flat roof decking material. The thickness of the boards is determined by the joist centres. All edges should be supported and noggins should be used as well. Plywood & OSB – Both can be used for roof decks provided they meet the necessary standards. The same methods are used to create falls as descried above and the same provisos apply. The gaps between the blocks/planks are usually filled with mortar. Pre-cast Concrete Decks – There are numerous systems available, generally consisting of planks or blocks set between concrete beams. However, remedial action may be necessary with saturated decks to remove moisture. In-situ concrete decks (and screeds) on existing buildings should have cured and dried out by the time the waterproofing needs to be replaced. Alternatively they can be laid level and the fall provided by a screed, timber firrings and decking or tapered/cut to falls insulation. In-Situ Concrete Decks – These are sometimes cast in situ with a fall. There are a great many different type of structural decks, and the following are common examples: If the roof covering is being replaced, the suitability of the deck should be considered.ĭecks should also provide a suitable fall for drainage, although this is often by modification, such as by using tapered or cut to falls insulation or the use of a screed. The structural deck provides the primary support for the waterproofing system and it must be able to resist the loads which will be imposed upon it, including storm loads. This is very rarely a practical option when replacing an existing flat roof. Because of the risk of condensation forming in the roof void the space has to be ventilated. An advantage of inverted roofs is that the waterproofing membranes are protected from physical and thermal damage.Ī ’cold roof’ is when insulation (fibre glass or mineral wood quilt) is inserted between the ceiling joists. Inverted roofs are common on new build projects but rarely used in roofing refurbishment projects.

In wet conditions, the insulation and the waterproofing become wet which reduces its thermal performance so that a greater depth of material is required to achieve the same thermal performance. These insulation schemes are called ‘ tapered’ or ‘ cut to falls’.Īn ‘inverted roof’ is when the insulation (a rigid Styrofoam board) is laid on top of the waterproofing. The insulation in warm roofs can be designed and manufactured with a gradient to provide or improve falls and assist drainage. The build-up of membranes which form the main waterproofing layer are laid on top of the insulation, sandwiching the insulation within the system. The insulation helps to maintain the roof structure at a regular temperature, which reduces the amount of thermal movement, and therefore the stress inflicted on the roofing membranes, increasing their life.Ī ‘warm roof’ is when the insulation (a rigid urethane board) is laid on top of a vapour control layer, which in turn is laid on top of the roof decking.

Insulation is usually incorporated into the roofing system so that it sits on top of the roof structure, which keeps the roof deck and structure ‘warm’. These features enhance both the performance and life expectancy of the new roof coverings. These include reducing heating bills, improving the environment within the building and reducing the risk of condensation. Introducing insulation as part of a flat roof system provides many benefits. Under current Building Regulations, when more than 25% of a roof area is being refurbished or replaced, it is required that the insulation is upgraded to meet the current requirement. Posted on 26th January 2023 by Jamie In this guide, we’ll look at the various insulation, structural decks and screed you will encounter when surveying a flat roof.

Flat roof materials