REFURBISHMENTAsesing the Requirements of the ProjectThe following factors should be taken into consideration when undertaking the refurbishment of an existing flat roof system;Condition and Nature of the Existing DeckThe first thing to examine when considering a refurbishment of a flat roof is the condition of the deck and supporting structure. If this is at all questionable, a structural survey should be commissioned.Generally speaking, decks made from chipboard or strawboard should always be replaced as their lifespan is limited and any water ingress that may have occurred will have reduced their load bearing strength. These products would normally be replaced with a suitable grade plywood or OSB. Metal decks should be checked for signs of corrosion and deflection; and concrete for cracks and movement. Woodwool is now classed as a fragile material and should be treated in accordance with the latest Health and Safety guidelines.Condition and Nature of the Existing WaterproofingIt is important that core samples are taken through the existing roof coverings in order to assess the roof build-up and its condition. This should form the basis of the type of remedial action to be taken.Bauder area technical managers are available to undertake this service free of charge as part of our no obligation survey and report package.Overlay or Strip the Existing Waterproofing?If the intention is to overlay the existing roof system, the following basic criteria should apply:1. The existing roof system should be generally sound, dry, free from water damage and suitable to take an overlay system.2. Overlay materials must be compatible with existing materials. In the case of Bauder bituminous systems this generally means asphalt and in some cases other bituminous membranes. Bauder Liquid systems can be used to overlay almost all types of roof membrane. Synthetic single ply can also be used for refurbishment applications in some circumstances. Other points to consider when proposing to overlay:1. Waterproofing upstands and details should generally always be stripped and replaced.2. There will be additional weight imposed on the structure by the installation of a new system.3. An increased surface level will be imposed by the new system (especially when upgrading insulation) and its effect on adjacent detailing must be considered. Upstand heights should not be compromised and it may be necessary to raise DPC's, cavity trays, edge kerbs and fascia boards etc.4. Products being overlaid may well have a shorter life expectancy than the new system and ultimately cause premature failure of the overlay system. For this reason, Bauder generally recommend that existing systems incorporating insulation are stripped rather than overlaid.5. Building Regulations now require insulation to be upgraded in most overlay situations.206The existing roof coverings should always be removed if there is any doubt over their long term integrity or if moisture is present; this may even include any underlying screed. Consideration must be given as to whether stripping the roof will also mean removing the drainage falls, if so, it will be necessary to incorporate new screed, or more conveniently tapered insulation to re-introduce new falls and maintain adequate drainage of the roof.Improving the Drainage of the RofA common fault with flat roofs is their inability to shed rainwater efficiently. This can be due to deficient original design, poor workmanship, deflection of the deck or a combination of all three.During refurbishment, the opportunity should be taken to address any ponding that exists, as this will have negative effects on the roof.If the problem is due to a lack of rainwater outlets, consideration should be given to the possibility of adding some, although this may often be impractical due to connecting to the existing drainage system.Tapered insulation can be used as a convenient and cost effective way of improving surface drainage, although it is not viable on every project and we advise that you utilise the experience of your Bauder Area Technical Manager for further advice. Tapered insulation will ultimately create a thicker build-up to the roof system at certain points and may encroach on recommended upstand heights or create a necessity to raise perimeter detailing, cavity trays, clerestory windows etc. and therefore may prove to be financially prohibitive.bauder.ie
207? Typical Bauder tapered insulation schemeIf ponding water is localised in a corner of the roof, occurring between outlets or along a perimeter edge due to lack of cross-falls for instance, a Bauder Tapered Deflector System can be used. These are available in triangular shaped kits ranging from 1 metre to 10 metres in length, and are specially designed for the purpose..Bauder tapered insulation schemes can be designed to suit any particular project following a site survey by your Bauder Area Technical Manager and should this product be considered beneficial, this will be offered as an option. ? Bauder tapered deflector system to alleviate crossfalls between outlets.Image courtesey of IRT Surveys Limited? Thermographic image showing thermal loss through mechanical insulation fasteners and around the base of a parapet wall. bauder.co.ukFLAT ROOFDESIGN GUIDEImproving Thermal PropertiesBuilding RegulationsBuilding Regulations state that when refurbishing or replacing an existing flat roof covering, the replacement system must also make provision for an upgrade to the thermal properties of the roof. Bauder can advise on the latest Building Regulation requirements, and make provision for the correct amount of insulation for your project within the bespoke specification that we provide. However, we would recommend that you seek confirmation of our advice from Local Authority Building Control before submitting the specification for tender.Cold Rof ConstructionIf the refurbishment project in question is a cold roof design, upgrading the insulation in the ceiling void is often difficult as it will be necessary to remove either the ceiling or the roof deck in order to achieve this. Once exposed, it may be discovered that the existing void is too small to take the volume of insulation required whilst continuing to maintain an adequate cross flow of ventilation above it. Even if it is possible to upgrade the insulation in the ceiling void, it will be impossible to provide a continuous uniform thickness, due to the presence of structural supports. Therefore a certain amount of thermal bridging will occur.It is often preferable to convert an existing cold roof to a warm roof construction, as this greatly reduces the problem of thermal bridging. However, this will mean that any existing ventilation provision below the deck will need to be sealed off and there may be a requirement to remove any existing insulation from the void, as this could cause condensation problems. The Bauder Technical Department is always available to provide specialist advice or undertake thermal analysis calculations should this be required.Warm Rof ConstructionIn the case of refurbishment of a warm roof, it is likely that the level of existing insulation will not be enough to satisfy current Building Regulations. There are commonly two options, either to overlay the roof and introduce additional insulation, or to strip the existing system and start again. The first option should only be considered if the existing roof is deemed suitable and compatible for an overlay.Detail DesignParticular attention should be paid to the design of the new roof system to ensure that thermal bridging at perimeters and details is reduced as much as possible. Guidance on detail design is given in the 'Robust Details Catalogue' published by The Stationery Office (TSO).