RESOLVING PROBLEMATIC DETAILSbauder.ie208The photograph above shows a low door cill. In order to conform to British Codes of Practice BS 8217:2005 and to create a satisfactory waterproofing detail, the upstand height needs to be a minimum of 150 mm from the top of the finished waterproofing. In this instance, it will be necessary to build up the upstand in a suitable material and provide a new cill and doors.(see drawing opposite)The photograph above shows a typical dwarf parapet wall with brick on edge detail. In this type of situation, it is never clear whether rainwater is finding its way through the brickwork into the building and we often recommend encapsulating the inside of the parapet with waterproofing membrane, terminating to a new trim or under a capping or coping system as shown in the drawings opposite. However, where the parapet is cavity wall construction, care must be taken to ensure that this does not block any cavity tray weepholes that may exist. It is a good idea to clad old brickwork with exterior grade plywood prior to installing the membranes, and in this example the creasing tile will first need to be cut back to provide a flush surface.When refurbishing existing flat roofs, it is important to correctly address and rectify any problematic details that exist as it is in these areas that water ingress is most likely to occur.Although similar problems arise on different roofs on a regular basis, there are often unique situations that need to be addressed and Bauder will endeavour to work with the client to resolve these issues at survey stage. Typically, we will provide a photographic report highlighting the problem areas on any particular roof and provide suggested solutions in the form of detail drawings for inclusion in the specification.Some examples of how to overcome common problems are shown on these two pages: A warm reinforced bitumen system is shown as the waterproofing in these illustrations but alternative waterproofing systems can be used.
209 bauder.co.ukThis photograph shows a typical example of an asphalt covered flat top mansard roof. The detail to the lead above the lower pitched roof is acceptable for asphalt, but inadequate for a built up roof system as the raw edge of membrane would tend to de-bond and curl up over time, allowing water ingress. As the detail drawing shows, a welted drip should be formed to provide a neat watertight finish, which will stand the test of time.The handrail featured in the photograph is bolted through the waterproofing creating many penetrations; this presents many possible opportunities for water to enter the building fabric. The basis for problem free roof design is to avoid penetrations to the waterproofing wherever possible. There are two alternatives here as shown in the drawings, either modify and relocate the mounting of the handrail onto the outside face of the building, or use a free-standing handrail system that sits on sacrificial pads.FLAT ROOFDESIGN GUIDE