Cockrams Surveying Ltd recently undertook a survey on a semi-detached bungalow within Truro city. This was a probate sale and our instructions were to undertake an RICS Homebuyers Survey and Valuation. This property had a double pitched and hipped roof all covered with interlocking double Roman style concrete tiles over a cut timber rafter and purlin structure. The rainwater provision to the main roof was formed in a system of sectional concrete (Finlock) gutters to fibre cement/asbestos downpipes. The main walls were of cavity concrete block construction which were rendered externally and plaster faced internally.
Finlock gutters not only form the guttering system but were also used to cap off the top of the cavity walls and to all intents and purposes, act as a cavity closer and wall plate to which the roof structure is secured/supported.
The problem with Finlock gutters is that they leak on the joints which is normally serious as rain penetration can seep into the cavity and cause wall tie corrosion and internal dampness. This can be far more severe if the cavity has been retro filled with insulation. Surveyors must always check the junction between the ceilings and walls directly underneath the Finlock gutters when undertaking a survey but also around skirting board level and randomly at the midpoint of walls also. These checks were undertaken on the subject property and all exposed parts were found to be dry at the time of inspection. However, there was a small area just above the wardrobes in the main bedroom which was difficult to access. Nonetheless, a surveyors’ ladder was used and significant dampness was found above the wardrobes. In this case there was no sign of deterioration to the backing within the fitted wardrobes to indicate any dampness, nor was there any damp smell. Surveyors must therefore be aware that defects may exist within these areas that are difficult to access and it is important to allow time to inspect these parts where Finlock gutters are fitted.
Our external inspection confirmed that the gutters have been lined with bitumen and self-adhesive flashing (Flash band) but this was also failing. The method of repair is to line the guttering system, commonly with Glass Reinforced Plastic (GRP); but there are other suitable products available for use. In addition to carrying out lining works, it is necessary to remove the bottom two or three courses of tiles, check for wet rot decay to rafter ends etc. and repair roofing felt before re-battening and re-fitting of tiles to overlap the new lining. Rigid plastic formers can also be used at the base of the roof slope to reduce the risk of the felt deteriorating where it is immersed in the gutters and susceptible to wind lash.
There are also methods of cutting the gutters off and fitting standard plastic gutters which is a better long term solution for this design defect. Whichever method of repair is undertaken; the wall should be monitored thereafter for internal dampness and wall tie corrosion both internally and externally. If the walls have been retro-filled with insulation, it may be necessary to rake out as much insulation as possible and ventilate the cavity to assist in the drying process. It may also be a good idea to fit perpends (vertical slots) just above DPC level to allow for any excess water to drain out of the cavity.