TAN 24 THEENVIRONMENTAL CONTROL OF DRYROT
gutter and lead flashing dressed over the top of the cope stone where a visible lead downstand may be deemed acceptable. Alternatively the lead capping may be dressed into a chase cut into the top surface of the skew stones, set back from the outside face. 4.3.1.3
Other gutter problems
There are many different wall head details that use eaves gutters to collect and direct rain water to downpipes fixed to traditional masonry walls. These eaves gutters are a frequent source of water penetration into masonry walls, usually as a result of lack of maintenance leading to a range of defects such as those identified below: (a) Defective gutter brackets allowing the gutter to sag, joints to open and water to run down the wall face. (b) A build-up of debris, particularly at outlets that encourages the growth of grasses, weeds and woody plants, which then obstructs drainage to the outlets forcing the water to discharge down the wall face. (c) Many of the classic sandstone terraces use a box gutter arrangement such as that as shown in Illustration 14. Rainwater downpipes are often fixed within a recess in the external stonework or within a duct on the inside wall surface. In either case, maintenance can be difficult and the wall can become saturated in the event of water leakage at failed pipe joints. (d) Snow and snow melt water can defeat most constructions unless snow is physically removed or melted by a gutter heating system.
Gutter problems may be also due to poor design, poor workmanship and inadequate maintenance. Gutters are frequently undersized and poorly laid with optimistic falls. Vernacular buildings with open eaves, freely dripping, may cause fewer problems as run-off is evenly distributed, splash water can evaporate and there is no concentration of water to penetrate should hopper heads and downpipes fail. The maintenance problems posed by access difficulties to roofs is demonstrated in Illustration 15. In this case a valley gutter on a Glasgow church roof is in a very inaccessible location between three steeply sloping roofs. Whilst the gutter appears to be of adequate width and laid to appropriate falls, the outlet from the roof has not been well designed and allows debris to collect and block the outlet. Because of access difficulties, clearing the outlet was ignored and resulted in water penetration at the wall gutter junction leading to an outbreak of dry rot.
4.3.1.4 Complex roofs The problems posed by complex roof designs, contributing to dry rot problems, can be seen in Illustration 16. A number of features have contributed to water penetration and the development of dry rot. (a) Internal valley gutter with inadequate falls. (b) Shallow pitch roofs, poorly maintained (note slipped and broken slates). (c) Poor quality repairs to the roofs around the cupola area, at ridges and ridge junctions, valleys and around the rooflight.
Loose a-d broke- slates at cavcs eaourages water
moisture cofittnk
Maso-t-8 wet through Leakiv~g gutter, outlet a d RW
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Route o f water penetration
Illustration 14. Detail at eaves using a box gutter set on the wallhead. This arrangement allows ready access of water is often exacerbated by loose or broken slates into the wall should the gutter become broken or blocked. The sit~~ation which allow access of water to the wall plate and beam ends (in the first instance)