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Valley, valley gutter A valley is the term used to describe where two roofs meet at the lower line, either on a slope, or horizontally. The line of intersection is a weak point in any roof system, and potentially a point where water can penetrate the building. Valley gutters are often formed in lead. They need regular monitoring. They should be kept clear of leaves and other debris. Fine cracks in the leadwork can cause water penetration, and hence rot in the underlying timber   Vault An arched cover for an enclosed space. The simplest form of vault is supported on each side by a continuous wall, and is known as a barrel vault. Most barrel vaults are round-arched, but a few are pointed-arched. In more complex vaults there is a framework of dressed-stone ribs, acting as a frame, with rubble filling the spaces between the ribs. Sometimes decorative ribs are applied to the underside - Soffit - of a barrel vault. Timber and plaster ceilings are sometimes made to resemble vaulting. Related Words  Plaster; Soffit Vegetation In building conservation terms, plants growing, in an unintended way, on a building. Seeds carried by the wind, or by birds, can germinate in small pockets of soil in gutters, in open joints, or in valleys. Their growth can often damage masonry directly, or allow water to penetrate a building. Moss on slate or tile roofs can encourage rot in sarking. Related Words  Masonry; Sarking Venetian window Actually three windows, a taller round-headed window, flanked by shorter flat-headed ones. Sometimes the outer windows are blind     Ventilator, ventilating brick, grille Devices to encourage air to circulate in a building. Under-floor ventilators help to keep rot at bay, and should be kept clear. Roof ventilators keep the air in the internal spaces fresh, and help to avoid condensation, and the growth of fungal infection. They should not be blocked up.     Vesica A window or ventilating opening with curved sides, meeting at a sharp point at the top and bottom.