Eaves are horizontal roof edges that project beyond a building’s external walls. Eaves connect the visual elements of a house at the junction between the walls and roof. They consist of the same material as the roof -- slates, tiles or thatch -- and the timber supporting them. Eaves overhang between 0.150 and 0.3 metres beyond the external wall of an average British family home. A fascia, or gutter board, forms the outside edge of eaves. The underside consists of a soffit, board or box that protects the roof’s rafters. Open rafter eaves are those where no soffit board is present.
The principal function of eaves is to prevent rainwater from penetrating the house structure. The eaves’ overhang stops rainwater from entering at the joint between the roof and a house wall. The same overhang provides a pathway, or eavesdrop, around the base of the building and reduces water inflow and splash around the house footings. Thatched roofs traditionally have a large overhang and provide protection from rainwater over the heads of doors and windows. The fascia provides a lip that channels rainwater along the gutter and into external drain pipes.
Eaves provide a shaded area around a house during hot summer months. They stop radiant heat of the sun from passing through windows and being trapped inside of the house. The width of eaves depends on local climate and latitude. Eave width is shorter in cold climates and high latitudes. Here, sunlight is weaker and rainfall is greater than in lower latitudes and hot climates.
Roof and attic ventilation is important for the long-term health of a house. Without it, condensation buildup causes rot, mildew and structural deterioration. Eaves with a low pitch and long overhang can trap moisture, snow or ice on their underside. Vents through eaves and soffits assist air circulation around the roof rafters, through roof vents and into the attic.
House martins, swifts and swallows prefer to build their nests in the outer part of house eaves. Their nests consist of mud and grass with a lining of feathers. The nests fit securely between the overhang and the house wall. They deter starlings and sparrows from nesting deeper in the roof. Squirrels cause serious structural damage to houses when they nest under eaves and chew through roofing material, birds nests and electrical circuitry.