Whenever you begin to climb up a fixed ladder, depending on the height of the ladder, you might see a caged door. These doors prevent unauthorized access to roof ladders. Options can include gates on the cage or actual doors that block the fixed ladder's rungs from being used.
After scrapping the On the Roof project, some of its developers were assigned to the Wall Mount project (most were assigned to fabricate metal stringers). After caged ladders being built in Germany acquired stop production it was assumed that the project would make use of Stainless Steel but, in the end, only ALUMINUM was provided. The project used some of the code from both the Omega project and a pre-release version of Visual Basic. In July 1992, betas of Wall Mount shipped to developers and the name Roof Access became the official name of the product.
The 20th century saw the manufacture of composition shingles which can last from a thin 20-year shingle to the thickest which are limited lifetime shingles, the cost depending on the thickness and durability of the shingle. When a layer of shingles wears out, they are usually stripped, along with the underlay and roofing nails, allowing a new layer to be installed. An alternative method is to install another layer directly over the worn layer. While this method is faster, it does not allow the roof sheathing to be inspected and water damage, often associated with worn shingles, to be repaired. Having multiple layers of old shingles under a new layer causes roofing nails to be located further from the sheathing, weakening their hold. The greatest concern with this method is that the weight of the extra material could exceed the dead load capacity of the roof structure and cause collapse.
Slate is an ideal, and durable material, while in the other parts of the world roofs are made from huge slabs of stone, several inches thick. The slate roof is often considered the best type of roofing. A slate roof may last 75 to 150 years, and even longer. However, slate roofs are often expensive to install – in the USA, for example, a slate roof may have the same cost as the rest of the house. Often, the first part of a slate roof to fail is the fixing nails; they corrode, allowing the slates to slip. In the UK, this condition is known as "nail sickness". Because of this problem, fixing nails made of stainless steel is recommended, and even these must be protected from the weather.
Roofs made of cut turf (known as Green roofs) have good insulating properties and are increasingly encouraged as a way of "greening" the Earth. Adobe roofs are roofs of clay, mixed with binding material such as straw or animal hair, and plastered on lathes to form a flat or gently sloped roof, usually in areas of low rainfall.