Editing Roof (section)

===Drainage===
The primary job of most roofs is to keep out water. The large area of a roof repels a lot of water, which must be directed in some suitable way, so that it does not cause damage or inconvenience.

Flat roof of adobe dwellings generally have a very slight slope. In a Middle Eastern country, where the roof may be used for recreation, it is often walled, and drainage holes must be provided to stop water from pooling and seeping through the porous roofing material.

While flat roofs are more prone to drainage issues, poorly designed or textured sloping roofs can face similar problems.<ref>{{cite web |url=https://platinumroofingandconstruction.com/how-can-a-bad-roof-impact-your-overall-house/ |title=How Can A Bad Roof Impact Your Overall House? |website=Platinum Roofing & Construction |access-date=Dec 1, 2024}}</ref> Standing water on a roof can lead to [[mold]] growth, which is highly damaging to both the building’s structure and the health of its occupants. Repairing drainage issues is significantly less costly than fixing the damage caused by [[mold]].<ref>{{cite book |last1=Cheng |first1=Jianwei |last2=Zhang |first2=Guanghul |chapter=Analysis of the runoff and seepage drainage effects of prefabricated roof double-layer drainage system |publisher=Taylor & Francis |year=2023 |pages=241-247 |title=
Advances in Frontier Research on Engineering Structures Volume 1 |isbn=9781003336631}}</ref>

Similar problems, although on a very much larger scale, confront the builders of modern commercial properties which often have flat roofs. Because of the very large nature of such roofs, it is essential that the outer skin be of a highly impermeable material. Most industrial and commercial structures have conventional roofs of low pitch.

In general, the pitch of the roof is proportional to the amount of precipitation. Houses in areas of low rainfall frequently have roofs of low pitch while those in areas of high rainfall and snow, have steep roofs. The [[longhouse]]s of [[Papua New Guinea]], for example, being roof-dominated architecture, the high roofs sweeping almost to the ground. The high steeply-pitched roofs of Germany and Holland are typical in regions of snowfall. In parts of North America such as [[Buffalo, New York]], United States, or [[Montreal]], Quebec, Canada, there is a required minimum slope of 6 in 12 (1:2, a pitch of 30°).

There are regional building styles which contradict this trend, the stone roofs of the Alpine chalets being usually of gentler incline. These buildings tend to accumulate a large amount of snow on them, which is seen as a factor in their insulation. The pitch of the roof is in part determined by the roofing material available, a pitch of 3 in 12 (1:4) or greater slope generally being covered with asphalt shingles, wood shake, corrugated steel, slate or tile.

The water repelled by the roof during a rainstorm is potentially damaging to the building that the roof protects. If it runs down the walls, it may seep into the mortar or through panels. If it lies around the foundations it may cause seepage to the interior, [[rising damp (structural)|rising damp]] or [[dry rot]]. For this reason most buildings have a system in place to protect the walls of a building from most of the roof water. Overhanging [[eaves]] are commonly employed for this purpose. Most modern roofs and many old ones have systems of valleys, gutters, waterspouts, waterheads and [[Drain (plumbing)|drainpipes]] to remove the water from the vicinity of the building. In many parts of the world, roofwater is collected and stored for domestic use.

Areas prone to heavy snow benefit from a metal roof because their smooth surfaces shed the weight of snow more easily and resist the force of wind better than a wood shingle or a concrete tile roof.

<gallery mode="packed" class="center" caption="Insulation, drainage and solar roofing" perrow="5">
File:Snow on the roof.jpg|[[Snow]] on the roofs of houses in [[Poland]]
File:Ashdod 2005, rooftop view p2.JPG|The flat roofs of the Middle East, [[Israel]]
File:Jakriborg, juni 2005 x.jpg|Steeply pitched, gabled roofs in [[Northern Europe]]
File:雪中紫禁城 7.jpg|The overhanging eaves of [[China]]
File:PA120016.JPG|[[Green roof]] with solar panels, [[Findhorn]], [[Scotland]]
</gallery>