Editing Roof (section)

==Functions==

A roof assembly has more than one function. It may provide any or all of the following functions:<br>
1.	To shed water i.e., prevent water from standing on the roof surface. Water standing on the roof surface increases the live load on the roof structure, which is a safety issue. Standing water also contributes to premature deterioration of most roofing materials. Some roofing manufacturers' warranties are rendered void due to standing water.<br>
2.	To protect the building interior from the effects of weather elements such as rain, wind, sun, heat and snow.<br>
3.	To provide thermal insulation. Most modern commercial/industrial roof assemblies incorporate insulation boards or batt insulation. In most cases, the International Building Code and International Residential Code establish the minimum R-value required within the roof assembly.<br>
4.	To perform for the expected service life. All standard roofing materials have established histories of their respective longevity, based on anecdotal evidence. Most roof materials will last long after the manufacturer's warranty has expired, given adequate ongoing maintenance, and absent storm damage. Metal and tile roofs may last fifty years or more. Asphalt shingles may last 30–50 years. Coal tar built-up roofs may last forty or more years. Single-ply roofs may last twenty or more years.<br>
5. Provide a desired, unblemished appearance. Some roofs are selected not only for the above functions, but also for aesthetics, similar to wall cladding. Premium prices are often paid for certain systems because of their attractive appearance and "curb appeal."

===Insulation===
Because the purpose of a roof is to secure people and their possessions from climatic elements, the insulating properties of a roof are a consideration in its structure and the choice of roofing material.

Some roofing materials, particularly those of natural fibrous material, such as thatch, have excellent insulating properties. For those that do not, extra [[Building insulation|insulation]] is often installed under the outer layer. In developed countries, the majority of dwellings have a [[ceiling]] installed under the structural members of the roof.  The purpose of a ceiling is to insulate against heat and cold, noise, dirt and often from the droppings and lice of birds who frequently choose roofs as nesting places.

Concrete tiles can be used as insulation. When installed leaving a space between the tiles and the roof surface, it can reduce heating caused by the sun.

Forms of insulation are felt or plastic sheeting, sometimes with a reflective surface, installed directly below the tiles or other material; synthetic foam batting laid above the ceiling and recycled paper products and other such materials that can be inserted or sprayed into roof cavities. [[Cool roof]]s are becoming increasingly popular,<ref name="10.3390/su13094665">{{cite journal |last1=Farhan |first1=Syed Ahmad |last2=Ismail |first2=Fouad Ismail |last3=Kiwan |first3=Osamah |last4=Shafiq |first4=Nasir |last5=Zain-Ahmed |first5=Azni |last6=Husna |first6=Nadzhratul |last7=Hamid |first7=Afif Izwan Abd |title=Effect of Roof Tile Colour on Heat Conduction Transfer, Roof-Top Surface Temperature and Cooling Load in Modern Residential Buildings under the Tropical Climate of Malaysia |journal=Sustainability |year=2021 |volume=13 |issue=9 |page=4665 |doi=10.3390/su13094665 |doi-access=free }}</ref> and in some cases are mandated by local codes.  Cool roofs are defined as roofs with both high [[reflectivity]] and high [[thermal emittance]].<ref name="10.3390/su13094665"/>

Poorly insulated and ventilated roofing can suffer from problems such as the formation of [[Ice dam (roof)|ice dams]] around the overhanging eaves in cold weather, causing water from melted snow on upper parts of the roof to penetrate the roofing material. Ice dams occur when heat escapes through the uppermost part of the roof, and the snow at those points melts, refreezing as it drips along the shingles, and collecting in the form of ice at the lower points. This can result in structural damage from stress, including the destruction of gutter and drainage systems.

===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>

===Solar roofs===
{{unreferenced section|date=September 2021}}
Newer systems include [[solar shingle]]s which generate [[electricity]] as well as cover the roof. There are also solar systems available that generate hot water or hot air and which can also act as a roof covering.  More complex systems may carry out all of these functions: generate electricity, recover thermal energy, and also act as a roof covering.

Solar systems can be integrated with roofs by:
: integration in the covering of pitched roofs, e.g. solar shingles,
: mounting on an existing roof, e.g. [[Photovoltaic module|solar panel]] on a [[tile]] roof,
: integration in a flat roof membrane using heat welding (e.g. PVC) or
: mounting on a flat roof with a construction and additional weight to prevent uplift from wind.