08 pitched and flat roofs fundamentals

08. Pitched and Flat Roofs. Fundamentals p01

Session 8Pitched and Flat Roofs. Fundamentals

8.1. IntroductionParts of the roofClassifications

8.2. Functional requirementsStructural performanceCovering and waterproofingThermal performance

8.3. Elements8.4. Blibliography

The California Endowment, L.A. Archs: RCHS + H&R, 2006

Based on the original presentations by Prof. M. Ángeles Beltrán. Adapted by

Prof. Julián García [email protected] by Luis M. Martín

mailto:[email protected]


8.1. Introduction· As with the façade, the main function of the cover is the protection against inclement weather. Secondary but equally important functions are separation, etc. · It constitutes the upper cladding of the building, and therefore is more exposed to rainfall, solar radiation, wind, etc.· It must fulfill the same functional and structural requirements as façades did, with special emphasis on certain aspects discussed below.

“The Primitive Hut”. Laugier, 1753.


Part

sof

the

roof


Basic components of a roof.Base Structure: A structure that supports the deck and gives stability. Might be flat or inclined.Superficial Support: Smaller elements, supported on the base structure and creating a proper base for the covering material is based. Including insulation materials, waterproofing complimentary layers, etc.Coverage: cover material, with or without a finishing protection.

Parts of the roof


ClassificationsA) According to the slope (according to Spanish CTE):

· Pitched: slope> 15%, 9º· Low Slope: 5-15%, 2º-9º· Flat: <5%, 2º(According to CTE, flat roofs with a 0º slope are not allowed)

B) According to the relationship insulation/watertight layer:· Cold roof: Insulation above the ceiling keeps warmth inside the house. In flat roofs this would be the traditional system.· Warm roof: Insulation is located near the watertight layer, keeping warmth in roof space. In flat roofs, this would be similar to an inverted solution.


ClassificationsC) According to the finishing material:

· Covered by parts: tiles, slates, etc. Open but overlapped joints.

· Covered with panels: fiber-cement, metal sheets. Lap joints and flashings.

· Covered with continuous sheets: copper, lead (folded or crimped together) or asphalt or plastic sheets, welded or stuck together with adhesive.


ClassificationsD) According to its function or use:

· Walkable (pedestrian or road)· Not walkable (or only maintenance access)· Landscaped


8.2. Functional requirementsA) Structural performance. Resistance to the following actions:

· Weight (of both the structure and covering material)· Use load and maintenance load· Snow overload· Wind pressure and wind suction· Thermal actions (expansion and contraction)· Seismic actions

Base structural types can be superficial (horizontal or pitched slabs) or linear (trusses, lattice beams, etc)


B) Covering and waterproofing:Creating a watertight cover is essential. Two systems are possible:

· Continuous waterproof membrane(flat roofs)· Overlapped tiles with the correct slope (pitched roofs)

Water tightness. Relationship inclination/material according to Spanish CTE HS DB


Pitched vs. flat roof, or covering vs. waterproofingPitched roofsAdvantages: A certain air permeability. Provides quick water drainage and prevents the accumulation of snow.Disadvantages: Problems in setting the different layers and components due to the slope.Flat roofsAdvantages: The layers may overlap simply by their own weight.Disadvantages: Air tightness –this might be an advantage in some areas. Snow accumulation. High need of maintenance in drainage systems.


C) Thermal performance:Being the roof the element of the building most exposed to solar radiation, a proper thermal control is essential.According to the Spanish regulations, a minimum of 10-15 cm. tchick insulation should be used in roofs in the Madrid area.

Insulation. Relationship element/transmittance according to Spanish CTE HS DB


8.3. Detailed elementsA) Covering/waterproofing layerMaterials already introduced. Its situation in the general layering of the roof can be:

· As a finishing layer (and therefore materials must be resistant to weather conditions)

· Protected by other layers.

B) Thermal insulationMaterials already introduced. Its situation in the general layering of the roof can be:

· Located outside the waterproofing layer.It must be a a waterproof insulation: extruded polystyrene, or other closed cell materials.

· Located inside the waterproofing layer. Other open cell materials, such as rockwool, are allowed.


C) Acoustic insulation

Facing noise impact against the action of rain, foot traffic, etc would require a damping layer. Other acoustic properties of a roof depend on the following basic factors:

· Mass Factor: Cover structural base slab concrete horizontal or inclined, good acoustic performance

· Multilayer Factor: Cover ventilated chamber· Dissipation Factor: Absorbent material on camera improves behavior

D) BarriersBarriers can be made of specific materials, or by other indoor general roof materials that accomplish the same function, such as Air barrier or Steam barrier. In many cases only one layer can fulfill all these functions

E) Expansion and contraction jointsBecause of their exposure, roof surfaces they will suffer expansion and contraction movement of components due to temperature changes. Expansion joints should be designed to allow the movement of components without producing cracks.Several materials and solutions can be used for joints. Fixed sheets are a good solution, but does not allow the expansion of the various components; small pieces require mortar and mechanical anchors; Floating sheets are the best solution, as they allow free movement and can be covered with heavy protection, pavement, gravel ...


8.4. Bibliography

Deplazes, A (Ed.) (2009) Constructing Architecture. Materials, processes, structures. Birkhäuser, BaselKnaack, U.; Klein, T. (2009) The Future Envelope 1: A multidisciplinary approach. 2009. Research in Architectural Engineering SeriesKnaack, U.; Klein, T. (2009) The Future Envelope 2: Architecture - Climate – Skin. Research in Architectural Engineering Series Schunk, E. et al. (2003) Roof Construction Manual. Pitched Roofs. Birkhäuser, BaselSchunk, E. et al. (2003) Roof Construction Manual. Flat Roofs. Birkhäuser, Basel

Spanish regulations:· Código Técnico de la Edificación:· Normas UNE-EN 10077-1, UNE-EN 12210, UNE-EN 12207, UNE-EN 12208, UNE-EN 12400, UNE-EN 12567-1, UNE-EN 14351-1 y UNE-EN -ISO 140-3

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08 pitched and flat roofs fundamentals