Accessories (for roofs)

Complementary pieces for roofing.


Formed through the disaggregation of feldspar rock that becomes malleable when wet. Argil can be found near riverbeds, often forming banks along the margins. Argil can be white, red, gray and brown. It is composed mostly of hydrated alumina sillicata - - Al2O3 · 2 SiO2 · 2 H2O, has low cristallinity and minute dimensions (particles under 2 µm in diameter). Mineralogically, its main components are quartz, illite, caulinite, anatase, hematite and feldspar.


Same as fracture.

Clay tiles

Products for non-continuous application on inclined roofs and wall linings, made by standardizing processes (extrusion and/ or pressing), drying and baking prepared argil, with or without additives.

Construction products

Products to be used or applied permanently in construction projects.


of composing elements (roof tiles and accessories)


Structural defect that consists of a gap with a more or less regular shape affecting the thickness of the piece and is visible to the naked eye.

Distance between laths or gauge

Length of the exposed part of a roof tile or accessory, measured longitudinally.


Edge of a roof along the outer part of a protruding roof slope, made of roof tiles


Edges of a roof along the outer part of a roof slope, projecting beyond the side of a building and composed of accessory pieces.

Effect of ice

This term refers to the wear caused on roofing pieces by successive frost-defrost cycles.


Type of coating, permeable or impermeable, or the material used therefore.


Production process.


Crack with a more or less regular shape that does not affect the whole thickness of a piece.

Fixation orifice

Open or easily pierced orifice for the fixation of a product on the support structure.


Structural defect that consists on the breaking of a product into two or more fragments.


Space under a roof slope

Gutter / Joist

Concave, open piece, usually made of metal, through which liquids run, placed horizontally along the eaves of a roof to drain rainwater, thus avoiding infiltrations.


Property of materials relating to their capacity to absorb water. Ceramic materials are less hygroscopic than concrete or mortar.


Secondary structural piece of a roof arranged in a perpendicular line in relation to the highest inclination of a roof slope, where coating elements are supported.


When used in relation to flat or fitting roof tiles, the value of linearity is given by the deviation in a straight line as measured from the roof tile brim, both longitudinally and transversally.
For Canudo roof tiles, linearity is given by the deviation in a straight line as measured along the generating line at the bottom of a roof tile’s concave end.

Mechanical resistance to flexion

This test is conducted by applying an increasing force on a roof tile until it breaks. The value registered at the breaking point indicates the flexion of the roof tile.

Outeiro da Cabeça

Village located 18 Km from Torres Vedras.
The village covers an area of 5,7 Km2 and has a population of 932 inhabitants. Its main economical activities revolve around red clay ceramic industries (roof tiles and bricks) and agriculture.


 PDM: Municipal Master Plans (Portuguese).


Fixation orifice that is not fully pierced through.

Recommended overlap

Roof tile length that must be overlapped to the next roof tile.

Roofing functional demands

Minimum criteria to be met by a roof. The proper performance of any roof depends on three main factors: correct conception at the project stage, good individual performance of clay pieces and their correct application on the roof.

Roof slopes

Where joists are placed.

Roof tile fixation

Use of nails, screws, metal hooks or any other auxiliary fixation mechanisms that prevent pieces from moving.

Roof tile gap

Gauge or distance between laths.


Also known as pitch or roof surface; any flat surface of an inclined roof.


Surface defect over 7mm on average, consisting of a fraction of the material, separated from the ceramic body on the visible side of the product.

Support spindle

Relief at the underside of a roof tile or accessory allowing its fixation on the support structure, generally consisting of laths.


Colour shade variation on the same make of pieces.

Transversal profiles

This term is applied to Canudo roof tiles and refers to the width of its internal edges.

Underside roof tile ventilation

Also known as micro-ventilation; this refers to the circulation of air near the underside of a roof tile. Aids in the drying of absorbed rainwater and eliminating water vapour from inside a building, which could otherwise condensate on the underside of the roof tile; also aids in the conservation of the lath work, when it is made of wood. Improves roof tile resistance to the effect of ice.


Air circulation process.


In this context, the term relates to the capacity of a roof to completely prevent the entry of water. Impermeability of the clay material used and total roof coverage must be ensured, as well as the correct inclination of the roof. Wind and rain, which in conjunction can provoke ascending water movement along the roof surface, are a serious challenge to the watertight qualities of a roof.

Technical Support

Anomalies resulting from planning and conception

Planning a roof is a big responsibility, as it is such an important part of any building. When planning, the technician in charge must consider the framing and location of the building, as well as the materials to be used.

The most common anomalies resulting from incorrect planning are:

Inclinação da cobertura

The roof tile maker should always provide the minimum requisites regarding inclination for each tile type, area and exposure profile. However, roof inclination might also present problems stemming from the building plan itself.

Insufficient Inclination
Insufficient inclination leads to poor rainwater draining, which could lead to infiltration problems. It will also favour the accumulation of rubbish, moss and other elements that might impair the proper functioning of a roof.

The roof tile maker should always provide all relevant information regarding inclination with its products, but the architect or technician designing the roof should also state this information clearly in the project blueprints.

Excessive Inclination
If the roof is designed to have a steep pitch, the architect or technician designing it should also plan how to fixate the composing elements of the roof, so as to avoid their fall as a result of gravity or other external factors, such as wind.

Roof Ventilation

Lack of proper ventilation is one of the most common anomalies found in roofing work.

Air circulation should always be carefully planned when designing a roof (for more details, please refer to the section regarding roof ventilation for each tile type: Lusa, Marselha, Canudo and Milénio).

The roof project plan should include the number of ventilation tiles to be applied on the roof, as well as their exact location, so that no doubts regarding this matter arise when laying them.

Without ventilation or with insufficient ventilation the roof might suffer from:

  1. Peeling from the frost-defrost cycle;
  2. Premature appearance of moss;
  3. Proneness to condensation;
  4. Rapid degradation of support elements and other accessories.

Without ventilation a roof will quickly degrade and present serious functional problems.

Geomety of structural elements

Proper calculation of structures is fundamental at the planning stage. The structure will have to withstand not only its own weight but also the effect of climate variation for the entirety of its usable existence.

It is not uncommon to see a roof with deformations along one or more of its sides. These deformations are usually the result of structural deficiencies and will seriously compromise the roof itself. Deformed areas will have openings and misaligned roof tiles which will lead to the infiltration of water and other elements.