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 incorrect application

Ensuring the quality of the products and of the project used is essential to a good roof performance, but it isn’t enough. If the composing elements of a roof are not properly applied, neither the roof tile maker nor the project designer can be said to be at fault should any problems arise.

Some of the most common and relevant anomalies resulting from incorrect application are detailed below.

Fitting of the roof tiles

A badly fitted tile might compromise the whole roof. In this manual you can find the basic rules for laying roof tiles, ridge tiles and eaves (for more details, please refer to the chapters regarding the application and laying of each tile type: Lusa, Marselha, Canudo and Milénio).

Longitudinal and transversal misalignments of the roof tile rows are some of the most common error regarding the fitting of roof tiles. Often, problems resulting from defective fitting of the roof tiles will be dealt with by applying mortar to the tiles, thus compromising the whole roof.

Roof tile overlap

Roof tile makers should declare, for each roof tile model produced, the number of roof tiles to apply per m2  and their individual dimensions.

The difference between average measured values and declared values should not exceed 2%, as was discussed in chapter 2. The number of roof tiles to apply in each row should consider the declared coverage value rather than the upper and lower limit values.

In any case, proper roof tile overlap should be ensured. Not complying with this requisite may compromise the whole roof. Insufficient overlap may result in the incorrect calculation of lath work values or its incorrect application.

Trying to reduce the number of roof tiles to apply to the roof by reducing overlap to a minimum (maximising coverage using a minimum of roof tiles) will seriously compromise the roof and its proper performance.

Misaligned rows

To correctly align roof tiles on a roof, the specifications indicated in the chapter concerning the application of each roof tile type (Lusa, Marselha, Canudo and Milénio) should be strictly followed.

Not complying with these specifications, as well as not executing lath work properly, will lead to the presence of crude faults on the roof, and seriously compromise both the aesthetical and the functional aspects of the roof.

Incorrect use of mortar

The excessive use of mortar to compensate problems related to fitting, roof tile alignment and finishing elements (such as the ridge line, for example) is a common mistake. The belief that this provides solidity to the roof is also a misconception.

Throwing mortar to a problem is not a solution. Mortar does not behave like clay materials in the presence of humidity, due to their different hygroscopic properties. Products can be classifies according to their degree of hygroscopy.

  • Hygroscopic Products:  when the amount of water fixated by absorption is high; cellular concrete and plaster are highly hygroscopic, for example.
  • Non-hygroscopic products: when mass is constant regardless of humidity levels; ceramic is a non-hygroscopic material, for example.

Mortar takes longer to dry than a clay piece. Thus, when high quantities of mortar are in contact with clay pieces, the latter will take longer to dry. This will in turn aid the appearance and development of moss and microorganisms, as well as damage from the frost-defrost cycle and will ultimately have negative effects on the roof as a whole.

The excessive use of mortar or the use of strong mortar (see section regarding the preparation of mortar in the chapter pertaining to the application of each tile type: Lusa, Marselha, Canudo and Milénio) will often result in the appearance of cracks, leading to infiltrations through the mortar itself.