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

Roof ventilation

Absence of proper roof ventilation might sometimes compromise the whole building. For inclined clay tile roofs, there are two possible types of ventilation:

Ventilation of the underside of roof tiles or micro-ventilation

Ventilation of the underside of roof tiles is essential for the proper performance of a roof. Air circulation dries rainwater absorbed by the roof tile, avoiding condensation and the appearance of moss.

In areas subjected to high thermal variations, proper ventilation ensures higher resistance to peeling as a result of the frost-defrost cycle, as can be seen in the picture below:

This type of ventilation helps in:

  • Eliminating water vapour produced inside the dwelling;
  • Prolonging roof tile durability;
  • Improving roof tile durability against ice and frost;
  • Preserving the lath work, if it is made of wood;
  • Reducing heating by convection during summer.

It is therefore necessary to ensure there are air vents in place on the roof by means of:

  • ventilation tiles (minimum 3 per 10 m2); ventilation tiles must be unevenly placed near the eaves and ridge;
  • air vents near the eaves;
  • applying adequate finishing when laying the ridge of the roof so as to prevent excessive use of mortar that might prevent  proper ventilation.

However, so that air can circulate, there must be free space under the tiles (2 to 4 centimetres), corresponding to the standard size of laths.

Laths, on the other hand, must be interrupted for 2 to 3 centimetres at alternate points each 3 to 4 metres to allow air circulation, as shown in the picture.

Ideally, counter-laths will be placed where laths are laid. Counter-laths should have at least 2,5 cm, so as to allow air circulation, as exemplified in the picture bellow.

1. Slab
2. Counter-lath
3. Lath
4. Roof tile

In any case, ventilation should always be enhanced by applying ventilation tiles, as will be discussed later in this manual.

Roof performance can always be improved. However, performance is intimately linked to the roofing project. While at the project phase, it is necessary to carefully consider the materials to be used, how to apply them and the technical qualifications of those applying them. Choosing the best materials will never substitute their proper application.

Garret ventilation

The garret of a roof must always be ventilated. This ventilation will ensure the durability of materials, thermal comfort in summer and a dwelling’s habitability.

If the garret is not used as a living space and the structure is not continuous, ventilation will be performed by the entry of air through the roof, as by wind.
If the garret is used as a living space or similar, where hygienic conditions must be ensured, then some care must be taken, especially if using wooden panelling. In this case, insulation should be applied directly over the panels, and roof tiles must be laid over lath; the space between the insulation and the roof tiles must be ventilated. If the structure is not continuous, insulation does not have to be continuous either. For more details regarding the application of insulation, see that specific section.