Glossary

Accessories (for roofs)

Complementary pieces for roofing.

Argil

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.

Break

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.

Coverage

of composing elements (roof tiles and accessories)

Crack

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.

Eave

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

Eaves

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.

Engobe

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

Extrusion

Production process.

Fissure

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.

Fracture

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

Garrett

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.

Hygroscopy

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

Lath

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.

Linearity

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

PDM: Municipal Master Plans (Portuguese).

Pre-hole

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.

Slope

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

Splinter

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.

Tone

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.

Ventilation

Air circulation process.

Watertight

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

Functional Anomalies

It isn’t unusual to see roofs that worked perfectly for years and suddenly no longer fulfil their function properly. If the roofing work was properly executed, why isn’t it doing its job?

Some of the more likely causes are detailed below.

Fractures

When first applied, roof tiles and other roof components will be in perfect state. However, with time, external elements might affect product performance.

Roof tiles may suffer impacts that will open cracks, fissures or even break them. Applying support structures or similar (such as solar panels) over the roof tiles, moving heavy loads or walking on them might leads to similar damages. When this occurs, the affected elements should be promptly replaced so as not to compromise the roof.

Whenever it is necessary to walk on a roof, as is the case with the installation of antennas, solar panels and similar equipments, walkways should be planned and Torreense safety step tiles should be used.

Accumulation of moss and debris

The basic function of a roof is to be watertight. However, its function may be affected by the appearance of moss and debris.

When this occurs, the roof will no longer function properly, as these elements will constitute obstructions. Water will no longer flow freely and wind may move accumulated water, leading to infiltrations. The solution to this problem is to follow a preventive maintenance plan.

Peelinf from the effect of frost

This is one of the most notorious problems a roof may suffer from, and this type of damage will usually be clearly visible.

This problem may occur with clay roof tiles, even if they comply with the EN 539-2 norm. Even when using certified roof tiles in full compliance of relevant specifications, peeling from the effect of ice is always a possibility.

A number of factors contribute to peeling from the effect of frost, such as:

Absence of ventilation, when clay elemets aren’t properly ventilated, their drying time will increase. The mass of the clay piece will be subjected to constant temperature variations for long periods of time, and will therefore be subjected to the frost-defrost cycle. The water present in the clay piece will suffer sudden volume variations, which may ultimately lead to the piece breaking. It is essential that heat and humidity may flow towards the exterior, to retain a balance between the clay piece and the surrounding atmosphere.

Unfavourable geographic orientation, facing the north side will increase the risk of peeling as an effect of the frost-defrost cycle, but this doesn’t mean roofs shouldn’t face north.

Excessive use of mortar and strong mortar will greatly increase the risk of peeling, especially near the ridgeline. Mortar absorbs more water and releases it slower than clay. Clay pieces in contact with mortar are more exposed to frost-defrost cycles and will usually be the first to present problems.

This problem can be prevented by resorting to execution techniques – especially on the ridgeline – that do not use mortar and instead allow for proper ventilation, thus contributing to the optimal functioning and longevity of a roof.

As has been pointed out, this type of problem will be visible near the ridgeline and in areas in contact with mortar. It will usually affect friezes and ribs first and then move on to the hollow (in the case of the Lusa tile).
Once peeling occurs, all affected roof tiles must be substituted. However, in many cases a complete re-roofing will be necessary.

Water infiltration

As has been mentioned before, being watertight is one of the basic functions of a roof. However, infiltrations are not uncommon, and the quality of the products used is not always the cause.

Many factors may lead to the occurrence of infiltrations, such as insufficient inclination and/or incorrect application of elements. The critical points are:

Ridges;

Walls and chimneys;

Roof tle fittings;

Joists (where water converges);

Eaves.

It is never too much to emphasise the importance of two fundamental factors that will reduce the risk of infiltrations on a roof: adequate inclination and correct product application.

Differences in tone

Differences in tone are a result of the ceramic process and the use of raw materials. In some cases, different shades are a much sought after aesthetical effect that is intentionally put in place by producing roof tiles with a more thorough finishing work.

However, when the intended effect is a homogenous tone, it is advisable to use differently shaded tiles.

The differences in tone of clay pieces affect merely the aesthetical aspect of a roof and do not interfere with their functional characteristics.