Clay tile roofing

Clay tile roofing

Applications for system

  • Roof sheathing

Basic materials

  • Fired clay tiles
  • Solid roof decking or strapping
  • Fasteners

How the system works

Clay roofing tiles are made from naturally occurring clay and sand, fired in a kiln at high temperature. Some tile manufacturers will add fluorite, quartz, feldspar or other fluxes to reduce porosity. The tiles are formed when the clay mixture is wet, using a variety of form shapes to meet a desired appearance. The color of the tile depends on the color of the clay, with shades of red being the most common. Tints can be added to provide a range of color options.

While there are a multitude of different clay tile profiles available, the system is essentially like all other shingle-style roofing materials. A solid roof deck or appropriate strapping is placed over the framing, along with any required membrane or un- derlayment. Overlapping courses are fastened to the roof such that there are no exposed seams or joints. The type of overlap and/or interlock on clay tiles will vary depending on the profile of the tile. The tile will have one or more holes cast into the top edge for nailing (using galvanized or copper nails) and some form of interlocking between neighbouring tiles. Some systems use metal clips that slip into the tile and are tacked to the roof deck.

At hips and ridges, tiles cast with an appropriate profile are mortared in place, typically with a cement-based mortar. Penetrations through the roof like vents or chimneys are handled with cast tile pieces and/or metal flashing. Cuts are made in tiles at hip and valley with a tile cropper or a wet saw.

In northern climates, clay roof tiles gained a poor reputation when European-style tiles were prone to cracking due to water absorption and freeze/thaw cycles. Higher firing temperatures and the addition of mineral-based fluxes have reduced porosity to the point where clay tiles are suitable for harsher climates, but the poor reputation lingers.

Tips for successful installation

  1. Include the significant dead weight of clay roofing tiles in calculations for the roof structure beneath.
  2. At the design stage, be certain that details for the chosen profile of clay tile are incorporated. Some clay tiles are thicker than other roofing choices, so intersections with other building elements need to account for this depth. Chimneys and vent pipes should also be appropriately detailed.
  3. In northern climates, select roof tiles that are made to ASTM Grade 1 standards (or equivalent). These tiles are made to have low porosity and to be able to handle repeated freeze/thaw cycles.
  4. Installation must be done such that workers do not stand on finished sections of roofing, as this is the primary cause of failure of clay tiles. Roofing ladders, scaffolding or other work platforms must be used.
  5. Care must be taken when nailing clay tiles. If the nail is left proud of the top of the tile, it could prevent the next tile from interlocking properly and can create a pressure point where a crack could occur. However, if the nail is driven too deeply (or the hammer misses it), the tile can crack.
  6. Cutting clay roof tiles takes practice and appropriate tools. A tile cropper or a wet saw can be used to shape tile at hips and valleys, but first-timers are likely to break a few tiles while getting the hang of the process.
  7. The mortaring of ridge and hip caps is done with a cement-based mortar formulated specifically for clay roof tiles. There will be mortaring procedures particular to each manufacturer’s tiles.

Harvesting — Low to Moderate. The clay that forms the bulk of the material in a roof tile is an abundant resource, with useful deposits in many regions of North America. Clay pits are usually shallow, surface-based harvesting operations that do not use any chemical processes on-site. Many clay pits are in or beside waterways, and pit operations can silt the water and disrupt flow patterns. In general, clay pits are not considered high-impact mining operations, and are excellent candidates for rehabilitation at the end of the pit’s life span.

Manufacturing — Moderate to High. Clay for tiles requires very little mechanical processing. It is ground up and squeezed into a homogeneous mix before being formed. This work is typically all completed by machine in factories, though traditionally it would have been done by hand on or near the building site. The largest impact from clay tiles comes from the firing process, during which the tiles are heated to temperatures of 900 to 1300°C (1650 to 2350°F) for several hours. No toxins are released from the clay during this process, but a lot of fossil fuels are consumed and emissions released into the atmosphere.

Tiles that are glazed or painted will require additional processes, and these can be more toxic. Paint coatings, in particular, can contain chemicals that are emitted into the atmosphere and/or mixed into water at the factory.

The mortar used at ridges and hips is a very small amount of material, but as it is cement based, it carries a high carbon footprint.

Transportation — Moderate to High. Sample building uses 5,125 kg of clay tiles:

7.7 MJ per km by 15 ton truck

4.8 MJ per km by 35 ton truck

1.3 MJ per km by rail

0.82 MJ per km by ocean freight

Production facilities are typically located very close to clay pits, minimizing the transportation of raw materials. With only a few manufacturers supplying the entire continent, this heavy material may have to travel long distances to reach some regions, accumulating high transportation impacts. Installation — Clay tiles require the use of power tools for cutting. Chemical products used in mortar, caulking and flashing will be the items with the highest impact, as the tiles themselves are inert.

WASTE: MODERATE TO HIGH

Compostable — Clay tile offcuts can be left in the environment or crushed to make aggregate or

growing medium. Quantities will be negligible for simple roofs, but can be quite high if there are numerous hips and valleys.

Recyclable — Metal flashing offcuts and fasteners, wood strapping scrap. Quantities will be negligible for simple roofs, but can be moderate if there are numerous hips and valleys.

Landfill — Mortar bags, plywood decking. Quantities will be negligible for simple roofs, but can be moderate if there are numerous hips and valleys.

ENERGY EFFICIENCY

A tile roof has a moderate effect on cooling loads in hot weather, with most common tile colors certified as Cool Roof by the Cool Roof Rating Council, with a SRI value greater than 29.

MATERIAL COSTS: HIGH

While clay tile roofing is quite cost competitive in other parts of the world, in North America it is much less common and therefore prices are comparatively high.

LABOR INPUT: HIGH

A clay tile roof is quite labor intensive. The labor input will depend on the size of tile, with larger tiles requiring less time to be laid. Clay tiles are heavy and fragile, so they take longer to move on-site than more flexible and lighter materials. Cutting custom tiles is slower than with most other shingles, and the mortaring of ridge and hip caps also takes additional time. The requirement to do the roofing without standing on the finished tiles will be an additional labor factor.

SKILL LEVEL REQUIRED FOR THE HOMEOWNER

Decking — Easy. Homeowners able to perform the general carpentry required to frame a roof would be able to deck the roof with strapping and/or sheet materials as required.

Membrane (if required) — Easy. If membranes must be used, they will typically be roll-type products that are straightforward to install.

Tiling — Moderate. A homeowner with some training, workshop experience or good written instruction can place the tiles on a simple roof. Practice is required for the cutting of tiles and to be able to nail quickly and accurately without damaging tiles. Capping and Flashing — Difficult. Mortaring ceramic caps and creating flashing for valleys and roof

penetrations requires experience or training from a professional. A workshop or practice on a small structure is recommended.

SOURCING/AVAILABILITY: MODERATE TO DIFFICULT

Clay tiles are not widely manufactured and distributed in North America, with only a handful of plants responsible for the production of the vast majority of tiles on the market. In regions where clay tiles are a common option, sources and competitive quotes for installation will be readily available. In many regions, clay tiles will be difficult to come by, and experienced installers rare.

DURABILITY: MODERATE TO HIGH

Clay tile roofs can last from 75 to 150 years. Cracked or broken tiles will need to be replaced as part of a regular maintenance schedule to keep the entire roof healthy. Annual checks of the roof and immediate replacement of damaged tiles is important.

CODE COMPLIANCE

Many building codes will recognize clay tiles as an accepted solution. Code officials will want to ensure that the roof structure has been designed to accept the weight of the tiles, and may insist on the need for an experienced installer. In jurisdictions where clay tiles are not part of the accepted solutions, adequate standards, documentation and historical precedent exist to make a reasonable case for their acceptance.

RAINWATER COLLECTION CAPABILITY: HIGH

Clay tiles are generally accepted to be a good solution for rainwater collection for indoor applications.

FUTURE DEVELOPMENT

Clay tiles are a dominant roofing choice in much of the world, but much less so in North America.

Aesthetics and a reputation for being unreliable in cold climates are two factors that have limited their acceptance. As a very small part of the market in most regions, the cost of clay tiles and installation has also kept the system from becoming more widely accepted. With the development of tiles that meet cold-climate standards, there is no practical reason to avoid clay tile roofing. As a roofing product made from natural materials with a long life span and the ability to be recycled into useful growing medium at the end of its life, there is much to recommend clay tiles for sustainable buildings. It remains to be seen if these benefits will move the system into more widespread acceptance.

FLOORING PLAYS A DEFINING VISUAL AND VISCERAL ROLE in a building, as we see it and touch it constantly. The homebuilder is faced with a wide range of options when making flooring choices, and these choices represent a substantial financial investment. They are not decisions that are easy or inexpensive to change.

Flooring obviously receives a great deal of wear and tear, and durability is of utmost importance. Patterns of wear, aesthetic preference and type of construction may all dictate that a home has more than one type of flooring, so the decision-making process may include multiple choices each of which suits a particular need in a particular part of the home.

Flooring considerations are actually twofold: the flooring material itself and the type of surface finish used to seal and protect it. In some cases, the two can be considered separately, with a single flooring product having several options for finishing. In other cases, the materials come pre-finished and the choice for material and finish must be made together. However, in many of the categories of comparison in this book, the flooring material and the finish may have very different ratings. We will attempt to clarify the choices and differences for each option discussed.

Building science basics for flooring

Flooring choices will have few impacts on the performance of the building in the parameters examined by building science.

If an in-floor heating system is used, then the conductive properties of the flooring will have an impact on how quickly heat transfers from the source to the space (and the toes!) above it. Assuming proper insulation levels have been installed under the floor, the conductive properties of the floor will not affect the overall performance of the heating system, but it will have an effect on response-time and perceived sensation of heat in the floor. The greater the density of the flooring material, the better heat will transfer through it and the “warmer” it will feel to feet in contact with it. More dense types of flooring will also require longer periods of heat input to reach a set temperature and will cool down over a longer period of time, potentially resulting in less “cycling” of the heating system.

Concerns that wooden flooring is not suitable for in-floor heating systems are not fact-based. Wood does not shrink or swell to any problematic degree through temperature change; it is changes in moisture content that cause expansion and contraction issues in solid wood flooring. As long as humidity levels are relatively constant and changes in humidity do not occur rapidly, a solid wood floor (or any other flooring type examined in this chapter) over in-floor heating is not a problematic choice.

Some flooring choices can introduce a large amount of moisture into the building at the construction phase, and some will continue to do so for as long as a full year after occupation. Floors that are wet-poured, such as earthen and concrete slabs, bring high quantities of moisture into the building that will not have long-term implications but may affect humidity levels in the early stages of home occupation. Wood and stone floors will carry less moisture, but may contain enough to be noticeable after occupation.

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