Slate tiles are associated with being a very heavy roofing material – 100 square feet of typical slate tiles weigh as much as 1,300 pounds. This, in turn, means that in order to install them, it is very often necessary to extensively rebuild the roof structure, incurring additional costs. In addition, thick slate tiles also mean a slightly different roof appearance and higher material costs. On the other hand, thin slate tiles offered by a growing number of manufacturers are much less durable and appear brittle. In this article, our experts will explain to you what thickness of slate tiles you should choose for yourself. Feel free to read on!
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How Does Slate Tile Thickness Affect Roofing?
As a rule of thumb, the thicker the slate tiles, the more durable but also more expensive your roof will be. As is the case with the tires on your car, the outer layer of the roof becomes weaker and thinner as erosion continues all the time.
On the other hand, installing thick slate tiles can put a lot of strain on your roof structure. Every pound of load transferred to the load-bearing elements shortens their lifespan, as wood subjected to constant compression and side-to-side pushing will gradually but regularly crack. The whole process can take 20 or 80 years, but sooner or later, the rafters, purlins and ridge will not last.
You also need to be aware of the costs associated with installing slate tiles of great thickness. The heavier they are, the more time it will take to install them, so the more expensive the roof replacement service will be. The price of labor is, of course, followed by the cost of purchasing the material – although twice as heavy slate is not necessarily twice as expensive, you certainly won’t purchase it at the same price as the thinnest models available.
Durability and Lifespan
Let’s return for a moment to the topic of durability and longevity of slate roofs – after all, these are their key advantages.
Longevity of slate roofs is the most debatable issue. While no one should dispute the fact that the thicker the slate tiles are, the more durable they will be, in our state, you won’t feel any real difference if you opt for models thicker than 3/8 inch (9.5mm). The thinnest tiles available on the market are about 1/4 inch and may actually be more susceptible to wear and tear, but even they usually last more than 50 years.
It is definitely worth opting to install slate tiles with a higher thickness (3/8 or 1/2 inch) if you live in an area prone to regular hailstorms and high winds. However, if such weather conditions are infrequent in your area, it is not worth the extra cost.
Weight and Structural Problems
The weight of slate tiles, on the other hand, is their biggest disadvantage – if your roof previously had cedar shakes or any other material installed, you will almost certainly have to do a major rebuild of the supporting structure, and in extreme cases, even the load-bearing walls of the house.
| Material | Weight per 100 sqft (lb) |
| 1/4″ slate tiles | 935 |
| 3/8″ slate tiles | 1400 |
| 1/2″ slate tiles | 1870 |
| DaVinci composite slate tiles | 275 |
| Cedar shakes | 450 |
| Asphalt shingles | 300 |
Most roofs in the United States, including Illinois, must withstand dead loads of no less than 15 pounds/sqft. In practice, therefore, this allows the installation of typical slate tiles on a roof without major structural changes, but this is strongly discouraged – using virtually the entire load-bearing capacity of a structure always results in accelerated wear and tear, and this increases the risk of an accident.
In order for your roof to be durable and stable, its structure should be designed to carry about 3 times the load. This, in turn, means that rafters and purlins should be spaced with less spacing. We probably don’t need to explain that rebuilding an existing roof truss is expensive and complicated.
Aesthetic Impact
Although it’s not that important to most people, the thickness of the slate tiles has an undoubtful impact on the aesthetics of the roof. The thicker the tiles, the more outlined the pattern, and the more massive the whole house looks. You may not believe us, but standing a few dozen feet in front of the building, a skilled observer can easily distinguish the different thicknesses.
It is also worth remembering that the choice of thickness of slate tiles is largely related to the style of laying them. Some homeowners deliberately buy tiles of varying thicknesses and widths to achieve an effect of artistic chaos. On the other hand, slate roofing in contemporary architecture requires uniformity and repetition, which is achieved by using smooth and even pieces of stone.
Material Quality and Thickness Correlation
Unfortunately, the source of slate tiles is extremely important from the point of view of roof design – as it affects the thickness of the tiles.
It can be assumed that the most durable slate tiles are those made from stone from Wales, Canada and Argentina. The structure of slate quarried in these countries is more compact and dense, so that tiles of smaller thickness can be cut from it and successfully used in roofing.
Other parameters are the most popular slate tiles, which mainly come from Spain and Brazil. Stone from these countries is used by major companies such as CUPA Pizarras. The popularity of these slate grades is due to their high availability, lower price and easier processing, but the more porous surface and less compact structure make them less durable.
If you want to install the thinnest possible slate tiles for aesthetics or roof design reasons, it is worth choosing stone from Argentina, Canada and Wales. This is a more expensive solution, but the weight of the rooftop can be reduced by up to 25%.
Building Codes and Structural Standards
The International Building Code, which is a set of regulations governing roof design in much of the United States, does not impose thickness requirements for slate tiles. The regulations cover areas such as fire, wind and overload resistance. However, the creators of the regulations probably felt that setting a minimum or maximum thickness for slate tiles was not necessary.
Common Slate Tile Thicknesses in the United States
Manufacturers of slate roofing tiles are outdoing themselves in creating products that will satisfy every customer. The thinnest roofing tiles made of natural stone are only 4 mm (~0.16“) thick, while you can easily find tiles over 1” thick as well.
The standard thickness of slate roofing tiles in the United States is about 1/4 inch (6.35 mm), referred to, incidentally, as “nominal quarter-inch.” It’s a good compromise between durability, weight and price – this type of slate tile, often made of Spanish slate, is suitable for virtually any architectural style and for installation on homes that did not originally have a stone roof.
Homeowners with greater requirements for this roof strength may want to consider slate shingles 3/8 inch (9.5 mm) thick or thicker. Heavy and extra heavy slate roofing tiles weigh up to 3 times as much as a nominal quarter inch, but as long as the design of the roof and the entire building allows, they are worth considering. By paying more, you gain peace of mind for an even longer period of time and above-average roof aesthetics.
On the other hand, slates with a thickness of 4 to 6 mm (0.16“ – 0.375”) are used where hail resistance and loads are not as important. Clearly lower structural load, potentially attractive price and visual softness are highly desirable qualities for slates. In many countries, it is lightweight slate tiles that are the market standard!
Slate Tile Thickness Offerings from Leading Manufacturers
When planning a roof replacement, you can use slates from many manufacturers. In the United States, the list of most recognizable brands includes:
- SSQ International;
- Buckingham Slate;
- Evergreen Slate;
- Vermont Slate Company;
- CUPA Pizarras;
- Greenstone Slate;
- Hilltop Slate.
Each of the aforementioned companies offers slightly different products – some focus on distributing a wide range of colors, while others are limited to dark gray only. Vermont Slate Company’s selling point is the above-average low weight of their slate tiles, while CUPA leads the way due to its low price and shorter delivery time.
It’s worth remembering that the availability of slate tiles depends on where you live. In the States located in the Northeast, you’ll have a greater selection of tiles manufactured in Canada as well as locally, while residents of California, New Mexico or Colorado will be doomed to import slate from further afield. This, in turn, makes it much quicker to find a house in California with a roof covered with Chinese or Brazilian slate.
If you live in Illinois and are planning slate roof replacement, don’t hesitate to contact us. Our specialists will help you choose the best possible tiles and take care of importing them, even from the other side of the world.
Is Investing in Thicker Slate Tiles Worth the Extra Cost? Pros and Cons
When considering slate tiles for roofing, the thickness of the tiles plays a significant role in determining the overall performance and cost of the roofing system. Thicker slate tiles offer certain advantages and disadvantages that should be carefully evaluated.
Pros of Thicker Slate Tiles
Enhanced Durability
The obvious advantage of slate tiles 3/8″ thick and higher is their increased level of resistance to external factors. Environmental stressors such as heavy snowfall, strong winds, temperature fluctuations and hailstorms lead to degradation of the stone surface – freezing and thawing water causes the slate to start cracking and crumbling. Increased thickness does not slow down this process, but makes it able to last longer before it starts to pose a threat to your home.
Improved Aesthetic Appeal
In most cases, thicker slate tiles look better on the roof – the patterns are more clearly outlined, which is important especially if you opt for a multicolor roof. Although minimalist designs call for a roof surface that is as uniform as possible, the vast majority of our customers expect exactly the opposite effect.
Cons of Thicker Slate Tiles
Higher Material and Installation Costs
Much more stone is needed to produce heavy and super heavy slate tiles. Slate is sourced from large blocks mined from underground, and in a nutshell, you can assume that ordering twice as much of it will cost you twice as much. It’s worth adding that the thicker slate tiles can be really heavy – 1″ thick tiles weigh as much as 40 lbs. Bringing them onto the roof and laying them is time-consuming, cumbersome and dangerous, making labor costs rise dramatically. For a large roof, the price differences can reach tens of thousands of dollars.
Structural Reinforcement Requirements
When replacing asphalt shingles with slate tiles, you must take into account the fact that you will almost certainly need to reinforce the roof truss. Sometimes these are relatively minor changes, but there are situations in which you need to completely dismantle the framework and build it from scratch. If the roof consists of multiple planes, has dormers, windows and mansards, the costs can skyrocket.
Potential for Limited Availability
As we have already written, the availability of slate tiles of certain thicknesses, origins and colors may be very limited in your area. When planning to install niche tiles, you must be ready for a complicated, expensive and time-consuming import process. Asphalt shingles are the most popular roofing material in the United States, which simply makes purchasing slate tiles complicated, especially if they are very thin or above average thickness.
Cost Differences Between 1/4-Inch and 1/2-Inch Slate Roofs
The cost of a natural slate roof varies based on thickness and quality. For instance, a standard 1/4-inch-thick S1-grade hard natural slate roof with lifetime exceeding 75 years averages around $6 – $8 per square foot (labor not included), while a 3/4-inch-thick high quality slate costs roughly $25 per square foot. These figures highlight the premium associated with thicker slates, emphasizing the importance of aligning choices with budget and performance expectations.
In conclusion, selecting the appropriate slate tile thickness requires a balance between aesthetic preferences, structural considerations, and budget constraints. Consulting with roofing professionals and considering regional climate conditions can aid in making an informed decision that ensures both the longevity and beauty of the roof.
