What is Sarking on a Slate Roof and Why is it Installed?

Sarking, or insulation foil, is a flexible plastic sheeting with foil laminate applied to one side. It is applied on top of the rafters and under the battens the slate tiles are mounted to.

Sarking has several benefits which include:

  • Provides good weather protection during the installation of slate tiles
  • Prevents dust from entering your ceiling cavity
  • Creates additional insulating to your ceiling batts
  • Offers temporary weather proofing if your roof slates get damaged

A Byproduct of Space Program Technology

Outer space is much more brutal than Melbourne weather. Interestingly, though the benefits of foil insulation were well known decades ago as the result of the space program, only more recently have those benefits been applied to home insulation technology.

Foil insulation provides a “radiant barrier” that works equally well to retain heat in your home during cold weather and inhibit solar radiation (heat) from entering during hot weather. Heat transfer is accomplished through the infrared spectrum and foil thwarts that transfer so effectively that it’s used in outer space.

The conventional batt insulation in your home only slows down this transfer and becomes a radiant sponge in the process—soaking up heat only to leach it toward the cold. A little known law of temperature exchange is that heat seeks out cold. Summer heat seeks out the cooler air in your home. In the winter, cold is not actually coming in, heat is going out.

Understanding this nature of temperature exchange will help you realize why your home heats up noticeably at the end of a summer day and into the evening. Once your batt insulation is overwhelmed with stored heat from the day, it begins radiating it inward toward your cooler living space.

Foil inhibits this process by bouncing the heat back toward its source, therefore keeping you cooler in the summer and warmer in the winter, all while reducing energy bills. You may not think of a new slate roof as being a means of reducing energy bills, but because we use sarking on all slate roofing projects, you’re getting this additional benefit too.

How Long Does a New Slate Roof Last?

There are basically 2½ answers to this question:

  • As little as 10-12 years with signs of failure as early as 3 years
  • As much as 150 years or more—or somewhere in between

To arrive at the answer for you, it’s like pretty much anything else in life; the quality of materials and workmanship will determine the lifespan of your new slate roof. That will come as no surprise so let us help you better understand how to acquire a slate roof you’ll only need to do once in a lifetime.

One good reason so many Melbourne homes and buildings have slate roofing is the proven performance to withstand everything the Melbourne climate can throw at it: salt air, high velocity winds, torrential downpours, hail, snow and ice, intense solar heat and rays, our roofs take a beating. Yet there are period homes in excess of 150 years old with the original slate roofs. That’s proven performance!

To achieve that on your own roof, you’ll need roofing slate with proven performance and a slate installer with proven experience. You also want to be sure you’re getting a written warranty.

Since we’ve outlined these important factors, it’s only fitting we include our own credentials. We’ve been doing slate roofs since 1980 and the experience predates that back to the 1970’s apprenticing under a lifelong master slater. Most of our slating team members exceed 10 years experience. Our workmanship warranty is 50 years and we offer slate tiles with up to a 100 year warranty.

Qualified slate roofing companies are easy enough to identify because they can prove their experience and are not put off by your wise concerns. The dodgy slate roofers do not stand up well to scrutiny. Considering what’s at stake, that bit of due diligence on your part is well worth the effort. Do that and the 100+ year life expectancy on your new slate roof will be your reward.

What Maintenance Does a Slate Roof Require?

Many of the slate roofs around the Melbourne area, like many other places, are located in leafy places. A leading cause of slate roof failures that we see is from leaves and other debris clogging the gutter and drainage system. For this reason, an annual or biannual cleaning of the gutters is highly recommended.

Beyond that, a properly installed new slate roof of good quality, or a fully restored original slate roof, will be essentially maintenance free for many years. However, as the slate roof ages, we advise a professional inspection at least every 2-3 years. Many homeowners wisely choose an annual inspection to safeguard against unpleasant and expensive surprises from water damage.

This isn’t technically maintenance but a word of caution is also appropriate. If other services such as painting, TV or satellite antennas, solar heating, and so on are performed on your home or structure, a slate roof professional should also be consulted. Other tradesmen, or kind souls helping out, are not always aware of the damage they can inflict on a slate roof.

The operative word here is good quality slate properly installed. Once you have that, very little maintenance is required.

What Roof Frame Structure is Required for Slate Roofs?

We get this question quite frequently, mostly from architects and builders, so we wanted to answer it as best we can. There are of course variables and we’re answering it from the perspective of our market here in Melbourne, AU but the principles apply elsewhere. The answer is also technical, but that’s okay since usually only technical people ask it.

The simple answer is to design and build according to the structural requirements used for terracotta roofing tiles. The weight of the lightest “Marseille” pattern terracotta tiles currently available in the Melbourne area is almost 10 kg/sqm heavier than the commonly used Del Carmen 500×250 slate tiles.

Here are some approximate weight comparisons for roofing tiles:

  • Natural slate – Del Carmen 500×250: 30.5 kg/sqm
  • Terracotta tiles – Marseille pattern: 40kg kg/sqm
  • Terracotta tiles – Swiss pattern: 43.5 kg/sqm
  • Concrete tiles – – Flat slate pattern: 52 kg/sqm

The terracotta and concrete tiles listed are also the lighter weight options available. Other tiles on the market are considerably heavier. Also be aware that slate tiles vary in thickness and therefore also in weight. Plus, as the dimensions of slate tiles decrease, the weight per sqm increases conversely. Larger tiles reduce the per sqm weight.

The 500×250 though is the most commonly used in the Melbourne area. Other options include 400×250, 450×250, and 500×300.

Another consideration during roof framing is the heights at which fascias, tilt battens, verge, sole and lear gutter boards, etc., are set and finished at. This is nearly impossible to give a generalized answer on since there are many factors at play and each job has its own set of unique circumstances.

If you’re in our service area, a simple phone call to Abardeen Slate Roofing at (040) 302-2137 is the best answer we can give. We work directly with architects, builders, and the carpenters doing the framing to assure the framing method matches the slate roofing tiles that will be used. If you’re not in our service area, a good slate roofer will offer the same service because it benefits everyone.