Slate roofing is a learned craft. As opposed to using electric tools to mindlessly attach mass produced roofing shingles, there is very little in the way of gas or electric power need for slate roofing. Cranes, trains and saws maybe, but angle grinders? Really?  Once the big slabs of slate come out of the ground, individual slates are hand split from a larger block. They are then typically punched using an iron jig and stacked by hand. When it comes to installation, its all done by hand, cutting, punching, nailing and layout. Not much is needed in the way of tools. A slater's stake, slate hammer, a story stick, some nails and paper (and a modicum of skill) and one could slate just about anything. 

This video is not unique. There is ample evidence out there of people with just enough knowledge to seem like they know what they are doing, and yet their lack of skill or understanding is quickly unmasked. I am all for encouraging people to take up a craft, but at least read a book or ask an old timer how it's done and go practice on a barn or shed. 

Mineral Deposit Leak

Yes, it seems like an odd title for a post, but we recently replaced a shed dormer roof, the shed flashing and the flashing around a vent pipe. The only problem was, after we did the job, the home owner complained of a leak in the vicinity of our work. We went back out to inspect the job, including the head lap, side lap, broken slate, etc. The installation appeared to be fine. Everything began to point to a leak in the cast iron pipe itself. But after measuring the leak in the dormer from the front wall, the leak was actually several feet behind the dormer and vent pipe, unrelated to the work on the dormer. First, we inspected the keyways of the slate behind the dormer. Nothing. We had to resort to pulling slate. This yielded a slate that appeared to be normal, but where the slate above it overlapped, there was a dimmed sized hole in the slate. Yikes! This slate had a mineral deposit that eventually deteriorated enough to leave a hole. It was close enough to the keyway so that during a heavy rain or wind driven rain, a leak resulted.

I guess after eighty-three years of protecting the house, a few slates are allowed to yield to their faults.

 
Pictures on left, front of Vermont Slate, right, back side of same slate.

Faulty Slate Installations

It can be an expensive surprise for homeowners to find faulty slate installations, especially after moving into a new house. Occasionally, we will find one or two mistakes in new slate roofs. Rarely, will mistakes be found on older slate roofs. Usually, when doing an inspection of an older slate roof, some of the fundamentals don't need to be checked. Had these fundamentals been violated, the roof wouldn't have lasted. On newer slate roofs, the fundamentals should be checked.

Fundamentals

• Install a cant strip of the same thickness of the slate. (For further reading, see "The Slate Book," page 108, by Stearns, Stearns, and Meyer, 1998).  
• Use the correct exposure for the size of slate AND roof pitch. (For further reading, see "The Slate Roof Bible," page 198, by Joe Jenkins. 1997) or find a copy of the NSA (National Slate Association) Installation Guide 
• Install the first row of the Starter Course chamfered side down and be careful of the sidelap. 

For further reading about inspecting slate roofs, slate roof jargon and installation and repair problems, 

see, Buying and Maintaining a Slate Roof, by David Robinson

Below are a few pictures of some of the fundamentals violated on a lower sloped porch roof. 

Also See:

Our Neighbor's House: Installing Slate Roofs: from http://www.slateservice.com A new slate roof is a big investment. Whether you are reslating an addition, or installing slate on your ...

Signs of Recent Damage

Signs of recent damage. Occaisionally, I'll be on a job that involves an insurance claim relating to a leak. Usually, normal wear and tear wont be covered by insurance. It may seem obvious, but if the leak is in the field of slate, new damage can often be determined by the presence of small chips of slate (not always though).

These small chips will wash away with the rain. Larger chips and pieces will hang around and eventually end up in the gutter. So, if there is every a question of whether some damage is old or new, look for small chips of slate around the problem. This picture shows tree damage and there are lots of small pieces.

The kind of damage shown in the picture is usually caused by falling tree limbs, falling snow and ice and people.

For other information on slate roofing, visit: Slate Roofing

Winter Snow Storms Can Wreak Havoc on Roofs

Winter snows can cause lots of damage to your roof. As snow accumulates on the roof, damage can occur in many forms. The first type of damage can occur from the shear weight of the snow sitting on the roof and in the gutters. Not all snow is the same. The water content in heavy wet snow will be much greater than dry light snow. One cubic foot of heavy wet snow can weigh up to 20.81 pounds. That's twelve inches of snow. Keep adding snow, and we can see how quickly the weight can add up. Thirty-two inches of snow on your roof can weigh over fifty-five pounds. Excessive weight can lead to structural failure. It is no wonder that we see roof failures after major snow storms. But these types of structural failures are most often seen on commercial buildings with flat or low sloped roofing. Some of the worst collapses occurred where a winter storm was followed by a heavy rain some days later. The rain simply has no place to go. This happened in Frederick, MD with the collapse of the roof on the Leggett department store after the winter storm of 1997.   Signs of structural problems can be seen by bowing roof rafters or sagging roofs. An engineer should be consulted when excessive bowing or sagging is encountered.

A more common type of damage from snow storms is cosmetic damage, including damage to individual shingles or slate, damage to gutters and fascia that has been ripped from the home. As the snow melts each day, some of the water re-freezes at night. As this cycle continues, ice can accumulate in valleys, gutters and at the eaves of the roof.
 Picture showing cosmetic storm damage where the gutters and fascia were torn off, and slates were damaged.

This freeze-thaw cycle is the cause of most of the cosmetic damage we see each year. Ice will expand in the gutters and cause seams to fail and the weight can bend and break the brackets holding the gutters to the home. Down spouts can split especially as water freezes in the down spout. As ice builds up in the gutters, down spouts and eaves, there is no where for the melting ice and snow to go. Some of the water will back up under the roofing material and show up inside as a leak. This condition is well known as an ice dam. Unfortunately, while an ice dam is occurring, there really isn't a safe way to stop it. Damage can be minimized if access to the eaves in the attic is easy, but often, the underside edge of the roof is very difficult to reach from inside the attic. In some cases, once all of the snow and ice is gone, there maybe no indication on the roof surface that there was ever a problem. But more often, there will be damage to the roof surface, slate, snow guards, gutters and fascia. At this point, one can plan to minimize future ice dams.
 Minimizing Ice Dams:

• Increase Attic Insulation Above Heated Spaces
• Increase Ventilation in the Eaves including Soffit Vents
• Add a Layer of Ice and Water Shield above the Gutter Line
• Include a Well Thought Out Snow Guard System
• Consider a Snow Melt System

We often try to solve the problem while its happening, meaning we find ourselves or our neighbors climbing onto roofs in very dangerous conditions. Nobody wants water dripping into their homes. I know from personal experience what a disaster it may seem like while the problem is occurring.   But I can assure you, drywall, paint, carpeting and other damage is a lot easier to repair than the physical trama that can occur from fall from a ladder or a roof. If water is dripping through your drywall or plaster, take a screwdriver and poke holes near each of the leaks. This will allow the water to flow out and it can then be collected in buckets.  More importantly the holes will help prevent the water from accumulating in the ceiling and causing the plaster or sheetrock from collapsing. Of course, shut the breaker off to any light fixture that is leaking water.  

New Book

If you are in the neighborhood, you can always come by and pick up a copy from our offices in Roland Park and save on shipping.

There are few reliable sources on slate roofing practices. Hopefully, this will be considered one of them. This book was written with the focus maintaining old slate roofs, especially with new homeowner's, or homeowner's unfamiliar with slate roofs. Contractors and real estate agents may also find this information useful. Contractor's involved with renovations that include renovating old houses can use this book to help monitor the quality of their subcontractors working on slate roofs. Real estate agents can use this information to help advise their clients.

I have been working on and inspecting slate roofs since 1989. I have attended numerous seminars on historic and slate roofing, and I conducted slate roofing seminars for local neighborhood associations and historic commissions.

I am indebted to Joe Jenkins, author of the "Slate Roof Bible" for his input on this book. Check back soon for a link to purchase your copy.

Installing Slate Roofs

from http://www.slateservice.com


A new slate roof is a big investment. Whether you are reslating an addition, or installing slate on your custom home, you want your new slate roof to last its intended life span. There is only one way to install a slate roof – the correct way. Installing slate correctly only comes from experience.

This home in the Guilford neighborhood of Baltimore City, demonstrates the need for quality workmanship. A lack of a consistant 3" headlap, shody workmanship, and missing lathe strip show how going with the low bid can be a very costly mistake. Usually, we might see one important element of a slate roof being violated, but this roofer violated all of the rules of a quality slate roof. Unevenly spaced and crooked rows in the curved section of roof demonstrate poor workmanship. It was revealed to me that this roof was installed for $35,000 and we can see why. This roof, if installed by a professional slate roofer would have cost over $50,000. But it will have to be redone.

Experienced slate roofers know how to drive the nail in to hold the slate, what type of nail to use, and how to lay out the roof and starter coarse. The fasteners holding the slate on the roof have to be set correctly, not driven too loosely and not driven too tightly. The slate should just hang on the nail, with the head of the nail driven just into the recess of the pre punched nail hole. If the nail is driven too tightly, the slate wont hang loosely, and will break with the change of temperature, load, and other forces acting on the roof. Each slate must move independently of every other slate on the roof. If the nail is driven too loosely, the nail head will break the slate above it.

Using the wrong fastener is detrimental to a new slate roof. Many inexperienced slaters are quick to reach for the wrong nail when applying slate. A large head copper slating nail should be used in the correct length to match the thickness of the slate. A non-corrosive metal is a must. Copper should be used at all times, especially on low sloped roofs where water tends to shed slowly. I have seen a few roofs both repaired with the wrong fastener and installed with the wrong fastener. Corrosive fasteners disintegrate to the point where virtually nothing holds the slate in place - and the slate fall out!

Going back to the Guilford house, this picture shows a lack of headlap. Even though this section of roof is steeply sloped, adequate headlap should be used throughout the roof. Two inches might be acceptable on this slope, but no headlap is not acceptable.

Finally, among the most frequent problems encountered with new slate installation are inadequate side and headlap and the failure to install lathe strips under the starter equal to the thickness of the slate.

Slate is sold by the square. One square equals one hundred square feet of coverage using a 3" headlap. Shortening the headlap or trying to "stretch" the slate out over the roof using less than a 3" headlap is an unacceptable practice sometimes used to cover more square footage with fewer slate.

One of the most detrimental omissions on a new slate roof, however, is the failure to install a lathe strip under the starter course of slate. Absence of the lathe strip will result in a condition where all of the slate above the starter slate will be cantilevered across the slate below it, or rather the exposed part of the slate will be unsupported by the slate below. This condition will reveal itself after the roof has been installed after a heavy snow, or storm. The result will be a small percentage of slate will crack down the middle and slide down the roof.