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John Sweeney
| | Posted on Wednesday, February 20, 2002 - 09:10 am: | 
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In response to your Fall 2001 Traditional Roofing article entitled Why Slate Roofs Dont Need Ice & Water Membrane, I have a difficult time either accepting or disputing your point because it is unsupported. You state that slate roofs can last for hundreds of years without membrane, but that doesnt prove that they can not have improved performance with a membrane. Wood roofs last in excess of one hundred years also, if properly maintained. Unlike wood roofs which require a discontinuous sheathing deck for breathing, every contemporary slate roof detail that I have seen recommends a continuous decking. Logic would suggest that the decking would perform better if protected by a membrane in the event that a roof fails for whatever reason to shed water, be that ice dams, backed gutters, etc. The slate is part of a system, if any one item fails, the system fails.
I recommend wood, slate or metal over asphalt shinlges to every owner, but that doesnt mean we cant learn from moderm materials and methods ways to improve upon traditional details. If you can prove to me that a slate roof suffers from the addition of a membrane, I wont spec one. Otherwise, I remain an advocate. |
Joe Jenkins
| | Posted on Wednesday, February 20, 2002 - 01:10 pm: |
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You say "every contemporary slate roof detail that I have seen recommends a continuous decking." Why is that? I'm assuming by "continuous decking" you mean plywood. You obviously haven't been outside the United States. I have never seen a plywood roof used under slate or tile in Europe. When and if *they* downgrade their roofing systems to incorporate plywood decks, they will be doing what we are doing in the US: abandoning a tried and proven system that exhibits fantastic success and replacing it with one that is simply oriented toward the convenience of the building contractor.
You also state that "Logic would suggest that the decking would perform better if protected by a membrane in the event that a roof fails for whatever reason to shed water, be that ice dams, backed gutters, etc. The slate is part of a system, if any one item fails, the system fails." Slate roofs have traditionally incorporated 30 pound felt or other heavier felts during installation. These felts lose their effectiveness as a roofing material after a period of time, maybe a century or much less (they dry up). Ice and water shield will experience the same fate. The underlayment does provide some bit of insurance against a leak, temporarily. However, it makes no sense to me to rely on the underlayment to keep the roof waterproof. It's the slate and the flashings, properly installed, that keep the water out. If a slate breaks, it should be repaired. felt or no felt, it will still leak.
The statement "If you can prove to me that a slate roof suffers from the addition of a membrane, I wont spec one," is perplexing. If *you* can prove to *me* that a slate roof benefits by the addition of ice and water shield *then* I would consider incorporating it in the specs. So far no proof has been revealed, while there are millions of slate roofs all over the world that clearly show that ice and water shield is not needed.
Architects do not spec plywood and ice and water shield under slate or tile because its the best system. They spec it because it's the current trend or fad in roofing. It's what they grew up with, what they were taught, and what they feel comfortable with. They believe that if they can put a waterproof roofing on the building before the slate is installed, then they can beathe easy knowing that the roof will not leak. Funny that - because underlayments have notoriously short lifespans. It would be much better for architects to learn how traditional slate roofs are constructed and thereby gain some confidence in them, than to try to alter the style of roof construction to suit some passing trend.
At the end of the day, there will be two roofing schools in the US: the traditional and the "modern." The customer can decide which roof system they would rather have constructed on their home or building. I am in the "traditional" school and will, frankly, not have my name and reputation associated with a plywood slate roof system, having seen plywood roof failures. I'll stick with what I know works and works well. People looking for the tried and proven roofing system will seek out the traditional roofers. |
John Sweeney
| | Posted on Wednesday, February 20, 2002 - 05:10 pm: |
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Mr Jenkins,
First allow me to say that I dont intend to offend you or suggest that you are wrong. My writing is nothing more than an honest inquiry of an experienced professional.
By continuous roof deck, I do not imply plywood specifically. I do imply a roof deck without any breaks in the sheathing (for example a slatted deck that would be used for wood shingles). The contemporary details tend to show plywood (you're right, this is due to present custom) but planks could/should be used instead. I have had different 'slaters' tell me that the underside of slate should and should not be vented. What is your opinion?
Regarding passing trends, once upon a time slate was a new building material, it wasnt until someone figured out how to install it properly that it became a viable product. The ultimate question is can the building system be improved upon? Does a membrane improve the roof system? Your opinion seems to be, why bother finding out. If nothing else, I would argue that the ice shield helps in two possible ways, it seals the penetration from nails into the deck and because of its very limited rate of expansion might just prevent shingles from working loose. |
Walter Musson
| | Posted on Wednesday, February 20, 2002 - 05:20 pm: |
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You are both partially correct.Plywood is a terrible sheathing to use for a slate installation,but the way I understood the prior comment was that the decking should be solid not skip sheathed.Tongue and grooved board sheathing makes a marvelous deck on which to nail slate.In fact its just as rugged and certainly can't delaminate.As to the issue of ice and water shield;Because heating and cooling requirements are far different today than they were 75 to 100 years ago,some roofs do not function the same as they did when constructed.Technology is not all bad either,and I am more than willing to change if it means more security and more peace of mind for both me and the homeowner.That said,yes there are definately places in the Northeast where slate and felt and wonderfully soldered metal are not adequate to keep out ice dam backup.If we only had liquid precipatation and it could exit the roof in a timely manner than i'd be inclined to agree with Joe that Grace is not needed.However I've removed too many tons of snow and ice from too many roofs in Maine winters to not adapt somewhat.I can take you to past problem roofs that I have cured through the judicious use of Grace and re-laying the slate over it.Will Grace last 100 years?I don't know that answer,but I do know I have many thrilled clients who don't have to suffer through a yearly ritual of ceiling problems due to backup.If it lasts 35 years than it could be done again, although I suspect it will last longer.Sometimes I might increase the use of metal in a real tricky spot,but I take great pride in being able to solve their problems whatever solution is deemed appropriate.A blanket statement that one thing or another is not workable is not in the best interests of the building owners.An open mind to all the possibilities is the way to problem solve,and incredibly rewarding when you solve a persistant problem.In repairing the old one learns what is workable for the new construction problem areas which are being designed for the next 100 years. |
Joe Jenkins
| | Posted on Thursday, February 21, 2002 - 09:23 am: |
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Regarding a broken or unbroken roof deck, lath slate roofs are still the norm in Europe and there are still many of them that are a century old and in quite serviceable condition. I prefer a solid wood deck because it's stronger and easier to work with, but I know I can put slate on lath and it will work fine.
What irritates me about ice and water shield is the current presumption that it's a necessary element to any roof. It is not. In a heavy ice area I would apply the slates with an extra headlap at the eaves. We have ice build up here in western PA which, on occasion, does a lot of damage - gutters torn off, slates ripped out, etc. However, *so far* in every case of a leak, the leak has been caused by a fault in the roof (cracked slate, old repair nail, etc.) and has not been a global problem with ice backup and water penetration. In one instance where I was dealing with a low slope shed roof dormer with eave problems, I simply inserted 6" wide copper bibs (slid up until they hit the nails, then trimmed off so nothing was exposed) under the slates at the eaves and that solved the problem. I don't think ice and water shield is the solution for problem roofs, although obviously Grace Co. wants you to think so. Ice and water shield or *other* fortified underlayment could be beneficial in certain unusual situations, but these would be the exception rather than the rule. Most of the persistent problems associated with slate roofs that I have seen can be directly attributed to a design problem such as insufficient slope, poor drainage pattern (i.e. water dams on roof caused by obstructions), etc.
And by the way, slate was a new roofing material several hundred years ago. A lot of intelligent people have spent centuries developing this roofing system and they have done well. How old is plywood and ice and water shield? Is it being developed because it's a wise alternative or because it puts money into the pockets of certain manufacturers?
Yes, I am also interested in improving upon the traditional slate roof with modern technology, if possible. So far I can advise the use of stainless steel metals in association with slate - stainless steel nails and TCSII flashings. I think these are likely improvements based upon my experience with old roofs and flashing and nail deterioration. However, the jury is still out on TCSII. No one seems to know how long it will last. Regular 304 stainless is a fantastic metal which, I think, will greatly outlast copper. TCSII probably is also, depending on the gauge.
Finally, do slates need to breathe? No. Slate lasts longest if it's left buried in the ground with no access to air. This argument, like ice and water shield, is a common one among roofing circles. Some insist that roof slates need air circulation underneath them. One day, while working on a century old farm house roof with an apprentice, we began discussing this issue. So as we removed the old slates in order to expose the flashings we were replacing, we looked at the back side of them to see what deterioration was occurring. This was a solid wood deck with 30 lb felt. The felt was still intact, although brittle. No effort had been made to ventilate the underside of the slates. There was a horizontal strip of deterioration along the back side of each slate - where the slate was not touching anything and air was able to get to it! The part of the slate that was lying flat against the felt was perfect. So it appeared that the more air that accessed the back side of the slate, the more deterioration. You can also see this on the back side of barn slates on lath roofs. There is a lot of delamination - thin, fluffy, crumbly stuff, hanging off the back of the slate (except where the lath covers the slate). This may be due to air exposure, moisture, condensation, or all of the above. The front of the slates remain smooth despite air exposure probably because of constant wearing away by water. In any case, I have seen no evidence that extra ventilation prolongs the life of slate. |
Walter Musson
| | Posted on Thursday, February 21, 2002 - 04:25 pm: |
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I agree whole heartedly that ventilation under slate is totally unnecessary.A cedar shingle roof may require breathability but slate definately does not.
The use of membranes which congeal around nails which penrtrate it, making the roof deck impervious to water backup problems is an area where I do have strong opinions.Having worked with slate and metal for 25 years in all seasons of the year in the great state of Maine I profess to have gained much hands on info as to how water acts and reacts to a multitude of situations. |
Walter Musson
| | Posted on Thursday, February 21, 2002 - 04:34 pm: |
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I ran out of space to continue in the last box.
Suffice it to say the are areas which can benefit from the use of Grace but this certainly isn't an an advocacy to use it where it's unneeded,since the cost is far higher than 30 lb. felt.A roofer can't change a design problem from 100 years ago, but he can keep water off his clients thru the use of some new and some old technology. |
John Sweeney
| | Posted on Thursday, February 21, 2002 - 06:55 pm: |
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Mr. Jenkins and Mr Musson, thank you, I appreciate the heart-felt responses. I am not suprised to see that two experienced professionals can have differing opinions, its what keeps this work of building so interesting - and perhaps so frustrationg to home owners.
By the way, have you considered allowing arhcitects into your association? Some of us do still try to sway our clients to use slate - the real stuff only. |
Walter Musson
| | Posted on Friday, February 22, 2002 - 10:44 am: |
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John'
Thanks for the feedback.I'm glad for the chance to express viewpoints on this site.Joe is providing a real valuable tool to all of us slaters,owners, architects,and anyone else who cares about slate.My hat goes off to him for providing this great forum.I listed on the contractor directory and had an inquiry about selling some salvaged slate yesterday.
As in any field knowledge is furthered by the exchange of ideas. |
Joe Jenkins
| | Posted on Friday, February 22, 2002 - 01:04 pm: |
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Regarding ice and water shield (again), I was thinking about it in the back of my mind since the last time I wrote in here. I think I can sum it up briefly. I have never used ice and water shield. It is specified as an underlayment around roof penetrations and under valleys by many architects. Why don't I use it, or, for that matter, *any* underlayment under valleys of around chimneys when I'm replacing the flashings? [I do use 30 lb. felt when installing new roofs or flashings.] Because I know my work will not leak - and that's 100% guaranteed. If it leaks a drop, something was done wrong and it needs to be redone. It's that simple. If it isn't going to leak a drop, then what's the point of an underlayment - just in case it leaks? If it leaks I want to know it immediately and find the problem and fix it. I have had a couple of instances over the years when a chimney reflash job leaked. It took me a while to figure out the problem, but I did, and once I figured it out, repair was simple. A heavy underlayment would have hidden the problem. I am very grateful when I can learn from my mistakes - these are the best lessons. So I don't want to obscure my work with the false security of a waterproof underlayment. It's the slates and flashings that keep out the water, not the underlayment.
One reason to install an underlayment, it seems to me, is to hide any leakage, at least until the contractor is paid and long gone. This is not to suggest that contractors who use ice and water shield are bad contractors. However, when a slate roof is installed properly, or reflashed properly, not a single drop of water will penetrate the roof. This is a fact of roofing that is taken for granted among professionals. Knowing that, I marvel at the insistence that ice and water shield is an essential part of any roof system.
Also, as far as ice build-up along eaves causing roof leaks is concerned, think of it this way: *If* the leak is being cause by water penetration through the slates due to ice back-up, *then* the water penetration will occur along the entire length of the eaves. Make sense? If that happens, more headlap may likely solve the problem (unless the problem is due to insufficient slope or other design flaw). In any case, water penetrating a slate roof anywhere, for any reason, means the roof was not installed properly.
What I have found during times of heavy ice build-up and leakage along eaves is the leakage does *not* occur along the length of the eaves at all. It occurs in one spot or two along the eaves, showing up inside the building in pin-pointed places. When I have examined the roof closely, I have found holes, nails, or cracks *at those points on the roof*. Once these points are repaired, the problem is solved. This is a simplified scenario, as roof insulation and other factors influence ice build-up and can be remedied without impacting the roofing itself.
Do I think it's wrong to put ice and water shield along the eaves of a slate roof? I think it's unnecessary in western PA, even though almost the entire state is categorized as benefiting from ice and water shield according to the NRCA. It may be a design improvement in Maine or other area of more severe weather. It may also simply be a way to extract more dollars from the property owner. I see roofing contractors here in western PA advising homeowners to take off the slates along their eaves and install ice and water shield and then re-install the slates. This is a costly approach compared to just finding a leak and fixing it. |
Walter Musson
| | Posted on Friday, February 22, 2002 - 03:01 pm: |
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Leaks that occur during Winter ice backup are not the same as rain water leaks.The water is traveling backwards up the roof since it can't escape at the eaves as it normally would.As more melting takes place more water is introduced to the roof behind the dam.Water is capable of going back under the slate until it finds a gap in the sheathing and then into the house.Therefore an impenatrable barrier is sometimes needed for winter protection.Summer rain is a totally different matter.Grace not needed then. |
Kevin Sullivan
| | Posted on Tuesday, February 26, 2002 - 10:29 am: |
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My family has been in the slate roofing business since my great grandfather immigranted here from Ireland in the early 1880's. He was trained in England first as an apprentice and then a roofer. My grandfather started our slate roofing company in the 1920's, we have been in operation ever since.
I just spoke to my uncle that is now running our company and discussed with him and my great uncle Joe about the use of ice and water shield under slate and have the following comments.
Ice and water shield under slate as well as other roofing material becomes brittle and can crack. We assume this happens due to the high temperatures slate roofs achieves or the expansion of different materials. Slate as well as roofing shingles stick to the ice and water and can be difficult to replace without breakage. "Ask any of your asphalt shinglers what it is like to strip a roof totally covered with ice and water with the shingles installed directly to the ice and water." The same happens to slate and the slate can be destroyed or become unsalvagable.
Some of the places we have observed ice and water shield failures are at dormer/ roof deck intersections and chimney/ roof deck intersections. The materials expand and contract differently and can cause cracking of the ice & water at these areas. We install ice and water to our felt underlayments on shingle installations and not to the roof deck. So beware!
We only use two solutions when it comes to ice damming on a slate roof. First one is a copper ice belt. The second involves installing two layers of 30 pound felt with a layer of slaters mastic in between. We have never had a failure.
My uncle spoke to the manufacturer of the failed ice & water system and they told him they now make a new improved high temperature ice & water shield for slate and metal installations. we don't utilize ice and water under slate and can not vouch for this new ice & water shield. |
Walter Musson
| | Posted on Tuesday, February 26, 2002 - 10:49 am: |
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Because of how slates are laid with a void above the top of the underlying slate,the point of contact for slate to underlayment is only at the very top of the slate.Most of the shingle is lying against the slate below,hence the concern in other discussions about nails coming up thru.Slate doesn't lay on ice and water like asphalt shingles do,so salvaging later on shouldn't be a concern.I'm in total agreement with the use of metal at the eaves to help prevent Winter back up. |
Dino
| | Posted on Tuesday, February 26, 2002 - 11:45 am: |
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Wow I love this discussion! Almost done with the garage here in Hawaii. Bringing the hips up to meet the cupalo at the peak. Yep it's a 4 hip three pitch roof. A good one to learn on. Working on a 5/12 to 7/12 pitch while standing on mineral coated tar paper is nuts!! Slippery stuff. As I have mentioned before, this roof has two layers of ice and water shield over (yuk) plywood. One MAJOR problem with plywood under slate is nailing. The plywood tends to bounce and flex with each hammer blow and sometimes causes the slate to break. I have adopted the use of a nail set made from an old 3/8" drill bit. Sometimes it's so bad near the hips that I have to drive a 3" nail in so it penetrates and then I have some control over seating it to the slate. If I ever get to spec a house before construction for a slate roof I'll do it the taditional way with T&G boards and felt... thank you.
As far as the Guild goes, I'm interested. Please bear in mind that some of us are all alone out here and our only connection to the rest of the trade is through places like this forum and email. As far as I know, I'm the only person here on Maui with this much knowledge and experience. Most roofers here don't even want to touch a slate roof. "Can't walk on it? How do ya get down!?"
Slate is not very common here. Lots of tin roofs, tile and shingles. I know of one other house on the island with slate but I don't know who installed it. There is also a church with some beautiful large slate on it. Very flat and very old and still functioning just fine. I'll bet there's just felt and boards under them.
Thanks for all that you share folks. I am really enjoying the fact that I'm learning an old world trade that I too can one day pass on to others. |
Walter Musson
| | Posted on Tuesday, February 26, 2002 - 12:36 pm: |
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Dino,
Glad your'e back.I've missed your updates.Our Maine winter has improved but I'm still envious of slating in shorts. |
Dino
| | Posted on Tuesday, February 26, 2002 - 11:14 pm: |
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Yeahh well,
Today was a rain-out so I worked indoors on another project.
I've got two new guys on my "crew", one show's promise. He's "got it" and it's exciting watching someone else learn and love what their doing as well. He said that once he learned to slow down and feel what he was doing he did better, and I must say it shows.
So that makes at least two of us that are really into it for the "traditional artisan" aspect of slate roofing. I for one am proud to be joining a long line of slaters, who's work still stands as will ours.
The weather looks good for tomorrow so I'll be up there building those hips. The flashing where the hip meets the cupola is a real challenge. You just have to think like water. Where's the easiest path... build on that. It's such good brain exercise. I'm laughing here thinking what you all must think of me. Well I just love things that tease my ol noggin. The more meticulous the better. So there ya go. Walter knows what I mean, methinks...
Hey The Slate Roofing Guild Maui Chapter invites you ALL over for some Mahi-Mahi!
(for those who don't know that's some goooood fish)
Aloha and Mahalo.
Dino |
Walter Musson
| | Posted on Wednesday, February 27, 2002 - 08:26 am: |
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Dino,
Youv'e got a great attitude for slating and problem solving when you said "you have to think like water".I've never heard it said any more relevant than that.I can tell your clients are going to get the best possible job that you can provide,within the parameters of the slate selected.I hope this roof generates many more for you on the Islands.Keep us posted. |
Kevin Sullivan
| | Posted on Monday, March 04, 2002 - 12:45 pm: |
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To: Walter Musson
We just finished the New England Home Show in Boston yesterday so I'm sorry I haven't responded to your comments on February 26, 2002.
My comments regarding the slate actually sticking to the ice and water shield were made by actual observations. I also have experienced nails backing out of slate brackets (staging)when slate has been installed over plywood. It is difficult to hit rafters when working on slate roofs although we encourage our men to do so.
You seem to be a guy who really cares about slate roofing and my uncles have asked that you come down to Boston at the beginning of April so that you can see first hand what I am referring to.
Hope to hear back from you!
Kevin Sullivan |
Walter Musson
| | Posted on Tuesday, March 05, 2002 - 08:26 am: |
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Kevin,
Thanks for the response.All of our experiences in our slate endeavors help to form our opinions of what technigues work best for our localized conditions.In my comments I don't profess to know what works elsewhere,but I do have strong convictions on what is the best way to solve roof problems in my area.I think it's great that this forum allows us to share our ideas on technigues and solutions to numerous problems.I use copper in many situations but still need to use protectionabove it in some instances.The majority ofmy work is restoration,so plywood isn't encountered often.My brackets are made of three 1x6 boards to match the roof pitch.They are more stable and less apt to damage slate already laid.I attach 3" wide copper strips long enough to be nailed to the roof deck and extend down below the exposure of the slate.I nail the strip to the back of the bracket prior to nailing to the roof.In this way i can shingle right over the copper,it acts just like a bib ,even though thats not it's function.I don't have to leave any slates out so no need to worry about leakage from slates missing during slating.I simply nail my tabs to the roof with my copper slating nails.When the roof is completed,I simply remove my planks from the brackets on the way back down,then score the copper at the exposure line several times,then while holding the slate above I lift the tab back and forth to break it.Be sure to hold the slate down so the metal can't flex and break it.You can do the whole roof and not have to hook any slates back in unless one breaks during installation.Yes I'd love to come to Boston for a day to meet you guys and swap some stories.Thanks for your comments about my caring about this trade,it was most appreciated. |
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