| Author | Message | ||
     Joe (Joe) Moderator Username: Joe Post Number: 814 Registered: 07-2006  |
Run horizontal nailers such as furring strips over top of the poly, screwed through the poly into the rafters. Nail your slates to this. You will have to run a row of nailers for every course of slates. Alternatively, run them vertically directly over the rafters, then resheet the roof with 3/4" boards screwed to these nailers, felt, and slate normally. | ||
| Ecologic (Ecologic) New member Username: Ecologic Post Number: 1 Registered: 01-2014 |
I am building a small cottage that I initially planned to roof with standing seam, then I read the Slate roofers bible and I am now contemplating going with slate. The building has a 50degree slope, 2x10 rafters on 2' centers, 3/4" cdx plywood decking and a 2" layer of rigid polyiso insulation on top of that. I realize that if I decide to use slate my first mistake was the plywood, too late now, but what about the 2" polyiso? I am concerned about the weight of the slate on the nails and potential sagging. Should I just stick with my original plan to use the metal roofing? Has anyone tried this before? Any advice is truly appreciated. Thanks | ||
| Joe (Joe) Moderator Username: Joe Post Number: 759 Registered: 07-2006 |
Via email (Sorry, man. I normally have no trouble with this sort of thing. Can you throw this one up in the "Plywood Decking" thread of Slate Roofs? Thanks. Andy) "How about slate over OSB? Spare me the judgments--I know it's crap, but bear with me here, people. I'm building a house for myself with Structural Insulated Panels (SIPs), which is styrofoam sandwiched between OSB. The roof structure will be SIP, allowing for the attic to be fully conditioned. I want to put the best possible roof on. Slate, right? Seems logical to use timber battens nailed to the SIPs, even though conventional wisdom in the SIP community is that you can install any roof directly on the SIP as if it were conventional OSB sheathing over rafters. I'd appreciate feedback from anyone with experience with slate over SIPs. If that's not forthcoming, I'd appreciate feedback from anyone with a reasoned opinion about the concept. At least OSB won't delaminate...although what it does when wet may be even worse. Besides the relative weakness and impermanence of OSB, the concept is troubling because with a SIP roof structure, it's impossible to monitor the underside of the roof for leaks. Besides the required 30lb felt, I've wondered about installing other barriers between the OSB and the timber battens." | ||
| Joe (Joe) Moderator Username: Joe Post Number: 755 Registered: 07-2006 |
Robbins Super-Elite Plus BS1088 Marine Plywood Guaranteed for 25 Years This is our top-of-the-range board! Cost: Medium to High Stick with solid lumber. Guaranteed a century or two and cost is very reasonable. | ||
| Old_school (Old_school) Senior Member Username: Old_school Post Number: 934 Registered: 01-2009 |
welcome Lou, I see it is your first post. good to have new posters. | ||
| Lou_hale (Lou_hale) New member Username: Lou_hale Post Number: 1 Registered: 01-2013 |
One reason I have always sighted not to use plywood is plywood expands and contracts across both axis where as wood will only move across the grain (width). Slates are free to move up and down with seasonal movements in solid lumber where as movement across the length of a sheet of plywood can lead to broken slates. I don't know if it's true or not because I only install slate over boards but that's what the old timer I learned from told me and it seems logical | ||
| Scottishslater (Scottishslater) Senior Member Username: Scottishslater Post Number: 145 Registered: 01-2012 |
http://www.robbins.co.uk/marine/sheet_materials.asp | ||
| Scottishslater (Scottishslater) Senior Member Username: Scottishslater Post Number: 144 Registered: 01-2012 |
Marine plywood is manufactured from durable face and core veneers, with few defects so it performs longer in humid and wet conditions and resists delaminating and fungal attack. Its construction is such that it can be used in environments where it is exposed to moisture for long periods. Each wood veneer will be from durable tropical hardwoods, have negligible core gap, limiting the chance of trapping water in the plywood and hence providing a solid and stable glue bond. It uses an exterior Water and Boil Proof (WBP) glue similar to most exterior plywoods. Marine plywood can be graded as being compliant with BS 1088, which is a British Standard for marine plywood. There are few international standards for grading marine plywood and most of the standards are voluntary. Some marine plywood has a Lloyd's of London stamp that certifies it to be BS 1088 compliant. Some plywood is also labeled based on the wood used to manufacture it. Examples of this are Okoume or Meranti | ||
| Scottishslater (Scottishslater) Senior Member Username: Scottishslater Post Number: 143 Registered: 01-2012 |
here better grade ply is called marine ply | ||
| Lazeyjack (Lazeyjack) Senior Member Username: Lazeyjack Post Number: 72 Registered: 04-2012 |
Futhermore, (marine ply) no such thing, all construction ply rely on same glue There are ply timbers such as oregon pine, spruce, that'll stand up betterbut at the end of the day, if I and other build a boat out of ply we protect the ply So please if you are going to comment abt this be very sure of facts signed--a boatbuilder  best rgds Stuart | ||
| Lazeyjack (Lazeyjack) Senior Member Username: Lazeyjack Post Number: 71 Registered: 04-2012 |
as I have said many times here Ply will last a very long time BUT only it is either painted with 300microns of high qual epoxy two pac or, it is coated in resin two pac if not, then the first layer will soon absorb moisture and rot Simple because the ply will be thin layers of to put it mildly, fast grown crap However if you had say ply of spruce or oregon pine then your chances are better Taking it to extreme , if you had teak pl;y, made up of 7 plys, then also you would be ok The short answer is PLY NEEDS PAINT best rgds Stuart | ||
| Old_school (Old_school) Senior Member Username: Old_school Post Number: 878 Registered: 01-2009 |
The laminated woods will last, but not forever. The "sarking" boards will last a long time.(yours was 140 years old)and while they will rot, they can't "delaminate" because they are solid. what you have will last as long as it doesn't leak. It is good, but not as good as it could be. that is why we recommend solid decking. | ||
| Scottishslater (Scottishslater) Senior Member Username: Scottishslater Post Number: 141 Registered: 01-2012 |
some will use marine ply it aint unheard of it just dosent last as long as sarking board | ||
| Rdsherman (Rdsherman) New member Username: Rdsherman Post Number: 5 Registered: 11-2011 |
I had some slate work done on a 140 year old house by a very, very reputable company. While doing the work, they found structural damage. I was very grateful they were able to fix it at that time. However, when I got the change order I found out they used 3/4 plywood instead of hardwood decking. Isn't this a big no-no? I pointed this out and the on-site supervisor pointed out they the work comes with a 10 year warranty. How do I handle this? |
