| Author | Message | ||
     Barnbuster (Barnbuster) New member Username: Barnbuster Post Number: 4 Registered: 10-2010 |
Slates nails are tight and not easily puled out. The picture does not show roof deck nails popping only copper ring shank slate nails. I think the idea that full Ice & Water Shield is a "moisture trap" is a misconception. Ideally, every roof stops moisture 100% from the outside, so why would one expect the moisture proofing to work in only one direction? If you are speaking of interior moisture being trapped in the roof system (a classic condensation problem) one must deal with this issue separately from the waterproofing against ambient precipitation. There are several method to do this: 1) roof ventilation to exhaust moist air from the rafter bay system, 2) A vapor barrier on the warm side of the roof structure (above the exposed decking on the rafters) to stop moisture from entering, or, 3) Controlling interior moisture through mechanical measures such as dehumidifiers or visquene on the ground beneath the subfloor. The idea that a constant wet/dry cycle flexes the wood and pops the nails is interesting and plausible. This unique construction had no plywood shear other than an 18G GSM sheet incorporated in the middle of the roof construction. No question condensation is a real design problem contributing to the perception that the roof was failing, but did it make the slate nails pop or was there another cause? | ||
| Blue_sky_roofing (Blue_sky_roofing) Intermediate Member Username: Blue_sky_roofing Post Number: 39 Registered: 05-2010 |
definitly rejected. Every once and a while when I go on a leak call, I find an old rusty 8d sticking up through the shingle about an 1" or better Here's another thought for Barnbuster's problem; what if it is also caused by the wind trying to lift up the slate. Try pulling out one of the nails and see just how much 'holding power' those copper nails have. Maybe even try lifting a slate with your hand - does the slate feel like it is going to break, or can you feel the slate prying the nail up. | ||
| Bud (Bud) Member Username: Bud Post Number: 26 Registered: 02-2010 |
Were they being rejected by the roof or did the 'roofer' not set them after removing the jack. | ||
| Blue_sky_roofing (Blue_sky_roofing) Intermediate Member Username: Blue_sky_roofing Post Number: 38 Registered: 05-2010 |
Come to think of it, I've seen 8 & 16 penny nails (used for roof brackets) into 7/16" OSB push back up through shingle roofs. Someone want to explain this  -and don't say it was the homeowner in the attic with a hammer after he punctured his head LOL! | ||
| Bud (Bud) Member Username: Bud Post Number: 25 Registered: 02-2010 |
I have seen this alot on shingle roofs where it has completely pushed the nails out of the roof to the point where they are laying about the roof. 2 things that we can attribute this to in the shingle world is > too short of nail, the nail point if buried in the deck will be lifted by the wood fibers and pushed out. Consider a post that is not buried in the ground below frost level, just a visual aid there. > the other reason is improper attic ventilation. this manifests in the cold season where condensation is high, my rational is that the high moisture content caused greater movement of the substrate (deck) which works the nails out. similar to the effect caused by the short nails. If you have both conditions it could be amping up the concern. I am curious, did you cover the entire roof with ice&water...please say no. It can cause a moisture trap. What has me wondering is there seams to be some deck nails protruding on the left of the photo and a slate nail on the right. | ||
| Barnbuster (Barnbuster) New member Username: Barnbuster Post Number: 3 Registered: 10-2010 |
The CA Construction Code says to penetrate roof sheathing 3/4" or through the sheathing (shiners) if decking is less. We are certainly getting 1" penetration or more into the 2" decking. These are not thick slate. Penetration would mean using 2 3/4"-3" nails. That is more than I have ever seen. Can this be right??? | ||
| Blue_sky_roofing (Blue_sky_roofing) Intermediate Member Username: Blue_sky_roofing Post Number: 37 Registered: 05-2010 |
The boards are 2" thick? It was installed with 1 3/4" nails? That means the nails have not penetrated all the way through the wood, and the wood is probably pushing the nails back out as it shrinks / moves - especially with the moisture you mentioned. It's amazing how wood can do that. | ||
| John_chan (John_chan) Senior Member Username: John_chan Post Number: 71 Registered: 08-2006 |
Usually nails pop through the slate because of under-nailing. The nails should be nailed flush with the slate so that the nails don't put strain on the slate (over-nailing), and they don't stick up and rub against the slate above it (under-nailing). Under-nailing is much more common with ring shank nails from roof inspections that I've done. It's also much more common on softer slates. If this is Dublin Green, I'm not even sure it would grade out to be S-3. Deck shrinkage and other factors are possible, but it's hard to answer these questions with certainty without seeing it in person. But if it's just in one section, you should probably just pick up and re-lay this section. | ||
| Barnbuster (Barnbuster) New member Username: Barnbuster Post Number: 2 Registered: 10-2010 |
Any specific ideas on the cause of the nails popping through? Is that related to the grade of the slate? Why might it just be happening in one area of the roof? Is it possible that the nails are backing out because of the deck shrinkage or condensation issues in the substrate? I consider it might not have happened with a better grade slate and that the slate may be inconsistent quality. I do know it was China in origin and I think Dublin Green might be the name. | ||
| John_chan (John_chan) Senior Member Username: John_chan Post Number: 68 Registered: 08-2006 |
Depending which American distributor it came from, it looks like Sierra Pass or Dublin Green to me. It's hard to say for sure with just those two pictures. These slates don't generally grade out anywhere close to S-1, and they shouldn't be used in freeze/thaw climates. You can probably get away with using this type of slate in Southern CA, or FL, but it's not a good idea for any location which gets 90#/sf of snow fall. I think this falls back to whoever specified it, the architect or contractor. We have flat out refused to install this product in our Ohio offices, but I would probably install this product in the South under the right conditions. | ||
| Barnbuster (Barnbuster) New member Username: Barnbuster Post Number: 1 Registered: 10-2010 |
We have an unknown grade 3/8" Chinese slate roof about eight years old. Many slate have broken. It was laid over 2x12 fir boards (they have since shrunk to leave 1/4"-3/8" gaps) with WR Grace Ice & water Shield and a roof system that has a significant condensation problem (wet insulation). It is in a winter cold climate, summer moderate/hot with an average snow load of about ninety pounds per square foot. Workmanship on entire system is above average, very professional. Copper 1 3/4" ring shank nails are popping right through the slate in a few dozen places. See pictures. Anyone with a similar experience seen this problem before?   |
