Comp shingles on 2:12 to less than 4:12 pitch.

Who else wonders how "double coverage", a term historically referring to double-coverage of comp shingles on 2:12 - less than 4:12 pitches, somehow morphed into meaning double coverage of underlayment - To the extent the UBC, then IBC/IRC adopted?

I don't know about the morphing, but around here, I seem to be the only roofer who laps the underlayment for double coverage on low slopes. I always did it because the directions said to do it. It makes sense, although it does not help a bit if the fastener goes through the cracks in a plank deck or otherwise does not hold into solid decking. That is the major problem with low slope comp roofing here in N. Texas.

Used to be "double coverage" referred to double coverage of shingles on low-slopes....Then somewhere along the line it became to mean double felt....I may be crazy, but that's my recollection.

Wood shingles were installed in the same manner - Back when lower-slope porches were more common - The courses would shorten-up as the pitch decreased. Tore off plenty back in the day.

I also tore off lots of low slope roofs that had wood shingles that had 3-1/2" to 4" exposure. Came across a few old 3-tab that were done on 4" exposure. I know for at least the past 30 years all the manufacturers called for double lapped 15 lb. on a deck under 3:12. I think tinner666 used to install laminates on some of his roofs at 4" exposure plus lap the ends if I recall.

If we eliminate wood and we eliminate angle laps and french locks (which lasted unbelievably long) and confine the topic to 3-tab "strip" shingles, then before any morphing could have taken place they would all have been English-measure, normally layed five inches to the weather. Getting double coverage out of them...assuming a minimal headlap...would mean laying them at less than two and a half inches to the weather. It would also mean you'd go through four distinct layers of comp anywhere you cut a hole except in the area of the headlap where you would go through five.

They used to make a mineral surface roll roofing that was "half-lapped." It was before my time, but not much before, and I never came across one in reroofing. In that case, as it was described to me, the bottom half was granulated and the top was smooth. I would take a wild guess and say that half-lapped morphed into double coverage and didn't refer to shingles.

Wood shingles are typically sixteen inches long and when installed normally yield a three-ply wood roof with a one inch headlap. The term "double coverage" therefore would not really pertain to them either, unless you layed them at less than two and a half inches to the weather. I have also seen many wood roofs run with eighty per-cent of normal exposure on low slopes. But when you start bunching up material as they do in those specialty pseudo-thatch roofs you have to start using some serious nails abd on anything low-slope that would not be a good idea.

When the manufacturers, et al, say double layer, they also usually specify "layed shingle-style" meaning you lay thirty-inch stock eighteen to the weather, not two layers stacked and two subsequent layers stacked on the two-inch line as most homeowners and handymen seem to choose to do when they read and attempt to comply with the instructions.

When it comes to underlayment I agree with those that say water ought not to be getting there in the first place, but I put it on anyway, and I have seen the benefits over time of using it. There was a year when one major manufacturer provided letters stating that its use was entirely optional, although they rescinded that in pretty short order. I might even have that letter in my files, but producing it would be a challenge I'm not up for right now.

Opinions are like radiant energy, they radiate in all directions...I got hammered during that year for "not using your fire felt." Golly gee. The only thing that really sweats is the poor guy trying to make sense of it all. One of the things I liked so much about Dick Fricklas was that when he addressed a subject at hand, he would take it all on directly, all the truths, half-truths, misapplied truths, and just plain untruths.

egg Said: If we eliminate wood and we eliminate angle laps and french locks (which lasted unbelievably long) and confine the topic to 3-tab strip shingles, then before any morphing could have taken place they would all have been English-measure, normally layed five inches to the weather. Getting double coverage out of them...assuming a minimal headlap...would mean laying them at less than two and a half inches to the weather. It would also mean youd go through four distinct layers of comp anywhere you cut a hole except in the area of the headlap where you would go through five.

They used to make a mineral surface roll roofing that was half-lapped. It was before my time, but not much before, and I never came across one in reroofing. In that case, as it was described to me, the bottom half was granulated and the top was smooth. I would take a wild guess and say that half-lapped morphed into double coverage and didnt refer to shingles.

Wood shingles are typically sixteen inches long and when installed normally yield a three-ply wood roof with a one inch headlap. The term double coverage therefore would not really pertain to them either, unless you layed them at less than two and a half inches to the weather. I have also seen many wood roofs run with eighty per-cent of normal exposure on low slopes. But when you start bunching up material as they do in those specialty pseudo-thatch roofs you have to start using some serious nails abd on anything low-slope that would not be a good idea.

When the manufacturers, et al, say double layer, they also usually specify layed shingle-style meaning you lay thirty-inch stock eighteen to the weather, not two layers stacked and two subsequent layers stacked on the two-inch line as most homeowners and handymen seem to choose to do when they read and attempt to comply with the instructions.

When it comes to underlayment I agree with those that say water ought not to be getting there in the first place, but I put it on anyway, and I have seen the benefits over time of using it. There was a year when one major manufacturer provided letters stating that its use was entirely optional, although they rescinded that in pretty short order. I might even have that letter in my files, but producing it would be a challenge Im not up for right now.

Opinions are like radiant energy, they radiate in all directions...I got hammered during that year for not using your fire felt. Golly gee. The only thing that really sweats is the poor guy trying to make sense of it all. One of the things I liked so much about Bill Fricklas was that when he addressed a subject at hand, he would take it all on directly, all the truths, half-truths, misapplied truths, and just plain untruths.

On any product that has thick butts like shakes or tile, shortening the exposure can actually lesson the surface pitch enough that it does more harm than good.

I don't see how any underlayment that doesn't self seal, like felt, gives you much advantage to have two layers with lots of holes vs one layer with lots of holes.

It's to eliminate the two-inch lap vulnerability at all of the horizontal seams.

egg Said: When it comes to underlayment I agree with those that say water ought not to be getting there in the first place, but I put it on anyway, and I have seen the benefits over time of using it. There was a year when one major manufacturer provided letters stating that its use was entirely optional, although they rescinded that in pretty short order.

I read somewhere and have experienced the fact that fiberglass shingles are not impervious to moisture; therefore, that underlayment is crucial in keeping the deck dry. And, a properly driven nail will cause the underlayment to act as a gasket at that vulnerable location. I have seen nails that did not hit solid decking, over time, cause a hole to form and leak.

wywoody Said: On any product that has thick butts like shakes or tile, shortening the exposure can actually lesson the surface pitch enough that it does more harm than good.

I live in an area where there are hundreds of 2 1/2 pitched roofs. Most have gone to the laminate shingle but are still slapped on without a care. Hence, most leak and they get reroofed in less than 10 years. No one seems to learn.

If I go to the laminate, I only use Malarkey, reduced to a 5" exposure, because its laminate lap is 2" and tapered. It makes all the difference. I can adjust the nail line and always hit solid wood. And the tapered edge won't make a hump to hold water like the other laminates.

Egg, I', 12 years or so younger than you and put down 1/2 lap (Selvage roll?) before I gained confidence and gave rubber a go.

In it's cheapest form, I'd use the old stuff over the present day peel and stick modified

natty Said:

wywoody Said: On any product that has thick butts like shakes or tile, shortening the exposure can actually lesson the surface pitch enough that it does more harm than good.

I live in an area where there are hundreds of 2 1/2 pitched roofs. Most have gone to the laminate shingle but are still slapped on without a care. Hence, most leak and they get reroofed in less than 10 years. No one seems to learn.

If I go to the laminate, I only use Malarkey, reduced to a 5 exposure, because its laminate lap is 2 and tapered. It makes all the difference. I can adjust the nail line and always hit solid wood. And the tapered edge wont make a hump to hold water like the other laminates.

R U saying that the Malarkey is angled in like the old Celotex, as opposed to flaring out like all others except the straight IKO Cambridge?

twill59 Said: R U saying that the Malarkey is angled in like the old Celotex, as opposed to flaring out like all others except the straight IKO Cambridge?

That would be the dragon teeth. No, I am talking about the nail area. Malarkey has a 2" nail area patented as THE ZONE and the bottom layer is tapered. When exposed at 5", there is no hump. Most laminates have only a 3/4" nail line which most slap-on roofers can not hit.

THE ZONE was invented to compensate for poor roofing practices. It is much like the Owens-Corning "sure nail technology" which is pure crap in my opinion.

natty Said: THE ZONE was invented to compensate for poor roofing practices. It is much like the Owens-Corning sure nail technology which is pure crap in my opinion.

That's my only problem with the Zone haha. I'm conflicted because I complain about how the jacklegs are costing consumers thousands(individually) but then I benefit from it by having a never ending supply of repairs and 10 year old re-roofs. I do think it's a good thing though.

Not sure how I feel about OC's strip. High nailing is a problem, but the blowing through is worse in my eyes. The high nails eventually break through, especially if they are just barely high. With OC's strip, at least it's reinforced so the nail shouldn't be able to go completely through.

Me and my Dad have argued about this many times. He is in the "pure crap" camp. I don't mean to defend not nailing the low part, but I'm just speculating that it's infinitely better than standard 3/4" line.

Malarkey's are the best shingle to install. Consistently square cut, come out of the wrapper easily, and naturally a larger nail zone.

Dragon's teeth, yeah. Never really liked that inward-taper look but I have to say Pabco makes a tough shingle which has proven itself to be a long-lasting beast and I find myself using them more and more. In fact, their Radiant Elite has now ascended to the position of my shingle of choice. I believe that material is poised to last virtually forever when installed in all but the most merciless locations. You can work them on even the very hottest days. When you take out that much infra-red, I'll bet you get another ten years. jmho/fwiw

Love the CT Solaris Gold series as well. Not sure who was responsible for packaging them three to a square though. That's downright heartless.

The kicker is that whatever shingle we love to install and give the best performance, it is always up to the customer and how much they want to spend. The tragedy is that with so many choices all it leads to is confusion.