Expert opinions differ - Who is correct?

bcicio

Yes. They are available.

Nonsense. See Roof and Attic Ventilation Help

The average roofer will need a half cricket/saddle behind that chimney to prevent leaks.
More chimney flashing information here.

Tear off the old shingles. Just nailing the new shingles into voids of the shingles beneath is enough to shorten the life span of the new shingles.

Ok, here goes…my 2 pennies:

When I roofed as a teen in a galaxy far far away a longggg time ago, re-shingling was no problem. You could go up to 3 layers (3-tab) and they’d last reasonably long.

But lately, re-shingled roofs don’t seem to last as long as they used to.

Here are my theories.

Houses today are far less drafty (read: well ventilated) and are far tighter (requiring far more ventilation than previously). I believe that this contributes to the premature deterioration of new roofs not only on re-shingles, but also for new work.

Roofs just don’t last as long as they used to. I also think this has to do with material changes.

And in my opinion, while it’s always better to start from a fresh deck for a roof, I personally see no problem with re-shingling over a 3-tab roof (only this time, no more than a 2nd layer).

However, having said that, I always push for removing all roofing down to the substrate. I honestly can’t remember the last time I actually re-shingled a house.

:slight_smile:

It is kind of like spraying new paint on a car without wet sanding the old paint layer. It is always better to remove the original roof, because it will affect performance of new roof.

[quote=“-Axiom-”]One of the theories as to why a second layer of shingles won’t last as long as a clean install is that with a 2nd layer the roof will retain heat for longer.

It has been scientifically proven that the deterioration of asphalt is primarily due to UV and heat.
Experienced roofers know that when tearing off a multi layer shingle roof the shingles are more brittle and dried out.
Many of us refer to this as “baked” shingles.

Based on what I read here and elsewhere it appears that asphalt shingles don’t last as long in the hotter climates of the south and southwest.
It also appears that the thicker the shingle the faster they will dry out and become brittle.
This is consistent with the theory that asphalt degrades quicker under conditions of prolonged high heat environments.[/quote]

And a real quick way to confirm this theory is on a low-sloped roof where there is a build-up of asphalt in one area. Do an infrared scan on the roof and you will see that places where the asphalt is thickest retains the heat the longest. Heat breaks down asphalt, so thick layers of shingles will retain more heat and cause the asphalt in the new shingles to break down prematurely.

Why do they print instructions for a lay-over on the wrapper? Did they not have anything better to do? Nonsense.

[quote=“dennis”]bcicio

Yes. They are available.

Nonsense. See Roof and Attic Ventilation Help

The average roofer will need a half cricket/saddle behind that chimney to prevent leaks.
More chimney flashing information here.

Tear off the old shingles. Just nailing the new shingles into voids of the shingles beneath is enough to shorten the life span of the new shingles.[/quote]

Dennis, you think it is ok to have a ridge vent and a power vent?

[quote=“RooferR”]

Why do they print instructions for a lay-over on the wrapper? Did they not have anything better to do? Nonsense.[/quote]

I thought the same thing.

I think that answer would depend on the manufacturer.

Besides, something else I thought about, if there’s that much heat getting to roof shingles that they deteriorate the shingles faster, then they have bigger problems than just their roof.

I’ve been on 3-tab roofs that have lasted 40 years as layover roofs. Are the newer fiberglass shingles “that” inferior to the older shingles?

#3

difinitely go with #1

[size=300]#1[/size]

lol, late by a year, but an “A” for effort.

Has anyone thought how a cricket will go on that chimney without affecting the siding? That could bring up a whole other issue as to how the siding will be flashed under and if you might messup the siding. I would definately discuss that with whomever you choose.

[quote=“bcdemon”]

lol, late by a year, but an “A” for effort.[/quote]

You caught that too.I was hoping to fly under the radar on that one. :slight_smile: