Owens corning fiberglass shingles

Yesterday my sister-in-law was telling me about their leaking roof. Newer fiberglass archetectual (sp) shingles. The roofer told them the leaking was because the seal strip was bonding to tight and water was collecting behind the seal strip and seeping into their house.???
I watched the shingle videos on the thermal fracturing a few weeks ago, and it makes sense that the tight bonding between fiberglass shingles could cause thermal fracturing.
The shingles on my brothers house leaking because of the bond, I’m not so sure.
Any experience with this anyone?

My first question is, what is water doing behind the seal strips and under the shingles and how is it getting there? Secondly, I have never heard of a seal strip being “too tight”. Down here in the Deep South these are literally welded to the course of shingles below. I have exactly these brand of shingle on my own home (installed in 2007) and I have not one single leak in spite of the recent torrential rains we have experienced. I detect the odor of bovine droppings.

I agree Doug, water shouldn’t get there in the first place. I ask my sister-in-law to keep me posted.

Was this roofer the same one who just put this roof on?

Nailing through the seal strip can cause some issues.
Is the slope less than 4/12 ?

I would start to look for exposed nails further up the roof for some possible water entry points, nails that were not or did not get set properly. I find a lot of roofers that use nail guns do not set those nails that are left “standing proud” due to low pressure or the gun was not flush when it shot the nail. Some Realtors get all pissy with me when I report on exposed or unset nails until I show them the picture of the roof I did once where the sheathing underneath in the attic was all black and delaminating just from the water seepage through a seemingly benign nail hole left after the nail rusted away.

Shingles don’t leak because they’re fully bonded. That’s a desirable condition. Water can enter through thermal cracking, but that means that the shingles were installed when the sheathing had a high moisture content. As the sheathing lost moisture, it contracted and that can split shingles, but splits are visible.
Although it’s called “thermal” cracking, changes in moisture content cause much more extreme expansion and contraction than changes in temperature.
If this is the cause, it would be the fault of whoever scheduled the installation. For it to happen to an existing home, they would have had to tear off the old roof-covering material and underlayment, exposing the sheathing to the weather, then it rained, and right after it rained the roofers showed up and installed the new roof.

Nails that are left protruding can wear through the shingles and cause leaks, but those are also visible.

If it’s leaking near penetrations, check for proper flashing installation. Sidewall failure is usually something like no counter-flashing or continuous flashing instead of step-flashing. Headwall flashing can be improperly lapped and so can flashing for penetrations.

If it’s leaking in the field, is it in specific areas, or randomly (or uniformly) across the roof?

This sounds like an installation problem to me. Shingles have installation requirements that can vary a lot and it’s not uncommon for roofers to not read the manufacturer’s instructions and to just install shingles the way they’re used to. Improper installation is not always apparent and requires reading the manufacturer’s instructions and then examining the roof closely to make sure it complies.

if you can’t spot it, a contractor other than the one who installed the shingles should get up there and confirm proper installation.

You should check out the InterNACHI Mastering Roof Inspection series. It covers this subject.