3 Tab Shingle Corner Tenting - Opinions

I had the opportunity to inspect an historic 1800s home with a separate guest house in Houston’s Sixth Ward yesterday.

Both the main and guest house had the same 3-tab shingles of the same age, however the guest house roof exhibited tenting at the corners of all tabs. I’m curious as to opinions regarding possible cause. It’s not likely to be from hard butting the shingles during installation as the tenting occurs at all tabs, not just at the seams.

I could not see the underside of the roof decking as the underside was sheetrocked as a cathedral shingle. There is obviously no ventilation for this roof. I’m thinking that the likely cause is expansion and contraction of the roof decking. Many of these older places have planks for roof decking that can expand and contract quite a bit with temp and humidity changes. I expect that this roof gets pretty hot in the Houston summertime with no ventilation. Yesterday was a cool day so the decking would have contracted.

I’d like to hear if this sounds likely to others or if there are alternative theories.


Not sure , but it looks like the ridge cap shingles are turning up on the edge also. I would be more inclined to think shingle defect from manufacture.

I also see a lot of tree debris under the corners, which may be preventing them from laying back down. But, something caused the curling in the first place. Probably inadequate ventilation, differential expansion, and/or limited adhesive strip. Could you tell if they were organic or not? Also looks like maybe two layers there.

In cold weather, did they do this inadequately?:

Screen Shot 2015-12-03 at 12.29.46 PM.png

From figure 10-4: http://www.certainteed.com/resources/XT25Install.pdf

Installed during cold weather is my guess…? Expanded during warm conditions and didn’t retrac.

Same shingles as on the house and installed at the same time by the same installer. I was able to walk the roof on the house. The shingles installed on the house do not exhibit this phenomenon (probably not mfr defect). Shingles have fiberglass scrim, non-organic. Shingles on the house roof were well bonded by the bonding strip, except for the first course due to improper starter course (the curled corners on the guest house are below the bonding strip).

Couple of pics on the house roof below. You can see the fiberglass scrim and the shingles lay flay with spaces at tab cutouts.

You say they are the same age, what age is that and how did you determine it?

Almost every time I see curled shingles there is a very poor ventilated attic space.

What’s the point of your question?

I didn’t give an age nor did I attempt to estimate an age. I do know that they are the same. Do you feel that you need me to validate what I have already told you? The difference between the performance of the two roofs has nothing to do with age. Take my word for it.

Goodness, gracious!
I was just attempting to help and asking a question that might provide more information.
Apparently that’s a problem for you. Wow.:roll:

In the future take what I tell you at face value and you won’t get your feelings hurt.

You have some anger issues, will leave you to them from now on. :wink:

There is definitely a ventilation issue and I expect that is at least partially contributing. When you look at the shingles in the field, they’re not just curled, but tented - the adjacent corners are pressed together causing them to push each other up.

Yes I see that. Honestly I have never seen an application like yours where Every tab/every course has the same exact issue. And I have inspected many roofs with curled shingles.

As others mentioned I’m leaning toward being installed too close together during cold weather, then expanded when the temperature increased, maybe rapidly within a day or two.

Could it be they jammed them to close/tight on installation.

Looks like cold shingles not warmed up to allow expansion before installing .

Chuck I have the same thing on my roof that I installed back in 2002. The funny thing it is only in one patch of the roof about 6’X6’ just under the large overhanging branch of a city tree. I put the roof on in the summer but I do know that the area of the house affected is a partial southern exposure and the tree blocks a lot of the sun except in the winter. Roy might have a point with the shingles warming up differently cross the roof on that side.

Looks as though the hips are doing it as well. I would be looking inside. I do not think it was a cold install, Stagecoach does not get that cold in the winter from what I read.

Yea. I’m confident that it’s heat related with no vents on the roof and a cathedral ceiling throughout. I regularly see roof surface temps hitting 160+F here in the summer. I wouldn’t be surprised to see that one get quite a bit hotter in the summer. Given that the house is so old, 120 years is damn old for Houston, (though I’m not sure how old the second story over the old garage is), I thought that wide sawn lumber roof planks may be a contributor because the expand and contract so much. I know that it can cause splitting. If the shingles were installed on a hot (expanded) sawn lumber deck, I could see how they could get tight when the decking contracts in cooler conditions.

Won’t know for sure on this one, because the deck is not visible from below.

What’s puzzling to me is that it’s so uniform. Old wood board roof decks often used lumber of varying sizes and even if the boards were all the same size, most were originally spaced because the roofs originally had wood shakes, although sometimes tile. Anyway, they often get overlaid with plywood or OSB before shingle are installed. Anyway, my feeling is that it’s not related to the roof deck.

It seems to me also to be heat related somehow, but expansion wouldn’t cause curling at the shingle cutouts because the cutouts are a gap. I would expect to see expansion-related buckling appear first where shingles in each course butt, but consider that shingles are commonly installed in cold weather and expand in warm weather without buckling (like in the other house). Also, I’d expect to see areas of failed bond if expansion was that extreme.

Expansion/contraction-related bond failure in asphalt shingles always happens first where they bridge the joints between shingles in underlying courses. Expansion extreme enough to cause buckling to that extent would probably cause a lot of bond failure.

My guess is that lack of ventilation has caused curling from shrinking asphalt due to evaporation of volatile compounds. That too is seldom uniform across the roof but not unheard of.

Logically, heat-related distortion from lack of roof structure ventilation would start and be more extreme near the roof peak, but in the real world, patterns of distortion often differ from one house to another. I finally gave up trying to figure it out. I think a number of different factors combine to influence patterns of distortion.