Roof Issue Lesson

Took me a long time to find one that would actually show the problem well.

But I finally did.

Let’s let some of the newer guys give a few guesses before identifying the cause of this patterning.




I won’t say a word Erby…:lol:

I’m going to guess expansion of the sheathing, which was installed without spacing or H-clips.

Incorrect spacing, no “H” clips

Incorrectly installed (too thin) roof decking and/or too great a span for the thickness…

telegraphing those ‘ribs’…:wink:

The same install issue can and will cause cracking in hardcote stucco!:mrgreen:

H-clips aren’t needed for plywood. Was this OSB or plywood?

This roof is either missing the roofing felt barrier which caused the sheathing edges to wick moisture, expand and become loose or improper nailing at the sheathing edges or last but not least, rigid board insulation that is improperly installed (picture framing).

David, H clips are required for plywood, rafters 2" O/C or trusses.

According to the building code (and APA 30) H-clips are not needed with 5/8 plywood at 24" o.c. spacing and they are obviously not intended by the code to be spacers since T&G panel edges and/or blocking are considered equivalents. And wouldn’t H-clips actually resist expansion of the panel?

When the last time you seen plywood installed 24" o.c. anyways? Maybe the older homes…

I will confess, I hardly ever see H-clip’s, perhaps because I have never seen a roof with such thin sheathing or wide spacing where they were needed or required. Usually, in Massachusetts, if the rafters are spaced 24" or more, it’s wood plank backing, not sheathing.

Hi Dave, down here many homes will only have 1/2 ply and I frequently see truss roofs 24 inch O/C.



Hi Gerry,

That’s Florida for ya. Not too much truss out here. I see it, but not too often.

David, Many garages I build have trusses 24 OC and clips are required.

The same with homes, I always use 5/8 fir plywood on my roofs and if it’s trusses 24 OC they get H clips, been doing it that way for years.

You mentioned T&g, which I assume you are referring to 5/8 T&G Advantech, if so I’m not sure if that requires clips as the cost is usually prohibitive and rarely do we use it on roofs.

I don’t come here to argue. Keep up the good work.

David, what gave you the idea I was arguing with you?

I was just trying to explain that this is a current practise with roofs built with trusses 24O/C Has been for years.

What code are you referencing that says their not required? Not that I’ll change what I’m doing, just curious for the info. I’m not sure but I also believe the shingle manufacturers will void their warranty if clips aren’t used on a 24" O/C roof.

PS the clips are designed to stabilize the roof sheathing in between the bays not for expansion and contraction.

The only one who I have seen on here that has an extremely rounded and thorough understanding of roofing issues on a consistent basis, is Marcel.

I know what this is, and so far everyone is incorrect regarding H-Clips.

Certainteed and the APA have a document regarding this.


Erby, is the answer going to take us back to the “V” disagreement? Because there are no voles, viceroys or vermiculite visible on that home.

I’ll take a stab - the decking was wet before the shingles were laid? Just by coincedence, I took a similar pic this AM, this on a townhouse.:stuck_out_tongue: Different pattern though…

Ed, that’s a pretty broad brush you’re painting with there …just as long as my client’s don’t find out :roll: