Roof Issue Lesson

It’s spacing. OSB expands and contracts based on humidity.

This just shows the edges bridging up where they’ve pushed together.

Get all the OSB facts at the Structural Board Association website.

Dowload the gjuide or brochure suitable for your area and usage.

While H clips are not always required based on thickness and support spacing, they do help maintain space between sheathing.

Goes back to “minimum standards” (i.e. building code) versus “best practices”.

This may help explain somewhat;


I would always use H-clips on trusses 24" oc

More on h-clips and sheathing spans.

Seems like Code compliance and standard building practice don’t match. ha. ha.

Imagine having a 3/8" roofing underlayment at 24" spacing. Hey its ok by code.

Marcel :slight_smile: :slight_smile:

Here we go, let’s eliminate the h-clips and felt paper alltogether.

Marcel:) :slight_smile:

Sorry Barry,

That remark was in no way intended to diminish my appreciation for the knowledge and fact finding capabilities of many many other posters. It was more of an affirmation about Marcels working background, which seems to have a deep root in roofing techniques.

If I came off the wrong way, I will personally write your customer testimonial letters for you.

That other, more recent photo posted, looks like deeply sumped decking deflection, by the way.


Would this be simply using way too thin OSB? Combined perhaps with a ventilation deficiency?

No ventilation at all in roof or gable. Ridging looks uniform accross the roof so is the source of the moisture the home interior?

Were the pictures taken in late evening? Many times raised sections stand out more depending how the sun is angled on the roof.

Well, without being able to count the shingle tabs for width, it looks like 24" O.C. rafters.

My guess from seeing similar roofs is the rafter spacing is too wide in addition to the decking thickness being either a cheap 3-ply cdx or a 3/8" cdx.

The improper ventilation just compounded the deflection by steaming away the glues that bond the plies together.


That would be a good guess, 3/8" being cheap. Too bad for the tenants of this complex, for a saving by the builders of a couple of hundred bucks. Building inspection from ground level, no doubt.
That’s the morning sun making the pattern standout. A good picture for the roofing gallery.:smiley:

My 2 cents again!!

That was my observation as soon as I saw the 2nd photo. I’ve seen too many of those…mainly on pre-fabs built in the late 70’s and early 80’s.


How’s your penmanship? :mrgreen:

I guess I need to clarify.

I would have to have my secretary hand write you those testimonial letters.

I have to print or type for it to be legible.


you are correct!

I would bet that if your inspected the edge of the sheathing it would be 3/8". Many home in the 70’s (primarily… the larger builders such as Ryan, Toll Brothers ect.) used 3/8" roof sheathing for a period of time.