Wavy roof

[Stephen G Sheldon]

What is likely to cause a wavy apppearance to a particular section of roof and what is the remedy?

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[Gunnar Alquist]

What is likely to cause a wavy apppearance to a particular section of roof and what is the remedy?

Stephen,

There are a variety of potential answers. I have seen wavy roofs caused by rot damaged siding, improperly installed roof sheathing, improperly installed framing, etc. Without more information and maybe a picture or two, it really would be impossible to give you any kind of intelligent answer.

[Nick Ostrowski]

What is likely to cause a wavy apppearance to a particular section of roof and what is the remedy?

Stephen, what did the framing and decking inside the attic look like? I often see sagging roof rafters that have been overspanned and sometimes plywood roof decking that has delaminated can result in a wavy appearance. If the roof had more than one layer of shingles, that could be a cause.

[A.D. Miller]

What is likely to cause a wavy apppearance to a particular section of roof and what is the remedy?

SGS: Usually poor framing practices, vis a vis lack of proper rafter crowing, etc. are the issue. Repairs are usually simple. In more egregious situations, where foundation movement is involved, the repairs required are more extensive.

[Bruce Breedlove]

SGS: Usually poor framing practices, vis a vis lack of proper rafter crowing, etc. are the issue.

What is "rafter crowing"?

[Gunnar Alquist]

What is "rafter crowing"?

Where the rafter is connected at the top plate of the wall, the cut is called a "birds mouth". The noise that you don't hear is the rafter crowing. Cock a doodle doo!

Crowning

[Bruce Breedlove]

Yeah, I am familiar with 'bird's mouth' but never heard the term 'crow' used with 'rafter'.

[Nick Ostrowski]

Bruce, I'm guessing that was a typo on Aaron's part and that he meant to type "crowning". However, if the work is bad enough, the correct term would be rafter "clowning".

[Jonathan Cartwright]

While this does not typically show on the whole roof I have seen a lot of "waves" or uneven areas where the carpenters had to do a portion of the trussed roof framing by hand for a direction change.

It seems that around here it is not a requirement to match the height of the hand stacked framing with the height of the adjacenent trusses. Because I see this alot. The most pronounced waves are found on the tile roofs where the tiles telegraph the defects much more so than shingles.

I also see quite frequently that the roof rafters are not secured to hip trusses and after some time and some snow loading the hip trusses begin to lean backwards causing the roof at that area to sag.

[Scott Patterson]

I see this more on truss construction than with site built designs.

[Brandon Whitmore]

Some possible causes:

Multiple layers of roofing.

Not crowning (crowing) all of the rafters.

Overspanned sheathing, or moisture issues in an attic causing sag in sheathing that is not technically over- spanned.

Buckled or delaminated sheathing.

Structural sag in the home.

Loose sheathing that starts to pull up.

Hmmmm. that's all I've got at the moment.

[Scott Patterson]

Some possible causes:

Multiple layers of roofing.

Not crowning (crowing) all of the rafters.

Overspanned sheathing, or moisture issues in an attic causing sag in sheathing that is not technically over- spanned.

Buckled or delaminated sheathing.

Structural sag in the home.

Loose sheathing that starts to pull up.

Hmmmm. that's all I've got at the moment.

Could be improperly set trusses or rafters. This I think will be the most common reason.
Could be lack of "H" clips
Could be warped truss members
Could be gnomes playing tricks!

[Gunnar Alquist]

Apparently he wasn't really that interested.

[Todd Strickland]

With older home I see allot of roofs having that issue, due to them being constructed with plank boards instead of sheathing…