What I'm Seeing Now

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Roof Deflection, Sag And Creep

You have probably seen this and it is most likely due to roof deflection, sag and creep.

This roof is composed of rafters which meet a center ridge beam.  The center beam is probably not terribly thick.  What you see is the result of weight and time and gravity.

Such a roof looks a little bit like the saddle on a horse.

Why the sag and creep?

The sag is what happens to the center ridge board as it spans from side to side.  In this case the span is about 20'.  The rafters are nailed to it, forming the framing from ridge to the top of the walls on the sides.

The creep is the permanent sag that happens over time.  It will stay that way as it gets used to its position.

I say "gets used to" and that's just about it.  Over time the wood fibers stretch and change and adjust to gravity's effect on the span.  Slowly the wood "remembers" its new shape and sticks to it.

And the weight of what it's holding up - in this case the shingles, wood sheathing and wood rafters - works with gravity, and slowly pushes and pulls downward on the beam.  And it slowly, over time, takes a new shape.  In this case it is a sagging, saddle shape.

If you have a book case, or shelf in a kitchen cabinet, and put a load of heavy books or plates and such onto the shelf, the wood might sag.  But once the weight is removed the sagging goes back up and the shelf becomes level again.

But, if you left that load on the shelf over time, years later you might remove it only to discover that the sagging, or creep, is permanent.  Even lifting up on the shelf does not change it back.  It has taken a new form. 

In this garage we could not actually see what is happening.

We only can tell from the outside that it is.

These rafters have been completely covered with insulation as this garage is used as a work shop.

Can anything be done?  Likely not.  Will it get worse?  Probably.

But this is a very slow process.  Like all of us, sagging happens with age.

My recommendation:  gravity works!   Things happen over time.  Sometimes such things happen and are normal, with the evidence obvious to the eye.  Is this structure frightening?  Not really.  But don't add any more undue weight to the roof, like another layer of shingles.  That will only aggravate gravity's efforts over time.  Then the roof would look really creepy.

 

 

Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560

www.jaymarinspect.com


Comment balloon 14 commentsJay Markanich • November 13 2014 03:44AM

Comments

Hmmm...in our part of the world...very heavy snow is cause for roof raking...amazing the weight that those little flakes have..not likely to help this kind of condition.

Posted by Sally K. & David L. Hanson, WI Realtors - Luxury - Divorce (EXP Realty 414-525-0563) almost 5 years ago

That would occur here too S&D and cause more problems with this.  But that is part of the process that happens over time.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 5 years ago

Creepy indeed. 

It isn't easy to understand that roofs and other housing materials are actually,

Over time the wood fibers stretch and change and adjust to gravity's effect on the span.

THAT is a very important fact that many don't understand.

Fact is, age changes things.

 

Posted by Lenn Harley, Real Estate Broker - Virginia & Maryland (Lenn Harley, Homefinders.com, MD & VA Homes and Real Estate) almost 5 years ago

Good morning, Jay....ha...sagging with age....it also comes with extreme weight loss....we don't leave that one alone though...I have a great plastic surgeon who takes care of that!!!

Posted by Barbara Todaro, Marketing Agent for The Todaro Team (RE/MAX Executive Realty ) almost 5 years ago

Good morning Jay,

As you said these types of things are meant to happen; too bad we can't have "gubment" handing out suspenders for the other sagging problem.

Make yourself a great day.

Posted by Raymond E. Camp, Licensed Real Estate Salesperson Greater Rochester (Howard Hanna Real Estate Services) almost 5 years ago

Lenn - well, things do change with time!  As do we all...

Barbara - I am down 65 pounds in 4 1/2 months.  No plastic surgery ... and not looking creepy.

Raymond - that's an idea whose time should come.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 5 years ago

So if the sagging with age is inevitable Jay, can the ridge be built with a crown so that it settles into a flat and straight ridge?

Posted by Tom Arstingstall, General Contractor, Dry Rot, Water Damage Sacramento, El Dorado County - (916) 765-5366, General Contractor, Dry Rot and Water Damage (Dry Rot and Water Damage www.tromlerconstruction.com Mobile - 916-765-5366) almost 5 years ago

Jay, I gotta disagree with you on this one (sorry) :)  The ridge board should have nothing to do with why the roof is sagging.  Typically if the ridge is sagging it is due to inadequate cross tying of the side walls.  As the side walls go out---the ridge goes down.  Alternately if the rafters are not supported and they can sag, the ridge will also drop.  Just like modern trusses the ridge board is totally unnecessary to the support of the roof.  You can have a ridge beam that supports the roof---but that is not what a ridge board should be doing.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 5 years ago

Good evening Jay. There is a lot to be said about things stretching sagging with age. I reckon we don't have to worry about that eh?

Posted by TeamCHI - Complete Home Inspections, Inc., Home Inspectons - Nashville, TN area - 615.661.029 (Complete Home Inspections, Inc.) almost 5 years ago

Have you ever seen that Tom?  A well-done roof should never sag.

Charlie - as you know I don't diagnose on inspection reports.  So I sent my photos to my engineer friend.

I have seen sagging before when the ends of the rafters rest or slip, like this photo of an older house (common here with so many older houses), or with a bird's mouth that has slipped outward. 

But in this case the rafters were attached with straps that had not moved and the walls did not bulge.  You can see that they don't overhand the top plate.  I could not detect any movement down there at the top plate.  It did have a thin ridge beam with the rafters toe nailed.  He said that since it peaks on each end and sags so uniformly that this was probably deflection and creep.  You may be right and it might be some of both.

We went back and forth a couple of times.  I'm thick and he tries to help me!  You can see the date on the photo.  Hence the post so many weeks later.

Again, no such diagnosis happened on the report!

Not a worry at all Michael.  Sag?  I don't see no sag.  Only that eight pack...

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 5 years ago

Jay, this is a problem that is not going to go away! When I see it, I avoid it! Enjoy your day!

Posted by Wayne Martin, Real Estate Broker - Retired (Wayne M Martin) almost 5 years ago

What?  You aren't up there with your riding crop, straddling that ridge and seeing how the saddle feels Wayne?

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 5 years ago

I got a little sagging going on.... but I don't want to talk about it! Creepy!!

The older homes trusses were built on site, and maybe were sagging from the get go!

Posted by Fred Hernden, CMI, Albuquerque area Master Inspector (Superior Home Inspections - Greater Albuquerque Area) almost 5 years ago

Could be Fred.  Don't know!  But riding your hog should help keep the creepy sags at bay.  And keep those creepy hogettes at bay too!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 5 years ago

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