# Sagging roof



## Haney1

My husband and some friends of his re-shingled our roof 6 years ago, and event put down new plywood. Now, the roof is sagging in the middle. We are planning on selling our home in a few months, so we need some good ideas on how to support the roof, without breaking the bank. Any suggestions on how to do this? ANY HELP IS APPRECIATED!!! THANKS!


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## jkrodger

We just bought a house that had a little bit of a sagging roof in the garage. The owners called out some contractors to come in and sister the rafters (I believe this is what was done). This appears to have improved the sagging a bit but we know at least it won't get worse and can easily be fixed when we eventually replace the roof. If you either get the sistering done or at least disclose that you will get the sistering done then you might be able to talk a buyer into ignoring the roof issures.


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## Haney1

Thanks jkrodger!

I will let my husband know. Do you know if this is something a "regular" man can fix, or do you need to be a professional? I don't want to spend money having someone else fix it if we can save money with him doing it.


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## jkrodger

Without knowing how handy he is, I'm not sure. If he's experienced and feels confident enough, he probably could, just remember that if it's done poorly, an inspector (a good one at least) will catch it. Here's some info I got by googling "sistering rafters"

Double the rafters by sistering a 2x6 or larger to the sagging ones. These need not extend over more than the middle three-fourths of the sagging member, unless the saggers exhibit signs of distress at their ends (cracking, splitting). In this case, the sistered rafter(s) should extend over the full length and bear solidly at both ends. Nail or screw new to old at six-inch intervals, using a staggered pattern. (from NBN)


Depending on the damage to the existing rafter, you can decide of sistering it is a good idea or not. 

I don't like to see sistering of a rafter if the damage is on either end of the rafter. The ends of the roafter is where the weight is transfered to. If the damage is in the middle, the sister rafter can easily have the weight transfered to it and then the weight transfered back to the original rafter on the ends and to the ridge beam and the top plate of the walls. 

If the original rafter is damaged on the ends, it is hard to get the birdsmouths cut or the top angle cut and the new rafter fit into place. It will never fit as good as the existing rafter and you will almost always have a sag or a hump in the decking. 

But a sag or hump, depending on the price to install a new rafter, may not be too bad ?!?! (from Roofing.com forum)


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## concretemasonry

Sistering will not get rid of a deflection or sag. All sistering does is make it more difficult to sag or deflect more.

To do it right, you have to get everything back in place and where you want it. After that, you can sister to make sure it does not go back to where it was.


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## Ron6519

You need to first find out why it is sagging. It wasn't sagging before and now it does sounds like a structural issue. If you can't diagnose the problem, call someone in who can. He should be able to tell you how to fix it and then you can decide if you are qualified to do the work correctly.
Ron


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## the roofing god

you should probably install a kneewall in the attic to bring the rafters to where you need them.sistering bad rafters w/out going for the whole length between support ares adds a lot of weight and can create further problems because of it:whistling2:


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## Ed the Roofer

Sistering is a good idea and so is the knee wall concept too.

But, if you do not repair the sag, you just have reinforced the sagging condition so it will remain a cosmetic and potential structural deficiency.

You must run a board or plate across the entire span and then jack it up making sure that the floor area where the jack is on is reinforced and transmits its load bearing weight across the entire floori of the attic rather than just on one joist. 

Once the sag is jacked up sufficiently, then you can sister in the rafters and potentially also install a knee wall to prevent future sagging conditions.

Ed


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## the roofing god

WHICH BASICALLY EXPLAINS THE PROCESS OF BUILDING A KNEE WALL,AND THAT BEAMS SHOULD BE SISTERED FROM SUPPORT POINT TO SUPPORT POINT:huh:


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## Malcolm

I would like to build a knee wall for 3 slightly sagging rafters. Should I add a top plate or just brace the rafter directly with a 2X4? I will put a 2 X4 across the bottom to spread the load. I just wasn't sure about the top.


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## Ed the Roofer

TRG,

If someone does not know much about construction, they may just build a knee wall and fit it in as where the rafters are already sagging, thinking that that would be good enough.

They need to jack them up first to alleviate the bow as much as possible from them prior to sistering the new rafters in to the existing sagged ones.


After they have the sagged rafters jacked up as much as possible, without creating any seperation from the ridge board or top wall plate, then they can install the sisters and then they can install and fabricate the knee wall.

Ed


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## Ron6519

What happened when they did the roof that caused this problem? Roof rafters don't all of a sudden sag unless there's a reason.
You can't just jack up these rafters, it won't work. As you push up on the roof rafters,they push back causing floor deflection. You need to build temporary walls under the jacking positions all the way down to the basement so when you push up, it has resistance below.
Ron


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## AaronB

I have never had to do this, but laying a couple of framing members across the floor joists has provided excellent even support without floor deflection. The roof framing members can be "retrained" by jacking a little at a time over a long period of time without anything dramatic happening to the floor or roof.


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## Ed the Roofer

That is exactly the point I was tying to make. By spanning the attic floor joists, I have been able to spread out the dispersement of the weight distribution.

Also, this usually is observed on homes which had too much weight from too many layers of old roofing on them, and when the tear-off is complete, the rafters move much easiear.

Ed


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## Malcolm

OK, it worked. All the rafters are level again. When the previous roofers did the roof about 16 years ago, it looks like the cracked a rafter. It is a 2X8. They just wedged a 2X4 under it. It only had a 1/2" sag because of the cracked rafter. I guess this caused the two rafters on either side to sag 1/4" each. That is why I had a wavy roof deck. Here is what I did. I placed a knee wall half way down the rafters. It goes under all three rafters. The load doesn't seem that great. I could lift it with my hands level with very little effort. There isn't any shingles on the roof of course. I do not, however, get any snow in my area either. I sistered a 8 foot section of the 2X8 with another 2X8. The top portion rests on a load bearing wall. The bottom portion of the sister rafter extends a foot beyond the cracked portion of the rafter. I then used 1/2" bolts on either side of the crack to connect the sister to the rafter. The sister and the original rafter both rest on the knee wall now. I notice sometimes on long trusses they are spliced together. This seems similar to that construction, but with better reinforcement. What are your thoughts?


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## Ed the Roofer

You work fast Malcolm. :thumbsup: 

That is what I was saying. Once all of the weight of the shingles are removed, then it usually does not take much effort to lift the bowed rafters back into position to enable a proper sistering job.

I like the added strength with the bolts. We usually just nail 16's through the sistered rafter and into the crippled one.

Ed


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## Malcolm

Ed the Roofer said:


> You work fast Malcolm. :thumbsup:
> 
> That is what I was saying. Once all of the weight of the shingles are removed, then it usually does not take much effort to lift the bowed rafters back into position to enable a proper sistering job.
> 
> I like the added strength with the bolts. We usually just nail 16's through the sistered rafter and into the crippled one.
> 
> Ed



Yeah, I have a couple of friends helping me out today. I was just going to leave the sag in, but I'm glad I read this thread. My roof will look much nicer in the end now.


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## Ed the Roofer

Get back to work with your friends now and quit telling them you have to go downstairs to check out the DIYchatroom.com forum for additional advice

They are wise to your tricks now Malcolm.

Ed


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## the roofing god

ED,when I build a knee wall,It would include a plate top & bottom for the whole distance,that was the point of a kneewall vs. justpushing up rafters and nailingf 2x4s to the rafter and then to the corresponding floor/ceiling joist(to spread the load evenly),so no problems lower,I`m not sure where the misunderstanding came in--I didn`t like the idea of sistering a few and having the weight transfer down/or damage the rafter further because it didn`t go fully from 1 support point to the other:wink:


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## Ed the Roofer

Malcolm said:


> Here is what I did. I placed a knee wall half way down the rafters. It goes under all three rafters.


John,

As you can see from what Malcolm did for his repair, not all people, homeowners or contractors think alike.

I suggested laying a plate spanning the entire attic floor to transfer the weight load from the jacking up of the rafters prior to sistering in new rafters to the bowed ones.

Not everyone is going to do the maximum work to eliminate future potential reoccurrences of the same problem. In some scenarios, good enough is good enough, and without being able to personally see the structure, I have to leave the ultimate decision to the person who has first hand knowledge about the existing problem needing corrective actions taken.

Ed


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## the roofing god

the point was that the term knee wall constitutes that very thing!,a bottom plate,a cap plate and stud members to join the two---aknee wall is a knee wall is a kneewall is a kneewall


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## slummy

*sistering rafters in an old house*

My 2 x 4 *rafters* are 24" on center. They support 3 layers of shingles, a layer of cedar and a layer of pine sheathing - that's a lot of weight. So much so that it has cracked _several_ of the *rafters*. 
After consulting buddies of mine that each have twenty plus years of roofing experience I am going to follow their directions;

*First *replace floor joists from *end to end* (the entire span in all structural framing is key) Use nail gun and circular for this
*Step 2* lay a 2x6 plate across and above the entire span of my attic floor / ceiling joists
*Step 3* climb step ladder, use speed square to measure pitch of roof, set chop saw (u can use a circular or handsaw for this just make sure you measure the pitch correctly for the base plate cut) and cut base plate side of 2x6 sister rafter
*Step 4 *Have a friend hold base plate flush to floor (I don't need a seat cut - you might) 
Grab other end of sixteen foot 2x6 climb step ladder use square to draw a line down from my 1x8 pine ridge plate, cut 2 x6 - lay sister rafter across step ladder then
*Step 5* use a four foot level against cracked rafter and good rafter to inspect the difference in pitch (get a mental picture of how the good rafter looks) 
*Step 6 *jam a kneewall sized 2x6 between new base plate (step 2) and cracked rafter to take the sagg out of the roof (check pitch with level) 
*Step 7* from *end to end* nail up the sister rafter that I just cut both sides of with the nail gun my buddy lent me.

*Step 8* remove kneewall from new 2x6 *rafters* and put them under good 2x4's

Now it's strong enough to hold me while I ripit to the pine and install a galvanized roof in late spring

Peace out y'all
Slummy 
:jester:


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## scott j

*sagging roof*

Hi,

There is some great information provided in this thread. 

I have a similar Hip roof, 1920's house, old 2x4 roof rafters supporting old wood roof, with 4x8 sheets over the top and one layer of shinges. The longest span is about 13 feet on 4 rafters in the middle sections. There is some sagging but no splitting that I can see. I also have old 2x4 floor joists in the attic.

I don't see how to fix the sag and jack up the rafters with a knee wall if I don't have much support below, 2x4s floor joists and an open bedroom below. Load bearing wall in some a few areas.

Is it possible to sister 2x6's to the 13 foot rafters and live with the sag? Or is it possible to create the knee wall ro run the entire span of the floor joists and have it support the long and short roof rafters as well without sistering?

Thanks all.


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## Niltag

I have a question. My house is just 1 year old and there is a depression on the south side. it looks to be about a 4 foot area. We are adding it to our 1 year list for the builder to repair, but the foreman has already started saying that they can sag a little and still meet code. Which is his standard answer for everything.

Is this a problem? 
Is there an allowable limit of sagging?


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