Rafters Sagging???

 
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Old 11-02-2006, 12:20 AM   #1
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Rafters Sagging???


Hi guys. I know there was a similar thread recently about collar ties and bowing out walls etc... It was interesting but, just went and looked at a job with a slightly different problem. A smaller house with a low pitch roof and when built they used no collar ties or rafter braces (and the 20' long 2x4 rafters are sagging). I know I have to add collar ties and some braces down to bearing walls but the customer wants the sag in the rafters remedied.

What would you suggest is the best way to aproach this. How would I go about getting rid of the sag in the rafters and then secure them so it won't be an issue in the future. Any input would be greatly appreciated!!!
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Old 11-02-2006, 05:01 AM   #2
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Re: Rafters Sagging???


What size are the ceiling joist? Possibly depending on wall locations and size of c.joists build a knee wall under rafters mid span, after raising roof with temp. supports.

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Old 11-02-2006, 07:47 AM   #3
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Re: Rafters Sagging???


Collar ties won't do a lot on a low pitch. The problem sounds like using rafters that will not carry the weight of the room....bad framing job in other words. You will have to brace up from bearing walls, or look for a more costly option, like sistering 2X6's or 8's, which just adds more weight.
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Old 11-02-2006, 08:36 PM   #4
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Re: Rafters Sagging???


Thanx for the replies. Joasis, it is bad framing but the house is at least 80 years old and I guess it was acceptable back then. And now that I I've thought about it, you're right, collar ties won't help. Ceiling joists are 2x4 as well but there is a supporting wall basically running down the center of the house. My question is basically the best method to jack the rafters back up (I know how to support them once they're back at least close to where they should be).

Jmic, you said raise the rafters with temp supports but what method do you use to raise them (I'm thinking beams, a couple of posts, and hydrolic jacks). Your continued opinions are appreciated...
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Old 11-02-2006, 09:15 PM   #5
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Re: Rafters Sagging???


I would determine the location of load bearing wall, and then plan on cripple bracing the rafters, and possible using a runner crossing perpendicular under the rafters. This allows you to brace the runner back to wall locations. When you start actually taking the sway out, remember to do it in stages, and work from one end of the roof to the other. Another trick is to stretch a string line 6 inches or so lower then the rafters at each end (or other reference point, so you can monitor the progress and not go too far, since it is also possible to crack a rafter. Do not make the mistake a lot of DIY'ers do, by propping a 2X up to a rafter and nailing it or screwing it to the rafter, while the end of the cripple actually is touching or close to the roof deck, because when it fails, and it will eventually, you will have a bulge in the roof deck, or worst case, a hole where it comes through.
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Old 11-02-2006, 10:07 PM   #6
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Re: Rafters Sagging???


Think I'd try sistering maybe every other ceiling joist with a 2x8, then a strong back going perpendicularmid span of your rafter run and build a knee wall from strong back to bottom of your rafters. Sort of hard not actually seeing what ya have there to work with. Spans, bearing wall locations ect.
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Old 11-04-2006, 09:43 AM   #7
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Re: Rafters Sagging???


Quote:
Originally Posted by joasis View Post
I would determine the location of load bearing wall, and then plan on cripple bracing the rafters, and possible using a runner crossing perpendicular under the rafters. This allows you to brace the runner back to wall locations. When you start actually taking the sway out, remember to do it in stages, and work from one end of the roof to the other. Another trick is to stretch a string line 6 inches or so lower then the rafters at each end (or other reference point, so you can monitor the progress and not go too far, since it is also possible to crack a rafter. Do not make the mistake a lot of DIY'ers do, by propping a 2X up to a rafter and nailing it or screwing it to the rafter, while the end of the cripple actually is touching or close to the roof deck, because when it fails, and it will eventually, you will have a bulge in the roof deck, or worst case, a hole where it comes through.
Joasis is right on. It sounds the the end result may take on the look of a roof truss. Hydraulics would be awkward but doable. An alternate jack would be a hardwood flooring jack. It looks like the jack on the front of your tailer. Just crank & go. 2000 lb capacity and a 20" throw on most. LOL
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Old 11-04-2006, 11:13 AM   #8
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Re: Rafters Sagging???


Worx, first go to the lumber yard and get some metal strapping (the bands they use to tie and bunk material work well). Use the straps to tie the tail and the ridge down by pre drilling the bands and then run screws.

Without securing the ridge and tail you may get lift on the ridge or facia.

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Old 11-05-2006, 01:44 AM   #9
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Re: Rafters Sagging???


Thanx again guy's. All good advice. Bob, good suggestion. But instead of the straps you're talking about I think I'll just pick up some regular strapping (holes already there) would save a step - no drilling required. If I get the job (still pricing it) will be lots of fun crawling around in that attic with 80 year old wood chip insulation and the 2 layers of fiberglass insulation on top of that. It's a low slope roof and will have to cuddle into that stuff more than I'd like too!!!
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Old 11-05-2006, 06:35 AM   #10
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Re: Rafters Sagging???


Did you give thought to maybe renting a ventilation fan since you will have a ton of dust and dirt?
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Old 11-06-2006, 01:31 AM   #11
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Re: Rafters Sagging???


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Did you give thought to maybe renting a ventilation fan since you will have a ton of dust and dirt?
No, but plan to wear a mask. Will have to cut a whole it in though to be able to enjoy a smoke or two while I'm working !!!
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Old 11-06-2006, 01:43 AM   #12
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Re: Rafters Sagging???


worx ,i did a retrofit on similar house few years ago.Used 12"x3 1/2" glulams to span from gable end to center bearing wall,then jacked 2/4 roof and built knee wall on top of beam to carry roof load.

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