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Old 12-03-2010, 11:54 PM   #1
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rafters poorly attached to ridge beam


Hi all, my late 70's vintage house, located in Houston Tx, has a gable roof with some rafters that are poorly connected to the ridge beam, as shown below. Can you advise how to make this more secure?
Roy
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Old 12-04-2010, 12:11 AM   #2
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rafters poorly attached to ridge beam


Its not going anywhere unless the heels of the roof rafter / truss slip off the top plate at the opposite end on the exterior wall. That is the important attachment point.

The two exterior walls are not falling away in opposite directions from each other and making the ridge become lower causing the trusses to detach from the ridge beam.

Its actually, from over the years, "lifting" of the trusses

Anyway, if it bothers you, add hangers or brackets or gusset the two opposing rafters together where they meet at the ridge

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Old 12-04-2010, 03:50 PM   #3
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rafters poorly attached to ridge beam


Are these the top cord of an actual truss, or lone rafters? If loan rafters, I see what was said above, but I'd make sure that the walls are not, in fact, pushing away from each other. If the walls on the outer end of these are traveling, then that needs attention asap. j
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Old 12-04-2010, 04:03 PM   #4
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rafters poorly attached to ridge beam


They are definitely single rafters and are pulling away for a reason. As jklingel says, check that the walls aren't spreading. Does it have adequate bracing from wall plate to wall plate? Also, is that black stuff I see the inside of a ridge vent? Seems like there's too much cut out of one side from the ridge than the other.
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Old 12-05-2010, 11:12 AM   #5
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rafters poorly attached to ridge beam


It may have been built that way. It may be due to shrinkage. The walls may be spreading because there is no effective rafter tie.

The ridge board should be equal to the plumb cut of the rafter in depth, which, indicates that the builder cut a corner. Knowing that and seeing that the other rafters in the picture are tight, I would suspect that it was built that way or it was a really green board when it was installed.

Not being able to see the rest of the construction or knowing the placement of multiple short rafters makes a true determination impossible.
If there is no rafter tie, it is never too late to install one.
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Old 12-05-2010, 11:20 AM   #6
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rafters poorly attached to ridge beam


Quote:
Originally Posted by Tigerloose View Post
It may have been built that way. It may be due to shrinkage. The walls may be spreading because there is no effective rafter tie.

The ridge board should be equal to the plumb cut of the rafter in depth, which, indicates that the builder cut a corner. Knowing that and seeing that the other rafters in the picture are tight, I would suspect that it was built that way or it was a really green board when it was installed.

Not being able to see the rest of the construction or knowing the placement of multiple short rafters makes a true determination impossible.
If there is no rafter tie, it is never too late to install one.
what he said
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Old 12-05-2010, 02:31 PM   #7
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rafters poorly attached to ridge beam


Thanks guys for your thoughts. There are 17 rafters visible, there's also a cathedral ceiling with another ten or so rafters I can't see. All the visible ones have some degree of separation on one side or the other, generally just at the bottom of the rafter, but there are several similar to the one I pictured above. I include another pic below showing some more.

The roof spans about 32 ft of ceiling. There are ceiling joists parallel and connected to the rafters for most of the roof (except for the cathedral part and also another 5 ft or so on the gable end). However they do not traverse the entire ceiling - the central part has joists running perpendicular to the rafters. Does this mean that the joists could not be effective rafter ties?

Is adding rafter ties something I could do myself (I can crawl around and nail things)? Reviewing online, rafter ties should be at least 1" thick and should span opposing rafters about every 4 feet. Is there a standard way to join lumber together to make a tie this long? I might add collar ties as well.

The gable end and last five feet or so are different - here the ceiling joists also run perpendicular to the rafters for the whole span of the roof. There would appear to be no rafter ties here. Also the roof beam was extended by toe-nailing another board as shown in my 2nd pic below. Is this something that should be strengthened?

The cathedral end does not have any rafter ties (3rd pic). The ceiling is sheetrocked. There is a sheetrocked cover over what might be a roof beam at the top (except that the real roof beam is definitely above that), and another covered (fake?) beam half way down the slope.

Thanks again for all your input!
Roy
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Old 12-05-2010, 02:53 PM   #8
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rafters poorly attached to ridge beam


Oh, I should add that there are purlins on each side of the roof about half way down. Would this alleviate the need for rafter ties?
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Old 12-05-2010, 08:16 PM   #9
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rafters poorly attached to ridge beam


The rafter plumb cuts look like poor workmanship.

The ridge splice doesn't look like it is fastened together. LPT4 can help that. I have also seen 3/8" lag bolts used on such a splice.

The "purlins" are actually knee walls and the rafters appear to be spliced at the knee wall. The purpose of a purlin or knee wall is to shorten the span of a rafter and does not negate the need for rafter ties. Purlins and knee walls should be bearing on a support such as a wall or beam and not be supported by ceiling joist unless the ceiling joist are over-sized to accommodate the load. In as much as the rafters seem to be spliced at the knee wall, solid blocking would be a good idea.

The vaulted area appears to be constructed with a beam for the ridge so that is ok.

Per your description, there is a section of joists that run perpendicular to the rafters running the length of the house in the middle of the house. If this is correct, there is no continuous rafter tie and installing one is simple enough.

What is the history of the roofing material? IE. The original roofing and what is there now.
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Old 12-05-2010, 09:53 PM   #10
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rafters poorly attached to ridge beam


Collar ties: http://www.finehomebuilding.com/how-...llar-ties.aspx

Read: http://books.google.com/books?id=iwS...rafter&f=false

Add some rafter ties just above the perpendicular ceiling joists, nailing them per: http://www.engineersedge.com/civil_e...onnections.htm

Your gaps look like poor workmanship as they are even, if tight at the top as in the 6th picture down: http://www.unified-eng.com/ch/thrust.html

Blocking at rafter laps on interior walls may not be required in your area, although it is recommended: http://www.buildingsmartalliance.org...pter6final.pdf

http://publicecodes.citation.com/ico...002_par028.htm

The ridge board is non-structural, not requiring plates or blocks at ends. Code accepts an omitted ridge board with only gussets at opposing rafters: http://publicecodes.citation.com/ico...002_par017.htm

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Old 12-07-2010, 12:12 AM   #11
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rafters poorly attached to ridge beam


@Tigerloose, the roof is currently asphalt shingle in pretty good shape, hopefully 10 years left. Previously it appears was cedar shake given all the scraps littering the attic. Why do you ask?

@GBR, thanks for all the references. I'm studying them.

My main question right now is: to add rafter ties, I will need to splice 3 2x4s (or 2x6s) together to cover the 32' span. Is it good enough to make this splice by overlapping the 2xs by several feet and nailing them together using the engineersedge nailing count at the splices? or should they be bolted together?

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Old 12-07-2010, 08:17 AM   #12
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rafters poorly attached to ridge beam


I asked about the roof covering for several reasons. The first picture shows a short rafter. If the rafter was cut short the skip sheathing nailed to it would most probably not have a gap between it and the ridge board as it would have been installed straight without a gap at the ridge. So perhaps there is movement.

What I am not seeing is shingle nails sticking through the plywood. There are a few 8d nails and several narrow crowned staples visible. These would have been appropriate for fastening the plywood but not the shingles. Shingles in a high wind area require nails, lots of nails.

It's really is difficult to form an intelligent opinion from pictures.
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Old 12-07-2010, 08:30 AM   #13
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rafters poorly attached to ridge beam


The building code allows 1x4 rafter ties. I recommend 1x6 to provide enough contact area where the tie meets the rafter to nail it without splitting the 1x. A 12" nailed lap splice is sufficient and it should be supported at the splice to prevent sagging. The building code also allows 4' spacing but since you are trying to correct a possible problem, I would recommend a tie at every other rafter.
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Old 12-07-2010, 03:21 PM   #14
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rafters poorly attached to ridge beam


@Tigerloose, all I know about the roof is that it apparently survived hurricane Ike, whose eye passed about 40 mi east of here. I didn't own the house then. Not sure whats holding it on. If not visible nails or staples, then what could it be? just very short staples?

My rafter ties can rest on, but should not be connected to, the ceiling joists, correct?
I would like to use some 2x10s in the central area (linked to 2x6s going out to the eaves), then put some floor boards over it to be used for access and lightweight storage after I insulate, or would that be a bad idea?

Also my A/C unit is blocking about 6 ft of the ceiling. I guess the best I can do in this area is run the rafter ties over the top of the AC unit and support them as you suggest. This means those rafter ties will be around the midpoint of the rafters. Unless I could figure out a way to lift up the AC and put it on some 2x10s, that would let me insulate under it. But not sure that is practical.

Finally, I have a bathroom extending out from the back of the house, with a small roof extension - not sure what you call this technically, but the roof for this section does not rise to the main ridge line. This section has a separate ridge that is perpendicular to the main ridge of the roof and starts halfway down. This little extension is done hip roof style, not gable style. Does it make sense to run rafter ties all the way to the back of this extension? Or is that going to stress the extension roof? If its not a good idea to do that, then what should I do about tieing the rafters opposite this roof extension? I'm at work now, can't get a picture of this until later.
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Old 12-07-2010, 03:28 PM   #15
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rafters poorly attached to ridge beam


That gap at the ridge in the first pic could've come from a number of things besides wall spreading. If the walls were not strung to a straight line and sufficiently braced (this includes that knee wall also), would create a gap and the framers just nailed it up anyway. Possibly the framers knocked the braces off before the roof was properly secured.
Same goes for keeping the ridge board straight while nailing up the rafters. In that picture of the knee wall, that second from left rafter looks like its sitting on a shim or my eyes are getting old.

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