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Question for an experienced roofer, re: rafter ties

Posted by xbeerd (My Page) on
Mon, Dec 30, 13 at 22:27

Hi there. My house is a 1700 sqft ranch with an attached garage circa 1964. It's basically a T shape. House front to back and garage off to the left with a fireplace room in the middle

My roof I believe is a 4/12 with 3' eaves. actually here's a pic from google... http://photos2.zillow.com/p_d/IS5gftsrkyiftv.jpg

My question is this...
The rear half of the roof has the ceiling joists and rafters parallel. The front half of the roof, the rafters are perpendicular to the ceiling joists.

The collar ties are there as they should be on the upper third every 4' ( maybe every other?, just didn't actually count but I know it's not every one) but on the front half of the roof shouldn't I have rafter ties spanning the width of the house to help against any outward wall pressure?

If I were to put rafter ties in, being a span of approximately 28' how much overlap would I need on the boards? I think I read somewhere one every 3 rafters on 16" oc spacing, vertically 2x4 or larger

Would love to hear from someone with real experience in this area

For reference this is basically how my roof is setup. Minus the purlins, wind brace, and props. We'll there is a prop, but in would assume it was put in later by a previous home owner.

Thanks much!


Follow-Up Postings:

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RE: Question for an experienced roofer, re: rafter ties

Your question should be directed to a structural engineer or a framing contractor, not to a roofer.

Without knowing all of the framing details, I'd say if the house was built in the early 60's and there's no signs of movement of the walls to date...then it's a non-issue.


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RE: Question for an experienced roofer, re: rafter ties

I suspect a problem with terminology in this case. Is this question actually about collar beams?

Here is a link that might be useful: collar beam


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RE: Question for an experienced roofer, re: rafter ties

"The rear half of the roof has the ceiling joists and rafters parallel.:"

A "carpenters truss" is 2 opposing rafters tied at the wall top plate by a continuos ceiling joist, with 5-16D's each end.
When the ceiling joist is in 2 or more pieces and the rafters do not exceed span, the collar tie is of the rafter material and placed tight to the bottom of the ridge,

When the rafters do exceed span and purlin rafters are installed, the collar tie is of the ceiling joist material and is placed tight to the bottom of the purlins with 3-16D's each end.

Purlin braces are typically 48" oc. as are the collar ties.

"The front half of the roof, the rafters are perpendicular to the ceiling joists."

Typically where the ceiling joists oppose the rafter run and purlins are installed the collar ties occur just beneath the purlins.

It is my practice to install an additional rafter tie just above the ceiling joists, where a 24" lap could be achieved without the affect of crowning affecting the ceiling finish.


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RE: Question for an experienced roofer, re: rafter ties

If there hasn't been any failure in 50 years, there isn't going to be.


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RE: Question for an experienced roofer, re: rafter ties

Are you sure the rafters in question are not supported at the ridge by a structural beam? If that is the case, no rafter ties (between the tops of the walls) would be required.


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RE: Question for an experienced roofer, re: rafter ties

hey thanks for responding, sorry to be away for while..

probably right, i should have directed at a structural/framing engineer. anyways... reason all this started is a few things.

little history.. we bought this house as a foreclosure. there is some slight sagging in the roof along the north south edge (front to back). the walls in the front section of the house where the cieling joists are perpendicular to the roofs rafters. appear to be about 1/8" inch out of being straight vertically. we had a 45 degree temperature swing a week or so ago which lead to some fantastically loud thermal contractions. to which point i got a crack in my cieling drywall in one area. i also noticed that when we have some snow and then a day where the sun melts some of it, at some spots the melting snow creeps under the sofit and runs down the side of the house, which i expect is a result of the roofs sag.

the ridge beam at the top of the rafters i'd guess its a 1x10 with out measuring or having been up there recently due to it being winter, i might try to pop up there today and snap a few pics of whats going on if i can.

i was referring to rafter ties being laid perpendicular to the cieling joints. atleast thats what i seen them called on some of the websites i been reading on.

being that we want to live here for the next 17-18 years at least (till our children are out of high school) i would like to combat this early if it is indeed a problem or if there is something i can do to distribute the snow weight better so i dont A, have a real issue down the road, B, go crazy and have medical problems from worrying about this every winter. LOL.

i am definately not opposed to having someone come out and look at it when the snow goes away but that wont be any time soon. atleast 2.5 months i would say. cant see much with a foot of snow on the roof.


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RE: Question for an experienced roofer, re: rafter ties

If your ridge is in fact a 1x, you have an old house.


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RE: Question for an experienced roofer, re: rafter ties

for reference, here is a shot of the rafters etc in my garage, consistent with the rest of the house, house is built in 1964. you can see the size of the ridge board.

http://i18.photobucket.com/albums/b133/FscottF/photo1-2.jpg
http://i18.photobucket.com/albums/b133/FscottF/photo2-2.jpg


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RE: Question for an experienced roofer, re: rafter ties

You are the proud owner of a house framed near the end of that technique of 1x ridges and collar ties.


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RE: Question for an experienced roofer, re: rafter ties

LOL. so am i pretty much F'd? or is there hope of fixing my sagging roof?


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RE: Question for an experienced roofer, re: rafter ties

Probably not, though depending upon the assessment of a civil or structural engineer you may find it prudent to remove and replace.


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RE: Question for an experienced roofer, re: rafter ties

do i even want to know what it would cost to remove and replace?

i'd guess my house is 55'' long and main width (walls) is roughly 27', and then the extension out towards the garage. problem area being right of the chimney to the right side of house mainly front half. but i'm assuming its not a 'replace the front half' kinda job. (attached pic)

Here is a link that might be useful: pic of my house from Bing Maps


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RE: Question for an experienced roofer, re: rafter ties

first I'm not a structural engineer..disclaimer!!
is the ridge sagging or the rafters. a point between the ridge and the outside edge?

these require different solutions..

the ridge..yes check with a structural engineer!!!
more collar ties after the ridge is straightened..
or something of a truss nature.. a cross brace
maybe a double up of the roof rafters on every other one..
does you roof have 2 layers of shingles instead of one..lots of added weight
reroof to a single layer.

sagging in the middle...

harder to answer..where are the load bearing walls inside..
vertical posts from the walls to the roof rafters?
jack the sagging rafters and double them?
double with a large size..if you have a 2x6 add a 2x8 or a 2x10..yep from the cap strip( low end to the ridge)

-dkenny


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RE: Question for an experienced roofer, re: rafter ties

Given the width of the building and your assumed roof pitch the clear span for the rafters should have been 2X8, however, I would have used the rafter ties just above the CJ as well as the collar ties.

If 2X6 rafters were used then there should also be purlin rafters and kicks to load bearing walls, because the 2X6's are over spanned.

Given the age of the framing members, jacking to straighten, would more then likely lead to more problems from other pulled and dislodged connections.

You can address just the front half and in some measure of salvation, you may be able to use the removed rafters as the rafter ties.

Most framers are familiar with the correct method of joining ridges.


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RE: Question for an experienced roofer, re: rafter ties

its gonna be warm this weekend (like in the 20's and up to 40 one day. hopefully enough snow melts i can try to snap a pic of the ridge to show whats goin on.

im pretty positive i have only one layer of shingles,. when it comes time to reshingle, i would opt to strip it off rather than going with 2 layers.

maybe my roof was just built all jacked from the get go. LOL.


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RE: Question for an experienced roofer, re: rafter ties

i got a shout out to a guy i know who is a home builder. will see if he has a trusted engineer he could send over and take a look at things when the weather permits.

i agree with you snoonyb that jacking could possibly open up another can of worms and maybe the best course of action is to just maintain it from the inside to eleviate further developments

my question to you (well, or anyone but you seem like you know a few things about this stuff) tho, since you mentioned the purlins, how do you do the purlins when the CJ are perpendicular to the rafters? and the load bearing wall holding up the CJs is right about the center of a 22' span? i woudlnt think you would want to tie them all in to the same CJ that is unsupported thru its course until it hits the wall or load bearing wall.


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RE: Question for an experienced roofer, re: rafter ties

"If I were to put rafter ties in, being a span of approximately 28' how much overlap would I need on the boards?"

28' span needs metal I-beams,c-purlins or truss construction. Even if you were able to pull everything back into perfect alighment,there's no way of holding alighnment with 2x scabs. I would wait and see if it gets bad enough to cause a problem. Either way,it will require removing deck and rafters so why do it unless you have to.


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RE: Question for an experienced roofer, re: rafter ties

Even an expert carpenter may not completely understand the dynamics of your situation. Certainly the original one did not do so. As it is, the slightest bowing out of the supporting walls means that the system is less able to resist the outward push on the walls and the sagging of the roof peak than it was originally. So progression of the process is expected to continue. It is possible to gradually pull the walls back to vertical with rods or cables Those or suitable substitutes will be in place permanently. Or use them temporarily and then remove the roof structure and replace it with engineered trusses.
A competent engineer is needed now.


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RE: Question for an experienced roofer, re: rafter ties

Ok, lets do some orientation.

From the "BING" picture and assuming both the garage doors and that end of the house, are the front of the house, and that is the referenced area where the CJ are perpendicular to the rafters.

Does the 22' wall fall in line with or near that of a continuation of the garage door wall?


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RE: Question for an experienced roofer, re: rafter ties

correct, the 'front' section is what im talking about being perpendicular to rafters.

the interior wall 22' from the front wall of the house is a tad farther away than the peak of the garage roof section by maybe 4'


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RE: Question for an experienced roofer, re: rafter ties

At 4:12 a DF #2 2X6 rafter at 16"oc can have an unsupported run of 12'3", or 10'7" at 24"oc which would be the respective locations of a 2X4 purlin rafter. The purlin "kick" would be, at a max. 45 degree angle, back to the 22' bearing wall and the gable end wall, as well as 2X collar and rafter ties qt 48"oc.
I suspect that you may have 1X ties and several layers of asphalt shingles.

At 28' width a 4:12 roof pitch would have a rafter run of 14'9".
A 2X8 DF #2 at 16"oc has an unsupported run of 16'2" and would still require rafter an collar ties.


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RE: Question for an experienced roofer, re: rafter ties

heres a pic i took , i was hoping more snow was to be melted but oh well.

so talkin about purlins, if there are no beams to get the kicks to with in reason due to the span, would you need to do something of this nature to distribute the weight down to the foundation?

http://s18.photobucket.com/user/FscottF/media/ROOFPURLIN.png.html

im just trying to further edumacate myself.

only 1 layer of shingles as far as i could tell, i was removing some ice build up over the weekend and made sure to check. i've seen some roofs with like 3 layers (which is a no here in WI, and im sure everywhere)

you would be correct in assuming 1x ties. definately are not 2x's up there of any sort.


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RE: Question for an experienced roofer, re: rafter ties

There are a couple of other methods, Beams or tripling of joists, however, even then an engineers approval would have been needed.

At the era of the construction, the 1x material would have had a nominal thickness of 3/4" and been nailed with 8D or 8 common.
I'd bet a closer inspection will reveal cracking originating near the nails, and other signs of pulling.


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RE: Question for an experienced roofer, re: rafter ties

right, i dont plan on doing this one with out an engineered solution or professional involved. if anything, for sake of my home owners insurance policy in the event something catastrophic happened.

in the event of losening nails. is there a solution for that?


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RE: Question for an experienced roofer, re: rafter ties

"in the event of losening nails. is there a solution for that?"

Not with 1x. As aged and dry as it is, any nails will split them.

Your best bet will be to replace the roof framing and use the correct size rafters and 2x collar and rafter ties.

You should not need an engineer, just a simple drawing, a permit and a good roof framer.


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RE: Question for an experienced roofer, re: rafter ties

is there a floor in the attic space?


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RE: Question for an experienced roofer, re: rafter ties

Negative. Just the ceiling joists and insulation. There is probably 3-4' of height in there at the peaks

I made an appt and am having a structural engineer come out Monday. He is familiar with homes in the area and has an idea of what might actually be happening with it. I think I'll need to get some more wood panels to crawl on in the attic haha


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RE: Question for an experienced roofer, re: rafter ties

The 2x4's you first mentioned should work fine and the overlap only needs to allow enough nails to resist the horizontal force which is not too great (perhaps six 16d clinched). So in order to get the 2x4's in the attic you might use three 12 ft lengths and overlap them about 3 ft. and nail them every 5 to 6 inches staggered across the grain and hammer them over on the back side. Don't use screws.

If you nailed the 2x4's to the tops of the attic joists you wouldn't need to nail them together and every third rafter could be tied to the nearest attic joist with a steel strap or a rafter tie. The same could be done using a subfloor in the attic instead of 2x4's.

You could also tie the bottoms of every third rafter pair together with an aircraft cable and a turnbuckle.

You are not building a truss, you're just trying to prevent the tops of the walls from spreading so if there are no other issues you don't need an engineer, just a carpenter. The best method will be determined by the size of the access to the attic space and connection points at the eaves.


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RE: Question for an experienced roofer, re: rafter ties

i get what you are saying Renovator8, but i do have other issues to sort out as well.

the inspection showed the walls slightly out of plumb but nothing that the engineer was too concerned about. he was more concerned about the valley beams that were supported by a vertical 2x4 "posts" in a couple spots that do not seem to be properly supported from below. (braced to cieling joists with out structure wall below) it appeared.

there is also some 2x4 'posts' bracing from the structural wall up to the ridge board (non structural, causing it to bend the ridge board, I am not happy that our home inspector didnt see and mention this to us in the inspection. one of them is literally 6' from the attic access. but whatever, thats in the past.

i cant seem to find any good pictures of these cable/turnbuckles in place in a situation like mine, i found some info about using them and needing to be sure to use ASTM A193 B7 rods, like 3/8 or 1/2", i was noticing the cost for a 36" rod (can get custom lengths) was $4.99 for a 16 TPI and $21 for 24 TPI, i was suprised at the cost difference.

this was at Speedy Metals (speedymetals.com) which is local to me.

guess just the extra metal involved in making it with more threads?

Anyways. we'll see what the guy comes up with and i have a contractor in mind, who i think is a good fit for the job based on referrals. im hoping that the bank will be nice to me and i can work in my garage addtion with this. ;) but one step at a time, no sense having a sweet garage with a house about to fall down


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RE: Question for an experienced roofer, re: rafter ties

Something to keep in mind is that the rods and turnbuckle will do nothing to correct the "bowing" of the rafters and will only serve to "arrest" the outward deflection of the walls.


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RE: Question for an experienced roofer, re: rafter ties

I don't understand how braces from a structural wall to the ridge would cause a problem unless there are enough of them.

It the valley is not adequate a possible remedy is to add larger LVL ceiling joists to support the vertical braces under the valley rafters.

These are all simple structural issues that probably only require reinforcing of what is already there.


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RE: Question for an experienced roofer, re: rafter ties

right, i know the turnbuckle approach is only going to keep the walls from spreading, not address any rafter sagging.

the braces from the structural wall caused a problem proboably because the structural wall is not quite in line with the 1x ridgeboard so they are at a slight angle and caused the ridge board to bend.

i found some pics of the awesomeness that i took a while back. ill up date the post once they are uploaded.


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RE: Question for an experienced roofer, re: rafter ties

http://s18.photobucket.com/user/FscottF/library/roof pics

here is a link to some photos from inside the attic, mostly of around the area where the valleys are.

Here is a link that might be useful: attic pics..


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