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Add support bracing for roof


ronjohnson's Avatar
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11-22-14, 05:36 PM   #1  
Add support bracing for roof

Hi, I am going to be working in attic with insulation and while up there I am thinking of adding some extra support for my roof. It is all open in the attic right now. The size is roughly 27' long gable to gable, and 26' across. It is a standard roof with 2x6 rafters and the joists run the same direction as the rafters, although they do not all meet up evenly as the spacing on everything varies. I do have a wall in the middle of the house that has support all the way down to the basement floor. I was thinking of maybe only adding the extra support in the middle 1/3 area of the roof since the middle would be the weakest part where a heavy snow would start to collapse? Is there a usual way to go about doing this?

 
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Bud9051's Avatar
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11-22-14, 06:24 PM   #2  
Hi Ron, sounds like you have been watching the weather reports from the Buffalo area as many others have.

Here's my thoughts. My 35 year old home, cape, has some roof irregularities (dips and bumps) that I will be addressing next year along with new shingles. As it turns out, the variations are due to some areas having more support than others. All regular lumber will sag over time. Brace some and not others and the results will often be visible in years to come.

Wherever you decide to brace, do it all the way across and do it uniformly.

Also, make sure you have good attic ventilation and air sealing to limit the moisture level up there, which weakens that structure. And buy a couple of snow rakes when they get back in stock.

Here's some good reading for all home owners:http://www.buildingscience.com/docum...build-renovate

Bud

 
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11-22-14, 07:33 PM   #3  
A stick built roof is obviously not as strong as an engineered truss roof. An engineered truss roof works under the principle of a triangle being the strongest simple shape, geometrically, with multiple triangles that are joined together acting as one complete unit. Any improvements you make should probably be based on that same idea.

Depending on the shape your roof is in, changes you make could actually do more harm than good. For instance, let's say the roof has sagged here and there. Adding a beam style support under all the rafters on each side of the roof might move some of them dramatically, which might cause the ends of those rafters to react unpredictably... perhaps pulling apart from the members they are nailed to... separating either at the ridge or the top plate. Similarly, lifting a ridge beam back to straight would affect all the rafters that are nailed to it in some way, stretching apart what took years to sag. So that's just my word of caution.

If you are just adding individual supports so that things don't sag any further, that's another matter.

The first thing I'd suggest that you do is add collar ties (a horizontal 2x6) between the rafters on each side of the ridge... positioned in the upper 1/3 of the roof line. So if it's 9 feet from your center wall's top plate to the ridge of the roof, those collar ties would be no lower than 3 feet below the ridge.

The collar tie does a couple things. It prevents your rafters from ever separating from each other at the ridge, creating a triangle in the peak of the roof. It also stiffens the rafters under snow load, when used in combination with kickers, mentioned below.

IMO, the easiest way to brace the rafters to reduce deflection (for snow load) is to position a single 2x6 perpendicular to the rafters (but on edge, as a beam would be) then position kickers underneath that 2x6 that extend to the load bearing wall. The kickers are usually notched out around the 2x6, and are usually spaced out every other rafter... 32" or 48" on center, depending... then they are fastened along side the rafter, the brace, the ceiling joist and the top plate.

As Bud mentioned, the best method would be to do this consistently across the entire roof, not helter skelter, here and there. Whatever you do, don't brace anything to an unsupported area of ceiling space. And don't be tied to the idea that you have to brace the rafters exactly in the center of their span. The ends of your collar ties would be an ideal location for the kickers, no matter where that falls in the span of the rafters.

 
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11-22-14, 09:40 PM   #4  
Thank you for the information. What you have described is in line with what I was thinking. As you mentioned about lifting the roof, I am not, I just want to add extra support. There is a slight sag along the ridge, but you can not see it unless you really look for it. It is an older house and so the roof has held up this long, but when I look at it, it just looks a bit under built. It has been on my mind since we moved here 5 yrs ago and the home inspector did actually mention about adding the collar ties.

 
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11-23-14, 04:09 AM   #5  
The sag in the ridge line with a stick built home is almost inevitable. On the gable ends the height off the foundation is controlled by the sheathing which doesn't really shrink. The center of the house rests on support beams and joists which can start out at 10.5 to 10.75, or 11.5 to 11.75 whichever. When I measure my 2x10's and 12's in the middle of my home they have shrunk up to 1/2". My main support beam barely measures 11 inches and the resulting sag confirms it. I started several years ago jacking and shimming to reverse as much of the center sag, but with two levels (the cape) you can't raise the bottom beyond level to compensate for the second floor.

Your thoughts about reinforcing those rafters is right on as much better to begin correcting now than 20 years from now. BTW, many of the corner cracks in my drywall have closed and stabilized due to my jacking and added support. Much better solution than spackle and paint.

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Bud

 
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11-23-14, 01:56 PM   #6  
Collar Ties vs. Rafter Ties - InterNACHI

Collar ties are installed to prevent uplift of the roof in high wind areas. Rafter ties are the ones that prevent the rafters from pushing apart under load. The floor joists act as rafter ties.

I wouldn't automatically say a roof truss is stronger than a stick built roof. They certainly maximize strength when using the least amount of lumber.

Why do you feel as though you need to reinforce your roof? How old is the house? How steep is the roof? Is there any evidence of roof failure?

 
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11-23-14, 02:37 PM   #7  
Drooplug, the source you quoted confirms the things I mentioned regarding collar ties. The only thing I left out was the part about uplift, which didn't seem to apply to his reason for reinforcing the roof.

 
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11-23-14, 02:52 PM   #8  
I apologize. I read through your post quickly and didn't digest it completely.

 
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