Hi:

I am looking for information or repairing a storage building roof. The building now has a saddle look. The center is sagging and I would like to know why and if my plan to fix is on the right track. I have a good general knowledge of building things but do not work in the construction field.

The building was built some 20 to 25 years ago. It has 2 x 4 rafters on 2 foot centers. The center board is .75 x 4 inches. There are 4 lengths of 2 x 4 which run from the top sill across the width of the building (stringers I believe they are called) which are on every third rafter. There is a .75 x 4 inch board (collar ties I believe they are called) located at about the halfway point on the rafters but only located on every second rafter and not on rafters with stringers. In general I believe there should have been more stringers and collar ties. Am I right is assuming this is why the roof sagged?

As for fixing the roof I am planning to raise the roof, add stringers and collar ties, and then run two wire cables fastened to the outside of the top sills. The wire cables would be about 1/3 from each end of the building. I plan to use building screw jacks to lift the building slowly until the roof is level (or close to level). I am using two 4 x 4 x 8 foot beams, one for each roof half and positioned near the roof peak. Am I on the right track?

Thanks for your comments.
PamND

you need to remove the roof and put in a beam as a starting pointproblem is the center beam is weak. you will need to add suports for this large beam then you can rebuild the roof.
if this building is falling apart you might concider just knoking it all down and rebuild it.

Hi:

A beam as in a 2 x 4 as in one 2 x 4 running the lenght of the storage building?

I have looked at several (older than mine) and most have 2 x 4 or a 5 inch board for the center board and seem to be doing fine.

PamND

if it had a 2x4 and is saging then replace it with a 2x6 or 2x8 and that should do it for ya as for beam i mean 4x8 or bigger
some call those TIMBERS

You probably don't need to "replace" the smaller members - just sister new larger joists/rafters onto them. It's very hard to understand the issues when you haven't given us the span lengths for these members. We have no idea how large or small this roof is (just give the building dimensions). The span is what determines the depth of member required so without that information it's pretty tough to advise you. My first thought is to add deeper 2x's between the existing 2x4's so that you don't have to remove anything.

But again... don't even know how big a building this is. Unless it's a big building then the wire tie method is totally unnecessary. It basically sounds like they used 2x4's when 2x6's were required or used 24" spacing when 16" was necessary. The collar ties should be fine as 2x4's but those braces that you are calling stringers - commonly called bridging, should be the same size as the roof rafters.

quote:

Originally posted by aminator2002:
You probably don't need to "replace" the smaller members - just sister new larger joists/rafters onto them. It's very hard to understand the issues when you haven't given us the span lengths for these members. We have no idea how large or small this roof is (just give the building dimensions). The span is what determines the depth of member required so without that information it's pretty tough to advise you. My first thought is to add deeper 2x's between the existing 2x4's so that you don't have to remove anything.

But again... don't even know how big a building this is. Unless it's a big building then the wire tie method is totally unnecessary. It basically sounds like they used 2x4's when 2x6's were required or used 24" spacing when 16" was necessary. The collar ties should be fine as 2x4's but those braces that you are calling stringers - commonly called bridging, should be the same size as the roof rafters.

Hi:

The size of the building is 16 by 24 feet so each rafter has to span 8 feet. Not what I would classify as a large building.

The bridging/stringer is the same size as the rafters (2x4) and run the 16 foot width of the building and there is only four of them. Was that enough?

The collar ties are boards 4 inches wide by 8 feet long and there is five in total. Is that enough?

To me the weakest part of the building is the middle and in this building there is only one collar tie near the middle and only one bridge/stringer. I would have thought that the four rafters making up the middle would have been fastened.

The building has bowed out (about 3 inches on each side) and the wire ties were to bring the sides back together. Do you think the building will come back together as I level the roof and stay together after I add more collar ties and bridges/stringers?

Thanks
PamND

Let's see if I can help here. It is rather hard because I think we might be using different terminology for the same thing.

The reason your walls are bowing out is because there is unsupported thrust from your roof. This means that because your roof is sagging, there are uneven distribution of forces around the supporting walls. I don't see any reason you should have to use wire ties on a structure so small if the roof structure is corrected and tied into the walls properly.

Let me try to clarify the terms I'm using such that at least you'll be able to understand me. drawing Rafters are the members that run with the pitch of the roof and perpendicular to the walls. Collar ties are horizontal members that run from about midpoint of rafter to midpoint of rafter across the span of the roof. Bridging are members that are placed perpendicular to the rafters and in the same plane - they brace the rafters against one another.

I'm entirely unsure what this member you are calling collar ties being 4" wide and 8' long. A collar tie is typically a 2x4 or 2x6 used just to brace up the roof. I think 4' spacing is pretty typical.

Going back through your posts and trying to figure the problem, I remain convinced that it is the spacing of your 2x4 rafters that is the problem and perhaps they should have been 2x6's spaced at 24" centers or even 16" centers.

You should also check that your sheathing - whether it be plywood or decking material that runs over the rafters and under the roofing material is in good shape. Sometimes it is the sheathing that causes the most problems especially when you are seeing a wall buckle on the exterior. The sheathing makes the roof system act as one, and to me it sounds as if you've got some parts of that roof that are trying to kick the wall out from under it.

I'm sorry to keep leading you back to more questions but it really is difficult to do this via internet. It would be much easier for you to have a home improvement savy neighbor come by and look it over with you.

Looking at load charts, it certainly seems that a 2x4 at 24" isn't going to span 8' of pitched roof without deflecting quite a bit.

Hi:

Thanks for taking the interest. I really do not mind all the questions and you are absolutely correct about terminology. Makes a big difference if we are both talking about the same thing. Also I really appreciate the understanding part you are helping me with. I am curious why this building let go and others that I looked at did not.

The collar ties you describe refers to what I call a collar tie except the one on this building are not 2 x 4 but boards which are .75 thick and 4 inches wide placed about "run from about midpoint of rafter to midpoint of rafter across the span of the roof" and the middle 3 rafters do not have any.

I have been looking at other buildings like garages which are similar in size to my building without the sag. Most of them either have no collar ties and more bridging or just bridging. The bridging/stringer I refer to is nailed to the top sill and to the rafter (your drawing refers to them as ceiling joist) and run across the building like the rafter but the span the entire width without splicing. So yes they are perpendicular to the rafter.

The sheathing is tongue and groove boards and are in solid condition, not rotted or loose, or broken or missing. The decking from underneath looks real sound. The walls a bowed I believe because when the rafters came down and the extra length had to go somewhere. I also believe that the rafters came down because something prevented them from staying together and to me that something was collar ties or bridging or center ridge. Now the problem could be nails or not enough ties and bridges but I do not have enough knowledge to point to a problem. My other though is the center board or ridge beam. This is also a board and not a 2 x 4 and has a splice in the center of the building. To me this is another weak point and the three weak points combined may be the problem. Nails are 3 inch twisted type so they do not quit penetrate thru the bridge and rafter.

I did have some people come to estimate repairing and two of them said insufficient stringers (I believe that to be another name for bridging) but they said it is cheaper to tear the roof off and redo with trusses. Well unfortunately I do not have funds for that so either I repair it or down it comes.

I do not like 24 inch centers but again I have seen several buildings with that doing very well. So why does mine have a problem? But again if I were to build from scratch it would be 16 inch centers.

I plan to raise the roof slowly checking often and if the walls come back in then maybe I do not need the wires but I have them from some previous scavenging so as extra insurance I was going to put them up.

Thanks again for all your comments
PamND

After you jack it up, pull it together, whatever, your options:

A. Support the Ridge Beam (the center beam that runs the length of the building). Add 2 posts (dividing the 24' length into three sections of 8' length). If you want a clear span then you will need to beef up the ridge beam which is basically cutting the ends of your rafters (pitched members) and either sliding in a 2x --- on either side of the existing beam tying together with screws/nails, or replacing with a 4 x 6 or greater member. You have to make certain that the walls on either end have a central (under the ridge beam) support "posts" that can handle the additional weight. Half of your load of the roof will essentially be placed on that beam. Sounds to me that presently all of your load is being transfered to the short walls that support the outer rafters the ridge beam is essentially tying together both pitches not actually doing much to support the weight vertically.

B. (And/or) Tie in cross beams (like the short cross piece in the letter 'A'). This will give the functionality of a truss. I would tie together with 2x6 members with through lag bolts and nuts (washers too) 2 bolts at either end through existing 2x4 roof supports. Depending on the pitch of the roof you could go down only half way forming an A shape, not at the ceiling sill plate level. Of course you tie in after you jack up the sag. Set every 48" starting at either end wall that should give you 7 horizontal cross members (truss). If you are in snow country your added snow load may require more members (like all of them).

I have seen in some old churches which were built with cathedral ceilings a series of cables that span across the width of the structure - these are tied into beams on the exterior of the building and through come-along winch the structure is pulled back together then the cables are set permanently. This is essentially the same idea.

Also tie the rafters together with short spanner pieces set ever 48 inches (unless already there). That would be between each 2x4 running from the ridge beam to the wall sill plate. Stagger them so you can screw in to the end of the butt joists through the rafter. This will create a grid 24" x 48".

C. The best and honestly the cheapest (in the long run) and easiest thing to do is to remove the roof and re roof with either 2x8 rafters and a decent ridge beam of 2x-- material (2x10 or 2x12), or go with a prefab truss system composed of 2 x 4's tied together.

I say 2x8 because I assume you do not have this as a heated structure and I assume you have snow to deal with - an unheated structure will build up more snow than a heated structure.



http://www.mcvicker.com/resguide/page013c.htm Gives some good numbers for span distances in roof framing. Please note that 2x4's are supposed to be 12" on center for a span of 8' 7" (Lower grade fir)