More Ridge Beam Fun

[spiller]

Hi all, this is my first post.

My wife and I have bought a house, the main part of which was built in 1868. An addition was made in 1898 and my questions concern this part.

The addition is balloon framed and the main floor ceiling/loft floor is composed of 2x8's on 16" centers resting on a let-in ledger. Main floor ceiling height is 9'. The loft has a 32-1/2" knee wall, which is just an extension of the main floor wall studs. The structure measures 28'x14' with the roof running longways. This is where the fun begins.

The 9/12 pitch roof is made up of 2x5's on 24" centers with 1" pine board sheathing and maybe 4 layers of asphalt shingles. The rafters meet at the peak. There is no ridge board. I am assuming that at one time there must have been a ridge beam of some heft but at some point over the last 106 years someone, for reasons unknown, cut it out.

Though there are no clear signs that a beam was ever there I can't imagine that that structure could have stood for that long without some support. There are clear signs of posts and a bearing wall at approximately the 18' point. The posts now just rise from the floor and attach to air.

My questions: I'm pretty sure I need to put something there. I'd like to run a beam from one end to the other with no center support. That beam would be approximately 29' from end to end. Is this realistic given that the loft is only now about 93" high under the peak? Would I be better off rebuilding the bearing wall at the 18' mark and run 2 separate beams? The first floor ceiling has a header to take the load.

I can crunch some pics and email them if my words do not do this post justice. Thanks.

[mjpliv]

You may be very surprised to learn that it is unlikely there was ever any ridge "beam" in place.

Right up until the 1940-50's most homes were built using roof rafters and ridge boards. In this type of construction the ridge board has no structural value and there only because it makes the roof easier to build (something to nail the rafter ends to and maintain the centers). In fact, you will still find a lot of builders who prefer to build using this method (but its a dying art).

Roof rafters are designed to push against each other under load. these loads are transferd to the walls causing the walls to want to "bend" outward. This problem is solved by one of two methods. Either the ends of the rafters were restrained with collar ties or ceiling joists or the tops of the walls were restrained with floor or ceiling joists. In your case the tops of the walls are restrained with a floor/ceiling diaphram located 32" below the bearing for your rafters. This was not an uncommon practice.

The problem with this type of setup is that over time (a little over 100 years in your case) the wall studs have a tendency to bow out above the floor assembly and bow inward below it. As the walls bow out, the roof ridge drops giving the house a "sway backed" look. The roof at the gable ends does not drop because the rafters are supported by the wall assembly below it.

There is nothing structurally wrong with your house. Its just cosmetic. It is conceivably possible to add a beam under the ridge but you would be creating very large loads that would have to be accomodated through the structure to adequate bearing (footings). If you do not require the attic space then you could attach a continuous 4"x4" angle iron to the tops of the studs (outside - hide it in the soffit details) on both side of the house. Between the two angle irons run 1" steel rods about 4' on center joined with a large, heavy duty turnbuckle in the center. Over a period of several months, slowly tighten the turnbuckles to bend the walls back to the plumb position. This will also straighten the roof.

Or you could just leave it alone. Its not going anywhere!

[spiller]

:D Thanks for the reply but I don't know if what you completely understood my post. First off, the is no ridge board. The rafters just meet one another at the peak. I think any "renovations" that were done to the loft were done by the people who owned it immediately before us...with a chain saw. That being said, it hasn't been like that for long because they were there for only 3 years, lost their shirts by getting in over their heads and they bailed. I'm somewhat familiar with roof framing having framed houses for 10 years, albeit with trusses. I've never cut a roof except on my 10'x12' shed. The lack of any kind of ridge former was quite surprising. I know for sure that there's no way it stood like that for 106 years.

I want to be able to use the space, thus my concern for head clearance. I can't see putting up a ton of iron as practical for my desired use. Right now the walls are square and plumb. The end walls will handle the load from a beam. My concern now is the side thrust from the rafters on the balloon framed walls. The joists are fastened to the studs with nails and just rest on the ledger. The nails won't withstand those kind of sheer loads for long. I know that over time the walls will buldge.

I guess my questions were more along the line of, when I put a beam back in, will I be able to run the entire 28' length unsupported, or will I have to place columns part way down? With such a small roof area (600'sq) and span, is there a wood product that will run that length or can I use a built up beam and how big?

[spiller]

UPDATE

I just finished speaking with my grandfather. He built houses after he got back from Europe after WWII. He told me that it's not surprising that there's no ridge board because back then they didn't "believe in them".

So I'll just go based on the assumption that that's the way it was built and that's that. I can't use iron to brace and tie the walls and still use the space. My wife wants to make her stained glass windows up there. So from the stand point of of structural integrity, is it advisable to just insulate and drywall or should I really be looking at making the roof resistent to gravity? Something about looking at the way it's framed just doesn't sit right with me.

[mjpliv]

Sorry about not being clear in my first post. When I said that the ridge board had no structural value I suppose I should have said it was optional. In your case they did not use one.

With regards about the structural integrity, I wouldn't be too concerned. Its been sitting there for 100+ years and as long as nothing starts to rot, it could be there another 100 years. Unless the wall studs snap off or the floor/ceiling joists pull away from the wall then the roof is not going to move much more than it already has.

[Tom R]

As stated above, a ridge board is not really necessary. It is installed more for convenience, it provides both a reference point and a nailer. But otherwise it's nothing but a 'glorified' spacer.

[spiller]

Thanks, Tom and mj. I'll verify that there is no rot and I'll go ahead and hang the sheet rock.

That's one less worry on my troubled, confused mind.

[colonial carpentry]

Wow!