Tie beam size

[SuperDad]

Hi!

I'm looking into removing a tie beam from my screened porch. The problem is that its the only tie beam, and it runs straight across the middle of the space. I want to put in a ceiling fan and possibly light, and the beam is pretty much right where the fan blades should be, heightwise.

It is currently a 4x6, and it sits on and is nailed into the top of the walls. Its pretty warped(twisted) as well, so the nails are quite visible on one end.

The porch is 12x12, and is attached on one side to my home. It has a cathedral ceiling, rafters and roof sheathing are exposed.

My thought is to put two tie beams evenly spaced instead of the one down the middle I have now. I'd attach them with lag screws, since they are stronger and I couldn't nail them even if I wanted to. I don't have the roof off.

I was thinking 4x4 was much more than enough, but am interested in other opinions.

[randall]

>Hi!
>
>I'm looking into removing a tie beam from my screened porch.
>The problem is that its the only tie beam, and it runs
>straight across the middle of the space. I want to put in a
>ceiling fan and possibly light, and the beam is pretty much
>right where the fan blades should be, heightwise.
>
>It is currently a 4x6, and it sits on and is nailed into the
>top of the walls. Its pretty warped(twisted) as well, so the
>nails are quite visible on one end.
>
>The porch is 12x12, and is attached on one side to my home.
>It has a cathedral ceiling, rafters and roof sheathing are
>exposed.
>
>My thought is to put two tie beams evenly spaced instead of
>the one down the middle I have now. I'd attach them with lag
>screws, since they are stronger and I couldn't nail them
>even if I wanted to. I don't have the roof off.
>
>I was thinking 4x4 was much more than enough, but am
>interested in other opinions.


A photo is worth 1,000 words, I don't think anyone here can really effectively give an opinion to you without seeing what your porch looks like, what is above it, etc.

From what you describe however, your project SEEMS like it would be okay, if you fully install the two beams as you described BEFORE removing the one in the center.
I imagine from your description your "tie beam" would be stretching from the wall of the house across the width of the porch and ties into the outside wall/opening of the porch, that of course ties that wall/opening framing into the house and stiffens it in the middle.
It might be redundant to a degree but redundancy in construction is never a bad idea, and even if the current beam is loose/warped etc it might make the difference between your porch going South in a windstorm, or NOT!

I am also assuming there is nothing being supported by the top of this beam like a vertical post in the center, so it 's function as you describe and I as I imagine how it looks would be to stiffen and secure the outside porch wall to the house and keep it in place laterally, not to support the roof of the porch.
a 4x6 seems like a little overkill but given it has exposed cathedral ceiling etc maybe it was kept large for appearance sake I.E. a 4x4 might look "weak" or "dinky"
.
I would be inclined to stick with 4x6 if possible, a 12' span is
kind of wide and you might get some sagging too, and also a 4x4 in that space to me WOULD Look "dinky" or on the "weak" side in comparison to the other framing members.

[SuperDad]

>
>A photo is worth 1,000 words, I don't think anyone here can
>really effectively give an opinion to you without seeing
>what your porch looks like, what is above it, etc.

Yes it is. I'll see what I can do.

>
>From what you describe however, your project SEEMS like it
>would be okay, if you fully install the two beams as you
>described BEFORE removing the one in the center.

I had planned to do that.

>I imagine from your description your "tie beam" would be
>stretching from the wall of the house across the width of
>the porch and ties into the outside wall/opening of the
>porch, that of course ties that wall/opening framing into
>the house and stiffens it in the middle.

Pretty much, but your impression of the porch relative to the house is off by 90 degrees. The walls which account for the roof peaks are on the sides nearest and opposite my house, and the sides that the tie beam are holding in are the walls to the left and right.

>It might be redundant to a degree but redundancy in
>construction is never a bad idea, and even if the current
>beam is loose/warped etc it might make the difference
>between your porch going South in a windstorm, or NOT!

I'm pretty sure the main reason for the tie beam in this case is due to snow loading in the winter. I've seen the roof 1 foot deep in solid ice in spots(luckily that was at the short walls, not the point)

>
>I am also assuming there is nothing being supported by the
>top of this beam like a vertical post in the center, so it
>'s function as you describe and I as I imagine how it looks
>would be to stiffen and secure the outside porch wall to the
>house and keep it in place laterally, not to support the
>roof of the porch.

Yes, there is no vertical post. Its only possible function is to hold the two walls in. Neither of those walls is my home's wall, and both are connected to my home on one end, in case you didn't understand my mental image above. That said, I'm sure they are holding up the roof, since it defines the third leg of a triangle, the other two are the roof itself. Remove that leg, and the roof is free to collapse.

>a 4x6 seems like a little overkill but given it has exposed
>cathedral ceiling etc maybe it was kept large for appearance
>sake I.E. a 4x4 might look "weak" or "dinky"

I hadn't thought of the dinky aspect.

>.
>I would be inclined to stick with 4x6 if possible, a 12'
>span is
>kind of wide and you might get some sagging too, and also a
>4x4 in that space to me WOULD Look "dinky" or on the "weak"
>side in comparison to the other framing members.

Perhaps. I doubt that I can get a 4x6 in there, though, without wrecking the roof.

I hadn't considered the likelyhood that a 4x4 would sag under its own weight. Perhaps I could notch the ends of a 4x6 to allow it to hang down into the room just a bit.

Maybe I'll just leave it alone for now!

Thanks.

[TDHofstetter]

Hi, Supes. Welcome!

I'm with Randall in that I'd like to see a pic - and in that I think a 4x4 would visibly sag across a 12' span.

Rather than lagbolting the two replacements in place, I'd personally be inclined to use carriage bolts if you have enough room to tighten the nuts on top. You could even countersink the nuts into the tops of the new timbers before you hoist 'em into place if there's enough room for a ratchet above.

Is it possible that there's some additional reason for the existing timber? Maybe the walls weren't built using 12' top & bottom plates, for example - and are therefore weaker at the center than you think they might be? What's the window situation below the timber in question? Again, pics would be a good thing here.

-- Tim --


If you require the approval of others,
You probably don't have your own.

[paulh]

Bear with me for a sec, recalling textbooks from years ago ...

There's a straight relationship between the width of a beam and the strength of a beam - if it's twice as wide it will support twice as much weight.

There's a "squared" relationship between the depth of a beam and it's strength - a beam that's twice as deep is four times as strong, three times as deep is nine times as strong...

Because of the above, if a 4x6 is replaced with a 4x4 you've got a beam approximately 1/2 as strong as the existing one.

When I'm renovating I don't do any engineering calculations on something that's stood the test of time - I just make sure that what goes back in is at least as strong.

paulh

[SuperDad]

I'll agree with your recollection, although I haven't verified it in my "Pocket Ref".

But I think you are describing a horizontal beam under vertical loading. In my case, the beam is strictly used to hold two walls together, in tension. It will never have any vertical load beyond a plant or some christmas lights on it. I suppose in very strong winds it could be in compression, but not much.

As an update, I went over to the neighbors house which is largely of the same construction, yet he built his porch enclosure himself. I understand ours was not built by the homeowner.

In his, there is no tie beam at all, but each rafter is joined to its opposite mate by a collar tie (1x6 or thereabouts). I was rather surprised to see that the collar ties are quite close to the apex of the roof, like maybe only 6" vertical between the bottom of the ridge beam and the top of the collar tie. I wouldn't expect that to be very strong at all.