LVL Beam above Rafter ties

[Mark.alan65]

I would like to remove a portion of a load bearing wall and replace it with a LVL beam. The only issue is that I need the LVL to go above the rafter ties, and need some way to attaché the rafter ties to the beam that cannot be seen from the interior of the room. Is this possible to do? If so what type of strong tie would I use, or do they even make something to accomplish this?

Thanks,

Mark

[Don_P]

I'm not following, do you have a sketch?
Are the rafter ties also the ceiling joists and you are wanting to support a lap joint that was over the wall? Or, what is the elevation of the ties and what is the need to connect to them? Have you figured out a way to support the ends of the beam?

[John Raabe]

Yes, a sketch would help. Are you working with one of our plans?

[Mark.alan65]

Let me see if I can do a sketch. But we would like to remove a portion of a load bearing wall, and that would allow us to open up the living room. The original rafter ties sat on top of the wall that we would like to remove. Since the ceiling is so low in the house, we were thinking about removing the drywall from under the rafter ties and installing boards on top of the rafter ties to give 8 to 10 inches more head room in the room. So as to not see the LVL beam from inside the finished space, we wanted to install it above the rafter ties, and connect the rafter ties to the bottom of the beam instead of the sides or on top. If that is even possible.

[Mark.alan65]

I copied this drawing off of a post that MountainDon posted. The width of the house is not correct but the way that the rafters and rafter ties are drawn is correct.

[ChugiakTinkerer]

I'm guessing the rafter tie isn't continuous across the span shown?  Because if it is, then any interior walls wouldn't be load bearing.  I'm sure life isn't that simple, so you will probably want to help the guys understand the situation more completely.  If you've opened up the ceiling then some pictures would be ideal.  Short of that, a sketch like you just posted but showing actual dimensions seems to be in order.  You could probably even re-use MtnDon's sketch, just note each board's dimensions, where the interior walls are, and any rafter splices.  Also room dimensions.  I think if all that information is available you'll get suggestions that are exactly on point.

[Mark.alan65]

Here is an updated drawing that reflects what I am talking about. I am 6 foot tall and can lay my hand on the ceiling sheetrock. So I would guess that the ceiling is around 7 to 7.5 feet tall. I would like to raise the rafter ties/ ceiling joists a little bit to gain height in the rooms. I am not sure if this is possible without just doing a complete tear down and install trusses. But I thought I would ask to see if anyone had any ideas.  The walls are 2x4 and the rafters, and rafter ties are 2x6 going to a ridge board.

[ChugiakTinkerer]

Thanks for the revised sketch.  The good news is that the center wall is not load bearing.  It can be removed without affecting how the roof load is supported by the exterior walls.  All you need to worry about is keeping the ceiling joists (also serving as rafter ties) from falling down.  Those joists serve two purposes: 1) to attach a ceiling to, and 2) to keep the exterior walls from spreading out due to rafter thrust.  I think you can address both of those concerns by creating a truss out of the rafters and joists.  Assuming the ceiling joists are joined in a flush butt joint, you could insert a king post in the middle and secure with plywood gussets on both sides, glued and nailed (not screwed) with sufficient penetration and density to meet engineering requirements.  It's possible to do the same if the ceiling joists overlap above the middle wall, it just take a little more work and finesse.

As to the ceiling height issue, I don't see that you have many options.  One would be to make the walls taller.  You could do that by jacking up the entire roof and adding in top plates to get a few more inches.  It would have some challenges but would be cheaper and maybe easier than replacing the walls altogether.  Though that would be better from a code standpoint.  The other option I see is to scrape off the roof altogether and replace it with cathedral or scissor trusses.  With an engineered truss you would have the peace of mind of trusses constructed to meet the loads of your area.  And it probably could be done much quicker than by re-engineering from below.  I would give that some thought, especially if the asphalt shingles (?) are in sad shape and need replacing anyway.

[NathanS]

The way those rafters sit on top of the current joists complicates things...

Ignoring that, there are code provisions that allow attic joists to be raised up above the top plate.. they still need to be on the bottom third of the rafter. The way it works in the code is that you apply a factor (less than 1.0) to your allowable rafter span, and then see if you will still meet the requirements. You will also have to put more nails into the connection, which I believe there is a factor for that too.

Like Chugiak said, the attic joists primarily stop rafter thrust - they stop the rafters from doing a split and pushing the tops of the walls outward.

If the rafters were bearing directly on the top plate, I would say you could install new attic joists 1-2 feet higher than current (assuming you meet code) and then remove the existing joists. Your ceiling would be higher everywhere except where you would have that 5-12 angle running down to the wall near the edges of the room.

[Mark.alan65]

Thanks for the replies.

I had thought about moving the rafter ties up into the one third section, but I was not sure about it due to the way the rafters sit on top of the rafter ties. The only way that I could see moving them was to sister in new rafters, and add rafter ties up into the upper one third, I think I would also install collar ties.  Then cut and remove the existing rafter ties.
 

[Mark.alan65]

ChugiakTinkerer are you saying to add a king post to each set of rafters? If so could I also raise the rafter ties up into the upper one third and add a collar tie and king post running down to the new rafter ties?

[NathanS]

Thanks for the replies.

I had thought about moving the rafter ties up into the one third section, but I was not sure about it due to the way the rafters sit on top of the rafter ties. The only way that I could see moving them was to sister in new rafters, and add rafter ties up into the upper one third, I think I would also install collar ties.  Then cut and remove the existing rafter ties.

Yeah, that is complicated. Also, the rafters are bearing on the cantilevered joists.. so you certainly don't want to cut them for that reason.

Just to mention, collar ties prevent the top of the roof from splitting apart in a wind event. They don't do anything to prevent rafter thrust.

[Mark.alan65]

Ok let me ask this. What if I had heavy metal plates made that could be bolted to the rafter ties to hold them and the king post at the top and bottom? I have an old barn on the property that I could get the wood for the king post, and even a queen post if needed. I have seen on here a build that a person built the same plates using plywood painted black to look like metal if I had to use the plywood instead of the metal.

[ChugiakTinkerer]

ChugiakTinkerer are you saying to add a king post to each set of rafters? If so could I also raise the rafter ties up into the upper one third and add a collar tie and king post running down to the new rafter ties?

No, my thought about making a truss does not in and of itself do a thing for your roof height.  It would enable you to remove the center wall.

Kingpost could probably be 2x4 like so:


And then put gussets on all the connections:


The funky rafter design makes it impossible to modify the ceiling while still using the rafters.  Well, at least it is an extreme challenge.  You could attempt to fashion a scissor truss with the existing lumber in place.  I'll sketch that up...

[ChugiakTinkerer]

Bear in mind I have no clue how viable this is from an engineering standpoint, nor even the practicality of trying to do this to an existing structure.  But if you want to kill two birds with one stone you might consider something like this.

First, create bottom chords and post for a scissor truss...




Second, Secure everything with gussets of appropriate size and strength:




Finally, cut away the old joists and remove the interior wall.  Voila!




If I wanted to end up with a roof like this I'd probably prefer to remove the old roof, rafters, and joists and start from fresh with engineered scissor trusses.

[Don_P]

Similarly, you could harden up that lower rafter end with blocking and gussets and install a raised tie, in the lower third of roof height. With any of these scenarios you should get an engineer to detail it. I do agree with R&R'ing it though, I'd probably start by pricing it out with raised heel scissor trusses. If the roofing is about done it would help sway that.

In the real world... I've recently applied gussets to that type of ceiling joist/rafter joint in an old house. It is very difficult and sometimes impossible to pull all that dried and twisted old wood into one nice flat package. We discussed the same scenarios and in the end it just wasn't worth modifying it. I gusseted everything together better and added hurricane ties. Straightened the ceilings back out and recovered it at the 7' height. Last summer we totally removed an old roof and put new trusses on. I don't know that the labor is much different but quite a materials difference. The new roof is much nicer than the repaired older roof.

[Mark.alan65]

Thanks for the input Don, ChugiakTinkerer, Nathan. It is a tough call on which direction to go. I hate to loose the look of the old timber that make up the current design. I have been looking at converting the current setup into a type of scissor truss. I have a friend that has a plasma table, and I can get him to cut out some metal plates to construct the modified truss. This would add a large amount of strength to the design. I could add the king post, and raise the rafter tie easily. I have an old barn on the property that I could get any wood that would be needed to make modification to the current truss.

Do you guys think that the heavy metal plates would help my situation?

I do plan on having an engineer review my plans before any modification are made.

[NathanS]

If you raise the joists aren't you still going to create a problem where the rafters are bearing on them?

It seems like the main obstacle is figuring out how to make the current rafters bear down on the top plate instead of the joist. If you can figure that out, cathedral vs raised flat ceiling is probably more of an aesthetic choice.

I can't remember, are you living there full time or is this more of a getaway? Maybe try living with the lower ceiling for awhile? If the old joists look nice you could maybe even move the drywall or some T&G to the top side of the joists to create the illusion of more height? Tudor homes are some of the most beautiful houses I've ever seen, and those ceilings are probably 7ft a lot of times.

Don is probably on the money about having to fight with old twisted wood. My house was all brand new kiln dried, and I had to fight just about every piece \of it into position.. not fun even when you have more space for leverage.

[Mark.alan65]

If I added the King post in the center and then used the heavy gage metal to tie it all together (king to rafter tie, king to peak/rafter) from what I gathered that should fix the current setup, so that the wall can be removed. I am not removing the complete wall, just about a 10 ft section. I also plan to add the metal to where the rafters sit on top of the rafter ties. Once all of that is installed, I believe that I could move the rafter ties up about a foot on the rafters, keeping the king post, just making it shorter. All of this would be reviewed and blessed by an engineer.

Thoughts?

[ChugiakTinkerer]

The problem you're faced with is you can't move the joists, because they are what attach the rafters to the top plate.  You might be able to do the following without messing with a kingpost and still be within code, sort of.

- Buy some 2x8 at 20' to use as your new ceiling joists.  I am suggesting 2x8 because they will be stiffer than 2x6 and thus less likely to sag noticeably.  Some analysis of that to follow.

- Nail the 2x8 as rafter ties as high up as you want, up to a max of 20" above the top plate for the top of the rafter tie.  This would give you 12"of additional head room and still keep the rafter tie in the lower third of the roof height (a code requirement).

- Put plywood gussets or metal plates at the existing rafter/joist junction.  This is to strengthen and stiffen this connection, because you need to keep this part of the joist in place to support the rafter.

- Cut away the old ceiling joist flush with the wall or perhaps at an angle to give a little more meat to the remnant portion of the joist.

With a rafter tie that is long enough to span the ceiling as a single board, there is no need for a king post in the center.  You might still put one in where you remove the wall underneath, to minimize sag once the ceiling drywall is hung.  Where the interior wall remains, you can stub up to the height of the new ceiling and have this taller wall support your rafter tie.  I think this could work without too much drama except at the point where the rafter currently rests on top of the ceiling joist.  You would want to reinforce that sufficiently such that it performs as if it is an extension of the rafter.