Inverted Header...nagging concern...help appreciated.

[c_kott]

Hello all, I have lurked on this site for a long time and have learned a lot here, but this is my first post.

I have a nagging concern about a remodeling project that I am working on and I would really appreciate any advice.

I am remodeling a small 1940's wood-framed house. It's a single story with an attic that has been converted to 2 bedrooms. The roof of the house is a simple gable with the ridge running front to back. Roof pitch is about 8 in 12. There is a knee wall running down the sides of the attic bedrooms.

As part of my project I have removed a 13.5 foot long, first floor bearing wall. This wall ran through the center of the back half of the house. To replace the bearing wall, I used an inverted header which I read about in JLC about 2 years ago:

I cut the existing ceiling joists where they crossed the bearing wall, inserted a beam built up of (4) 1.75" x 9.75" LVL's, then hung the ends of the exising ceiling joists on the LVL beam with joist hangers.

This plan was stamped by an engineer and city official issued the permit.

However, I still have a nagging concern that I have increased the chance for rafter thrust to spread out the exterior walls of the house. Before I cut the ceiling joists, they obviously tied the rafter ends together stopping any spread.

Now that the the ceiling joists are are cut in the middle and nailed into Simpson joist hanger, I am wondering if the diagonal nails that go into the joist ends are enough to resist any spreading.

The beam has been installed for a couple weeks while we are waiting for electricians to finish their work and no spreading is noticed yet, but I'm concerned about the long term & snow loads on the roof.

So before I close up this ceiling, do you think this is something to be concerned about, or should I take additional steps to resist the spreading of the rafters? If so, what do you suggest?

Thank you very much for your help!

[David Meiland]

Re: Inverted Header...nagging concern...help appreciated.

I would call the engineer and ask if s/he accounted for that thrust in the calcs. It's not just a beam size you needed...

There are various tension ties you could use to add strength. A bulletproof method would be to install hold-downs on the sides of the rafters and run chunks of all-thread through the beam. There are numerous other strap applications you could also use.

[Top Notch]

Re: Inverted Header...nagging concern...help appreciated.

Hangers nailed in double shear have value, probably good enough in your case.
If your beam sits flush with the top of the ceiling joist you can install floor sheathing long wise or 2x4 to bridge the sides. Obviously its not a calaculated plan but one that will help against thrust and ease your concerns.

Of course a phone call to the engineer to ask him if he considered ridge thrust would hurt. May piss him off but at least you will know.

[c_kott]

Re: Inverted Header...nagging concern...help appreciated.

Thanks David and Tom for responding, I really appreciate it.

All-thread through the beam makes sense, I suppose there is no problem drilling some 5/8" holes through the LVL Beam, right?

Also, regarding strapping, would that be installed on the underside of the joists & beam? Note that the underside of the joists and beam are not flush to each other.

The floor sheathing point is a great idea, but (I did not mention earlier) the existing attic subfloor is already tongue and groove boards (running parallel to beam) and covered with carpet.

I will try to call the engineer today to see what he says.

Thanks again guys.

[dlhunter]

Re: Inverted Header...nagging concern...help appreciated.

I'm interested as to what the Engineer will say. We always strapped the bottom of flush beams but can't remember if we ever had a drop beamin an attic.
Maybe a few of the lateral restraint ties required for the new deck codes?

[mike maines]

Re: Inverted Header...nagging concern...help appreciated.

I don't know what St. Louis load requirements are like, but around here, if the house was 24' wide and rafters 16" o.c., in a snowstorm with reindeer on the roof, you would be looking at something in the ballpark of 1200 lbs of "thrust" at each rafter and joist.

That's not taking into account the kneewall, wall plates, roof sheathing, or collar ties, which will all work in your favor, but not enough for me to feel safe with just toenails. Simpson does not offer values for their joist hangers for this type of loading. If you have plywood spanning the center beam you might be ok, but I'd feel safer with metal strap. Or whatever your engineer says.

[Top Notch]

Re: Inverted Header...nagging concern...help appreciated.

You would need to have a pair of tension ties for every bay, plus rod. Or at least every 4ft which is prescriptive.

Very expensive. The code says when joists are run perpendicular you can install 2x4 above the system to maintain the tie. So treating it like that gives you a cheap alternative but you will build up the floor and lose hieght if the spaceis finished.

I forgot the you could use metal straps instead of the sheathing but once again your pulling the rug and existing T&G.
Given all the factors, the pitch and the kneewalls etc... you may be fine. Again the main who did the calcs is best to confirm. If not peeling up the rug and laying a plywood skin over the existing T&G with longer nails should be cheap insurance.
Just my opinion

[NW Architect]

Re: Inverted Header...nagging concern...help appreciated.

Simpson VB series?

[c_kott]

Re: Inverted Header...nagging concern...help appreciated.

I spoke briefly with the engineer today but he was busy so I set up a time to to discuss with him in more detail on Thursday.

Thanks to everyone for the helpful suggestions, it's always good when you have options.

NW Architect - I did a quick look at the Simpson VB Series and that looks like it may fit my situation exactly.

I will post again after I meet engineer.

Thanks again!

[AndyGump]

Re: Inverted Header...nagging concern...help appreciated.

What the hell is an "inverted Header"?

Andy.

[jimAKAblue]

Re: Inverted Header...nagging concern...help appreciated.

What the hell is an "inverted Header"?

Andy.

I was wondering that myself.

His description indicates a flush header but he must have found that term somewhere.

To me, an inverted header means it's upside down; crowned down. I've only seen that technique used for some cantilever situations.

[Top Notch]

Re: Inverted Header...nagging concern...help appreciated.

I assumed he meant "upset".

[David Meiland]

Re: Inverted Header...nagging concern...help appreciated.

Upset? Do you mean "inset"?

I recently installed a beam with the joists hung below it, precisely to avoid cutting continuous framing (attic joists under tension) that he's got there. I guess that might be considered inverted...

[JayNos]

Re: Inverted Header...nagging concern...help appreciated.

Upset? Do you mean "inset"?

I recently installed a beam with the joists hung below it, precisely to avoid cutting continuous framing (attic joists under tension) that he's got there. I guess that might be considered inverted...

That is an inverted header. Additional bonus is that you don't need to build temporary support walls. Install the beam then remove the wall below.

[David Meiland]

Re: Inverted Header...nagging concern...help appreciated.

That is a bonus, but the downside was the hole in the gable necessary to fly the beam into the attic. It needed a gable vent anyway.