Which Way Is Stronger?

TaitINC

we are in the process of remodeling current attic space. we have raised the floor level in all but one location. the main reason for rasing the floor level is clearance over some beams. the other two reasons are for insulation and strength. all the areas we have finished didn't need it for strength purposes, but the area is question is. there is a 16' span with 2x6 ceiling joist at 16" O.C. my question is this; would we acheive more strength from putting 2x6 on top of existing 2x6 and webbing them together with ply, or running 2x6 at 16" O.C. perpendicular to the existing?
sistering the existing would be very time comsuming with exisitng electrical in the way. so i didn't consider this an option.

spencer

genecarp

You have said the area in question needs it for strenth purposes, in what regard? how is the structure failing? if we dont understand how it is failing, it is impossible to comment on ways to improve. G

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Meetre

I don't think he's saying that it is failing, just that it will need more strength than a 2x6. you need to do load calc's, figure out the span and what kind of beef you need to support it. 2x6 might not be enough either way you frame it.

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TaitINC

gene-thanks for your response, and i apologize for not enough info.
the area in question needs strength do to flex. when someone walks over the area, the current floor/ceiling joist flex a little more than i like. i doubt they will ever break or fail, but i would like to sure them up. I would also like to cut back on flex so they don't have any issues with the drywall on the first floor ceiling. there won't be added weight that would cause the existing joist to sag. your thoughts are appreciated

genecarp

Ok, i got the picture, given your situation, running your new joists the same direction, and webbing with plywood would be the strongest way to go, that being said perpendicular will also work, and would be quicker, just be sure to strap, (connect). the middle 5 or 6 of the new to the old, this will essentially, (in a weird way), reduce your span, and solidify the deck.

ps, that connection could be done with some type of clip, check the teco catalouge, or you could make a connection with wood, screws, and glue. this connection is important. G

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neolitic

My SOP for attic to living space floors
is to lay 2X4 blocks on the top plates
and run the new floor joist on that.
Gives an 1½" for wiring, etc. and
isolates the existing ceiling below.

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neolitic

The only way I would be confident
in laying one on top of the other
would be with ½" ply gussets all the
way down both sides.
That I would trust to make it a single
unit.

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TaitINC

i didn't want to give my thoughts on the situation until i got some feedback.

gene- if we go perpendicular to the existing, the new would be nailed to the existing at each intersection. maybe to minimize the nails we could use H2.5 hurricane clips?

neo- i agree with running plate to plate and create a void between the new and old. the only problem in this situation is ceiling height, so it won't work. this is common practice when framing a second floor for us. doing so alleviates unnecessary weight on center bearing walls. in most older homes the beam in the basements are under sized anyway.

my thoughts on my current situation are this... if i run the new 2x6 on top of the existing and web them together, the still absorb most of the weight per joist. if i run them perpendicular i feel they will disburse the weight across many joist in turn making it stronger. it is a form of unibody construction. if they are all locked together in a grid type pattern, you will get minimal flex due to wide spread deflection and disbursement of weight.
i don't know if i'm correct in this hypothesis, and if i'm not i'm sure someone will speak up and let me know. i feel the perpendicular works better in my head.

spencer

neolitic

Seems to me that only works if the new
perpendicular span is shorter, and/or
the ends are picked up by a beam with
good bearing.
I try to avoid it because the physics of it
give me a headache.


As to the plate to plate:
you can clip the top corners
pretty severely, and you only need
2" of bearing at each end....
just thoughts. 2¢ worth.

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TaitINC

neo- the perpendicular span is shorter by 2 feet. the one end would sit on the end ceiling joist nailed at 16" O.C. over the gable end pins. the other end would butt into a triple 2x12 header.
here are some pics

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genecarp

If you are going to run perpendicular, you will need to teco int existing header, and on the gable end you need to build a structural header the support your new beams. or build up off the plate.

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neolitic

Sounds reasonable to me.

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Burby

Even if perpendicular to existing you are spanning 14 ft with a 2x6 on top of a 16 ft span of 2x6. Maybe a redundant question but, are you comfortable with doing this?
The 16 ft span must have sags already does it not? And from pic it seems the bracing of the rafter is also supported on these same 16 ft 2x6 with no bearing below, is this so? Is there snow loads in your area to further add weight to this?
If built as you say, please use straps longer than 2.5s & screws in place of nails in the clips. If possible, if you could slide a strap under the existing 2x6 between drywall and c/j then bring it up both sides to the tops of the new joist to completly wrap both if this is to be used as living space.
Additionally verify bearing of end beams / headers, to the basement for continous bearing.

Looking at the wires in the pics, no boxes, wirenuts only, would it be that much problem to remove wires to add 2x10's at the least as sister joist.
Even 2x10s if converting to living space would have some bounce to them if @ 16" centers spanning the 16 ft.
If i am correct in the 16 ft existing span with 2x6s & no bearing below in this span, adding the weight of the new 2x6s, plywood flooring, walls (transferring some of the load to the roof rafters, which is good, just strap as well to joist & rafter), then added furnishings once Owners begin to use this space, --=phew, that is a bit of added weight.
Finally, is the service in the house enough to handle the additional electric that will added to this finish space as well?

You may have already crossed all these bridges and end result very nice & functionable. Maybe it has just been so long since I have done any old renos, just my thoughts and questions from what is available & not actually being there..
Please let us know how it all turns out in the end.

Those pics bring back memories of years gone by remodeling older homes back in New England.

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Tom M

I cant tell whats happening in that pic but I see a few red flags. Its looks like the existing is balloon framed into the wall or worse cripple wall, Adding to those connections is iffy. Your also going to have a hell of time fireblocking this thing much less doing a grid. If you cant add new 2x8 or 10's to the opposite side of the studs then I would lay over the top and join them with the ply. At least the load path is transfered equally. A grid creates point loads where those beams and hanger end up. I wont pull those rafter/ceiling connectors out either.

buletbob

I agree with the above, and also if you do teco the 2x6's into that girder your now undersized that header with the added weight. Could you bolt 2x12's along side the studs . BOB

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wallmaxx

I don't see how you can take what is already below code and build on it.

Even at the best lumber...your place is over-spanned.

1. Try the sistering method. Use 2x10s. And, I hope there is a stud or something other than spikes holding the joists up, next to the balloon framed studs. Rework the electrical.

2. Can you install another girder/beam like in this pic but at the other side of the room?
Then you could install hangers and 2x10s perpendicular to the 2x6s. This would also work for span.



3. If you just can't sister due to all the wires...and can't install an extra beam, use 2x10s directly on top of the 2x6s (parallel). Treat them as if they aren't even there (for load purposes, since they are not rated for floor system support.) I sure hope you can create a positive load path for each joist. i.e. put a stud under each joist.

Here, in WA state, having a floor system being completely held up by the lateral shear strength of nails is typically only seen when you hanger joists into a beam. That's specific nails at a specific number and pattern in a hanger.

3 or 4 nails from a 2x6 into the side of a stud would not pass here. (funny though, that the 100 yr old houses are still rock solid)

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TaitINC

thanks for the input guys. keep in mind this only going to be finished attic space. this house was built in the late 60's. the wall is not balloon framed, but i'm assuming the arch either drew it like this or someone messed up. it is a typical 2x4 @ 16 O.C. but the wall extends about 16" up from the existing ceiling. the ceiling joist are nailed to the sides of the studs @ 16" O.C. with a jack stud under each. the braces you see in the pic were put in place by us the stiffen up the ceiling joist a little. burby- not sure how this could be thought to support rafters? by the sounds of what you are saying, i would be better to spend the time to move the wires and sister w/ 2x10's. when walking on them now, they don't seem to be incredible weak, so i thought another 2x6 on top would be plenty. i will contact my engineer and see what he suggest after a sight visit.

spencer

A W Smith

if you stack the joists one on top of existing in the same direction and sister with plywood glued and nailed both sides you will be in effect building a truss, top joist will be compression member, bottom tension member. laying perpendicular you will be just adding dead load with no appreciable increase in strength.


edit to add

I hope those joists are resting on plates or blocked underneath, not just spiked to the studs of that knee wall.

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Burby

I think you will be very happy bringing in an Engineer, at least for your liability.
Finished attic space can be considered finished living space by another should present H/Os decide to sell. You know some people if they can squeeze in a hole they can and sometimes do turn this space into living space.. hahaha And that is some of what the codes try to prevent or if it is possible to be considered living space, it be built to code for living space in the even someone tries to do this without proper permitting.
For the span you have with present 2x6s that is what i was suggesting, to move wires and sister new joist, especially if height is an issue. I just don;t feel adding either way will offer strength and if floored in you have no idea how much weight others will store there and you know if flooring is down it will get loaded up over time.. lol
If those wires with the wire nuts are existing and with the house being built in the sixties, chances are unless been upgraded, is under for todays electrical use. So should be fairly easy to move then drill holes in the new lumber and install. But again that is from assumption with not being there.
Today's lumber for the most part is forced grown and or from newer generations of trees having less time to have grown before being cut down & milled leaving it to not be as strong as wood of yesterday, (virgin lumber). As well as finished lumber dimensions a bit less. And with lumber having a greater moister content allowed to be considered as kiln dry, it just don;t seem as strong as once was years ago.
Knee wall bracing, webbing, is installed to offer support for rafters from wind & loads and as well as to reduce spans of rafters for the loads above is why it should always be supported over bearing points. Once a c/j is connected to a rafter if not over a bearing point it will transfer loads & vibrations to the ceiling joist and each time a rafter moves so will the joist.
It looked like the braces were added after the initial construction, but not sure as when, but if no support below that is what it will doing.

Best to you

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Tom M

Spencer --Thats still balloned if there is no contiuous plate seperating that cavity.
If the braces you put in were angled to a suppoting wall below the ceiling then you would have created a purlin support for the roof. Although it was clever that you took the bounce out of ceiling below that connection probably should have been there in the original construction to assist in the collar/rafter tie. Because the roof pitch is likely a 10 or 12 there wasnt a big push on the outer walls so it lasted this long. I would think in the end its easier anyway.
It certainly couldnt hurt. What you have may be okay especially since the walking area of the proposed room will likely be over the center area but better to be safe. Let us know what you end up with.