# Attaching bottom plate to subfloor



## bduncan118 (Jan 16, 2013)

Hey folks. I just stumbled on something I haven't thought of yet. I am building a room in my attic. On one wall there is no floor joist under where the wall will be. Do I just nail the bottom plate into the subfloor? Thanks for your time!


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## kaschmid3 (Jan 28, 2013)

I assume its too late to put blocking between joists to be able to nail bottom plate to


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## bduncan118 (Jan 16, 2013)

Unfortunately yes. The subfloor was already down when I bought the house. Essentially what I'm doing is framing 4 walls on an existing sub floor in a large space.


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## kaschmid3 (Jan 28, 2013)

Not structural u will be fine if u r worried about moving just put little bit of glue under but not necessary


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## Gary in WA (Mar 11, 2009)

Do the walls tie to the rafters?

Gary


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## hand drive (Apr 21, 2012)

placing any type of wall between joists and onto sub flooring only is asking for a sagged floor under the wall in the future. how tall the wall is and how thick the sub flooring will determine the rate of sag. subflooring can be cut and removed to allow access for blocking and then the subfloor can be put back down


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## stadry (Jun 20, 2009)

since the sub-floor's nailed to the floor joists, i wouldn't worry,,, just did a room over the garage which was about the same,,, 4' kneewall & i screw'd the short vert 2x4 studs into the side of the roof trusses,,, finished off great & have no fat friends under 4'' tall so no problemo :laughing:

use long drywall screws &, if you want overkill, some const adhesive under the plate ( i didn't )


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## md2lgyk (Jan 6, 2009)

I would use construction screws, not drywall screws.


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## stadry (Jun 20, 2009)

uncertain what ' construction screws ' are but i use what on the shelf :yes: then again, never said i was a carpenter :no: another advantage of being raised on a farm - baling wire & chewing gum now updated to version 2.0 - duck tape :laughing:


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## joecaption (Nov 30, 2011)

Sheetrock screws are to brittle for framing, infact no scews should be used in any framing, only nails.


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## stadry (Jun 20, 2009)

just to hold a btm plate ? c'mon, joe - i wanted to finish this part w/o having to run to the nearest apron/vest store,,,,,, scheeeeschhh, there's lateral force on this sole plate,,, IF it makes you feel better, i used lead-shield drop-in's for btm plate on the bsmt exercise room's wall,,, i can see you never had to finish anything w/my bride, nagzilla, hanging over your shoulder :laughing:

i'm not taking any more abuse today ! :no:


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## hand drive (Apr 21, 2012)

itsreallyconc said:


> just to hold a btm plate ? c'mon, joe - i wanted to finish this part w/o having to run to the nearest apron/vest store,,,,,, scheeeeschhh,there's lateral force on this sole plate,,, IF it makes you feel better, i used lead-shield drop-in's for btm plate on the bsmt exercise room's wall,,, i can see you never had to finish anything w/my bride, nagzilla, hanging over your shoulder :laughing:
> 
> i'm not taking any more abuse today ! :no:



at the orange big box store spax has some construction screws made that work like cabinet screws with shear strength. an exterior decking screw will also work sometimes for framing applications but will still snap if sheared... can't beat the good old hand driven nail in certain apps, and even nail guns if you got em...


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## bduncan118 (Jan 16, 2013)

Gary,
The walls do not tie into anything up there. They will be 4 independent walls (with a ceiling of course). The rafters are above where the room will be. The subfloor itself is 3/4" T&G that is glued and nailed. I will be screwing it down before the carpet goes down. 

Where u see the bottom plate on the right of this picture is where the wall will be going. It is 3 1/2'' off the exterior wall.


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## kevinb70 (May 5, 2008)

hand drive said:


> placing any type of wall between joists and onto sub flooring only is asking for a sagged floor under the wall in the future. how tall the wall is and how thick the sub flooring will determine the rate of sag. subflooring can be cut and removed to allow access for blocking and then the subfloor can be put back down


I would go with this advice ... and 16D nails which is probably what you used to build the stud wall.


I myself and quite familiar with the bailing wire method we have here down South, grew up in rural areas myself, but if you ever want to sell that house without having to tear out those rooms, I would make sure you do it to code. I think each space in an unfinished basement needs at least 1 electrical outlet, I would research that and to make sure something similar doesn't apply to unfinished rooms in an attic.


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## bduncan118 (Jan 16, 2013)

The room is definitely going to be up to code. I pulled permits and it will be inspected. Unfortunately the code doesn't specify this situation. I can put 300+ pounds on the floor and jump and down and the floor is solid.


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## joecaption (Nov 30, 2011)

bdunkin please take the time to add your location to your profile.
Main reason is I see you did not add to the rafters so there's no way to fit much insulation and the needed baffles.
http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table
There also need a be a window that meets egress code.


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## bduncan118 (Jan 16, 2013)

Southeast Alabama. 5/0 window is going in existing exterior wall on Tuesday for egress. I will frame a sill around the window on the new wall. There is already a room on the second floor so I have full size steps for second monastery of egress.


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## kaschmid3 (Jan 28, 2013)

Why wouldn't u just use the exterior wall itself with insulation.( if u just need thicker insulation add whatever thickness u need an screw into the exterior studs)


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## robertcdf (Nov 12, 2005)

bduncan118 said:


> Gary,
> The walls do not tie into anything up there. They will be 4 independent walls (with a ceiling of course). The rafters are above where the room will be. The subfloor itself is 3/4" T&G that is glued and nailed. I will be screwing it down before the carpet goes down.
> 
> Where u see the bottom plate on the right of this picture is where the wall will be going. It is 3 1/2'' off the exterior wall.


The only way the subfloor would sag under the weight of that wall would be if the subfloor was 1/8" sheathing. Seeing as how you've said you have 3/4" you'll be fine without blocking, just add construction adhesive if you want to make it a little stronger, also criss cross your nailing pattern to hold the bottom plate in the subfloor.


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## bduncan118 (Jan 16, 2013)

First off thanks everyone for your replies! The reason I am not using the existing exterior wall is the fact that it is structural and I don't want to cut all the studs to put a header in. And the fact that the wall possibly could not be straight. There is a cross brace (2×4) against all the studs at 7' that would have to move. I would rather not mess with anything structural. That is why I'm having a contractor put in the egress window.


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## md2lgyk (Jan 6, 2009)

itsreallyconc said:


> uncertain what ' construction screws ' are but i use what on the shelf :yes: then again, never said i was a carpenter :no: another advantage of being raised on a farm - baling wire & chewing gum now updated to version 2.0 - duck tape :laughing:


Construction screws look like drywall screws but are much stronger. The head on drywall screws is specially shaped on the underside so it will dimple the drywall, and will often snap off if you screw them into wood too fast. Drywall screws are always black (in my experience anyway), while construction screws are usually gray, brass-looking, and sometimes green. Then there are deck screws, which are coated (or made of stainless steel) to prevent the chemicals in pressure treated lumber from eating them away.

Check the fastener aisle next time you're in a big box store. Each of these three types of screws usually come in different-colored boxes.


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## hand drive (Apr 21, 2012)

bduncan118 said:


> Gary,
> The walls do not tie into anything up there. They will be 4 independent walls (with a ceiling of course). The rafters are above where the room will be. The subfloor itself is 3/4" T&G that is glued and nailed. I will be screwing it down before the carpet goes down.
> 
> Where u see the bottom plate on the right of this picture is where the wall will be going. It is 3 1/2'' off the exterior wall.



looks like you are good to go with setting the walls onto the sub floor, the only questionable wall would be the one on the left in pic as it goes parallel with joists though the joists might be going 12" centers which helps a lot. what type of attachment detail is at the top of wall where it is against the roof rafters? looks like the very back corner of plate bumps rafter?? also, you will need access into the attic area somewhere along the knee walls forming the rooms in the attic, attic access weather sealed door.


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## bduncan118 (Jan 16, 2013)

The walls won't touch the rafters. That back wall is where the roof slope comes down and there is about 8" of clearance from the top of the wall. The left wall is actually on a floor joist so nailing won't be an issue there. To the left of the left wall will be a storage room with a full size door going into it.


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## kaschmid3 (Jan 28, 2013)

That exterior wall on the right is a gable wall only load bearing points are 2 corners and possibly under the ridge, if u r putting a window there u gave to put header anyway. 2nd if the new wall is separated from the exterior u r not going to be up to fire code


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## bduncan118 (Jan 16, 2013)

I'm very curious about not being up to fire code. Can you explain a little further? How would I put a header in the existing wall If that is what i need to do?


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## kaschmid3 (Jan 28, 2013)

Fire code if any fire were to happen in a bay u wsnt to prevent from getting to another bay if they r not connected you would have direct flow all a fire needs to grow is air


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## kaschmid3 (Jan 28, 2013)

I do it all the time on existing houses. Determine height of window header cut studs to line with saw cut a little bigger than header height ways grind or saw all nails insert header put in jacks. Measure down from bottom of header the tough opening size for window add 3 in cut remainder of 2x4 in the way insert 2 sills and 2 crips on jacks under sill ready for window. Everything done from inside


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## bduncan118 (Jan 16, 2013)

My plans are to insulate that cavity. There's got to be a way around that. Any thoughts on connecting the 2?


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## kaschmid3 (Jan 28, 2013)

Connect 2 x to your exterior studs and bottom, top plates with screws


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## bduncan118 (Jan 16, 2013)

I am thinking how would I put a top plate in the existing wall for the ceiling joists to attach to. The ceiling joists will run perpendicular to that wall due to the span of the room.


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## kaschmid3 (Jan 28, 2013)

Or use 2x 6 and sister next to studs by nailing together


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## kaschmid3 (Jan 28, 2013)

I would run them say way as rafters they would double up as collar ties


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## bduncan118 (Jan 16, 2013)

Thank you so much for the help. But I'm lost on your last post. Are you saying run the ceiling joist the same way as the roof rafters? The reason I was doing this the other way was the span of the room is 21ft long by 14 wide at the biggest part. The room is L shaped. The long wall is 21ft


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## bduncan118 (Jan 16, 2013)

kaschmid3 said:


> Or use 2x 6 and sister next to studs by nailing together


Do you mean take a 2 x 6 and connect both walls together? That seems the easiest way to make it so its one cavity.


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## kaschmid3 (Jan 28, 2013)

U could always do non conventional top plates 2 x nailed to exterior wall with a 3 3/8 rip of 1/2 in plywood then another 2 x nailed to that so your top plates would be 3 1/2 by 3 1/2


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## kaschmid3 (Jan 28, 2013)

Yes connect the rafters on top of your top plates.


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## kaschmid3 (Jan 28, 2013)

Ps I want your attic


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## bduncan118 (Jan 16, 2013)

The rafters are 10 ft or so above where the top plate will be. This is a video of the attic. I think it starts at 3:20 or so https://www.youtube.com/watch?v=XaFkSU1Rh9Y&feature=youtube_gdata_player


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## kaschmid3 (Jan 28, 2013)

Those little 2x up top are the collar ties connecting the roof rafters. U would want your new ceiling joists to connect the roof rafters at the height of your ceiling probably want 2x 6 since a long span. where it tees off just double up your furthest one I would even make those 2 a 2x8 and use joist hangers for the ones that butt into it


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## kaschmid3 (Jan 28, 2013)

That one 2x4 on an angle connecting ridge to gable wall is to Keep everything ridged so to replace that after ceiling joists r in put 2x4 on flat nailed into ceiling joist and butt into sheathing next to stud on gable wall and nail into stud


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## bduncan118 (Jan 16, 2013)

That 2x4 is high enough to accommodate 8' walls.


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## bduncan118 (Jan 16, 2013)

Im still thinking that I don't need to tie this room into the existing structure. Just build 4 independent walls on the subfloor. The ceiling joists of the new room will tie in on the new double top plates of the walls I am building. This is how the other room is that is already on the second story, however it is tied into the external wall on one side.


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## kaschmid3 (Jan 28, 2013)

Ok good luck. Ps nice size house and attic I'm a little jealous


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## bduncan118 (Jan 16, 2013)

Thanks so much for the help! I moved in this house in 2010. The builder built the upstairs so you could build another room if you want to. The flooring is 2x10 16" on center with a span no bigger than 16' . This was done when the house was built. I am turning the room into a dedicated home theatre. I've got 2 walls up so 15% done with framing. Understanding everything is getting a bit overwhelming. I've researched the hell out of this project and just when I think I've got it all planned something else comes up that I haven't thought of yet. . . . Like not having a floor joist to nail the long well into, or the fire code. I am learning as I go.
Stage 2 is building a half bathroom and more storage to the right of the top of the steps. I may let a contractor do that part! 

Thanks again for the help.


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## kaschmid3 (Jan 28, 2013)

No prob anytime it's what I do for a living and I enjoy it. I'm always willing to help someone who wants to learn. With this trade it's not about what I can build but how u can fix what u messed up( hopefully u only make that mistake once. I get to build custom high end housed on jersey shore. And some really old houses so I'm always learning. As i said good luck


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## hand drive (Apr 21, 2012)

if you put the new joists onto the long wall you build half of the ceiling weight is going to be on that wall (the other half on the other wall) and you are just sitting on one floor joist with the wall. usually a double joist or something like that is used in the floor framing under the walls to hold up the walls and the ceiling weight. if possible you will be better off tying new ceiling joists to the rafters and making the joists 16'. there will be a roof slope on the ceiling past your knee walls because of the span across the room and the fact that the ceiling joists are limited to 16' and cannot cover the entire span (top of knee wall to top of knee wall). you will want to fir down the rafters where they are part of the ceiling above the knee walls for insulation and ventilation...


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## bduncan118 (Jan 16, 2013)

hand drive said:


> if you put the new joists onto the long wall you build half of the ceiling weight is going to be on that wall (the other half on the other wall) and you are just sitting on one floor joist with the wall. usually a double joist or something like that is used in the floor framing under the walls to hold up the walls and the ceiling weight. if possible you will be better off tying new ceiling joists to the rafters and making the joists 16'. there will be a roof slope on the ceiling past your knee walls because of the span across the room and the fact that the ceiling joists are limited to 16' and cannot cover the entire span (top of knee wall to top of knee wall). you will want to fir down the rafters where they are part of the ceiling above the knee walls for insulation and ventilation...


This space is big enough to not have to tie anything into the roof. The roof comes down about 5 ft in the back of the back wall. I can't go back there do to a tray ceiling downstairs and plumbing ventalation.


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## hand drive (Apr 21, 2012)

bduncan118 said:


> This space is big enough to not have to tie anything into the roof. The roof comes down about 5 ft in the back of the back wall. I can't go back there do to a tray ceiling downstairs and plumbing ventalation.



where the long wall sits are there other walls right below it in the main part of the house. in other words, does the joist you are sitting on have something under it or is it spanning long distances and such?


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## bduncan118 (Jan 16, 2013)

Yes there are multiple rooms below the joist. Bathroom closet and bedroom underneath. The biggest span will be maybe 10'


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## hand drive (Apr 21, 2012)

bduncan118 said:


> Yes there are multiple rooms below the joist. Bathroom closet and bedroom underneath. The biggest span will be maybe 10'



directly below the joist is the only exact spot I'm interested to know about as it will hold the wall weight placed from above...

I would cut up the subflooring in that area and establish some wall bearing attributes to the space...


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## bduncan118 (Jan 16, 2013)

I am working on scrapping the new wall and using the existing external wall. I started a new thread wanting to know how to tie into the old wall.


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## hand drive (Apr 21, 2012)

that still does not help the other side of the new ceiling where it sits on the wall out in the middle(edge) of the room. tie-ing into old wall is the easiest part, establishing a linear running load point out in the floor system to hold everything up is the hard part and you will get more answers keeping your questions in this thread as opposed to starting new ones...


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## bduncan118 (Jan 16, 2013)

hand drive said:


> that still does not help the other side of the new ceiling where it sits on the wall out in the middle(edge) of the room. tie-ing into old wall is the easiest part, establishing a linear running load point out in the floor system to hold everything up is the hard part and you will get more answers keeping your questions in this thread as opposed to starting new ones...


Thanks for the advice. So Assuming I am using the existing wall for the right side, the left side will sit directly on a floor joist for 11'. The room is going to be shaped like an L. The rest of the room will be 5 ft wider than the first part for 10 ft (21' length total). Attached is a sketch of the plan. 
Now is it better to run the new ceiling joists parallel to the floor joists? The span would be 21' at the longest, 10 ft at the shortest.


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## hand drive (Apr 21, 2012)

you would have a much easier go at it framing the new ceiling joists parallel with the floor system. is there any way to go up in ceiling height to accommodate a 16' joists that went roof rafter to roof rafter? you are at 21' length now so 2.5' either side the 16's would be short to cover the span. you could even run the 16' joists past the 5' room area and tie all of your wall top plates into the joists thereby leaving no load points out in the current floor system

looking at your vid it looks like what I posted might work, you have the long hip ridge to the right of the camera that looks to come into the room enough to work with the new cross joists


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## bduncan118 (Jan 16, 2013)

Thanks for the input. Why the 16 ft span?


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## hand drive (Apr 21, 2012)

certainly, my pleasure. up to 16' is standard on the size lumber available , if you want longer give your lumber supply house a call and order longer joists.


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## bduncan118 (Jan 16, 2013)

Doing a span at 16' would put the ceilings right at 10' 6'' at the top. The shape would be similar to what is below. 

The roof rafters are 24" spaced out. I don't know if that matters. 

I am thinking this is not the way to go as I have already bought most of the lumber.

I am going to use the existing wall. If I run the ceiling joists parallel to the floor joists I will need 10- 2 X 8 X 24's for the big span. The weight of the ceiling will be spread out between all the floor joists (Which are 2X10's 16" on center with a span no greater than 16' ). Attached is the plan of my house. The


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## hand drive (Apr 21, 2012)

bduncan118 said:


> Doing a span at 16' would put the ceilings right at 10' 6'' at the top. The shape would be similar to what is below.
> 
> The roof rafters are 24" spaced out. I don't know if that matters.
> 
> ...


thanks for the pic of the layout. do you have the 2 nd floor ceiling framing plan (attic floor)showing the framing detail (beams,joist layout etc...)of where you want to build the load bearing wall? that is a long span for the 2nd floor ceiling joists so there must be a beam in there mid span to break the joists up. do you have the details of that?

you building a load bearing wall on a single joist is not ideal in any way and more planning is needed.


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## bduncan118 (Jan 16, 2013)

I don't. Looking at the house at the way things lay out the new room walls will start at about 6" past the master bedroom wall. It is most definitely load bearing as the roof support land there. There is a beam going from the garage across the hallway near the entrance. I can not tell if it extends to the other side of the house as the corner near the second bathroom is right there. The ceilings in the living room and the hall are 10 ft. All other rooms are 8 ft. So there's no way of telling if the beam goes the span of the house (without cutting up the subfloor of course). 
Ideally I would want the load bearing walls of the new structure to sit on top of the walls fr the first floor right? I don't know if that is possible. I stopped framing and am deciding how to proceed. I reached out to my builder for advice and he said he can't give me advice. He can only tell me how he built the flooring. I am going to reach out to an engineer I know before I touch anything else. But any input is appreciated from you guys!


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## hand drive (Apr 21, 2012)

great idea! get someone there who can establish load points for your wall and you are good to go. I can say though that landing your wall on walls below it in most cases will solve the problem and support your wall. just need to work out the transference of the weight correctly throughout the structure. gravity can be your friend


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## bduncan118 (Jan 16, 2013)

Yeah an engineer is most definitely my best choice right now. The flooring was built for future construction I just didn't think about where the walls will sit. Depending on what the engineer says I have 2 options. 

1. Land the new walls on a load bearing point.
2. Tie the ceilingceiling joists into the roof rafters. 

#1 when likely change the room dimensions which I don't want to do.
#2 will add a lot of money to the project.


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