Wall height on story n a half

[CjAl]

Can i increase wall height in the story and.a half to 12' and use a 8/12 roof pitch as you have the plans drawn? Or is that too tall? I will have a loft over 20' and increase it from.30 to either 32 or 34'.



I it wont work as drawn would it work with a ridge beam which would be supported on the ends and the middle all directly over footings?

Btw, i got the plans yesterday. Thanks

[John Raabe]

If you are doing a full loft (no side walls over 10' tall on the main floor) you can extend the sidewall studs to 12' and set the trusses on this taller wall.

Alternatively, for a more open ceiling in the loft, you could do a structural ridge beam and post it down to appropriately sized footings. This would allow you to frame the roof at your desired pitch with single rafters such as 2x12's.

[CjAl]

I am considering the ridge beam. I have some large oak logs cut into 17' lengths i can have milled. Did i mention my nose bleed on a step stool? Lol. I can work.on a 8/12. Not so much on a 12/12.


So you are.saying if i have 20' of loft and 14' openbover the great room( with rafter ties) that i can gp 12'? Only if i have full loftl

[John Raabe]

If you have a full length loft (no cathedral ceilings) then the loft wall can be balloon framed or platform framed - as long as the roof is framed with trusses - trusses put no outward pressure on the loft walls. It is unlikely you will be able to use rafters with a collar tie as this does not resolve all the outward pressures on that sidewall.

If you do a ridge beam (as opposed to a ridge board) then there will also be no outward forces on the sidewall.

The maximum height of an unsupported and non-engineered wall is 10'. This is what limits the wall height in a partial loft partial cathedral situation.

[CjAl]

Dont the double rafter ties every other rafter hold the walls together and limit their spreading?

Full loft isnt.an option. The open area over the.living area is my wifes one and only request. Happy wife, happy life. The doubled up rafter ties evedy four foot i can deal with for collar ties i would use metal straps over the top.



Another option i guess would be to use ten foot walls and use a roof that comes out ten feet past the side wall to the edge of a porch. Would make it 30' wide.so i could get my height with the lower pitch and would open up extra room in the loft. Only draw.back i.see is running the supports for a ridge beam down would put them between two footings. I would have a row of footing at 0,10', 20' and 30' but the ridge would be at the 15' mark. Could i run a heavy header to distribute the weight out 5' to each side to the support posts ove the footings?

This.is.the.type of roof but.its a bad pic

[John Raabe]

Latest codes do not allow rafter ties @ 48" o/c - now they have to be on every rafter pair. Every other rafter pair ties have been built into millions of existing homes.

Check to see what is required locally. In hurricane and tornado areas I'm sure it adds extra structural strength to the roof.

[CjAl]

There is no codes here. I am building in a lke community. Only thing they care about is they want to check the foundation, plumbing and electrical.

[redbird]

I have a question about the loft height too.  So I understand 10", does that mean that the walls in the loft are 2 feet and then the roof is over that?  My main concern is that I'm a bit claustrophobic and I personally think I might have an issue with a loft, especially if we made it a full length.  Every week I change my mind, one story, 1.5, 2 story back to 1.  I'm back on the 1.5 right now

Thanks in advance!

[John Raabe]

redbird:

If you do a full loft plan without the tall walls in an open cathedral main floor section then you can you can have higher sidewalls in the loft and set the trusses on that. A 4' or 5' sidewall gives a nice wide loft with lots of options for dormers and windows.

Here is a diagram I'm working on for such a loft that can be stick framed.

[Don_P]

John, the answer to "How Many Nails?" is in table R802.5.1(9)... but I wonder what happens if you design it out to the limit of prescriptive , 70 psf snow load, at which point engineering kicks in anyway. The widest acceptance for 1 plan.

For a 20' wide, framed 2' oc, 70 psf, rafter in lower third is 9@ 16d commons. A connection strength of 999 lbs Assuming they probably going to shoot it with 3"x.128" nails, 14 gun nails per end... 111lbs and 73 lbs/nail capacity respectively.


2x12 rafters work at 70 psf. A 2x8 ceiling joist works.

Hmm, you could make an interactive PDF plan. Details like your comment "Strap @ Peak" could be a clickable link that would take the builder to the code citation or table needed. It could also pop up a detail drawing or photo of the detail properly executed.

[John Raabe]

Thanks for helping out with that section design, Don. Good ideas all.

[drbuilder]

redbird:

If you do a full loft plan without the tall walls in an open cathedral main floor section then you can you can have higher sidewalls in the loft and set the trusses on that. A 4' or 5' sidewall gives a nice wide loft with lots of options for dormers and windows.

Here is a diagram I'm working on for such a loft that can be stick framed.

John, Am I interpreting your statement correctly that this modification (a 4' or 5' kneewall) can be used with your site-built trusses?  I ask because your diagram includes a ridge board.  Also, is the "hinge joint" effect not an issue with this design?  In past discussions on similar designs you (and others) seemed to be opposed to such designs.

[Don_P]

IF the rafter ties are in the lower third of roof height and the connection is made according to the heeljoint table (read the footnotes) THEN a ridgeboard is fine. IF each pair of rafters cannot be tied in the lower third of roof height THEN a ridgebeam is needed. So yes if you take John's gusseted rafter pairs, what you are calling trusses, set them on a 5' kneewall and drop the rafter tie to the lower third of roof height, it works correctly. The code and engineering violation occurs when the kneewall height requires that the rafter tie be raised above the lower third of roof height for headroom. When that happens you need a ridgebeam and the ties are then not needed. If the rafters hang from a stiff ridge, assuming the ridge cannot sag, the rafters can not shove the walls outward. The trick is to make a rigid triangle or hang the rafters from a stiff ridge.

This is what is happening when untied or poorly tied rafters sit on a balloon framed kneewall and there is no ridgebeam;




Now think about it, if there were a string across the rafter feet the rigid triangle would restrain the rafter thrust. That tie can creep up 1/3 of the roof height and the forces can still be safely restrained. If the tie is raised above that the connection forces get out of hand and the rafter gets into one of those combined loading situations we were just talking about in the stud thread.

[drbuilder]

Understood.  Thanks.

[Steve_B]

Very closely related to this open post here....

Just so I understand this correctly, if I were to take the 20x30 1.5 plan and extend it to 20x40 with a loft on each end of the house above first floor rooms with a 20x20 open living area in the middle of the house .... I can make the loft area with a 4' kneewall as long as I use engineered trusses? Is anything else needed to safely to build this design?

I ask as this is very close to what he is asking here

Steve

[MountainDon]

One thing that is missing in your question or scenario, Steve, is what about the open area (20x20) in the middle. What will the roof be like in that area? Will it utilize engineered trusses, like a scissors truss that will provide a vaulted appearance on the interior? Or rafters? If rafters then we need either rafter ties in some form, from side to side, at the wall top or in the lower third of the rafter, OR a ridge beam in that section with the requisite column supports down to the foundation/earth.

[Don_P]

The roof system could be stick framed, the ceiling would be in the lower third of roof height at just over 7' so the roof is considered tied and there is adequate headroom. It might be counterintuitive but as you raise the wall height from this level the rafter tie can be effectively lower and does its' job better.


But there is a problem that we got into on the 2x4 vs 2x6 thread. The 13' unbraced wall studs in the center are bearing the roof load so are limited to 10' without engineering. Someone made a point that if a beam crossed that area to support the roof the wall would not be loadbearing and longer studs would be allowed. It is getting into what should probably be engineered with that approach as well. The area of that unbraced wall in a wind can put serious stress on the connections of the wall to the frame. The detailing there would need careful thought. A catwalk/ plant shelf/horizontal beam at floor level along the walls connecting the lofts would act as lateral bracing thus cutting the effective stud height to 8'. Just another thought.

[Steve_B]

The roof system could be stick framed, the ceiling would be in the lower third of roof height at just over 7' so the roof is considered tied and there is adequate headroom. It might be counterintuitive but as you raise the wall height from this level the rafter tie can be effectively lower and does its' job better.


But there is a problem that we got into on the 2x4 vs 2x6 thread. The 13' unbraced wall studs in the center are bearing the roof load so are limited to 10' without engineering. Someone made a point that if a beam crossed that area to support the roof the wall would not be loadbearing and longer studs would be allowed. It is getting into what should probably be engineered with that approach as well. The area of that unbraced wall in a wind can put serious stress on the connections of the wall to the frame. The detailing there would need careful thought. A catwalk/ plant shelf/horizontal beam at floor level along the walls connecting the lofts would act as lateral bracing thus cutting the effective stud height to 8'. Just another thought.

Don... your drawing is pretty much dead on there!!!

I went to Builders First Source just yesterday to price out some materials to start the build... when I asked about roof trusses he actually directed me down the hall to the engineer in charge of designing them.... I explained my house concept with dual opposing lofts and the large open living area in the middle being the 20x20 space, and this is what he came p with for an idea

There would be two different engineered trusses for the house....

the first set being a scissor design which will run 2' OC above both loft areas giving the most headroom possible

the second set being more of a vaulted ceiling truss running 2' OC across the living area made most of 2x6 #2 or better

The vaulted trusses seemed to have the cross bracing about mid height in the trus or so.... working on the theory that the firsst floor is 8' and the secnd floor knee wall is 4'.... he said the vaulted part of those center trusses would be 16' above the floor level.... now thinking the stock plan said the total height of house with 12 on 12 pitch is 22' tall...

A few questions....

Going by what was just typed by me, does this sound feasible and safe and up to code?

Would it just be easier to just build 12' 2x6 first floor walls and set the first floor ceiling height at or a hair below 8' tall which would effectively give me a pseudo 4' high knee wall height in the loft to set the trusses on?


What I need is the easiest way to build this house with the most "livable" space in the loft BUT keeping safety just as important with this desire.... I will be doing as much labor as I can to build the house so the easiest way and safest way possible is my main desire!!!

BTW... I do like the plant shelf idea across the living area and adding lateral support as well

Your thoughts?

Steve

[Don_P]

I came up with a 13' tall wall,8'+1'+4'. I think you're missing the floor thickness, I figured it would be 1', 2x12@11.25" + 3/4" ply.  In my drawing I got the tie to land in the lower third of roof height @ just over 7' off the floor, 7' is min code height, I do prefer 8' of headroom. The engineered solution allowed him to raise the tie with materials and connections engineered for that situation, which is a plus. I really can't follow the rest of the description well enough without some pics.

The unbraced tall wall sections plus the mean roof height in the middle of the building give an effective wind area of around 17x20' and the wind load most often used for seat of the pants guesses is 20 psf pushing and pulling on the wall. So for a seat of the pants number about 7,000 lbs pushing on that area in a gale, 7k pushing in on one side and sucking the wall out with 7k on the other side. Since we know wood can take that 3 second gust much better than the same load pushing continuously for 10 years the material strength is allowed to be bumped up 1.6 times. For a WAG I'm going to say the horizontal beam along the walls is taking half the wind load or 3500 lbs uniformly distributed along its' 20' length from loft to loft. A single 14" deep LVL laying flat, plant shelf fashion attached to the studs and especially at each end back to the loft floors, they are the "posts" if you think about how this is resisting the wind, would work. I'm no engineer, you just saw a string of assumptions take it for what it's worth, but something along those lines across each side would work. Building a wider sheathed catwalk to connect the lofts along one side could replace one of those plant shelves.

[Steve_B]

Don... with the two different sets of trusses I spoke about.... the 20x30 1.5 plans from the site here call for 10' walls

I have done much much reading on the site here and there are different answers for this question I am about to ask

If I have the 20x30 1.5 plan from the site here, can I substitute the plan's 10' walls for 12' walls and keep the first floor height the same and add that additional 2' height to the loft area and use my engineered trusses and throw in the two "plant shelves" you spoke of to add lateral support?

Is there any downfall or safety concerns in just adding 2' of height to the plan's walls?

I would like to somewhat follow the plan, and just modify it by adding more length to the house and more height to the house...

[Don_P]

If the rafters do not thrust horizontally against the kneewalls then they can be 0' to 10' tall, a truss does not thrust against the walls. There should be perpendicular brace walls <25' apart inside the building, usually not a problem. Something along the lines of the plant shelf idea to provide lateral support to studs over 10' tall will work. There's nothing wrong with this idea, its just a short second story. Where we have run into trouble in the past is when there is a kneewall and rafters that are thrusting against the kneewalls. Your trusses solve that problem.

[Steve_B]

Don...

Almost forgot I had a scanner here at home.... here are the printouts for the trusses and the I joists I had mocked up for the build that we are talking about here

Could you kindly check them and see if they are suitable, safe, up to code, and feasible?

[Don_P]

Complaints on a quick first pass thru, if you look at the deflections for both, under full load the horizontal deflection is about 13/16" and reading the reactions that amount of motion is accompanied by >300 lbs of horizontal thrust at each truss. I misspoke, these scissors do thrust a fair amount. It appears W1, one of the internaal webs is not shown on the drawing, they run from 4-9 and 4-8, the labels are there but there should be 2x4's drawn.

alternatives as I see it
1) satisfy yourself that this is acceptable... I'd want an engineer to say that if I went that route
2)Have the truss co beef the design and cut down on the horizontal deflection and reaction
3)The loft truss level ceiling chord is about 10" higher than if you were to stick frame this to code. In other words is allows you to lower the kneewalls (and the height of the house) 10" to get the same headroom in the loft. If saving 10" isn't a big deal then a stick framed roof would work.
4) But that option won't get you a vaulted greatroom, posts at gable walls and loft ends with beams at the ridge would allow the rafters to hang from the peak, no thrust and no ties needed. You could stick frame the lofts and use a ridgebeam over the living room.

I have a personal thing with 19.2" centers, I prefer 16"oc and think it washes out in plywood cuts.

Just for educational, look at the forces in the members, these are the forces the connection plates are resisting. For those thinking of building a homemade truss or maybe thinking they have built an adequate truss, notice that with those raised ties some of the connections are resisting over a ton of force at full load. Plywood and an 8d is good for about 75 lbs off the top of my head. Don't skimp and the members might need to be upsized to hold enough nails. We've had folks call some creations trusses that are kinda lightly connected looking.
On a wall thread I mentioned that wood can take wind loads better than long term loads and we are allowed to adjust the allowable loads 1.6 times for those loads, you'll see that DOL, duration of load, increase for the wood and the truss plates.

[Steve_B]

My scanner may not be the best in the world, hence the missing lines not showing up

I would say that number 2 is my choice.... go to the truss company and have them beef up those trusses.... I am looking for more of the plug and play feel with just having trusses delivered and not having to build a rood on site myself, as this will be mainly done by me and a friend

I will repost the beefed up truss sheets when I get them..... assuming they beef them up, you see no issues with them sitting on a platform framed 3' to 4' knee wall atop a 8' high first floor?

[Don_P]

Sure, if they can limit the horizontal deflection to keep it within limits... less than 1/180th of wall height. Being conservative 1/180th of 36" is about 3/16" deflection horizontally from the trusses. I think balloon framing it would be better.