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RazrRebel
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# Posted: 20 Apr 2015 17:40
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Hey guys I have got my 16 x 24 floor joists done. These are 2x6 on 16 of. I have a question about the loft design. My wife and I were wanting almost a full loft. My plans were to do ten foot walls with 2 x 4 on 16 in centers. The loft would be at 8' leaving a 2' section that the rafters would sit on. The floor joists for the loft would be 2 x 8. I am going to attach a 2x4 ledger board to the studs for the floor joists to rest on, and nail them into each stud also. I have a brother in law who says 16' is too long of a span. I went to Lowes and looked at their two story 16x16 storage building and it's almost exactly as I have planned. The only difference is their second story is on top of the wall. He says I have to have a beam and a post holding everything up. We want our floorplan open with no supports in the middle of the room. Will I be allright with my plan? Also I don't have to have plans or inspections or approval from anybody. My cabin is on a ridge on my property, no power, no utilities, no road. Everything is hauled up on my Polaris Ranger.
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Steve_S
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# Posted: 20 Apr 2015 17:58
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I'm doing almost similar (16x20 cabin) but the walls are to be 2x6x10 @ 24oc. Local Building Inspector (a really helpful & cool guy) suggested I use a 2x6 Ledger on each side and to run the joists to the outside edge of the wall's 2x6 and anchor that in as well. Means futsing with the foam board insulation but that's ok. For the joists I'll be using 2x8 as well.
I'm only going 1/2 the building with loft and the other half open to above, it will have a partition so I can support the loft in the centre for the most part.
Big Q in my mind (percolating full time now) is if I want to run a "ring" all around the inside of the cabin with this ledger board & if I should use rough cut, live edge 2x6 for a little touch of detail. I've seen a cabin done that way and it looked pretty sharp but that also had drywall which had to be worked for the wavy edges... I envision some drunken sailor talk resulting from that effort ....
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Just
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# Posted: 20 Apr 2015 19:26
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No expert but i'm with the brother in law .
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MtnDon
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# Posted: 20 Apr 2015 20:12
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Loft floor loads can be calculated lower than a main living space floor. But even using 30 PSF even the best grade of 2x8 won't pass. The 16 foot span could be done with some grades of 2x10. A lot depends on what species and grades you can readily get or afford.
But if you plan on using regular rafters with a ridge board those 2 foot high side walls can be a problem. The rafters exert a horizontal outwards force. If you notch the 2x4 wall studs to accept a 2x ledger that does not leave much material to resist the outwards bending. If you over cut the notches even a little that provides a perfect place for a split to start. These are some of the reasons you won't find 2 foot wall extensions like that approved by any building code official that actually goes by the book. The only real solution that retains full strength of the wall studs is to use a ridge beam to carry one half the roof load down to the foundation and earth. Or do away with the short upper walls and tie the wall tops together with the loft floor / main floor ceiling joists right on the wall top plates. That does take away from the headroom in the loft though. Using a ridge beam would permit the use of even taller side walls and increase the usable space. Doing that might require increasing the loft joists to 2x12 as with the increased headroom comes a more or less natural tendency to use the upper floor for more things and end up with greater floor loads.
I've heard, second hand but from a reliable source, of a VA build that received a stop work order and then a dismantle order, all because it was not up to the IRC code that covers the state. Be careful there.
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RazrRebel
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# Posted: 20 Apr 2015 21:04
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Would the steepness of the roof make a difference? We really want plenty of headroom. So it's not the loft as much as its the rafters?
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Just
Member
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# Posted: 20 Apr 2015 21:47
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my solution
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RazrRebel
Member
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# Posted: 21 Apr 2015 07:32
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Ok, all this brings up one more question. If I can't have a knee wall off of the original studs, how about a second story. This raises the question for me. I really don't know so I'll ask. What size constitutes a wall. If the loft joists have to sit on the top plate of the wall. How tall does the wall have to be? I've seen people mention a short wall and everybody says no it would be weak. Wouldn't there be more leverage from a tall wall. I'm not going to build a second story ,but apparently you have to have a wall to sit the rafters on, so is a short wall still a wall or is there a minimum height? I'm not arguing or anything just trying to figure this out.
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MtnDon
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# Posted: 21 Apr 2015 09:51 - Edited by: MtnDon
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Quoting: RazrRebel Wouldn't there be more leverage from a tall wall.
Yes. That is why the ceiling joists (rafter ties) are supposed to connect across the wall tops... to restrain them.
Quoting: RazrRebel apparently you have to have a wall to sit the rafters on
... and the wall tops need to be ties together from rafter tail to rafter tail, across the width. OR a ridge beam is needed along with support columns.
Note that you can also use rafter ties up 1/3 the height.
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RazrRebel
Member
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# Posted: 21 Apr 2015 14:57
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So how tall would the wall have to be for your rafters to sit on? 2', 4', 6, 8'?
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rwoods
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# Posted: 21 Apr 2015 16:35
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I once had an old house that had 12ft balloon walls. when we redid the upstairs i nailed a 2x10 to the face of the studs then hung 2x10 floor joist on hangers off of it .the span was 14 ft and that passed inspection. I think as long as you don't cut into your studs with your ledger and upgrade to 2x10 joist you would be okay
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rwoods
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# Posted: 21 Apr 2015 16:38
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is what you are calling the ledger a bean that you are setting the joist on
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RazrRebel
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# Posted: 21 Apr 2015 16:45
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I figured if you did use the ledger then all the weight would be placed on the fastener. I thought of that first, and realize that would be wrong. I'm going to build a 10' wall and run my 2x8x16 floor joists all the way in against the wall studs. I'll fasten them to the studs, but I'm also going to put another 2x4 against the wall stud for the joist to rest upon. I'll still have the rafters on the top wall plate, and I'll have the floor joists resting securely on the foundation. A few extra 2x4 will be all I'll need. What do you guys think?
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MtnDon
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# Posted: 21 Apr 2015 18:11
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Quoting: RazrRebel I figured if you did use the ledger then all the weight would be placed on the fastener. I thought of that first, and realize that would be wrong.
Correct. Just nailing a ledger to the stud places all the load on the fasteners. Not good, not allowed by code.
2x4 jack studs supporting the loft joists will provide a solid support, though also take away from the R-value of the wall.
Follow this link. Scroll down to FIGURE R602.3(1) TYPICAL WALL, FLOOR AND ROOF FRAMING.
There you can see that a 1x4 let into the wall stud is sufficient to support the floor joists when the joists are also face nailed to each wall stud.
The illustration shows a full second story with rafters and ceiling joists.
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Wilbour
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# Posted: 21 Apr 2015 18:46
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Quoting: MtnDon 2x4 jack studs supporting the loft joists will provide a solid support, though also take away from the R-value of the wall.
That's exactly what I did to give me one more foot of headroom in the crawl loft
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RazrRebel
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# Posted: 21 Apr 2015 18:53
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Ok, if I didn't go the route with the jack studs, I'm still wondering how short of a wall could be used, like a second story but not full size. Am I correct in thinking an eight foot wall is standard, and if so a four foot wall would end up making a story and a half, and a two foot wall would be a story and a quarter?
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Don_P
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# Posted: 21 Apr 2015 20:01
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A wall is a wall, no matter the height. Preventing the wall tops from spreading out as the rafters push down and outward is the problem. The most common way to restrain that horizontal thrust is to tie the bottoms of the rafters together with a ceiling joist. You can raise that horizontal joist, or tie, up to 1/3 of overall roof height. Using that raised tie height and overall roof geometry you should be able to figure out a wall height that will put the tie above 7', usually if the walls are around 5' tall with a steep roof pitch that works out. The easy solution is ofeten to use a ridgebeam capable of carrying half the roof load with posts supporting if directly down to the foundation.
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RazrRebel
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# Posted: 22 Apr 2015 13:27
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Ok, will this work for a loft?
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razmichael
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# Posted: 22 Apr 2015 14:06
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Hey RazrRebel,
Lots of great advice from people with more more experience than me. I really suggest you take a closer look at the Ridge Beam option mentioned a number of times, especially if you want some good headroom in the loft. Pro - gives you way more flexibility in your loft allowing for more headroom. Con - may be a bit more expensive, need to have a design to allow the supports to the beam to carry the weight to the foundation (which may limit a bit location of windows and doors on the ends. Depending on your design you may or may not need a central support (if going with LVLs, any good building supply store will be able to give the size and spread). If you want to see an example, my build pictures are located at
Build Photos with my build story at
Build Story.
My cabin is 16x 24 but the front 8' is a covered deck with the main loft above this and extending into the 16x16 footprint by 2 or so feet. I used a Gambrel roof which may or may not be allowed where you are without engineering approval - this certainly provides a wonderful amount of space. I would estimate that standup room in the loft for me is about 10x13 within the 10x16 footprint.
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Rebel300r
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# Posted: 22 Apr 2015 21:15
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MtnDon, what do you think about using a longer stud? Is the stud on the right side of drawing in 602.3 full height? If so, that is what I am doing with a shorter 2nd floor. It seems stronger that way then to have two sets of studs with top plates and floor between.
Scott
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Don_P
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# Posted: 23 Apr 2015 22:05 - Edited by: Don_P
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Quoting: RazrRebel Ok, will this work for a loft? CABIN_DRAWING.JPG
Only if there is a structural ridgebeam, otherwise there needs to be a rafter tie in the lower third of roof height, I've drawn it in red below... at about 6', either raise the sidewalls or increase the roof pitch to raise the tie.
Quoting: Rebel300r MtnDon, what do you think about using a longer stud? Is the stud on the right side of drawing in 602.3 full height? If so, that is what I am doing with a shorter 2nd floor. It seems stronger that way then to have two sets of studs with top plates and floor between. Scott
Other Don here, the stud in the text is full height but it will work as drawn on either side of that drawing,platform framed or balloon framed. The key is really the rafter tie or structural ridge. If you do balloon frame it be sure to fireblock the stud bays between floors, that was the real downfall of balloon framing, if unblocked they were a tall open flue inside the walls, those old houses burned very fast.
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MtnDon
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# Posted: 24 Apr 2015 09:26 - Edited by: MtnDon
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what he said 
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RazrRebel
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# Posted: 24 Apr 2015 14:30
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Thanks to both Dons. I could get along with those rafter ties. I'm glad you guys explained ballon framing. I never did google it, but was wondering. When I build the walls I'll let you guys know which way I went. We have the floor joists done. As soon as I get the subfloor down, I'm going to take a couple of 2 X 4 and stand them up and see how much room we'll have with different pitches. I'll also nail up a couple of 2' studs and check the pitches with that to see the difference. Thanks again for the help.
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