Hi, I am a lurker, and first time poster.
I live on a gorgeous plot of land, off the road. An ideal setting for me, but my house is much less than ideal. I am in the process of planning a new house build. I have a very non-traditional log cabin with vertical logs. The design was done by a homesteader in the 70's using timbers from the land. A good idea in theory, but lots of design oversights were made, plus a couple of generations of owners who did not keep up on maintenance have left this house in somewhat poor shape.
Several attempts at planning renovations that would weatherproof the house kept pointing to a tear-down and rebuild using more traditional construction.
It does have a very good full basement, which I had evaluated by a structural engineer.
My budget is pretty tight (aren't they all), but I believe I will be able to afford building on the existing foundation, using the existing power and septic etc. I have worked up estimates with a local builder who would do all the framing, doors, windows, siding, roofing etc and leave the house with plywood foors. I would do the electrical, HVAC, finishes etc.
The plan is to build on the existing foundation with a full two story (small) house. Straight roof line, metal roof, 8x12 pitch.
Now for my question: The floor plan is very small, which makes fitting stairs and a kitchen difficult. If the floor was 24x25, things would fit much better and allow me to have a decent kitchen with a full stairway to access the second floor.
The basement measured 20x25 at the exterior currently. My kitchen guy has suggested cantilevering two of the walls out 24" to give me a house with exterior dimensions of 24x25 as opposed to 20x25. I like the idea of more space, but have reservations about this design. So far, most people I have talked to have varying opinions, and I wanted to gather some more.
It seems that the 24" cantilever with 2 stories and a roof load would require engineered floor joists for the first floor. It seems that 2x12's can only cantilever out 11.5" in this situation.
Other concerns would be insulation in the cantilever space. It seems that spray foam in those cavities would be a good solution with some kind of cap on the bottom side.
Does anyone else have some thoughts on this design? The extra space provided would be great, but I only want to do it if I can still ensure the structural integrity of the house build. I plan to stay here for the rest of my life if possible.
Thank you in advance!
It looks like table R502.3.3(1) is the only thing in the IRC code for prescriptive construction of cantilevers with a bearing wall and roof. Nothing for 2 bearing walls and a floor. I am curious how much it would cost to engineer that 2' cantilever vs just doing traditional framing without the overhang and then finishing off the basement if you decide you don't have enough space. (Or simply putting on an addition down the road).
Does the interior of the foundation have footings for posts that would support a beam? If not, you might need I-joists either way as 20' span is the absolute limit for 2x12 @ 12" OC for a floor.
Be careful taking too much advice from people in construction. You will end up with a million dollar mcMansion if you say "yes" too much.
Also make sure you really don't/can't do the framing. I find that framing is very enjoyable and not terribly difficult.
I don't think I really want to finish the basement. It is dry most of the time, but there has been a couple times when some water has come in during extremely wet springs, and I was very glad it wasn't finished. I would like to keep it a basement for storage and maybe a workbench, but no real finishes.
I would love to do the framing, but I don't think I can frame the house and get it weather tight before winter without the help of a professional, while still working full time. Hiring a builder is to ensure I get my house safe against the elements before the winter. Project would start as early as possible in the spring of next year.
I do not know if my basement has footings or not. There are 3 poles in the center of the 25' length spanning the 20' width, but I cannot tell if there is a footing below. There isnt any cracking or other problems with the floor where the posts sit, but I can't know what is down there from just looking at the surface. A TJI might be the safer bet in that respect.
There must be footings under those posts if it's still in good shape after all these years.
The Cuyamaca cottage thread.. he cantilevered almost his whole house to meet local ordinance requirements. That might be an interesting read and give you some insights.
You might be right about those posts. However, they are not carrying any roof load since its a clear span on the first floor, no posts connecting second floor to first floor or roof to first floor. Its all transferred (badly) out to the exterior walls with skinned logs spanning the whole 20' (very bouncy). The only thing those basement posts are carrying is the first floor itself, and the woodstove/woodbox right above those posts.
I will look through that thread, thank you for the suggestion.
I am going to try and figure the price difference of engineered joists VS 2x12. I know they cost quite a bit more, but advantages would be no center beam, no posts in basement, less deflection, and less labor cost to install.
My major concern with them (besides cost) is the fact that the ends would be sticking out in the elements with the cantilever. I think I would want to spray foam the cavities and cap the bottom with something like fiber cement, so maybe there is no concern.
Any thoughts?
Also, I should add that my foundation is pretty high above grade, 24" at minimum, so my cantilever would be out of the way of splash.
You can look at my build, I use several cants. all done with standard 2x12 all done to wisc. code, you will want to check yours there are several rules to follow.http://countryplans.com/smf/index.php?topic=12988.0
Patrick, nice build!
Am I correct in saying that your cantilevers are supporting a single floor, and are mostly bump-outs?
The cantilevers that I am referring to are the entire 25' length of the house and have the outside walls for the full two stories resting of the outside of them. So the majority of the wall and roof loads are resting on these two cantilevered sections.
See my sketch for my plan. Basically I am trying to add 4' of overall width to my 20x25 foundation to make it 24x25.
(https://i1103.photobucket.com/albums/g472/danapcurtis/Capture_zpsffg0ib8f.jpg)
Or put one side of the house on top of the existing foundation and then on the 4 feet on the other side, pour a footing and add cinder block. Don't worry it is not a full basement.
Not sure what your floor plan is but for that size I'm envisioning an open first floor, perhaps a powder/ utility, stair, and upstairs a couple bedrooms/ bath? I think the way I'd manage it is to cantilever the first floor joists only where necessary (kitchen counter, stairwell) , header off these openings, and keep the second floor and roofline at 20'...or in other words, bump outs. Done carefully, you can add a lot of visual and spatial interest and avoid the "boxy mushroom" look....
Here is some code requirements,They are Wisconsin's but everyone is similar,but it should give you an idea of what to expect
(6) Overhang of floors.
(a) General. Except as provided in pars. (b) and (c), a floor joist overhang shall be cantilevered beyond the outer edge of the supporting wall below it by no more than the actual depth of the joist or shall be designed through structural analysis in accordance with s. SPS 321.02 (3).
(b) Joist overhangs parallel to the main floor framing system. Joist overhangs that are extensions of, and parallel to, the main floor framing system may extend beyond the depth of the joist without structural analysis provided they meet all of the following conditions:
1. The overhang is cantilevered no more than 2 feet beyond the outer edge of the supporting wall below it.
2.
a. The overhang supports a uniform load limited to the weight of the bearing wall and the tributary roof area above it.
b. The tributary length of the roof area, excluding the eave overhang, is no more than 2 feet greater than the actual length of the joist directly below.
c. The eave overhang is no more than 2 feet.
Note: The tributary length is usually half the span of the joist or rafter.
3. The joist overhang does not support any concentrated loads. For the purposes of this subsection, a framed opening in the wall with a rough opening of 4 feet or less shall be considered uniform loading.
4.
a. The cantilevered joist is doubled at the supporting wall.
b. The doubled joist length extends inward beyond the inner edge of the supporting wall by the same distance as the cantilever.
c. The added joist member is secured to the main joist as stated in the nailing schedule in ch. SPS 325 Appendix A, under the heading for "floor framing, built-up girder and beams, top loaded".
(c) Joist overhangs perpendicular to the main floor framing system. Joist overhangs that are perpendicular to the main floor framing system, or lookout joists, may extend beyond the depth of the joist without structural analysis provided they meet all of the following conditions:
1. The joist overhang is cantilevered no more than 2 feet beyond the outer edge of the supporting wall below it.
2.
a. A double floor joist is used to support the lookout joist.
b. The double floor joist is located a distance of at least 2 times the cantilever length inward from the outer edge of the supporting wall below.
c. The lookout joists are fastened to the double joist with metal hangers.
3. The joist overhang supports no more than either a non-bearing wall or a wall that supports only a roof which spans no more than the floor overhang cantilever length plus the eave overhang.
(d) All overhangs longer than the depth of the supporting joist that do not meet all of the conditions under par. (b) or (c) shall be designed through structural analysis.
WI code is unique, that section is to my knowledge unique to it. Even there, I'd be conservative using those exceptions.
Doing a quick napkin check I was getting into both bending and shear territory. I'd bet the doubling would take care of it. This is legitimately an engineers job. An engineered floor system, whether TJI's or floor trusses, can be ... engineered. Since they are installed to manufacturer specs rather than to prescriptive code tables, that industry performs the engineering upon request as part of the sale. We can look in their tables for typical situations but the minute you stray outside of those, just take your plans and ask them to design the floor. If you need a stamp, let them know.
If you want solid sawn lumber... well, that industry has been slower to think in that way, you need to hire a structural engineer. More expensive but they visit the site and see more than just the plan. I've had one walk on the job for one problem and dope slap me for something else, that's a good thing.
Quote from: vtpsd on March 28, 2016, 01:13:32 PM
My major concern with them (besides cost) is the fact that the ends would be sticking out in the elements with the cantilever. I think I would want to spray foam the cavities and cap the bottom with something like fiber cement, so maybe there is no concern.
Any thoughts?
Yeah, aside from the structural thing, code will call for an exposed floor to be insulated closer to ceiling R-value than wall R-value. And, corners in general are where a lot of heat loss occurs.
Rockwool (pests don't like it) could be a good option from the cavity insulation. Then you could wrap the entire house with rigid insulation (including the cantilever) to prevent thermal bridging.
Floor trusses could be the way to go.
Quote from: vtpsd on March 28, 2016, 12:34:52 PM
You might be right about those posts. However, they are not carrying any roof load since its a clear span on the first floor, no posts connecting second floor to first floor or roof to first floor. Its all transferred (badly) out to the exterior walls with skinned logs spanning the whole 20' (very bouncy). The only thing those basement posts are carrying is the first floor itself, and the woodstove/woodbox right above those posts.
I will look through that thread, thank you for the suggestion.
Yeah, that's not good.
What area of the country are you in? What's the required footer depth out of curiosity?
Would it be possible to use 3 or 4 24' LVLs, one on each 20' basement wall and one or two between them, hanging 2' over the long walls to make the 24' width? Joists could run between them, parallel to the 25' wall.
The first thing I thought of when reading this was a "tip out" for just the stairway. Now idea how zoning requirements would view this.
I am located in VT.
I am in the process of consulting a structural engineer about using 24' TJI's.
I am also considering rotating my roof ridge 90 degrees and that way the eves and roof load would be sitting on the foundation wall and the cantilevers would be out the gable ends. This would make the house 24x25 with the roof spanning the 25' dimension. A little funky, but probably a better option structurally to not carry the roof loads out on the cantilevers.