acceptable cantilever for cabin subfloor?

[CabinNewbie]

Hi,

I am gearing up to build a 16' x 24' cabin.  I have a question about my design for the subfloor.  I plan on using 2 x 8 x 16 joists with a 10' span between underlying beams and 3' cantilevers on both sides. 

I'm having trouble determining acceptable cantilever distances.  I'm assuming that it depends on the weight of the wall/roof/load etc...  but I'm hoping that I'm well within the acceptable distance.  The cabin will be a 1 1/2 story.

Are these 3' cantilevers going to be oK?

Thanks.

[rocking23nf]

my beam was only allowed a 1 foot cantilever on a 12x12. 3' feet seems long, but someone else should know.

[MountainDon]

You would be seriously advised to increase the joists to 2x10 minimum and increase the span between the support beams to bring the amount of overhang down to 12 inches or less per side. This would be okay in most cases as long as it was a single story with maybe no more than a small sleeping loft, and as long as the snow loads were small. John's Little House plans (maximum width 14 feet) have cantilevers designed with the above mentions limitations. That also is dependent on using one piece joists.

I would personally be very nervous building anything with a three foot side wall overhang. Extremely nervous.


Further on this subject... what spacing on the joists? what grade and species of lumber? what size beams are in your plan?  how many piers or posts, spacing, depth, footing? Is this a one story building, what are wind loads, snow loads, frost depth, soil type?  There are a lot of variables that need to be considered when designing a structure. We can help on a lot but need to know all the details. Many first time builders use a good set of comprehensive plans that they can modify to get things right. John has some plans that would likely suit you. There is no obligation to use his plans to participate in the forum, I just mention them in case you would like to explore that avenue.  The forum is open to anyone with questions and/or ideas.

[CabinNewbie]

Thanks for the replies.   

I have seen the plans for the Little House (14 x 24) and I thought that there was a 2' 2" cantilever using 2 x 6 joists.  That is actually what I modeled my floor plan after.  Can anyone clarify for me?

Many thanks!

[MountainDon]

You are right about the specs on the Little House; the 14' wide does show a 2'2" overhang.

However, if I recall correctly, John stopped at 14 feet wide for using overhung side walls. His 16 foot and wider plans all have foundation beams located under the side walls. The forces acting on a building are not necessarily linear as the width increases. Perhaps John will see this question and comment on it further. There are a few 16 foot wide builds here that have short cantilevers or overhangs, but nothing in the neighborhood of three feet.

What are the local rules and regulations you will have to meet? That could influence what you do. Or maybe there are none or they are very limited in scope.

In any event increasing the joists and spacing the beams further apart will not increase costs much. My current local pricing on 16 ft. 2x8 vs 2x10 works out to a difference of about $90 for a 24 foot long building, using 16"OC joists.

[John Raabe]

Yes, to be cautious you should not attempt to "scale up" the small single level Little House project. It was designed for a lightweight one-story max 14' wide building.

For a 16' wide building you can go to 2x10 joists at 16" and do a small cantilever on either end in order to tuck the beams and piers back under the skirting. If you keep the span inside the two beams to 14' to 15' or so you can use any #2 grade framing lumber. This will also allow some limited expansions such as an addition or deck load without overstressing the cantilevers. You can always freely "cantilever" the depth of the joist - in fact that isn't even counted as a structural cantilever so it can work for a 1-1/2 story design as well.

If you have any questions, please check locally with a designer who knows your local snow and wind loads. Either of these could suggest a modification to the above advice.

[Don_P]

This is one of the cantilever charts from the codebook;

Do remember that attaching a deck to a cantilever is not a prescriptive condition. The standard situation and the one specified in the codebook is attachment to a "nominal 2" rim or band joist bearing on a sill plate or wall plate", not an unsupported rim. The concern here is that decks hanging on nails have a history of landing on the ground. A deck or addition attached to a cantilever should be designed as a freestanding structure.

[CabinNewbie]

Thanks for all of the information.

Great forum!