Piers on addition
eorr
| Posted in General Questions on
Hello,
We hired someone to add a 16’x26′ addition to our tiny house and a couple of people have told me we don’t have a proper foundation which may cause issues like roof leaks down the road.
We have 2’x12′ floor joists on 16″ centers with just 4 block piers on each of the 26′ sides (0′, 8′, 16′, 26′). So the floor joists span the full 16′ with no support in the middle.
According to some charts, 16′ is the maximum span of a 2×12. Is this enough support or do I need to figure out how to build 4 more piers running down the middle?
Thanks.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
eorr,
From your description, it sounds like the floor joists spans are fine, but even if they were over-spanned a little all that would happen is that the floor would deflect a bit leading to some bounce, not any structural failure - and I'm having a hard time understanding how it could in any way cause roof leaks. Not seeing drawings or photos it's had to tell if maybe people are worried about some other issue? Roof loads? Loads on the existing house?
Thanks, Malcolm, I think I may have influenced the roof leak response when I asked, "What would be the issue? Roof leaks or something?" And then I got, "Yeah that could happen."
One potential issue is that if your house is well above grade, the piers may not have adequate lateral stability. Another is that if your pier footings are undersized, the building could sink into the ground a bit, especially with an addition adding more weight.
Both are easily calculated if you have enough information, such as soil type, footing size, pier size and type, snow load, and any additional atypical issues such as a steeply sloping site, a high wind zone or a seismically active zone.
Michael, the piers are poured block, 16" x 12". The tallest pier is 3'. I can check with the builder but I think I remember the footings are 30" x 30" x about 16" deep.
It's a level lot. According to the NRCS soil survey tool, it's "Allegheny loam" or "Allegheny and similar soils: 80 percent". I'm not entirely sure about snow load but we usually don't get more than 4" to 6" at a time on the roof. It's not windy and so far not seismically active.
How would you go about calculating stability based on that?
That all sounds pretty good. The calculations and data are in the IRC model code but doing the calculations for the first time would be pretty difficult. Ideally you would check with a structural engineer who could do the calculations quickly. Some architects and builders can as well.
Thank you.
godsbluehills,
Unless the people who are suggesting there is a problem can point to something concrete to base that on I wouldn't lose sleep over it. Nothing you have described rings alarm bells for me.
As I often seem to do, I read the original question a bit too quickly. I'm not sure what size the existing house is but I interpreted it as having four piers, one in each corner, and that the 12'x26' addition would have piers on the outside corners. Clearly I misunderstood those important details.
I'm still not sure what size the current house is but if I understand correctly that there are a total of 8 piers just for the addition, 4 along each 26' side, I agree with Malcolm that it sounds quite safe.
It's a tiny house and you want to add a 16x26 addition? How big is the house?
Deleted