20' x 32' A-Frame Footings question

Started by Alan_K, May 22, 2017, 02:27:30 PM

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Alan_K

Dear Forum,

New to the Forum & New to the idea of building my own retirement getaway. Anyways, the reason for the post.... Trying to figure out how many footings my intended build requires.

Location, as of yet has NOT been determined, so, I figured I'd get everything else in place.

As the caption states.... I'm intending on a 20' x 32' A-Frame. I'm taking a wild guess.. in that it is an A-Frame, it would have a lower load on the roof, hence maybe the need for fewer footings.

I looked for any kind of calculator, other means of determining the amount, but everything I find seems to be on Slab or a Foundation.

Any feedback would greatly be appreciated.

Thanks

Alan

MountainDon

Quote from: Alan_K on May 22, 2017, 02:27:30 PM
Location, as of yet has NOT been determined, .....

Location can influence the foundation design; both local frost depth and local soil composition can make a difference.



Quote from: Alan_K on May 22, 2017, 02:27:30 PM
........... intending on a 20' x 32' A-Frame. I'm taking a wild guess.. in that it is an A-Frame, it would have a lower load on the roof, hence maybe the need for fewer footings.

I'm not sure I follow the thinking?  Do you mean lower load on the roof because any snow is more likely to slide off? In that case if there is a lot of snow it piles up and may press on the roof wall some. Just guessing.



Quote from: Alan_K on May 22, 2017, 02:27:30 PM
I looked for any kind of calculator, other means of determining the amount, but everything I find seems to be on Slab or a Foundation.

The reason you find most building done on slabs and perimeter foundations is that those types have prescribed methods, prescribed width, depth, thickness, rebar size and quantity, etc for specific loads. The load carrying ability of the soil can affect how wide a perimeter foundation needs to be, for example. Being built to a prescribed formula means no need to hire an $$ engineer. If the project will be carried out in a location that requires building permits and inspections a pier foundation may end up costing more than any perceived savings if an engineer is required to design and certify the piers.

Slabs and crawl space foundations all have a steel reinforced concrete footing that runs full perimeter. Sometimes a slab may have the footing and a short stem wall poured first and then the floor slab added in a second step. (Slabs are common where frost depth is not very deep, such as the SW where we are.) The entire foundation / footings acts together to spread loads and nature's forces out. A pier foundation does not usually have the footings for one pier tied to another. They are each independent. If the earth under one piers footing is not able to carry the same load as adjacent piers it may subside. Or maybe the loads on some piers are greater due to other factors.



The foundation should really be designed last as only if you know what all is above, what all must be supported can the proper foundation be chosen. As well, the ability of the soil to support loads, the frost depth for the location must be known. Some locations get more complicated if the soil has lots of clay as clay increases and decreases in volume with changes in moisture.

I'd concentrate of designing a floor plan that you love as well as looking for a location. Then choose foundation as per what is needed to do the job. Personal preferences vary a lot... I do find some A-frames attractive on the outside, but I have not seen many that had what I thought had livable interiors. Window positions are limited as are walls where one can hang cabinets.

Most locations in the USA use the IRC, the International Residential Code for the building "rules book". There are different versions, effective different years. States do not all use the same version. Check with the building dept in the locations you consider to see what they use. There is an online version available That's the 2015.  States and municipalities / counties may also make changes to suit local needs.


Just because something has been done and has not failed, doesn't mean it is good design.


MountainDon

You could also investigate whether or not Bigfoot Systems footing for piers have achieved code acceptance. The last I looked they were not but they had told me they were pursuing approval.
Just because something has been done and has not failed, doesn't mean it is good design.

Alan_K

Don,

TY for the novel  d*
Some aspects of what you said I had floating in the back of my mind.
The rest is very much appreciated.

Thanks

Alan