Permanent wood foundation question

Started by Beavers, December 09, 2017, 11:59:17 PM

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Beavers

Planning doing a permanent wood foundation like this for a 10x16 addition.



This is what the existing foundation of the house looks like (I've added more bracing and enclosed the piers with 3/4 plywood since this photo).



My question is...should I run the new foundation around all four sides of the addition butting up to the existing piers or should the new foundation just be on three sides?  Hopefully that's clear ???

I'm worried about disturbing the existing piers and footings during excavation. I would of course dig by hand near them.  Being a one man operation the piers and footing could be exposed for a while during construction. 

Do you think it's worth the risk to install the new foundation under all four sides of the addition?  I don't really want to add any additional load to my existing pier foundation.

ChugiakTinkerer

It may just be the equivalent of an internet wive's tale, but everything I've read says additions should be on the same type of foundation as the main structure.  Is a consultation with an engineer in the cards?
My cabin build thread: Alaskan remote 16x28 1.5 story


Beavers

No engineering planned.  Which is why I want to use a code approved non engineered meathod for the addition. Are you thinking of the main house settling at a different rate than the addition?

I've ran basically stud walls between my piers and sheeted with plywood. Above grade my pier foundation is as close to the code book permanent wood foundation as you can get.

I really don't want to continue to add on with a pier and beam foundation.

Don_P

QuoteDo you think it's worth the risk to install the new foundation under all four sides of the addition?  I don't really want to add any additional load to my existing pier foundation.
QuoteAbove grade my pier foundation is as close to the code book permanent wood foundation as you can get. 

However a permanent wood foundation is continuous bearing, you are on I believe 8 footings@12" dia... already overloaded. Is there a reason not to expose that line of piers down to the footings, put in gravel or concrete between and turn that pier wall into a permanent wood wall?

Beavers

I hadn't thought of doing it that way Don.   It would be nice to beef up the existing foundation. My big concern is that while I have all the dirt removed from around the piers we get a big wind storm and the house moves.  Do you see that as a problem?


Don_P

LOL, since the day you built it. If it keeps you up figure out how to brace it during that period, cables and ledgerlocks on the house to mobile home anchors, etc.

Beavers

Haha thanks Don...I'll make sure my homeowners insurance is paid up before I start construction.   :)

I'll see how it goes with this first wall...would be nice to retrofit the other sides too.

Don_P

Another thought, can you bear on the 90 degree intersecting walls, Tie to existing to pick up lateral on that end, which braces the current wall if you want to do more work then. You've only contacted the current foundation with 2 trenches.

Gotta sketch?

Beavers

This is the existing.  10x16 shed roof addition to the north side of this drawing.  Master plan is to add 10' shed roof additions to the north, south and east sides.



If I understand you right.  The addition will provide lateral bracing to the existing house?


Beavers

Ok thinking more about what you said...
The ends of my cantilevered beams are still exposed.  I could tuck my 10' walls under the beam. Build the 3 foundation walls of the addition then retrofit the existing pier foundation.  The new foundation walls would help to stabilize the existing while the piers are retrofited.  Am I picking up what you are putting down?  ???




Don_P

Yup, that's it.

With all these additions you could wrap 3 sides in porch and build with a full perimeter pwf. Basically leave the existing alone on those 3 sides. Intermittently convert that to rooms or porches.