Can I use treated poles as the foundation of a addition?

Question

I would like to add an addition to the back of my garage 16x20 and was wondering if I could build it using 4x6 treated poles as the foundation? It would have a 2x8 wood floor suspended from the poles.

Is this allowed by building codes in Sebewaing Michigan?

The poles would be sank down probably 42" and concrete poured in - --

This would be a "finished" addition - with a wood floor ... creating a crawlspace below it. I have seen other people build like this around here - but I need to know if it would pass inspection?

Answer 1

Pole structures are permited in almost all locals. My county building dept has a handout with special requirements for pole construction, just go ask them where you live.

Do use .60 treated lumber when in contact with ground.

You can follow most of the suggestions above, except do NOT completely encase the post in concrete. set post on an 8" solid concrete footing, you can precast them if you like or pour them with a batch that sets early [i think they add calcium to the concrete for that]. then add a foot or so of #57 stone [to allow for drainage], you can pour concrete to grade for stability.

Do dig the full frost depth or risk a frost heave. Don't cheat on this!

If you pour a pier, as one person suggested bring the top concrete to about 6" above finish grade so wood isn't in ground contact. you gain very little lateral stability building as they suggested.

Answer 2

Yes, here I MI where I live you are allowed to build your garage "pole barn stye". Even if it is connected to a home on a typical foundation. You need the treated poles to go 42" down on a concrete pad footing. Footings here are usually 2' diameter 8 inches thick. Many garages and outbuildings are done this way. I suspect a house type concrete foundation would last hundreds of years longer but the post type construction is approved with treated wood posts.

Answer 3

Not really a good idea. While treated wood is more resistant to water and insect damage it will still rot. I assume you want your structure to last and be safe. I do not know the building codes is your area, but most codes for a permanent structure require a concrete foundation. with a footer. You may be able to use concrete piers but I do not think that meets current building codes. You also have to consider freezing in your area, most foundations must go below the frost line.

Answer 4

The poles, themselves, don't have to go down 42". You make your hole 2' in diameter and fill it with concrete to about a foot below grade. Then set the pole on top of the concrete with anchors and anchor plates and backfill the 1 foot with gravel. It's better if the poles sit on top of the concrete, rather than in it. As long as the concrete is below the frost line, neither it or the poles on top of it will heave.

And you can have a crawl space under a garage, but 2x8s won't support a vehicle unless you have lots of intermediate timbers supporting them and thick, real wood decking. A typical floor system of 2x8s and plywood decking won't cut it.

Answer 5

treated poles foundation addition

Answer 6

I agree with those who said no. Wood does rot. If you do it, spend the extra cash and put a "stub foundation" of concrete as a bare minimum...just be sure it goes below the frost line! It will outlive all of us and save you a lot of grief years down the road.

Answer 7

morris is right 42 plus the fotting 50 total you want a concrete pad . Build from there . .YOU CANNOT have a CRAWL SPACE under the GARAGE . CALL a LOCAL CONTRACTOR. ps sorry for the sarcasm
25 years carpenter ,remodeler.

Answer 8

Listen to Morris. 42 inches it fine for frost line.

Answer 9

ALL wood rots, just a matter of time. You're better off using concrete footings.

Answer 10

ask when you get the building permits that you're suppose to get before you start . no Certificate of Occupancy= home insurance void .