Any foundation experts?

[Jeff Monson]

I'm looking for a 2nd opinion on some foundation advice I have received. 1st off I have a lake cabin that needs a foundation of some type, it is currently on some heavy timbers on grade, thus I'm getting alot of movement that I would like to eliminate. The cabin is only about 2 feet above lake level so it doesnt take much of a hole to find water.

So I had a guy in the yellowpages that specializes in lake cabins and foundation work. He is suggesting a floating slab would be the best bet for the situation. He would like to raise the cabin, put in a bed of sand, and then install a 4" slab with rebar and a 6" thickened edge.

I know nothing about foundation work or concrete slabs, is this a viable option, or should there be some type of footing? or is a footing even possible this close to water?

Its alot of money to spend, there are not many people in this area that do this type of work, and I only want to do this one time. Any professional advice is greatly appreciated.

[Cliff Rohrabacher]

Floating? Yah well it may just float away when the sand underneath becomes fluidized in high water years.

I'd put some seriously deep sonotube type footings in. depending on the length of the wall runs maybe as many as one on each corner and one in the middle of the wall run and maybe another one or two supporting the middle of the building leaving Re-Bar sticking up for the slab to bond to. Then pour large crushed stone and a slab poured to bind to the footings.

[David G Baker]

I agree with Cliff 100%. Won't be cheap but it will anchor your cabin.

[Chuck Wintle]

I'm looking for a 2nd opinion on some foundation advice I have received. 1st off I have a lake cabin that needs a foundation of some type, it is currently on some heavy timbers on grade, thus I'm getting alot of movement that I would like to eliminate. The cabin is only about 2 feet above lake level so it doesnt take much of a hole to find water.

So I had a guy in the yellowpages that specializes in lake cabins and foundation work. He is suggesting a floating slab would be the best bet for the situation. He would like to raise the cabin, put in a bed of sand, and then install a 4" slab with rebar and a 6" thickened edge.

I know nothing about foundation work or concrete slabs, is this a viable option, or should there be some type of footing? or is a footing even possible this close to water?

Its alot of money to spend, there are not many people in this area that do this type of work, and I only want to do this one time. Any professional advice is greatly appreciated.

what about frost in the winter? what if you made concrete pylons in the ground with sonotubes?

[Stephan Larson]

The sonotube approach would work if you take it below frost line and the create a bell shaped at the bottom of the tube. The bell shape will keep it from heaving in the winter. If it were me I think I would raise the cabin a bit and enclose it. That far North it would be easier to heat and storage is always a plus at a lake house or cabin. (canoe, lawn furniture, grill, bogey boards etc.)Just my $.02
Stephan

[Peter Luch]

The sonotube suggestion is a good one but to do it correctly would cost a bit of money. You would need to drill it and with the water table so close it may not work if the soil just falls into the hole as its drilled. The other option would be pounding in a metal sleve to fill with rebar and concrete like they do for bridges and piers.
Even with this I think it's overkill for a small house by a lake.

I would ask the contractor about his suggestion and question How it works and why it works. Might make your mind up right there.

Depending on the house and what you want out of it in the future should help you determine how much you want to spend on it.

Good luck!

Aloha, Pete

[Greg Cuetara]

First of all I would not take the contractors word as gospel. It seems as though you are starting out doing the correct thing with trying to get a second opinion. As a Professional I would suggest you call up a few engineers and get them to come out, take a look at your location and come up with a plan which will work for your location. Hiring an engineer is well worth the money because they can truly provide professional advice for your specific situations, location etc. The engineer will be able to come up with a few quick sketches for a contractor to follow.

Another piece which I might be worried about is that you probably need a permit to do this work and the local jurisdiction might have some say in what they want as a minimum. You may even be able to call up your code official and get their advice on what has been done in other locations similar to yours.

Again hire and Engineer to help you out. Do it right the first time.

Greg

[Ben Hatcher]

In my experience with foundation contractors, they typically suggest what they're best at/capable of doing. That's not always the right way. However, some times it can be good enough. I think that the only way you're going to eliminate any movement is to drive piers into the ground deep enough to get high enough pressure to support the house. That could be 5', it could be 50'. It depends on the soil. Perhaps you can find an engineer who has worked in the area and might have a better idea of what could be required to do it "right". The again, for the price, the floating slab might be good enough.

[Jeff Monson]

Good replies and advice, thanks. The movement I'm getting and most concerned with is the uneven ground shifting, not so much the whole cabin moving. Thus, I have problems with my patio door, exterior doors, etc.

I like the idea of getting an engineer out to give me an option also. I think that will be my next move. As I stated before, I'd like to do this only once. But I dont want to break the bank either. I wish they had done it right when the cabin was built.

I have attached a photo to make more sense of this.

[Bruce Koch]

Jeff, the floating slab is very common in northern Mn. I am licensed contractor in MN and my son lives in Warroad MN who just finished his new house using a floating slab just as you described. Everything is looking good. Bruce

[Cliff Rohrabacher]

what about frost in the winter? what if you made concrete pylons in the ground with sonotubes?

You go deeper than the frost line. Standard practice in cold weather regions.

[Lee Koepke]

Good replies and advice, thanks. The movement I'm getting and most concerned with is the uneven ground shifting, not so much the whole cabin moving. Thus, I have problems with my patio door, exterior doors, etc.

I like the idea of getting an engineer out to give me an option also. I think that will be my next move. As I stated before, I'd like to do this only once. But I dont want to break the bank either. I wish they had done it right when the cabin was built.

I have attached a photo to make more sense of this.
is this an existing building? are you planning on moving the building? If not, conventional 'floating slab-on-grades' and pile foundations mentioned above would be difficult.
That picture looks like you have timbers resting on concrete blocks, I can see where you'd have some stability issues.

[Matt Brawley]

My suggestion as a professional in the field would be to talk an engineer in the area and get a soil boring done on the site to see what the soil is capable of bearing. Then if it was me and the soil has sufficient bearing capacity (1500-2000 psf) I would put in a concrete block stem wall on a strip footer that extends below the frost line. Once the stem wall is complete you can either jack the existing structure and timbers on the wall or tie in a slab to the stem wall. There you have two different ideas with two very different budgets. Disclaimer: Without knowing the soil conditions on your property this is what I would do.