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Foundation questions, options

Posted by sochi (My Page) on
Tue, Dec 4, 12 at 18:13

I'm trying to educate myself a bit about foundations ( and 100 other things) before we start talking with General Contractors.

We are building a 1500 sq ft cottage/cabin in a rural, wooded and rocky area. It will be a vacation home. We are in a cold climate (hot summers, cold winters). We don't want or need a basement. We have two potential building sites, one sloped facing south, one flat facing east. I prefer the south facing sloped lot as it is more accessible from the road/driveway, and because we may be able to take advantage of passive solar heating.

What foundation options are there for sloped sites? There isn't a whole lot of soil on either site before you hit rock. I had assumed piers might be the best bet, but I'd appreciate your thoughts.

Thank you.


Follow-Up Postings:

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RE: Foundation questions, options

Where I had cottages on the Canadian Shield, it was either piers anchored directly into the exposed bedrock. Or dynamite.


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RE: Foundation questions, options

In a cold climate, you are already having to excavate so much to get below the frost line that it really doesn't add that much to go ahead and do an unfinished basement. In some cases, it might actually be more expensive to do pier and beam than do do the basement.


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RE: Foundation questions, options

That is exactly what I'm doing, a cottage on the Canadian Shield. No dynamite. How does doing piers into the bedrock compare cost wise with other foundations? I did wonder about heat loss, insulation, using radiant heat etc., with a pier system. Thanks for the information.


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RE: Foundation questions, options

GreenDesigns, thanks. I'll have to see what the costs come out at. The area where we will build is purportedly a high risk area for radon, that is one reason I'd like to avoid a basement.

Forgive my ignorance (I'm learning here), why would you need to excavate regardless? Wouldn't you just drill for the piers, or is that what you mean by excavation?


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RE: Foundation questions, options

In a cold climate, you are already having to excavate so much to get below the frost line that it really doesn't add that much to go ahead and do an unfinished basement. In some cases, it might actually be more expensive to do pier and beam than do do the basement.


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RE: Foundation questions, options

Green, I think the point is that the level of bedrock is so high, perhaps on the surface in some points, that excavation is not practible. It's pretty hard to excavate throught 15' or more of solid rock. That's why the alternative is blasting!

Without knowing the contours, terrain and area/spread/depth of bedrock, I'd think that the simplest thing might be to forget a basement, drill piers into and anchored to the bedrock, level up and build the first floor from there.

This isn't my area of building expertise (I'm more used to expansive clay soils), so I'll be interested in what the experienced builders have to say.

Good luck on your project.


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RE: Foundation questions, options

I've done with piers, crawl space and a partial/full basement with dynamite. It depends greatly on the actual location of the rock, it's condition, site access and your budget. I would prefer a perimeter foundation and crawl space (or slab on fill) to a house on piers. Animals, especially beavers, can be a problem not to mention heat loss through the floor.


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RE: Foundation questions, options

Whatever you end up doing, be sure to insulate under the foundation floor. It makes a big difference in comfort level.

Also, I wouldn't be afraid of radon. It is what it is. It is easy to ventilate away with a very quiet and essentially no maintenance fan. What we did was to put the piping in beneath the cement slab for radon control in case we had an issue. We did, so were very easily able to just hook up a fan and fix the issue. By putting the pipes in below the slab, you are keeping the radon from getting into the house.


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RE: Foundation questions, options

It's pretty hard to excavate through 15' or more of solid rock.

Let alone 18 km!

In fact, the entirety of North America rests on the Canadian Shield.

I was referring to the many areas of Ontario where the Shield is completely exposed or barely covered.

That's why my main cottage was anchored directly to the bedrock. The other two were resting on blocks with crawlspaces.

Here's a typical Kawartha Lakes cottage anchored to the exposed Shield. Your shorefront is likely to be solid rock and your first step in the water may be 30'-40' deep.

This post was edited by worthy on Wed, Dec 5, 12 at 10:34


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RE: Foundation questions, options

Worthy, yes, that is what we're facing. Our land is just north of Ottawa in southern Quebec.

Most cottages in this area are built on rocky slopes, so no doubt contractors will know how to deal with the situation. I just want to make sure I know enough to have an intelligent conversation with them. Most cottages on slopes here have walk-out basements too (finished or not).

Annie, like in Worthy's picture, we have a far amount of exposed bedrock right at the site(s). If we do end up with a walk out I'll have to consider the radon issue I guess. Our home is on bedrock too, it was built in 1877 and we just a 4' crawlspace, but it is well ventilated and sealed (now post our reno anyway).


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