Dennis_Gavin

grade distance from foundation to overcome frost level

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I am working on an addition that has a high water table and I want to AVOID it.

Looking at placing footings bascially just below grade and then using back fill to get

my 36" footing depth.  Does anyone know how far out the 36" back fill  has to be from the addition

to qualify as 36" delow grade?  IT will then taper down to existing grade.

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The diagram shown in the IRC shows it starting right at the exterior of the foundation. I would probably at least start at the exterior width of the footing just in case you get a picky inspector.

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The diagram shown in the IRC shows it starting right at the exterior of the foundation. I would probably at least start at the exterior width of the footing just in case you get a picky inspector.

 

Not sure this is correct unless we're talking about different things.  Logically, it would have to be a minimum of a 45 degree slope measured from a point directly above the outermost edge of the footer.  I'd imagine 45 degrees would be enough, but just to be safe you could add some insulation above the footer to match that slope. 

 

Anyway Dennis, I'm really not sure what the actual code is off the top of my head, but I'm relatively certain its just 45 degrees measured like I said above. 

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Dennis just from memory doesn't there have to be 6" from any wood to any dirt backfill by code

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I Know in Washington state we cannot have a 1 to 1 slope (45 deg) max is 3 to 1. We would be forced to tier the grade or put in a retaining wall on a 1 to 1 slope. I guess it might depend on jurisdiction on where its built. We have and 18" min coverage.

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DIrt and wood are not an issue.  I think the answer is about the same as footing depth on a sloped terrain. 

There is a ratio of how far down the footing has to go to overcome a steep terrain. Can't remember what

ratio/formula is.

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How about a frost protected shallow foundation? post-1284-0-24709300-1460581661_thumb.gif

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DIrt and wood are not an issue.  I think the answer is about the same as footing depth on a sloped terrain. 

There is a ratio of how far down the footing has to go to overcome a steep terrain. Can't remember what

ratio/formula is.

 

You described that you are adding fill and did not mention you were excavating and or placing the building near a slope. That is a totally different situation.

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Not sure this is correct unless we're talking about different things.  Logically, it would have to be a minimum of a 45 degree slope measured from a point directly above the outermost edge of the footer.  I'd imagine 45 degrees would be enough, but just to be safe you could add some insulation above the footer to match that slope. 

 

Anyway Dennis, I'm really not sure what the actual code is off the top of my head, but I'm relatively certain its just 45 degrees measured like I said above. 

 

I see what your saying yes the bottom of the footing has to be figured 1 to 1 against the downhill slope next to the bottom of the footing. Like if you place the bottom of footing next to a 3' slope the footing would have to be 3' away or excavate down 3' at the slope. Down hill slope to the building on the other hand is a totally different formula is used.

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I think 1 to 1 is it.  Footing sits 1' below grade to bottom of footing.  The fill would have to b2 2'

and extend out 2' before sloping away from the foundation.

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DIrt and wood are not an issue.  I think the answer is about the same as footing depth on a sloped terrain. 

There is a ratio of how far down the footing has to go to overcome a steep terrain. Can't remember what

ratio/formula is.

 

At one  time it was "5'-0" TO DAYLIGHT"

 

it is now "MINIUM 7'-0" TO DAYLIGHT"

 

what this means is if you were to project a horizontal line from the bottom of the footing to "daylight",  the distance must be at least 7'-0".

 

I would bet Perry and Joe and Larry would confirm this.

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What if it's night time?   :rolleyes:

Sorry, couldn't resist.  That is what I am looking for.

Can Joe & Perry confirm?

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I attached a slope diagram out of the IRC (2012) page 80. If you are just scraping the surface to avoid a water table not adjacent to any slope you have nothing to be concerned with. whether there is a slope or not just back fill over the footing to the required cover for frost protection and slope final grade at away from the foundation minimum 6" (5%) out to 10' and a maximum of 3:1 or what ever the max slope is allowed in your neck of the woods. On side yards just slope 5% to the drainage swale.

 Depending how deep the water table is you may not find suitable bearing for the footings and most likely require an onsite visit from a soils engineer.

I built 11 houses that required boring 12" holes at 8' on center to pour concrete piles for the footing to be supported due to water table and soil conditions. If you are designing a crawl space foundation you may want to consider sloping the grade inside the foundation enough to direct any water to a foundation drain or use a sump pump if a drain will not work.

Hope this helps

.Slope diagram.pdf

 

PS; sorry for the quality of the scan as a could not get the page tight enough to the scanner.

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Jeff - yes, you have it.  The slope is not great but the owner had 4 sumps in his existing basement and they

all run.  I am worried about the township not allowing the builder to pour into a wet/soggy footing and the deeper

they go the greater the chance.  Planning on going down the minimal amount and back filling to overcome frost line.

Thanks for your input!

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Jeff - yes, you have it. The slope is not great but the owner had 4 sumps in his existing basement and they

all run. I am worried about the township not allowing the builder to pour into a wet/soggy footing and the deeper

they go the greater the chance. Planning on going down the minimal amount and back filling to overcome frost line.

Thanks for your input!

Just a thought here, but have you considered using piles or helical piers and grade beams?

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Jeff - yes, you have it.  The slope is not great but the owner had 4 sumps in his existing basement and they

all run.  I am worried about the township not allowing the builder to pour into a wet/soggy footing and the deeper

they go the greater the chance.  Planning on going down the minimal amount and back filling to overcome frost line.

Thanks for your input!

Dennis,

 

I would strongly recommend a good drainage system (french drain) to prevent the water from getting to the basement.  If the site is sloped the drains could be around 3 sides and route the water completely away from the house.  It will solve a lot of other problems at the same time.

 

When we built our house in 1990 we had underground water coming up in the foundation trenches - everyone up the hill is on septic systems - so we dug a trench and put in a french drain to intercept the water.  It's worked perfectly and the basement/crawl space is as dry as the Sahara. 

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Right now I am considering MONEY!  Trying not to create a massively expensive project. 

There will be a civil engineer involved to some degree.  A friend of the owner.  Just not sure

to what degree as I do not know him but trying to connect with him now.

But who knows it might go that way.......

post-132-0-05304900-1460658468_thumb.jpg

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Just a thought here, but have you considered using piles or helical piers and grade beams?

 

Great Idea. That's how I built my home except used creosote pilings and creosote beams due to tide considerations. Creosote has been outlawed for over 10 years now and no longer available.

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Dennis,

 

I would strongly recommend a good drainage system (french drain) to prevent the water from getting to the basement.  If the site is sloped the drains could be around 3 sides and route the water completely away from the house.  It will solve a lot of other problems at the same time.

 

When we built our house in 1990 we had underground water coming up in the foundation trenches - everyone up the hill is on septic systems - so we dug a trench and put in a french drain to intercept the water.  It's worked perfectly and the basement/crawl space is as dry as the Sahara. 

hydrostatic pressure can be of concern with high water tables but what you suggested is of great advice for containing water from entering the from the exterior.

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