[Stubits]

We are in the process of designing a 3 story addition to our DC rowhouse. The addition will add approximately 150 sq. ft. or 50 sq. ft. per floor. Our architect is just about done with the schematic design and has sent us some draft drawings. Obviously as a rowhouse, we are attached to neighbors on both sides.

In an effort to avoid encroaching on our neighbor's property, the architect has suggested we use a turned down footing. She indicated that frost protection would be required because the footer wouldn't be deep enough to meet the frost depth requirement of 30". I think the major concern, however is that my neighbor's property at that point is about 14" lower than mine.

I've attached two elevations to show what we're planning on doing, as well as how our property is relative to the neighbor.

So, what do you all think of this idea? Is it strong/stable enough? Does the neighbor's lower elevation matter? Cost wise how does a turned down footer/slab compare with a standard footer and slab? I'd imagine it is much less concrete.

[ballengerb1]

What we say matters little compared to the DC building inspector. Have you applied for a permit yet? What she suggests we call a thicken slab footing. In Illinois I can not attach a thicken slab footing to a traditional full footing, they will move at slightly different rates. Your DC inspector knows your climate and how it will behave, trust him.

[21boat]

I think the major concern, however is that my neighbor's property at that point is about 14" lower than mine.

If the finish grade on that side of your house 14" lower, then to meets the standard building code specs then that footer will be lowered 14" to meets codes.

She indicated that frost protection would be required because the footer wouldn't be deep enough to meet the frost depth requirement of 30".

I would be a bit concerned here as to what's accepted as "Frost protection" Why not dig deeper even if its hand dug?.

My other concern there is such detail on perpendicular rod or coat hooks shown But not a PSI for the footer and floor. Its required here for a separate foundation print showing in detail everything including PSI of concrete and anchor bolts. Not sure how it works there..

I have seen architects design and submitted drawings that omit some important things.

A good inspector can be a good friend. They drive me nuts at times and its usually because they FORGOT to mention a code was changed/tweaked. Seen it swing both ways..

Depending how detailed the specs this "flat layout is normal. Very seldom a residential shows footer elevation brakes. Simply because it can change 6 to 8" or more when finish grade is done or site conditions..

The inspector and good tradesmen will adjust footer depths to meet the code. It's a given, or should be.

My slight concern there isn't a PSI speck for the concrete footers/floors.

We call this footer a mono pour. Its rarely done here because we need min 3' deep for the footers. Our frost footers are 18" deep. They are not considered a structural footer here.

Bottom line is check with the inspector yourself and be pro active.. Actually I prefer my customers to do so. It helps explain why the cost is what it is..

[Stubits]

21 Boat- Thanks so much for weighing in on this. I know as a mason you must have plenty of experience I am including some photos that show the change in elevation.

No worries about the plans/architect. She's great and comes highly recommended. These are just some preliminary drawings, mostly to help my wife and me make decisions (hence the coat hanger). I am confident the notes will be comprehensive at the end.

So, based on the photos and the plans, what type of footer would you recommend?

We would like to come up with a plan that would minimize how much excavation and destruction we need to do on our neighbor's property.

Any thoughts would be great!

[21boat]

Hi stubits I'm laughing because when I first looked at the plans here I didn't see the name and got sucked into the prints.

I'm a full footer man myself. Its not a very big area to put on in.

Either or you need to get below that 14" for the basic if anything is done there your footer in low enough. Below enough form any finish grade, weather its your neighbors grade or not. Grade is grade.