[oatlord]

I'm planning the deck I want to build, and I noticed this in my local city's deck code book:

"DECK FOOTINGS CLOSER THAN 5'-0" TO AN EXISTING EXTERIOR HOUSE WALL MUST BEAR AT THE SAME ELEVATION AS THE FOOTING OF THE EXISTING HOUSE FOUNDATION."

Given that it's all caps, it must be important, but I'm curious why, and if I can get around only having footers that are 30" deep and ~2' from the exterior wall. I'm using 6x6 posts, and attaching to the house via a ledger. The close footings are to frame around a bay window that's 9 feet wide. Anyone have any thoughts? Thanks.

 

[dvatt]

That is bc it is a backstop zone. How old is the house?

 

[oatlord]

It was built in 1996.

 

[Daniel Holzman]

The rule comes out of the International Residential code. The reason for the rule is to avoid destabilizing the house foundation due to excavation for the deck footers in the zone of influence of the house foundation.

In order to deviate from the rule, you are probably going to need to talk to the building inspector and discuss your situation. They might require an engineer's letter explaining why it is OK in your specific case.

 

[oatlord]

The rule comes out of the International Residential code. The reason for the rule is to avoid destabilizing the house foundation due to excavation for the deck footers in the zone of influence of the house foundation.

In order to deviate from the rule, you are probably going to need to talk to the building inspector and discuss your situation. They might require an engineer's letter explaining why it is OK in your specific case.

Ahhh....that sounds like fun. Thanks for the information!

 

[concretemasonry]

Since you not list your location on your registration or post, it is difficult to know the frost depth required. You probably assume the neighboring house is legal (but not always). Since it is a ledger supported deck the depth of the posts is more critial than a free-standing deck.

Do you actually know the depth of the near-by home footings?

Since it is a deck, there are probably not many posts too close, so a little extra depth on the Sonotubes to get to the depth required for those few holes.

An engineer could help get a variance, but it may cost more the a little extra augering an tube lengths. The cost of the xtra material is minimal with tubes, but if they are hand dug the amount of concrete is also more and it scares inspectors because of the reliability.

 

[jomama45]

The correct answer to the question is:

The code assumes that a maximum of 5' of soil (most often far less in actuality) was disturbed around the perimeter of the foundation when the excavation was done. Setting these tubes on top of backfilled soil will ultimately lead to the tubes settling. They need to bear directly on undisturbed virgin soil.

I'd recommend re-designing the deck so it bears completely off of the ledger, or completely off of the tubes, but not a combination.

 

[oatlord]

The correct answer to the question is:

The code assumes that a maximum of 5' of soil (most often far less in actuality) was disturbed around the perimeter of the foundation when the excavation was done. Setting these tubes on top of backfilled soil will ultimately lead to the tubes settling. They need to bear directly on undisturbed virgin soil.

I'd recommend re-designing the deck so it bears completely off of the ledger, or completely off of the tubes, but not a combination.

Humm, I misread our deck code sheet. It says the frost depth is 12" here not 24" like I thought before, so would I need to go 30" then or would that be overkill?

When you say completely off tubes or ledger, I'm not sure I'm following. Wouldn't one end have to be supported by tube footers?

 

[Knucklez]

how old does the house have to be in order to consider the once disturbed soil (backfill for foundation wall) becomes compacted over time?

 

[Gary in WA]

There is no time-line involved. Similar to “Footings shall be supported on undisturbed natural soils or engineered fill.”---- http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_4_sec003.htm

You don’t know if it was originally back-filled and tamped or filled with top-soil and logs which could rot and cave-in, forming a void below the new footing.

If you had to build that close without digging down--- need an engineer to pass it—may have a hard time finding one; “Fill soils that support footings and foundations shall be designed, installed and tested in accordance with accepted engineering practice.” From: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_4_sec001_par001.htm

Gary