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Forums» International Building and Residential Codes -- Structural Issues» Footings for a deck on bedrock; Cliff hanger of a deck

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Footings for a deck on bedrock; Cliff hanger of a deck
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Footings for a deck on bedrock; Cliff hanger of a deck By  Keith Fravert

Posts: 1

8/2/2012 4:12:00 PM

I am a homeowner living in Birmingham Alabama and have a question for anyone familiar with the construction of a deck. Home has the original cedar deck built in 1976, but is in need of replacement. Wanting to construct a replacement deck in the same spot of more or less similar size (approx. 600 SF). Current deck location is within inches of a 50' drop off of a cliff (Shades Crest). Current posts are either in the ground OR they are on preformed concrete pads.  The new deck will come back approximately two feet AWAY FROM the cliff face.  Ground is very uneven. and has large limestone, rockface and boulder protrusions and I have a red oak that will have to be removed. Can anyone tell me how these footings can be mounted/installed and still be up to "code"?  I am spending around $15K-18K which includes a pressure treated wood support structure, IPE wood deckboards a screened area (12"x24') with a gable roof, electricity and a gas line for winter heat and a gas BBQ (power and gas already on old deck).  The balance (+/- 312 SF) will be an open deck with rails.  The overall shape is a rhombus with the center square being the screened area.  I would like to know because this is alot of money for me and I do not want to have to pay to rebuild the footings on the darn thing.  Have not removed the old deck yet and I do have a licensed, bonded and insured GC (good for jobs up to 1.5 million in Alabama). I just do not want to be ignorant when he tells me we are going to do it "this way" or "that way".  Please forward any questions that you in the forum would deem important for me to ask the GC/builder.  Thanks in advance.  Any advice or direction is welcome.  I should be starting the demolition process by mid to late August. Our municipality utilizes the IBC/IRC 2009 code. We have no "frostline" per se in Alabama.

So, the following are my questions:

1) How should the deck footings be secured and be code compliant? What type of material (metal, pressure treated, etc) should the sub-structure be made of?

2) What would/should the terms/lingo be for this application? (I.E. Trying not to look like a total idiot in front of the GC and be able to tell if I am being taken to the cleaners).

3) Can any of these cedar decking boards (some 8' to 12' in length) be replaned and reused.  Is that possible or even cost effective? Can they be recycled?

4) Does anyone have an opinion on IPE (ironwood) deck boards, their install, cost, pitfalls or success stories on this product?

5) A rough "guesstimation" of cost for this deck

Many thanks in advance,

Keith

kfravert5920@charter.net

 

 

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Footings for a deck on bedrock; Cliff hanger of a deck By  Gary Brackins

Posts: 66

8/3/2012 4:18:12 PM

Here is what the code states for decks and their foundation .....

 

R403.1.4 Minimum depth.
All exterior footings shall be placed at least 12 inches (305 mm) below the undisturbed ground surface. Where applicable, the depth of footings shall also conform to Sections R403.1.4.1 through R403.1.4.2.

R403.1.4.1 Frost protection.

Except where otherwise protected from frost, foundation walls, piers and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:

1. Extended below the frost line specified in Table R301.2.(1);


2. Constructing in accordance with Section R403.3;


3. Constructing in accordance with ASCE 32; or


4. Erected on solid rock.


Exceptions:

1. Protection of freestanding accessory structures with an area of 600 square feet (56 m2) or less, of light-frame construction, with an eave height of 10 feet (3048 mm) or less shall not be required.

2. Protection of freestanding accessory structures with an area of 400 square feet (37 m2) or less, of other than light-frame construction, with an eave height of 10 feet (3048 mm) or less shall not be required.

3. Decks not supported by a dwelling need not be provided with footings that extend below the frost line.

Footings shall not bear on frozen soil unless the frozen condition is permanent.

 

I would recommend hiring a professional engineer to evalauate the ground to determine if it stable enough to support the imposed loads of the proposed deck and room. Just because it was stable in the past does not mean it is stable today. I'm sure the building inspector will want an engineer's evaluation. I would if I were the inspector. Have you discussed this with the building official?

The engineer can design this as a free standing structure that is connected to the house, or can design it for use of a ledger. I have pinned foundations to solid rock (ledge) in the past with approval of the engineer. It is allowed by the code as shown above. You would need enough bearing area to distribute the weight onto the ground. It takes a set of eyes on the site to determine the best way to accomplish this.

I can't do pricing for your area, but the amount you stated seems cheap to me, at least for the area I am in, especially for IPE. The cost of an engineer may seem like an unneeded expense, but then you are paying out a good sum of money, its best to make sure your money doesn't end up in the valley below.

At least my humble thoughts .....  Good luck!

Gary

"If you don't have time to do it right the first time, when will you find the time to fix it?"

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