Deck pier footings

[dfar]

I'm building a deck on piers in Massachusetts. I've gotten conflicting information from contractors about building code concerning pier footings, and I can't find anything specific in the "Foundations" section of the MA building code online (http://www.mass.gov/Eeops/docs/dps/780%20CMR/780054.pdf).

I understand that piers must be set 48" below finished grade, but I see nothing about whether or not a bell footing (Bigfoot) is required for a deck. The difference between a 10" pier and a 24" Bigfoot is the difference between renting a Bobcat with a 10" auger or hiring an excavator to dig trenches. I would greatly prefer to avoid trenches (especially with all the rain we've been getting), and I don't think footings are necessary.

Does anyone know if Bigfoots are required on deck piers in Massachusetts? I can ask my building inspector, but he rarely gives straight answers.

Ken Benson

[MountainDon]

Section R403.1.4.1   may contain the answer. Scroll to the end of the section below.

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 of600 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.

That is copied from the MA code for 2011 located at...
http://ftp.resource.org/codes.gov/ma_residential_2011.pdf

So it seems that as long as the deck is fully supported by piers; no connection to the house via a ledger board, for example, then footings are not required.  I'm not/not sure I like that idea; it would seem the deck with its people load might be too much weight for the earth to provide proper support with only the pier end resting on the soil.    I am not/not an engineer, so that opinion is worth everything you paid for it.



Here's an article on decks from an engineer...
http://www.structural101.com/Support-For-Exterior-Deck.html
Scroll down to the last section "Posts & Foundations"

[dfar]

Thanks, MountainDon

The consensus among three local contractors I talked to over the weekend is that we need pier footings, regardless of code. And because we were planning on using a ledger, it looks like building code requires footings anyway.

The excavator I've been talking to suggested precast piers. These remove the problem of leaving lots of open holes for the inspector to measure frost depth. He just digs a hole, sets a pier, digs another hole backfilling into the first hole, etc. No open holes, no hand digging. Anyone have any experience with precast piers?

[Don_P]

They are forbidden here and in many jurisdictions. Code does require footings, in some cases you could catch a break on depth. Since this is attached you need to be full frost free depth.
Our inspector, and every one I've worked with, requires the hole be open with steel in place for him to inspect prior to placement of the footing concrete.
as you've found the codebook pretty much avoids decks. This link has a good deck construction guide that many building departments use, open DCA6;
http://awc.org/codes/dcaindex.html

[dfar]

Precast piers forbidden? Why? I did some reading about them over the weekend and they seem like the sort of "manufactured" material building inspectors like.

[Don_P]

I am talking about a precast pier block. Inadequate bearing size, they have too small a footprint. A concrete footing conforms to the dig, a precast settles into place, or further if it's footprint is inadequate for the load. They are unstable and there is no positive attachment to the post. The only thing that really matters if you are sold on them though is whether your building department allows them.

When in doubt while looking at a "manufactured" product, look for an ESR number on the labelling. You can then look up the conditions of accepted use at iccsafe.org under the ES tab. For most products you'll also see labelling from an independent third party testing agency. An inspector doesn't "have" to respect these but those are the kinds of engineered products that tend to make them smile.

[dfar]

I don't know what a precast pier block is. The precast piers I'm looking at have a 24" base, same footprint as a Bigfoot. They come with a lag bolt on top, so the post attachment seems pretty positive. They look a lot like the ones at http://www.youtube.com/watch?v=Iaicu30fLvw. I can't speak to settling, except to say that they'll be set on undisturbed earth 12" deeper than we would set sonotubes with Bigfoots. They're made with 4000 psi concrete poured with rebar and fiber.

My building inspector doesn't like them either. He says I'll need an engineer's stamp, and that I won't be able to get an engineer's stamp because no self-respecting engineer would approve precast piers. He says they're made from what's left over in the truck when the truck returns to the cement plant, but the piers I'm looking at are made by a company that makes precast products, not a concrete delivery company.

[Squirl]

I thought you meant one of these.  They are sold in big box retailers as deck pier blocks.  They are fine for sheds and such, but not for quality code building.  Personally, I like a concrete pour.  It is easy to make very minor adjustments with level when poured in place.  I'm surprised the company doesn't have an engineer's stamp.  Truss and beam manufactured products usually do. 

[dfar]

No, that would never work here in Massachusetts. Piers have to be buried 48" or they move all over the place.

I don't know yet whether the precast piers are stamped. I have specs on them, but I'm waiting for the company (Washburn Vault in Brattleboro VT) to tell me if they have an engineer who can stamp the specs.

[SouthernTier]

A couple of years ago there was a blog on NY Times written by someone from Boston building a cabin in Maine.  He used precast piers.  The blog entries are still available at http://topics.blogs.nytimes.com/tag/from-the-ground-up/  You'd have to go to the start of the posts to see the part about the precast piers: http://topics.blogs.nytimes.com/tag/from-the-ground-up/page/6/

[rick91351]

I like Squirl thought those funky deck pier blocks.  I was seeing big problems.  I myself would just dig, form and pour.  How rocky is your soil?  And how many piers?

I loved your line "I can ask my building inspector, but he rarely gives straight answers."  Funny then when it comes to final, there are all these why did you, didn't you things! 

[dfar]

In the end, we did dig, form, and pour. Very rocky and wet.

Building inspector made precast piers extremely unattractive. He required an engineer's stamp, which he assured me I would not get. I did manage to get the pier company to get stamped plans from the engineer who designed their piers 17 years ago. He faxed them to the building inspector, who told me he shredded them because he could only accept a wet stamp (which apparently means original, not copy). The pier manufacturer paid $500 for the stamped plans and did not want to give up his only original.

I decided to stop fighting and so we started digging holes. We got 10 holes dug down to water (about 3 ft) in one day. The next day we dug the last foot, got the holes inspected, dipped about 20 gallons of water out of each hole, dropped a bag (or sometimes 3) of concrete mix in the hole to dry things up, set sonotubes and backfilled. We cut rebar and set two long pieces into the concrete at the bottom. We covered the sonotubes, and the rain came.

The next morning (this morning) all the tubes had at least 12" of water in them, so we started mixing and pouring. We managed to get all of them poured before the sonotubes self-destructed. Lotta water in the ground here.