How To Build A Second Story Deck With Tube Steel Posts

You would want one, too, if you lived in Sausalito with a beautiful view of the San Francisco Bay. A stroke of luck for my company, several other builders were not willing to deal with steel deck supports. True, steel is far less forgiving than wood, yet that made this an interesting challenge. And who would not love having a job with a view like that?

The reason this 2nd floor deck received steel posts is to keep the view from downstairs windows relatively unobstructed, and to maintain usability of the flagstone porch. Sausalito is located in earthquake country, and had the deck been designed using wood posts, it would necessarily have included an X-shaped brace between them to resist lateral movement. As you can tell from the photo below, this would have impeded the view substantially.

Just so you have an overview of this second story project, we:

• Removed the stairs and garden shed below;
• Replaced the master bedroom window (top left);
• Replaced the bedroom door with a new Marvin door;
• Added a new Marvin door to right of door shown, into the kitchen; and
• Kept the opening at the bottom of the stairs, but filled-in the lower half with a railing.

Preparing For Construction

The owners already had construction drawings made by an engineering firm, so all that was left was to obtain a building permit and get to work.

The single most important preparation was figuring out the height of the tube steel posts, just over 14 feet. This was determined by putting a laser level on the finished floor of the 2nd story master bedroom, and projecting the laser beam at a grade rod, placed on the patio where each support post would be located. The reason this measurement had all of our attention is obvious: if a wooden support is a bit too tall, it can easily be cut. If it’s too short, shimming is always an option. With steel, however, adjustments are a bit more tricky. Once we were satisfied with our work, we verified placement of the posts, and called-in the cavalry.

 

Pier Drilling

The engineer had established that each pier should be 12 inches in diameter, and about 7 feet deep. They ended up a little deeper than that, based on soil inspections while drilling took place.

Tip:

If your project includes drilling or excavating of any kind, remember to:

• Call 811 or visit Underground Service Alert if your project is located in California. At  no charge to you, these friendly folks notify local utility companies who will come out in a jiffy to mark most utilities that may be underground. If you do not call and cause damage, you will be held responsible for repair costs.
• Have plenty of thick plywood around to securely cover any pier holes or other excavations. It is easy for a child or pet to fall into.
• Consider what to do with all that dirt. Where will it go? Can you spread it out around your property? Do you know of someone who needs dirt? Having it hauled away is expensive.

Another Tip:

I highly recommend you insert a sleeve akin to Sonotube to protect your newly drilled holes from caving in. If they do, you can pretty much start all over again, and who wants that?

Lastly, remember that the hydraulic drill rig is powered by a tow-behind compressor. See to it that you have adequate parking space, and make sure there is sufficient clearance for ambulances and fire trucks to pass by. Typically ‘No Parking‘ signs can be obtained from the same authority that issued your building permit. One of our projects required that an entire street be closed to through-traffic. We had to obtain special permits, install road signs days ahead of time, and have extra personnel on hand to re-route traffic.

Rebar Cages

Once the holes are drilled, you are ready to install rebar cages. Here’s a photo of one used on a different project. This baby is a nearly eleven feet long, as compared to the 7+ feet we used for the 2nd story deck. The latter had a coil design, unlike the one shown.

When rebar is installed right next to dirt, there needs to be a 3 inch space between the two. We ended up tying a bunch of 3″ so-called dobies to the outside of the cage. This helped center the it as we lowered into the freshly drilled holes. (A dobie is a square chunk of cement, measuring 3x3x3 inches in this case. It also has two pieces of tie wire sticking out, so it can be attached to rebar). When determining the diameter of the hole to be drilled, figure as follows: take the engineer’s spec (16″ in our case), then deduct a 3″ clearance on each side of the cage, so the actual cage diameter is 16 minus (2×3) 6= 10″. That 3 inch clearance also applies to the bottom of the cage. Unless you want the whole thing to rust out in a few years, take these clearances seriously and install with care.

If you want to do things fancy, you could have the rebar cages coated to prevent rust. I often see these coatings on CalTrans projects. Anyone in northern California knows where to get this done? I’d be interested. As an aside, here are photos of a huge rebar cage being lowered by a crane, and of note are guiding wheels welded to the outside of the cage. They help center the entire unit while being inserted into the hole. Cool!

Setting J Bolts And Pouring Concrete

As the name implies, J-bolts are bolts shaped like the letter J. The hook at the bottom provides good protection against uplifting motion. These bolts are supposed to be tied to the rebar cage with tie wire, and this entire contraption should be rigid so it won’t move during the concrete pour. Easier said than done. Sure, there are many ways to rig up some lateral supports, but we were faced with another obstacle. One of the pier holes was taking on water, and I really didn’t want to see that.

A garden hose was guided to the bottom of the pier, and connected to a transfer pump. That was all fine and good, but there just wasn’t enough room for the hose plus the cage plus a rig that would keep the j-bolts steady, plus room for the concrete pumping hose. On top of that we also wanted to stick in a vibrator during the pour. All this had to be in place for the building inspector to see, hence my concern. In the end, the J-bolts rig was not secured, and the inspector was grumpy but yet he did not interfere. CVAN Builders did several projects in Sausalito back-to-back, and received many compliments from the local building official. Good relationships with inspectors go a long way. A lonnggg way!

How Much Concrete? What Kind?

There are many calculators on the internet for just this purpose. Once you know how many yards of concrete you will need, add about 10% to what you calculated. The reasons are that:

• When an auger pulls dirt from a hole, it tends to scrape additional dirt off the hole wall, thus requiring more concrete to fill; and
• Once piers are drilled and soil is removed, dirt begins to dry and shrink. This is a minor issue, but some holes do linger due to inspection delays, and so forth.

When you order concrete, you will be asked about the size of rock, slump, sack mix, and PSI. It is outside the scope of this post to delve into these, but gaining familiarity will help you.

Using a concrete vibrator helps eliminate air bubbles, and provides greater density. Don’t keep this tool in one place too long, or you risk gravel sinking to the bottom, and thus decreasing pier strength. Dang! One more… be sure to wrap the threaded part of the J-bolts with duct tape before concrete is poured. The threads will stay clean, making it so much easier to install the nuts.

Oh, before I forget: in many cases you’ll use a subcontractor who provides the concrete pump and hoses. When your pour is done and they get ready to clean up, what will happen to the concrete that’s inside the hoses? For a marginal charge, the left-overs can be pumped back into the concrete truck, and the manufacturer will recycle it. Just remember to add this to your budget.

Lastly, you may be required by the building department to have so-called ‘special inspections’. This means that either the original engineer, or, and more likely, an independent engineer, be present during the pour. He will verify that the work was done according to the construction drawings, and his lab may test the concrete to verify it meets the required strength. Your local building department may also require an ‘observation letter’, signed and stamped by the independent engineer. Special inspections and observation letters can easily add $1,000 or more to your project, so keep it in mind. when making your budget. An independent engineer (aka testing engineer) can be hired only by the client, not by the contractor or architect. This is to prevent any conflict of interest.

Installing Tube Steel Posts

While all the other work was underway, our steel contractor was putting together the posts. He left the base plates for last, so we could make precise measurements of the j-bolt locations after they were installed. A little tweaking of these is possible, but take great care in doing so. The last thing you want to do is compromise structural integrity.

Keep in mind, too, that you will want room for a ratchet or wrench, and you will want the bottom of the nuts to fasten flat agains the top of the base plate. In addition, this plate has welds that attach it to the tube steel, and this takes up some space. I admit I forgot about that until it was pointed out to me; it pays to have great subcontractors. First install nuts that will go below the base plate. Level them out as well as you possible can. Next install the posts, and take care to not bur threads or bend j-bolts. Once in place, fasten the top nuts, hand-tight, and put a 6 foot level along each post. Once you’re good in all directions, tighten all nuts, and fill the space below the base plate with epoxy grout.

Deck Framing

We installed a 6×10 header between the posts. It was made of pressure-treated fir, and since the post buckets were not galvanized steel, we used bitumen tape instead. As long as you install a long-lasting barrier between steel and pressure-treated lumber, you’re good to go. Perpendicular to this beam, we installed a 3x ledger that was attached to the house. Similar to the project I described in ‘Curved Ipe Deck — Photos & Tips‘, we installed deck-to-house spacers to create a break between ledger and siding. All holes into the house framing were pre-drilled and filled with silicone caulk prior to installing galvanized lag screws.

I can quickly think of several scenarios in which a ledger would be attached straight to wall framing, without any deck-to-house spacers. In such cases, order up some GSM flashing. Have it run at least 4 inches up the studs so the wall’s vapor barrier (aka ‘building paper’ will cover it.

One Simpson Tension Tie at each end of the ledger were bolted through the ledger and new blocking in the wall framing with a piece of 5/8″ all-thread, with washer and nuts at each end. After that, framing was conventional. Two-by-six pressure-treated joists fastened with LUS26Z joist hangers (‘Z’ denotes  being galvanized). Decking and railing material were all clear heart redwood, which the client unfortunately decided to paint.

Clearances

Deck railings have to be 42 inches high, which can wreak havoc on a nice view once you’re seated at a table. One way around that is to install a cable railing or glass panels. Call your local building department to see if they are allowed. Spindles under the deck railing have to be spaced less than 4 inches apart. For that matter, all spaces that are part of the deck have to adhere to this requirement. Just so little kids don’t get their heads stuck or squeeze through.

Exterior Electrical Receptacle

If you build a deck on a first floor, code requires an electrical receptacle. It should be a GFCI-protected unit, enclosed in appropriate housing. However, on a second story this does not apply. Or so the inspector told us. Call your local building department to make sure they are in agreement.

Hopefully this was of help to you. As always, don’t hesitate to ask questions, no matter how simple. There are other deck projects I want to share, so subscribe to the RSS feed.

Resources

• Deck construction: CVAN Builders
• Design and engineering: Pheif Engineering
• Structural steel: Marin Manufacturing, San Rafael, CA
• Special inspections: Columbia Research & Testing, Windsor, CA