Thursday, October 28, 2010

Progress on stem wall forms and rebar layout

Today they finished the formwork on one side of each stem wall.  The crew also made a lot of progress with the rebar steel.  The engineer dictates the spacing of the rebar and it is based on the height of the wall and the loads it will take.  He has asked for #5 bars for the verticals.  You can figure out the diameter of the rebar steel by taking the # and dividing it by 8; the #5 bars are 5/8" in diameter.  He has detailed them to be 16" on center.  16" will recur over and over in the structure of the house because all american products are based on typical dimensions that are evenly divisible by 16" to minimize waste.  For example, plywood sheets are 48" and 96".  The horizontal bars are #4's (1/2" in diameter.)  To minimize waste and (if you're interested) save money on a project you can base you're dimensions with this in mind.  For example wood studs come in 8', 10' and 12' lengths or any length over that if they are special ordered.  If you can stick with the 8' stud they are a lot cheaper than the 10' stud...and so on.

view of formwork (one side done) and rebar...

As the Architect we have dictated the layout of the walls based on where we want them relative to the floor above.  In some places we wanted to minimize the apparent height of the wall so we held the foundation wall in from the footprint of the building above.  In those places the building will cantilever a couple of feet and create a visual break and a shadow.

We also have several openings in the wall that were dimensioned on the Architectural Exterior Elevations.  Some of the openings are for ventilating the crawl space below the house and are required by our local building code.  We had to calculate the square footage of crawl space and provide ventilation based on a percentage of the area below the house.  Other openings are for access and for equipment.

The photo on the left is of the rebar layout at the West wall.
The photo on the right is a detail of the opening.  They will attach wood block outs to the formwork so that concrete does not get into this area.

The large opening is for access to the crawl space under the house and also for a new furnace for the addition.  The new furnace will be 93% efficient using very little energy and qualifying us for a rebate from our local gas company and also a 30% tax credit...yay

Some walls already have the formwork on both sides and rebar done.  The two form walls get connected by "ties."  The ties keep the walls connected during the pour so that the weight of the concrete doesn't bow them or make them actually blow out.  There are many many different types form ties and they create different looks on the exterior wall and also have different structural strengths.  For very large, heavy thick walls the engineer and architect may need to spend a lot of time making mock-ups of the effect of different ties.  Ours are pretty minimal and won't be very visible on the final wall.  When you see what look like evenly spaced holes on a large concrete wall those are the marks of the ties that were used to hold the formwork.

At the top of the wall the concrete will be connected to the wood framing by a "sill plate" and "anchor bolts."  The sill plate is a very thick piece of wood that has been treated against rot and insects by infusing it under pressure in a bath of chemicals.  To connect the sill plate to the concrete a hole is drilled in the sill plate and a long bolt with a "j" shape is hung from the sill and held in place by a thick square washer.  The anchor bolts are spaced such that every third one gets tied with wire to the vertical steel.  In this way the wood and concrete are stiffly connected which protects our houses in California from literally "jumping" off of their foundations.  Because we are subject to more than just gravity here our engineers have to account for lateral and vertical loads also!

Our addition is 2' lower than the original house so that it steps with the is a photo of the footing stepping...

...and Bea taking a last peak below the house.

If all goes well the crew will wrap up the steel placement tomorrow get it inspected by three different people and then pour by Wednesday....

Tuesday, October 26, 2010

Framing the Stem Walls

After a week of rain the crew is back on the site and framing the stem walls.  We are going to have Cast-In-Place stem walls that will run from the footings to just below the wood siding of the house - at their tallest point they are about 7' high.

First the crew nailed down wood runners with a special gun and nail system that uses gunpowder to drive nails into the concrete, the nails are called redheads.  Then they will frame the walls with wood studs and attach 2x12 board to them on the inside face.  This is what they call the formwork and is what will hold the concrete to form that walls.  When the concrete has had time to set they will pull off all the wood.

framing the formwork for the stemwalls...

Pete the contractor nailing the formwork for the wall that will support our existing house...
Here the foreman Chillo is using a surveyor to locate the top of concrete height to make sure that it is the same at all points around the house - this way our house will be level.


View of formwork from inside the trench...

 the youngest member of our crew - "Giovanni"

Formwork at the corner...

Friday, October 15, 2010

Pouring the Footings

Yay Concrete!

We passed the steel inspection this morning and were pouring concrete by the afternoon.  After we passed the inspection the crew installed a few screeds to help guide how deep to pour the various footings since they are all at different elevations.

The wood board in the foreground is the screed for the higher footing, there is another one beyond for the lower footing

The structural engineer specified 3000 PSI concrete and specified that we provide 'test cylinders' to prove the concrete was mixed to the appropriate strength.  The concrete will need to cure for 28 days first before it reaches it's maximum strength.

This video is from the beginning of the pour.  It takes about twenty minutes or so to unload a full 10 cubic yard truck of concrete - we had three full trucks today...
The device on Gordon's belt is a remote so that he can start and stop the pump if the crew needs to move to a different location or adjust the hose

The concrete is poured into a concrete pumping truck - that is Gordon in the background guiding the truck back to just over his pump.

After they pour the concrete for awhile they vibrate it with a special vibrating wand to make sure that there are no pockets of air...

 This is a tamper and it helps to level the concrete.

That's Pete the contractor in the background.  He's re-calculating the yardage of concrete because he's worried that we might not have enough....

He's using a finishing trowel to make sure that the top of the footing is smooth.


Thursday, October 14, 2010

Stem Wall Layout and Steel Inspection

Yesterday and this morning they finished placing the vertical bars that would tie the footings into the cast-in-place concrete stem walls.  To facilitate laying the vertical bars out the crew constructed guides out of wood studs that were surveyed according to the plan and then staked into the ground.

The wood studs are layed out at the centerline
of the exterior walls.  The vertical rebar then gets attached to it
so that it stays true during the pour.

Rebar "L's" get connected to center of footing and wood studs.

Steel is done and awaits inspection by the city.

Inspector reviewing steel placement

After verifying that we had all the necessary reports (Soils Engineer certificate for excavations, Deputy Inspector approval of epoxy into existing footings and Structural Engineer Observation Report) the City Inspector performs his own review of the steel placement.  

There is always a little variation from what is drawn exactly on the plans due to the site conditions.  In our case the inspector has asked for two corrections.  The crew made the corrections and the inspector will come back tomorrow morning.  If the inspector gets to the site before 11 am and approves the adjustments we can pour the concrete at 1 pm.  Otherwise...the concrete pour gets moved to Monday!

Tuesday, October 12, 2010

Setting the Steel

Today they are getting all of the steel in for the footings but still need another day to tie the vertical bars that will become the walls.  We called for an inspector to approve the steel on Thursday morning.

Here are a few photos of the steel:

They tie the rebar together with steel wire to hold it in place while the concrete  is being poured in

The cages which are sitting inside the footings and are held off the ground by little concrete blocks - this allows the concrete to surround the bars on all sides

This is where the engineer has called out for extra reinforcing at a corner

The new footings also need to be connected with the existing footings - to achieve this they drilled into the existing footings and used a very very strong glue called Epoxy to attach the rebar into the existing footing.  This rebar will get connected to the rebar from the new footings so that they all act together in case the house settles or in case of an earthquake.

Monday, October 11, 2010

The Excavations Inspection

Today we had our first inspection.  The soils engineer came out to evaluate the excavations.  He made a sketch of them in plan and then went around the entire site with the contractor and the foreman and surveyed each one for depth from the top of natural grade to the bottom of the footing and also from top of bedrock to the bottom of footing.  

Inspector making the sketch

surveying the excavations

Approval letter 

Now that we have approval on the excavations we can proceed with laying the steel in.  The crew has already started forming the cages that will be set at the bottom of the excavations.  These are for the footings and will be the first concrete pour.  If they get all the bar in place today and tomorrow and we pass the steel inspection on Wednesday we could pour concrete as early as Thursday.

They build the cages outside of the trenches and then lay them on top of spacers which are little blocks of concrete.  

Friday, October 8, 2010

Taking out the last of the footings

Today they are taking out the last of the footing and digging the final trench 
where the old footing used to be. 

...they perforated the concrete with holes...

 using a roto hammer...

...and then got out the sledge hammer...

This was the last corner to was the hardest to get out..

Time to take out the jackhammers...

view from the back...sans footings

profile of remaining footing

view from under the house

Dumping the demolished footings in the back via the raised ramps...

Pile of demolished footing