Floors are poured

This has been a slow week by design.  We did get the slab poured last Friday with a coat of sealer on it.  It was a crisp clear morning when they began pouring the slab.  The first truck driver had completed his load and had pulled off to the side to wash out his truck.  As it happens, he was washing it out on the topsoil pile right next to a small pine tree we were planning to save. 

I asked him to stop washing out in that location as we have set aside a location on the site for washout. When he ignored my request I admit I yelled at him at which he asked me what my problem was.  When I responded that concrete washwater has a PH of over 12 and it could damage the plant material, he responded with as much scorn as he could muster “Oh, you’re one of those guys!” and packed up and left.  He succinctly summed up my philosophy and his in one terse statement.  I’m now proud to be officially included in the “one of those guy’s club” as there are many in that clan I much admire.  

 

Placing the tinted concrete

Concrete sealed by end of the day

We also began drilling the well on Friday, and got to a good quality aquifer.  It was a little bit deeper than we had hoped for, but will happily settle for quality and quantity.  Fortunately the soils in the region are all pervious from top to bottom, so the aquifer is in no danger of depletion.  On Monday they finished piping it into the basement.  Subject to having the test results and permanent power to the pump we are good to go with the water supply.

Getting ready to drop the well casing

Saturday we sawcut the control joints in the slab.  These joints provide a weak place in the slab for the concrete to break as it expands and contracts from temperature and shrinkage from curing.  At best locating control joints in a slab will only reflect a desire that the concrete will break where you direct it.  There are some age old formulas for locating control joints based on experience with concrete. 

The rest of the week, the job has been without activity.  Since the slab is our finish floor, we had planned for a week of cure time on the concrete slab before we put any significant activity on it.  We added a dark stain to the concrete, and had a hard trowel finish placed on it to give it a near mirror finish which you can see in the pictures.  The dark color will absorb sunlight during the winter months when the sun is low on the horizon and has the most exposure to the concrete slab. 

We considered a number of options for protection measures against accidental damage from construction activity and rejected all of them as too costly, fragile, or a hindrance to productivity.  We have settled for having the contractors just be careful.  The most exposed part of the project will be during the setting of the trusses when it is not uncommon for hammers or boards to be dropped.  During this phase we will use some of the rigid insulation and spread it under the work area as a protection measure.

The lumber for the framing will be delivered tomorrow, and if all goes as planned we will begin framing on Monday and potentially be in the dry by the end of the week.  The windows and doors are in town, the trusses are ready to deliver, and the roofer is on tap to dry in the building as soon as the sheathing is in place. 

 

PICs - Preping for the slab

Underground plumbing ready for inspection

Installing under slab foam insulation

Vapor/Radon barrier installed and taped at seams.  6" foam insulation underway

Installing the foam

Underground plumbing and slab prep

Underground plumbing and slab prep           

I spent Friday and Saturday at the Passive House conference in Washington DC while the job managed just fine on its own.  The conference provided inspiration and insight into some of the issues we have been struggling with on this project.  Of particular concern, expressed throughout the conference and weighing on my mind, has been the transmittance of vapor through the wall assembly.

The essence of the problem is that trying to eliminate vapor migrating through a wall in a tightly constructed home will create moisture problems.  Minute air leaks around outlets or pipes or windows will form a tunnel for moisture to escape and condense inside the wall cavity, creating mold and rotting conditions.  A better solution is to allow for vapor to diffuse slowly through the entire wall assembly. 

The net result is that we redesigned the wall section by reducing the wall thickness to move the dew point in the wall closer to the outside of the wall cavity.  We will be installing a plywood ceiling and taping all of the joints with a special vapor permeable tape.  We had already limited the number of penetrations (outlets, ducts, pipes) through the exterior walls and ceiling, but now have a heightened awareness of the implications of failure in these areas, and we will pay careful attention to sealing these penetrations.

The completion of the backfill makes getting around the site much easier.  The plumbing was completed, inspected, and backfilled.  The slab was graded in the bedroom wing, the vapor/radon barrier was installed, and we added 6” of rigid foam under the slab. 

We used staples in the basement to hold down the radiant floor heating tubing, but they did not hold well and we had to fight the wind to hold down the foam sheets until the tubing was in place.  In the bedroom wing, we opted to install a 6 x 6 wire mesh to ballast the foam against the wind and to fasten the radiant tubing.

The radiant floor distribution manifolds are in place and pressure tested.  We will keep air pressure in the lines during the pour.  If there is a catastrophic leak during the pour, a small concrete geyser will announce itself.  We have a quick patch kit on standby. 

We experimented with the cement stucco base coat in a couple of areas.  We have a window well around the basement egress window, so we installed the fiberglass lath and base coat of stucco in the area around the window so that we can install the window well.  We will install the finish coat with the rest of the house, but in the meantime we can backfill the window well.

Multiple attempts to get the phone company to install the underground cable to the house finally succeeded after they sent someone to install phone jacks.  In 40 years of dealing with this behemoth I have never been able to navigate their system. It is ironic that a communications company cannot communicate how to place an order for a new phone service. 

We met with the truss manufacturer to finalize the details of the trusses which should be delivered next week.  The windows are nearly completed.  We got pictures from the factory showing the construction.  The window headers have been engineered, and we have only a couple of minor revisions based on a change from the window manufacturer which affects the header size.  That should be resolved in a day or two, and we can place the lumber order for delivery next week.   

The well driller is drilling another well in the area and wants to drill tomorrow.  We plan to place the concrete floor as well.  The weather is supposed to turn cold next week, so we need to take advantage of the opportunity.  After that we will let the slab cure for a week before we begin framing.  

Precast and backfill in pictures

The plank is set in place by the crane and positioned manually.  The joints between the planks are filled with grout to lock them in place.  The gray tube is a foam rod to prevent the grout from leaking through to the basement.  The round dots at the bottom between the holes are the tension cables.  

The stairwell is formed by installing a hanger to hold the end of a shorter precast concrete plank.

We have backfilled as far as we can before we finish the concrete floor.  The Spiderlath around the basement egress window will show in the window well and be in the same plane as the wall above it.

We laid out the wall and cabinet locations, and tied the radiant floor system to the wire grid.  We will pour a 3" concrete cap over the precast to encapsulate the radiant floor piping.

Precast is set and backfilled

In spite of the fact that I have been out of town for several days, this has been a remarkably productive week.  Maybe I should draw some conclusion from that.   

The precast concrete plank was set on Friday.  This is always exciting because it seems so much gets done so quickly.  Precast plank is concrete that is extruded from a machine on about a 300’ long flat table.  You can see in the pictures the embedded steel cables at the triangular section between the hollow cores on the bottom.  It is hollow to conserve materials, and make it light weight enough to transport.  The system functions as a series of linked I-beams. 

When the concrete is fully extruded, they stretch the steel cables and tension them.  The concrete hardens, and the cable tension is released, tightening up microscopic cracks that occur in the concrete drying process.  The 300’ extrusion is cut up into the lengths for specific projects.  This is called post tensioned concrete, and is very strong.  We can clear span the entire basement without having to pour a footing, place columns or center beams to support the floor.

The decision to have a concrete floor is to create thermal mass.  We can store heat or “coolth” in the thermal mass of the concrete.   It retains the temperature for long periods of time and releases that temperature slowly.  This strategy will be useful in the winter when the sun is at a low angle through the generous southerly windows.  The sunlight will penetrate the windows and charge up the heat in the floors, storing it for the night.   The inverse is true in the summers.  We can open the windows on cool nights, and store the “coolth” for radiation in the daytime.  That’s the theory anyway, and we will soon get to put it into practice.

When the precast was set, we installed a wire mesh on top of the precast and zip tied the radiant floor tubing system to it in preparation for pouring a 3” concrete cap over the top.  The tubing is zoned by room to provide maximum controllability.  This will encapsulate the tubing in 13” of concrete, and we can heat or cool the slab as we need to adjust temperature.  More on that in a future blog.

We added a single wood frame wall on the east wall of the garage to allow for the early installation of the electric meter and underground wire service for electric and phone.  The underground phone wire was to have been run this afternoon per instructions given over the phone.  The electric meter should be installed and inspected later this week.

We were fortunate to be able to backfill the foundation walls this week with very wet weather.  The sandy soils on the site are no impediment to backfilling the foundation, and assisted in the compaction of the soils after such a dry fall. 

We had a pretty big setback with our intent to install cement stucco on the exterior of the house.  We had planned to practice on the area below grade so that we might be proficient at the application by the time we got to the finishes that showed.  The compressor we were using is too big for my 6500 w generator, and we (ok I) roached the motor.  We have had to abandon the plan to practice on the foundation, in favor of maintaining the schedule.   We may end up with either really thick stucco on some walls as we master the application skills, or end up hiring it out to a competent contractor. 

The plumber completed his underground plumbing and is waiting for an inspection tomorrow to backfill his trenches.  He was a great help to me (as I choked back my frustration with the compressor) when he brought his small hand held compressor to help put a test charge on the Pex tubing for the radiant floor system.  We found a few leaks at some of the joints, which we fixed, and the system held pressure the rest of the day.  It was great peace of mind to leave on my trip knowing we had that hurdle behind us.

Next week we will be able to install the rest of the underslab insulation on the bedroom wing, install the radiant floor system, and pour the slabs, weather permitting which will be a big milestone.  I have a week of cure time after that before we start the framing.

The week in pictures

Waterproofing done, fiberglass lath installed

Radiant floor heating loops just before pouring concrete

Placing the concrete slab

Getting cemented into a corner

Garage wall installed to accommodate electric meter and phone

Building Plans