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.