Thursday, December 16, 2010

PassivHaus Aiming

Holy Smokes, is it really only 15 days  to 2011?!  Madness.  Time has been screaming by down here and we have quite a few new developments for y'all this week.  First up is a brief overview of the simple, French drain that has been installed around the exterior of the footings.  This tried and true system has been in use for over 200 years and has been helping people direct water away from areas vulnerable to degradation over long periods of time from exposure to groundwater.  The three main components to create a French drain are:

(1) A perforated pipe of at least 4"/100mm diameter (the larger the less chance of clogging)
(2) Tightly woven fabric or 'geotextile' to wrap around the pipe.  (In his original systems, Mr.Henry French used narrowly spaced tiles to dual purpose as his fabric envelope and drain pipe)
(3) Tons o' gravel (a bit smaller than fist size to fine pebbles for the varying depths)

After digging the trench adjacent/parallel to the area needing drainage/diversion, create a (for lake of a more technical term/analogy) hot-dog bun out of the geotextile/fabric and then put the perforated drain pipe in the bottom (hot dog), and cover it with a good 3-5"/75-125mm of chunky relish, aka gravel.  This chunky gravel topping lets water pass through quickly as opposed to silty or spongy soils which retain water.  After dousing the pipe in gravel, it then becomes a bit like a burrito as you wrap the fabric around itself and secure it so that no small particles can enter/clog the drain pipe.  With luck and attention to detail, the pipe will remain unclogged for upwards of a decade-after that who knows, maybe you can leave some bits of cheese in there and send some rats in to tunnel it out for you.  After the hot-dog-burrito piping part is completed it is then just a matter of back fillng the trench with more larger sized aggregate on top (enchilada style) and then progressively finer material to the top of the trench (depending on how deep the trench is).  To the right is a photo of the 'topping' stage of our French drain along the back wall-in the bottom right corner you can see the blur of the gravel being dumped on top of the black pipe which is uncovered in the top left corner.

                                                                   Next up on this massive post, we'll cover the process of pouring concrete bond beams on top of the rammed earth walls for roof integration.  On the left here you can see the same trench in the foreground as pictured above with the French drain start (now back filled to height), but let's focus on the wall and its crown of formwork in the distance.  The main force at work here is compression, which is imparted on the shutters/forms via the calipers.   Basically a caliper is composed of to vertical squeezing 2x4's which are connected by a horizontal 2x4 (at the top) which sets the desired width of the compression.  The cinching action comes from a half inch/15mm threaded rod that runs through drilled holes in each of the vertical pieces with nuts and washers on each exterior face.  Once the shutters are in the correct place/height (overlapping the top of the wall by a good 3"/75mm) start cranking.  To place our shutters we affixed mini trapezoidal wooden 'studs'/chucks (for the eventual use of drilling into to put a board to cover the seam of the rammed earth and concrete beam) on the inside face of the shutter at the correct heights, dual purposing as a ledge/lip for the shutters to rest upon the wall with.  Once the calipers are all tightened down, and the vertical 'squeezers' have been checked for  plumb-ness you're set.  Psyche!  Don't forget about sealing the small gaps and irregularities in the connection between the shutters and wall.  If left unchecked, it is possible that the concrete could seep out the bottom and down along the rammed earth walls which wouldn't look too well-done-unless you're into that.  Doug and Trent were all over this and mixed up some clay putty to patch all the  possible escape routes of the concrete.  Following, is a rough sequence of the caliper's job:

Starting in the first photo, you can see Doug on the top of the wall in between the calipered forms that will encase the bond beam's pouring.  The next picture to the right is a detail of the clay putty sealing he was doing.  In the bottom left shot, the compressed forms are filled with setting concrete-the threaded rod just above the shutters.  Also, note the board screwed across the tops of the two shutters for added support. The final picture is merely for visualization purposes: it is a caliper placed over one of the footings for an idea for the thickness of the shutters.  

Lastly, we will talk about the radiant floor slabs under the bathrooms and laundry room along with their related energy saving additions and supplementary systems.  Very similar to the solar energy absorption and re-radiation of the rammed walls; in-floor piping is a way to heat a thermal mass and good option for a slow, balanced, and relatively efficient way of warming a home.  Two crucial criteria will determine the effectiveness of the slabs delivery and appropriateness.  

(1)  There needs to be a well insulated envelope to capture all of the heat being emitted. Able to lose much of its energy to the cold sink of the earth below during the winter, one must heavily insulate between the slab and the ground.  Our engineer, Paula, is a big proponent of Passivhaus principles and has decided to shoot for a level of Passivhaus certification.  For those of you who haven't heard of Passivhaus standards and requirements it is basically a efficiency standard which places a limitation on energy needed to heat and cool a house, the less energy needed the higher level of certification (please go to the wikipedia link here: for a more in depth look).  In our home we are on a bit of a budget and have gone with a 100mm/4" thick, super dense polystyrene board (by the name of Goldfoam with an R-Value of 4 in S.I. (mteric) or 23 in U.S. units) for the buffer between the ground and the slab/floor.  Perlite (an expanded natural ore) is an alternative option for a thermal barrier between the floor and earth, but is more costly and half the R-value.  A R-value represents a material's thermal resistance or it's conductance of heat/energy.  One can look at this resistive property somewhat analogously to electric flow through conductors and resistors.  Metal, for example, is a good conductor of electricity as well as heat, and thus has a low R-value.  The big difference between electricity and thermal flow is that thermal resistance is based on air-pockets/buffer areas within the insulation which plays a minimal role on the electric side of things.  

(2) The second factor to consider when looking into radiant floors is: how will the hot water pumping through the slab will get up to temperature?  In New Zealand natural gas prices are quite expensive, so to run the in-floor heating off of gas alone would/is a costly endeavor.  As seen in the posting about the Pyroclassic (on the site), we will be integrating a wetback system to supplement the gas hot water heater for heating the slab.  Wetbacks are an ingenious water heating system that make full use of a fire's output.  

Here are some pictures of the creation of the whole slab and piping process:

Above left shows an early stage of the slab with the shutters in place and outer trenches dug and Goldfoam placed.  Directly above is a shot after a sifted layer of soil had been leveled/scree for easy laying of the Goldfoam boards.  After the Goldfoam was laid, a metal grid was placed on top to strengthen the concrete slab's integrity.  This grid was then used to tie the piping for the radiant heating system to (shown to left).  
Below is a photo taken during the pouring of the slab and shows a bit better detail of the piping about to be entombed in the concrete.

And one closing photo and piece of info is about the Laser Level which has helped out immeasurably with keeping areas at correct height and levelness.  To the right you can see the 'broadcaster' in the foreground which has a spinning 45 degree angled mirror that sends out a lazer beam which is picked up by a reciever affixed to a staff (held here by J.J. in the white t-shirt) for a consistent measure of height.  Well, I think this posting takes the prize for the longest one yet, and if you've made it this far you deserve some sort of reward.  As always if there are any areas you would like a bit more info or detailing on, please give us a holler @ or in the comment box, and we will get back to you.  Thanks for your endurance and talk to you later!

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