Thursday, December 22, 2016

Construction - Insulating the Earth Contact North Wall

Intentional Compromise
In a perfect world, the earth contact north wall would have been a full two stories high, i.e., at least 16 feet.  But to have done so would have increased its cost so significantly that I decided to stop at 12' with the concrete and carry the wall to second story height with a short truss wall.  The latter could be done with salvaged lumber and my free labor as opposed to paying for professional labor and buying several more yards of concrete to increase the height, not just of the 12" thick wall itself, but the three substantial deadmen behind the wall as well.

Moreover, it will be easier with the truss wall to achieve an R-48+ to match the other external truss walls than to insulate a concrete wall to this R-value.  But the advantages of a higher wall of concrete would have been an additional 200 sq ft of earth contact for the AGS system and more of the wall totally impenetrable by air infiltration/exfiltration. However, I am betting that (a) the large floor area of the house, (b) the +/-10' of uninsulated north earth contact wall, (c) a partial earth contact west wall and (d) the insulation/watershed umbrella will provide all of the insulated and dry thermal mass the house will ever need without the additional 4' of concrete for the north wall.  Therefore, I think the additional 200 sq ft of earth contact would have been expensive insurance for a problem that probably does not exist.

Tweaking the Platon Damp-Proofing 
As described in a prior post, the Platon damp-proofing system was used on the lower 8' of
Original Platon installation
the tall section of the wall before backfilling began.  The top 4' still needed damp-proofing before it could be insulated.  I decided to keep the Platon system below the bottom of the metal channel that holds the insulation. Otherwise, the extra bulk would cause unevenness of the insulation because the top of the channel would be directly against the concrete and the bottom would hang over the bulky Platon material. Consequently, I installed only enough additional Platon to bridge the gap between the original material and the bottom of the channel.  As will become apparent presently, the two layers of plastic sheeting that waterproofs the metal channels and insulation will also waterproof the concrete even better than would the Platon material.  The exception to this arrangement was the first four feet at the ends of the wall where the insulation extended down nearly 6' behind what will eventually be retaining walls running more or less perpendicular to the wall.  Here the channels did overlay the Platon material and did flare out somewhat at the bottom.

Materials Preparation
First is was necessary to calculate how far the insulation should extend below the mudsill of the truss wall.  Code specifies a distance of 8" between the grade and the mudsill. Figuring downward from the mudsill, the first 8" will be exposed stucco, the topsoil over the
insulation/watershed umbrella will be 8" deep and the umbrella will be 6-7" thick, so the wall must be insulated to a depth of at least 23" below the mudsill to get below the umbrella. (Below that, of course, the wall should remain uninsulated so that heat can pass back and forth through the wall between the earth and the living space as a function of the AGS system.  For more on AGS, click on the "Featured Post" in the column at the left.)  I settled on 32" of insulation 3 1/2" thick for an R-14 to a depth of 8-9" below the bottom of the umbrella. The nearby photo shows these dimensions drawn on the cement board before stuccoing (click on the photo to enlarge it for better detail).

Parenthetically, in order to achieve an overall R-48, the inside of the wall will have to be insulated to another R-34, which is the subject of a future post.

I used a plywood blade in a circular saw to cut two thicknesses of expanded polystyrene foam board -- 2" and 1 1/2" -- into 24" x 32" pieces .  I also cut 
3 5/8" wide 20 gauge galvanized steel channel (the kind that is used as the top and bottom plates for steel studs for wall framing) into 24" lengths using a metal blade in a radial arm saw.  I cut 1/2" cement board into 48" x 28" pieces using a corded fibercement nibbler.  Next, I cut lengths of 6 mil plastic sheeting into 8' wide pieces.  At this point, all I needed in order to begin insulating the wall were 1 1/4" x 3/8" Tapcon screws for fastening the channels to the wall and 1 1/4" cement board screws with high-low threads for fastening the cement board to the outside of the channels.  I then followed the same installation procedures that were covered in a previous post with a few deviations that were so minor as not to warrant special discussion here.

Installing the Insulation
As described in the previous post, the channels were readied for installation in the shop by cutting to length, drilling holes for the Tapcon screws in half of the channels and then screwing channels with holes back-to-back with channels without holes.  I started the installation at the east (left) end of the 12' wall so that the channel with the holes would be facing to the right each time so as to make it easier to use the hammer drill in my right hand; if I were left-handed, I would have started at the other end of the wall.

The first four feet of the wall needed to be insulated to a depth of +/-6'.  The additional depth was necessitated by the transition from an 8' wall to a 12' wall which will be accomplished by a retaining wall running more or less perpendicular to the wall and butted up against the first four feet of insulation.  (The first book on earth sheltering that I read some 8-9 years ago was Rob Roy's Earth Sheltered Houses in which he cautioned against butting a retaining wall against the concrete house wall without insulation between the two in order to reduce heat loss and to eliminate moisture condensation during warm months.) The same 4 x 6' configuration was necessary at the west end of the wall for another retaining wall.  In between, there was a span of approximately 52' where the insulation was only 32" in height.

Before the channel and the insulation could be started, the 6 mill plastic had to be positioned so that roughly half of it would be trapped under the insulation and half lapped
Insulation installed on about half of the wall with the inner
layer of plastic showing beyond and below the foam;
 bare concrete is in the distance; notice that the metal
 channels are shorter than the insulation
over the insulation, completely sealing off the channel-insulation complex. The rolls of plastic I buy at the farm supply store comes 24' x 100'.  I divided the 24' dimension into thirds.  The 8' wide pieces provided 4' of plastic between the insulation and the concrete wall and 4' between the insulation and the cement board. And the individual pieces of plastic were overlapped by a couple of feet.  In this way, the metal channels were totally sealed against rust-inducing moisture, rather than relying solely on galvanization, and the concrete wall was not just damp-proofed but was actually waterproofed in the process.

Without going into all of the details covered in the previous post, the installation was a
Completed installation of the foam; notice the outer layer
of sheet plastic, thrown back and weighted down on the
floor of the scaffold, that will be brought forward and
 draped over the foam before the cement board goes on 
matter of screwing a pair of channels to the wall over the inner layer of plastic, mating a piece of 2" foam board with a piece 1 1/2" thick, slipping the left side of the foam into the channel, slipping the next pair of channels over the right side of the foam and applying pressure leftward while drilling the holes and inserting the Tapcon screws.
The 32" length for the foam and 24"length for the metal meant that the foam protruded below the foam 7-8" in order to keep the metal well up inside the sheet plastic to keep it dry.  I also kept the tops of the channels an inch or so below the tops ot the foam in order to keep any rough edges from perforating the sheet plastic. The inside diameter of the channels is 3 5/8" and the foam is 3 1/2" thick so there is enough tolerance that the insulation can be moved somewhat.  Accordingly, after all of the insulation was in place, I used a mason line to level the tops of the foam to match the bottom of the mudsill that will eventually hang over them.  Any remaining gaps between the sill and the foam board will eventually be sealed with mortar as described in a subsequent post.

Installing the Cement Board
Installation of the cement board required two cordless drills and a driver for phillips head cement board screws.   Before taking a piece of cement board to the wall, I used one drill
Completed cement board installation; notice ample outer
 layer plastic sheeting exposed below the board; the
backfill will press it against the edge of the foam and
the wall below to seal the channel/foam assembly against
with a 3/16" masonry bit to drill a hole in the upper left corner and the upper right corner.  I As soon as the left side of the board was butted against the right side of the previous piece, aligned flush with the top of it and proved level with a torpedo level, I used the second drill with a bit designed for metal to drill a pilot hole in the metal track through the hole previously drilled in the board in the upper left corner. Then, while holding the board steady, I used the driver to fasten the board to the track with a cement board screw.  The remainder of the screws could then be installed in a similar manner, i.e., masonry bit, metal bit and cement board screw.

Installation of the cement board is best done by two people because it is heavy and difficult to manage working alone.  I overcame the problem by leaning a 2 x 4 against the wall at the level of the bottom of the board as a support.  However, the rest was rarely at the right height necessitating a lot of juggling which probable quadrupled the installation time.  It didn't help either that the ground was uneven and snow-covered part of the time and beginning to thaw the rest of the time.  In either case, the slipperiness underfoot made things interesting.

Stuccoing the Cement Board
This last step in insulating the concrete wall followed exactly the procedures described in detail in the previous post.  The only difference was it had to be done in late December instead of warm weather, which complicated and slowed the process considerably.  Not knowing when the stuccoing might get done, I am publishing this post without pictures of the stucco on the assumption that the curious will be checking out the previous post anyway.

Honest Perspective
The DIY concrete wall insulation described here and in the previous post is a good example of a green building approach that would not be practical in a production setting because it is too customized, cobbled together from disparate materials and time-consuming.  In a way, though, it is a microcosm of our entire house project.  Jo Scheer in the book, Eco Architecture says, "Though extreme eco-architecture may not be a solution to a thoroughly sustainable building industry, it certainly provides ideas. It is a model of ideas and concepts that beg to be assimilated".  Who knows what impact on sustainability some of our "impractical" ideas might have somewhere down the line.  

Sunday, December 11, 2016

Construction - First Exterior Truss Wall

The actual "first" exterior wall was described in the previous post  but its ten-foot-plus height from the second story floor and a preponderance of windows caused it to be a hybrid instead of a pure truss wall.  The wall described here provides an opportunity to detail the building of an 8' wall using trusses made ahead of time in a jig. Rather than going over the details of truss wall construction when blogging on the rest of the exterior walls, I will link back to this post as a reference.

The wall is the exterior wall between the garage and the living quarters.  By not having windows like most of the other stick-built exterior walls, it allows us to focus on the use of trusses instead of 2 x 4s or 2 x 6s for framing.  The fact that it has a door only means that a couple of trusses are positioned differently than would be the case for a plain wall.  While the garage will be insulated and passively conditioned to a higher comfort level than most garages, the design for the wall is no different than for the rest of the exterior walls, i.e., 15" thick and an R-value of just under 50.

Although I intend to refer back to this post in the future for the details of truss wall construction, it is atypical in one respect.  The wall was put together on the floor of the garage and tipped to place from the exterior side.  The remaining truss walls will be assembled on the house floor and tipped up from the interior.  I will try to nuance the difference during this narrative.

Building the Wall
I took eleven trusses for the wall from the stash of pre-made trusses and built the wall on the floor as is typical of most wall construction.  I failed to photograph the wall while it was laying on the floor so I've included the following photo from the most recent post as an example of horizontal assemblage.  

After cutting the 2 x 6 pressure-treated bottom plates (mud sills) and the salvaged lumber 2 x 6 top plates to length, I laid them side-by-side and used a tape measure to mark lay-out lines on 24" centers as if laying out stud positions for traditional walls. The future pedestrian door to the garage was laid out in the process, centered over the mini-ramp that had been formed into the garage floor to make the doorway ADA compliant.  I stood the trusses on edge in the approximate positions they would occupy in the lay-out. I stood straight pressure-treated 2 x 6s on edge against the bottom of the trusses with the lay-out lines facing the trusses.  The trusses were moved to match the lay-out lines more closely and "eye-balled" perpendicular to the 2 x 6 longitudinally. Then, starting at one end, I aligned each truss accurately with its lay-out line on the mud sill and nailed it with one nail.  I then used a rafter square to make sure the truss was perpendicular to the sill before adding more nails.  

Digressing for a moment.  The rest of the 8' exterior walls will be framed on the floor of the house as opposed to the garage floor.  For them, getting the framing as flush as possible on the interior profile for smoother drywall would be more important than for the sheathing and cladding side of the wall. So, the following procedure applies specifically to the other walls but I used it for this wall while knowing that any minor discrepancies would be reversed and face inward and the garage wall would be the smoothest. A smooth interior profile is another reason for using the straightest 2 x 6s next to the floor which puts them on the interior side when the wall is raised.  

I slipped enough shim(s) under the 2 x 6 and the end of the truss for the truss and the 2 x 6 to be in simultaneous contact with the shim(s) before sending home the first nail  Since the trusses, having been assembled in a jig, are quite true and uniform, the shims merely compensate for any unevenness in the floor that might cause misalignment of the straight 2 x 6 with the trusses and result in a rougher interior profile.

The next step was to attach the interior-most (current situation; exterior-most for the rest of the walls) top plates in exactly the same manner.  (I use the plural form "plates" because the pressure treated 2 x 6s would have had to have measured 20' to have spanned the entire length of the wall.  It is hard to find straight pressure treated two-by-sixes this long so, I used two boards of varying lengths for each plate so that the junction between them on one side of the wall did not fall opposite the junction on the other side of the wall.  The top plates were salvage lumber so I used two of varying lengths such that the junction of one set of top plates were staggered not only with each other but with those of the bottom plates. 

Finally, it was a simple job to nail the second set of 2 x 6s to the trusses.  The trusses were already properly aligned as for perpendicularity and therefore already matched the layout lines on the top plates.  Although the 2 x 6s were salvaged lumber, the two used for the exterior-most top plate were pretty straight while the one of them used for the inner top plate was bowed slightly.  I made sure the bow was facing towards the center of the wall so that it would not hang over the top of the wall and interfere with proper mating to the floor joist as described below.  For the other walls, a plate that bowed outward would make for bumpy drywall or sheathing so I have made it a practice to fasten all crooked plates with the convex profile facing inward towards the middle of the wall.  Since the second set of plates had to be suspended while nailing, I cut spacers to fit over the plates nearest the floor that held them in place but slightly too low.  Then it was a matter of shimming them a little into a nailing position flush with the edge of the truss.

Only one other job remained before the wall was ready to raise.  I scabbed together the segmented plates with short boards and drywall screws.  This maneuver stiffened the wall for raising; the scabs were removed later.  In fact, one of the scabs interfered with proper placement of a truss so its installation was delayed until after the wall was raised and the scab had been removed.
The wall aligned, secured and ready for covering (click on the image
to enlarge it for more detail)

Raising and Aligning the Wall
I used a spirit level to check the north concrete wall and the south truss wall and found that they were both plumb.  Therefore, I could use the distance between them at the floor as the measurement for the length for the wall while allowing a 1/4" tolerance.  The three guys helping me raise the wall were skeptical about such a close tolerance only to have to witness me puffing up and strutting around when it went to place exactly as planned.  

After it was in place, I secured the top by clamping it to the adjacent floor joist to which it would eventually be nailed after the wall was aligned.  The wall had no choice but to be plumb in a north-south direction as it fit tightly against the concrete north wall and the truss south wall.  And fitting against the floor joist took care of its straightness at the top. All that remained for alignment was getting it plumb in an east-west direction after fastening it to the joist.  Plumbing also automatically aligned the bottom longitudinally. The top of the wall ended up being pretty level despite the concrete floor being anything but (see Major Concern below).  Minor differences will be handled as the rest of the rake wall is stick-built on top of it. 

Fastening the Wall To Place
I nailed the top of the wall to the second story floor joist and to the existing south wall. Fastening to the joist took the place of a second layer of 2 x 6s commonly found in double top plates to bridge over joints in the first layer and to tie together intersecting walls.  The need for a double top plate was further diminished by having two top plates side-by-side to begin with.

I fastened pressure treated two-bys to the north concrete wall with robust (1/4") Tapcon screws and nailed the north end of the new wall to them.  I supported any gaps between the bottom plates and the insulated concrete foundation or the concrete floor with composite shims under each truss.  I then used the 1/2" galvanized anchor bolts, that were installed into the top of the foundation when the concrete was poured, to tie down the bottom of the wall.  Because one of the bolts fell in the doorway and had to be cut off, there were only three bolts for the entire wall so I added three more using 1/2" concrete anchors.

Shielding the Wall from the Weather
Since the trusses have gussets made from interior plywood and OSB board and, since my
snail-paced construction schedule means they will be exposed to rain and snow unduly long, I immediately covered the wall with lumber wraps.  I expected to be using relatively expensive 6 mil plastic sheeting (at nearly $100 for a 100' x 24' roll) until realizing that the lumber wraps were free for the asking from my local lumber yard.  I used a lot of staples and a few batten boards to fasten the wrap. How well it resists the wind remains to be seen.  At least I get to test it on this short and easily-accessible wall before using it for the tall wall described in the previous post.
The inside to the left also needed covering

Looming Problem
The concrete floor on which the wall sets is not level, in one area being 1/2" out of level over a distance of only 6' or so.  Nor is the concrete foundation perfectly level within itself or level with the floor in many places.  Consequently, there were some serious spaces under the bottom plates that have to be air-sealed in some manner.  At the time of this writing, I am not entirely sure how to do it, whether to use mortar or spray foam or caulk or ???????.

This will be a common problem for all of the exterior walls so I will have much to say about it in future posts starting with the next post on building the short truss wall on top of the earth contact north concrete wall.  The top of the concrete wall is decidedly unlevel so the challenge of standing a level wall on it without gaps between will be addressed.

Thursday, December 1, 2016

Construction - Second Story South Wall

The previous post concerned the construction of a permanent and temporary second story floor on which to work on the second story walls and roof.  Here we are dealing with the 10+ foot south window wall for the second story, the top of which is a little over 20 feet above the first story floor.

Change in Window Configuration
Click on the drawing

Originally I planned to use seven double-window sets as clerestories in the south wall, as shown in the drawing. When I laid out side-by-side the seven pre-made window sections containing two windows each, they clearly were too crowded. Consequently, I reduced the number to five double-sections, stood them up and viewed them from the street. The proportions were definitely better.  Then it made sense to add back a couple of single windows as a way of softening the monotony of the facade and to stay in compliance with the minimum code requirement of 4% glass-to-floor area.  So I dismantled the two extra sections and reused the components to make wall sections for single windows that will have the same 3' x 5' dimensions as the individual windows in the double sets.

Adding Height to the South Wall
An end of the truss jig was cordoned off with
 2 x 4s for making 24" x 15" inserts; the plywood,
  nailed to a 2 x 4 frame, serves as a gusset 
The plans call for 12" thick cathedral ceiling for the first story shed roof that extends southward from the second floor wall.  Accordingly, the height of the wall was designed to be high enough to accomodate windows above the roof that will be pitched at 12/2.5. However, I will be using ceilings that are +/-20" thick. If the wall height isn't increased by at least 8", the pitch of the roof would have to be lowered to keep the roof from overlapping the bottom of the windows.  This is not an option because a slope of less than 12/2.5 is not recommended for metal roofing. The pre-made window sections that will comprise most of the wall were designed for an 8' wall and will therefore have to be heightened by a total of 24"  -- 16" to satisfy the original drawing plus another 8" to accomodate the thicker roof. Unfortunately, the additional 8" will place the sills above the 44" maximum height for egress windows but, fortunately, only the single window in the bedroom at the east end of the house will be affected.  For it to meet code, there will have to be a permanent riser below it on which an occupant could stand while exiting in an emergency.

I temporarily modified the jig that I used for wall trusses to make 24" high inserts to go between the window sections and the floor.  Admittedly, the inserts looked a little goofy but, when tied in with bolts, nails and strapping, they did the job.  

Raising the Wall
The four wall sections before raising; the section with the saw
laying on it and without its top and bottom plates is to be
raised last (click on the photos to enlarge them for more detail)
The window sections comprised most of the second story south wall but a couple of wall trusses were needed at both ends of the wall to connect later with the east and west rake walls. As soon as the extra trusses were ready, I cut the four 2 x 6 top and bottom plates to length, laid them side-by-side and marked them for attaching to the wall sections and the new trusses.  Then it was a matter of nailing them to the trusses and wall sections while keeping the outer edges of the tandem 2 x 6s exactly 15" apart, the same as the wall components.  I divided the 58' wall into four units in order to keep the weight within reason for raising.  I left the top and bottom plates off of the shortest unit since it would be the last to be raised and might need narrowing in order to fit into the space between the adjacent units that were already up.
Unsuccessful attempt at using wall jacks

Step-son, Keith, helped raise the walls. We assumed that the sections would be too heavy for raising without wall jacks but, after we were half through with using them for the first unit, we realized that they were not properly adjusted for a 10' wall and had to lower the wall back to the floor.  Instead of adjusting the jacks, we removed them, under the assumption that we had under-estimated our ability to raise the wall without them. So, in order to keep the wall from sliding over the edge of the floor, we used rope to tie the bottom and the top of the wall to the existing wall to the north.  Then two of us raised the first unit surprisingly effortlessly and continued to do so for the other three units.

As soon as the first three units were upright and the bottom plates were temporarily fastened to the floor with duplex nails and the top plates fastened together with clamps, we could dry-fit the unattached 2 x 6 plates for the last unit then attach them to the unit.  When we raised the unit, it fit nicely between the two adjacent units.

Aligning and Securing the Wall
As the units were raised they were stabilized with braces between the wall and the floor.
Second story wall housing a total of twelve 3' x 5' windows
Fortunately, the raised wall was perfectly plumb in an east-west direction, which was to be expected because the individual window units were shop-made in a jig. And each of the four wall units was checked for square while still laying on the floor before nailing on the top and bottom plates. All that remained was to get the wall (a) straight at both the top and bottom, (b) level on top and (c) plumb in a north-south direction. The braces were attached to the wall with drywall screws so the screws could be backed out and refastened as the wall was tweaked.  The duplex (double-headed) nails between the bottom plates and the floor provided the same flexibility.
The wall from a different perspective; notice the nailers over
the window openings for safety reasons; the height is just
over ten feet; the window sills are slightly too high to meet
 code for egress

We started the alignment by straightening the bottom and the top using taut mason's lines while loosening and refastening the tops of the braces and the duplex nails as needed. The clamps sufficed for the top temporarily.  As with conventional 2 x 4 or 2 x 6 walls, we used a double top plate, i.e., a second layer of 2 x 6's stacked on top of the ones that were nailed to the wall sections before raising the wall.  We installed the ones on the interior side of the wall first and used them to pull the wall perfectly straight and hold it straight, assisted by a mason's line.  Of course, as is standard practice, we staggered the locations of the ends of the boards relative to the first tier of top plates so as to stiffen the wall.

The floor under the wall was not perfectly level so the top of the wall also was not perfectly level, primarily in one area.  In order to correct the problem, we used shims under the bottom plates to level to a mason's line the top of the wall.

All that remained now for proper alignment was to plumb the wall in a north-south direction and secure it definitively to the floor.  For plumbing, we used shims under the bottom plates as necessary while loosening and reattaching the braces.  Then we used 6" construction screws and nails to fasten the bottom of the wall to the floor joists and band-joists.  

Our location places us at risk for two catastrophes.  Two hundred feet below us is an abandoned coal mine and subsidence is not uncommon in ours and the surrounding counties.  Also the New Madrid fault in southeast Missouri near its border with Tennessee has a 25 - 40% chance of a magnitude 6 earthquake within 50 years and a 7 - 10% chance of a 7.7 magnitude.  Either would cause serious damage in the St Louis region. Consequently, the final job to secure the wall was heavy hurricane strapping to tie it to the lower floor framing and to the major beam under the catwalk.

Installing Cripples
The purpose of cripple studs under the window openings is mostly for fastening sheathing
Cripples anchored at the bottom by 2 x 4s
and drywall but a secondary function is to support the sills under the windows which, in turn, supports the window. The latter function is more important for conventional 2 x 4 or 2 x 6 walls whereby windows are supported usually by one 2 x 4 or 2 x 6 installed flatways.  With our truss walls, each window is supported by two 2 x 6 sills installed on edge thereby making the secondary role of the cripples largely moot.  

I spent a few minutes making a temporary jig in which to nail the double cripples to a short 2 x 4s before nailing them in place.  I opted for the 2 x 4s cross-ways of the bottom plates rather than toenailing the cripples directly to the plates to make the cripples easier
Quickey jig for nailing cripples to 2 x 4s
to install and for more secure fastening at the bottoms. The tops were notched around the sills so they were well-nailed on top.  I might have opted for toenailing if the bottom of the wall was to be exposed to the exterior in order to avoid
 thermal bridging by the 2 x 4s. But not to worry, the bottom of the wall will serve as the top part of the wall for the first story and the bottom third of the cripples will receive drywall instead of sheathing.

All exterior walls for the house are designed for trusses 24"oc due to their stiffness. The cripples, however, are 16"oc just like the typical 2 x 4 wall framing of most houses.

Monday, November 21, 2016

Construction - Second Story Floors (Permanent and Temporary)

Subfloor in place; the catwalk will join the bedroom in the
distance with the balcony office in the forefront; the open
space overlies the living room and reveals the vaulted
second story ceiling
As explained in a recent post, I elected to build the interior bearing walls ahead of the exterior walls which is probably something a contractor would never do. And the stick-built first story exterior walls will remain in abeyance until the second story is built clear to the roof.  The reason for this sequence is that the first story floor is weather resistant concrete while the subflooring for the second story is OSB that needs to be covered as soon as practical.  And the second story exterior walls support the roof so the floors have to be in place before the the walls and roof can be built. 

A temporary floor (light color) fills in the open spacethe dark wood in the next photo is salvaged lumber supporting a temporary floor
I use the plural form, "floors", because only about two-thirds of the second story floor is permanent, as described in a prior post. The other third is temporary in order to serve as a scafflod on which to build the south and west exterior second story walls before raising them.  One of the temporary floors was built soon after the permanent subfloor went in (above photo)  but the other had to wait until more beams had been erected.

More Beams and Another Temporary Floor
As the drawing shows, the second story west wall will be suspended over the master bedroom on beams. Their construction using LVLs was not unlike that described in a prior post. Once the beams were in place, I could then fill in with a temporary floor the space between the new beams and the permanent floor such that the entire second story now had a floor of some kind on which to work safely while building the
exterior walls and the second story roof.
Click on the drawing to enlarge for better viewing

Fortunately, I have enough lumber salvaged from several tear-downs to frame out the temporary floors.  I screwed down 1/2' plywood sheathing as the floor surface then painted it with exterior stain in order to protect it as much as possible since the plywood is not intended for exterior use.  I am hoping to be able to recycle it or sell it on Craigslist when the temporary floors are removed.

The plans specified a beam comprising two LVLs fastened together but, since the exterior wall resting on it will be 15" thick to match the other truss walls, I installed a third LVL such that the outer edges of the two beams were 15" apart.  Then I covered the beams with subflooring to add rigidity.
The three-LVL beam stained for temporary
protection from the elements

Stops for Wall Raising
In order to add a measure of safety for an eighty-something, agility-challenged DIYer, I added a couple of safety ropes around the periphery of the second story. However, the main purpose of the 2x4s supporting them is to act as stops to keep the second story south wall from slipping off the edge when it is raised. Consequently, I used construction screws to fasten the supports more securely than could be done with nails or drywall screws.  And I inclined them slightly outward at the top to be sure they would be out of the way of setting the wall later.
Temporary floor between beam and permanent floor stained
for protection until under cover

As described in the next post, the wall was controlled with ropes during raising and the stops were superfluous. But the ropes proved invaluable as I assembled the wall on the floor only a few feet from the edge. The ropes would have stopped, or at least, slowed any falls but I am inclined to think that their presence was more psychological than physical.  After they were in place, I could relax and work near the edge instead of being preoccupied and overly cautious about falling.
A view of the ropes and of the larger temporary floor after staining
The stage is now set for unwrapping the pre-made wall sections, stored in the background under plastic, and laying them out on the floor for assembly; the "boxes" strewn about on the deck, will be used to heighten the wall -- all to be described in detail in the next post.

Saturday, November 5, 2016

Design - Thermal Bridging and Air Infiltration (Cont'd)

This is the second of two posts on thermal bridging and air infiltration. The first post defined the three ways heat gets transferred -- by conduction, by convection and by radiation -- and what is meant by the building envelope.  Then the post focused on the transfer of heat by conduction through the building envelope. This post covers the other two heat transfer modes -- convection and radiation.

Convective Heat Loss
Air infiltration and exfiltration refer to the heat transferred in and out through the building envelope by air in motion -- convection.  Air infiltration is at it worst when winter winds push air through holes in the envelope, especially on windy days when there is a air pressure differential between the side of the building against which the wind is blowing and the leeward side of the building.  Heat is lost even in the absence of wind, however, as interior air exfiltrates, not only because heat seeks cold, but due to a pressure differential.  In summer, air infiltrates for the same reasons.  So here is my understanding of the best practices for controlling convective heat loss via what has come to be known as air sealing:

  • In the first place, design intentionally and build with precision in order to minimize potential holes in the envelope
  • Then seal all unavoidable holes with gaskets, caulk, tape, spray foam and drywall mud
    • Between parallel and touching structural members, such as double top plates
    • Between mud sills and concrete foundations
    • Between structural members and the sheathing
    • Between windows and doors and their rough openings
    • Between drywall intersections, especially walls meeting ceilings
    • Around penetrations in the envelope for such things as vents, furnace pipes, wiring, coaxial cables, electrical boxes and can lights
    • Within window frames; choose those that close against a sealing gasket instead of sliding -- such as casement, awning or hopper instead of horizontal sliders or single or double hung
    • Within double-glazed window panes by the addition of argon gas which, by being heavier than air, impedes heat-conveying convective currents between the layers of glass
    • Through fireplace doors and dampers
  • Use an airlock between outdoors and living spaces
  • Orient exterior doors away from the prevailing winter winds (in our locale, that would be south and east sides of the building)
  • Use air (and moisture) barriers such as latex-painted drywall interiorly and house wrap exteriorly*
  • Then, use a blower door test to measure the integrity of air sealing and identify leaks to be corrected before insulating and drywalling
Convection and Our Project
Super-insulating the walls and ceilings and going all out to eliminate thermal bridging
would not produce a zero energy, or energy neutral, home unless air infiltration is eliminated as well.  Johnston and Gibson in their book say, "A typical house has 2,000 liner ft. of cracks and gaps that allow air in and out, which can represent up to 50% of the heat loss in a building".

One of the advantages of being a task oriented DIYer instead of time oriented contractor, is that there is no reason not to be precise with construction first then compulsive about hole plugging.  I intend to buy a pneumatic caulk gun because I know how tedious, tiresome and time-consuming the caulking will be.

For at least the first story and as much of the second story as my stash of 3/4" salvaged lumber will allow, I intend to use the 3/4" individual boards for sheathing.  I will install them at a 45 degree angle as was commonly done before sheet goods were available.  The 45 degree orientation has two benefits.  When the cladding is attached over it, a row of fasteners will be spread over multiple boards so as not to cause splitting of a given board. And the diagionalization provides shear strength to the wall. The disadvantage of using 1x lumber is that it is impossible to seal all of the spaces between so many boards.  Consequently, I will use recycled 4 x 8 sheets of Masonite on the wall trusses before nailing on the sheathing boards.  I can then caulk from the inside just as if the wall was sheathed with OSB board. The Masonite will also add a quarter inch of thickness for fastening of the metal cladding. Unlike most of the contemporary man-made sheet goods, Masonite is manufactured with natural binders so that there is no worry about VOCs.

As far as air coming in through exterior doors, we will have a large 8' x 14' airlock so that the semi-conditioned air in the lock will attenuate incoming outside air before an interior door is opened.  The door between the kitchen and the screened patio will not be protected by an airlock so it will see little use during the winter.

And needless to say, the earth sheltered parts of the envelope totally eliminate any chance of convective heat loss -- air doesn't pass through dirt and concrete very well!

We are seeking green building certification by either HERS or NABH Green Building Standards (Timeline - Alternative Certifications to LEED).  Part of the certification process is blower door testing to measure air infiltration.  I think we will be ready.

Aside from stoves and fireplaces in the living space, the principal source of radiant heat is the sun.  The game here is to admit solar gain when you want it and and exclude it when you don't through the following measures for the northern hemisphere:
  • Orient the building for major solar gain through south-facing windows in winter but block the gain during summer with overhangs, deciduous trees and trellises
  • Incorporate well insulated thermal mass into the structure so as to trap and hold any intentional gain
  • Minimize the amount of glazing on the north and west and, to a lesser extent, the east
  • Use low-E glazing so as to slow the loss of solar heat back through the glass
  • Distribute (diffuse) incoming solar radiation with by either using translucent glass, rather than transparent, or light colors where the sun shines (ceilings, floors and walls) unless there is enough thermal mass to absorb the energy without overheating
Radiation and Our Project
We are intentionally avoiding stoves and fireplaces for the sake of better indoor air quality and to eliminate air infiltration/exfiltration via envelope-piercing chimneys.  Our heating (and air conditioning) system will be passive solar by virtue of the AGS system. But, rather than depend on solar gain in the winter, the gain will come from the summer sun.  (For basic information on the AGS system, click on "Timeline - Annualized GeoSolar" under "Featured Post in the column to the left and follow the trail of posts.  Or go to Wikipedia for a more succinct explanation.)  

Our design calls for south-facing glass with overhangs except possibly one east-facing window in the laundry room.  The overhangs will restrict direct solar gain to the cool/cold months (but with too much in the early fall, which will be grist for a future post on the design of the overhangs). We intend to use translucent glass in most of the second story clerestory windows backed up with light colored ceilings and walls so as to diffuse incoming sunlight instead of creating hot spots on the walls and furnishings. Because of
the AGS system, the concrete floor will remain essentially the same temperature year-round and will absorb the diffused energy gradually. Sunshine falling directly on it will be absorbed without hot spots by coloring it with medium, rather than dark, tones.  (My information on color selection and translucent glass comes from "The Passive Solar Energy Book:  A Complete Guide to Passive Solar Home, Greenhouse and Building Design" by Edward Mazria -- a good read for anyone contemplating passive solar construction.)
*As I will discuss in detail in upcoming posts on air barriers and vapor barriers, air control and moisture control are closely related to the extent that to control air is to control moisture as well.

Wednesday, October 26, 2016

Design - Thermal Bridging and Air Infiltration

This the first of two posts on the subjects of thermal bridging and air infiltration

Our building project is defined more than anything by the use of the heat from the summer sun to eliminate conventional heating and air conditioning by a system called Annualized GeoSolar (AGS) but it is also unique in another extremely important way  -- having an envelope that is not just well-insulated but super-insulated.  "Super-insulated" has become the term for envelopes that exceed industry norms and building code R-factors with respect to the thickness of the insulation and control of thermal bridging and air infiltration.

If you are new to the blog or do not know about AGS, a quick study can be had by clicking on "Timeline - Annualized GeoSolar"  under "Featured Post" in the column to the left. Also Wikipedia's description of AGS is also a good overview.

The Envelope
The skin of a building in contact with the outside environment comprises the walls, roof or ceiling, floor, windows and doors collectively known as the "envelope".  A good part of green building boils down to keeping heat from entering (summer) or exiting (winter) the envelope.

Heat Transfer
Heat is transferred in three ways: 
  • Conduction - through solid objects, called "thermal bridging" when it is
    applied to the envelope of buildings; examples are heat passing through a window, both through the glass and through the frame, heat passing through 2 x 4 wall studs and heat passing through uninsulated foundations 
  • Convection - through fluid motion (air is a fluid); when air passes inward through the envelope, it is called "air infiltration"; when air passes outward, it is called "air exfiltration"; examples are air leaks around ill-fitting exterior doors, air leaks around receptacles and switches in exterior walls and air leaks between structural members such as top plates
  • Radiation - in a straight line through space, such as sunlight warming a floor or heat from hot water radiators, infrared space heaters and fireplaces
Best Practices
Following is a review of my understanding of best practices for controlling heat transfer back and forth through the envelope of a house.  The bulleted items that apply to our situation are linked to other posts on the same topic.

Thermal Bridging
The ways to control thermal bridging are..........
Thermal Bridging and Our Project
Instead of using through-and-through framing, we are using wall trusses that virtually
Wall truss
eliminate heat transfer through the wood members.  The walls will be insulated 
to R- 48 with rice hulls 15" thick. Our cathedral ceilings will be insulated to 16", again with hulls, with slightly more thermal bridging through the structural members than the walls, but not appreciably more because we will be using either I-joists or trusses rather than solid 2 x 12s.   We plan to splurge on high-end windows and doors in order to minimize conductive heat loss through these virtual "holes" in the envelope. There will be no windows on the north or the west to suffer wind washing and the windows on the south will be set into the wall 10" to further reduce wind washing.  Insulating the slab floor of our house will be a non-issue since it will be warmed by the AGS system. The slab floors of the garage and screened porch are already insulated as part of the insulation/watershed umbrella.

Cathedral Ceilings
Cathedral ceilings are a conundrum.  They enhance the aesthetics of interior space but can be a challenge to insulate compared to an attic into which any amount of insulation can be piled.  For our cathedral ceilings the jury is still out at the time of this writing as to whether we use man-made I-joists or custom trusses, either of which are a better choice than 2 x 12s for three reasons: (a) the maximum depth of ceiling insulation is determined by the height of the rafters and the height of 2 x 12s is limited to 11 1/4" whereas the height of I-joists can go at least to 16" and trusses can be any height; (b) as we pointed out above, through-and through dimension lumber transmits heat while I-joists and trusses minimize through-and-throughness; (c)  I-joists and trusses are a greener alternative since both are made from sustainable forest products whereas 2 x 12s are almost certain to come from old growth timber, especially in 20+ foot lengths that our project requires.

North Wall and Floor
Since the AGS system requires free exchange of heat between the inside air and the soil behind the wall (and below the floor), thermal bridging (conductive heat transfer) through the concrete is a good thing except for the top few feet of the wall protruding above the insulation/watershed umbrella,   The concrete above the umbrella will be super-insulated to nearly, or the same, R-factor as the stick-built truss walls using EPS solid foam panels on both sides of the concrete portion of the wall (DIY concrete wall insulation).  The top 3' of the wall above the concrete will be stick-built to match the other exterior walls and insulated with at least 15" of rice hulls. 

At the time of this writing, I am thinking about using rice hulls to insulate the inside of the concrete wall above the umbrella by increasing the thickness of the 3' stick-built portion on top of the concrete to, say, 21".  At this thickness, 2 x 6 framing could be butted up against the stick-built wall from below to hold rice hulls against the concrete.  With 3 1/2" of foam board exteriorly and 5 1/2" of rice hulls interiorly, the R-factor of the concrete wall would then match that of the truss walls for the rest of the house.  The extra bulk interiorly would not be intrusive because it would be overhead.

The slab floor is an automatic.  The AGS system will keep it at 74 degrees (+/-4 degrees) year-round.  In winter, it is thermal bridging through the slab that will heat the house; in summer, it is thermal bridging through the floor that will siphon off excess heat. But in order to do so, the soil under it must be bone dry.  Otherwise, water would carry heat away to the water table faster than the solar collector could generate it. Accordingly, the French drains located 10' below floor level and the insulation/watershed umbrella extending 20' outward from all sides of the house should take care of any surface or subterranean water threatening the AGS system.

Conductive Heat Loss (Thermal Bridging) To and From the Thermal Mass
The AGS system is predicated on a large thermal mass comprising the slab floor and the
Umbrella installation in front of the house; the foam board
layer was the third layer among a total of ten layers that
comprise the umbrella
gravel and soil under it as well as the tall earth contact north wall and the soil behind it.  The imperative is to control heat loss from the mass during the cold months so that the heat gained by the solar collector during the warm months is enough for a comfortable year-round floating temperature
 in the living space.  In order to increase the amount of thermal mass and push heat loss at its periphery as far out as possible, waterproofing and insulation extend outward from the house 16 - 20' in all directions, as discussed in design of the umbrella and as demonstrated in three subsequent posts starting with the installation phase.

This post has detailed conductive heat loss through the envelope by thermal bridging. The next post will cover convection and radiation.