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.