Design - Passive Solar and Mean Radiant Temperature

The number of visitors to our building site has been steadily increasing as it begins to look more like a "real" house.  And now, while its bones are still exposed, is a good time for the uninitiated to see it and get a feel for how it will work.  (Note: This post and the next two were written approximately two years before we moved into the house.)  Some of the visitors have been groups who do self-guided tours of the grounds and then come inside for a look around followed by a sit-down session on passive solar in general and earth sheltered passive solar in particular.  We compare three types of construction:  (1) typical stick-built houses, (2) classic 1970-80-era earth sheltered houses, as ably articulated by Rob Roy in his book, and (3) what has come to be known as Annualized GeoSolar houses like ours as described first by Hiat and then Stephens.  (For details on AGS, click on "Featured Post" in the column to the left; it will take you to three posts that follow the evolution of AGS.)


I have always had difficulty describing the many nuances of passive solar and earth sheltering.  A couple of months ago, I read again for the umpteen-time Edward Mazria's book, where, on page 64, he discusses the relationship of mean radiant temperature and human comfort.  This time it hit me that the concept of mean radiant temperature would be the perfect vehicle for making passive solar more understandable.

Mean Radiant Temperature

Understanding Mean Radiant Temperature

A cold evening campfire is one of my favorite things but, being skinny, I need to sit at exactly the right distance from the fire to stay comfortable.  If I sit too close to the fire or it blazes up, I quickly get too hot; if I sit back too far or the fire dies down, I begin to chill.  When I visit Missouri's underground caverns, I need a warm wrap.  Otherwise, the low temperature of the enveloping rock soon raises goosebumps.  The reason for these phenomena is that my comfort level depends upon a balanced thermal environment whereby the wave energy radiating from the fire or the walls of a cave that my skin absorbs is more or less equal to the wave energy that I am emitting -- equal actually to a 100w incandescent light bulb.  The mechanism at play here is called mean radiant temperature (MRT) and here’s how it works.

The feeling of comfort for us humans is best realized by maintaining a thermal environment in which the human body can lose heat at a rate that is equal to its production – no shivering, no sweating.  The need to lose heat stems from the fact that the body is essentially a heat engine with a thermal efficiency of only 20% (Mazria).  The waste-heat (80%) is dissipated in three ways:  perspiration, convection and by radiation to surrounding objects (walls, floors, furniture, etc. and, in the case of earth sheltering, thermal mass).  Of the three mechanisms, radiation accounts for about half of the heat loss with perspiration and convection (heat carried away by air) accounting for the rest. 

MRT is simply the average temperature of solid matter in the surrounding environment and it is more important for comfort than the air temperature in the same environment.  In fact, a 1 degree change in MRT has a 40% greater effect on body heat loss than a 1 degree change in air temperature (Mazria).  Therefore, when designing living space, it is far more efficient to control MRT than it is to control ambient air temperature.  And the higher the MRT, the lower the air temperature can be.  For example, if we can maintain the MRT at say, 76 degrees, the ambient air temperature could be as low as 62 degrees but our comfort level would be the same as if the air temperature were 70 degrees. Although MRT applies to matter such as wall studs, drywall, wood floors and furniture, it takes something much more massive to provide comfortable environments.

In a nutshell, the temperature of the thermal mass of a structure is more important for human comfort than the interior air temperature.

Mean Radiant Temperature in Stick-Built Homes

In stick-built homes, it is impossible to maintain a reasonably comfortable thermal environment without HVAC systems even with plenty of south-facing windows, because there is no thermal mass for storage and insulated 2 x 4 walls rated (optimistically) at R-13 or 2 x 6 walls rated at R-19 (optimistically) hemorrhage heat in winter and absorb heat in summer.  The temperature of the entire structure is at the mercy of outdoor temperatures that can be up to 30 degrees too hot or 70 degrees too cold.   Consequently, it takes a robust HVAC system to keep up with the heat gain or loss through the building envelope.  And, in lieu of thermal mass in which to store heat, the HVAC system cycles on and off repeatedly in order to keep the air warm or cool enough.  Meanwhile, the effect of MRT on human comfort actually becomes a negative -- in winter, the human body radiates heat faster than the cold walls and, in summer, it radiates heat slower than the warm walls.  And, heaven forbid, the occupants' furnace fails while they are on a winter vacation; the water damage from freezing is not a pretty sight!

Mean Radiant Temperature in Classic Earth Sheltered Passive Solar Homes

The thermal mass in the classic earth sheltered passive solar home is limited to the concrete in the floor, exterior walls and sometimes ceilings at the exclusion of the soil below, behind and above the concrete.  This peculiar situation occurs because the soil is kept from

A nearby earth sheltered passive solar home built just
after the oil embargo in the late 70s - early 80s; the living
quarters are one room deep and the roof is fully earth
sheltered.

being part of the thermal mass by insulation applied to the outside of the concrete shell. However, this arrangement does protect a large portion of the building envelope from extreme summer and winter temperatures, a significant improvement over stick-built homes.  The problem is that the amount of solar gain through south-facing windows and the limited storage capacity of the concrete shell are not able to keep up with the loss of heat through the insulation behind the shell and under the floor, to say nothing about heat loss through the south-facing stick-built wall.  Consequently, the mean radiant temperature remains so cool in winter that supplemental heat is the norm although the amount of supplemental heating is much less than stick-built structures because it has only to raise the temperature, say, 10 degrees – the difference between the soil temperature beyond the insulation and a 70 degree temperature in the living space.  As in a stick-built house, though, most of the supplemental heat goes towards keeping the air temperature comfortable.  But at least the modest amount of thermal mass in the form of concrete is enough to store some excess solar or supplemental heat as well as any waste heat from cooking, water heating, showering, drying clothes, illumination and radiating from human bodies.  Any heat that does make its way into the mass and is held there rather than bleeding through the insulation and into the cold soil would indeed improve the MRT of the living space, something that could never happen with a stick-built home.  A major advantage of the classic earth sheltered passive solar house is that the coolness of the MRT in summer means that conventional air conditioning is sometimes unnecessary (gleaned from conversations with owners of classic earth sheltered homes in our area).  And the probability of frozen pipes is negligible.

To be sure, there are non-classic earth sheltered passive solar designs that are more MRT-centric than just described but they are not as common.  Typically they utilize the most efficient thermal mass possible -- water -- in containers (like darkly-painted metal "oil" drums or polymer vessels of various shapes and sizes) staged to collect winter sunlight through south-facing windows during the day and release heat at night and on cloudy days.  Less commonly, roof ponds comprising water in waterbed-like bags strategically situated on the roof are used to heat in winter and cool in summer.

Mean Radiant Temperature in Annualized GeoSolar Homes

What sets our Annualized GeoSolar earth sheltered passive solar home apart from stick-built construction and the classic earth sheltered home is the total absence of supplemental heat or conventional HVAC.  This is possible by controlling profoundly the mean radiant temperature in three ways:   (1) increasing solar gain by harvesting the summer sun to supplement and vastly exceed the heat-gain from the winter sun, (2) significantly increasing the storage capacity of the thermal mass, and (3) retaining heat (winter) or rejecting heat (summer) with a R-60 to R-73 building envelope.  Based on the Hiat/Stephens design, we expect eventually a year-round comfort level in the mid-70s with a fall-off  to the upper 60s by the end of winter and an uptick to the mid-80s by the end of summer. 

It may take a few years for the temperature of the thermal mass to stabilize during which we will use infrared space heaters for supplemental heat and, with numerous ceiling fans and the use of windows for nighttime ventilation, may or may not have to worry about air conditioning.  However, the kicker is that our build is patterned after designs by authors who live in climates -- Montana and Washington state --  that are dryer and cooler than ours near St Louis, MO where summertime temperatures and humidity levels are more like the southern states.  With global warming, our passive heating will improve but passive cooling might become even more challenging.  We have to remain open to adding a minimal amount of air conditioning and trust that our photovoltaic array will handle the additional load or, at least, with net-metering, that our electricity cost on a yearly basis still zeroes out.

(Thanks to Jason Graklanoff, my engineer friend, for his thoughtful input to this post.)

*     *     *     *
Two additional posts continue the story of how our house works.  The first one is an outline, the second delves into the details. 

Construction - Window Installation

Most of the north and west exterior walls of the house are earth sheltered and the garage abuts the east wall.

Only 12 second windows were built instead of the 14
shown on the plans.  The first story windows stayed
true to the plans, making a total of 19 large and 1 small
 south-facing windows 

  Therefore, we would have been hard pressed to fit glazing into any of these walls.  But, no loss, we intentionally designed the house with all south-facing glazing (except for one small east window under the entry portico).  It took twelve 3' x 5' windows on the second story, four 3' x 5' and three 3' x 6' windows on the first story to meet minimum code for the ratio of glass-to-floor area.  The interior of the house is laid out so that all spaces except the bathrooms and the TV viewing area have windows.  The living room has no ground level windows but, since there are no second story rooms above it, it is generously lit by the second story clerestory windows.

 Green Features 

All the windows and the two exterior doors are designed for maximum sustainability.

     -  Energy efficient glass                -  Recessed profile               

     -  Energy efficient frames             -  Overhangs                

     -  Fixed vs.Operable                     -  Angle of incidence 
     -  Swing closure                            -  Peripheral seal            

     -  Translucent (frosted) glass        -  Glass-to-floor ratio

(Click on any photo to enlarge it for better viewing.)
    
Energy Efficient Glass
Our windows and doors have all of the bells and whistles,

like double glass and low-e coating, that make them first quality.  But, at +/-R-4, they are like holes in the wall compared to our fifteen inch, R-60 walls.  According to Daniiel Chiras in his book The Solar House; Passive Heating and Cooling, the problem is not just the glass -- about a fourth of heat gain or loss occurs through the frames, making it imperative that both the glass and the frames be energy efficient.

Energy Efficient Frames
A fiberglass frame has the same coefficient of thermal expansion as window glass unlike wood and vinyl frames (vinyl is by far the biggest mismatch).  When the frame and glass expand and contract at the same rate, air leakage between the frame and glass that might compromise the seal of the double panes or admit air into the living space becomes moot.  Unlike vinyl, fiberglass is resistant to UV rays, is much stiffer and accepts paint.  And it is made from sand, the most abundant substance on earth, rather than petroleum.

Fixed vs. Operable 
The top label at the right contains a map of the US with shading to indicate the area for which the window is designed.  Notice that it encompasses all but the southern reaches of the country.  The second label shows a reverse picture; only the southern reaches are shaded.  Fortunately, both labels cover St Louis.

Each label has a series of four numbers near the top.  The first number is the U-value which is an inverse expression of R-value in that the lower the number, the higher the R-value.  Notice that the U-value for the top label is lower than for the bottom label.

The two labels were photographed on side-by-side windows.  The top label is on a fixed unit and the bottom on an operable unit.  The fact that the maps and the U-values show an energy rating that is better for the fixed glass window validates our decision to limit the number of operable windows.  Since we will be depending on the energy recovery ventilator for most of our fresh air, having only 8 of 19 windows that are operable will be sufficient for additional ventilation when it is needed or desired.

Swing Closure
Windows and doors that are hinged prevent air infiltration better than sliding doors and windows.  To say it another way, casement, hopper and awning windows and hinged doors are more energy efficient than double- or single-hung windows or doors and windows that slide horizontally.  The reason is that swing doors and windows can be locked tight against a gasket-like seal while sliding units need a looser fit to be able to move up and down or side-to-side.  While the fit of modern sliding units are infinitely better than their ancestors, their air sealing still falls short of the gasket-type.

Frosted Glass
Greenhouses utilize the solar advantage of translucent  glass.  The glass in old-time greenhouses was painted with whitewash.  Newer greenhouses use "clear" sheet plastic that is, in reality, translucent in that you can't see clear images through it or they utilize translucent corrugated fiberglass panels.  Accordingly, we have 19 south-facing windows at least 3' x 5' in size of which more than half have translucent (frosted) glass instead of clear glass. 

The solar performance of the two types of glass differ in this way.  Sunshine through clear glass warms whatever it shines on.  If "it" is thermal mass, like concrete overlaid with ceramic or porcelain tile and of an appropriate color, the solar heat is absorbed into the mass without overheating its surface, which is a good thing.  If "it" lacks thermal mass (think wood or carpet floors, furniture and even drywall), "it" overheats and warms the air when it is not needed.  In a sense, precious heat is wasted.  

Frosted glass, on the other hand, diffuses (scatters) the sun's rays.  The heat rides the air currents within the dwelling until it either finds thermal mass or it conserves heat in the thermal mass by providing heat that would otherwise be coming from the thermal mass.  In our case, the thermal mass is the downstairs floor, the lower 10' of the long concrete back wall of the house and the soil under and behind them as well as the soil  beneath the insulation-watershed umbrella adjacent to the house.  Consequently, all of our first story windows are transparent because of their proximity to the thermal mass whereas all but two of the second story windows, where mass is missing, are frosted.

Recessed Profile
Today's new construction windows have nailing fins that position

the surface of the glass flush with the outside surface of the wall.  While this design eliminates air leakage between the window and the wall framing, it is not as energy efficient as it could be if the glass were not flush with the wall.  Here's why.

The rate at which heat is lost through the glass is dependent on the rate at which heat is removed from the outside surface of the glass.  If the heat can pass through the glass and linger for awhile on the outside surface of the glass, it slows the transfer of more heat.  What determines the amount of lingering?  Air movement.  Wind can remove the heat as fast as it forms and, since heat seeks cold, the rate at which heat is drawn through the glass accelerates, a phenomenon called "wind washing".

Our windows, by being positioned about 10" inside the plane of the wall and being south-facing, are sheltered from the prevailing north and west winter winds.  As such, the amount of wind-washing is about as minimal as it gets.  The red arrows in the nearby photo bracket the 15" thickness of the wall; the green arrows delineate the area on which the window rests; the blue arrows show the distance from the window to the outer surface of the wall -- about 10" after the trim boards are in place.

The distance between the top of the windows and the 2'
overhangs is greater for the first story than for the second
story but the difference in the amount of sunshine reaching
 the floors inside is negligible even for the taller windows
 in the foreground.  (The sheathing is protected by lumber
wraps and sheet plastic which will be replaced with proper
house-wrap and metal siding eventually.)

Overhangs
Sunshine through the windows is a blessing during the cooler months of the year but very unwelcome from May through September.  At our St Louis latitude, it takes a two-foot overhanging soffet to block the midday sun during the hot summer months.  

Early morning and late afternoon sun can shine under the overhang but, with the windows recessed, the adjacent wall offers shade in a way not possible with flush-mounted windows.  However, after the end of May and until the first of September, the sun angle increases enough that sunlight is completely blocked all day, even during the early and late hours. With the windows recessed, though, the sun that does reach the floor during late spring and early fall covers an area a third less than would be the case with flush-mounted windows.  As long as the overhang is reasonably close to the top of the windows, the height of the windows

Even with tall windows and an overhang a good
 distance above the tops of the windows, very little
 midday sunshine reaches the floor in early May;
 later in May none will.

is not critical. The nearby photos show the extent to which the sun reaches the floor during the first week of May through windows 6' tall and an overhang +/-2' above the tops of the windows.

Angle of Incidence

The same windows in late afternoon after the sun has
dropped low enough to shine under the overhang; the
amount of sunlight reaching the floor is restricted by
the recessed profile.

Another important concept in understanding passive solar is the angle of incidence, the angle at which sunlight strikes the glass in windows or the roof of a greenhouse.  The more perpendicular the sunshine is to the glass, the more energy absorbed by the glass.  The steeper the angle of the sunshine, the more energy reflected by the glass.  The practical take-away is that at least 90% of the sun's energy reaching a vertical window during the summer months does so at such a high angle that it is reflected rather than raising the temperature inside the house.  By the same token, the amount of energy absorbed through vertical windows at winter solstice time is at least 90% of what could be expected through glass that is tilted toward perpendicularity with the winter sun, as often seen in pictures of passive solar homes and greenhouses.  But tilted glass is not a good idea because it absorbs too much unwanted heat in summer unless it is covered with an exaggerated overhang, which is rare in the pictures I've seen.

In summary, our passive solar design utilizes three things to maximize solar gain when it is needed and minimize solar gain when it is not..  First, our windows are vertical rather than tilted for the reasons just discussed.  Second, we have overhangs designed for our latitude that provide adequate overhead shading.  And, third, our windows are recessed for lateral shading.

Peripheral Seal
The decision to recess the windows meant using "replacement" rather than "new-construction" windows.  No doubt about it, the latter with their nailing fins are better at blocking air leakage between the windows and the framing and sheathing that surrounds them unless the air sealing around replacement windows is done with extreme care.  

Sealing our windows was complicated by the fact that I built the housing for them as premade wall sections using custom jigs several years in advance of even ordering the windows. I deliberately made the window openings larger side-to-side and top-to-bottom than the window manufacturer specified because I knew that it would be extremely difficult to enlarge the openings once the units were in a wall.  As a result, the gap on either side of the windows averaged 1/2" and the gap at the top of the windows more like 3/4".  

All three sizes of backer rod --  3/8", 1/2" and 5/8" -- were
 needed in various combinations to close the gaps 
between the window frames and the rough openings on
 the exterior side 

At first glance, it would seem that all one would have to do for fool-proof air sealing is to fill the gaps with spray foam but even minimal expanding foam that is designed for this purpose is capable of distorting window frames if used in excess.  Rather the window manufacturer recommends that the foam be limited to a 1" strip located about 1" into the space between the window frame and the rough opening on the interior side.  On the exterior side, it recommends a course of properly-sized backer rod just inside the outer edge of the frame and, in doing so, leaving enough room for a bead of caulk.  Since our windows are inset, the caulk will be added when the jam extension between the window frame and the trim boards around the window opening are installed.  In this manner then, the spray foam provides the air sealing and the backer rod and caulk provide weather sealing.  The wide 3/4" gaps at the tops of windows were partially filled with plywood ahead of the foam and backer rod.

Glass-to-floor Ratio
In his definitive book, The Passive Solar Energy Book; A Complete Guide to Passive Solar Home, Greenhouse and Building Design, Edward Mazria recommends for our temperate climate (average winter temperatures of 35 to 45 degrees) a ratio of 0.11 to 0.25 sq ft of south-facing glass for 1.0 sq ft of floor area "in order to keep the space at an average temperature of 65 to 70 degrees during most of the winter".  Only our concrete first floor can be counted as floor area for calculating the ratio, so 2,800 sq ft of floor area to 354 sq ft of south-facing glass gives us ratio of 0.13, which falls at the lower end of Mazria's recommended range.  

Such a low ratio could be discouraging for us older folks who do better with temperatures in the mid-70s and the numbers get even worse because Mazria's figures for the temperate zone do not differentiate for cloud cover.  Here in the St Louis region, according to Daniel Chiras, only 47% of possible sunshine during the months of December, January and February actually reaches the glass.  Therefore, a conventional winter-centric passive solar house would definitely require supplemental (CO2-emitting) heat.  However, when heat coming through our windows during winter is added to the heat generated by our Annualize GeoSolar summer-centric system, it is almost certain that our thermal mass will maintain a comfortable year-round temperature hovering around our preferred 74 degrees without any supplemental heat.  Don Stephens, the father of AGS warns that too much heat could actually be a problem eventually that would necessitate mothballing part of the solar collector.  (For an understanding of AGS, click on "Featured Post" in the left column above.)

Installation
Not much needs to be said about the actual installation of the windows except for some considerations dictated by working alone.  Most of the windows were 3 x 5' and about, I would guess, 60-70 lb.  Knowing that I would be working alone, I requested that the double windows be shipped as individual windows rather than joined together with a factory-installed mullion.  Even then it was a stretch to hoist the second story windows to place without using a ledger on which to set them part way up.  By using temporary vertical stops against which to set the window, I could lift it into the opening without its falling outward and, by installing the stops exactly plumb and at the exact location of the exterior surface of the window in the rough opening, the window ended up automatically in the position it needed to be in except for plumbing in a left-right direction. 

The additional work required for the site-made mullions is at least partially compensated by the knowledge that they are more energy efficient than factory-made mullions would have been since they are filled with foam board insulation.

Construction - Standing Seam Steel Roof - Part II: Installation

The prior post covered the preliminary steps leading up to the actual installation of the steel.  This post details the installation of the garage roof that was actually the third section of roof that I had installed but I am using it as exhibit A because, by being a simple rectangle, it is easier to describe. In a subsequent post, I will deal with the hip-roofed porch which is far more challenging.  

Installing Moisture Barriers
After I identified the truest eave-rake corner, I proceeded with the installation in the following order
1.   Metal drip edge over the junction of the sheathing and the fascia (eave side only; the rake sides would be handled with a steel rake trim over the roof panels later); the drip edge is installed first so it can be overlapped by the ice shield in step two.
2.  Two courses of stick-down ice shield paralleling the eave; the ice shield covered the drip edge; code requires that the ice shield extend 24" beyond the interior face of the exterior wall and, since our eaves overhang 24" and the wall is 15" thick, two 36" courses of shield were necessary to meet code.  Unfortunately, the installation was being done on warm-ish winter days that were still too cool for proper adhesion of the shield to the sheathing so we used a torch to seal the edge at the eave then held our noses and used roofing nails to secure the remainder, hoping that the hot summer sun will activate the adhesive later; ordinarily, the ice shield would be unnecessary for an unheated garage but, since ours will be seriously insulated and warmed considerably by the AGS system, I decided to error on the side of caution.
3.  Roofing nails to fasten as many courses of 30# felt paper as it took to reach from the ice shield to the wall of the second story (first photo below (clicking on any of the photos will enlarge them for better viewing)); the junction between the future steel siding on the second story wall and the steel roofing panels would eventually be protected from moisture by a metal trim piece called "dormer flashing"; however, rather than depend on it alone, I continued the felt paper from the roof up the wall a ways as a secondary barrier, taking care not to bend it so abruptly as to compromise its integrity; most roofing contractors use staples in a slap stapler in a rather random fashion but I like the idea of using roofing nails along the overlapped edges of the felt because, when driven tightly, the heads help to seal the hole in the felt against water in a way that staples may not, especially when the paper is damaged by the head of the slap stapler should it be held at an angle to the surface of the paper.
4.  A mason line paralleling the eave to which the ends of the panels could be referenced for a straight installation (second picture).  In our case, the line was positioned for the 1 1/2" overhang specified for the  Rain Handler system that we are using on all sides of the house in lieu of conventional gutters.

It is important to point out that the virtually impervious 30# felt can be used in this situation only because the sheathing, which will inevitably collect moisture, will be able to dry from underneath even though the roof is of cathedral design.  The trusses supporting it are 12" thick and I plan to hold the insulation down from their top edges several inches to allow air to circulate between the insulation and sheathing.  (For a in-depth discussion of moisture abatement, check out the previous posts on Design - Vapor and Air Barriers and Design - Vapor and Air Barriers (Cont'd)). 

Major Problem
As described in the post preceding this one, the metal panels for the garage were the wrong length and had to be reordered.  Unfortunately, I did not catch the mistake until the moisture barrier was in place and, as luck would have it, a strong wind soon had its way with the 30# felt despite its toughness.  A small section blew away but most of it stayed in place even after pulling loose in many areas.  I re-nailed it with Grip-Rite Round Cap Roofing Nails which held it reasonably well until the replacement 

Green arrows = felt paper being unrolled just ahead of
the installation of the steel panels; red arrow = felt paper
extending up the wall a ways for better protection of the
wall-roof interface

panels were available but knowing that it would not be wise to leave the Grip-Rites under the metal panels because they would be proud enough possibly to dent the steel from below if it were stepped on.  Consequently, it was just easier at little additional cost to pull the Grip-Rite nails and lay down another layer of felt but doing both a little at a time just ahead of the next panel to be installed rather than laying it all down at once and risking another wind event.

Observation of Note
I bought 30# felt paper from our local (traditional) lumber yard as well as from one of the big box retailers and, despite only a small price spread, found a significant difference in quality.  Fortunately, I found the discrepancy early enough on the first roof to replace the big box paper with the better quality lumber yard paper before the first panel went down.  And, of course, I used the heavier paper for the rest of the roofs.

Installing the Steel Roof Panels
After the taut mason line has been installed along the eave as a reference for the ends of the steel panels, the panels can then be installed from left to right or from right to left, depending on the location of the truest corner

The mason line is tautly strung so that it designates the
amount of overhang for the steel panels but situated just
low enough that the panels do not touch and distort it

that was identified by using the 3-4-5 method (actually, 9-12-15 or 12-16-20 for more accuracy if the roof is large enough).  Knowing which corner forms the best right angle is a starting point but it is probably not accurate enough to install the first panel without further checking.  If the first panel is not aligned perfectly perpendicular to the mason line, the rake edges of the panels will not align with each other, forming an amateurish saw-tooth edge to the roof, the jaggedness of which is directly proportional to how much the first panel is off.  

To satisfy the 9-12-15 right triangle, the lower end of the
 first panel is anchored with one screw then the "0" end of the
 tape measure is held at the 12' mark on the mason line (red);
 the other end of the tape measure is held on the outside
 edge of the panel at the 9' mark (green) while the upper end of
 the panel is swung in or out until the 9' mark on the panel 
precisely underlies the 15' mark on the tape measure

I installed the first panel next to the rake with the standing seam side towards the rake.  In order to verify the absolutely critical right-angle-ness of the first panel to the mason line, I drove a screw through the predrilled hole in the panel closest 

to the eave then, with help from a neighbor, redid the 9-12-15 measurement.  Any right-angle discrepancy could easily be corrected by moving the top end of the panel slightly left or right to align it with 15' on the tape measure.  As long as care was taken to align succeeding panels with the mason line, the ends of the panels were nice and even.  By contrast, our first installation was the smallish rectangular roof on the west side of the house that we did before cold weather.  I did not think to double-check the right-angle-ness of the first panel as just described and ended up with a little sawtoothness.

Resulting smooth, versus 
saw-toothed, edge

The leading edge of each panel contains a row of holes to receive the screws that are furnished by the manufacturer (for a better understanding of the components, visit ProSnap Steel Roofing on Menards website).  The screws should be no further than 2' apart which meant one in every other hole.  The next panel is lined up with the mason line at the lower end and its standing seam ridge is aligned over the lessor ridge of the preceding panel.  It is then a simple matter of snapping the panels together by pressing on the ridge of the second panel, starting at the eave, until it snaps to place over the ridge of the first panel then repeating the process up the slope of the roof until the panel is fully seated on the prior panel for its full length.  The snapping can be done with the heel of the hand or with a rubber mallet.

Installing the Rake Trim
After the panels were in place, it was time to add the trim pieces that divert water from the rake edges and the junction between the house wall and the roof.  First, the rake trim.  On the side of the roof where the first panel was installed, the trim fits against the surface of the fascia in a vertical direction and overlaps the standing seam ridge in horizontal direction.  It is fastened to the flat part of the panel with screws having neoprene grommets under the heads that keep water from penetrating around the screws.  Since the trim overlaps the standing seam, any water that runs under the edge of the trim is caught by the standing seam so that it is unnecessary to use any sort of caulking under the edge of the trim.

The installation of the rake trim on the opposite

The panels nearly installed; notice the block on the
 fascia to hold the ladder off of the mason line and
out of the way of installing the panels behind it; notice
that the felt paper extends up the wall a ways to be
covered later by the house wrap and cladding

side of the roof is complicated by the fact that there is no standing seam under the trim to divert water.  Therefore, to serve as a water barrier, so-called "tape mastic" that has the consistency of very dense plumber's putty but looks like weather stripping is applied to the under-edge of the trim before the latter is screwed to place.

The rake trim came in 12' lengths so I started the first piece at the eave and overlapped it for a few inches with a second

The rake trim did not fit snugly against the fascia; it had
to be tightened down with screws after painting the
 fascia with the final coat of paint

12-footer.  It took still another shorter piece to reach the second story wall.  The trim did not fit the facia tightly in several areas, especially where two pieces overlapped, so I resorted to a few grommeted screws to snug up the vertical part of the trim after the fascia had been painted.

Installing the Dormer Flashing
The dormer flashing is used at the top of the roof to divert water from the junction of the second floor wall and the roof panels.  It slips up under the house wrap and the wall cladding and overlaps the ends of the steel panels.  In doing so, it rests on the tops of the standing seam ridges leaving gaps under it.  In order to keep water from blowing in through the gaps, the latter are filled with so-called "closure strips" that are die-cut to fit the contours of the flat part of the panels and coated with adhesive. They are pressed to place between the ridges just inside the lower edge of the dormer flashing to prevent, or at least minimize, water penetration.  Once the closure strips are in place the flashing is secured with grommeted screws long enough to penetrate through the tops of the standing seam ridges and screw into the sheathing.  The vertical flange of the flashing is also screwed or nailed to the wall sheathing before the house wrap and wall cladding are installed.

Construction - Standing Seam Steel Roof - Part I: Shopping, Ordering and Receiving

Two and a half years ago, I posted on two design options for steel roofing that we needed to consider, viz., standing seam with concealed fasteners and the exposed fastener type that is used for siding more often than for roofing.  The former is less likely to leak because the standing seam diverts runoff from the junction between panels and almost all of the fasteners are located and protected under the seam where leakage around them becomes moot.  The exposed fastener panels have two drawbacks.  All of the screws remain uncovered and are subject to leakage if the hex-head screws are not tightened precisely for a good seal of the elastomeric washers under their heads.  Also, the seams are relatively flat lap joints that do not divert water to the degree that standing seams do.

At the time of that posting, I was leaning towards the cheaper exposed fastener option in order to stay on budget.  Since then, reality has set in; the budget has become so distorted (grist for a future post after construction is completed) that, when it came time to order the roofing, the additional cost of the concealed fastener design was easy to justify.  Also, the roof pitches turned out to be lower than I imagined at the time of the posting to the extent that the exposed fastener design would have been too much of a gamble.


But First, Why a Steel Roof At All?
Because it is more sustainable.  It contains recycled steel initially and it can be recycled again at its end-life, unlike petroleum-based shingles that end up land-filled.  The life expectancy of a steel roof is several times that of even the most expensive asphalt shingles.  And the steel panels resist hail damage better than shingles and can be purchased in highly reflective colors to reduce solar gain for a cooler roof.  White panels, for example, are 100% reflective; the light gray that we are using is almost as reflective (upon request, Menards corporate provides information on the reflectivity of its steel roofing colors that may not be available at the store level).  The energy embodied in raw materials, manufacturing and transportation to the end-user must also be included in any assessment of sustainability.  Shingles and steel panels both require extractive sourcing but the former is a one-use product while the latter is recyclable.  A comparison of the energy embodied in their manufacture is beyond my pay grade but I suspect the recycled content of steel may tip the scales.  Energy embodied in transportation to the end-user is a case-by-case scenario.  Our steel panels from Menards came from a plant near Omaha, NE that is +/- 375 miles away which is well within the LEED standard of 500 miles maximum for the transfer of materials to the building site.  

Should a Steel Roof Be DIYed?
In my experience, the learning curve for steel roof installation is flatter the than for some other phases of home-building such as plumbing the waste system or cutting stair risers and certainly less challenging than drywalling cathedral ceilings.  Perhaps the most difficult task is cutting panels that cannot be pre-cut by the fdactory.  As I will describe in a subsequent post, even that is manageable.  Having said all of that, I must admit that, for someone my age, hanging out on roofs is a little more iffy now than it used to be. Otherwise, a steel roof is easily within the scope of a DIYer home-builder.

Placing the Order 

Crates of roofing haphazardly strewn about by Menards'
crude delivery protocol 

I compared the price, quality and color selection of several manufacturers of steel roofing and decided to buy ProSnap Steel Roofing from Menards.  Apparently, one of its subsidiaries fabricates steel cladding products which makes their purchase relatively hassle-free for consumers and DIYers.  Indeed, I found the latter to be true except for their delivery equipment that was so awkward and inefficient that the outsize containers were dropped haphazardly at the building site.  Thank goodness I had forks

The damage to the long crate at the rear in the picture
above by the time it was moved to the garage;
 fortunately only one panel was unusable

for my trackloader with which to gather them up and move them to storage in the newly-built garage.

All that is required for a quote and to place an order are reasonably accurate scaled drawings of the roof(s) and a color selection.  I found out the hard way that not all drawings are treated with the same degree of thoroughness by Menards.  When achitectual drawings are submitted in parallel with the scaled DIY drawings, the steel plant emails digital drawings to the customer for approval and a signature.  However, with only DIY drawings, there is no digital feedback from the factory -- the order is shipped without any further communication.  

The accuracy of the factory drawings is best documented by remeasuring the roof with the factory drawings in hand before signing off on them.  Special attention should be given to panel lengths for intersecting slopes on either side of a valley.  And there are a myriad components other than the panels themselves that must be vetted such as flashings of several types, roof edge protectors, vented and unvented ridge caps, and several different fasteners, moisture blockers and mastics. 

Our color selections for roofing and siding were based on reflectivity, i.e., the ability to reflect the sun's rays, in order to maximize the efficiency of wall and ceiling insulation in summer.  Accordingly, we chose highly reflective light gray for the roof and bright white for the siding instead of less reflective, but perhaps more interesting, darker colors.

Staging the Components
The first step in the installation process is to unpack the delivery crates and organize the contents so as to verify that all the components have been received in good condition and to get a leg up on finding them as needed during installation. The latter was particularly important in our situation because three roofs of different sizes were involved, one of which was a hip roof for which the panels varied in length.  Also, as a DIYer, it was important to familiarize myself with the ancillary components that were specified by the factory as add-ons after the order was placed.

In our case, there were two glitzes, one minor and one extremely major. 

The minor one was a panel having localized damage -- denting and abrasion of a small area --  that rendered it unusable but for which Menards readily issued credit.  The bigger problem stemmed from the fact that the measurement I gave Menards for the length of the panels for the garage roof was 10" too short due to a transposition.  The steel for the garage roof had been a last-minute add-on to the original order and, after reviewing the paperwork, I realized that I had not received a digital drawing of the garage roof from the manufacturing plant for dimension verification and a signature before the order was processed.  In the absence of architectural drawings, the cost of the mistake was entirely on me as far as Menards was concerned at a cost of about $1,000.  The reality message here is that a DIY home builder accumulates a lot of knowledge and skills, sometimes the hard way, that have limited or no future value, especially for someone my age.  But that doesn't diminish the joy of the onetime  journey.

The next post covers the installation of the roofing.

Construction - Porch , Solar Overhang, Soffets and More

My blog posts over the past several months have had more to do with dirt work than with carpentry.  While there is still some dirt work to do, mainly installation of the insulation/watershed umbrella west of the house, it is good to get in some carpentry for a change.

Framing for the Screened Porch
Glen, a journeyman carpenter friend, and I took advantage of some warm and dry weather in January to do most of the framing for the porch

Framing for the hip-roofed screen porch

but we were not able to carry it to the sheathing stage until mid-summer because of rainy spring weather and the fact that I needed time off from carpentry to finish the dirt work that I described in recent posts. The hip roof for the porch was well beyond my expertise so it made sense to stand aside and let Glen lead rather than learning its complicated construction for a one-time situation.  In order to save money and to be able to design as we worked, we stick-built it in lieu of trusses.  The framing included ceilings for both the porch and the walk overhang to make them cooler and have a more finished look.

Covered Walkway
We framed and sheathed a roof for the walkway that runs between the porch and the front door of the house.  Since it even extends slightly over the nearest garage door, we will be able to navigate undercover from the kitchen/porch door to the front entry or garage door.  The walk overhang is a continuation of, and blends in with,

This photo shows partial framing and sheathing of the
overhang for the second story clerestory windows as well
as the covering for the walkway between the screened
porch and the front entry; also visible is the beginnings
 of the temporary second story scaffolding against the
south wall

the porch roof.  It is carried by a double 2 x 12 beam running from the porch to the house without intervening post support.  Since the overhang is wider than the walk, a post would have required unwanted penetrations through the insulation/watershed umbrella (the installation of which was covered in a prior post).

Clerestory Window Overhang
All that is needed to keep unwanted midsummer sunshine off of the second story clerestory windows an dedicated overhang extending about two feet outward from the house just above the top trim for the windows.  Here pre-made trusses did make sense for saving time and money.  Closed cornices at each end of the overhang handle the transitions between the facia of the steeply sloped overhang and the facia of the low-slope second story roof.  The one at the west end could be built from a ladder standing on the first story roof but the one on the east was 25 ft above the ground and its complexity would require an impossible number of trips up and down a ladder. 

Po Man's "Cherry Picker"

Second stage scaffold

Construction of the east end of the overhang was a perfect example of the extraordinary measures one uses when working alone with a tight budget.  A contractor would probably have called in cherry-picker-like equipment for the job or set up steel scaffolding whereas I knew that working alone would take sufficient time to make rental fees for either approach off budget.  I constructed instead a substantial temporary scaffold from which to work safely.

The scaffold, that was anchored to the floor and ceiling inside the house and cantilevered through the wall, was done in two stages.  The first was adjacent to the south-facing wall for the purpose of framing, sheathing and roofing

Anchoring design for the cantilevered scaffold

the overhang as well as installing the facia and soffet.  The second stage was added later at a right angle to the first and wrapped around the corner of the house for the sole purpose of building and painting the closed cornice at the junction of the overhang roof and the second story rake roof and the associated soffets. The second scaffold, though, was in the way of installing the garage roof so it gave way to a successor that I will describe in a future post.  The south scaffold stayed in place until the metal roof and the soffet for the overhang were completed but will be in the way and have to be removed before installing the first story metal roof, the clerestory windows and the second story metal siding.

Soffet / Cornice Construction
The framing for the underside of any roof overhang comprises either rafter tails on the eave side or their equivalent called lookouts, on the rake side.  The tails and lookouts can be left exposed for a rustic look or can be veneered on the

Wedges added to the rafter tails (green);
notice the use of the Rainhandler instead
of a conventional gutter

bottom with a soffet, which means that, on the rake side, the soffet follows the slope of the roofin one direction and is horizontal in the other while, on the eave side, the soffet simply follows the slope of the roof.  The transition of the facia at the corner between the eave and the rake is uncomplicated whether there is a soffet or not.

However, the eave side is often modified to give a more finished look by making the soffet horizontal with special framing or by using
proprietary soffet materials like vinyl or metal to effect horizontal-ness without the benefit of framing.  But doing so creates an awkward transition of the facia and the soffet at the corner between the eave and rake that has to be reconciled by what is called a cornice return.

Our design called for a horizontal soffets and cornice returns for all overhangs.  Since the pitch for all of our roofs is low, it was easier to add 2-by wedges, to the bottom of the rafter tails than to frame horizontally or use proprietary materials.  The cornice returns were relatively simple except for the abrupt change from the second story overhang and the low-pitch second story roof.

Using a jig on the table saw for cutting the wedges

Steel Soffets
Modern soffets are usually not framed in.  Instead they are created with short pieces of vented vinyl or aluminum, and occasionally steel, running perpendicular to the wall of the house.  I opted for steel soffet material that can be purchased in convenient 12' lengths that run parallel to the wall.  The way I used them was to frame (as in picture frame, not structural frame) the periphery of the soffet with salvaged 1x lumber that I rabbeted underneath to accept and hide the edges of the vented steel panels.  Once the panels were tucked under the frame, I screwed them to the bottom of the wedge-added rafters and the rafter tails.

Metal Roofing and Siding At Last!
The roof sheathing has been protected by either 6 mil plastic sheeting or 30 lb felt paper, or both, for many months while awaiting the day the steel roofing could be installed (prior post on temporary protection).  Finally, the completion of the porch and the overhangs made it possible to measure and order both the roofing and the steel siding.  (For a discussion of and the rationale for standing seam steel roofing, go to the post on roof design and for steel siding, go to the post on wall cladding.)

All that was needed for estimates on roofing and siding was to produce homemade scaled drawings that provided the information the manufacturer needed for both the steel panels and associated steel trim pieces. The manufacturer countered with two things:  (a) a list of components for careful vetting and (b) digital drawings that could be taken back to the building for dimension verification before finalizing the order.  In order to reduce the cooling load, we ordered roofing and siding with color shades that had a high solar reflectance -- light gray for the roof and white for the siding.

The next task is to get the garage undercover in order to have dry storage for the steel cladding.