Brett Thibault

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since Aug 11, 2017
Architect specializing in historical preservation and building science.  Sustainable gardener.
Southern Worcester County
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Recent posts by Brett Thibault

Good day to you Bannerd Div.

I have designed Massachusetts-local stone (granite) foundations with hydraulic machines.  This is not a sustainable course of action in the strictest sense, but I have been cautioned by senior participants on this forum to follow a course of least resistance, so I demur. (That's how I read the post anyway.)

A hydraulic (bush) hammer will be the best course for this kind of effort because you need to make relatively flat surfaces on the rock you use.  You can make superior flat bonding surfaces with hydraulic hammers that will counteract wind and (if applicable) seismic forces when bonded with measured bonding agents for your foundation if you mix the bonding agents competently. (sand and cement 50/50 is a good place to start if you can source finely ground materials that will cohere)  If you don't measure and mix you will be rolling Las Vegas dice because the only things we have as a community are the successful measurements we've used before. If this is anathema to you, please do your own thing but record what you do so we can all benefit from your progress.  Thanks in advance!
3 years ago
There are several polyester-based insulation products available; Bradford makes polyester based "Polymax" batts which were formulated to reduce the dust and skin irritation produced by traditional fiberglass batts.  The garment industry has a regulating body that, among other things, classes apparel fabrics according to ignition hazard.  Polyester has a high rating which makes it safe in relative terms.  ASTM E84 tests interior building finishes for flame spread after ignition, and polyester fabrics are often rated Class A, which means relatively low flame spread.  Most large drapes you might see in hotels are polyester or have a generous amount of polyester fiber to allow them to hang with good sheer and little wrinkling.

Almost all building insulation is required to be covered by an ignition barrier, like gypsum board, in conventional light frame or steel frame and infill.  It is far more likely that ignited room contents, furnishings and interior finishes will reduce occupant escape probability than insulation located within a stud bay due to this fact.

The two issues I see with using scrap fabric for stud cavity insulation are lack of homogeneity and consolidation.  The fabric scraps will have to be spun or ground to create a homogeneous, air-entrapped material to provide an efficient insulation, and then supported to avoid consolidation at the bottom of the stud bay and air gaps at the back of the interior wall finish.  I have witnessed the removal of interior finishes on hundreds of walls during my career, and every single loose-fill application and most of the batt applications were in support failure at the time of removal.  Many failures for loose-fill occur after only 2-3 years; batts fail usually after 5-8 years if improperly supported.

The three best practices for insulation design are continuity, support and location within the wall section.  So, for example, low R-value well-supported continuous insulation installed dead tight against the back of interior wall board will provide more comfort and energy savings than discontinuous high R-value poorly supported insulation installed with an air gap between the interior wall board.  If you decide to use the scrap fabric, I'd be interested to hear how you end up installing it.
3 years ago
Adding thermal mass to building walls to provide a dampening effect on temperature swings within the building can be both effective and sustainable if adequately designed.  One of the most vexing design challenges is maintaining a high performance thermal envelope while incorporating a functional dampening system via thermal mass.  Because most thermal mass systems must function as a "black body" to achieve their desired dampening effect, they cannot be insulated; they must be designed to emit as much as they absorb.  They can therefore not be constructed as an exterior wall and function as a dampening system with any appreciable effect.  Traditional wall sections for functional dampening systems generally include a winter sun-facing exterior wall glazed with low iron, uncoated lights, an interior thermal mass system, and an environmentally controlled interior space between the exterior glazed wall and interior thermal mass system.  The exterior glazing is generally 100% of the non-structural portion of the exterior wall, shaded by an overhang to decrease summertime heat gain.  The environmentally controlled interior space is generally continuously insulated to the lowest practical U-value on all non-glazed and non-thermally absorptive surfaces and finished, and temperature sensitive dampers are used to transfer heat from the controlled interior space through the thermal mass system to well insulated living areas.

I have designed 37 of these types of systems, and have been mostly successful using the above design parameters as a basis.  One of the most successful was an unheated greenhouse retrofit where we used water filled 3" X 72" re-purposed schedule 40 PVC pipes to provide thermal mass.  Water is by far the best material for use in these types of systems in my opinion.  The greenhouse maintains a reliable night time temperature gradient 12F above exterior temperatures, even when exterior temperatures fall below 32F.

Simply filling stud bays with loose granular material as a stand-alone system will provide negligible dampening results, if anything, if located in an interior wall.  If stud bays on an exterior wall are filled in this way, it will likely produce an effect opposite of what is desired, especially in winter, and will probably provide the added nuisance of organic growth within the cavity.   Not recommended.
3 years ago
Hi Norah,

Load bearing walls must be designed using verifiable measurements.  Both above ground and below ground load bearing walls are subject to a range of different forces; however, the ranges are not the same.  For example, below ground walls and above ground walls both must have the compressive strength to equalize the force of gravity, but above ground walls must have adequate compressive and tensile strength to counteract wind forces where below ground walls are not subject to wind forces.  Below ground walls can be subject to hydrostatic forces, where above ground walls usually are not in inland locations.

All the forces acting on a wall must each be measured so the wall can be designed to equalize them; we're in luck, because the forces gravity and wind exert on walls have been studied for ages and there is publicly accessible data available to help us design our walls.  To begin your design, gather all the data you can on the type of soil you will be building your foundation upon so you can calculate the compressive strength and shrink/swell characteristics of it.  Your foundation wall design must be able to equalize these forces as well as any hydrostatic and lateral pressures from the earth, the dead load of the building above ground, the uplift and torsion the wind forces acting on the above ground walls that are transferred to the foundation, and many others.

If you excavate a portion of the basement hole to a depth of 3 meters, you can take soil samples based on the color and physical composition and look up their respective compressive strengths online to begin designing the footing you will construct to support your foundation walls.  If you have trouble finding a good match for your soil types, photograph them and post the photos here and I will help you.  Be sure to note any subsurface water or bedrock encountered when you excavate.
3 years ago
Hi Ionel,

Zone refers to the average climate data available for the area in which one builds or lives.  For example, climate data would include average seasonal temperatures, humidity, wind and rain/snow moisture as well as elevation.  Exposure is specific to a building in this case, and refers to the amount sun, wind, and moisture the building will be exposed to within its microclimate.  Building system refers to the physical components of a building and how they work together to provide the occupant(s) a sustainable, durable, comfortable, and delightful shelter.

For example, a house built on the Baltic coast will be subject to a very different climate than one built in La Mancha because they are in different climactic zones; one house built on the Baltic coast in the mountains will have a far different exposure or microclimate than one built in a sheltered valley on the same coast.  A straw bale house built in the mountains on the Baltic coast will require the use of a different building system than a house built in La Mancha.

I recommend the SMACNA sheet metal guide as a reference for all sheet metal work.
3 years ago
Hi Jane,

If there's a good stand of birch on your homestead, I recommend rendered birch oil as an exterior wood preservative.  I coated the 1X6 reclaimed yellow pine esterior decking boards I have before I installed them, and have reapplied the oil every other year for 18 years; the wood is well preserved and has a wonderful honey color.  After application, it will remain tacky for two or three days depending on temperature and humidity conditions. I always apply the oil in October or November here in Massachusetts, and it takes two days to cure.  Birch oil extraction is sustainable and easy. Water beads up on birch oil, and it has a marvelous fragrance.  I also use it to waterproof leather goods and canvas tarps.  There are many articles and videos on how to extract and render the oil from different parts of the tree, but I always use the bark.  There are also several informational resources online regarding sustainable birch bark harvesting.
3 years ago
Hi Ionel,

Some things to consider:

1. Wind howling through your attic may indicate excessive air changes.  Too many air changes will likely result in excessive air-borne moisture migration into the space.  To strike a balance between adequate ventilation and minimal moisture migration, use a 1/200 ratio (free vent/surface area of attic floor) in zone 5. (different zones, exposures, and roofing systems require different ratios.) The roof vent shown is manufactured for tile roofs; a metal roof will likely get too hot and cause the butyl tape at the edge of the exterior membrane apron to fail.  The most reliable ridge vents for metal roofs are mechanically installed without relying on sealants, adhesives or tapes.

2. Air leakage through building components is a major contributor to residential moisture migration, energy loss and HVAC equipment failure.  Attic spaces are the major contributor to residential building air leakage. Over/under venting attic spaces have substantial effects on building health and occupant comfort and health due to the above.  I have tested more than 100 residential ridge vent installations on metal, asphalt shingle and tile roofs, and moisture leakage/migration via wind blown rain or snow through a ridge vent that has been installed per the manufacturer's instructions has never been an issue.  The issue is almost always over/under ventilating an unoccupied attic space.

3. Draped membrane installed over rafters under battens in an attempt to create a continuous waterproof membrane results in no effect on testing I have performed on tile roofs.  This is likely because it provides no benefit or detriment; a membrane that has been punctured hundreds of times by the fasteners securing the battens is no longer a continuous membrane in any case.  I have never seen it installed under a metal roof so have no data on that.  

3 years ago

I'm new to this site.  I'm responding to T.S. Moss' post and sketch.

Q: Should there be a layer of clay covering it all?
A: Clay has a relatively large capacity to absorb moisture and swell, and an equal capacity to expel moisture and shrink.  A volume of clay placed as you indicate--as a cap over fill*--would not likely have an appreciable effect on moisture intrusion into the fill; however, because of the swell/shrink capacity mentioned above, it would likely negatively affect the plinth stones by raising and lowering them.
* Gravel is a material which is suitable for consolidation through vibration and pressure. Consolidated fill is usually suitable for structural bearing if properly designed.  Small stones do not consolidate.

Q: Should there be layers of clay alternating with gravel, stone layers?
A: No--for the same reasons outlined above.

Q:How does any of this design change, if at all, due to the surrounding soil being sand, silt or clay?  
A: Depending on its characteristics, the surrounding soil mechanics would have an appreciable effect on the type of foundation illustrated.  There's not enough information regarding the soils.  For example, depending on the shape characteristics of sand, it can be consolidated or not: round grains will not consolidate, irregular (called sharp) grains will consolidate.  If there is organic matter present in the silt mentioned, it will continue to decay and the volume will lose mass.  Clay will shrink and swell.
3 years ago