Bob Yapp isn't exactly hitting on all cylinders here- he doesn't appear to have a good grasp on the moisture transfer mechanisms. He IS correct that the most cost-effective energy improvement you'll ever make on the place is air sealing, but seriously:
We create warm moist air in our homes by cooking, taking showers, having plants, breathing etc. That warm, moist vapor is attracted to the exterior walls. This vapor enters the wall through hairline wall cracks, outlets, switches and window trim. In new construction, the plastic vapor barrier under the drywall stops the wet air from getting to the insulation and condensating.
In old houses with plaster walls, there is no vapor barrier under the plaster so the wet air hits the insulation and condensates. This wets down the blown-in insulation making it a wet mass at the bottom of the wall cavity creating an inviting place for termites and dry rot. Then the moisture enters the exterior sheathing and wood siding causing permanent exterior paint failure.
Ignoring the fact that "condensating" isn't a word in English, he is conflating air-leakage with vapor diffusion, which are not the same thing. Air leakage can move orders of magnitude more moisture than vapor diffusion, and air-sealing/air-retardency is key to getting good performance, which is why dense-packing would be preferable to 2.5lb density "2-hole method". With dense-packed cellulose in the cavity it's sufficiently air retardent that vapor diffusion becomes the primary moisture transfer method, and it's much slower than air.
Installing plastic vapor barriers in new construction causes as many moisture problems as it solves, ESPECIALLY when the vapor barrier is not detailed as an air barrier (which it usually is, in Canada, and almost never is in the US), which allows convection to accumulate the moisture, but blocks drying via vapor diffusion.
The word he's looking for is "condensing", but even that isn't what's going on- it's adsorbed moisture into the wood that makes it susceptible to mold. Wood and paper take on moisture as adsorb, not condensate, and you won't see liquid water until it is saturated (well over 30% moisture content). Adsorb is a different physical state than liquid or vapor- it's a molecule-thickness layering on the microscopic structures of another material, and does not behave as a liquid. The only way the insulation becomes wet is if there is COPIOUS air leakage from the interior, but the more likely proximate cause (almost always), is bulk water leakage, usually at unflashed windows. If you had replacement windows installed they SHOULD have installed proper flashing, which needs to be verified, but that's an orthogonal issue. (If you have deep roof overhangs bulk water intrusions would be rare even without flashing.)
He goes on:
The other big issue is "pillowing". Today we have dense pack cellulose insulation as well a foam. The installers cannot control the pressure of these products being jammed into your plastered wall cavity. They should only be used with open walls which means losing all your original plaster. Foam expands and the pressure used to install dense pack cellulose properly cannot be controlled within a closed wall.
Utter BS, but with a caveat. Any competent cellulose installer inspects the integrity of the walls ahead of time. Installers absolutely can and DO control the pressure of the equipment. There are some walls where the lath nails are too far gone or the plaster too thin/weak to dense-pack to 3.5lbs density, but even a paper bag can handle 2.8lbs density without failing. A competent cellulose installer warns you if that's going to be a problem, and adjusts accordingly. Competence & experience is key- so vet the installer carefully.
It's true that the pressures can't be controlled with slow rise foam pours, and that IS a blow-out risk, but it's still do-able (if expensive.) The better installers will do an initial shot not intended to fully fill the cavity, use infra-red cameras to track the expansion, then top it off with a smaller shot for the finish, mitigating the risk of catastrophic blow out or pillowing.
He is correct that insulating a house with painted clapboards usually results in paint failure. With a cellulose insulated wall that would be due to the lower siding temp (= higher moisture content of the clapboards). Back in teh 1930s/40s/ 50s when low density fiberglass and rock wool became standard products paint manufacturers and insulation manufacturers had finger-pointing matches that never fully resolved, but that's when the whole notion that vapor diffusion as the primary culprit took hold. But since the 1980s when polyethylene sheeting vapor barriers became the rage it didn't fix things, it made things worse, with "sick building synrome" etc, but it didn't improve paint longevity much. It's been studied to death by building scientists at this point- it's the inability of the siding to dry quickly enough, not moisture drives from the interior that causes the paint failure on siding. On replacement siding primering the back side of the clapboards limit the amount of moisture that wicks into the siding from direct wetting, but isn't a perfect cure. There are more effective means in new construction:
Best-practices on new construction is to build a "rainscreen", which is to build in a vented air gap between the siding and the next layer, which allows both the siding and wall assembly to dry evenly. It also forms a capillary break, to keep moisture from wicking from the rain/dew wetted exterior to the interior layers- liquids don't wick through air.
But
you don't even need a rainscreen. Vinyl doesn't take on moisture, and is inherently vented- the air gap is already there, it's effectively it's own rainscreen. In a MA climate, simply building with a rainscreen (or vinyl siding) is sufficient protection for the sheathing to be able to use standard interior paint as the interior side vapor retarder, no sheet plastic necessary (provided you don't have a foil facer or some other vapor barrier between the siding and the sheathing to block outward drying...) A bit further north you'd have to take other measures, but I won't get into the details here.
His economic assumptions are also a bit provincial, and back-dated to 2009 when that article was posted:
The other factor that must be examined is payback. Lets say you spend $4,000 to have your old house walls insulated. In my experience you would probably save about $200 per year on heating and air conditioning costs
Yapp is located in Hannibal Missouri, which is US climate zone 4, not 5, so he has far fewer heating degree days, in a state where electricity costs are (or were at the time) well under 10 cents/kwh (instead of 18-22 cents, like MA), and natural gas prices run about 40- 50 cents/therm (instead of $1-1.50 as in MA). NOBODY heats with oil there, which is still significantly more expensive than heating with $1-1.50/therm gas even at this year's $2.20/gallon spot price. So, his pre-2009 experience in a low-cost energy state has no bearing on your local energy markets.
If you want to chase down the science on this stuff, Building Science Corporation has a searchable vast
array of well written articles available on line, and unlike Yapp, they do real science- they actually test and measure things, both in test-assemblies and in-situ in real occupied buildings. Another decent source is Martin Holladay's
green building blog (some of which is behind a pay wall, but a great deal of which is gratis).
In MA you can usually get the walls insulated for under $4000 after subsidy, and if you're heating with oil you'll be saving more like $600-800 /year (more, if oil heads back north of $4/gallon again.)
As far as indirect tanks go, think local- the HTP SuperStor is from a company located in New Bedford. If the thing fails you can drive on down and launch it through the window at the front office!
(Or maybe get better local support than you might get from another vendor.)