The first thing I noticed on the outside were these little round vents in the siding about 2’ off the ground and about 6’ above those. I know when they blow in insulation they drill holes, but they usually plug them with a solid plug, not a vent. Sometimes I will see these vents used for soffit venting.
They were only on 3 exterior walls (the house had more then 4). Any ideas on why these vents would be here? The 2nd floor is finished bedroom space with about 6’1" of clearance with “cathedral” ceilings but does have gable venting.
If these are poor insulation plugs on only 3 sides of the house, it’s possible that the owners at the time of insulating, only wanted or had enough money to do these walls. They would usually do the west/northwest around to the east/northeast walls where the cold winter winds blew from and left south facing walls undone.
If not poorly plugged insulation holes:
The house being 250 years old would have had or still has a damp, dirt floor in the basement/crawlspace that moisture would evaporate from constantly. Moist air could move upwards from stack effect/buoyancy into the cavities from the basement/crawlspace or moist air from in the house into the walls through cracks, etc. With many layers of lead based oil paint applied over the 250 years, these walls would become virtually airtight at their outer surface. The moisture may condense on the wood and move outward later causing blistering/bubbling/peeling of the paint.
It used to be recommended to install “toothpick” spacers under the clapboard to break the paint “seal” and allow “breathing” of the moisture outwards. These folks may have had these vents installed in an attempt to stop the paint “failure” as an alternative. This may work …or not!! CMHC found that in some cases, the moisture problem got worse as the vents allowed more moist air movement from the house into the walls.
Were the vents on the southern or south east/west walls of the house?
In the 1970’s, the Heritage Properties group in Portland, Maine and others from the state found that in some heritage properties, some rot was going on in south facing warmer walls!! Why not the colder north walls where condensation should be occurring? They had neglected the air leakage and airflows through the houses during the very cold winters. Cold dry air entered the house on the north sides as this is where the prevailing winds are from in winter. As this air moved from the house, it picked up moisture from human activities as well as from damp basements, then “dumping” at least some it in the southerly walls leading to slow rot over the years, not extensive rot but a bit.
That would help disperse moisture from the interior but that system is a commercial rendering of what we have been doing up here for 10-30 years (depending where you live). Its known as the rainscreen system, installed to allow rain that got by the primary line of defence, the siding, to drain freely and then dry any remaining adhering moisture.
It was recommended for walls in the Atlantic Provinces in a Special Advisory document by CMHC in 1985 (Construction Principles to Inhibit Moisture Accumlation in Walls of New Wood-frame Housing in Atlantic Canada). The concept with guidelines was adopted as a building regulation in 2004. (Notice the near 20 year lag time between a non-regulating body, but very respected group/agency recommending it and the actual adoption into the codes!!!)
During October last year, I was hired by the second longest practicing architect here to save him from having to strip about $20,000 of #1 western red cedar siding from a seniors care home. He had done the design for the whole facility as it grew from 1973 to present. last year, he did not read the 2004 amendments to the code when received and designed a good size addition with clapboard nailed directly to the sheathing with Typar, no rainscreen space.
I wrote a letter stressing (1) the non-failure of the original siding nailed directly to sheathing with tarpaper (system has a history of satisfactory use), (2) that the Typar permeabity was of the same magnitude as the old tarpaper, (3) old and new wall systems are insulated, (4) the building has 2’ eave overhangs to keep a lot of rain off the siding, (5) the addition walls were not exposed to the prevailing wind driven rains …but…it was decided by vote of the code appeals committee to have it stripped and new siding with rainscreen be installed!!
A friend of mine is the building codes co-ordinator for the province and heads the appeals committee but only votes to break ties. Said the debate was one of the longest he ever sat in on but in the end…it was better to err on the side of safety by a 4 to 3 vote!! But they couldn’t prove it would fail!!! The original buildings over 33 years hadn’t failed.