We have a 1951 Cape Cod in the DC area (environment zone 4A)– the north side-attic has no official venting (but is most likely quite leaky) while the south side appears to have soffit vents however along only about 1/3 of that side thanks to a one-room addition. The leading attic has gable vents, not 100% sure if the soffit vents southern side connect up through the sloped upstairs ceiling to the top attic or not. No obvious signs of moisture/mold in any of the attics thus far, however we’re not 100% sure what to try to find (and there have actually been some modifications over the last few years.)
I comprehend that to do things “right,” we should utilize either exterior stiff foam on top of the roofing system deck or spray foam under the roofing deck to make all 3 of these areas into unvented conditioned attics. Presuming those alternatives are off the table, I am attempting to find out how risky the scenario is and what is most likely to make the circumstance even worse rather than much better. A few questions:
1) Should we proceed and improve insulation and air sealing on the side-attic flooring and kneewalls and the top-attic floor (we can get rebates to make this fairly affordable)? Is there any opportunity this will make things worse moisture-wise? Probably there will be an advantage because less of the moisture from the indoor air will enter the attics (although I make sure some still will), but on the flip side, those spaces will likely now be cooler (presently they tend to run about 10-15 degrees different from the outdoor air)– might that increase the opportunities of dewpoint issues with the sheathing? And exists a chance that the air leaks through the ceiling are actually contributing to ventilation and obstructing them would trigger problems?
2) If need be, I believe including additional vents is probably a much better service for us than utilizing spray foam or outside rigid foam to go unvented, but it will be relatively complicated and pricey itself (we have a metal roof.) Would it be reasonable to make the air-sealing and insulation changes initially and after that keep an eye on the areas and wait to add better venting in future years if it appears to be required? If so, what should we be looking out for?
3) Anything else to be knowledgeable about that would help or hurt? Does having batts on the side-attic roofing system slopes (with baffles or another form of space) make it most likely for the sheathing to get damp or harder for it to get dry, or does it not make much difference? Is using blown-in loose-fill cellulose on the floorings most likely to be practical or harmful to the humidity/moisture/mold situation in the attics compared to utilizing blown-in fiberglass given that it soaks up moisture, or does it not matter? Would a smart vapor barrier make a distinction, and if so where should it go? How about using a dehumidifier? Anything else you ‘d suggest?
Thanks for any advice you can give! Let me understand if you have any concerns or want pictures of anything. More details about your home below– but do not hesitate to skip.
(Details about your home for the curious: Roofing system deck is wood planks. Roof is metal– dark grey metal shingles on the north side and the majority of the south side (with I think common black felt underlayment, put on in the early 90s), except for white standing-seam over the addition over ice + water guard with solar panels above it– the slope of the addition roof is likewise on the low side at 3:12. Blown in insulation (I think fiberglass) on the top attic and side attic floors, inadequately fitting fiberglass batts in the kneewalls and cathedral ceiling between side and leading attics, ancient mineral wool batts in the side attic slopes that is most likely initial to 1951. The house is quite leaking (blower door test around 4200 CFM50, and I believe the ACH50 is about 16?) The side attics do not get that hot (generally in the 65-85 range during summer)– I have actually had a gauge monitoring RH in the north side-attic for about 6 months and it’s generally around 45-55%; simply moved it to the south side-attic this week and it’s been around 55-60% but with some short spikes around 70%. Humidity inside the house is generally around 30% in winter season and 60% in summer season. Typical month-to-month outside temps in winter are around 40F, but undoubtedly a fair number of colder days and nights. House is on a piece. There are two heating and cooling ducts going to the new south-side addition (R-8 versatile insulated ducts) however we are thinking about switching to mini-splits for a/c so could perhaps get rid of those– no other ducts in the attic space. Bath and cooking area vents go through the first flooring ceiling and out through the soffits on the north side. No super-obvious indications of past mold issues, however we have actually made some modifications in recent years– including the addition a couple years back, in addition to including some thin wafer-style recessed lighting on the very first flooring– so it’s possible that issues are now brewing that we’re unaware of …)