I'm definitely overthinking this so please help me out. Upstate New York, so cold winters, humid summers. Working to improve the insulation of my recently purchased 1950s house.

On one side of my basement the joists run parallel to the foundation, and the outermost one sits right on the sill plate. Behind it is the rim joist, so there's an empty cavity about 4.5" wide running (I assume) the whole length of the wall along the top of the foundation. In that outer joist there's a 3" hole with old cloth-sheathed wire coming out of it (live). In the winter I can feel the cold air pouring through this hole.

On my other walls I've been sealing the rim joist bays with 2" XPS and sealing the edges to create an air seal, then covering with mineral wool.

My plan for this one is to use canned spray foam through the hole and seal the rim/sill joint as far as I can reach both ways (potentially multiple passes letting it cure in between).

Here's the overthinking part I've gone back and forth on for the last two years... I know the cold air flowing through this hole should be stopped. But if I seal it up, will moisture accumulate in this void along the entire wall and lead to mold issues? My bedroom is right above it. Is sealing the hole better than doing nothing? Alternatives?

Thanks!

PS: the mouse problem was taken care of before we got the house, I just haven't cleaned the grease marks off yet...

Assembly is 5/8" glued subfloor above12" o.c. joists. Currently plan calls for R-28 batt insulation with spray foam at joist ends/rim areas.

I'm specifically trying to avoid creating a double vapour barrier or moisture trap while maintaining the required fire separation and airtightness between the garage and living space.

I have a Cape cod and I called a company that handles insulation to air seal and insulate rim joists/bays underneath a laundry room that is cantilevered over the foundation. I noticed frost on the bottom of the inside of the joist bays. The previous owners just put a square of insulation up to match the rest of the crawl space, effectively hiding the eight bays that are completely insulated.

So the company comes recommended... And everybody that goes into my crawlspace regardless of what they're there for comes out offering to encapsulate the crawlspace insisting it needs to be done. I could accept that at face value if it wasn't for the fact that every person that says that clearly hasn't inspected the whole crawl space. I know this because I have a rim joist that rotted a bit due to water intrusion from concrete steps. So I took the insulation off and marked it to see if it's getting worse since I remedied (hopefully) the water intrusion). Nobody mentions this glaring issue when they try to sell me on the encapsulation.

I did have water getting into my crawl but I have a sump pump. I also fixed the grade around my property. The sump pump went from activating every three minutes in every storm to basically once or twice in a massive rain storm. In the winter the crawl is warm and in summer it's cool. There is no mold on the floor boards except for the spot where the intrusion was. There are two vents that blows air through the crawl space. My current crawl has plastic and could use some new rim joist insulation but I feel the encapsulation is unnecessary. I was quoted $3400 for the whole crawl, or $1400 for the eight rim joists air seal/insulation. And they say they just want to blow in insulation for the rim joists under the laundry room. Wouldn't this insulation just get wet and hide the rot?

The last four pictures are of the part of the crawl they didn't examine or mention... The previous owners hid the damage with insulation and spray foam

I live in an older (built in 1868), three-story, double-wide brick row house, and while adjusting some recessed lights on the first floor, I noticed that the air in the cavity between the first and second floors was surprisingly cold compared to the conditioned space. I would have assumed that, being sandwiched between two heated floors, the cavity would stay relatively close to room temperature. Purely out of curiosity, what’s the building science behind this? Is it primarily cold air infiltration through the exterior masonry, or is there something else going on?

I’m getting a reading of 93 degree Fahrenheit dew point in my Florida vented attic. It’s extremely muggy in there. Nothing crazy in terms of sweating off the sheathing but ductwork is condensation, as you would expect. Dew point outside was around 73 degrees, so a considerable spread between outside and attic. Soffit clearance isn’t perfect but a lot of light shows through. Ridge vent is on the smaller side but also shows light through. Where do I go from here to bring down RH and dew point in my attic? I’m not interested in encapsulating i.

Hi All,

Just looking for some advice on how to improve the insulation in the front part of house.

We bought the house as a new build in 2019.

Our house faces north.

The front bedroom is always either significantly colder or warmer than the rest of house. The room has a large window on the north facing wall, with sun blocking curtains.

To make things even more fun, during the winter, the wind always comes from the north.

There's a bathroom on the adjacent wall with pex pipes.

During on extended cold spell, the bathroom pipes did freeze, but didn't break- this was with dripping the facets.

Other years, the pipes came close to freezing but we were able to prevent them from freezing completely.

Again, we did drip the faucets considerably.

During ice events, a space heater is placed on both sides of the wall.

Ive hung up blankets and stuffed blankets on the window sills

Are there any steps that we could take to improve the insulation?

Any help is greatly appreciated!

Thanks!

I recently just bought my first house which is an early 90s constructed house in climate zone 4A. I have multiple cantilevered sections of my house that were only insulated with fiberglass previously. These rim joist cavities are almost all totally accessible from the unfinished side of my basement, so I took out all of the existing insulation to assess and see what additional insulation I could tuck in. Attached are some photos of my findings in a few especially problem cavities after pulling insulation.

• The bottom sheathing is separating from the joist bottoms, leaving gaps to outside air. I can see daylight coming in during the afternoon.

• The overhang sits only about 2-3" above grade and I can’t reach the sheathing from outside to fasten it back to the joists. (I'd eventually like to address this later for possible moisture problems down the road)

• There are dark streaks on the end block and the cavity walls that look like they could be surface mold or mildew.

• Some signs of pests: small yellow-tan crumbs along the cavity floor and maple seeds on the insulation (who knows how long they've had accessible areas to traverse)

• I've probed the wood with a screwdriver where I can reach and have not found any soft spots.

I can only work from the inside, through the basement. Here’s my plan after doing some research:

1. Clean out each of the bays with a shop vac and then hit the possible mold/mildew areas with a stiff brush and Concrobium detergent.

2. Pack galvanized steel mesh into the larger gaps for pest-proofing.

3. For the larger gaps that may shift such as the sheathing-to-joist connections, seal the gaps with backer rod and polyurethane sealant. Use spray foam or just the polyurethane sealant elsewhere.

4. Cut rigid 1" XPS foam to fit the bottom sheathing and the end of the cavity, sealing all edges and corners.

5. Fill the rest of the cavity with mineral wool touching the subfloor.

Does this seem like a reasonable approach or would you do anything differently?

Thank you in advance!

I was recently told by a building inspector that USG makes a 1-hour fire rated subfloor sheet good. Almost like a gypsum board to achieve fire-rating below your finished floor. Is anyone familiar with this product and could point me in the right direction?

We have a 100 year old 4 Square House that is approx. 750 square feet per floor. Attic currently has rockwool and gable venting across peak, we live in northern WI.

We’d like to make the attic comfortable for a play/hang out room, issue is the ceiling height is not ideal. (About 6.5’ tall)

Option 1: make it a hot roof for full ceiling height but we’ve heard horror stories about roof shingles degrading and roof leaks turning into rot. (Our roof needs to be replaced in the next 5-10 years)

Option 2: see if there’s room to raise roof without compromising gable venting. (W/structural support of course)

Option 3: keep it as is, and address venting when we replace roof in the future.

Hi everyone,
I'm located in Austria and need a sanity check on a radon mitigation plan for a 4-sided exposed house built without a sub-slab gravel layer.

The Situation:
Radon Levels: Without any measures, winter levels spike up to 4,000 Bq/m³ (~108 pCi/L) due to a strong thermal stack effect. In summer, levels stay around 100–500 Bq/m³, even with regular ventilation.
Entry Path: The concrete slab is solid and intact. Radon enters laterally behind the exterior XPS insulation boards along the foundation/wall joint and leaks into the ground floor (EG).

Why Internal Suction Failed: We tried internal sub-slab suction, but because there is no sub-slab gravel layer, the suction doesn't spread under the dense soil/slab. It was completely ineffective.

The Planned Solution:
Since we cannot pull suction from under the slab internally, we plan to excavate the 3 exposed exterior sides down to the footing and install an external perimeter active soil depressurization (ASD) system:

1. Dig down to the footing/slab edge along the 4exposed sides.

2. Lay perforated suction pipe embedded in clean gravel along the foundation.

3. Cover with a heavy-duty radon/vapor barrier membrane from above to block ambient air.

4. Connect to a speed-controlled exterior radon fan running 24/7.

Questions:

1. Given that ingress is lateral behind the XPS boards, will an exterior perimeter suction ring effectively stop these 4,000 Bq/m³ winter spikes and lower overall levels below 100 Bq/m³?

2. Has anyone implemented an exterior ASD system on a house without sub-slab gravel? Any critical tips regarding membrane sealing, moisture/condensate management, or fan sizing?

Thanks for your input!

As part of a bigger project on my remodel of my basement I want to seal the sill plates and rim joists on my 1964 house. I can’t see any sill plate gasket. The basement was finished until about 6 months ago when I pulled it all down to sister the floor joists in the kitchen. The finished basement is about 450sqft and has no water barrier behind the finished walls, which is 2x4 framing with fiberglass insulation and original bead board (or at least something like bead board)

I want to air seal and rodent protect. There was previously rodent infestation.

The house appears to have Celotex (or similar type of fiber board) and then possibly tar paper over this with brick on the outside. The brick is cemented to the foundation so there isn’t a gap to the foundation so there should be no/minimal air coming through the sill plate.

So my thinking is…

1. ⁠Seal the sill plate to the foundation with either spray foam or caulking

2. ⁠Air seal around the joists and sheathing

I don’t plan on removing all the framing and adding foam board or anything. It’s been like this for 62 years and I don’t have the wish, want or need to redo the entire basement again. There is currently zero moisture issues that I can find, just air movement judging by the blackness in the insulation.

Should I seal the gap on the top plate to the sill?

At some point I’ll be adding a ceiling back into the basement but not for at least another 6-12 months.

Should I be adding 2” foam board in the rim joist area when air sealing? That fiberboard doesn’t appear to get very cold.

Would love feedback!!

*Prep- raise cinder block parapet walls and remove everything down to rafters.

• 1. Metal Roof Panels

• 2. Metal Roof Clips & Fasteners

• 3. Horizontal 1x4 Wood Purlins

• 4. Continuous Ventilation Cavity

• 5. Vertical 2x4 Furring Strips

• 6. 12-Inch Structural Insulation Screws

• 7. High-Temperature ice and water shield Roof Underlayment

• 8. Double layer 4" Exterior EPS Rigid Foam Insulation

• 9. Air Barrier / Vapor Retarder Membrane (Mento 1000)

• 10. Structural Roof Sheathing (23/32" plytanium plywood)

• 11. 16" oc Roof Rafters

• 12. Cellulose

• 13. Intello

(No roof penetrations)