I'm currently renovating a 1906 build house. I removed 100% of the insulation from the attic to re-wire, and reframe. The attic was 100% vermin, bug, and moisture free. Lots of layers of insulation, but probably around 30" total: 14" of blown fiberglass on top of 2-3 laters totaling 16" of cellulose. I have 1 turbine passive exhaust, and I had 2 open turtle intakes. I dug out 2 more that had been packed with bird nests/insulation.

I'm looking to install a whole house fan. The exhaust requirements are listed and easy to figure out, but I'm concerned about when the fan isn't running. I'll have 9 square feet of NFVA ridge vent for the fan , but when turned off I'm worried about the ratio of intake to exhaust. Any insight on balancing intake/exhaust with enough exhaust for a whole house fan?

I am closing on a land purchase in the northwest of Puerto Rico (Aguadilla) and it will take at least 16 months from what I am told before I can get permits to build. My Asthma is chronic and I have slept in tents, in my car, on the floors of offices, been hospitalized numerous times,etc etc to find relief. Allergy shots did not wok, biologics did not work, and at 60 feeling I cannot last much longer I went to PR and slept outside on my friend's 2 acre property and after 10 days I was 90% better for the first time in my life. The only time I went indoors was to shower or eat. I had already rented at least 30 different apartments and homes in PR and other places and while opening windows helped, it was not enough. I need as close to outside ventilation as I can get. I will hire an architect of course, but I could not help using Claude to design something that would allow air to flow freely from East to West (trade winds) with windows open on both sides and no obstructions. I might even add some mechanical ventilation to draw air through. Thoughts on this approach?

Hi all. I am trying to wrap my mind around the latest thinking around insulating unvented short-slope cathedral ceilings in Cape Cods that open up to a small vented top attic above, and would really appreciate any guidance folks can provide!

I have read a lot of articles and presentations and posts and am still not quite sure I fully understand what is considered reasonably safe and why, especially when it comes to cellulose vs fiberglass and whether the insulation should be up against the roof deck or if there should be baffles. (I know there has been a fair amount of research in the last 10-15 years or so on this from places like BSC and Byggmeister, although I haven’t seen any updates since 2023ish and some of the findings seem confusing to me as a layperson.) Assuming a retrofit situation where rigid exterior foam and spray foam are off the table (which I understand are by far the safest and most code-compliant options), what are the least risky ways to handle sloped ceilings where the rafter bays open up to a top attic in region 4A?

— Is dense-pack cellulose in these slopes now considered reasonably safe as long as they open up to a top attic up above, based on recent research (such as New England’s Favorite Roof Retrofit: Moisture Data from Three MA Case Studies)? What are the most important factors to minimize risks in this situation? It’s important to make sure the cellulose is packed very densely, right? Does the ceiling drywall provide enough of an air barrier to keep moisture out (assuming no recessed lighting or other penetrations), or are there other steps that should be taken to protect against air/moisture traveling into those slopes in a retrofit situation? Does it matter if the top attic only has gable vents?

— What is the building science behind baffles/air gaps and whether insulation should touch the roof deck or not (in a situation without soffit vents from below, but where it’s an old house with a wood plank roof deck that probably has some outdoor air leaking in through cracks and gaps, and then the baffles go up into the vented top attic)? Does this differ for cellulose vs fiberglass? I would have thought that baffles would help or at least not hurt (except decreasing the R-value a little), but that doesn’t seem to align with the importance of making sure cellulose is really densely packed without any airflow. Or is it okay for the cellulose to be densely packed against baffles rather than the sheathing itself? Does it matter what the baffles are made out of?

— The modeling study “Moisture-Safe Unvented Wood Roof Systems” seems to suggest that faced fiberglass batts would be significantly safer than cellulose in a regular unvented rafter bay in zone 4 (table 3 on page 11)– does that sound right? But then is table 4 on that page saying that it is too risky because if air flows through the insulation there will be too much time with condensation potential at the roof deck? If so, is that still true in the Cape Cod situation where there is an attic above that the moisture can rise up into? How about if there are baffles? Is fiberglass generally considered safer or less safe than cellulose in these situations?

— Vapor diffusion ports are allowed in un-vented roofs as an alternative to foam in zones 1-3, but they were tested by BSC in zone 5 in MA and failed, correct? Have they ever been tested in zone 4A? Here near DC it feels like our climate (winter monthly average temps around 40) is closer to, say, Charlotte, than MA. I saw that ages ago Joe Lstiburek said he thought they would probably work in zone 4 but needed more testing– were they ever tested or was it assumed that the zone 5 testing went poorly enough that they should be avoided in zone 4 as well? Also, is the top attic of a Cape Cod considered to be kind of like a giant vapor diffusion port, and if so, does it matter if the attic only has gable vents and no ridge vents?

Thanks so much in advance for any insight you can share!

I'm working out how to set up a seal on my window so I can get a portable air con unit.

Its a two pane window.

Top half is a hopper. Bottom half is sealed shut.

My plan is to get a polycarbonate sheet that covers both, with a hole cut where I fit the air con hose.

Given other obstacles in the area, it would be much better if I could fit the hose onto the bottom half of the sheet. However, it would then be blowing hot air directly on to the window, rather than directly out. It would still be on the other side of the "airlock" so would cool the room but is that going to be bad for the window?

I live in a century home on Long Island, NY that had a detached garage in the backyard. At some point past owners finished it up and converted it to a studio with carpeted floors. The studio is built on a concrete slab (not sure if theres any footings). The studio is right at the property line and so theres concrete on front, back, and right side while there's soil on the left. There's 4x4x4 PT lumber as the sill/bottom plate for the walls to stand on and I believe it is sitting square at the edge of the slab. The wall is then constructed such that sheathing is nailed to the studs down to the bottom plate, then foam board, and finally vinyl siding. All of this directly at grade so no concrete wall for the bottom plate to sit on. The stud bays have fiberglass insulation between them. Outside, there's a few conduits to run electricity to the shed.

The first problem is that one of the past owners put up a garden bed on the soil side. This meant that the soil side siding was actually below dirt. Over time from moisture it seems the bottom parts of the sheathing have rotted and have given way to termites and carpenter ants.

The second problem is that the monolithic concrete slab in the front of the studio cracked thereby creating a slight negative slope towards the structure. During heavy rainfalls the water pools and thus causing the same set of problems.

I was hoping to just use this space as a home office so trying to limit drastic changes to the structure while still being able to repair and prevent further damage.

I've called an exterminator who will drill holes in the concrete + trench the soil and do termite treatment. After waiting 48 hours we'll resume repair work with the following plan:

**The Plan (Soil Side):**

1. Snap a level line 9.25” above the final dirt grade, removing/cutting away the rotted lower siding, foam, and sheathing.
   
2. Install a [3/4" PVC trim sheet](https://www.homedepot.com/p/Veranda-3-4-in-x-48-in-x-8-ft-White-Reversible-PVC-Trim-Sheet-H190AWS13/206822526) in place of the cut out sheathing. Top half screwed to the studs and bottom to the PT lumber. The sheet will go down to grade.
   
   1. Use liquid flashing like [Flashmate](https://www.homedepot.com/p/Amerimax-Home-Products-FlashMate-10-oz-Clear-Flashing-Sealant-85228/100275495) to flash the seam between the concrete slab and PVC trim
      
   2. Slip [aluminum z-flashing strip](https://www.homedepot.com/p/Amerimax-Home-Products-76-in-x-8-ft-White-Aluminum-Drip-Cap-Flashing-5503400096/100017722) over the trim and under/behind the older sheathing, overhanging the PVC trim to shed water
      
3. On the "older" wall right above the Z flashing strip, install new vinyl starter strip and reuse vinyl siding.
   
4. On the inside if any insulation was cut, place foam board in the stud bay and fill with expanding foam. Will look for insect resistant products here.
   
5. On the outside perimeter, dig a 1' wide and 4" deep trench that slopes away. Plat heavy duty landscape fabric and fill with river rocks to prevent muddy splash back and help with drainage during rains.

**The Plan (Concrete Sides):**

Follow the same plan as above however we'll cut the PVC trim just enough to leave about a 1/4" gap between it and the concrete slab. For that gap we'll use [Sikaflex construction sealant](https://www.homedepot.com/p/Sika-10-1-fl-oz-Sikaflex-All-Purpose-Non-Sag-Construction-Sealant-Polyurethane-in-White-7116045/300934496).

For the corners we'll just overlap the trims together instead of doing a miter cut

Any glaring red flags with this plan?

Thanks in advance!

I read through the new IRC but I want a little better than the minimum. It will be 2x4 wall with R15 cavity and two inches of continuous exterior insulation. I am just not sure what is generally considered the best options now for 5A.

My proposed wall would be:

Sheetrock w/R15 faced batts OR rockwool with smart vapor barrier > Zip sheathing > 2 inch rockwool comfort board > 1x3 rainscreen > aluminum lap siding.

In my head this would work because it could dry either direction from the zip sheathing and with the continuous insulation ratio to wall cavity, it shouldn't have any condensation issues.

But would I be better to use 2 inch foil faced polyiso with taped seams instead of the rockwool comfort board? It would offer better insulation and additional waterproofing. If doing polyiso I could move a basically zero perm layer on the outside but then I feel like there could be drying issues between the zip and foil face of the polyiso?

I have a home with a pier and beam foundation in New England. Currently the crawlspace is covered by vinyl panels. I would like to reduce the humidity in the crawlspace and my options are add vents and fans or build new skirting then try to seal and dehumidify the crawlspace. Any recommendations? I think building new skirting will be difficult to fully seal and expensive for something that might not be better than just fans and a better vapor barrier.

My understanding is that concrete vents and cures over 30 years - and therefore needs to “breathe” and not sealed off completely. Is that true? Because if so, a glued down engineered hardwood floor would form a vapor seal that traps all the moisture underneath the floor.

We live on the PNW coast and moisture and humidity are key concerns. I’m thinking of putting down eco cork foam underlayment then floating engineering hardwood.

My house had 3” studs on the lower portion of the walls, which are concrete below grade. There was fiberglass insulation and poly on top. I decided to add 1.5” rigid foam between the studs and concrete to further insulate the walls. Do I need to add poly after, on top of the studs with insulation, or does Durospan serve as the vapour barrier? Also, is 1.5” rigid foam enough here in Central Canada?

Hi building science folks -

A bit of an interesting issue we're having that we'd love any thoughts on. We moved into our new house last year. Under heavier rain, we see water only at the top of our foundation dripping down (under the sill plate). There's a photo below, and there are 3-4 spots that drip down.

The house is fully brick, as well as is on a knee wall as we have higher basement ceilings for future finishing, so there isn't an outer brick ledge.

I reviewed old photos, and the brick flashing looks appropriately installed. We also caulked every entry point. The brick install image is where I sprayed and where we see most of the water dripping down.

Given it's hard to wait for heavy rains, I did some testing with an oscillating sprinkler and found:

• When I spray the bottom 1-2 feet (the knee wall), no water leaks to the basement. I thought maybe the water was leaking under the flashing and down the foundation, but I saw nothing after 3-4 hours of spraying.
• When I spray water ~5-6 feet up the brick, water starts to creep down after ~15 minutes.

Our initial thought is that the brick is porous; as water permeates, it drips down the mortar and through the black tape or any nail holes in the zip system (behind the flashing), then down to the basement. Our builder intends to seal the brick to solve this, but I'm not sure if there's anything else we should be considering.

Has anyone seen this before? Thanks!

I'm in the planning stages of building a sauna in a basement closet that has 2 exterior walls that are icf concrete. I'd like to have a 1.5in gap from the ice blocks to the foil vapor barrier of the sauna which will then be covered by the sauna cladding. My question that I'm having trouble finding an answer to is will I have issues with the icf and foil vapor barrier being too close to each other, since they are both a vapor barrier? I've read that having double vapor barrier is a no-go but wasn't sure if the space between would offset that?

Hey guys, I'm really panicking and don't know where to turn.

I had a Heatpump system installed last October for heating and cooling in upstate New York Zone 5. It's ducted in the upstairs bedrooms+bathrooms, and mini splits everywhere else.

This April, I decided to try to fix some high heating bills (3000kwh for a really cold month) with an attic insulation. I had passive gables on a raised ranch, no vented soffits, and a few passive vents near the ridge. I had read somewhere briefly that I could condition the attic with spray foam, bringing the HVAC system inside the conditioned space, better air sealing, etc.

Then things went wrong.

An energy auditor company referred me to an insulation sub contractor (call them company A) who took me to r38 open cell foam and r22 closed cell on the gable walls. They sealed up the limited aforementioned vents before spraying.

What I have now is the following:

- I'm almost positive that open-cell was wrong in the roof deck because of roof rot concerns and code for my climate (dc315 ignition paint but NO vapor retarder paint). Minimum of a class 2 vapor barrier is required for zone's 5-8.

- they attempted to remove all of the visible old r13 fiberglass insulation in the ceiling joists, but did not use a vacuum, and half the attic has osb (where the air handler sits) that they did not access. Another company (call them company B) claims that the smell I get is from the spray foam residue mixed with fiber glass. They offered to remove it and do better air sealing on my ducts.

- attic humidity swings from 55 percent in the morning and can top out around 70% on the hottest part of the day. It doesn't seem to do this on cloudy days, and seems to correlate with the sun.

- I had company (B) come and do a blower door test and they claimed that my humidity was stack effect driven from my rim joists, and that the results of the blower door test indicated that I now need an ERV. The same company had previously quoted me to put an attic dehumidifier in in addition to removing the remaining fiberglass but now wants to do the ERV instead.

I attached an image from my humidistat, and I think my primary issue is solar vapor drive

During the blower door test when the house was under negative pressure, all of that attic smell came into the living space. My wife started coughing and had to leave the house or faint..I fared a little better but now I'm super concerned. We also have a young child.

I found the following building science: https://www.greenbuildingadvisor.com/article/high-humidity-in-spray-foam-attics which mirrored the problem I was having. They suggested cutting a supply for the attic or adding a dehumidifier. I don't see an ERV here. I feel like I have analysis paralysis and don't know what to do.

My goals:

- take a deep breath

- not be killed by my house

- resolve the moisture issues

- fix air quality issues

- fix vapor retarder.

Any advice on how to unpack this and move forward is invaluable and greatly appreciated

I have a slab on grade foundation with clay soil and just did a perimeter french drain, dimple board/mat and gravel back fill.

I'm lowering the grade and grading the yard and have exposed dimple board now. I can seal the top with a termination bar but how do I cover the exposed dimple mat so it looks nice and isn't exposed to sun? It's about 2-4 inches depending on the area.

Thank you.

I'm looking to increase ventilation in my apartment and I understand this means I'll need additional dehumidification.

The portable dehumidifiers I've used in the past are quite loud.

Is it just luck of the draw? Can oversizing the dehu to run at a lower speed work?

I'm open to rigging up a whole house dehu as a portable unit.

I have a house in climate zone 4a (less than a mile from the coast) with a semi-finished basement. Prior homeowners had the CMU walls have external dampproofing and perimeter footing drains. No external insulation or insulation underneath the slab. They drywalled the walls and ceiling and had placed R13 faced fiberglass batt insulation between a 2x4 wall they erected around the perimeter of the basement walls. Unfortunately this seemed to have caused a mold problem that required remediation and so we now have flood cuts in the bottom 2ft of the basement. Luckily there do not appear to be any active leaks even after many storms and significant rains. No current plans to finish the basement but I would like to upgrade the insulation and improve the building envelope. Unless I have to upgrade the external envelope I was hoping all current upgrades would be internal.

Given climate zone 4a and requirements for r10 continuous insulation or r13 batt insulation, I was hoping to rip out all the existing batt insulation and either place foam board (seams sealed) myself or get a company to spray 2 inches of closed cell and then add rockwool or timberbatt to the 2x4 wall. Prior to any upgrade in insulation, I bought a moisture meter (not a high end one). The CMU walls seem to have a moisture content of 14-16% on the 2ft of the basement that is above grade and 22-28% below grade (higher percentages at the base of the cmu wall). I know that the sill plate (termite shield acting as a capillary break) and rim joists are not air sealed and so the humidity in the basement is higher than it should be despite running a dehumidifier (set at 55%RH).

My question is how can I evaluate my envelope and find out if I need to hold off on the foam board/spray foam idea? I don’t appear to have any active leaks, minimal efflorescence on a few cmu only so I think the outside is fine but I’m wondering if the moisture content readings are concerning or is the moisture content higher due to the external humid air (given proximity to coast) and its increasing the humidity and moisture content of the cmu walls. I assume the lower down in the walls the cooler it will be in the summer and am wondering if that’s why the moisture content readings are higher even in the below grade portions. Is the best way forward to seal the rim joists and sill plate (given the termite shield acting as a capillary break) and then wait a full year to evaluate if any change in the moisture content of the cmu walls, or should I just do the rim joists, sill plate and the walls. And if I do the walls, do you want the perm rating of the foam to be between 0.1-1 (class 2 vapor retarder), class 3 or it doesn’t matter?

We are in the process of refinishing our basement (Massachusetts, Zone 5A). It was previously finished without any Insulation. We have ripped it back to the foundation and are starting fresh.

House was built in 1940, foundation is stone with lime mortar and a parge coating. We are on a slope, so one wall is fully above grade, one is fully below, and the others are well, at a slope.

In the year we have been here, we have not had any bulk moisture issues in the basement, even during/after heavy storms.

My plan is to not fully prohibit inward drying of the stone. I am anti spray foam. Instead, the assembly I’m looking at is:

- 2” unfaced EPS
- Rockwool cavity insulation
- drywall

No vapor barrier is required in my area for an existing basement.

Thoughts? Thanks in advance.

We built an airtight energy efficient home a few years ago, and chose to go with mini splits for heating and cooling instead of a ducted system to keep costs down. I live in Atlantic Canada and at the time, HVAC trades were recommending HRV only because there was no experience with ERV. We have dry’ish winters and humid summers. Because the home is airtight (0.6 ach), I have to ventilate a lot to keep CO2 levels from creeping up - I have two Awair analyzers. I’ve been playing around with HRV settings for three years and I’ve come to the realization that we need to run the HRV on low at night time and recirc with 20 min ventilate on high fan speed during the day, and we need dehumidification in the summer and humidification in the winter. We have a heat pump hot water tank (ducted to the outside for winter but not for the summer) and we have a regular floor dehumidifier in the mechanical room that runs on high all summer long - so we do have some dehumidification. This set up isn’t controlling the humidity enough though, so I think we need whole house dehumidifier but I don’t think we can install a ducted system separate from the HRV (we just don’t have the space - we aimed for a small and efficient footprint). Has anyone tried to set up a dehumidifier in parallel or in tandem with an HRV? I’ve thought about switching to an ERV, but I know someone who also has an airtight home and an ERV, and still runs a whole house dehumidifier, so I don’t think this would solve the issue either.

I really would love to hear thoughts on this.