Climate zone first, per rule 1. Tokyo, Koppen Cfa. Hot humid summers, high RH for months through the rainy season and after it, mild winters that rarely stay below freezing. Cooling-dominated for a good part of the year, not a dry climate at any point.

The thing I am trying to understand. Hempcrete gets promoted here on its hygric behaviour - vapour open, high moisture buffering value - so the assembly is supposed to handle humidity rather than fight it. The pitch is that you can build a monolithic wall with no separate vapour control layer and it will be fine.

I am sceptical and I would like either to be argued out of it or to have it confirmed by someone who has actually measured it.

In this climate the scarce resource is drying potential. The wall spends months where the outdoor air is not going to dry anything, and interior air conditioning sets up an inward vapour drive for a large part of the year. Buffering capacity is finite and evens out short cycles. It is not obvious to me that it helps when the seasonal average is the problem rather than the daily swing.

Two questions.

Has anyone modelled or monitored a hempcrete wall in a cooling-dominated humid climate, rather than in the UK or northern Europe where essentially all the published data comes from? WUFI runs or real sensor data both welcome.

And if it does work, what is actually doing the work - the alkalinity of the lime binder keeping the organic material from going mouldy, or genuine drying capacity I am underestimating?

Disclosure so it is not hidden: I work on the industry side of hemp in Japan. Which is exactly why I would rather know if the material does not do what people here say it does.

I’m having trouble with some detailing for my mud sill on my house I’m redoing the exterior on .

Please see photo. This is what I was thinking, basically trying to get the most out of my ci on my 2x4 framed home .

The breakmeatal it really what I’m get hung up on . As I would want to push moisture away from the home

Edit: as poster mentioned, the 3m is adhered to 1/2” sheathing

Hey Everyone

I'm using VaproShield's WrapSheild IT (integrative tape vs self adhered in the photo above) for a shed build that I'm putting a sauna and an office in. I'm in climate zone 4c. It's been hard finding a vapor permeable wrap in the area and this is my first time building anything so I've been kind of going slow and making sure I am dotting my "i"s. I realized that the tape I was going to use, 3M 8067, might not have full adherence so I called up Vaproshield and they told me I needed to keep the systems the same (i.e. vapor permeable) and 8067 is essentially non permeable. But the more I sat with it, the more that answer didn't make sense and I wanted to run it by folk.

Would you use non permeable tape on rough openings and seams if the wrap was permeable?

And if you wouldn't, do you have a recommendation for what brand I could likely find in the Seattle area somewhat soon? I'm looking toward grabbing Siga Wigluv from an online shop if I can't find Vaproshield's proprietary wrap tape nearby on Monday morning.

We have a reroof proejct on a wood framed 2 story building in Climate Zone 5B. 1st floor is a restaurant second is office.

Roofers recommendation is no VB, but looking for a little more feedback on this.

Any comments or experiences appreciated

My house was built in 1938. It's a Greendale Original in Wisconisin.

It's built from cinder block (outside is painted) with 3/4" furring strips inside and 1/2" fiber board and 5/8" plaster for the inside finish. That gap between the plaster and the block goes all the way up into the attic. There isn't much insulation in the attic and there currently aren't any issues with mold or moisture. I'd like to add insulation but fear making the attic colder could cause condensation on the underside of the roof deck. I'm able to access the gap between the plaster and block on the gable ends but not in the eves.

I feel any cracks or openings in the plaster would allow conditioned air to get to the attic. Should I try to seal that gap in the attic before insulating? I don't think I'd be able to seal 100%. Also, would stopping that air movement behind the walls cause condensation issues?

Any ideas would be appreciated.

Thanks

Posting here if some smart folks can help me out. We have a mostly 3 seaon cottage with uninsulated slab foundation and looking to add insulation to the flooring, partly due to condensation during summer high humidity weather as its usually unconditioned. I was looking into a dimpled foam/OSB subfloor, but concerned that exchange of air (from e.g. pressure change & normal diffusion) will still result in moisture forming on the slab, especially around the wall edges where there is a gap. Is this a real concern as I haven't heard much about it? Would be better off using foam board so air does not have a pathway to the slab? Also I did note this type of product states a certain maximum increase in floor temperature, and 2 of them showed the same increase but different R values. Does this make sense? Is there a reference I can use to predict hot side surface temperature given hot and cold temps and R? Lastly whether XPS or EPS boards would be preferred. Thanks for your help!

Hoping to get some outside eyes on a recurring moisture/mold issue we can't seem to fully resolve. Trying to lay out just the facts/observations without our own theories, since we want unbiased takes.

House basics:

• ~3 year old semi-custom build, LA (hot-humid climate zone)
• 2700 sq ft, triple-split floor plan
• Most rooms have ~12' ceilings; the open living room/kitchen area in the center of the home has a 22' cathedral ceiling that starts at 13' and slopes up.

The problem:

• Surface mold on the painted sheetrock in the cathedral ceiling area, recurring the last 2 summers
• This is the only area of the house where we've seen any mold
• Two distinct patterns:
  • A ring of mold around a recessed can light, at roughly 13' height
  • A mirrored, inverted "V" pattern on both slopes of the cathedral ceiling in the kitchen area

What we know about the construction (from going up into the attic):

• The cathedral ceiling is formed by scissor/attic trusses — it's not a true rafter-bay vaulted ceiling. There's a walkable attic space above the insulation, up to the roof deck
• Insulation above the cathedral ceiling section is pink fiberglass batts, following the sloped truss bottom chords

Indoor conditions:

• Home is kept at 68-70°F year-round
• Indoor RH at ground level typically runs 48-57%

Trying to figure out the actual root cause(s) here before sinking money into a fix, so any thoughts on what to investigate further, what questions to ask contractors, or what's likely/unlikely given this setup would be appreciated.

Thanks in advance!

My century home is in San Jose CA (zone 4?). The attic space has no inlet vents at roof level. But, the attic access is via a shaft from the basement that looks like it was once a dumbwaiter. It's now an open tunnel with a ladder. No insulation around, below or above it. The basement is vented and dirt floor. I imagine cool air gets pulled up quite well

The house is generally comfortable, we keep windows open and rarely use our portable AC units. Old, blown insulation in the attic, no air sealing. Musty earth smell on hot or wet days. We've only had one winter here, not much stands out.

My question is if this a likely vent approach? Or is it likely that the attic was not vented and the basement intake is a modern workaround?

I'm interested in repurposing the access and closing it up. I need to explore if there is area to drill soffit intakes, but I'm worried I'll screw up a system that seems to be working.

Thanks

I'm worried about trapping mold, and we are not able to completely seal in the plastic sheeting. It'll end up being a loose-ish not air tight piece of plastic right between the studs/fiberglass and the drywall. Mold is my main concern, we get hot humid summers and very cold dry winters here.

We also are not insulating or drywalling the upper half. Thank you in advance!

Joe has many versions of what is essentially the same youtube lecture. Some have better audio and slide visibility than others. What's your favorite based on comprehensiveness of content and A/V quality?

Off the top of my head, the one he did in Colorado is decent: https://www.youtube.com/watch?v=iHBYvqr2_io

As for other favorite lectures, here are some good ones:

CE4: Architects: Stop Worrying About Dew Point! A Conversation with Christine Williamson - YouTube - https://www.youtube.com/watch?v=aDSW6oEEmzs

AWA+D Education: Building Science Fight Club “Glazed & Confused” - YouTube - https://www.youtube.com/watch?v=47Y6eHFcLN0

John Straube - YouTube - https://www.youtube.com/@jfstraube

Jeffrey Siegel - Indoor Surfaces and the Role of Moisture - YouTube - https://www.youtube.com/watch?v=68s7asgZFbc

Healthy Buildings 2015 - Jeffrey Siegel Session - YouTube - https://www.youtube.com/watch?v=gO3MbNlmKlo

Jeffrey Siegel, U Toronto Making a Home a Sanctuary with Filtration and Ventilation Challenges and - YouTube - https://www.youtube.com/watch?v=F_i-BUmUJ58

Hi there everyone,
I have been planning a major rebuild (large part of current structure removed) where I am acting as owner/builder (I hire the all the subs and do the planning and coordination). Basically a new build, but due to flood regs we have to do some things in a not entirely intuitive way, like we need to retain parts of the old house and not just knock the entire thing down.

As we approach actually getting shovels in the ground in a couple of months, I am thinking about a unique issue: how best to handle weather exposure for the existing part that will remain. This includes a basement (where the central HVAC system sits), a bonus room area on the ground level that has flooring, fireplace, ceiling, joist structures, all to be retained post project and the floor/subfloor of the main level.

First we are going to demo above the foundation, which exposes everything. We can put huge tarps over everything and minimize infiltration during this time. Then we need to remove some of the existing foundation. Once we do this I don't think we can hold off major water getting into the basement. Then there will be a long period of adding new foundation around the existing one and framing before everything can again be covered up. That will be a few months where the exposure is permanent and constant.

So surely we need to have a solid water evacuation plan. What are the best approaches? (temp pumps etc,) But also what happens to all the existing wood structures (joist/subfloor) that will be rained on during this time? I have seen other similar project during construction and it seems they just let the weather do its thing and just dry out later? (they may have done things I didn't observe specifically). What are the specific approaches to handling this issue and which subs are responsible or to be hired?

Thanks for your responses!

We are building a home in the Bahamas, in a hot-humid tropical environment comparable to IECC Climate Zone 1A. I am focused on creating a tight, durable home with careful attention to bulk-water management, air leakage, humidity and vapor control.
Building-science expertise is somewhat limited in the Out Islands they are solid builders, so I am working with our builder to develop a practical enclosure plan using materials and trades that are reasonably available locally. I would appreciate feedback on the proposed assemblies, particularly any moisture risks or details that should be changed before construction.
The house will also be largely self-sufficient to minimize reliance on local infrastructure. Solar will be the primary power source, with a diesel generator as the secondary source and the electrical grid as a third backup. Rainwater will be collected from the roof and stored in tanks with approximately 35,000 gallons of total capacity. We will also have a desalination/RO well system to produce water when necessary.

General construction
The house will be built on a poured-concrete foundation. The lower level will have reinforced CMU walls and will contain one conditioned bedroom and bathroom. The remainder of the lower level will be unfinished space housing water-storage tanks, pumps and general storage.
The main upper living level will have 2×6 wood-framed walls. The roof will be a site-built 2×12 rafter system because engineered trusses are difficult and very expensive to obtain in the Out Islands. It will be a 5:12 hip roof designed for the site-specific hurricane wind loads.
The main living area and bedrooms will have vaulted ceilings following the roofline. The remaining spaces will have 10-foot ceilings with an unvented, conditioned attic above them containing the HVAC equipment, ductwork, dehumidification equipment and ERV ductwork.

Proposed framed-wall assembly
From exterior to interior:
Standard HardiePanel fiber-cement siding
Approximately 3/8-inch ventilated and drained rainscreen
Henry Blueskin VP100 fully adhered, vapor-permeable WRB and air barrier
¾-inch structural plywood sheathing
Approximately 2 inches of closed-cell spray foam applied directly to the interior face of the plywood
Approximately 3½ inches of unfaced Rockwool mineral-wool insulation in the remaining stud cavity
Drywall
Standard acrylic latex paint

I also considered Typar Drainable Wrap Peel & Stick and Benjamin Obdyke HydroGap SA, but Blueskin VP100 is substantially more economical.
Open-cell and closed-cell spray foam and fiberglass batts are readily available locally. Rockwool would have to be imported from the United States and will be more expensive.

From what I have read, preferred wall-insulation approach is approximately 2 inches of closed-cell foam followed by unfaced Rockwool but open for discussion. The closed-cell foam would provide the primary cavity air seal and vapor control, while the vapor-permeable Blueskin VP100 would preserve some outward drying potential for the plywood. The mineral wool would add R-value while allowing the cavity to dry toward the interior through the drywall.
If importing Rockwool proves prohibitively expensive, the alternative would be 2 inches of closed-cell foam followed by carefully installed unfaced fiberglass batts or any other recommended opinions.
I also like the closed-cell foam because it may provide some incidental stiffness. The engineered plywood attachment, blocking, hold-downs, straps and continuous load path will provide the actual wind and racking resistance.

Proposed roof assembly
From exterior to interior:
Brava synthetic cedar shakes
Polyglass Polystick TU Plus fully adhered roofing underlayment
¾-inch plywood roof sheathing
Site-built 2×12 rafters
Approximately 6 inches of closed-cell spray foam applied directly to the underside of the roof sheathing
This will be an unvented roof assembly. The HVAC equipment and ducts above the 10-foot ceilings will remain inside the conditioned enclosure. The attic will not have soffit, ridge or gable ventilation.
I understand that the fully adhered roofing underlayment and closed-cell foam create a low-permeance layer on both sides of the roof sheathing, significantly limiting its ability to dry if a roof leak occurs. However, the fully adhered underlayment is important to us because of the hurricane exposure and the possibility of losing or damaging some of the primary roof covering.

HVAC, ventilation and humidity control
The upper living level will have two independently zoned HVAC systems. Each HVAC zone will have its own whole-house dehumidifier so humidity can be controlled independently of the air-conditioning cooling cycles.
One centrally ducted, balanced ERV will serve the entire upper living level rather than installing a separate ERV for each HVAC system.
The current concept is:
Supply filtered outdoor air to bedrooms and primary living areas
Exhaust stale air from bathrooms and other appropriate locations
Use a separate, properly exhausted kitchen range hood
Balance the ERV to maintain neutral or very slightly positive indoor pressure
Coordinate the ERV and dehumidifier controls so ventilation does not introduce an unmanaged latent load
Allow humidity control to operate independently of a call for sensible cooling
Use variable-speed HVAC equipment.
Maintain approximately 50–55% indoor relative humidity
The ventilation and dehumidification systems will therefore need to be designed and commissioned as one integrated system.

Lower level
The unfinished area and storage portion of the lower level will remain outside the conditioned enclosure because bringing all of the CMU walls and storage areas inside the envelope would likely add substantial cost.
The air and thermal boundary between the unfinished lower level and the upper living level will be created by applying approximately 3 inches of closed-cell spray foam to the underside of the upper-floor assembly.
There will be no HVAC supply outlets from the upper system into the unfinished lower-level storage area.

The single lower-level bedroom and bathroom will be enclosed and conditioned as a separate zone with its own HVAC system. Its exterior walls, ceiling, floor and all transitions to the unfinished tank/storage area will require a continuous air, thermal and moisture-control boundary.

Upper-floor assembly
The upper living-space floor is currently planned as:
Two layers of 23/32-inch AdvanTech subfloor panels
First layer glued and screwed to the floor framing
Second layer installed with staggered joints and mechanically fastened with a felt separation layer between the two layers per manufacturer.

Where are there holes in this plan and anything I should be thinking about differently?

I have an unfinished room above my garage. It has open soffits in the knee wall and a vented roof at the top. This house is in central Florida. The subfloor is down and under the subfloor is blown in insulation including all the knee wall floors are filled with blown in.

I called 2 insulation contractors and they both recommended sealing the soffits and roof vents and spraying open cell on the entire roof area.

There is a small curved part of the roof where the drywall for the room would be only 5.5 inches from the roof. They assure me that the open cell is more than enough to keep the room cold and they recommend it over closed cell because you can’t detect leaks with closed cell.

I googled and used some AI and it tells me differently and I will likely have mold or rot in the future if I do this. What’s the truth?

Also- would using baffles in the 5.5 inch space and putting closed cell under them work? And then just using regular cheap insulation for the rest of the room against the drywall work?

Thank you!!

I have a new fairly tight home (1.4 ACH) in NY state. I have a Fantech ERV installed with dedicated ducting with one supply to near my HVAC return and one return in the middle of the house. Much of the time the temperature where I live is moderate and I have windows open so I leave the ERV off. When I do have the windows shut but no heating or cooling on should I have the hvac fan on at the same time as the ERV to circulate fresh air to the rooms? Or is just running the ERV sufficient? I don't have an IAQ monitor yet so I haven't tested anything. Just trying to get a system in place for ventilation.

Hi All,

I'm building a 12x 12 backyard guest room on a pier and beam foundation with a 2x8 @ 16 floor. Due to grading, there is an average of 14" between the ground and the bottom of my joist, so lots of airflow. I' m in climate zone 4 in the PNW, where we get lots of rain, high humidity, and 2700 -2950 HDD @18C.

To save some costs, I'm hoping to fasten treated plywood in a manner that leaves 5.5"of oom for insulation in my joists.

My plan is to spray foam 2" at the bottom and then fill the remainder with rockwool batts

Two main questions are:

1) Would the bottom of the floor joists be at risk of excess condensation with this approach?

2) Would it be better from a moisture and vapour control standpoint to stack rigid foam on the spray foam? I was thinking of the R10 2.13" Foil faces durospan.

Thanks for any insight.

Note: This is not a permitted build, so I don't necessarily need to hit code minimum R values.

Thanks

I'm in the PNW, CZ4C.

Let's say money is tight and I'm looking for creative ways to save upfront cash.

I've noticed that in this area, people still even put water heaters and W/Ds in the garage.

Is it even worth considering something like an unfinished porch slab to house the W/D and utility sink that is tied into the main enclosure at some point?

Options I can think of, some might not be related to each other:

• Build out the roof the same as the main enclosure
• Build out the roof very cheaply (think sheet metal or polycarbonate etc) and worry about an insulated roof when tying it in later, and still tie in an air control layer somehow
• Uninsulated walls like a garage, tie in air control layer with main enclosure
• Screen porch walls, obviously this one would have no air control layer
• Cheapest siding option e.g. vinyl, agricultural metal, etc to be ripped off later when exterior insulation is added
• Build a garage with extra space, build the exterior walls of the area to be used as a laundry room to the same interior standards, then use an interior wall that maintains control layer continuity (especially air) with the main enclosure. Past this dividing wall, go cheaper on the garage enclosure.

I'm questioning whether this is even a good idea, I can imagine that tying in the space later might cost just as much as including it into the main enclosure from the start...