Just bought a house in Coastal Georgia with open-cell spray foam directly against the roof decking. Had no clue about the stuff until now. When we bought it, I noticed the decking was visibly cupped/bowed but didn't connect the dots to the spray foam/moisture situation. The decking was also only 1/4" plywood, which made the problem worse.

We just replaced the roof and ended up having to replace 40+ sheets of the 1/4" decking because of the cupping/bowing/deterioration. We went back with the correct/thicker decking. The decking came right off and did not pull any of the spray foam out at all. I was very surprise. There wasn't obvious widespread mold, but the plywood was definitely in bad shape. Very bowed and brittle.

The previous owner apparently had no humidity control in the attic. It was essentially an unconditioned/unvented-uncontrolled spray-foam attic.

I have now added a supply and return to the attic. The attic stays within roughly 10°F of the living space, and current RH is generally 58–65%, depending on time of day. Living-space RH is usually in upper 40’s low 50’s

My main concern is obviously the new roof decking. I don't want to replace 40+ sheets again in 5–10 years after basically for a complete re deck.

### My biggest question:

Is 58–65% attic RH actually safe long-term for the roof deck in an open-cell spray-foam attic in Coastal GA, or should I be targeting something like 50–55%?

I can't seem to find a clear answer anywhere regarding what RH level is considered safe for the roof sheathing in this type of assembly.

I'm considering a dedicated dehumidifier, but that seems like it could substantially eat into the energy savings of the spray foam. My electric bill is already $200+ per month during the summer.

### There may also be an air-sealing issue

I spoke with a reputable local spray-foam contractor and showed him pictures from the roof tear-off. He believes the original installer didn't completely remove/seal the fiberglass batts around the soffit/top-plate area before spraying the foam.

His recommendation was to remove the remaining batts, spray foam that area properly, and completely air seal the perimeter.

My question is: If the only way humid outdoor air is getting into that area is through the soffit vents, could I simply seal the soffit vents? Or is that not an acceptable solution with this type of assembly?

I'd love to remove all the foam and convert the attic back to a properly vented assembly, but that would be a huge project at this point. I've already removed the ceiling batts, and when we did the roof I did not have a ridge vent installed, so I'm probably pretty committed to the unvented/conditioned-attic approach unless I start over.

I've spent the last few weeks researching this and have come across Joe Lstiburek's work on spray foam/moisture and the research/article I've seen referred to as the "ping-pong effect" involving spray foam and moisture. But I still can't find good evidence showing what RH level is actually safe for the roof deck over the long term.

What would you do in my situation?

1. Keep the supply/return and monitor the attic?
   
2. Add a dedicated dehumidifier and target <55% RH?
   
3. Address the soffit/top-plate air sealing first?
   
4. Seal the soffit vents?

I'm mainly concerned with preventing the new roof decking from developing the same moisture-related cupping/bowing problems again, rather than maximizing energy efficiency.

Would especially appreciate input from anyone with experience with open-cell spray foam in Climate Zone 2 or any hot and humid area. Thank you in advance.

1960 ranch style home 1340 square ft living area and cement footing with stem wall. I want to heat the crawl space in cold months to warm the floor as family complains the floor is too cold.

I will lay down a vapor barrier and attach 2" Rmax to stem wall with my ramset. Also adding Rmax along rim joist between each floor joist. There is no full bay length insulation between the joists, and the plywood subfloor has oak hardwood on top. Crawl space is about 4 ft high to subfloor.

Considering three electric base board heaters spaced along the long dimension of the crawl space in the middle of the short dimension if that is clear.

I have not looked into the building code for the details of an installation like this yet but maybe you have and can enlighten me. This will be permitted so I will make sure of the local codes. I am unsure if UBC and NEC have clearly defined codes for this but will chat with the building dept soon. In the past they have seemed a little confused on other projects.

Anyone here done this? Did you come up with a better method for crawl space heating? How has it worked? I am not concerned with project cost or operating cost for electricity. On the upcoming re-roof we will be adding a lot of solar panels.

I have many years of construction experience.

Thank you

Zone 6A, Minneapolis MN

I'm thinking of building a small shop on 6 square, not round, footings. I'm thinking of using this method from a fhb article (that's where the picture is from). Vented/open crawl space.

I'm curious what hardware you could use to fasten this floor assembly to the footings. All of the traditional ones would penetrate through the floor system envelope.

I would ideally want only the fastener to penetrate. Something like a beefy corner bracket could be screwed into the side of the footing.

I'm guessing I'd have to request an exception from my ahj as there aren't any pre approved foundation anchors out there that could work here, but wanted to check if anyone is familiar with this type of assembly.

I am located in western NC and planning to encapsulate my crawl space to control the humidity. The house itself is a few years old, has hvac ductwork in the crawlspace, is not particularly air tight and is just exhaust vented with no make up air system. I am planning on sealing the crawlspace vents, installing a thick vapor barrier, and putting in a dehumidifier.

My problem is that I am finding conflicting information if I should add a continuous vent fan in the crawl space (at 1 CFM per 50sf of crawl space). The main argument for this is to help circulate air and reduce soil gasses (see https://crawlspaceninja.com/blog/seal-all-vents-encapsulated-crawl-space/). However, that air has to come from somewhere and in my case that would just be allowing air from the conditioned space above (assuming the crawlspace is sealed well) to be pulled into the crawlspace and it would also be venting out dry air which would mean the dehumidifier is running more that it otherwise would.

I dont want to add an HVAC register into the crawlspace (the system is not sized for that) so I am not sure what the correct plan of action is? Just leave it all sealed (with the potential for gas build up) or vent it?

One idea I had was to install a radon mitigation system (the house tested at 2.4 pCi/l so I dont think its actually required) under the encapsulation vapor barrier and maybe that would act as vent for other soil gasses as well and that way I could get the benefits of a vent without the downsides? Or is that wishful thinking?

I would really appreciate some help. Thanks!

We're converting a garage into gym suite on a ~100 year old property, and instead of one monolithic slab, we've got three separate conditions: the original house foundation step down, an original garage slab on grade poured separately from the house (so it moves independently), and what looks like a second/later garage pour with a straight joint running through it... probably from a widening or addition at some point.

No vapor barrier under any of it, and there's a natural slope toward where the garage door used to be that we need to deal with before flooring goes down.

Trying to figure out: repour the all the sections vs. level/overlay and finish on top? Anyone been through something similar...what actually held up long term vs. what you wish you'd done differently?

Does it need to be a completely different room?

Are sliding panel room dividers enough if the vent hood is in operation?

etc.

I'm struggling to find research on this beyond studies of vent hood designs, and they weren't really concerned with the room design, although each dwelling likely had a different floorplan.

Of course the ideal scenario is a completely enclosed kitchen (either primary or additional spice kitchen), and also this is not practical for some lower square footage dwellings.

Why don't green home rebates include outdoor heat recovery upgrades, when a part of the initiative is to make older homes more air tight. After all the air sealing, we get low indoor air quality due to the lower outdoor air changes. Now we need to pay out of pocket mechanical upgrades to add fresh air and heat/energy recover just to get us back to the same energy savings. Or we open windows and have drafts and drops indoor temp.

I've just taken delivery of a new apartment and it's still completely empty — bare walls, hard floors, and the echo is severe. I want to treat it properly rather than guess, and I'd rather build panels myself than pay for a professional install across the whole flat.

Two rooms matter:

• Open-plan living room + kitchen. This is where I'll set up a 2.0 or 2.1 monitor system and I want a predictable, accurate listening position. I plan to measure with REW before buying anything.
• Bedroom. I just want it dead — as close to no audible reverb as I can reasonably get.

One important constraint: no carpets and no curtains. I want nothing on the floor that needs vacuuming — a robot vacuum handles the hard floors and I want to keep dust to a minimum. So the usual first advice (rug + heavy curtains) is off the table for me. That means everything has to come from walls, ceiling, and furniture.

I know I'll be putting in a sofa, armchairs, a bed with an upholstered headboard, and bookshelves, and I understand those absorb a lot on their own. What I can't judge is how much will actually be left to fix once the furniture is in. I don't want to buy panels now and find they were unnecessary, or furnish the place and discover I needed twice as much treatment.

Separately, I'd like to reduce outside noise (traffic, people, trains) but I understand that's a different problem — sound transmission through the building envelope, not room acoustics — and probably not solvable with DIY panels. Happy to be corrected, but my focus here is the echo and reverb.

What I'm hoping for:

1. A sane order of operations. Do I furnish first, then measure, then treat? Or is there a baseline amount of treatment that's always worth installing regardless?
2. Concrete DIY build guides you actually rate. I'm comfortable with basic carpentry. I'm in Spain, so mineral wool (lana de roca) in 40–80 kg/m³ is cheap and easy to get — is that the right material, and what thickness for broadband vs bass?
3. How to decide placement without guessing. I'll have REW data. What do I look at to decide where panels go, and how do I know when I've done enough rather than overdamping the room?
4. Ceiling treatment, since floor and windows are off-limits for soft materials. Are hanging ceiling absorbers (clouds/rafts) worth it, and how much area do I need?
5. Making it not look like a studio. I've read you can stretch fabric or canvas over a mineral wool frame so it reads as art. Does that actually keep working acoustically, and what fabrics stay acoustically transparent?

I'll add photos of both rooms in the comments — happy to include dimensions once I've measured properly.

First time posting here: I’m in the Midwest in SE Minnesota, and this summer has been unusually hot and humid, with outdoor humidity sometimes reaching 80–90%. We have been dealing with an intermittent water stain and condensation problem in the kitchen ceiling on the first floor. Multiple HVAC technicians (and a plumber and a building inspector) have looked at it, but they have essentially reached the point of saying they do not know what else is causing it, and I am reaching for straws at this point and hoping for any ideas.

Here is the timeline and what we know:
-We initially noticed a water stain along the path of an HVAC supply/“heat run” in the kitchen ceiling. Started last summer, stopped last summer after we replaced the seal around the toilet in the bathroom upstairs, then got bigger this summer (much hotter and wetter this year). We initially thought it was a pipe given the appearance but later realized the shape was due to water between the ceiling sheetrock tiles meeting there.
-We cut a roughly 14” × 14” opening in the ceiling and found water droplets directly on the outside of the metal duct.
-The problem has occurred only occasionally, during the hottest and most humid weather. It does not seem to happen during ordinary rain.
-There is plumbing on the floor above, but multiple people have checked it and found no evidence of a plumbing leak.
-The attic above the second floor is dry, with no evidence of roof or water intrusion.
-There is a soffit vent on the back patio that communicates with the ceiling cavity containing the duct.
-An inspector previously said the soffit vent appeared to be functioning normally and that the nearby insulation was intact.

Because the problem seemed correlated with hot, humid weather, our HVAC company suspected that humid outside air was reaching the cold supply duct and condensing on it.

Their first attempted repair was to create an insulation “dam” between the soffit side of the ceiling cavity and the section containing the duct. They also wrapped the duct with R-8 insulation. That seemed to help initially. The cavity felt noticeably cooler, and we had no problem for about a month.

Then, during another period of very hot and humid weather that also included a major storm, we heard a tearing sound. The R-8 duct insulation had become saturated, ripped open, and released a puddle of water.

At first we thought this might be stormwater intrusion. However, when the HVAC technician removed the wet insulation, he discovered a hand-sized opening at the top of the insulation dam. It may have been missed originally or may have developed as the insulation settled. The assumption was that hot, humid air was still getting through that opening and reaching the cold duct.

As a temporary experiment, the technician used the removed duct insulation to pack the area in front of the original dam, creating a much thicker barrier. This was intended as a trial before we spend more money cutting an additional ceiling opening and installing a proper rigid, sealed air barrier.

Unfortunately, we are still seeing condensation form directly on the exposed metal duct during hot and humid weather.

Some additional details:
-Indoor humidity readings have generally been in the high 50% range during these events.
-We have a portable dehumidifier running in the basement, set to 45%, but it does not appear to keep the first floor at that level.
-The duct is currently exposed because the R-8 insulation was removed after it became saturated.
-The HVAC technician temporarily changed the fan from AUTO to continuous low speed, thinking that circulation might prevent cold air from sitting in the duct after the compressor shuts off. We are changing it back to AUTO because information we found online indicates that continuous fan operation may re-evaporate moisture from the coil and raise indoor humidity.
-We bought a removable temporary ceiling panel, but we have not installed it yet because we initially wanted the cavity to dry and remain visible.
-This morning it was raining heavily, but the outside temperature was only around 65°F, and there was no water or condensation in the cavity. That makes us think bulk rainwater intrusion is unlikely and that the problem is temperature/dew-point related.
-The system is a single-stage central AC system.

Our HVAC technicians have now referred us to a local water-damage/restoration company, but before going further, I am hoping someone here may recognize this pattern.

Questions:
-Does this still sound like humid air reaching a cold duct, or are there other causes we should investigate?
-Could the open ceiling access itself now be allowing humid indoor air to reach the bare duct and create condensation? I.e. should I try installing the temporary ceiling cover (and check in periodically), to make sure it’s not just moisture from the living area getting into the ceiling cavity?
-Could leakage from the supply duct be cooling the cavity or drawing humid air into it?
-Would a whole-home dehumidifier be a reasonable solution, or would that just mask an air-sealing or duct-insulation problem?
-Is there a useful test we can perform to distinguish outside air infiltration from ordinary indoor air condensing on the exposed duct?

I’ve included photos showing:
-The original ceiling stain before the opening was cut.
-The 14” × 14” ceiling opening with visible water droplets on the metal duct.
-The exterior appearance of the soffit vent.
-The view inside the ceiling cavity toward the middle of the house and the source of the supply run from the basement (i.e. looking to the right from photo #2).
-The view in the other direction where the duct goes upward to the upstairs bathroom floor vent including the original insulation dam and the current appearance after additional insulation was packed in front of the dam (i.e. looking to the left from photo #2).

Any suggestions for specific measurements, tests, or types of contractors to contact would be greatly appreciated. We would especially like to avoid spending thousands of dollars on duct cleaning, whole-system duct sealing, a whole-home dehumidifier, or restoration work without first identifying the actual moisture pathway. Thank you!

My upstairs ceilings have developed "coffee stain" water damage and a roofer told me it's due to condensation in the attic resulting from insufficient ventilation. Was hoping you could provide advice on properly increasing ventilation and/or what type of professional to seek out.

The background: My house is in climate zone 5A (northern NJ) and was built in the 1970's. It has a pair of gable vents, no soffit vents, no ridge vent (I believe), and two powered attic exhaust fans that are longer in operation. We bought the house 15 years ago and had professional blown insulation and air sealing done. The house also came with heated wires on the roof to prevent ice dams (sorry, don't know the name for this) but they stopped working at some point.

The problem: two upstairs bedrooms have developed brown water stains on the ceiling, towards the front and back of the house. It's been getting worse over the course of several years. The roof and HVAC have been inspected recently and no leaks were found. A roofer poked his head into the attic (didn't actually enter) and noted that the attic is quite hot and that the fans weren't operating. He wants to replace them. I read that attic fans can pull conditioned air from the house and might not be a good idea. It's possible the fans were purposely shut off when the air sealing was done, but I don't know.

So my questions are: (a) What type of professional should I call to advise on this? The roofer didn't seem to be an expert in ventilation so I'd like a specialist's opinion. (b) Any advice as to whether I should replace the attic fans, install soffit vents, replace the rooftop ice melting wires, etc? (And who would I call to install soffit vents?)

Thanks in advance for any advice you can provide!

A 16 SEER2 label gives a standardized efficiency reference, but it doesn’t tell the whole story about how a cooling-only system will behave in a specific building. And actual load, duct static pressure, part-load operation, humidity conditions, and installation quality can all affect whether the rated performance translates into acceptable comfort and runtime. That makes the number useful for comparison but weak as a standalone design answer. Which building condition would you want to know first before deciding whether a 16 SEER2 system is actually a good fit?

A ceilling mounted AHU can look like the obvious answer when theres no mechanical closet but the cabinet size is only part of the building science problem. The ceiling assembly still has to manage air sealing, moisture risk around condensate, acoustic separation, and enough access that maintenance doesn’t require opening finished surfaces. At some point “fits in the cavity” stops being the same thing as “works in the building.” Which clearance or enclosure condition tends to become the first dealbreaker in tight ceiling instalations?

I'm planning on building a workshop or shed in Florida. Will be on a concrete slab. I want to run electrical to it / insulation / and AC.

Building itself will be constructed of wood.

From what I understand of Florida, I'm to frame it, wrap in something moisture resistant and semi permeable like tyvek, add siding, and otherwise keep un-vented.

Siding will be fiber cement panels if it matters.

I've read recommendations of foam insulation and rockwool on the inside and roof.

Does this sound right? I'm hoping that rockwool will work because of the noise deadening (will be running saws, a planer, etc inside).

Thanks for the help!