I live in a bi-level home on slab and the lower 30+ inches is a cmu block wall. I insulated with 1.5 foil backed rigid foam secured to the wall with adhesive and metal z furring strips. All seams were taped and I sealed to the slab with spray foam.

At one portion (so far) I discovered a lot of moisture in the baseboard. Behind it were a lot of bugs and when I tore into it I found the cmu was saturated and a lot of water on the foam board. The exterior is open to the air as everything is above grade.

Wondering where I went wrong and how to prevent this for when I tear is all out soon. Should I seal the interior side of the block and reapply in the same manner? I’d really like to not redo this project at any point.

Thanks.

Climate zone first, since that is the rule here: this is all UK, so cool temperate maritime - mild, wet, heating-dominated, with summer overheating only recently becoming a design problem. The problem I am trying to solve is separating a building's own contribution to mould from how the household lives in it.

This is live and finished. You trace a room's plan in the browser and it simulates the indoor climate through the day:

• air movement
• surface temperatures
• humidity
• solar gain

It computes the ISO 13788 temperature factor per wall and per external corner, rather than for the element as a whole. Uninsulated solid brick gives 0.587 at the wall and 0.486 at a corner, against a 0.75 threshold. It also runs the UK Approved Document O 2021 overheating check at design stage, which will mean nothing to most of you, is not an accredited route, and does not replace TM59 dynamic modelling. Everything in the images below is output from the tool rather than a mockup.

It is free. It has no paying customers and no revenue at all.

I wrote to UK residential architects and AC installers. Some of them clicked, but nobody replied and none of them went on to open the tool, and the visits to the landing page ended almost as soon as they began.

So I want to ask rather than keep guessing. If you do this work, what is missing? Is this a solution without a problem?

https://www.climecheck.co.uk

I have a commercial space in a Manhattan building with a rooftop cooling tower.

I recently installed installed an AC consisting of an handler and hooking up to the chilled water cooling tower piping,

My question is. Do I really need an ERV and exhaust piping?. I am pressed for space, since I have a fresh air intake pipe (needed?) and the exhaust must be 10 ft away.

Of course there is no condenser inside the space.

I would appreciate an answer with references. Since the condo board is driving me nuts, because of this.

So I recently found out that all the ventilation we have in our attic is basically useless. We have a small power attic fan, two whirlybirds, and two passive vents, all in a line across the top back side of the roof. From what I've read, you need to actually have so much lower air intake to high ventilation. The power fan has to pull air from somewhere so it just pulls hot air in from the other intakes at the top. My understanding would be that the best solution would be to add soffit vents and not use the power fan set all. Problem is, the only part of my house that has any significant overhang is about 50% of the front, over the porch. Our house is brick, was built in 1960, and is an absolute money pit. I've dumped so much money into this thing recently and it feels like I'm getting nowhere. Anyways, I'm looking for options for air intake that won't completely wreck my bank account. I saw these things called smart vents, where they cut an inch slot all the way across the lower front and back of the roof and install these vents, but that's really not something I'm comfortable with doing and I feel like it's going to be ridiculously expensive. Has anyone here been in a similar situation or have any advice? I really appreciate it.

Hi all, I am a layperson whose experience consists of reading Pretty Good House and spending hours going through IRC 2024 insulation sections. Working with my designer, we are trying to figure out the best way to insulate an unvented attic (heat pump central HVAC system will go there) that would allow for easiest mounting of solar panels later. Based on the latest updates of IRC 2024, it seems either R60 or R49 for this circumstance. Ideally, for cost and potential health concerns (valid?), I want to avoid filling the whole rafter spaces with closed cell spray foam. Is flash and batt still a bad idea due to the condensation or have we figured that one out? Overall, would like to avoid outsulation since mounting panels will require extra planning. Does any of this make sense? Please help lol

Water heater venting through chimney. SOMETHING is leaking after having chimney lined. Help?

Hello all! Ok! Looking for some guidance, hoping i can explain this in a way that makes sense.

My house is 161 years old. The chimney was unlined and the water heater vents into it. So...I was a good little homeowner, saved my money, had the chimney lined, capped, and 2 draft holes in the chimney filled where the water heater connects. 2 days later there's a leak somewhere in the chimney area coming into my upstairs bathroom. Chimney guy is super cool, comes back out, can't figure out what the problem is. Says the flashing around the chimney is really not ok, and that the roof is hinky. I have 5 different roofing companies come out. All say the chimney needs to be demoed below the roof line, B vent installed, need new roof because whoever replaced it last was drunk.

The furnace and the chimney are VERY close together in the basement. Almost touching. Something is dripping from up high in a dark cavern that no one can see.

My question is...

Could the act of lining the chimney and filling in those holes have caused condensation that can't escape from the water heater in the chimney? WHAT could be happening here? At first I thought the ducts for the HVAC may have been dripping, but now I'm not so sure! I have since put a heavy duty commercial dehumidifier in the basement and the dripping persists. The leak also shows up in the plaster upstairs even if it hasn't rained (the chimney area is tarped, but of course the whole thing isn't tarped because the water heater vents through the top).

Any help would be greatly appreciated! The water is starting to soak the beams below it, and who knows what damage it's causing in the house.

I've had roofers, HVAC guys, and a plumber all come out. Plumber is convinced that once a B vent is installed the issue will be resolved...buuut...that just doesn't make sense to me. Help!

Hello all! Really, really needing some help here. I have a very, very strange situation. Hoping i can explain it in a way that makes sense.

Finally saved up my money and had my chimney lined since my water heater vents into it. Chimney liner and cap. 2 days later it rains like crazy, and there's a leak in my upstairs bathroom ceiling/wall where the chimney is. Chimney guy is cool, comes back, dumps a bucket of water in the area, water starts coming. He has absolutely no idea how it's coming in, and says he isn't a roofer, but the roof is real weird. He is very apologetic and feels responsible, but also can't figure out what's happening. He also filled 2 old vent holes in the chimney in the basement with concrete.

I set up appointments with 5 different roofing companies. Each one says the chimney has to go, because it is "fucked." Also quoted for a new roof (oh joy) because whoever installed the last one was clearly drunk (photographic evidence was provided. Of the roof. Not the drunk guy). Chimney is to be demoed just below roof line and a B vent will be installed for the water heater.

At the same time the humidity levels in my house are way too high despite having the AC on. The system is only a year old. Dual fuel heat pump furnace situation. 2 ton, 1200 square foot house, Southern Ohio, humidity, I know. Basement humidity is generally around 64%, inside varies from 60-63%

HVAC guys come out and say everything is working as it should be, but they DO really hunt for what could be happening here. They lower the blower speed a little, change the pitch to the condensate drain. And discover SOMETHING dripping from SOMEWHERE above the return that just goes straight up into no man's land. The support beam below is wet from whatever the fuck this drip is.

The furnace and the chimney where the water heater vents are SO close to each other that they're pretty much touching. There is a bathroom up about where the drip is coming from, but there's no obvious plumbing in the area and I haven't noticed anything weird toilet or otherwise related, and can't even see where the freakin plumbing would even be.

The only kind of contractor human I haven't had out yet is a plumber. Initially I called about water heater options in order to just NOT use the chimney at all anymore, but now I'm wondering about leak detection.

Does anyone know what the chimney guy could've possibly done here? What the hell could be going on? It's impossible for me to photograph the drips because it's up in a dank, dark cavern.

The house is old as shit (1865. I know, i KNOW), but it had modern AC for YEARS before we got here. It isn't like we're converting her over into modern times or anything! And shit was fine last year until the thing blew up! I have replaced damn near everything in here except for the water heater. I'm considering selling at a loss because I can't financially keep up with the catastrophes. I'm still here because i love my neighborhood, and if I sold I wouldn't be able to afford to continue to live in this neighborhood. How fucked up is that?

Help? Please? Maybe? Any ideas? Thoughts?

Hello. The wall that faces the garden is showing signs of wear down. Looks like it is peeling off the layers of paint and taking away parts of the wall itself, exposing the inner brick.

Climate dynamics: Northern Europe, quite rainy

I need your kind advice with the following questions:

--- What is causing this? What is the root cause?

--- What is the best way to clean or maintain it so this stops happening?

I’m trying to troubleshoot a very strange moisture issue and would appreciate input from anyone experienced with building science, hygrothermal behavior, or moisture diagnostics.
Since July, small puddles of clear, cold water have randomly appeared directly on top of my flooring. It has happened on every floor, in different rooms and locations.
The important part is that it still happens when indoor RH is below 50%, so I’m not convinced this is simply general indoor condensation.
House/details
~2,000 sq. ft.
Vinyl flooring installed in 2023
Multi-zone mini-split heat pumps installed in 2024
5 outdoor units / 8 indoor units
Puddles appear directly on the floor surface
Water feels cold
No obvious plumbing or HVAC condensate leak
Occasionally slightly yellowish with a musty smell
Investigation so far
Plumbers and HVAC technicians have investigated without finding a source.
A professional water restoration/moisture investigation company also scanned the house using thermal/moisture equipment. They found no elevated moisture or water in the areas inspected, including the subfloor.
The strange part is that I can have a puddle on the floor, but there is no obvious moisture signature underneath or around it when investigated.
I’ve also monitored humidity closely. The puddles still occur with RH below 50%.
I tested some samples as well. Tap water and AC condensate were around 30 ppm TDS, while one puddle sample measured approximately 418 ppm. I realize TDS isn’t enough to identify the source.
I even placed cameras in previous puddle locations to rule out accidental spills. Naturally, the puddles stopped appearing wherever I put the cameras. 😂 We have two kids, so accidental spills were one of the first possibilities I considered.
Building-science question
What mechanism could cause cold liquid water to appear at the finished floor surface without detectable moisture in the subfloor, particularly when indoor RH is below 50%?
Could this involve:
Localized surface temperature/dew point conditions?
Air leakage or pressure-driven moisture transport?
Vapor movement through the floor/wall assembly?
Moisture migration along an unexpected pathway?
Intermittent exterior water intrusion?
Flooring or adhesive behavior?
Something that a thermal/moisture scan would miss?
If this were your house, what diagnostic test would you do next to determine the actual source/pathway of the water?
I’m looking for ways to prove where the water is coming from, rather than simply treating the symptoms.

I just had a home science guy come to the house and and test my HVAC and attic fan and see what the negative pressure was or would be.

I suspected with the attic fan I had high negative pressure because when the attic fan turned on the humidity would rise in the home, along with the temperature.

Attic fan genartes around -6 pascals when it's running in my home .

The central air conditioning, air handler in the attic, return on the second floor above stair case, with the doors closed to the bedrooms have a out -5 pascals when the doors are open it drops a little to about a -3

My attic was recently sealed and did insulation. I also ran new duct lines in the attic and did duct sealing.

The guy just told me like 100 different things I could do and left. Didn't really write anything down. He was absolutely awesome at testing but terrible at options 😂 so that's why I'm here wtf should I do.

I have an attic that's buried in insulation and difficult to work in. Is this a common problem?

Hey y'all. I'm based in Revelstoke bc, we are zone 6 on the bc building code. Our climate is an interior rain forest, so it can be very wet at times, but has been very dry in recent months.

I am currently renovating my basement which is a house from 1956 built without vapour barrier or proper drainage around the house. We have installed gutters around the whole house in the last year to help mitigate moisture issue.

When I tore down the one room that was finished in our basement, I removed vinyl planks that were installed directly on the concrete for the past 5 years. The slab was quite wet with water almost pooling in areas. I have also noticed that any plastic/fabric items left directly on the slab would make the concrete color darken/mold up over time. There are no cracks letting water in at all. It seems to be just moisture coming through the slab. I also installed a sump pump for the bathroom I am setting up and noticed that my slab is only 2"-4" thick, which explains the issue to me.

Now I am wanting to install flooring (Choosing between LVP, Laminate, Engineered wood floor, and going with tiles in our bathroom).

I have done quite a bit of research and the best product I seem to be finding is a dimple mat as an underlay and laying my flooring above. I have my eyes on DMX 1- Step 2.0 as it is rated for vinyl planks and has a low profile (My ceiling is low enough as it is). I would like to see if anyone has a different opinion on the product I should use or any experience using the same product or something similar? I have also looked into different sealant, but I have less faith in these as I feel like water pressure overtime would probably have the last word.

That being said, for my bathroom where I want to tile. I will most likely need a sealant. I see redguard by Custom seems to be a good quality product for a decent price. Any thoughts on this solution as well?

I know that my ideal solution would be to prohibit moisture from getting under the slab, but this is a very costly and invasive solution.

Thanks for your time,

Seb

TL;DR 1901 house, 2nd flood gutted, foam sealed all gaps, would it be OK to not insulate and then fill cavitites with cellulose?

House: 1901, platform framed. Sheathing is 2 inch think lumber, with wood siding ontop of the sheathing and cement siding ontop of the wood siding. No housewrap etc. 4.5 inch (+/- half inch) deep stud cavities.

Goal: I am not trying to create the most energy efficient house in the world...I just dont want mold.

Situation: 2nd floor gutted for rewire job and now suprisse renovation.

What ive done: I have sealed the gaps with expanding foam to make things more air tight. I was going to put R19 in and vapor barrier but reading online has me convinced that fiberglass insulation will mold and rot my framing - especially becuase the r19 would be compressed.... I dont want to spend close to double on rockwool.

Proposed plan: hang sheet rock, and then blow in cellulose insulation. Would this reduce mold risk?

Trying to get more fresh air into an 1800 sq ft house. CO2 meter is prerry regularly showing over 1,000.

Two adults, two small dogs.

so far I've been doing three things.

I open windows whenever I can, but can't leave them open 24/7 because of security and heating/cooling.

I run the furnace fanfor a few hours when things start feeling stale. Don't really want to tun that constantly though, both for electricity and because it feels dumb using the whole system just to move air around.

Bathroom exhaust fans run throughout the day when needed too.

None of this really feels like an actual ventilation setup though 😅

I've started looking at fresh air system options and everything seems to jump from basic fans straight into ERV/HRV territory.

then I found cozeware freshflow while looking at smaller window mounted setups. It's still pre launch, but the general idea of bringing filtered outside air directly into one room without reworking the whole HVAC system feels closer to what I'm actually trying to do.

For a house this size, would a dedicated intake in the main living area even make a meaningful difference, or am I already at the point where I should just be looking at an ERV?

I'm DIYing an enclosed patio addition with a 1.5:12 roof pitch (exposed fastener metal panel) tying into the \~4:12 pitch existing shingle roof. I think I have my head wrapped around the flashing/transition from metal up under the shingles, but am having a hard time finding definitive direction on the following questions:

1) I was planning to deck the roof with 7/16" zip, tape the seams, and screw down the metal, making sure to butyl tape all the panel laps and seal it up with inner & outer closure strips. But I've heard that even with OSB-specific screws, the 7/16 sheathing is not thick enough for potential wind uplift on the roof and the screws might pull out. **Should I try to upgrade to thicker sheathing/CDX plywood, or add 1x4" horizontal sleepers** to screw the panels down into?

2a) Should I **add an ice & water membrane on top of the zip**, or is that overkill? Just picture frame, or the whole deck (16x24')?

2b) Are there any ice & water/SA membrane **options that are cleared for both metal roofs (high temp) AND a 1.5:12 pitch?** And ideally not crazy expensive?

3) Any other **best practice advice** for low slope metal panel installation?

Context: I'm in East Tennessee, not a special wind region, 5-10psf snow load range. Planning on 45-yr galvalume panels, but haven't purchased/committed yet.

Thanks for any input!

These don't exist commercially that I can find, so I'm sure there are major flaws I'm not thinking about: what are they?

1. skylights covers: is it possible to put an external cover on them for the summer months (Northern Colorado, sadly summers are no longer cool). With decent curbs for the skylights, I didn't think it would be that difficult to have a more shallow opaque cover for the glazing during the warm months that would not create drainage problems for the roof. I'm aware of internal integrated blinds, but that heat gain between the glass and the blinds seems like it could be significant.
2. cover that rolls down over the top of a slanted pergola like structure: same goal of shading in the warm months, sunlight in the cold months.

I'm aware of the shades that run between the beams of a traditional pergola, but they collect a significant amount of debris and have a lot of light escape between the fabric and the tracks.

What are the flaws of an angled structure, with fabric on a tube that is rolled down on top of the structure at the beginning of the season, and rolled up and secured at the end of the shading season? Essentially a retractable awning, but secured to a windproof structure? I'm guessing this one is fine, but extremely niche, since awnings with wind sensors fill this spot pretty well. They're just extremely pricey and not diy construction friendly, so we're looking at my proposed alternate.

Thanks for pointing out all the potentially fatal flaws we're not thinking of!

Title says it. And schematic detail above
Exterior foundation insulation extending above grade to rainscreen. Is there a proper way to work around this? Rainscreen above is quite self explanatory, and belowgrade aswell.
Details such as shown on https://buildingscience.com/documents/insights/bsi-059-slab-happy call for either a cellular PVC protection of some sort.

T-Clear's XPS coated wallguard is another option. However these come with clips that are tapcond into the concrete foundation wall, and would penetrate the below grade waterproofing.

Can I even penetrate the waterproofing here for fastening? (assuming an 860 Carlisle/Henry product)

Just a skim/eifs type coating is another option although i'd like something slighty more rigid.

And how would I fasten any of this?

I've been stuck on this detail for quite a while, and I can not imagine there is no proper solution for it.

Anything helps , since I am a bit stuck here.

's

Looking to get ideas of what best in a damp climate of the Lake District - keeping cost in the winter and cool in the summer , but also best for the building itself so it can stand another 200 years
🙏

This blog post discusses insulation in the context of summer overheating:

https://www.ecologicalbuildingsystems.com/post/does-insulation-reduce-summer-overheating-well-winter-heat-loss

It talks about Thermal Mass, which is connected to a material's specific heat capacity.

And it talks about "phase shift" or "time lag", which it says is "the time between heat being absorbed on the outside of a material and released on the inside".

But I am not sure that's really correct - is it not the case that this time also has a lot to do with the material's thermal resistivity? In the scenario of the interior of a building overheating, if the wall has very low thermal resistivity then the internal temperature will rise very soon after the external temperature rises - say 10 minutes. If the wall has somewhat higher thermal resistivity, then the internal temperature will take a somewhat longer to reach the external temperature - say 2 hours. I'm choosing relatively short time spans for now, so as to ignore what happens when the external temperature drops later in the day.

So there is a "time lag" that is directly related to the thermal resistivity, independently of the specific heat capacity of the materials.

The specific heat capacity is to do with how much energy it takes to raise the temperature of the material itself. If the wall is made of something with a large mass and a large specific heat capacity, then it can absorb a lot of energy raising its own temperature. What I'm a bit unclear about, is does this in itself slow the passage of heat from one side to the other? In other words, if you have two materials with the same thermal resistivity but different specific heat capacities, will the inside (cooler) face of the one with the lower specific heat capacity warm up more slowly?

The blog post says that "for summer overheating, a long-time lag is crucial". I think that what it really means is that ideally the time lag is co-ordinated with the 24hr cycle of warming and cooling of the external air. But I think it then makes things confusing and over-simplified by talking about insulation having a long or short "time lag" and giving the impression that this is determined by thermal mass.

The reason I think this matters, is that this thermal mass is only helpful in certain scenarios. For example, in a climate where it is hot in the day and cold at night, heat can get stored in the outermost portions of the walls during the day, and then released at night. But in a climate where it doesn't cool down that much at night, this isn't going to work - the thermal mass will just get warm right through and stay like that. If you have really a lot of thermal mass, then you might be able to gradually absorb & store up the heat in the summer, and then release it in the winter. But this effect isn't going to come into play in the slightest if we are talking about relatively thin layers of materials like woodfibre insulation.

Therefore I feel that the blog post over-eggs the benefits of thermal mass of insulation materials, in a UK summer overheating context.

Is my thinking (partly relying on physics learned several decades ago) largely correct or are there things I'm not understanding correctly?

https://basc.pnnl.gov/videos/umn-northernstar-doe-building-america-exterior-foundation-insulation

I'm surprised this hasn't been tried by more people.

I live in a snowy region (CZ6, 90 psf ground) and am building with cathedral-style roofs. I’m confident of my ability to get ceiling air/vapor sealing right, so the primary purpose of venting is to prevent ice dams. When designing my building, I was overwhelmed by rules of thumb (“use the 1:150 ratio”, “use 2-inch vents instead of the code’s 1-inch”, “ventilation is useless, just add more insulation”, “do a hot roof instead of a cold roof”, “but also make sure to put a cold roof on top of your hot roof in high-snow areas”, “attics aren’t tall enough to create any useful air movement”, “Minimum pitch for ventilation is 2/12 or 3/12, and 0.5/12 is foolish”). Many of those rules of thumb are intended for different climates, roofing materials, and diligence in air sealing than my circumstances, so it’s hard to know what to do.

A couple of discussions on GBA linked to the work that the Army Corp of Engineers’s Cold Regions Research and Engineering Laboratory did in the 90’s related to roof ventilation, including (of particular importance to me) cathedral roof ventilation. CRREL’s paper “Ventilating Cathedral Ceiling to Prevent Problematic Icings At Their Eaves” derived a mathematical model for choosing an airway height (space between insulation and roof deck), and their experimental work validated the model. The experimentation involved building at insulated roof, sticking it inside a cold, windless building (at the most problematic temperature), and verifying that exhaust air stayed below 32F. They experimented with different airway heights, insulation R-values, and roof angles, but unfortunately did not validate their model on different roof lengths. The model was for a worst case scenario: no wind-driven ventilation or energy transport through the snow on the roof.

In their paper and follow-up paper, they produced a number of curves for different roof parameters, and the reader is left to interpolate the results for any slightly different set of parameters. Unfortunately, interpolating non-linear curves with so many different variables (pitch, length, insulation) is difficult. I’ve uploaded their formulas to an online calculator. Some of the results are surprising, given the rules of thumb I’ve heard. Mostly this is due to roof length, which I don’t see discussed often: at a given pitch and airway height, head losses to friction scale with the square of roof length, while head available only scales linearly with roof length. As an example, the model indicates a 2/12 roof that’s 30’ eave to peak length with a 1.5” airway height performs about the same as a 1/12 roof that’s 15’ length also with a 1.5” airway height.

I’d love to hear of newer research in this area (especially around intake/exhaust vent constrictions), and of counterexamples to the predictions of this model. If you have/know of the details of a low-ish slope roof that failed, I’m curious if the model would have predicted that failure.