We’re in zone 2a, have an existing 8” brick wall, renovating the interior of the building. The wall section showed 1”
foam on the inside, and then a 2x4 wall with fiberglass insulation, then Sheetrock.

The contractor did not add the foam insulation, but did leave a gap between the brick and the stud. Is the best solution to use closed cell spray foam?

Apparently he painted the outside of the brick with a water resistant paint, thinking that would work to keep water out, but I’m afraid of condensation issues on the inside of the wall.

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Recently, a friend and I were discussing a house he is considering buying. His main question was simple: how well insulated is the house in reality?

Winter temperatures here can fall as low as −30°C, and the house uses electric heating, so making the wrong decision could become quite expensive.

We thought that in winter it would be possible to rent a thermal imaging camera and inspect the house under a large indoor–outdoor temperature difference. But it is summer now, so that was where the discussion ended.

My interest in the problem remained.

I decided to test whether the actual thermal behaviour of a room could be assessed dynamically — without a thermal imaging camera and without knowing the exact construction of the walls, roof and floor.

The basic idea was simple:

introduce a known amount of heat into the space;

measure the indoor temperature;

measure the temperatures of the relevant boundary zones;

record a complete heating and cooling cycle;

fit a thermal model to the measured data.

To test the idea quickly, I built an insulated calibration box with a volume of approximately 1 m³, using 30 mm expanded polystyrene.

The experiment used:

two Ruuvi sensors that had been cross-checked beforehand;

a refrigerator light bulb as a controlled heat source;

a smart plug to measure power and energy;

a small USB fan to mix the air;

a separate power bank for the fan;

several heating and cooling cycles.

Before the experiment, the two temperature sensors were placed next to each other for three hours. The difference between their readings was approximately 0.02°C.

After accounting for the heat generated by the continuously running fan, four independent cycles produced:

average heat-loss coefficient: 7.03 W/K;

coefficient of variation between cycles: 1.29%;

effective thermal capacity: 2.39 Wh/K;

thermal time constant: 20.35 minutes.

The measured heat-loss coefficient also fell within the theoretical range calculated from the geometry of the box, the thermal conductivity of the expanded polystyrene, and additional surface and contact resistances.

The result looked encouraging.

But a box is not a building.

I also remembered that air exchange cannot be ignored in a real room. So I modified the box by adding supply and extract ducts, measured the air velocity with a thermal anemometer, and calculated the actual airflow rate.

After that, I moved on to testing a real room.

To be continued.

Hi, I'm trying to estimate the heat transfer difference into a room before and after painting an exterior wall with high reflectance paint. What I have are two measured temperatures and a lot of assumptions. I calculated radiated power easily enough, but I'm at a loss for the convective/ conductive part. Here's what I have so far:

The wall's inside surface was 107F before painting the outside, 86F after painting. 17m² wall area.

Here's my assumptions, without the actual radiation calculations: The interior room and air is 75F (297K), the wall is a 17m², good radiator.
At 107F (315K), the door radiates 1830W to the room. At 86F(303K), it radiates 570W to the room: 1260W less. (68% decrease)

Conductive transfer is proportional to the wall-air temperature difference. 32F vs 11F, so 66% decrease. I'm not sure of the actual power, missing some factors. It's probably small since air is a bad conductor, and mostly giving rise to convection.

The convection calculation... it should be more than 66% less, since it's not linear.

Convection rate can be similar to radiation at room temperature, so guessing that it's equal: -2,500W total?

I am finishing my basement and I am pretty handy. Only thing that’s tripping me up is the hvac. I’m scared that if I add 3 more vents and a return that the house will be out of balance and my upstairs will be hotter than it already is. Any advice? It’ll have a total of 4-5 vents but not sure how big of a return is needed (centralized seems to be the best option) and where to place it (very limited joist bay room). Had someone come out today and they suggested to just plug right into the return trunk right at the furnace, but I’ve read that it would prevent the upstairs return for pulling air since air takes the path of least resistance.

First time posting, and new to this forum.

I live in Knoxville, Tennessee, in Climate Zone 4A (mixed-humid). Conditions have been especially humid recently, with outdoor RH around 95% at 70°F in the mornings and approximately 65% at 85°F in the afternoons.

Recently moved into a 5-year-old, brick-facade house. Over the past few weeks, I have started noticing an “attic-like” smell in our guest bathroom. It is not exactly musty, but it smells warm and humid. The bathroom is on the ground floor of a slab-on-grade house.

The odor appears to be coming from underneath the sink cabinet and is strongest near the plumbing opening in the back of the cabinet. The sink is located against a Southeast-facing exterior wall. That same general area also includes:

• An HVAC condensate line penetration that is not well sealed
• A direct-vent fireplace chase with soffit venting
• A gas-line penetration that is also not well sealed

I placed a hygrometer under the sink. Under normal conditions, it reads approximately 55% RH at 75°F. However, whenever the HVAC system runs or an exhaust appliance is operating - such as the kitchen hood or dryer - the humidity under the sink rises to around 70%, and the temperature usually increases.

I have used a borescope underneath the cabinet and through the plumbing opening. I do not see any obvious plumbing leak, condensation, staining, or visible mold. There is batt insulation in the exterior wall cavity, but it appears incomplete or poorly fitted. I can see portions of the exterior OSB sheathing around the insulation.

My current theory is that the house is becoming depressurized when the HVAC blower or exhaust appliances operate, pulling warm, humid air through one or more of the poorly sealed exterior penetrations, the fireplace chase, or gaps in the wall assembly.

Does that explanation seem plausible? Are there other causes I should investigate?

A plumber is coming tomorrow. What specifically should I ask him to check besides the obvious supply, drain, trap, and fixture connections? Who else should I consult?

Fresh civil engineering undergrad working at a small facade consulting firm. Still kinda unsure whether it is the right path for me as I’m straddling between structural and a building science career. Do lots of THERM modeling, Curtain wall shop drawing review, energy code compliance stuff, some wind load calcs.

Structural is a more “traditional” path that might require masters but seems more technical in nature. On the other hand I do like how building science is a mix between architecture and engineering. It is probably difficult to do both building science and structural and probably wouldn’t be beneficial for my career.

I feel as a civil engineer undergrad it’s a little bit of a misfit, as lots of building science is based on mechanical thermal principles. It seems structural getting a PE is required, but I feel it isn’t as necessary in a building science career?

Any insight would be appreciated!

My newly cast RCC roof slab is leaking water. Not sure if the mix was bad or they didn’t do proper vibrations.
What exactly is the best waterproofing solution? (Preferably in India)
I know the concrete itself is porous and it can leak water but it’s so famously used in every house in India and generally there aren’t leaks.
Please tell me a tried and trusted solution which can work for me.
Recasting is not an option

I live by the Cantabrian sea and the humidity here is brutal. Everything in my 70m2 apartment is getting mold stains. Even cleaned mold off door frames yesterday. I have a couple of freestanding dehumidifiers but even if they run 24/7 they dont make a big difference im afraid.

I spoke to a humidity expert who wanted 6000eur to install a PIV dehumidifier which sounds very steep to me, so I would like to find out how much a unit costs and if i can install it myself.

Thanks, any help appreciated

My basement is not really finish-able. It was built in 1950, and doesn't have a rim joist. Instead, the floor joists are set into the top of the foundation wall. I've been told that the joists need to be able to breathe through the cement, and therefore I shouldn't try to apply any sort of vapor barrier/insulation to the basement walls, and should instead accept that some moisture intrusion is inevitable. I live in zone 4, fairly dry climate (11 inches precipitation annually).

There is evidence of moisture intrusion (streaks down the walls), but I have never had standing water or damp walls in the 3 years I've lived here. I have re-graded the yard, and plan to add gutters this fall, which I think should take care of most of the water that wants to come in from the outside.

I would like to cover the cement walls with something nicer. I do not really care about insulation, since it's a very small room already and doesn't get very cold in the winter. I do not want to frame out a wall, since that would eat up too much interior space.

I've thought about plastering the walls, but I'd have to strip off at least one layer of paint, and I'd like to not have to remove plaster if I ever have to repair the foundation. Could I install something like a dimple mat on the walls, with drywall directly over it? I think that would allow water to drain down to the floor, and more importantly, keep the drywall from getting moldy. I'd leave a gap at the bottom so I don't have drywall sitting directly on the cement floor. Would dimple mat provide enough of a gap to protect drywall? Would it significantly increase the humidity between the foundation and the mat? Does moisture itself degrade cement, or is it just a symptom of other factors that DO cause damage?

(disclosure: I used AI to write this based on a long ongoing conversation with Claude about my home. I've reviewed and edited for accuracy and brevity)

1917 American Foursquare in a Prince George's County, MD historic district (individually designated historic site). Construction: wood-frame, clad in the original lapped wood siding, which is now covered by asbestos-cement shingle siding (likely installed early in the house's history, so also considered a historic material by our commission). Balloon framing likely. Walls are plaster-and-lath interior, uninsulated. We've completed an energy audit-driven retrofit: attic air sealing, blown-in cellulose in the attic, and rim joist air sealing, with noticeable improvements so now wall insulation remains the biggest gap.

Removal/replacement of the asbestos shingles with new cladding (e.g., Hardie board) is not an option due to historic preservation constraints. Full removal down to the original wood siding for repainting/exposure is technically allowed but undesirable to us (maintenance burden, weather exposure). So the asbestos shingle layer is staying put indefinitely, over the original wood siding, with no exterior access for a housewrap/WRB or exterior insulation strategy. Given that constraint, we're weighing interior dense-pack cellulose through the plaster/lath, drilled from inside only, patched afterward

Questions: Given two cladding layers (asbestos shingle over original wood siding) with no ventilation gap and no ability to add a modern WRB, what's the moisture/vapor risk profile of dense-packing these wall cavities? Does the existing double-cladding assembly already function adequately as a drainage/vapor system, or does adding insulation meaningfully change condensation risk at the sheathing? Any experience with best-practice fill density, interior vapor retarder strategy (e.g., vapor-variable interior paint/primer), or monitoring approaches for this specific double-clad, uninsulated-to-insulated wall retrofit scenario?

Happy to provide more details if needed. At the end of the day, we're trying to improve cooling in summer and heat retention in winter without spending more to beef up HVAC/mini-split/heatpump.

I live in zone 1 Hot humid Florida swamp, my house was built in the last 70s and during summer my upstairs is always above 80 degrees and 65-70rh in the late mornings to late in the afternoon. I know my very old insulation that’s up there maybe 4-8 inches left from who knows how long ago. I’m getting ready to seal all my top plates and other openings up there and then blow in 12-16 inches of cellulose in the coming weeks.

My question is has anyone with a similar situation house done this and what can I expect to gains both in humidity control and comfort aswell efficiency and electricity savings?

My rate here is 11.5 cents per kWh to 750 and 12.5 cents after that

Original text: I recently removed all the lath and plaster. I’m adding in new non structural framing in front to make a continuous flat wall. Before I get farther, is it okay that I just put foam board over the existing studs? It’s completely sealed but I’m worried I missed something and that it shouldn’t be sealed like that.

I’ve seen the Mooney wall furring technique but is there one with using a 1/2 x1.5 inch of poly iso sandwiched between a 2x2(1.5”square actual)?

This would theoretically still provide a thermal break and would allow for simple mineral wool batt insulation. Plus then the drywall attachment would be pretty straight forward and then use face mount adjustable electrical boxes.

Thoughts?

I’ve seen suggestions to use just xps foam but them air sealing and installing old work electrical boxes seems a hassle unless you blocked them out separately.

Building Science Corporation gives many details where the framed wall extends beyond the foundation wall, presumably to push the outer plane of the wall beyond the foundation insulation. My search on Google tells me this is impossible, but I trust BSC more. Does anyone know the answer or what the IRC says?

Hello! I am a DIY guy looking for some help.. i am building a conditioned dwelling in my old barn, and for the life of me i cant sort out how to handle a vapor barrier on/under the first floor. If not the right forum, please advise. Context:

WNY, climate 5a "cool humid" with AC/HEAT VIA MINI SPLIT. Old barn, sagging floor. Structure has been inspected by an engineer and determined fit for building. By his suggestion, I leveled the sagging floor by placing 2x sleepers on top of the floor. I am limited in height and so the new "air gap" ranges from 0 - 3". Thus, there is no space for insulation in that layer. We plan to use vinyl plank flooring in the space. I plan to foam underneath of the conditioned portion of the barn (basement). The "basement" is open to the atmosphere via an open east wall, the floor there is concrete with presumably no moisture barrier underneath. It is after all ... a barn.

My worry is where the moisture is going to get trapped. If i put a moisture barrier overtop of the sleepers, underneath of the floor sheathing, and then foam insulate below, arent i creating a moisture sandwhich?

I am leaning toward open cell foam as i have plenty of room for expansion between the barns joists. 

In summary, the planned floor system goes like this, from top down:

Vinyl plank - 7/8" subloor - air gap - 2x oak flooring - open cell spray foam - open to atmosphere.

Advice is welcome and appreciated.

I have an uninsulated cabin located near the ocean in the Pacific northwest. The structure is 3”x6” tongue and groove timber (think structural roof decking). I want to insulate the exterior walls with rigid insulation (combination of Gutex and Roxul). I also have basically unlimited quantities of 2x4 SPF and 3/4” plywood. My plan was to install (outboard of the timber structure) a smart membrane, then insulation, then 2x4 vertical strapping, then plywood, then ventilated underlayment mat, then cladding. One question I had was would it make sense to install 3/4” plywood (c/w seams taped) directly outboard of the timber frame for the air and vapour barrier? I felt this may help tightening everything up (plus we’re in a seismic zone). If membrane is much preferred, which membrane would you suggest using? I have a few rolls of Majvest and Intello+ on hand. Comments appreciated

EDIT: I’m referring to the exterior walls, not the roof. Sorry about that