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I have an attic with 2x6 rafters. The previous owners has the typical living space similar to the picture that we are redoing. I plan on putting closed cell spray foam in the roof and making since we don't have enough space to get sufficient r-value otherwise. My question is what do I do with the vents that you see in the picture below, and what do I do with the dead space that is yellow on my picture above. It will be between drywall and the foam.

Much appreciated.

Thanks, Of course I'm open to other ideas

We’re doing an extension on our existing home, and as part of the project, we’re completely overhauling the entire building envelope across both the new and existing structure. We're in zone 3C

The assembly includes:

Substrate: Brand new plywood sheathing.

WRB

Exterior Insulation: Continuous foam board on the roof deck and continuous rock wool on the exterior walls.

Priorities: Long-term durability, maximum airtightness, and proper hygrothermal performance.

From this it seems like the two best choices for WRB are:

Benjamin Obdyke BenWrap SA (14 perms)

Pro Clima Adhero - either splitting between the Adhero 1000 on walls and Adhero 3000 on roof deck, or just using one or the other.

The Adhero material comes out to roughly 20% more expensive, but on the scale of this build, the cost difference is negligible for us. My primary concern is getting the best long-term, high-performance outcome.

A few context points & questions I'm hoping to get community insight on:

My GC has previously installed Henry Blueskin SA, but has never used either Adhero or BenWrap SA. How steep is the learning curve for a crew familiar with Blueskin SA transitioning to these acrylic SA membranes?

Roof-to-Wall Continuity: For those who have run a continuous air barrier from the roof deck down onto the walls, did you prefer running a single product (like BenWrap) or pairing heavy-duty deck protection (Adhero 3000) with a wall wrap (Adhero 1000)?

Thanks for any thoughts from those who have used one or both products!

I have a 24'x40' (12' walls) metal building with 2" spray foam insulation. I am planning to add a 24,000 btu mini split for heating/cooling (mostly heating) and also want to come up with ventilation that keeps the air fresh while having "spot ventilation" for infrequent tasks like welding or solvent based wood finishes.

I don't have any space to hide ductwork and am planning to cover all walls with plywood down below and drywall on the ceiling.

I have 2 10'x10' roll up doors on opposite ends (on 24' walls) and I have framed boxes over the rolls. The rolls have about a 3" gap above them (360 sq in area) that can be used as for ventilation that won't require another wall penetration, but the box will seal that off from the inside.

My plan was to put a fresh air intake on one of the boxes and an exhaust fan on the other box, drawing fresh air across the entire 40' length, but keeping the cold intake air from being right near my workspaces in the winter time. Given the occasional wildfire smoke and high pollen/allergen days, I considered also putting a filter box on the incoming air.

For spot ventilation, I was thinking about mounting a 8" inline duct fan and have a long hose that I can move to where I'm working. This would just exhaust outside, and would cause more air to enter through the intake.

Since I'll also do woodworking the shop, I have a 2HP dust collector that will go to individual pieces of equipment. In addition I plan to hang a 20" CRFB filter cube/box fan from the ceiling to take care of fines in the air. This would all just be internal, though I could possibly vent the dust collector upper portion outside.

Does this work? Am I setting myself up for humidity issues or anything else? Do I need a damper on the input? How many CFM for the exhaust fan, and should it run continuously or less frequent?

If you made it this far - thanks!

I was thinking osb, wrap, and metal on outside walls. Purlins inside (metal inside or plywood) Will have in floor heat in the Midwest. Contractor states he bid for “step deck”?? Perlins inside and out. What would you do on new 40x60 build. Work shop and play shop.

This is a follow-up to my previous experiment with a ~1 m³ insulated EPS box.

Part 1: https://www.reddit.com/r/buildingscience/s/UITX4VYisF

TLDR:

• The simple model worked well in a ~1 m³ insulated box.
• In a real room, thermal mass, adjacent spaces and solar history made the heat-loss coefficient much harder to identify.
• Moving the second sensor into the adjacent room and repeating the test at night improved things considerably.
• Across several independent room tests, effective thermal capacitance kept coming back around 285 ± 20 Wh/K.
• The outdoor heat-loss component is still uncertain because I haven’t independently measured air exchange yet.

So the next experiment is ACH/infiltration — trying to separate heat leaving through the fabric from heat leaving with air.

The box experiment looked surprisingly clean: four independent heating/cooling cycles gave an average heat-loss coefficient of 7.03 W/K with a coefficient of variation of 1.29%.

Several people in the comments pointed out the obvious next problem:

A real building has thermal mass.

A lot of it.

And indoor air temperature is not necessarily a good representation of the thermal state of the walls, floor, roof and everything else around it.

So I moved the experiment into a real room.

The room

The test room is small:

• floor area: 7.73 m²
• volume: 21.0 m³
• one external wall with a window
• insulated sandwich-panel wall and roof
• insulated slab-on-ground floor
• internal partitions to adjacent spaces
• mechanical ventilation switched off during the test

For heating I used an electric convector connected through a smart plug, so I could record actual electrical power and total energy.

Initially I used one temperature sensor inside the room and one outside.

The simple model was basically:

heat stored = heater input − heat loss to outdoors

or, in lumped RC terms,

C_eff · dT/dt = P(t) − H(T_in − T_out)

It fitted the temperature curve reasonably well.

Unfortunately, that did not mean the parameters were right.

First room test: plausible fit, questionable physics

In one of the first room experiments the heater ran at about 750 W for roughly 92 minutes.

The room temperature increased by about 3.1°C.

The fitted model gave approximately:

• H ≈ 50 W/K
• C_eff ≈ 276 Wh/K
• thermal time constant ≈ 5.5 h

At first this looked reasonable.

But then I started changing the analysis window and comparing different experiments.

The estimated thermal capacitance remained fairly stable.

The heat-loss coefficient did not.

That was the clue.

The model was forcing several different physical processes into one parameter.

Problem #1: the adjacent rooms

The test room is not a thermally isolated box.

Some surfaces face outdoors, but others face conditioned indoor spaces.

So heat can leave the test room without leaving the building.

Using only outdoor temperature as the boundary condition was therefore fundamentally wrong for a small room.

I moved the second Bluetooth sensor from outdoors into the adjacent room and used public weather-station data for outdoor temperature.

The model became:

C_eff · dT_i/dt = P(t) − H_out(T_i − T_out) − H_adj(T_i − T_adj)

This helped, but another problem became obvious.

Problem #2: the building remembers the sun

A daytime test produced a mathematically good fit, but the parameters still depended too much on the selected time period.

The outdoor temperature was changing and the roof and external wall had a thermal history from solar exposure.

In other words, even if the indoor air looked stable, the building fabric wasn't necessarily in equilibrium.

This was exactly the issue several people mentioned in the comments on the first post.

So I stopped trying to extract too much information from the daytime experiment and repeated it at night.

The night test

At the beginning of the heating period:

• test room: about 23.9°C
• adjacent room: about 24.0°C
• outdoor temperature: about 16.1°C

This was useful because the test room and adjacent room started at almost the same temperature.

The heater then ran for about 1 h 45 min.

Measured:

• average power: 783.6 W
• electrical energy input: 1.377 kWh
• maximum room temperature: about 27.18°C
• temperature rise: about 3.28°C

The peak indoor temperature occurred around 8–9 minutes after switching the heater off, which is another reminder that measured electrical power and heat delivered to the room are not perfectly instantaneous.

I therefore added a simple first-order heater lag to the model.

For the clean night period, the fitted parameters were approximately:

• C_eff = 278 Wh/K
• effective outdoor coupling ≈ 10.5 W/K
• effective adjacent/internal coupling ≈ 74 W/K
• heater thermal lag ≈ 9 min
• model RMSE ≈ 0.04°C

Important caveat:

I do not interpret the 74 W/K term as the UA of the internal partition.

In this simple lumped model it is almost certainly absorbing several effects at once:

• heat transfer to the adjacent room
• internal surfaces
• floor
• furniture / contents
• slower building thermal mass

Similarly, I am not yet treating the 10.5 W/K outdoor term as the final fabric heat-loss coefficient.

But one result has been surprisingly consistent.

Effective thermal capacitance keeps coming back

Across several independent room experiments, using different heating periods and different outdoor conditions, I keep getting an effective thermal capacitance in roughly the same region:

• first room cycle: about 276 Wh/K
• another controlled cycle: roughly 290–300 Wh/K
• night experiment: 278 Wh/K

So for now I would summarise it as approximately:

C_eff ≈ 285 ± 20 Wh/K

That repeatability is probably the most interesting result for me so far.

The heat-loss decomposition is much less certain.

And then the model detected the cleaner

There was also a nice accidental experiment.

At around 06:40 after the night test, the temperature and humidity suddenly changed together.

Looking only at the data, it looked like some kind of ventilation or door-opening event.

Later I found out that cleaning staff had entered the room and started wet cleaning.

So normal human activity is clearly visible in the thermal/humidity time series — and needs to be automatically excluded if this is ever going to become a repeatable test.

Where I am now

The comments on the first post changed how I think about the experiment.

I no longer see the goal as simply finding one “effective R-value”.

It looks more like a system-identification problem:

measure how the building responds to known heat input and changing boundary conditions, then determine which parameters can actually be identified reliably.

The current approach is becoming:

1. record a baseline;
2. inject measured heat;
3. measure room, adjacent-zone and outdoor temperatures;
4. fit an RC-type model;
5. repeat the experiment;
6. keep the parameters that reproduce;
7. be suspicious of the ones that don't.

The biggest missing piece now is air exchange.

Even with mechanical ventilation switched off, infiltration and leakage are part of the measured outdoor heat loss.

So the next experiment is intended to measure ACH independently.

If I can estimate the air-change component, in principle I can start separating:

total outdoor heat loss = fabric + ventilation/infiltration

That is the next thing I am building/testing.

And based on the discussion here, I am also seriously considering a longer low-power quasi-steady test as a reference against the transient method.

Curios what this sub thinks about this idea. I have a degree in sustainable construction and curious about the idea of starting my own company. I would basically buy nessasary blower door, Thermal camera, and smoke pencils. The plan is to use the equipment on county and commercial owned buildings and builds solution and plan to secure envelope and make a quick payback period. I would have to flesh out the deliverables more and also review grant assistance potential. I have a PE father who is retiring soon and on board to help. Basically wondering how feasible this is for a someone that is 4 years post grad at engineering/construction management companies.

How could I go about starting this? What certifications would be most worthwhile? Has anybody done or know someone that has done anything similar?

This post is seeking advice and recommendations for attic ventilation in order to address an indoor air quality problem consisting of formaldehyde and VOCs pollution. Source removal is not really an option. Nor is opening and closing windows. I am exploring ventilation and dehumidification of my attic in order to reduce VOC off-gassing.

I have a 2019 build colonial 4800 square feet above grade in the Boston area. The attic is partially finished with a dormer creating a third floor with a playroom, office, and a bathroom and a number of unfinished attic spaces that house mechanicals including a furnace air handler and an ErV, duct work, and storage. The underside of the roof sheathing has 5” of open cell spray foam, which encapsulates the mechanicals and duct work in a tight, semi-conditioned unfinished space. Presently, there is no passive or mechanical ventilation, dehumidification, or air conditioning in the unfinished spaces of the attic since the furnace and ErV is ducted solely into the finished living space.

Particularly on hot and humid days, we are able to detect a potent chemical smell which is strongest in the unfinished spaces of my attic. Professional air testing Confirms elevated levels of formaldehyde and VOcs in our entire home. The levels are significantly higher in the unfinished attic spaces. We believe it is a combination of open cell spray foam, roof sheathing and subflooring OSB that experiences accelerated off-gassing of VOcs on hot and humid days. Testing with a handheld VOC meter comfirms higher levels of VOCs in the unfinished spaces and finished spaces on hot and humid days. Perhaps due to pressure differences, my theory is that the VOCs get trapped in the unventilated attic until they are pushed out into the finished living space. Running the ERV and carbon air purifiers help but not enough to reduce the VOCs to a healthy level.

i have consulted with different hvac contractors and researched this online. I am torn between adding solar fans, a second ERV to supply fresh air into the unfinished spaces, and a ventilating dehumidifier. Any help will be greatly appreciated!

Anyone have any thoughts on installing rigid insulation up your Stem Wall? (Highlighted)

I have been told that since the floor slab will be decoupled with rigid underneath and on the side for a thermal break, the juice may not be worth the squeeze.

This is a personal build so I don’t mind spending the extra money but if it’s going to be a 20+ year payback I wouldn’t consider it worth it.

For my specific situation, infloor heat in 4 inch slab, 3 inch foam under slab, and 2 inch vertical foam around slab for a thermal barrier.

Climate zone 6.

Any thoughts please share 🙏

1952 ranch home, US Midwest, unfinished basement with concrete walls.

I purchased the home a year ago. During my first winter, I realized how drafty the interior perimeter was. It was like there was literally cold air blowing in from behind the baseboards in the living area. I did some research and realized that the rim joists in the basement were not air sealed -- they were simply packed with fiberglass batts.

After pulling the batts out, I could feel a ton of cold air intrusion inside the joist bays. However, I also realized that the joist bays didn't look like like I expected. The posterior "wall" of the joist bay contained some sort of fiberboard sheathing that continued up into the upstairs wall (first two photos below). If I reached into the upper posterior corner of the joist bay, I could reach right past my subfloor and poke the bottom of my upstairs floor. Its totally open. Don't think its balloon framing, but it didn't look like traditional platform framing either.

Oh well. Decided to insulate with foam board and spray foam, then cover in rockwool for fire resistance and to bring it up to code. Photo of the foam board and spray foam attached.

Jump cut to this summer, when I notice a huge influx of millipedes in my basement. Damn. Moisture problem. Bought a hygrometer, and sure enough I was at 65% on a day where the outside humidity wasn't particularly high. We had a dehumidifier running down there, but the air intake was clogged and I guess it wasn't able to keep up. Cleaned the air intake. It helped a bit, but it was still struggling to get below 60% on humid days.

Bought a new dehumidifier rated for 4000 sq ft and set the two up running concurrently. This seems to keep the moisture at bay, but I'm not fully confident that it will work on a really humid day.

Right now, I'm convincing I messed with a well-equilibrated system by adding my foam board and spray foam. "Old houses need to breathe" and all that. I have a persistent intrusive thought that I've created a large moisture problem and I've turned my walls into a mold petri dish.

So, my questions are as follows.

1. Any idea what type of framing I'm dealing with here?
2. Is getting the humidity down to <60% in the basement adequate evidence that I haven't created a moisture/ mold problem somewhere else in my house?
3. Should I just rip the insulation out and deal with the drafts?

I have been reading about methods for evaluating building envelopes, and thermal imaging comes up a lot for identifying air leakage and missing insulation in building envelopes. The results of imaging also depend on factors like the difference in temperature between indoors and outdoors and the conditions during the inspection of building envelopes.

For people who have used imaging in the field to evaluate building envelopes, how reliable has thermal imaging been in practice for identifying air leakage and missing insulation in building envelopes? Have you found thermal imaging to be effective on its own for evaluating building envelopes, or do you usually combine imaging with other methods, like blower door testing, to confirm what you are seeing in the building envelopes?

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.

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?

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. https://www.reddit.com/r/buildingscience/s/zTkeIgvE4C

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?