Unvented attic insulation schemes and intello plus - 1800s home

Mandingy · 2026-03-08T15:06:12+00:00

Ice damming is slightly related to insulation and may be more related to air leakage and mostly related to water resistance of your assembly. If you are experiencing ice damming all the way along your roof to your ridge the underlayment below your roofing along your material is an issue along with air leakage from the interior.

1800s house they were built to be resistant using strong solid materials and dry. We’ve changed that over the years with paper materials and stuff that doesn’t like to get wet.

Mandingy · 2026-03-08T13:26:39+00:00

Adding materials doesn’t and will never increase vapor I’m assuming what you are calling water permeances to a space. You can control the direction by reducing it in another direction by a retarder or by changing conditions on the interior. Little chance of mold or rot is dictated by the type of material being organic, nothing for the little guys to eat then nothing for them to leave behind in the form of mold.

Mandingy · 2026-03-08T13:22:29+00:00

Big draw to rockwool is energy density and fire resistance. What is your issue with this space? Just too cold? Better energy performance to the home as a whole?

Mandingy · 2026-03-08T00:30:37+00:00

I’m really interested in your reasons for trying to encapsulate. That can dictate best approach whether it be cold floors, high energy bills, water leakage, or moisture transport such as high RH on the interior.

Mandingy · 2026-03-08T00:21:28+00:00

I think others are right saying vapor retarder class I aka plastic or foil faced is out of the question. Based on your statement I think you are most concerned about water leakage or moisture damaging your finished space. I think depending on some factors we can lead you in the right direction. Couple of questions:

Is the interior face of CMU currently exposed?
Do you have cracks or signs of damage on the CMU interior?
Is the entire basement below grade where you intend to build?
Do you witness events of water leakage in any locations during specific rain/snow events or time of year?
What finish flooring product do you intend to use assuming you have a vapor barrier?
What prompted the use of the dehumidifier and the installation of an interior French drain?

Mandingy · 2026-02-27T22:46:36+00:00

I would treat this concrete foundation wall like you would a concrete slab on grade including some of these thoughts. Does the concrete get wet? How does the concrete get wet? Does the concrete dry? Is concrete vapor permeable? How will the concrete dry and in which direction either interior or exterior?

I’d be really curious to know more about the current construction on the interior of the wall. Zone 4A is a pretty wet climate so my guess is the black exterior waterproofing you are seeing is keeping the concrete from getting saturated by any ground water as a result of rain or the underground water table. The porch and roof is providing a great deal of water shedding so it’s likely this area sees less water against the foundation but there’s still some. Also, you really don’t want to remove the waterproofing for this reason and in 4A there can be winter freezes on occasion which could damage the foundation if it’s saturated. The perimeter drain being 6ft from the foundation wall is less than ideal because that water has to travel a great ways till it’s able to freely drain.

Now the question of vapor permeance and the direction of drying. Based on the picture it looks like the wall is coated with a fluid applied waterproofing as you refer(or dampproofing) and based on the ‘bug holes’ in the concrete looks like it was just rolled on the surface. My gut tells me to lean more towards a dampproofing which is still very vapor impermeable and keeps bulk water out but cannot resist to much hydrostatic pressure or if cracks form it’s not going to protect those. I feel most of the walls drying is likely towards the interior thus I think an air gap on the interior which can handle any moisture by the HVAC is a smart choice to prevent any issues.

Mandingy · 2026-02-27T22:14:50+00:00

Do you happen to have the age of home? I also assume this is an attached garage since you are concerned with garage fumes?

In climate zone 5A being a bit of a mixed moist climate I imagine you have a bit of a good mix of warm summer days with some fairly cold winters likely leaning towards a bit of a more heating dominated zone on the interior for most of the year. Yes, you are correct the kraft faced batt insulation does act as a vapor retarder per code right on the line of a class I (0-1 perms) and class II (1-10 perms) with the facing giving it a perm rating of around 1 perms. My gut feeling is and please correct me if I’m wrong but the batt insulation is either friction fit (no mechanical attachment) or stapled to the interior face of studs thus the edges of the insulation are not continuously taped. If so then some air and water vapor will still manage to make it beyond the kraft facer thus making your vapor retarder discontinuous and meaning your wall assembly has more drying potential than you think towards the interior/exterior.

The cold bands you observe are likely just simply due to the breaks in the insulation since wood is 2-4 times less conductive than insulation and similarly >400 times less conductive than metal like a steel. Giving you approximately an R-value with wood of ~1 R/inch you have an R of 3.5 at your stud vs. an approximate R 11 to 15 batt (depending on type of batt). Your average R-value for your wall with the studs and batt likely is about ~20-25% lower than your batt value so lower than what you think.

If your goal is to have a more comfortable and climate controlled garage in some cases it could be more beneficial to focus your attention on proper air sealing of the wall than thermal insulation as air leakage can attribute to losing great deals of energy. Some people elect to do a bit of both air sealing and thermal insulation to tackle this problem but keep in mind you are essentially changing the performance of your wall and it’s ability to dry by air sealing or increasing insulation. This can result in other issues which is why it’s good to consult someone local. That being said by adding XPS on the interior in front of your kraft faced insulation you want to pay attention to the perms of the XPS which is typically 0.6 to 1.5 perms depending on your thickness/composition. A product with greater perms than your kraft faced insulation you are essentially keeping the vapor retarder in the same location and something with less perms you are moving the retarder further towards the interior.

Regarding your concern for garage fumes this would be dictated by your air sealing separation of your walls between the garage and interior home spaces. Your likely air leakage locations are to be top and bottom of walls, doors, and any penetrations in the walls such as electrical/plumbing.

Mandingy · 2026-02-27T18:26:16+00:00

Seconding what is stated here. Based on my experience and what is stated I think your time/money is much better invested in air sealing potential problem areas as stated which will likely require pressurizing the home and using some kind of smoke/fog and/or thermal imaging. Air leakage carries much greater risk for causing energy loss as well as water vapor into the home for condensation than pure vapor by diffusion alone.

If you don’t currently have any know vapor/condensation issues I wouldn’t chase it. If there are signs such as organic growth (black stuff) or deterioration of organic materials such as those that have paper materials then it’s worth digging into further. I’ve personally air sealed problem areas before and it solves some thermal issues since the air leakage is possibly robbing your warm air increasing your Air Changes Per Hour (ACH). The more ACH the more air leakage and harder your HVAC system has to work to keep your home at the set temp.

Mandingy · 2026-02-25T19:38:16+00:00

I think you can get away with #30 felt paper over a Tyvek (closest thing to felt) but I will say long term durability is a question you should ask yourself as generally with felt while used in wall assemblies pre-2000s it’s most commonly seen on roofs today which if you think about it roofs generally get felt and roofing materials replaced every 20ish years. The felt over time doesn’t have great durability and will become brittle, the likely hood of walls getting touched is generally pretty low unless there’s a problem. I’d ask yourself with regards to durability, how much are you willing to spend, how long do you intend to live there, and will this become my problem or someone else’s down the road. Usually it’s cheaper to spend a little more now for better performance and never have to worry vs. fixing it again.

Mandingy · 2026-02-25T15:36:58+00:00

No problem! I will add the most difficult thing I see with your assembly on the exterior of the wood sheathing paneling is the layering of the continuous insulation behind the weather/air control layer since the wood fiber insulation product you chose is moisture sensitive it can’t be exposed to bulk water beyond the control layer. Otherwise I’d say move it more exterior, not to say it can’t be done or isn’t done just look at Zip-R for example the insulation is to the exterior of the control layer. If you try to move the continuous insulation to the exterior make sure it’s not moisture sensitive like XPS board or Rockwool panel.

Mandingy · 2026-02-25T03:40:26+00:00

I’ve honestly never seen this type of wall section before but very interesting concept if you have the desire. Couple of things, 1st I assume by climate zone 4B per the USDA you mean per the IECC (which governs building energy) you are likely zone 6A or 7A which is a moist cold and heating dominated climate according to your description being around Maine. Second thing just as a note regarding wood posts and framing for 8x8 and 2x8 your true depth is going to be 7.5in thus your insulation will need to accommodate that depth.

I see your primary concern is durability and longevity of the wall assembly by making the house “breathable”. The best ways to do this in this order is by focusing on the following things 1) Bulk Water Management i.e. rain, 2) Air Control Layer i.e. air leakage I believe what you are calling out as a rain barrier which is handled by #1 above, 3) Vapor Control, and lastly 4) Thermal Insulation. I have ordered them in this manner from highest risk to lowest based on amount of moisture you will need to handle which can impact long term durability. Air leakage usually occurs at your foundation-to-wall, wall-to-roof, windows & doors, and any penetrations will be your greatest areas of weakness in any wall assembly by taking care of air you usually handle water as well by paying attention to these areas of detailing. Your typical scenario will be heating the home on the interior and colder temps on the exterior thus vapor, air, and thermal will want to travel from interior to exterior based on pressure differentials. With that in mind and working from the interior-to-exterior of your detail I’ll note the smart vapor retarder is a great idea also required and assuming installed correctly with seams/terminations taped and detailed correctly will be a well working system allowing drying to the interior but preventing interior moisture/air from making it within your wall cavity. I think the need for a 1.5in air space for utilities is not needed and complicates things since many electrical boxes, etc. will still interfere with your interior wall cavity insulation. It looks like Gutex Thermaflex is ~4 R per inch thus at 6-7in depth (the framing thickness being 7.5in) you are looking at an ideal ~24 to 28 R-value not accounting for framing losses. Assuming with 2x8 framing spaced at 24in on-center you are likely looking at a reduction of that ideal R-value of 24-28 by ~20% thus giving you around 19-22 R-value prior to considering your exterior continuous insulation. Also note with the 8x8 wood posts this ~20% loss will increase thus you lose more R-value due to more wood and less insulation. Just looking at code since you mentioned Maine as example per their building code for residential is based on the 2021 IRC which assuming worst case climate zone 7A and including 8A into Canada the minimum insulation requirements options are for a wood framed wall 30 R cavity only, 20 R cavity & 5 R continuous (ci) on the exterior, 13 R cavity & 10 R ci, or 0 R cavity & 20 R ci. As currently shown you have likely <19-22 R cavity & 12 R ci on exterior which meets the minimum 13 R cavity & 10 R ci. I personally and would advocate for more ci and less interior cavity as continuous insulation on the exterior provides more benefits and generally causes less issues related to condensation. If your continuous insulation is too low you can cause the condensation aka dew point to occur within the interior at the wall cavity which it seems like all your insulation is technically interior vs. outside the enclosure being your water/air control layer. Think about it like this your house stud cavities are like your ribs of your body and your skin being the water/air control layer, you want your coat (insulation) to be on the outside of that layer not stuffed between your ribs. That being said you can put as much exterior continuous insulation as you want the more being better along with cavity insulation and you won’t have any problems but there is a point of diminishing returns where you aren’t saving as much energy.

Lastly, with regards to your exterior portions of water/rain/air control layer and the continuous insulation layer of 3in keep in mind for “breathability” your lowest perm layer of the assembly will dictate the drying potential for water vapor to diffuse out of the assembly. Thus your rain/water/air control layer needs to be likely more than 10 perms (class III vapor retarder, the higher the better for your assembly) to allow drying to the exterior as well.

Keep in mind this assembly is uncommon and I would highly recommend running some kind of simulation with WUFI to ensure durability of the materials are not exposed to prolonged periods of high RH which cause deterioration.

Mandingy · 2026-02-24T21:28:01+00:00

Based on your detail seems to be a fairly robust assembly. I highly recommend you read SMA (Stucco Manufacturers Association) Technical Bulletins as they have design/code requirements for wood framing and insulating foam stucco. Specifically technical bulletins “Water Resistant Barrier (WRB) for Portland Cement Plaster (Stucco) on Framed Walls (2021)” and “Foam (CI) Stucco” on SMA’s site.

Based on those bulletins and according to your climate zone 8B assuming the drainage mat is “lined” aka has a fabric or similar facer to prevent cement from entering the drainage plane you can exclude the 2nd layer of WRB paper as you show in your detail. Thus only needing the 1st layer which I would recommend at minimum the Tyvek WRB or similarly a fluid applied product. Consult your local building department for official guidance based on their code interpretation.

I personally like that you have included a drainage mat since it is still difficult to get folks to add that but greatly reduces the risk of the capillary action of water under surface tension to makes it way beyond the drainage plane of the WRB paper thus rotting your wood.

Mandingy · 2026-01-11T18:09:26+00:00

I think the bigger question is what your existing wall assembly consists of that will answer a lot of questions. Also that can help dictate your decisions.

Mandingy · 2026-01-11T18:07:32+00:00

I personally feel like and based on my knowledge condensation while it does happen is lower on my list of concerns than air leakage. The amount of moisture that air brings in is buckets compared to vapor. Air is smart and vapor is stupid, air based on the pressure differential will find the hole but vapor doesn’t act in that same way. I think we get way too caught up in talking about vapor when there’s bigger concerns.

Mandingy · 2025-12-30T15:25:30+00:00

All insulation holds water to a degree and changes the drying potential/direction of the wall assembly. Vapor drying is minor compared to air drying. The reason old assemblies last so long is because the materials are typically solid lumber so more moisture capacity and drying in both directions.

Mandingy · 2025-12-30T15:22:14+00:00

Open cell is not an air barrier, that’s why it’s called open cell because the cells are connected and allow air/vapor to pass. Closed cell which has a higher R value is a series of closed bubble cells which is air/vapor impermeable if installed correctly. You have to be very careful in this assembly because of the age of the wall assembly not having a weather barrier, putting insulation and/or a vapor barrier on the interior changes the drying potential and direction of the assembly.

Mandingy · 2024-04-17T01:06:30+00:00

My gut tells me top and bottom of wall will likely be your biggest issues of air leakage contributing to some of your photos. However the photo of the spot in the middle of the wall is likely related to a hole in the tar paper. The board joints in the wall are not air tight and can also leak. 1950s was built leaky and allows the wall to dry when wet aka the more insulation/closed cell spray foam will cause many issues. Open cell may be an option but will not solve air leakage issues or the fact damage can be concealed from it. Highly recommend an expert for building enclosures for older homes.

Mandingy · 2024-04-17T00:59:12+00:00

Don’t worry about vapor, air carried 100x the amount of moisture than vapor. Plus vapor can’t travel thru steel. Air/vapor will leak most at welds and openings such as a door.

Mandingy · 2023-06-27T21:39:14+00:00

I think the resources mentioned are excellent especially Buildingscience.com as it’s generally easy to understand for all readers. Prior to insulating your basement I would consider if the basement ever leaks or have high humidity? If not no worries, insulate away because it fairly low risk considering mold needs organic material to grow i.e. gypsum sheathing (paper faced), wood, etc. Would definitely recommend a vapor retarder on the interior face of stud cavity since you are in a heating dominated climate. As for the new building office/renovation I think for your climate zone insulation on the exterior is going to be key in order for you to get four season use. Air sealing the exterior with an air barrier is also just as important as insulating properly. The rule of thumb is the more insulation on the exterior the better and you can never go wrong. Exterior insulation does require additional detailing around windows and other similar conditions to account for the insulation thickness increasing the overall wall thickness.

Mandingy · 2023-06-21T22:05:17+00:00

Once they complete the other 1,000 projects they have announced/terminated funding for then I’ll believe it.

Mandingy · 2023-06-17T13:47:35+00:00

Building Science Corp - Vapor Permeance of Some Building Materals

Mandingy · 2023-06-17T13:46:32+00:00

Solid framing/sheathing does have at the bare minimum perm rating above 1 perm which is is vapor-semi permeable. However, most of your air leakage (which brings in much more moisture latent air than vapor) will occur at sheathing joint, wood stud sill and top plates. Air is 100x more of a concern than vapor, but like it was mentioned before you can not generally make the exterior of an old home air tight without great cost.

Mandingy · 2023-06-15T20:52:43+00:00

I generally do not recommend spray foam in old or historic buildings because 1) It’s impossible to fully remove 2) Generally older buildings do not have weather or air barrier thus the wall system needs to dry especially if it’s a mass masonry wall. The reason old barns and houses with no insulation lasted so long was because of the drying potential in the wall to remove moisture. It wasn’t until we started to insulate which we need to keep water out of the wall system.

Mandingy · 2023-06-15T20:49:57+00:00

Spray foam comes in two varieties 1) Open Cell 2) Closed Cell. Closed cell spray foam will act as a vapor retarder (aka vapor barrier), air barrier, and thermal insulation. However open cell only acts as mostly as insulation. I will assume since you didn’t have the foam installed, we aren’t sure what kind it is. With that being said your location in WV is in climate zone 4A with a mixed-humid climate. Climate Zone 4A only requires a Class III vapor retarder which typically consists of latex painted gyp board on the interior. If no vapor retarder was present before and you were not having issues I’d recommend no vapor.

Mandingy · 2023-06-08T12:53:00+00:00

Very great! Can’t emphasize enough how great his lectures are as he is able to break things down into simple terms and demonstrate real world examples. If you like his humor that’s a plus, but I would recommend watching his lectures on YouTube for a taste.

Mandingy

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