Vapor barrier facing in transition room between heated & not areas?

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AcidWater

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Between the back wall of my garage and the heated basement area there is a small workshop room that does not have duct work (but the main duct runs thru the overhead, so some heat from that).

Both the garage & this room are damp. Block wall B is below grade & moisture comes from it.

This room is constructed from 2x4 frame & gypsum wallboard.
Wall "F" between the garage has fiberglass insulation with a foil vapor barrier, and the foil is on the "room" side.
Don't know what is in walls "w" if any until I cut a hole.
The overhead of the room also has this foil faced insulation, with the foil "down" and the fiberglass between the foil and the floor above.

Wondering if I should remove the vapor barrier to allow this room to "breath." Or put it the other way around.

B heated
B basement
B area
B wwwwwwww
B w....ROOM...w
B w.................door
BFFFF..door.b
B...................b
B......GAR-....b
B......AGE.....b
B...................b
B...................b
 

Dana

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I can't quite visualize your ASCII drawing, but as I understand it the insulated wall in question is between the unheated workroom and the garage (?), and that the foundation walls are NOT insulated?

Insulating the foundation walls appropriately for your climate zone and ventilating the workshop space with air from the fully conditioned basement zone would control the humidity in the workshop room.

Location and local climate matters. If you're in US climate zone 3 or higher it's appropriate to leave the foil facers on the room side of the room|garage partition, but in zones 1A & 2A it's worth flipping them around, with the foil on the garage side. If it's climate zone 1B or 2B it hardly matters unless you're air-conditioning the workshop to some ridiculously low temperature in summer.

DOE%20climate%20zone%20map.preview.jpg


Methods for insulating the foundation walls without creating a mold farm is also climate specific- where are you?

A low-wattage bath fan moving air from the conditioned basement to the room near the ceiling, with a small return grille near the floor works for ventilating the space- a continuous 20 cfm is enough. Bottom of the line 50cfm bath fans are really cheap to buy and do the trick but have low efficiency motors that gobble significant power when used continuously. The top of the line would be something like a Panasonic FV-05-11VKS1, which uses about 3 watts when set to it's lowest speed.
 

AcidWater

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>as I understand it the insulated wall in question is between the unheated workroom and the garage (?),
yes
>and that the foundation walls are NOT insulated?
The garage portion of BBBB is block.
In the room there is gypsum and I think 2x4 space -- don't know if they put fiberglass in there or not. Need to cut a hole & see.

I'm in Zone 4A. I could cut a vent into the main duct and blow into the room from the ceiling -- but I hesitate to do that since I might unbalance the flow to the house. The room is kind of a dead air insulation area between the heated area & the garage. But if I create an "exit" vent into the house, it will blow moist & possibly moldy air into the house. If I create the exit vent into the garage, then I'm paying $$$ to heat or air condition the garage.

Forced hot air HVAC, but the downstairs has no vents except one in the unfinished basement area. The rec room to the right of the garage (not illustrated in the ASCII) has baseboard electric & a wood stove. Furnace is in upper left corner of my ASCII diagram. The main duct runs thru the ROOM & garage directly adjacent to interior block wall "bbbbbbb" in a chase made from gypsum wallboard with a piece of 3/4" white "popcorn" insulation board inside. I would like to insulate that chase with blown-in expanding foam but hesitate to prevent access if ever needed.

I've been reading this about "layering" the exterior wall for different climates vapor issues:
https://buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers
But it seems to cover only above-grade construction.

I think wall "BBBB" is just brick facing on block. Don't know if the brick is mortared directly to the block or if they left a drainage space. Did they use exterior foam insulation in 1966? I guess I should try to measure the overall thickness.

Looking at the house blueprint, I think this wall was intended to be mostly above grade, but they decided to build a retaining wall next to the driveway (leftwards of wall BBBB) & put in sandy fill to level out the front yard in front of the house on the garage side. I dug 5 bricks down and don't see any tar on the outside for waterproofing. So it might have been built as an above-grade wall & then they buried it.

I suppose that the best dampness solution is a French drain on the outside of wall BBBB but that will have to wait some months. That might be the only way to keep the dead air in the closed garage above the dew point.

Then maybe tear down wall "BFFFF..door.b" and build a solid (no air leaks) & double-thick insulated wall. Then turn ROOM into "completely conditioned" space.
 

Dana

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In zone 4A it doesn't matter which side of the assembly the vapor barrier is on, as long as there aren't vapor barriers on both sides. (Kraft facers on both sides would be fine, but not foil or polyethylene.) Vapor barriers aren't even needed at all, but if you're going to have one, putting it on the conditioned space "warm in winter" side is preferred. With any new construction or additions in your climate it's better to avoid true vapor barriers such as foil or polyethylene in wall assemblies, and use standard interior latex paint as the interior side vapor retarder.

It's also good practice to build out the siding as a "rainscreen", with at least 1/4" of air between the exterior sheathing and siding to promote rapid drying of the sheathing. (The ~1" air space of a brick cavity wall behaves as a rainscreen too, but you don't need it to be that deep for most siding types.) Vinyl siding is inherently back ventilated, and doesn't need a rainscreen for the sheathing to dry rapidly.

Very few homes in 1966 were built with foundation insulation of any type, and fewer still had exterior side rigid foam. Some brick clad concrete block homes of that era were cavity walls, many were not. In your case it doesn't much matter if it's a cavity wall or not.

If you want to insulate the foundation from the interior side, using 3/4" foil or plastic faced EPS (pretty cheap at box store) trapped to the foundation wall with a 2x4/R13 (kraft faced or unfaced) works fine from a moisture point of view year-round, both above-grade and below, and will beat code minimum performance (= R10 continuous, or 2x4/R13, which has potential moisture issues without the foam.) If you go this route, put a layer of the EPS under the bottom plates of the studwalls as a thermal & capillary break. The wall foam keeps the average temperature of the exterior side of the fiber insulation and studs on the above grade portion above the indoor wintertime dew point, thus avoiding wintertime moisture accumulation. The wall foam also impedes ground water migration (as either water vapor or liquid) from getting into the studwall too. The studwall dries toward the interior, all seasons.

An all-foam solution would be either 2.5" of EPS, or 2" of polyiso clamped to the foundation with 1x4 furring through-screwed to the foundation with 4" Tapcons. In many locations you can find reclaimed 2" fiber faced roofing polyiso for under $15/sheet, making this cheaper than a foam + studwall solution. With polyiso you need to keep the unfaced bottom edge off the slab, since (unlike EPS) it can slowly wick and store moisture, losing some performance. Even a half-inch of air is fine (or slip in some EPS and let it rest on the EPS, which doesn't wick water.)

The air in the garage is always above the dew point (of the air in the garage). The foundation walls and slab are often below the dew point of the OUTDOOR air in summer, and insulating the foundation walls won't change that, neither will adding a French drain. But the drain may limit the amount of bulk water that comes in contact with the foundation. Does the interior side have a history of water intrusion (real leaks of liquid) anywhere, or excessive efflorescence? Either of those conditions would be an argument for a French drain. If there is only a modest amount of efflorescence and it's only in the lower foot or so of wall digging in the drain isn't on the critical list before moving forward on insulating the basement.

The entrained air in the soil is almost always at or near 100% relative humidity at whatever temperature the soil happens to be. It's fine if the foundation is damp- you just want to limit the amount of moisture that gets into the living space. The wall-foam takes care of that, as long as you tape the seams and seal the top & bottom edges to the foundation with polyurethane caulk (not the cheap stuff) or can-foam to prevent slow convection of that 100% RH air in the micro-space between the foam & foundation into the room.

Putting a small register on the supply duct is fine, as long as you provide a return path such as a jump-duct or wall grille to the rest of the basement. It's better if you add a short length of hard-piped duct with a balancing vane between the register grille and main duct so that you can tweak the flow up or down, which may need seasonal tweaking anyway. Below grade rooms never balance perfectly with above grade rooms since their heating & air conditioning loads don't vary in the same proportion with changes in outdoor temperature.
 

AcidWater

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>Some brick clad concrete block homes of that era were cavity walls, many were not. In your case it doesn't much matter if it's a cavity wall or not.
>
Does "cavity wall" mean having an air gap between the brick & block?
Would the below grade block be solid or hollow with two cavities?

> But the drain may limit the amount of bulk water that comes in contact with the foundation. Does the interior side have a history of water intrusion (real leaks of liquid) anywhere, or excessive efflorescence? Either of those conditions would be an argument for a French drain. If there is only a modest amount of efflorescence and it's only in the lower foot or so of wall digging in the drain isn't on the critical list before moving forward on insulating the basement.
>

Doesn't sand fill hold a lot of water? The drain path is the gap between the corner of the house & the edge of the retaining wall. The mortar connecting it to the house is gone, and the wall bowed out a bit -- I shoved garden weed cloth in the gap to minimize loss of dirt.

I think there are tortuous paths thru the garage block wall that water comes through. After an extremely heavy rain (like a hurricane dumping inches in an hour) I have seen "pissers" in the garage wall. That is why I used Drylock in 1996. Since then it has remained adhered pretty well, mostly loose in the grout lines & very bottom near the floor. I don't see efflorescence in the failed areas. So I hesitate to put foam/fiberglass against the wall, and why I think a French Drain would be needed if I did insulate the garage wall. But I would have to add gypsum board on top of a stud wall for fire retardancy, and to keep fiberglass from getting damaged & so I can hang tools on that wall.

The other day it rained & the temp was 65-70. I came into the closed garage and touched an extension cord that was suspended in mid air and it was wet with a little condensation.
 

Dana

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Clean sand drains water fairly well, but not nearly as well as washed 3/4" screenings.

77%RH @ 64F has a dew point of 57F, which is not a very alarming number. That may even be below be the outdoor air's dew point when you took those measurements. Raise that garage air to a comfortable 72% and it's RH would be 59%, still a comfortable and generally healthy humidity level for humans.

When it's 70F and raining it's usually the case that the dew point is north of 65F, so if the garage was 64F there would indeed be condensation forming on 64F surfaces.
 
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AcidWater

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I want to tear down the old drywall on the back wall "BFFFF..door.b"
and replace it with the type used in bathrooms -- concrete board ?
because I think the gypsum holds a lot of moisture.
So that would be a vapor barrier, so the insulation should not be faced at all ?
 

Dana

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Fiber cement board & tile-backers are about as moisture retentive as drywall, and neither are vapor barriers. They are quite vapor open (30+ perms) unless coated with a vapor barrier type material such as foil or plastic facers. Cement board doesn't usually have paper facers for better paint adhesion the way wallboard does, and without the paper facer it is more moisture tolerant of bulk moisture. But swapping it out won't significantly alter the relative humidity in the space. Green board wallboard has heavier wax-infused paper backer to make it somewhat more moisture tolerant than generic wallboard, but it too is quite vapor open to water vapor diffusion.

If the partition wall between the workroom and garage is insulated, there is nothing to be gained (other than some sound abatement) by insulating between the workroom and the fully conditioned basement. Can I assume above the workroom there is fully conditioned space(?). Unless there are special needs for soundproofing or to maintain dramatically different temperature zones, insulation only goes on the exterior walls which make up the thermal & pressure boundary of the living space.

Since garages leak air like crazy and aren't heated or air conditioned, the partition wall to the garage should be treated as an exterior wall and thus insulated & air sealed. Since the work room and fully heated basement are both nominally inside the thermal & pressure boundary of the house, that partition wall would NOT normally be insulated.

In US climate zone 4A adding true vapor barriers such as foil or sheet polyethylene to walls tends to create more problems than they solve (even on exterior walls) , and are best avoided except for special purpose rooms such as a pool room or hot-tub room. Air tightness is far more important for controlling moisture migration through walls than water vapor diffusion. It's fine to use kraft faced insulation in your climate. A kraft facer is a "smart" vapor retarder that becomes vapor open if the moisture levels in the wall reach mold-support levels. It doesn't matter a whole lot which side of the assembly the facer goes, but if it's just as easy to install it one way vs. another, it goes on the "warm in winter" side of the assembly since yours is a heating dominated climate, with more heating degree-days than cooling degree-days. But from a practical point of view that's FAR less important than making the exterior walls as air tight as possible. The "contractor rolls" of R11 or R13 kraft faced fiberglass are super cheap, often cheaper than unfaced batts, and fine to use for the workroom <==> garage partition wall or other exterior walls.
 
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