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Basement remodel: basic newbie questions

hanzb | Posted in GBA Pro Help on

Hello. I am redoing a “basement” in a Californian split level out in zone 5 PA. I was hoping to ask for some advise. The basics: the “basement” is open to the upstairs. Built into a hill. Half above half below grade. The northwest-facing walls are 100% to 50% exposed with nice stone work and long horizontal windows. The southeast walls are below grade. the floor is a nice cement slab with a fairly open 1/4 inch cove joint. Radon mitigation installed. Radiant heat (water pumped) in the cement floor.

When we moved in 6 months ago it had wood paneling with horizontal furrow strips nailed into the cinderblock – touching, and fiberglass paper backed insulation directly against dryloc – like painted cinderblock. Suffice to say the entire joists and walls were mold covered and all the horizontal furrow strips were either wet or dry rot. The garage was open to the basement (via the ceiling joist – right above a furnace in a garage – so a spectacular a condensation point).

The garage joists spaced have been closed between the garage and “basement”. I’ve torn down everything to the cinderblock walls and I’ve sanded the wall, removed old fiberglass sill plate insulation.

im now in an observation phase. So far we’ve had 5 down pours. One causes flooding of a down hill creek a block away by 8 feet. The others less so. I’ve seen no water entry. I clogged the down spouts for one massive rain and saw damp cinderblock on the south west corner of the space where I clogged it. Still no water into the space itself. Cinderblock dried two days with dehumidifier on.

that back corner I plan on keeping as a unfinished 18 x 6 foot walk in storage area anyway so I will not be insulating other than the ground level rim joist areas

im thinking of Doing a mixture of insulation. There are some places because of where door frames were made originally that I cannot fit 6 inch wall. In those areas (1/2 north wall and west wall) I’d like to do 2 inches of foam core with vertical furrow strips And drywall. And other areas I’d to do what I think is recommended close cell spray foam and two by fours 1 inch off the wall.

This plan would leave half my under grade wall as breath cinderblock and the rest of the “basement” above grade as foam core or spray foam.

I have ordered and will use the rubber sill sealers below the framing floor plate treated wood since the cove joints are somewhat open.

Is this reasonable? Is this a set up for weird flash points because of three different insulation techniques?

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  1. Expert Member
    NICK KEENAN | | #1

    Some general comments and then some specific questions. You want the entire exterior of the house to have layers that keep the weather out, prevent the passage of moisture, prevent the infiltration of air and provide insulation. This seems like a simple concept but a lot of houses have issues with it. From your description of the wall between the garage and the basement it sounds like your house had this issue. Joe Lstiburek likes to say you should be able to take a plan of the house and draw the building envelope without ever lifting your pencil from the paper.

    There are lots of ways that moisture can get into basements. It sounds like it was getting in as vapor. You can think of the soil outside your basement as an inexhaustible source of moisture and an infinite heat sink. You need a vapor barrier on the basement walls to keep moisture from the soil from wicking into your basement. Your basement walls also need to be vapor and air sealed to the interior and insulated to keep warm, moist interior air from contacting the "coolth" of the basement walls and causing condensation. As you've learned, fiberglass has no place in basements, it allows vapor to permeate it and condensation follows.

    Specific questions:
    You write: "This plan would leave half my under grade wall as breath cinderblock." I don't understand what that means.

    "That back corner I plan on keeping as a unfinished 18 x 6 foot walk in storage area anyway so I will not be insulating other than the ground level rim joist areas." The entire exterior of the house needs to be insulated. Having part of the house insulated and part not is like having half of the roof shingled and half not.

    "I have ordered and will use the rubber sill sealers below the framing floor plate treated wood since the cove joints are somewhat open." I'm not sure what this means. Is this the interior walls? Again, think of drawing the envelope without ever lifting your pencil. Is it continuous?

  2. hanzb | | #2

    Thank you for the Advice.
    - I will need to insulated storage area against the fully below grade cinderblock walls. Will do this with foam core and fire proofing or spray foam and fireproof paint. My question was with radiant floor heat in this storage area as well as the entire below grade floor, if I were to treat this space as a “cut out” in my insulation plan and have my continuous insulation/vapor barrier ignore it. The cinder block in this area gets semi-moist with heavy rains but does not leak. My thought was if i leave this without a barrier and uninsulated (and since i ground off all the drylock paint) the radiant floor along with a dehumidifier in this space would be a better plan then trying to achieve vapor barrier on a section of cinderblock that moistens). I would isolate this area from the rest of the home (spray foam rim joist and ceiling beam, fiberglass insulation the interior wall (which will be open - dry wall only on the living interior side of this all). Hence This area becomes a little cinderblock box on the edge of the house that gets sort of “active” drying management instead of “passive”?

    - I will need to insulate the interior walls facing the garage. I will do this with spray insulation to be continuous. That makes sense and i have planned for this.

    - the rubber seal is typically used at the rim joist. However since i have a flexible cove joint that leaks cool air (and I think did lead to some wood rot as well) I used this sill seal under the framing plates around the entire interior.

    - the garage attached to the first floor were i had the vapor moisture entering the firsts floor I have sealed off with foam and foam core above and around the joists.

    - That leave the question of the best options for the garage ceiling itself? Garage is cinderblock not insulated. The previous own has fiberglass batting with reflective metal foil, enclosed in drywall for fireproofing. I have strong solid wood beams (not new construction / no glue). However he faced all the reflective material against the gypsum board, not against the interior (livening space floor above the garage) which i think is the opposite of what you want in an area being exposed to cold vapor air crashing into a furnace (in the garage).

    - my options are:
    - R31 fiberglass and re-enclose in drywall… there is a section that this is impossible to achieve above the furnace due to a massive amount of pipes and lines.
    - spray foam closed cell insulation 3 inches or so and cover the rim joints, this will reach most of the way toward the above furnace area but not fully. Spray Paint with fire proofer.
    - in either model will need to piece together mineral wool insulation above furnace (High Efficiency) area.

    Any thoughts? I greatly appreciate the guidance of experience over YouTube.


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