Remodeling of Basement questions/plan of attack

Discussion in 'Remodel Forum & Blog' started by barlow96, Jan 14, 2020.

  1. barlow96

    barlow96 New Member

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    Location:
    Pennsylvania
    Well after a few weeks of intensive research on here I think I have narrowed down my plan of attack (I just want to make sure I am not missing anything and/or I do have a few questions).

    Details:
    Lycoming County, PA Zone 5A
    House - newly constructed modular (2015) on poured 8'' x 9 ' foundation. 4'' slab floor
    Basement size = roughly 900 sq ft, but only 600 sq ft will be remodeled (see attached plans). never have encountered any water in basement.

    North side (top of plans/window side) is almost completely exposed (northwest corner land slopes towards window so NW corner goes from 3' exposed to fully exposed at windows).

    South side not sure what to call it as the front porch foundation ties into the south side foundation of the house, but the porch foundation is exposed approximately 2'

    West side exposed 2' and slopes down to approximately 3'.

    sill plate sits directly on top of foundation with a lip of approximately 0.5'' of concrete in front of sill plate.

    3 windows on north side with wood framing directly on concrete.

    Plan (on all three walls of the basement):

    2'' EPS on walls. 2'' EPS on sill plate and rim joist. Spray foam small 0.5'' ledge on top of foundation wall in front of the sill plate.

    2x4 wall in front of EPS with 1'' EPS under pressure treated bottom 2x4 plate

    R11 unfaced insulation in 2x4 walls

    mold resistant drywall with latex paint.

    Basement dividing wall (East side) - standard 2x4 wall with R-11 faced and drywall both sides)

    Floor - cut expansion joints will be sealed up with concrete (in finished portion only). DMX-1 dimpled mat placed down (for carpet)

    Questions:
    is the dividing wall a good plan or should some type of vapor barrier be used as well (I'm not sure)?

    Windows on north side (I planned on painting wood with latex - running the EPS up to the interior edge of the wood framing and then capping with trim) good idea or should I do something else to prevent moisture/mold?

    Overall is this a good plan of attack for the walls of the basement for the varying degrees of exposure and also (not sure if this matters), but 1/3 third of the basement will not be finished off.

    Should I seal up the floor slab to wall joint/crack with concrete?
     

    Attached Files:

  2. Dana

    Dana In the trades

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    Tape the seams of the 2" EPS with housewrap tape for air tightness to block the potential for air-transported ground moisture from getting into the stud bays. Be sure to carefully seal the seam between the EPS and foundation at the top with foam board construction adhesive or general purpose polyurethane caulk- don't count on can-foam or FrothPak's ability to keep that joint air-tight for the duration, but it's fine to use foam to fill-in as insulation. It's fine to leave the micro-gap between the foam and foundation unsealed at the bottom for drainage purposes, as long as it's air-tight at the top.

    Seal the gap between the foundation wall & slab with polyurethane caulk formulated for concrete. The soupy "self leveling" types will be able to flow into fairly tiny cracks for a good seal. This is a standard step in most radon-mitigation retrofits. Seal any cracks in the walls with a heavier bodied polyurethane caulk before installing the EPS.

    On the exterior side of the foundation wall, how much above grade exposure is there on the least-exposed part of the foundation? It sounds like it's 2' (?). A foot or more would be great- ground moisture will dry toward the outdoors- if it's less than that some sort of capillary break between the foundation sill and foundation might be prudent where it's going to be insulated. ( A 2-pronged wood moisture meter may be useful for figuring this out. )

    In your climate ~R8 EPS has plenty of dew point margin at the foam/fiber boundary for being able to use R13 instead of R11. As long as there is no flooding history cheap kraft faced "contractor roll" R13s with kraft facers (but not aluminum facers) are fine. Asphalted kraft facers aren't true vapor barriers- they are "smart" vapor retarders, and become substantially vapor-open (more vapor-open than standard interior latex paint) when the humidity levels inside the cavity reach levels that would support mold growth. R13s are substantially more air-retardent than R11s, and will pretty much block convection within the batt even at fairly high temperature differences. Low density R11s & R19s, not so much- they are more of an air filter than an air retarder.

    What is the purpose of insulating the partition wall? Is it heated & conditioned on both sides? Unless you're making one room into a sauna or steam bath do NOT install a vapor barrier on either side of the wall. In US climate zone 5 a true vapor barrier creates more problems than it solves even on exterior walls, and would buy nothing good if used in a partition wall between a fully-finished room and a mostly below grade unfinished uninsulated basement room.

    As a general rule it's more effective to insulate the entire foundation wall rather than partition walls and ceilings, even if some of the space isn't being fully finished or fully conditioned as living space. It's a lot easier to get the air sealing and moisture control details right at a foundation wall than a basement ceiling or partition wall. Making the exterior assemblies of the house from the foundation to the attic both the air pressure & thermal boundary of the house avoids a lot of "gotcha" problems from air transported moisture getting through unintended paths to create high moisture content in susceptible materials on the colder side of a partition. With insulated partitions or ceiling/floors the definition of what's inside vs. outside the thermal or pressure boundary of the house gets scrambled.

    It's fine to put the EPS up against the edges of the rough framing of the window, as long as the flat side can still dry toward the interior. Air seal it to the foundation with polyurethane caulk before painting. The edge of the EPS can't be left exposed, and needs to be covered with a material qualifying as a thermal barrier against ignition- half-inch wallboard meet's spec, half-inch MDF trim board doesn't. Don't use PVC trim board, since those are true vapor barrier.
     
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  4. barlow96

    barlow96 New Member

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    Thank you for responding Dana. The exterior foundation wall does have at least 2’ of exposure all the way around for outward drying

    I will go with unfaced r-13 then. Thank you for that info.

    The partition wall will separate the finished (heated) portion from the unfinished (unheated) side of the basement so I wasn’t sure how to construct/insulate this wall so as not to cause condensation?

    Concerning the floor disregard my previous statement as I will be laying down poly, 1” xps plywood and then carpet. Headroom is lacking in some areas so I would like as much clearance as possible. What would you suggest to be the minimum thicknesses of the XPs and plywood? I won’t be able to run the poly up 6-12” up the interior of the foam on the wall so I would be stopping this right at the eps installed under the 2x4 bottom plate

    Also should I seal up the exposed edge of the eps on the wall (between the eps and wall) when looking at it from the unfinished portion (due to my brick pattern I won’t have a tight fit between wall and eps)?
     
  5. barlow96

    barlow96 New Member

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    Actually I could run the floor poly up 12” on the inside of the eps board on the walls (if this is recommended)?
     
  6. Dana

    Dana In the trades

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    Condensation & adsorption requires material temperatures colder than the dew point of the proximate air.
    Typical mid-winter indoor air dew points are in the 35-40F range. Unless that unheated part of the basement drops below 40F for extended periods, there isn't going to be condensation or adsorption into the wood on the cold side of the partition wall. Without insulating the partition wall it's unlikely the temperature in the unconditioned part of the basement will drop to 40F. Even if insulating that partition it's unlikely to drop below 50F unless there is a LOT of air leakage to the outdoors (which should be fixed anyway. Is the ceiling in that part of the basement insulated?

    In summer the outdoor dew points are north of 65F in your area during the stickiest part of the summer, but if you're air conditioning the house the indoor dew points are lower. (Most people keep it under 60% RH @ 75F in summer, which corresponds to a dew point of 60F. It's highly unlikely that the temperature in the un-conditioned side of the basement will be that low in July/August.

    What is the ACTUAL wintertime temperature in the basement, as-is?

    An empty partition wall with drywall on both sides is about R4 "whole wall", compared to about R10 "whole wall" if stuffed with R11 batts. Unless that unconditioned part of the basement gets truly cold there would be no economic "payback" to insulating the partition wall. And if that unconditioned part of the basement DOES get truly cold, there would be much better payback in energy use and comfort by insulating the foundation wall instead of the partition wall.

    Regarding XPS- friends don't let friends use XPS. XPS is the least green insulation material in common use today, due to the extreme global warming potential (GWP) of the HFC-soup blowing agents used (the predominant component of which is HFC134a, with a 100 year GWP of about 1400x CO2.) Had Team America signed the Kigali Amendment to the Montreal Protocol those blowing agents would have been contraband since the beginning of 2019, but the US didn't sign, and the manufacturers haven't changed their processes.

    Worse still, as the HFCs diffuse out over the decades the performance of the foam drops toward EPS of similar density. If you read the fine print it's only warranteed to 90% of the labeled R value, and by all indications you'd be able to collect on that warranty in only 40-50 years, if you take the time to test a sample.

    EPS is blown with hydrocarbons, usually variants of pentane at only ~7x CO2@ 100 years, most of which escapes the foam while still at the factory, and recaptured, not vented to the atmosphere. The performance of EPS is stable over the decades, and is not at all dependent upon the blowing agents used.

    The differences aren't subtle:


    [​IMG]


    Bottom line: Use EPS, not XPS.

    Under a half-inch CDX subfloor and R1-R2 ish carpet it's prudent to install at least something like ~R3 under the subfloor, which would be enough to keep the temp at the bottom of the subfloor above the summertime ventilation air's dew point (~65F average in your area), or at least keep the mechanical dehumidification/air conditioning needs low.

    No matter what density EPS is used or how thick the subfloor, stagger the seams of the subfloor by a foot or more relative to the seams in the EPS to prevent rockering compression at the edges of the foam board. If using only a single layer of CDX or OSB as the subfloor, TapCon it to the slab 16" or tighter on center, or it's likely to develop waves or "potato chip curl", from normal seasonal humidity changes.


    Yes- seal the EPS to the foundation wall everywhere, except at the bottom to allow drainage. That prevents convective air & moisture transfer between the conditioned space and damp foundation. Any time insulation and/or vapor retarders are installed between the foundation wall and interior space, the moisture content of the foundation rises- which is fine- the masonry can take it (wood & wallboard, not so much.)

    It's actually good that the brick pattern leaves a micro-gap air space between the foam and foundation, since that allows any bulk water that gets in there to flow to the bottom, and it acts as a capillary break (though the EPS isn't very hygroscopic and behaves as something of a capillary break on it's own.).
     
  7. barlow96

    barlow96 New Member

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    Thank you for taking your time and helping out Dana...Yes the ceiling is insulated throughout the entire basement...The actual wintertime temperatures in the basement is 50 (right now) and summertime probably 60-65

    Yes the ceiling is completely insulated throughout the entire basement.

    I just wasn’t sure what to insulate the Partition wall to prevent heat loss from finished into unfinished and wasn’t sure if dew/point condensation would be an issue. It would just feel weird not to throw in some faced r-13 in the partition wall with paper facing interior (I hope this won’t cause an issue)?

    Any issues with floating the subfloor by glueing the 23/32 osb to the 1” eps to avoid all those tap cons?
     
  8. Dana

    Dana In the trades

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    Installing R13s into the partition wall is likely to make the unconditioned section colder, and if it's air-leaky, MUCH colder. (Is there any plumbing in there?) But if it's just wallboard on the unheated side (even painted with latex primer, if you like) wintertime moisture drives will just pass through and end up in the cold concrete, the way it has been doing all along. Unless the doorways to the space are fully weatherstripped there will be far more air-transported moisture between the fully conditioned and unheated portions that will ever get through a single layer of drywall painted with standard interior latex paint. Kraft facers on the batts will not hurt anything from a moisture management point of view but it's not really necessary.

    Also for the batts to function at their rated R-value the partition wall needs an air-impermeable layer on both sides, not just the heated side. But do NOT install polyethylene sheeting anywhere in the partition wall- even though it's makes an easy air-barrier it's just asking for trouble. Housewrap would be good enough as an air barrier if you're not up for sheet-rocking the unconditioned side. Just be sure that any seams between sheets get taped and stapled where it's supported by framing.

    Floating the subfloor usually only works well with double-layered half-inch CDX/OSB glued & and nailed together, seams between the two layers by a foot or more. With single layers of 3/4" it will almost certainly end up with some waves and curls over time from humidity changes, due to the lack of rigidity at the seams.
     
  9. barlow96

    barlow96 New Member

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    Ok floating the osb will be a no go so I guess the last thing I still need to finalize is the partition wall.

    The plans do show two doors, but I am scratching one with the only door into the unfinished portion being at the bottom of the stairs. I am going with an exterior door for better insulation. I guess I am still hung up on retaining heat in the finished portion from escaping into the unfinished area as I will be going with hydronic baseboards. There is a double door to the outside of in the unfinished area and if you say that insulating the partition wall will make the unfinished area colder then what the basement is typically now then I will scratch the insulation.

    I guess the way I am thinking of the partition wall is separating the inside to the outside like an exterior wall, but if you don’t think insulation would be a good idea then I will scratch that and just go with drywall on both sides with latex paint. I just don’t want a lot of heat loss through the partition wall (like having an exterior wall with no insulation)

    I have no plans of doing anything to the unfinished area (foam board etc) just keeping it as is as this is the area of the basement with my h2o heater, furnace,water treatment, toilet, utility sink etc so I wouldn’t want to make this area colder by insulating the partition wall but at the same time I don’t want to be heating this area with heat escaping through the uninsulated partition wall like an exterior wall would with no insulation
     
  10. barlow96

    barlow96 New Member

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    one more question/concern....The existing walls around the stair case are installed directly onto the concrete. Is this something i should be worried about? Is there something i should do (such as cobbling a 1'' section of EPS over the base 2x4)? i just dont want these existing walls to be a source of mold since they will not be insulated from the cold concrete...Also i plan on installing foam board on the walls, then foam board on the floor with subfloor, then installing the walls on top of the subfloor. is this a good idea or should i install the walls first and then construct the floor?
     
  11. Dana

    Dana In the trades

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    Insulating against a 50F basement room with an R4 "whole wall" uninsulated partition wall isn't a huge heat loss. If the heated space is 70F that's a 20F difference, and you're looking at less than 200 square feet. The heat loss is 20F/R4= 5 BTU/hr per square foot, for less than 1000 BTU/hr of additional heat load. That's the heat output of 2 feet of baseboard.

    Compare that to the heat loss of the 50F basement when it's 30F outside, which is also a 20F difference. An 8" poured concrete wall is about R1.35, for a per-square foot loss of 2oF/R1.35= 27 BTU/hr per square foot. With 2-3' of exposure along something like 50' of wall that's about 125 square feet, so just the above grade losses would 27 x 125= 3,375 BTU/hr, with an additional but smaller amount going out below-grade wherever the soil is colder than 50F. That heat is coming from somewhere- some through the partition wall, some through the floor, but it is still heat you're paying for. Even 1" of EPS on the walls would cut the 3,375 BTU/hr loss down to ~850 BTU/hr, bringing it to the full code-min R15 continuous insulation would reduce it to about 280 BTU/hr of wall loss. As the above grade wall losses drop, at some point the slab losses start to factor in, but it's still a far better reduction in total energy use than insulating the partition wall, with a far greater reduction in risk of mold issues.

    Seriously, spend the difference in cost of interior doors and batts for the partition wall on insulating the rest of the foundation. With an insulated partition wall you only need to sheet-rock one side- the "saved" sheet rock from the partition wall could cover what ever amount of foam-board you put on the exterior walls. An inch of EPS may cost more than R13 batts for the partition, but probably not more than the R13 batts + the difference in cost between interior doors vs. insulated exterior doors.

    If you did TOO good of a job of insulating the partition wall the risk of plumbing freeze-up on the plumbing to the water heater goes up. Insulating the foundation walls reduces (nearly eliminates) the freeze up risk.

    If the staircase wall doesn't have moisture issues now, it most likely won't later. If you're going to insulate it and inch of foil faced polyiso cut'n'cobbled against the foundation, sealed in place with can-foam then then compressing an R13 into the remaining 2.5" (where it performs at R10) is fairly moisture safe, even though it doesn't quite meet current code-min. The cold stud-edges may take on some moisture from the foundation, but with only an inch of wood to move through it usually dries adequately toward the interior through the batt & wallboard.
     
  12. barlow96

    barlow96 New Member

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    Thank you Dana for your responses and information Greatly appreciated!!….Concerning the 6 mil poly on the floor..What tape should be used to seal the seams? (same housewrap tape as used for the EPS?)…..also some posts say to wrap the poly up 6-12'' and seal to the inside of the concrete wall and some say to seal up to the interior of the wall foam board...I'm not sure what way in the best, but my thinking is if I seal it against the concrete wall, then any moisture that would happen to accumulate on the wall, would run down the wall and then on top of the plastic under the floor and be trapped...If I run the poly up the inside of the wall foam board, then any moisture accumulation on the concrete wall would run down the wall, under the unsealed wall foam board and under the floor poly where it would then (presumably) wick/absorb into the concrete (not talking about ground water penetration into the concrete wall, but rather any meniscal amount of condensation that may form)
     
  13. Dana

    Dana In the trades

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    Houswrap tape works fine for sealing polyethylene sheeting.

    If you need/want to preserve a thin drainage channel, seal the floor poly to the wall EPS.

    With polyiso foam board it can become a judgement call- having the polyethylene under the cut bottom edge of the polyiso is a good capillary break, and allows the polyiso to extend (all but the polyethylene sheeting thickness) down to the slab level on slabs that many not be very dry, preventing moisture from wicking into the polyiso from the slab. But where there's a risk of bulk water leakage through the wall it could aggravate the situation.
     
  14. barlow96

    barlow96 New Member

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    One quick question. If the stud walls were built first (not on top of the subfloor) what would be the best approach to then constructing the subfloor? Should the drywall be installed but leave a gap at the bottom of the wall for the floor foam and osb to but up against? Is fiberglass inside the wall enough to protect the bottom plate from any dew point issues since it wouldn’t be on top of the subfloor? Are there any diagrams out there showing the the proper way of the wall/subfloor connection if the wall is built directly on the slab so as not to worry about condensation?
     
  15. Dana

    Dana In the trades

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    It's fine to install wallboard ahead of time, cut high enough to accommodate the subfloor & foam, if you prefer to do it in that order. Leave a 1/4
    gap between the subfloor & bottom plate to deal with seasonal expansion/contraction issues. Don't worry too much about the fiber insulation creating a summertime dew point issue for the bottom plate, especially if it's pressure treated, or if you normally use mechanical dehumidification in the basement.

    The usual solution is to just use pressure treated lumber for the bottom plate- not sure if that really needs a diagram. I'm only aware of a few builders who bother installing foam under the bottom plates to deal with the summertime dew point issues- it's more protective, but has a time & labor cost. For DIYers it's easier to rationalize putting foam under the bottom plates of non-structural framed walls than for contractors with a burdened labor rate in the $100/hr range.
     
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