How best to dehumidify basement?

Discussion in 'HVAC Heating & Cooling' started by gplumb, Jul 24, 2009.

  1. gplumb

    gplumb New Member

    Messages:
    32
    Location:
    North Carolina
    In finishing my basement I am planning to install a heat pump. My dealer proposes a Trane 1.5 ton heat pump with a variable speed air handler that would enhance dehumidification also. The system would use a Trane Comfort Control thermostat that also senses humidity and has dehumidification controls. Since my basement stays around 70 in the summer the cooling cycle wouldn't be called for except when the humidity sensor triggers it. In the winter the temperature is typically in the upper 50's to low 60's. The finished and conditioned part of the basement will include three large rooms plus a bathroom and a walk-in closet and is approximately 1200 SF. It is a walkout basement so most of the rear wall is above ground. The whole basement is approximately 2000 SF.

    I currently use a stand alone frost-free dehumidifier which I run year-round. This is adequate now without sheetrock on the walls but not once the rooms are closed in. The basement is very dry with no mold or mildew and the exterior foundation is covered with the Delta-MS system with French drains. But I want to be proactive in lessening the typical "basement smell" that may develop over time once the walls are closed in. So I want to provide for forced air circulation. I plan to insulate the exterior walls according to the latest recommendations to avoid mold and mildew problems.

    In summer when the humidity sensor triggers the cooling cycle (with the fan running at low speed) it seems the basement would cool below the already proper temperature and maybe feel too cool.

    Will this setup actually do the job without cooling too much? Any thoughts on this?
  2. Dana

    Dana In the trades

    Messages:
    2,783
    Location:
    01609
    Humidity control in basements starts with controlling air-infiltration from the outside. Humid outdoor air getting into the basement is usually the largest source of basement humidity in the eastern 2/3 of the US. It's driven in part by stack-effect from combustion appliances (furnaces, gas hot water heaters, etc. but in multi-story homes it's the whole house height that becomes the stack. The biggest entry path is thin gaps in the band joists & sills, followed by clothes dryers (which you can't do much about.), then windows/doors. Foam sealing the band joist & sill is the first/best start. (Sealing the attic also reduces the infiltration pressures by a surprising amount as well, but for now we'll stick with the basement.)

    When you're all done, test any combustion appliances for backdrafting while running the clothes dryer, air handler, exhuast fans anywhere in the house, with all doors & windows shut tight. If need be, add a purpose-specific combustion air supply to the room with the burner.

    Then, treat ground moisture permeation paths- slab and walls can be treated with concrete sealers (radon sealer on the floor slab would be good, if it wasn't poured with an embedded polyethylene vapor retarder.) If you have a slab-depressurization radon system sealing the slab won't be necessary.

    Before finishing the walls, putting up semi-permeable rigid foam insulation against the foundation (wiith foam/caulk sealed seams & edges) under any fiber insulation is advisable. This can be either extruded polystyrene (XPS) "pink board" or "blue board", expanded polystyrene (EPS) beadboard (like Styrofoam TM), or fiber-faced (but not foil-faced) polyisocyanurate aka "ISO". Foil facers will trap ground moisture in the insulation, may end up rotting out the foundation sill. In extreme cold climates vapor retarders & foil facings can be used (and are a benefit), but not for most of the lower 48 of the US.

    Then, be sure to use high-permeability paints on the gypsum or you'll be looking at mold on the furring strips/studs in only a few years- it has to be able to dry toward the interior. Don't use vinyl or foil wallpapers- same story, only worse. There's a bunch of research & data on this- you can read up on it here:

    http://www.buildingscience.com/documents/information-sheets/5-thermal-control/basement-insulation

    and here:

    http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems

    Insulating your basement will make it warmer, lowering the relative humidity, but being warmer will increase the vapor pressure up from the slab (unless you insulate IT as well, which you might consider if you have the headroom. 1" XPS would give you R5, and much warmer floors. Standard density EPS and ISO don't have the compressive strength for use under floors, but 2lbs/ft^3 EPS does.)

    I you set your humidistat to 60% RH a 1.5 ton unit should be able to keep it dry without overchilling the space, if you set it lower than 40% (or when running in thermostat mode) you may have a bit too much basement coolth at times, but worst case you could go back to the standalone dehumidifier and close off the register to the basement. You don't need to keep the basement bone-dry to avoid mold. At about 70% RH and up it can really take off over time, but at 60% you'll be fine. Could be you've been overdoing it a bit, but it could also be that by keeping the basement under 50% RH it's kept the rest of the house under 60%RH- it's been part of your whole house air conditioning all the time.

    The low speed dehumidification mode is a great feature- at lower air speed it wrings more water out per cubic foot of air, which does indeed keep it from overchilling. If my (3x oversized) AC unit had that feature I'd be using it, but instead I keep the basement dehumidifier unit set to 60% RH year round, but this summer it's been high-humidity with low temps, and I've had to resort to running a half- ton window AC unit in an upstairs room as my whole house dehumidifier, leaving interior doors open so that all rooms get the benefit. If I ran the main compressor it'd get cold & clammy, not comfortable & dry. (I'm sure you'll be better off than me, but I'm not springing for a new AC unit any time soon...)
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    You won't get much dehumidification if your normal, unconditioned temp is already 70-degrees! Unless the air handler has reheat capability, it won't work all that well. The variable speed fan in the air handler works much better than a single speed fan for dehumidification, but even on low, it will be cooling the air and it has to be running to do anything. While you can force the fan to run, unless it's chilling the air, there's no dehumidification. A dehumidifer actually ends up heating the air space because it gets warm doing the work, and you aren't exhausting that heat outside like you will with the heat pump. It chills the coil, runs the air across it to condense the moisture and the air is cooler, but the heat created by running the compressor and fan is more than the cooling, and the net result is heat being put into the room. So, the only time the heat pump can dehumidify is when it is cooling the air. If it is already 70-degrees, unless it then reheats it (via electrical resistance heat strips), it will get too cold. This can get really expensive or uncomfortable.
  4. gplumb

    gplumb New Member

    Messages:
    32
    Location:
    North Carolina
    Dana,

    Your information and perspective are a great help. There is a lot more to this than I ever imagined and apparently the approach to insulation has changed in recent years because of mold problems. The buildingscience.com links are good references and I will follow their insulation recommendations.

    I have stud walls between the conditioned and non-conditioned spaces which I assume could be insulated using the traditional approach with faced fiberglass insulation on the heated side This is different than the situation with a stud wall very close to a cinder block wall that should be covered with semi-permeable rigid foam board. I also have a "false wall" two feet from a 12 foot long cinder block wall. This narrow space will be open to the space above the suspended ceiling of an adjacent room. I assume this could also handled with the traditional faced fiberglass insulation on the heated side since moisture would escape above.
    Last edited: Jul 25, 2009
  5. gplumb

    gplumb New Member

    Messages:
    32
    Location:
    North Carolina
    jadnashua,

    Yes I don't want to cool the already cool-enough air. My dealer says it would cool a few addtitional degrees until the dehumidification cycle was finished. I found a Lennox whole home dehumidification system that has a reheat capability. But to add this in addition to the heat pump would escalate the cost. Do you know what approaches there are to provide reheat capability?
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    A straight dehumidifer adds heat to the room. It has essentially the same parts as an a/c unit: compressor, evaporator, fan. It's just that it doesn't have an external exhaust to get rid of the heat it produces running the compressor (and the rest of the system). Your heat pump is designed to move heat from one area to another. In the process, it happens to make parts cold, and because they run the air over it, it condenses moisture out of the air. In the process, in circulating that air in the structure, it is cooling the air, while the heat is moving outside. With a heat pump, it reverses the heat flow, and extracts heat from outside and moves it inside. Since a heat pump has some trouble extracting heat from cold outside air, the air in the exhaust in the house is cooler than with a traditional heating system. this is somewhat a function of how cold it is outside. Again, a variable speed fan can help. Just like when cooling, running the air over the coil slowly removes more moisture while cooling the air, in a heat mode, moving it slower means it can absorb more heat.

    So, in the winter when you want heat, the heat pump will blow warm air into the house. In the summer, it will cool your already cool rooms trying to remove moisture. How often that occurs will depend on how much moisture migrates into the house. If there isn't a moisture barrier under the slab, and the walls let moisture in, it will need to run quite often in a hot, humid environment. If they are sealed, maybe not too often. But, for most people, a 70-degree room in the summer is cool...dropping it a couple more to dehumidify would make it downright cold. A system capable of reheating the air so it is comfortable requires a bunch of energy...enough to run the compressor (and since it can't make heat and cold at the same time), generally, just adds electrical resistance heat while cooling to temper the air for a net change of maybe zero...so, it can run and dehumidify, but not cool the room. While I suppose it is possible to take that heat moved outside to provide reheating to do dehumidifcation in an already cool room, I don't think anyone does this (it would get complicated).

    Personally, the (few) places I've been where they used a heat pump to heat the house, I've found it uncomfortable. It may be that it just wasn't set up well. In a traditional forced hot air furnace system, the air comes out of the registers probably 20-40-degrees hotter than it does with a heat pump unless it is so cold it triggers the resistance heat. The blowing of barely warm air on you in the winter just isn't comfortable to me.

    I think I'd start by taking a 2x2' piece of plastic and taping it to the bare concrete and another piece on a concrete wall segment. Let it sit there for a couple of days. If you have moisture trapped underneath it, resolve that problem first if you can.

    The heat pump would be quieter while dehumidifying, but I have my reservations. The dehumidifiers have their good points (and bad). You will want some heat in there fo rthe winter, as 50-degress won't cut it for anyone except die-hard penny pinchers (I know one guy who actually keeps his house at about 55 in the winter to save money...no thanks!). If my slab was insulated, and I could afford the loss of ceiling height, I'd consider radiant floor heat to make the floors nice and warm. If you don't have the slab insulated, this can get expensive, too.

    Some of the pros here may have a different take on all this...have some patience. Dehumidification is done all the time, but mostly in a commercial application. In a residential situation, people often just rely on the a/c to do it, and then only as a secondary function because it needs to cool the room...to make it the primary function is a lot tougher to do economically while maintaining comfort.
  7. Dana

    Dana In the trades

    Messages:
    2,783
    Location:
    01609
    jadnashua: The three biggest summertime contributors to basement humidity (in descending order of importance) are:

    *Bulk water incursions (which he claims/seems to have under control)

    **Outdoor air infiltration

    ***Groundwater vapor permeation.

    The plastic on the wall & floor test only addresses the latter. A blower door test & remedial air-sealing would be a better first-step. Some amount of vapor retarder concrete/masonry sealer would slow down vapor issues with fairly low risk.

    A highly retardent interior vapor barrier would be good on the floor, but not on the walls, since the ground moisture would then migrate upward, risking exterior spalling of the above-ground portion of the foundation (not a biggie- could be treated with a sacrificial parge layer) or increasing the moisture at the sill plate with the potential of creating rot/ mold conditions (unless it has a very good capillary break/sill gasket.) Retaining some amount of drying capacity toward the interior is a good thing in most climates.

    Getting the permeance of the foundation under 10perms (class-III vapor retarder) is safe, and will reduce the groundwater dehumidification load by a lot, but under 1 perm (class-II vapor retarder) has risks. A 6mil polyethylene sheet has a permeance of under 0.05. Aluminum foils are under 0.01 perm. These should NOT be a part of any basement wall treatment in most US climates.

    gplumb: If only parts of the basement are to be fully conditioned space, the partition wall shouldn't use faced batting, since even kraft facers tend to have a permeance of ~1 perm (foil facers, even lower), which would trap moisure in the "cold" area unless you left the dehumidifier in there. If you insulate them with fiberglass, use friction-fit unfaced batting.

    A better (and easier to get "right", from an air & vapor seal point of view) approach is to insulate the entire foundation making it all technically conditioned or semi-conditioned space, even if you only build out some portions of it as living space. The partition walls will limit air transfer between living/dead spaces, so your heat losses into the dead-space will never amount to much anyway as long as the basement is reasonably air-sealed. But insulating & sealing the entire foundation wall will keep the relative humidity down in summer, and in the winter the heat loss out the foundation will be lower (making the floor above warmer.)

    The details of which approaches make the most sense varies by region/climate. What's your zip code (the first three digits is enough, if privacy is a concern.)
  8. gplumb

    gplumb New Member

    Messages:
    32
    Location:
    North Carolina
    Dana,

    My zip is 27106. The concrete floor had heavy polyethylene under it before it was poured so I imagine that does retard moisture vapor somewhat.
    Last edited: Jul 27, 2009
  9. Dana

    Dana In the trades

    Messages:
    2,783
    Location:
    01609
    In NC's mixed heating/cooling but humid climate you definitely don't want poly on the wall. (In Saskatchwan or AK you would.) Having it in the slab is perfect- no need to treat the slab further.

    The Oak Ridge Nat'l Labs cost-effectiveness calculator indicates R11 foundation walls, and R11.5 for exposed masonry walls are cost-effective. See:

    http://www.ornl.gov/~roofs/Zip/tmp/results5251.html

    ...or if the walk-out basement wall is wood framed that portion should have R13 cavity fill + R5 of thermal-break sheathing (interior foam is fine) on the studwall:

    http://www.ornl.gov/~roofs/Zip/tmp/results5894.html

    2.5" XPS, or 3" unfaced EPS beadboard glued in place with blobs of foamboard construction adhesive, with horizontal furring strips (through-screwed to the foundation with long masonry screws) for holding up the code-required thermal barrier (half-inch sheet rock) for fire control is probably the most cost-effective method. That'll give you a true R-12. Alternatively you could use 2" thick FIBER-faced polyisocyanurate (often sold as high-R sheathing or roofing insulation), but it may be more difficult to find locally(?). EPS is usually cheapest per unit R, then iso, then XPS. You could go with a combination of sheet-goods + fiberglass, but at R10-12 the extra labor for the studwall etc. isn't usually worth it. (I went with R20 3" fiber-faced iso at my place to save labor and preserve floor area. I'm in a much colder climate than you. I considered spraying 2lb-foam, but didn't go that route due to it's very low permeance.)

    Avoid foil-faced & poly-faced variants of sheet foams. You might consider using an OSB-nailer-faced version to save labor if the OSB is thick enough to qualify as the thermal barrier. (Just screw the panels to the wall with the OSB facing the interior.) OSB has a permeance of about 1perm when bone-dry, but but increases to 2-3 in humid environments like basements (as much as 5 when actively wet), which makes it something of a "smart" vapor control system. The average is usually estimated to be ~2 perms.

    It may not be required by code on the interior, but if you're in termite prone district, paying slightly more for borate-loaded termite resistant EPS might be worth it for peace of mind. (Borates are non-toxic to humans, but they are to ants/termites/wasps etc.)

    Study the RR-202 document from BSC carefully- system #4 (Figure 13) with slightly thicker EPS than the example seems most appropriate for your situation. It will be the same wall thickness as a 2x4" studwall with fiberglass batts, but will outperform the studwall thermally, with near-zero mold risk. (Even with R15 batts a 2x4 studwall doesn't quite hit R12, due to the thermal bridging of the studs.)

    In NC it's probably not worth insulating over the basement floor with foam board as a retrofit from an energy savings POV, but insulating the footing/slab-edge at the walk-out section from the exterior might be. The floor near that edge might feel a bit chilly in winter otherwise. (If you were heating the basement with radiant you'd definitely want some R between the heating element & the earth though.)

    Still, if you wanted to totally cozy-up the floor in the built-out space, R4-5 of XPS between sleepers for attaching the finish floor can make it barefoot-worthy even in winter. I'd do it, were I to convert any of my basement into real living space beyond the laundry room, which may be coming soon enough. But my subsoil temps hover around 50-55F, winter & summer- YMMV. It only steals about an inch of headroom.
  10. gplumb

    gplumb New Member

    Messages:
    32
    Location:
    North Carolina
    What do you mean by putting R5 on stud wall? From the Oak Ridge calculator, it looks like they were specifying that R5 goes on the exterior if the siding was removed and there is an "empty wall". My walk-out basement wall is (from outside) brick, Dow Weathermate Plus Styrofoam Housewrap, 1/2" OSB and 2X6 stud wall. So in this case should I just use unfaced fiberglass since with faced insulation moisture would not be able to escape inward through the facing or outward through the OSB? This is the area where the approach to unfaced vs. faced fiberglass has changed over the years.

    HTML:
    2.5" XPS, or 3" unfaced EPS beadboard glued in place with blobs of foamboard construction adhesive, with horizontal furring strips (through-screwed to the foundation with long masonry screws) for holding up the code-required thermal barrier (half-inch sheet rock) for fire control is probably the most cost-effective method. 
    I don't know what climate zone the BSC RR-202 Figures 13, 14 and 15 are targeting, but 2" seems excessive for NC. The total insulation from the ORNI calculator is only R11 (the combination of rigid foam and fiberglass). Several below ground block wall sections already have a 2X4 stud wall with a small gap to the block. I won't be able to fish anything more than about 1/2" rigid foam behind most of that area. Where there isn't a stud wall yet, I will add rigid foam directly to the wall before putting up the stud wall.

    For stud walls between finished and unfinished (unconditioned) rooms should the fiberglass insulation be faced or unfaced? However I do plan to have a vent in the unfinished space that will allow a small amount of conditioned air to circulate.
  11. Dana

    Dana In the trades

    Messages:
    2,783
    Location:
    01609
    the ''...if the walk-out basement wall is wood framed that portion..."

    ...you'd want R5 of sheet-goods insulation beween either the studs & gypsum or studs & siding, was what I meant. (Coulda been poured concrete, cement block or wattle & daub for all I knew. This sounds like fairly recent construction, not an antique, using 17th century materials, eh? :) )

    Weathermate comes in different thicknesses with different R-values from R1.5 (3/8"), R3 (1/2") and R4 (3/4") . Whatever you have is probably "good 'nuff" with 2x6 studs, but for the sake of analysis, do you happen to know which it is?

    Unfaced fiberglass (or better, dry blown cellulose) would be the right way to go. The OSB is somewhat vapor retardent, and in mixed heating/cooling climates you can set it up to dry in either direction (in this case, drying toward the interior. It's when you stack it with highly retardent matierials on both side that you'd run into issues in a mixed climate. OSB is not very strong vapor retarder, but keeping the other materials vapor-permeable (but not necessarily air-permeable) guarantees it won't stay wet if it happens to GET wet.

    Blown cellulose will fill the gaps for a perfect fit, and will experience lower convection & air movement within the material, and provide significant hygric buffering, protecting wood from water damage/mold from occaisional wetting events. If you can, use "borate only" aka "sulfate-free" cellulose. The borate content of the fire retardent is somewhat protective against ants, termites & mold, and unlike the sufate fire retardent it's fairly innocuous stuff. The sulfates can erode metals if wetted, and if you don't catch the leak in time you experience some other damage- it's primarily an issue with copper, but not exclusively. (The borate only versions aren't usually available through home-center box stores, but some contractor supply houses would have it. Greenfiber Cocoon2 Stabilized Borate Formula is probably the most widely distributed/available, but there are others.)

    I'd still prefer even sulfated cellulose over fiberglass, if that were all that was available. In a 2x6" stud wall blown cellulose will perform to a true R20+, whereas real-world installations of even high density R21 batts are actually more like R16-R18 (due to imperfect fit, compressions and voids.) Using insulation blowers isn't rocket science, and the stuff is pretty cheap. Box store home centers that carry cellulose usually have cheap daily rental rates, and will often throw a day's rental in free if you buy over some minimum amount.

    The tests were done in MN, but the target is the entire lower-48- it's the groundwater vapor-drive issues that were of greatest interest.

    If you can insert even 3/8" XPS sheet in there it's worth it (but half inch is better). XPS is preferable to EPS here, since it provides some vapor-retardency. Once the stud bays are insulated the wood facing the wall will be cold, making it's relative humidity higher, with more mold risk. By putting even R3 (1/2" XPS) between the stud and the wall you're keeping it warmer, which lowers the relative humidity. Then R11 or R13 unfaced friction-fit batts for maximum inward-drying capacity would bring it well over the Oak Ridge recommended minimums with low risk of mold.

    If you're running conditioned air into the space there may be no point to insulating the partition walls other than sound-proofing. What sort of temperature differences do you anticipate between the conditioned/semi-conditioned spaces? If it's less than 10F difference (and I suspect that's the case) forget about it! I'm assuming the non-built-out portion is minimal-daylight back portion or something, which would be thermally coupled to the subsoil earth temp which is probably in the high 50s or low 60s F in non-highland NC.) But if you want to insulate it anyway, unfaced friction-fit batts (or blown cellulose like the exterior wall) would work, or even an inch or two of unfaced EPS (R4-R8) under the gypsum. Vapor retarders might work against you there, but kraft-facing probably won't make or break it with conditioned air being circulated on both sides- whatever is most convenient is fine.

    At the very least, insulating the upper half of the foundation in the non built-out areas to R10 with EPS sheet goods will have reasonable payback on heating (but not so much on cooling). Unless you have R15 or something in the joists between the basement & first floor the wintertime heat lost out of the foundation is significant. The cooling season heat GAIN through the foundation won't be much, unless you have a significant amount of above-grade portion of the foundation on an unshaded south or west wall (which could be remediated with some shrubbery.) If you later wanted to build it out you either could fill in the lower portion with the same and use furring for the finish wall, do the lower portion in R5 XPS and use 2x3 studs & R8 batts for the finish wall, or other variations on the theme.
  12. gplumb

    gplumb New Member

    Messages:
    32
    Location:
    North Carolina
    The Dow Styrofoam Weathermate (http://www.dow.com/PublishedLiterat...foam/pdfs/noreg/179-07173.pdf&fromPage=GetDoc) is a non-insulating Housewrap. The OSB would be the only insulating factor between the brick and the interior 2X6 stud wall. Who makes the 3/8", 1/2" and 3/4" XPS you mentioned? I couldn't find a thin Dow product (http://www.dow.com/PublishedLiterat...foam/pdfs/noreg/179-06487.pdf&fromPage=GetDoc) that was for interior walls (one that didn't have a plastic or foil film which I assume I don't want).
  13. Dana

    Dana In the trades

    Messages:
    2,783
    Location:
    01609
    I must have been getting it confuse with a different product (I thought there was a "Weathermate" fan-fold XPS product- could be wrong about that. I should look stuff up before I presume, eh?)

    If you go to the Oak Ridge online calculator, if you pick 2x6" ,16" oc no-foam, with cellulose you get a clear-wall of ~R18, a whole wall (with all framing of window & door framing thermal short circuits estimated) of ~R14, and slightly less with R19 fiberglass batts:

    http://www.ornl.gov/sci/roofs walls/AWT/InteractiveCalculators/NS/SimCalc.htm

    (And to get that performance the batts have to be perfect-fit, and perfect installation.)

    If you add R4 of foam (to either side of the studs) you get R17 whole-wall performance out of cellulose fill. If you add only R2 it's still over R15.5. If you went with half inch thick XPS sheathing (blue board, pink board) under the gypsum that would be R3, bringing the whole wall R value up to something like R16-16.5. Half inch thick 4x8' R3 sheets are about $11 at box stores, eg:

    http://www.lowes.com/lowes/lkn?action=productDetail&productId=15348-46086-201549&lpage=none

    One inch thick 2x8' tongue & groove R5 sheets run about $8 in similar venues:

    http://www.*********.com/webapp/wcs...3&productId=100320343&N=10000003 90039 527397

    This would also be the right stuff to try to sneak between your studwalls and foundation. At these thicknesses it's vapor semi-permeable.

    XPS isn't crumbly like EPS (bead-board) and is usually higher-density and higher R-value per inch, but it's pricier per R-value. 2" thick R10 XPS is commonly used for insulating basements in my neighborhood. It's probably available near you too. But 3" unfaced R12 EPS would be cheaper per square foot, if you can find it.

    With any foam insulation code requires a half-hour thermal barrier between it and living space. Half inch sheetrock qualifies- so does half-inch OSB. (In attics and crawlspaces without ducts or other free air communication with living space it's relaxed to 3/8" gypsum in most areas.) IIRC the concern addressed in the code is as much about toxic smoke as about flammability. (Some foams are hard to set alight, but make nasty stuff in the presence of flame. Get it hot enough and they all burn very nicely though.) Other than that there are no "issues" with using foam sheet goods marketed as exterior sheathing on the interior sides of stud walls (or foundation walls.)
  14. gplumb

    gplumb New Member

    Messages:
    32
    Location:
    North Carolina
    Dana,

    The above URL didn't work for some reason.

    I want to thank you for all the help you have provided in steering me through the myriad of information out there on insulation. This forum is a great resource. I'm now ready to go ahead with the basement project. By the way, I'm impressed with your depth of knowledge on this subject. If you don't mind me asking, what is your background? I'm a retired electrical engineer and worked in radar systems R&D.
  15. Dana

    Dana In the trades

    Messages:
    2,783
    Location:
    01609

    That URL got truncated & mangled I guess. If you go to the Home Despot website, search on insulation, then select "sheathings" amongst other things you'll see variations on Owens Corning "pink board", which is all XPS.

    My degrees are in math & physics, but I've been "moonlighting" as an electrical engineer for the past 25 years. :) (Mostly analog, a lot of video, a bit of RF but no microwave.) The building-science stuff is mostly a hobby, but over the past 15 years of fixing up my my ca. 1923 house I've learned not to trust the professionals- there's a wealth of ignorance out there, and many myths enshrined in building code have been broken over the past 30 years. It takes awhile for it all to filter into standard practices, and many mistakes have been made along the way based on misunderstanding of which principles were in play, particularly with the use of vapor retarders & waterproofing treatments etc resulting in mold & rot, which is critical to get right in basements.

    The web has made a lot of US- DOE and Canadian and other governmental & academic study results available, so I read up a lot before proceeding on any changes to my place. (eg. I did my own hydronic heating system design, with a burner fully 75% smaller what the last pro had installed, with a HUGE improvement in net efficiency- it improved comfort too.) Coming from a science & engineering background I tend to trust folks who actually measure stuff over installers/vendors/designers. I hear questionable recommendations that don't quite square with my physical-intuition from builders & trades folks a lot, which sends me running for the research- sometimes the recommendations pan out, other times it's long-since debunked industry lore.

    It can pay to be skeptical- I've cut my utility use by ~50% in the past decade while improving health & comfort and adding square-footage (and census) to the house, and there are still cost-effective projects on the list that will pay for themselves in on utilities alone. Had I accepted professional recommendations from seemingly competent contractors I would have paid more, gotten less. The heating contractor rolled his eyes a bit when I presented him with my intended system, but agreed to install it anyway since I had used him on other projects, but he was voiced caveats as he waded in... he's convinced it works now. :) (It wasn't really all that radical, but different enough that I had to walk him through the math and even then he wasn't so sure at first.) Without web resources I never would have figured I'd be designing heating systems.

    Oak Ridge Nat'l Labs, Florida Solar Energy Center, and Texas A & M all have massive amounts of readable research briefs on insulation matters, as does the Building Science Corporation, who has some of the best English language stuff on humidity control within building materials (much of their research was DOE funded, and therefore public.) There's a lot of good German language building-science stuff out there too, but I find it a bit tough to wade through some of it.
  16. he8833

    he8833 New Member

    Messages:
    18
    Location:
    Minnesota

    I'm with you up until the paint . Most paints do not have a low enough perm rating for this to be a concern, unless you buy one that specfically is designated as such e.g, vapor retarding paint.

    I do like you point of foaming any seams after installing the XPS....This is often over looked especially when the sheet meets the floor
Similar Threads: best dehumidify
Forum Title Date
HVAC Heating & Cooling identifying asbestos Feb 10, 2014
HVAC Heating & Cooling What is the best value 80-100 gallon tank for storage/buffering? Jan 7, 2014
HVAC Heating & Cooling what will be the best solution for heating and cooling? Mar 13, 2013
HVAC Heating & Cooling Looking for Best Heat Pump Brand from Asian Country May 16, 2012
HVAC Heating & Cooling Bathroom Fans: Best way to install ducting? Sep 21, 2010

Share This Page