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Community and Q&A

Another crawl space in the Northwest

ruffryder | Posted in Energy Efficiency and Durability on

Hello all, I have a 1150 sq ft rambler house in Fall City, Washington (near Seattle), zone marine 4c. I am currently in the process of redoing the crawl space. I have pulled the damaged and rodent infested insulation down, and removed the town vapor barrier. It seems I had some rodents that were digging past the foundation and getting into the crawlspace, ruining everything.

The crawlspace is tight, 18″ to the floor joists and uses the old style post and pier construction method of 4×6″ joists 48″ on center with 2×6″ tongue and groove on top, with hardwood floors finishing off the floor.

After cleaning up the crawl space I started doing research into how to insulate the area, and found the encapsulation method. I like the method due to not having to run insulation in the floor joists, giving me more space to work down there, and also in keeping the area cleaner for rodent inspection purposes and for when I do plumbing or other type of work.

The house currently has baseboard electric heat, though we are thinking of going to gas forced air. I had a recommendation from an HVAC installer to put the furnace in the attic, which will make it difficult to heat the crawl space. I would prefer the HVAC be in the crawl space, so the ducts don’t have to be insulated and the heat from the ducts would be used to heat the crawl space, though with the tight clearances, that would make access down there much more difficult. 6 of one, half dozen of the other.

Also, the issues of increased Radon exposure also has me worried. I

Some research I have seen shows that in this area (zone 4c) vented crawls spaces do a pretty good job.


1) It seems an exhaust fan in one of the crawl space vents with a floor register in the house (preferably opposite side from vent) would be enough to heat the crawl space with electric base board heat?

2) If I get HVAC in the attic, would it be preferable to run a heating duct to the crawl space (close off floor register) and keep the exhaust fan?

3) Would the exhaust fan be enough to mitigate the Radon issues? It seems most encapsulation projects don’t include Radon abatement issues. I am pretty ignorant on this subject, but I have three little kids under the age of 5.

4) Is there anything else I need to take into account or that I haven’t thought of?

Thanks everyone for your time!

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "It seems an exhaust fan in one of the crawl space vents with a floor register in the house (preferably opposite side from vent) would be enough to heat the crawl space with electric base board heat?"

    A. A sealed unvented crawlspace in your climate will not require any heat to stay warm. Once you have sealed the air leaks and insulated the walls, it will never freeze. For more information on the steps required to create this type of crawl space, see this article: Building an Unvented Crawl Space.

    The reason that many crawl spaces include an exhaust fan and a floor grille in the floor above the crawl space has nothing to do with heating the crawl space. Those features are included to control moisture.

    Q. "If I get HVAC in the attic, would it be preferable to run a heating duct to the crawl space (close off floor register) and keep the exhaust fan?"

    A. If your house has a forced-air system, you can install a supply register in the crawl space. In that case, you don't need the exhaust fan (but you still need the floor grille). Again, the purpose of these features is humidity control, not space heat. These two options are explained in the article I linked to (Building an Unvented Crawl Space).

    Q. "Would the exhaust fan be enough to mitigate the radon issues?"

    A. In most cases, no -- assuming, of course, that your your house has elevated radon levels. The only way to determine if your house has elevated radon levels is to perform radon testing. So test. For more on this issue, see All About Radon.

  2. ruffryder | | #2


    Thank you very much for your response. I have read the "Building an Unvented Crawl Space" repeatedly, but I guess it takes a while for the details to sink in. I understand that the crawl space won't freeze, but isn't heat required to get warm floors?

    Thanks for the clarification of moisture control vs heat / thermal control.

    Also, the crawl space currently has no vapor barrier (20 mil ordered last night and will be installed shortly. There are a couple areas where the soil is moist, though I have been checking for bulk water entry and I don't see any. With the vapor barrier off, should I let the soil dryout for a while? Or cover it ASAP? I am doing some crawlspace foundation repairs, and want to leave it off while I am making the area dirty / messy.

    I have a radon test coming, so it will be interesting to see the results.

    Thanks again for the help!

  3. GBA Editor
    Martin Holladay | | #3

    Q. "I understand that the crawl space won't freeze, but isn't heat required to get warm floors?"

    A. If you (a) seal the air leaks in your crawl space, (b) insulate your crawl space walls, and (c) implement one of the two humidity-control strategies listed in my article, then your floor will be warm and toasty.

    Q. "With the vapor barrier off, should I let the soil dry out for a while? Or cover it ASAP?"

    A. There is no need to "let the soil dry out." (The soil contains what amounts to an infinite amount of moisture. It will never dry out.) Once you have completed your construction work (repairing your walls), install the vapor barrier on the floor.

  4. ruffryder | | #4

    Sounds awesome.

    Thanks again for your time and help! Hopefully I will report back in a couple of weeks that everything was a success!

  5. Expert Member
    Dana Dorsett | | #5

    Almost any gas-burner is going to be ridiculously oversized for an 1150 square foot rambler in Fall City, especially after tightening it up a bit. That would be mistake #1

    Putting it in the attic rather than in insulated conditioned crawl space would be mistake #2.

    Your 99% outside design temp is about +20-22F (yes, it gets a lot colder than that sometimes), and with some air sealing the design load is likely to come in under 15,000 BTU/hr. You are very likely to be well within the range of a 1.5 ton ducted mini-split, either a Mitsubishi MVZ-A18AA or a Fujitsu AOU/ARU-18RLFCD either of which can deliver more than 20,000 BTU/hr @ +17F.

    With either of them you have the benefit of modulated ultra-quiet output (more so with the 18RLFCD than with the A18AA), and at your average wintertime temps you would beat their HSPF efficiency numbers if the ducts are all extremely short, and inside a conditioned insulated crawl space.

    If it's a fairly open space you can do it all with a 1.25 or 1.5 ton ductless too, at a lower installed cost.

    Puget Sound Energy has rebate money for upgrading houses with electric baseboards to heat pumps (I have several relatives in your area who have gone that route with ductless mini-splits), but the details vary from year to year.

    If you have a heating history on the place it's possible to determine the where-is as-was heat load prior to sealing up the crawlspace by comparing some wintertime billing periods against heating degree-days for your location, with adjustments for other power use determined by your mid-summer power use. See this:

    Even the smallest gas furnaces are likely to be 2x oversized for your actual loads. If you're committed to going with natural gas, a condensing gas water heater and a suitably sized hydro-air handler is probably a better solution than an oversized gas furnace + water heater.

  6. ruffryder | | #6


    Interesting comments and I appreciate your time and thoughts. We plan on taking over part / all of our garage in the next year, bumping up the house size to approximately 1600 sq ft. We are in the process of converting to natural gas for cooking, water heating (tankless gas water heater), space heating (forced air furnace), and possibly clothes drying. The baseboard heat and the old electric tank water heater are costing us a fortune. The house is not too open, and is 4 bedroom, 2 bath (1.75 bath in realtor speak).

    I am familiar with the PSE credits, as that is partly justification for going to tankless gas heater and forced air gas furnace.

    Again I greatly appreciate your comments. Please keep them coming if you have the time.

  7. ruffryder | | #7

    I finally found a source for the insulation in the crawlspace. Seems Rmax has a variety that can be used without drywall on it. Question though.

    1) Do I install the vapor barrier on the floor and walls first? Or the insulation on the walls first, then the floor / wall vapor barrier to the top of the insulation / rim joists?

    I have been looking everywhere for a more detailed how to, but I wasn't able to find one, am not looking in the right direction. I would appreciate any additional help you guys are able to offer.

    Thanks for your time.

  8. GBA Editor
    Martin Holladay | | #8

    Most people install polyethylene on the floor and walls before insulating the walls, but frankly, it doesn't matter very much. If you insulate the walls first, with either rigid foam or closed-cell spray foam (and no polyethylene on the walls), everything will still be OK. You can do the floor last if you want.

    Once again, here is a link to a useful article on the topic: Building an Unvented Crawl Space. If you are looking for more detailed how-to instructions than the article provides, check out the links in the "Related Articles" sidebar (including the non-GBA links near the bottom of that sidebar). There is an enormous amount of information available online -- which is why we provided the links.

  9. Expert Member
    Dana Dorsett | | #9

    Even a 1600' house is going to have a design heat load less than 25,000 BTU/hr, making only the very smallest gas hot air furnaces reasonable. Replacing the electric baseboard with hydronic baseboard, running off a condensing tank hot water heater would allow you to micro-zone with impunity, and never have to suffer the limitations of a tankless HW heater. It's a lot easier to find places to route pipes than it is to route ducts (which is how ducts all too often end up outside of conditioned space.) The 50 gallon all-stainless HTP Phoenix Light Duty is a good candidate for this type of combi-system, but there are others.

    Ducts only really make sense if you are also doing air conditioning, in which case heat pumps (ducted mini-split or traditional) make a lot of sense, especially at your modest outdoor temps and lower than national average electricity pricing they're about as cheap as heating with gas, have a lower carbon footprint, and the operating expense can be offset with rooftop solar if grid prices rise (or as solar prices continue the precipitous fall. Rooftop solar is now under $3/watt (all-in, pre-subsidy) at the national US average, under $1.25/watt in Australia where the market is more competitive. Even under the filtered-light skies of the Snoqualmie valley the levelized cost of PV would beat PSE retail at Australian pricing, and those prices will come to these shores in less than a decade.

    No matter what way you go, an aggressive (not conservative) room-by-room Manual-J is called for before specifying the equipment.

    If you insulate the walls with polyisocyanurate it's somewhat better to install the ground vapor barrier first, lapped up the foundation at least a foot (even up to the foundation sill if fine) so that the cut edge of the polyiso can never touch soil directly. Holding the polyiso in place with 1x4 furring through screwed to the foundation puts a few minor holes in the vapor barrier, but on the walls that doesn't matter.

  10. ruffryder | | #10


    Thanks again for your information. For reference, I have attached a couple of pictures of the crawl space. My plan is to install the vapor barrier up the foundation wall about 6" or so, then insulate from the bottom of the ceiling / top of rim joist (if word is applicable) to the bottom ledge of the concrete foundation where it would touch the ground if the poly wasn't there.

    Do I need to worry about insulating the whole part of the foundation to the ground? Or just the initial vertical piece assuming the rest is covered by the poly? See picture with plumbing in it. (Yes, I have some work to do there.. lol)

    Anything else odd / or to note with the pictures?

  11. GBA Editor
    Martin Holladay | | #11

    This crawl space has a fairly shallow footing, and the footing has been exposed (apparently because the dirt floor has been lowered to improve access).

    If you are able to insulate the exposed footing with closed-cell spray foam, using a two-component spray foam kit, that would help. But if you can't, you can't.

  12. ruffryder | | #12


    Thanks again for you help. Sorry that it seems you need to "type slow" for me. I started this process by trying to get natural gas run under the house and converting baseboard electrical heat to a forced air furnace. In looking for an alternative to putting back the insulation in the floor joists cavity (48" on center), stumbled upon the encapsulation method of crawl space conditioning and here I am.

    Martin, to clarify, the two component spray foam kit would be used from where the rigid foam insulation ended to cover the remaining part of the foundation? Instead of my wrapping that area with the rigid foam? It seems two-component sprays require a thermal barrier when used in crawl spaces, so that will add an additional cost / complexity.

    Again, thank you for your patience with me.

  13. Expert Member
    Dana Dorsett | | #13

    Rigid foam and spray foam can be simply painted with an intumescent paint in crawlspaces in most juridictions. It would be a good to find out if that's the case with your local codes & inspectors before diving in.

    The most critical portion of the wall to insulate would be anything above grade, down to a foot or so below grade.

    If the entire subfloor/crawlspace ceiling is 2x6 t&g rather than sheet plywood it's probably leaking a substantial amount of air with a vented crawl. It looks like they went that route to span the distance between beams without adding joists, but I would have though joists on hangers + plywood subfloor would have been cheaper than 2x t & g! (From the color I suspect it's douglas fir, too ubiquitous but still not cheap in WA.)

  14. ruffryder | | #14

    Dana, Martin,

    Is there anything wrong with cutting the insulation to cover all sides of the footing / foundation? I figure if I start at the bottom and work my way up, the tall side piece will hold the others (at least the one below it) in place. I know I will be using a lot of glue and also will need to tape all of the seams too. Since I plan on bringing the vapor barrier above the bottom section, this should further help in sealing everything up? My time is cheap here, so I would rather put forth the effort when possible, rather than paying someone, as long as I will get similar results.

    I assume once I seal up the crawl and have an exhaust ventilation fan, the leaky tongue and groove will help with conditioning the crawl? Not sure if it matters, but there is another layer (though thinner) of hardwood flooring on top of the tongue and groove.

    Have a good weekend.

  15. GBA Editor
    Martin Holladay | | #15

    There's nothing wrong with your plan to cover the horizontal and vertical parts of the exposed concrete footing with rigid foam. And, as Dana Dorsett pointed out, there's less heat loss through concrete components that are well below grade than through concrete components that are near grade. So you're fine.

  16. ruffryder | | #16

    Dana, Martin, thanks again for your help.

    Dana, you know have me looking into minisplits! This website can turn into a rabbit hole. Also, you mentioned in a previous reply about the limitations of a tankless hot water heater. Do you mind expanding on that thought.

    Thanks again for your time.

  17. GBA Editor
    Martin Holladay | | #17

    When Dana was referring to "the limitations of a tankless hot water heater," I think he was talking about the limitations of these appliances when they are used for space heating (rather than strictly for domestic hot water).

    For more information on this topic, see Using a Tankless Water Heater for Space Heat.

  18. Expert Member
    Dana Dorsett | | #18

    Tankless water heaters have limitations for domestic hot water applications too. The minimum flow requirements for reliable start-up is usually on the order of 1gpm, with a minimum flow to keep it burning on the order of 0.5gpm. That's a pretty high flow for a simple hand-rinse.

    Gas tankless units are also a problem for many Energy Star clothes washers that take intermittent draws short enough that the thing barely gets past it's flue purge and burner ignition cycles before flow stops, short cycling the water heater into higher maintenance and lower efficiency, often not delivering the requisite amount of hot water to the washer.

    And at the high end they are flow limited. A 180-199KBTU/hr tankless usually fine at WA incoming wintertime water temps for taking a standard flow shower (or even two), but filling tubs (especially big soaker tubs) is an exercise in tedium.

    Condensing tanks have none of these restrictions- you can dribble out 0.001 gpm when you want to, yet still crank out 10+ gpm when you want a significant slug of hot water fast. The burner only cycles on when the thermal mass of the tank has dropped in temperature then burns for several minutes, not having to run a flue purge and ignition on every hot water draw no matter how large or small. A typical tankless in a 3-4 person famlily cycles the burner 25-30 times per day, whereas with 50 gallon tank, 5-7 times. Every cycle adds wear & tear, and every flue purge blows some heat out the flue.

    Tankless combi-boilers typically suffer from both a minimum modulated output that's too high for the space heating load, unless you down-size it to the point where at maximum fire it only supports one shower flow with any amount of margin.

    A tankless water heater can make sense when interior floor space is at a premium (say, wall mounting it above the washing machine in a cramped laundry closet), and the standby losses are lower than a tank, though not usually enough to make it a reason to go condensing tankless over a condensing tank. I don't hate 'em, nor do I love 'em, but it's important to understand the practical differences and have realistic expectations around your rationale for going that route.

  19. ruffryder | | #19


    Thanks for your continued patience and advice to me. The condensing tank water heater looks pretty good, though on the more expensive side, and at initial glance looks less reliable.

    There is a small basement under the house, surrounded on three sides by the crawl space. I had plans of putting the tankless hot water heater in there, as it is centrally located by the bathrooms, and not too far away from the kitchen sink. Though this in depth discussion about tankless water heaters and their draw backs has me thinking maybe a tanked version is better.

    The condensing units seem too expensive for me now. To put a natural gas tank water heater will require a powered vent, which seems doable. Now I will need to figure out the issue of make up air. I wonder if the power vent of the hot water heater and its use of inside air would be enough to draw the air from the living space, via a floor vent and mitigate the need to install a separate exhaust fan? My head hurts...

  20. Expert Member
    Dana Dorsett | | #20

    The HTP Phoenix PH76-50 runs about $2K, and is all stainless, should last at LEAST 20-25 years in a 3-4 person household residential application, even though the basic warranty is only 10. It's a commercial hot water heater, but with a smaller burner that typical for commercial applications.

    The AO Smith PHE-50 is about $1700, but it's glass lined and much lighter-duty. If it craps out 20 minutes after the 6 year (seriously only six?) warranty is up your stuck, but it could go 12-18 depending on water quality, water usage, and dumb luck.

    A better class condensing tankless like the Rinnai RUC98IN runs about $1300, but comes with only a 5 year warranty on parts, 12 years on the heat exchanger.

    The somewhat heavier duty but comparable Noritz NRCP1112 or HTP HydraSmart RT-199 (same water heater, different marketing & support organizations) run about $1500, (less through distributors) also with 5 year parts/12 year HX warranty terms. The Westinghouse badged version of that same water heater (model WGRTNG199) sells at a discount, same warranty, and is currently listed for under $1K at the orange box store's website, if you're feeling ready to pull the trigger.

    A stainless condensing 199K tankless like that would last longer than a power vented tank, and would be fine (tankless quirks & all :-) ) unless you have a big spa to fill.

    Navien's NPE-240A is worth considering too, also about $1500, if Navien has better local support than the others. The warranty on the HX is a bit longer than most at 15 years, but the rest of it is the same 5 year parts/1 year labor type of deal.

    There are others, but don't go too cheap- there is some real junk out there.

    If you are a showering family and if the drains are accessible in that basement space, a 4" x 48" or larger drainwater heat exchanger can turn even the smallest gas-burner into an "endless shower" experience like a tankless, and would pay for itself. The longer & fatter, the higher the return efficiency, and the faster it pays off, despite the higher hardware cost. They need to be mounted vertically and typically need at least a foot more headroom than the length of the heat exchanger, but they're all copper, zero maintenance with an estimated lifecycle of 40+ years. Oregon has rebate programs for them for electric water heating customers, not sure if any such support is available in WA. A brief explanation can be found here:

  21. ruffryder | | #21


    The Navien's NPE-210A was the model of tankless that we were considering. Using that model and tying the recirculating pump to a momentary switch near the clothes washing machine should mitigate the issues of tankless. I have looked into the models of condensing tank heaters that you stated, and they look great, but 2k is getting to be a lot of money. Showers yes and I do have access to shower drains. I will have to look into that more.

    No recommendation to just a powered vent gas tank water heater?

    Keep in mind that I am converting from electric water heater to gas, so there will be / should be some big savings in that conversion alone. Also, I am doing a hot water relocation and converting my 1/2 copper all to 3/8 pex tubing too.

  22. Expert Member
    Dana Dorsett | | #22

    Any Energy Star power vent is about as good as another. It's a moving target, models change from year to year as do efficiency requirements etc. They also have fairly short warranty periods (6 years typ) compared to 10-12 for electric tanks, and you should be able to get a dozen years out of it, but don't count on 15.

    A drainwater heat exchanger is a chunk o' change. You can order them through the orange box store for only the left arm of your eldest child, but most of the manufacturers will sell direct. A database of apples to apples third party tested efficiency to a standarized test protocol of many different models & vendors is maintained by Natural Resources Canada, which can be downloaded in a spreadsheet format here:

    The buy-direct pricing is higher than through distributors, and if you have occasion to drive to B.C. you can probably get a better deal there.

  23. ruffryder | | #23

    The htp / Westinghouse heater looks interesting. HD has it for 2300, and seems to be pretty well liked here. With all the rebates and credits it would be about 1k out of pocket.

    What about the Rannai hybrid? That looks pretty interesting too.

  24. ruffryder | | #24

    It looks like my options for putting the water heater in the basement are a condensing tankless water heater or a condensing tank water heater. I want the HTP / Westinghouse but it is almost twice the cost of a tankless heater. Though I guess if the HTP lasts twice as long then the difference will be minimal over the long run.

  25. ruffryder | | #25

    Well, this has been quite the learning experience. It finally sunk in that the HTP / Westinghouse can do radiant heat as well as hot water. Based on the pictures above, is there a big negative to running the radiant heat under the flooring from the crawl space? Thanks again for the help, I am slowly getting there, I think.

  26. Expert Member
    Dana Dorsett | | #26

    With 1.5" thick t & g subfloor your water temps will need to be a bit higher than if it were 3/4" plywood, but at your modest design temps you should be able to do it all at condensing temps, provided you use some decent heat spreaders (not staple-up, not suspended tube) for the radiant.

    The HTP/Westinghouse units would still need an indirect tank for the domestic hot water. The separate port for the hot water loop is not isolated from the heating system water, unlike a typical wall hung combi.

  27. ruffryder | | #27


    Does the HTP / Westinghouse unit need an indirect tank to also be used with a hydro-air handler? I am close to purchasing the unit and want to get all my facts straight.

  28. Dana1 | | #28

    An indirect would only needed for hot water. The boiler (just like almost any other boiler) can be used with a hydro-air handler. HTP even markets a line of thin hydro-air coil consoles for micro-zoning with the UFT series boilers.

  29. ruffryder | | #29


    So anytime you are trying to use tank water heater for something else besides domestic hot water (dhw) you need to use an indirect tank to get dhw? I guess I need to look into this a little more.

  30. GBA Editor
    Martin Holladay | | #30

    You don't need an additional tank when you connect the HTP Phoenix PH76-50 to an air handler. Click this link for more information: Combination Heating with an Air Handler.


  31. Dana1 | | #31

    David: The UFT series boiler has no tank, and thus needs an indirect tank for DHW. The indirect has an internal heat exchanger that isolates the potable water from the heating system water. Using a water heater for space heating only requires a heat exchanger to isolate the potable water from the heating system water, which can be external to the tank, though there are tank-type combi boilers with internal heat exchangers and heating-system specific controls.

    When using a very low water volume heating system such as a hydro-air handler, the isolation requirement is usually waived, though some state codes require at least some minimum daily flow to avoid water stagnation in the the air handler coil & associated plumbing. Using potable water in the heating system puts constraints on the materials used, since the potable water can't be contaminated, and the heating system components must be resilient against the higher oxygen levels of potable water. (This means bronze pumps must be used instead of iron, etc.)

  32. Expert Member
    Dana Dorsett | | #32

    But the Westinghouse WBRUNG-080W isn't a tankless, it's a wall-hung boiler. It is set up to easily add an indirect tank, since it is internally pre-plumbed with ports for the indirect tank (out the bottom of the boiler) as well as space heating (out the top).

    Look closely at this installation (of the HTP badged version), that includes an indirect for hot water:

  33. ruffryder | | #33

    Maybe I just need someone to say "go buy the westinghouse condensing already, you fool" ? lol

    edited, sorry not westinghouse tankless, westinghouse condensing, AKA HTP Phoenix. sorry for the confusion

  34. ruffryder | | #34

    Sorry Dana, I screwed up my post above and said "tankless" when I meant "condensing". Sorry for the confusion and again I appreciate your patience.

  35. ruffryder | | #35

    Thanks again for everyones patience. I have been working on some structural issues with the foundation / crawl space so I have not progressed as fast as I was planning. Hopefully I will be able to lay the vapor barrier by the end of the week. We shall see.

    I am still torn on the water heater. In the crawl space area is a basement, accessed only from the outside of the house. The basement has an access port (4 ft by 2 ft or so) for getting into the crawl space. My plan is to put the tank water heater down in the basement to free up space in the garage for the conversion to living space.

    A power vent tank hot water heater (Rheem power vent) is about $900 while the condensing tank hot water heater (HTP Phoenix) is $1000 more. I don't think I will be able to save $1000 of natural gas over the life span of the domestic hot water system with the condensing unit, and we are looking into heat pumps for heating and cooling, so it is possible the condensing tank heater would only be for DHW.

    Currently the basement is sealed off with a wood door from the crawl space. When the crawl space is encapsulated, I would keep the wood door open to provide combustion air to the water heater.

    I guess I am just hesitant to spend almost $2k on a condensing tank hot water heater.

    edited for clarity

  36. ruffryder | | #36

    So, as always, life keeps getting interesting and in the way of this project. I have the HTP water heater and in the process of finishing up this project so that I can get on to the natural gas install and get the water heater running.

    I failed to mention that in the middle of this crawl space is a dug out basement. The basement is about the size of the master bedroom and is built out of concrete block with a wooden wall on top.

    Attached is another picture, showing the side of the basement. I planned on running the vaport barrier to the top of the concrete wall lip, keeping away from the wood, but I thought it would be an easier way to seal it. After the encapsulation project is completed, I anticipate keeping the basement open to the crawl space.

    Your thoughts would be appreciated.

    Also, the jack in the wood support has been remedied (replaced with new 4x8 beam on pad), and I have lowered the concrete pads in the foreground and replaced the beams there as well. I added fill to mitigate further issues with foundation at the corner. So the mechanical stuff in the picture has been fixed. It looks... interesting unfortunately.

  37. ruffryder | | #37

    I also have another question. Since my construction isn't typical, I am not sure of how to do the insulation. Please see the included picture. For now I thought it would be best to run the vapor barrier about 6" or so up the foundation wall, staying just below the foundation vents. I planned to fill the foundation vents with a piece of treated wood, 2x12 or something like that. Also, note that above the foundation, the sill plate (if that is what it is called) doesn't extend out similar to the foundation. Should I rip a piece of wood to go in there before I put the foam board up? Or just use spray foam (great stuff) right before I put the foam board up? I thought leaving the space empty kind of looks like a little raceway for mice and what not.

    Your thoughts as always are appreciated. I apologize that I haven't been able to put some of your advice to good work yet, but I am getting there!

  38. GBA Editor
    Martin Holladay | | #38

    In Comment #36, you posted a photo, but you didn't ask any questions.

    In Comment #37, you asked these questions:

    Q. "Should I rip a piece of wood to go in there before I put the foam board up? Or just use spray foam (great stuff) right before I put the foam board up?"

    A. When you insulate your crawl space walls, you can run the rigid foam almost to the subfloor boards. Leave enough of a gap to allow you to insert the straw from your canned spray foam dispenser. Then squirt enough spray foam in there to deter the mice.

    For more information, see Building an Unvented Crawl Space.

  39. ruffryder | | #39


    Thank you for your response. With respect to Comment #36, I wanted verification for the attachment method for the vapor barrier to the basement wall, ie attaching the VP to the top of the concrete blocks rather than the side of the blocks. Also, are there any other issues with the basement / crawlspace that need to be addressed? I have two entrances into the basement from the crawl space. My plan is to keep both of these open (maybe have a screen framed door to allow air movement but act as a safety net for for rodents), so the basement becomes conditioned as well. Since that will be the case, I assume I don't need to insulate the wall between the crawl space and the foundation, since they will both be conditioned the same.

    Thanks again for your time.

  40. GBA Editor
    Martin Holladay | | #40

    Q. "I planned on running the vapor barrier to the top of the concrete wall lip, keeping away from the wood. .. I wanted verification for the attachment method for the vapor barrier to the basement wall."

    A. Your plan is fine. Rigid foam is also a vapor retarder, so it doesn't really matter how far up the wall your polyethylene extends.

  41. ruffryder | | #41


    Since the wall in question is between the soon to be conditioned crawl space and the conditioned basement, I was not planning on adding any insulation to that wall.

    Understood that your statement does apply to my other exterior walls.

    Also, what is the best method for sealing the vents? Does my idea of using 2x12 treated lumber sound reasonable? I would do that on the inside of the crawl space, so that the wood sits flush, then also reinstall the exterior vent covers. Therefore I would hopefully get some redundant protection.

  42. GBA Editor
    Martin Holladay | | #42

    Whatever you use to seal the vents, the materials (a) should be as airtight as possible, (b) should have a decent R-value, (c) shouldn't present a fire hazard, and (d) should be weather-resistant on the exterior.

    Some type of sandwich of materials, with rigid foam in the center, makes the most sense.

    It's also possible to fill the vent openings with bricks and mortar, and then to install rigid foam on the interior side of the bricks and mortar.

  43. ruffryder | | #43


    My plan was for the rigid foam to completely cover the opening on the inside of the crawl space. So the above mentioned 2x12 treated and outside metal closure would be in addition the rigid foam.

    Also, do you have any recommendations for a best practice for laying vapor barrier with all of these posts everywhere? This part is going to be a lot of fun..... I saw an idea where you would lift up the posts slightly to put the vapor barrier underneath the posts, between the posts and the concrete. I have the ability to due this, but I am not sure it would be the best way to go about it, and would still be a lot of work.

  44. GBA Editor
    Martin Holladay | | #44

    Q. "Do you have any recommendations for a best practice for laying vapor barrier with all of these posts everywhere?"

    A. The usual method is to bring the polyethylene up to the bottom of the post and to tape the polyethylene to the post (using housewrap tape). The seams of the polyethylene should also be taped.

  45. ruffryder | | #45


    I thought it wasn't a good idea to wrap a wood post with the vapor barrier? I would agree with a concrete post though.

  46. GBA Editor
    Martin Holladay | | #46

    You're not wrapping the post with polyethylene. You are taping the polyethylene vapor barrier to the base of the post.

  47. ruffryder | | #47


    I apologize if I am being dense here, but if you tape the vapor barrier to the base of the post, is not the bottom of the post wrapped in polyethylene?

    I thought it was not appropriate to wrap any wood with a polythylene sheet?

  48. GBA Editor
    Martin Holladay | | #48

    If your tape is 4 inches wide, about 2 inches of tape will be needed on the base of the post. The rest of the post is exposed to the air.

  49. ruffryder | | #49

    Martin, Ha, I guess I was trying to be too literal and not using my brain. Thanks again for your help.

    On this note, since I plan on closing the vents up with pressure treated wood, I assume I should not cover the vents with the vapor barrier? As that would trap the moisture and potentially rot the wood?

    Sorry for all of these questions. I have the material and everything ready to go in the crawl space, I just want to make sure of everything before the install. You have been a tremendous help!


  50. GBA Editor
    Martin Holladay | | #50

    If you are closing up your vents with pressure-treated wood, you still need to insulate these areas. As I wrote earlier, I suggest that you include one or more layers of rigid foam somewhere in this sandwich assembly.

    The rigid foam is a vapor retarder. You don't want or need any polyethylene in this sandwich.

  51. ruffryder | | #51


    Crap, I guess I am confused again. I planned on ceiling up the vent with the pressure treated plywood so that it is flush with the inside of the rest of the concrete foundation wall, as these vents are cut into the foundation. I will then bring up the vapor barrier to just below these now enclosed vents, so as to not cover the the wood and trap moisture with the wood. I will then bring then attach rigid foam insulation on the inside crawl space for the foundation wall, going from near the floor to the bottom of the crawl space ceiling. Gaps will be filled in with spray foam and seams will be taped.

    The attached figure shows my plan. Are you saying that in addition to the 2" rigid foam on the inside of the crawl space foundation that I should include additional insulation in the cavity of the vent?


  52. GBA Editor
    Martin Holladay | | #52

    Your approach will work fine. However, if you want to add more rigid foam insulation between the two pieces of treated wood, you certainly could.

  53. ruffryder | | #53


    Thanks for your confirmation. Since the rigid foam is itself a vapor retarder, is there any harm in raising the height of the vapor barrier to above the vent?

  54. GBA Editor
    Martin Holladay | | #54

    No harm. But you are overthinking.

  55. ruffryder | | #55

    Well, I guess it is time for a status update. I finally finished the vapor barrier. It was a ton of work, taking much longer than anticipated. I am still not completely done, as I need to wrap the concrete piers, but that will be for another day. I have been contacting HVAC installers, and have not found one to utilize the HTP Pheonix with an air handler for space heating, so I will be going with a conventional forced air system. I do like the idea of separate components, so an outage of one won't leave us with heat and hot water. Just a consolation discussion I guess. I have yet to close the vents off, since I appreciate the light and air flow while I am working down there and have yet to install the insulation anyways.

    Speaking of which, Rmax sells a foam insulation, TSX-8500 that includes an ignition barrier. I have been looking at spray foam vendors and I have not found one that includes an ignition barrier yet. I like the spray foam idea as it would be a good method for sealing too.

    I included a couple of pictures, hopefully you guys appreciate them. It sure is much nicer being down there with the vapor barrier installed.

  56. GBA Editor
    Martin Holladay | | #56

    Nice work! That floor looks clean and pretty.

  57. Expert Member
    MALCOLM TAYLOR | | #57

    I've done a couple of those. Never with as nice a result. It's horrible work. I sympathize.

  58. ruffryder | | #58

    Thanks everyone for the kind words. My wife is currently wrapping the pier blocks to make sure everything is sealed up tight.

    I am actually going to be going through the permitting process for the crawl space conversion with encapsulation. Going to be some fun time with King County.

    The local building code states to use R15 rigid continuous insulation for below grade walls. The only insulation locally I was able to find is the Rmax TSX-8500.

    Information can be found at the link below.

    It is interesting that the thermal property data has a Thermal R-value and a System R-Value, the system R-Value including the 2.77 R-Value associated with the use of a reflective foil assembly.

    The 2" thick sheets have a thermal value of R13.1 and a system value of R15.87. System value meets code, otherwise I would need to use something thicker.

    Permit was almost $500 for this, about the cost for the insulation itself! Didn't want to do it, but when the HVAC system gets installed without insulation on the ducts, I didn't want to get called out and have to redo things at that time.

    Anyone have any thoughts on the usefulness of the System R-Value? Any thoughts on dealing with permits and this?

    Down the rabbit hole I go.

  59. ruffryder | | #59


    I forgot to mention, I put the vapor barrier on the wall first. The plan was then to put the insulation over it. After my wife's conversations with the building department, they might want me to pull the vapor barrier off the wall and attach it to the insulation instead. Not too big of deal, as I hadn't gotten around to attaching all of the plastic anchors yet, but something I will try and keep everyone updated with. If anyone cares.

    Oh, and I should be installing my new water heater soon too!!

  60. GBA Editor
    Martin Holladay | | #60

    The "System R-value" column in the table you linked to refers to the R-value of a wall assembly that includes a 3/4-inch-thick dead air space adjacent to the foil facing of the rigid foam. It's possible to create such an assembly with 1x4 furring strips and drywall if you want the extra R-value associated with the air space. But you can't claim the R-value of the air space unless you build it.

  61. GBA Editor
    Martin Holladay | | #61

    If your building inspector makes you remove the polyethylene that is now sandwiched between the concrete and the rigid foam, and install the polyethylene on the interior side of the rigid foam, then your building inspector is ignorant.

    Every layer of this assembly is a vapor barrier. The polyethylene is a vapor barrier. But the foil facing on the rigid foam is also a vapor barrier. (Frankly, the polyethylene is unnecessary, but that's another issue entirely.) Whether the polyethylene is behind the foil-faced foam or in front of the foil-faced foam makes no difference -- the stackup is a vapor barrier in either case.

  62. ruffryder | | #62


    To clarify, I have not installed the insulation yet. I wanted to make sure with the building department that the insulation I was choosing would be sufficient. Therefore, removing the vapor barrier from the concrete, installing the insulation behind it, then reattaching the vapor barrier won't be too much of a deal for me. Do I want to do it? No, but it can easily be done.


  63. ruffryder | | #63

    Further update. They didn't want anything removed. Got the permit and everything will be going in next week. I ended up getting 3" insulation due to limited ability to get the needed 2.3" without having to purchase twice as much as I need. Oh well, an extra R5 never hurt anyone. My crawlspace will be the best insulated part of my home! lol.

    I am having a furnace put in next week in the basement (note crawlspace surrounds the basement on three sides). The basement floor is concrete and there is an all purpose carpet over it. Should I pull the carpet and put down a vapor barrier? I do not know if one was placed below the slab. Note the crawl space is at a level of just at 4ft from the floor of the basement. Anything else I should be doing?

    Attached is a picture of the basement. This house sure is interesting. I also added a picture of the hot water heater. Thanks for everyone's suggestions. The water heater will come in very handy when my three kids turn into teenagers.

  64. ruffryder | | #64

    Well all. The journey is pretty much complete. I slacked off the last year as I got the furnace and water heat installed and was done and tired of the work. Flash forward to a month ago and all of my permits were expiring so I finished up all my plumbing, electrical, mechanical, and construction permits for the crawl space and passed them all. I got complements on the crawl space being so clean. It was a lot of work but it is done.

    I will update with some pictures tomorrow.

    Thank you to everyone that provided information, help, guidance, and patience!

    Now onto the garage conversion...

  65. Deleted | | #65


  66. ruffryder | | #66

    Some pictures

  67. exeric | | #67

    It looks to me like a very well done job. That should feel like a real accomplishment. The biggest problem with an unimproved crawlspace is that one wants to avoid the whole space. You know that in the unimproved state the moisture and humidity down there is like cancer in that it's rotting the house from the foundation. Plus, it's so unwelcoming down there in its raw state you are almost afraid to go down there and actually see what might be going on.

    The final touch is to have a permanent switched lighting system down there so you, or the next owner, doesn't feel intimidated to actually go down there occasionally. Good job.

  68. ruffryder | | #68

    Thanks for the compliments. It is hard to see but there is permanent lighting down there. Just that it is hidden by the duct work. I have thought about expanding the lighting and such, but that is a lot of work for minimal gain. Headlamps work better as my body always seems to block the light. A diet might help that better. Lol

    Well, I guess that is all. Thanks again to everyone and have a great holiday season!

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