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I’m debating this idea for my Huron house.
I have a 6′ crawl space on a very sandy site. An HVAC guy suggested that I insulate the walls and drop a few heats into the crawl. He claims that this is a good idea because heat rises. He thinks that I can eliminate the insulation around the duct work and also eliminate the insulation in the joists.
I think I agree, but am not convinced. The floor of the crawl is about 40″ below grade.
Please forgive me if this has been discussed before.
blue
Replies
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I'll chime in.
Even if its dry and sandy, there is still humidity unless your in an arid climate. I vote for a vapor barrier either on ground run up against the walls or attached under joists, well sealed at laps and edges.
Why bother heating this space? Insulation in the cavities can be protected from convected heat losses by attaching 1/4" OSB or celotex to bottom of joist bays.
*Blue, How did you end up with a 6' crawl space?? What is that ...Basement Lite ?? I'm guessing you dug down to near water table and didn't want your cabin sticking up in the air any farther , so you compromised ?I would treat that much space as I would a regular basement. I would pour a floor with a vapor barrier under it and insulate the walls with 1 1/2" foam. Cover the foam with material of choice.You certainly have enough room to put your mechanicals in this space if you want to save room upstairs. Possible Bilco door on outside ?Are the walls waterproofed?
*G.Lalonde, I was concerned about high water tables enough to decide against a full basement. But I didn't want to slither around like a snake or walk around half squatted over. I am sticking out of the ground more than I would like.Basically I didn't want to be deep, and wanted to be high enough to see over the dune. Kinda caught between a rock and a hard place.I'm not interested in saving space upstairs, because I'm not sure how high the water table will be, once the Great Lakes come back to their high mark. Right now they are at an all time low, and I'm being cautious.I'm thinking about putting 1/2" foam on the perimeters, then framing and putting fiberglass batts too. I was going to lay visqueen and tuck that up under the foam at the walls. But I don't see any need to lay concrete down there. That seems like a waste of money and time and effort.I'm going to put the access inside the attached garage.blue
*Blue: IMO, there's no contest; insulate and condition it (with vapor barrier, of course.)I haven't seen any conditioned crawls with moisture problems (mold, decay) in the sill plates, box ends or floor framing, even where there have been large amounts of water ponding on the VB. (I probably go through 5-8 crawls a week in NW Ohio.)You i mightbe "wasting" some heat, although with a warmer floor you might break even or save because with warm feet, you'll be setting the thermostat lower.I think the rat floor is a good idea: makes it a lot easier to work down there, but, of course, I'm not paying for it. (Think of the money you'll save on viz-queen though )Bob
*blue.... i always wrestle with this one.. but my pref. is to insulate the walls and condition the space..the alternative is to insulate the floor.....so , how ya gonna do that..?usually with fiberglass batts...try this site..http://www.r-control.com/they license eps foam mfr's around the US..they have a product of eps in various densities.. .. you can get it treated with borates so it is vermin proof.. and they can even bond cement board to it so you can line crawl spaces and not worry about flame spread...my next crawl space (whenever that is).. will have 3"eps with borates and ""fire finish "" quoted at $52 for 4x8....R-12.5..so i could insulate the wall of a 28x40 foundation with 17 sheets... $884..
*Okay, I'm convinced. Nw Ohio is close enough to me. The sand actually is a very good drain to, if water should enter. Now, I'm concerned about putting foam down there, which might contribute to a fire. Is covering it with insulation batts enough, or should I be thinking about a different type insulation? I don't want to skin the walls with drywall.I suppose I should have thought all this out before I framed it, but I admit, I'm a lousy builder/designer. All I really know how to do is frame them.blue
*Mike I went to the site but couldn't read the charts.Does that figure include only materials?Are the borates for vermin control or fire control?r 12.5 sounds good enough for a crawl.blue
*the borates are for the vermin...and the fire coating is for flame spread..also.. i didn't want to cover with drywall ,, cause it would wick up moisture and disintegrate.. they bond this material to the skin .. just like a stress-skin panel...so the quote was material only... but .. what's the labor /dig a little trench around the inside of the wall drop the sheet into the trench.. have the top of the sheet flush with the top of the joists..and pour cellulose into the box formed between the band joist and the 3 inch eps against the concrete..then put the plywood deck on...voila'..insulated crawl space....vermin proof, no fire exposure.. r12.5.. what's not to like ?
*Mike, I like the idea. Now, I just have to move the house to one side and do your thing.blue
*Blue, I would go with the other HVAC guy. Close the crawlspace, insulate the walls and put a vapor barrier down on the ground. Then pour concrete over the vapor barrier. This keeps the moisture from evaporating out of the ground. That can amount to as much as 12 gallons per day per 1000 square feet of crawlspace. If you drop some heat vents into the crawlspace, also add some returns. Otherwise you pressurize the crawlspace and the HVAC system acts like a big exhaust fan. That makes it very hard to heat & cool the house, especially in extreme weather. It can also bring in a lot of moisture. Note sandy soil usually evaporates less moisture than clay. Kevin
*Kevin:> Otherwise you pressurize the crawlspace and the HVAC system acts like a big exhaust fan. Interesting concept, although I don't understand why that would happen. Could you expand on that? (E.g., furnace location, other factors?)The concern I would have is if the crawl doesn't have a rat floor (which very few do in my area, just plastic) we're pulling air from the crawl into the circulated house air. Not to tasty, IMO.
*Bob, If you have a supply duct blowing into the crawlspace, air is being drawn into the house return(s), then blowing outside the house (unless there is a door from the house to the crawlspace. This is because there is no return path for the crawlspace air to get back to the heated part of the house. The same thing can happen in a sun room or outside laundry room. If air is blown into any room that does not connect to the rest of the house or return duct system, you have a net loss of air from the house. The house is then under a negative pressure, and air will leak back into the house through any cracks or holes; from the outside, attic or crawlspace. As you said - it is not very healthy. Kevin
*Mike. You said "dig a little trench around the inside of the wall drop the sheet into the trench.. have the top of the sheet flush with the top of the joists." My understanding of borate is that it is not tolerant of moisture. How are the edges of the panel moisture protected in the bottom of the trench?"have the top of the sheet flush with the top of the joists." Are the sheets between the floor joists? And if they are how do you get the cellulose in given that the tops of the sheets are flush? with the plywood subfloor? GeneL.
*gene..both good questions..but not what i understand..the eps is designed for burial... the high density can be used under road beds..you yourself have posted studies showing no appreciable wicking or absorption of moisture in eps..that is why i took another look at eps.... i had always dismissed it for ground contact use previoulsly.. but htose studies convinced me.. and the pricing is so superior to Styro-sm.. or Poly-iso..especially where i'm looking mainly for a thermal break (trade money for r-value ).. the borate is encapsulated in the eps process ? (my guess.. else it would be self-defeating..)also.. Bora-care loves moisture.. actually penetrates better in a moist enviornement (from reading their literature.. i'm not an expert )my method of installing is all in my head.. ..if it is say.. 3 ft 10 inch from the bottom of subfloor to the crawl space floor.. dig a 3 inch trench,, slip the sheet into the trenh and shim it so it is even with the top of the joists.. on the long walls .. cut notches in the eps so they will fit around the joists.. again shim the bottom so the eps will be flush with the top of the plywood..all of the eps would be installed PRIOR to the plywood subfloor being installed...and the cellulose could be poured into the box formed by the eps sheet and the band joist...what cha think ?
*Kevin,Good points, thanks.What do you think about putting a return-type register between a conditioned crawl and the furnace room?Btween a conditioned crawl and a basement (assuming combination sub grade spaces - common with newer construction in my area?)
*Bob,If there are return grilles in the return plunum in the furnace room, you could have return grilles between the furnace room and the crawlspace. That should work fine if the crawlspace is conditioned & closed off from the outdoors. Putting grilles between a conditioned basement and a conditioned crawlspace should work OK also, provided there is a return duct connected to the basement. Make sure you filter the air from the crawlspace & basement. If there is a return grill in the return duct in the crawlspace, the furnace must have a sealed combustion chamber. Otherwise flue gasses can be pulled down the chimney into the return duct, then distributed into the house.Kevin
*In the area we have our cabin, NW Wisconsin, crawl spaces around lake places are the norm, rather than the exception. All the locals recommend one of the two following applications: 1) Cover floor and 6" up the walls with heavy poly, then place 1" or 2" (your choice) rigid insulation around the inside or outside (your choice) perimeter walls. OR 2) Cover floor and 6" up the walls with heavy poly, then place fiberglass batts in the floor joists. Some people think that if some insulation is good, more must be better, so they do #1 and #2, in which case they create a "refrigeration unit" in their crawl space, and they either have to close up the vents in the humid summer, or place a dehumidifier in there, OR put a giant blower in the crawl space. We did #1, and even without a heated crawl space, it ALWAYS stays above freezing, and the floor is not uncomfortable. Note reason we didn't choose #2: rodents LOVE fiberglass insulation for the same reason we love down comforters. Plus, it's much easier to work down there without insulation dust all around. Hope this gives you more ideas to consider...........
*Thanks Anne for the input. I tend to agree about the batt insulation. I'm probably going to take a serious look at Mike's idea and insulate the walls.blue
*Along these lines, was talking with an insulator yesterday, an older gentleman with a family owned & operated business who has been blowing cellulose since 1980 (in all its various forms). He suggested two things which were interesting.One was to blow about 1" of wet cellulose onto the bottom of my upstairs floor for soundproofing. Says he makes it stick by mixing glue with it and it "works really well." Never heard of this, and he said he's never seen anyone else do it either, but developed the technique because people asked if it could be done.Secondly, he can do the same thing on the inside of the foundation wall. He starts about 6" off the ground (so termite folks can look for "tracks") and goes all the way up to the subfloor.He gave me a price on both of these "options." Has anyone else ever seen this done? Obviously moisture could be a problem, but my crawlspace is dry as a bone, even after the rainiest November on record. I am a "no crawlspace venting" guy (I put them in, but will block them off) and will of course put down a heavy vapor barrier. What are the drawbacks? Will this work? Ever seen it???
*I've done many projects such as yours, up in ccccold Canda. Each projet varies but we usually line our grade beam or concrete wall with 2" styrofoam SM, poly and pour aprox. 2" on concrete to seal the grade and duct heat into the crawl space. It makes for warm floors and no cold spot. We do it on all our cantilevers as well.
*Crusty, Advanced Energy is doing that in North Carolina, only they use foil backed foam insulation and leave a 3" gap at the top to check for termite tunnels. They lay plastic sheeting on the ground and seal the over-lap with RCD#6 duct mastic. They seal the plastic to the foam insulation the same way. They cover the foundation vents with the foam insulation. John Tooley at advanced energy told me that they have managed to get the code changed in North Carolina so that they can seal crawlspaces now with only a VERY SMALL exhaust fan for ventilation, on the order of 20 CFM/1000 sq ft of crawlspace. They fasten the foam to the foundation wall using nails through wood (1 x 4s).I don't know how the glue and cellulose would work but it sounds like a good idea, probably would be easier to apply than foam insulation.Kevin
*The bid for "soundproofing" the upstairs with blown-on cellulose seemed high; I need to check the numbers again, but I can completely fill the upstairs floor cavity (16" floor trusses) with cellulose for much less money if I do it myself. Also, I think I will have a small section of my crawlspace walls blown over so I can test the durability for a while. Will report back.
*Have been reading this thread with great interest as we finalize specs for our new home with partial basement and crawl space. I see Kevin’s point (post #12 above) about negative pressure problems associated with running a supply duct to a crawl space without a return. However, even if you filter the air coming back from the crawl space I’m a bit nervous about potential problems with radon (we're in a high radon area),off-gassing termite treatments, etc. So, am wondering about the pros/cons of an approach recommended in Lstiburek’s Builder’s Guide for Mixed Climates. A detail for "Combined Controlled Ventilation, Soil Gas and Crawl Space Ventilation System" involves placing supply registers (but not returns) in conditioned crawl spaces while creating a continuous exhaust from the crawl space by running a fan to pull air through a duct that runs up and out through the roof. Wouldn’t this be a viable alternative to installing returns in the crawlspace? We are planning to use a central fan-integrated supply ventilation system, (eg, AirCycler) so assuming the fresh air intake can be regulated to balance the amount being supplied to and then exhausted from the crawl space, there should’t be a problem with negative pressure...am I right? I’ve learned a lot from the Builder’s Guide, not to mention FHB and JLC, but sometimes find it confusing when trying to adapt the recommendations to my particular situation. That’s why these forums are so helpful...thanks to all who contribute! Donna
*Crusty - any chance of the "insulator" telling his mix of glue and cellulose? I've just looked into foam insulation for the undersides of my floor(150 year old home without subfloors, what I walk on is what I've got). The prices are out of sight. Perhaps you would give me his name/buiness name/pho or phone number. Thanks for your time.
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I'm debating this idea for my Huron house.
I have a 6' crawl space on a very sandy site. An HVAC guy suggested that I insulate the walls and drop a few heats into the crawl. He claims that this is a good idea because heat rises. He thinks that I can eliminate the insulation around the duct work and also eliminate the insulation in the joists.
I think I agree, but am not convinced. The floor of the crawl is about 40" below grade.
Please forgive me if this has been discussed before.
blue