Crawlspace insulation - be careful to get it rightA crawlspace comes with all the downsides of a basement, but it is just too low a space to be functional either beyond the folded plastic christmas tree and a couple of boxes of baubles. Unless there is a good reason for it, going through the process of pouring a footing, then a concrete wall, then building a subfloor above and only be able to access it on your hands and knees is a lot of effort for the value you will get from that space. If you don't want a full basement, a great alternative is to build a.Important note: The following crawlspace solutions are recommendations for how to deal with moisture and heat loss only, and provide only an anecdotal overview of how to deal with. We would recommend having your air tested for radon, and if it is above Health Canada’s recommended safe levels ( 200 Bq/m³), please see our pages on. Fixing a dirt floor crawlspace:All too often a crawlspace will have nothing but a dirt floor, and probably some un-insulated walls. The result of that is an unending source of humidity as moisture in the ground evaporates into the air and can condense on cold walls and joists where mold can establish itself.That dank air will inevitably be circulated throughout your home, providing humidity, mold spores and a pretty nasty smell that will be the dominating odour of your home, furnishings, and your clothes, so you will take that aroma everywhere you go.
Crawlspace vapour barrier © Pescrawlspaces.comFor those with nothing but a dirt floor, the single most important thing to do will not cost much - cut off the moisture supply to the air by laying down polyethylene directly on the ground. The standard 6 mil poly vapour barrier will work fine as a DIY solution. Do the best job you can and seal the joints, but remember - if you did nothing else beyond laying it down over most of the floor, even without taping or sealing it, you would reduce the amount of moisture in the air. If your crawlspace access is inconsistent and you can only hope to do 80% of it, do it anyway; you will notice a very big difference.The 6 mil poly is far from being a complete crawlspace solution, but we’re putting that out there so as not to leave those with really tricky crawlspaces or tight budgets feeling dejected. This is not an 'all or nothing' situation where there is no point doing anything if you can't do it all - do as much as you can, it will help.
Insulating crawlspaces:The best way to insulate a crawlspace would be to do it from the ground up and consider it just part of the conditioned space as you would with any basement. We make no secret of the fact that we aren't huge fans of spray foam due to the emissions associated with it but this is one place where it can make a lot of sense.Spray foam is done quickly, it has a high R-value, provides an air and moisture seal and fills all the tiny holes. This is not a DIY job so it will be among the more expensive options, but it will work well, and best of all. Someone else will be slithering around in your crawlspace rather than you. Since it will act as a vapour barrier, there is no need to lay down poly ahead of time; it can go right against the dirt.When it comes to insulating the walls, there are a couple of ways to go about this – Building Code requires any crawlspace more than 5 feet high to have fire protection covering any foam products, in which case you can frame a 2x4 or 2x6 wall 1 inch away from the concrete wall; sitting it on small chunks of foam will keep it from being in contact with the ground and absorbing moisture. Spray foam is then applied to the walls behind the studs and into the cavities, you can leave enough room to do any wiring if required.
Spray foam insulating basement walls © Bala StructuresThe foam needs to then be covered with drywall as fire protection, which can be attached to the stud wall. No vapour barrier is required in addition to spray foam. Building codes change and can vary by region, so confirm this locally, but currently The National Building Code in Canada for example allows without fire protection on crawlspace walls that are less than 5 feet in height.An additional option, for walls only, that you can do yourself is to apply EPS foam boards directly to the concrete using either strapping and tap con screws, or an appropriate adhesive that is suitable for foam boards (it should say so on the tube). EPS can be substituted with XPS foam, but given its much higher greenhouse gas emissions, we prefer to recommend EPS.
Many houses have workshops in the basement. If you like to work on things, but don’t have the space, a converted crawl space gives you the perfect chance to create a full workshop. One advantage is that you don’t even need to fully finish the space, as cinder block walls are perfectly acceptable in a workshop. Convert Your Crawl Space into a Storage Area There's nothing stopping you from storing off-season items in your crawl space—nothing except for moisture, mold, insects and potentially rodents.
XPS qualifies as a vapour barrier at 1 inch, and testing shows that EPS foam acts as a vapour barrier (1 perm) at 2 inches or thicker. Rock wool insulation batts on basement walls © EcohomeRock wool (mineral wool) boards are an alternative product you can use and they are made from recycled stone dust, so it does not burn and does not need to be covered for fire protection.
But mineral wool is not a vapour barrier, so it is best to apply a poly membrane against the concrete first.Note: Taped XPS foam is an air barrier, but EPS and mineral wool are not. Air doesn’t leak through intact concrete but it is quite likely that crawlspace walls will leak air. If you have a stone foundation, old cracked concrete or cinderblocks, bringing the poly barrier up the wall and sealing it to the rim joists will provide you with an. Preparing a crawlspace for vapour barriers and insulation:First clear the space as much as possible so you have room to move around. Ensure there won't be any problems with bulk water accumulation by installing a sump pump at the lowest point. Even if you’ve never had flooding in the past, that does not mean you will never have it in the future. We’ve never heard anyone say they regretted installing a sump pump.Remove any sharp rocks and obvious obtrusions for a more even surface so that you won't tear the plastic as you walk on it.
Should you vent a crawlspace?No, you should not. Drawing humid air into a cold crawlspace in summer or winter defeats the purpose of stopping the source of moisture. A moisture protected crawlspace will probably be quite cool in summer and should be less humid than outdoor air, so moisture can condense on the cold surfaces of wood and concrete. It's better kept sealed up once you have dealt with moisture and. Be sure to monitor the humidity levels once work is completed, you will likely need to include a dehumidifier to keep humidity down.When shopping for a dehumidifier make sure it can be operated continuously with a drain hose, don't get one that needs to be manually emptied. They can easily fill up at least once in a day, and if you're not there to empty it regularly it will stop working.The volume of water that will be produced by a dehumidifier is not so great in quantity that it necessarily needs to be directed to a drain, which likely won't even exist in a crawlspace. You can have it set it up to drain right into a small pit in the dirt below the membrane and it will absorb back into the ground.
Removing radon gas from crawlspacesWe highly recommend getting your air tested for radon gas before beginning work to determine if any measures will be needed to protect your air quality. Air contaminated with radon gas is a serious health hazard and is the second leading cause of lung cancer after smoking. Please see our page on for more information. For more details on in the EcoHome.
Ecohome Sept. 3, 2019, 4:12 p.m.Yes, Lee, unfortunately they are wrong. If you'd be more comfortable hearing it from a different source then please have a read on the following -The author, Joe Lsitiburek, is one of the most internationally respected names in building science. Here is his bio, and if your credentials are comparable to his and you can provide a counter argument we would be most happy to hear it.And - if you are able to read the article with an open mind, you will no doubt learn about several other building techniques that are allowed / required by Building Code that are contrary to the basic principles of building science.
Mike Reynolds Oct. 21, 2019, 8:25 a.m.Hi Geroge, sounds to me like you mean a 'floating' vapour barrier of some kind that you could crawl under, is that right?
Let me know what benefit you see in that, I can't think of any off hand. James O'Neal Jan.
6, 2020, 10:42 a.m.Mike,Thank you for the thoughtful artice and information. I have a few questions if you wouldnt mind answering.I have a humidity problem in my vented crawl space (I believe) and am looking to mitigate this prior to installing hardwood flooring. Presently I have been seeing 70-90% humidity in my crawl space (as indicated by a hygrometer I placed there). Granted, I live in the PNW and we are in our rainy season. My subfloor is reading (using humidity probe) around 12.5 humidity while my hardwood flooring tested at 6.5 - so this is well above the allowable limit to install)At present there is a vapor barrier installed (haphazardly and not covering all of the groundspace) and upon close inspection I have found no standing water.
( As a side note, I intend to install radiant heating (hydronic) in the joist bay beneath the subfloor with transfer plates).What would be the best approach to condition the crawl space to lower the humidity to within an acceptable range to install the hardwood flooring? Mike Reynolds Jan. 7, 2020, 1:23 p.m.Hi James,That could be a pretty quick fix. I would repair the vapor barrier first and make sure it covers the entire If its ripped and in really bad shape then install a new one if you have to; this is also the time to do a passive radon stack if you don't already have one. I would certainly encourage you to test the air for radon contamination if haven't already.The other problem is probably the fact that it is vented. If you live in a humid region (which being in the Pacific North West is a strong possibility), then bringing in humid air is not helping matters.
A crawlspace is best treated as part of the conditioned space. Those two steps and adding a dehumidifier may solve your problems.
Mike Reynolds Jan. 17, 2020, 12:39 p.m.Hi Duncan, there is no situation I can think of where I would list 'crawlspace' as my preferred building technique. I'd pretty much always choose a slab unless there is a need to be below grade with a basement.Building a slab on grade on land with a high water table can be tricky if you are building a thickened edge slab (a footing), so a raft slab is perfect in that situation in such a case. You can also ad a lot of fill and raise the home, though that comes at a cost and it may not be a final level that you want. A raft slab is flat on the bottom and has been engineered to spread the load evenly over the entire surface. So you can build on softer soils, and you don't have to dig down for a footing, so there is no risk of hitting water.
We just built one in Wakefield, QC, here is a so you can see how this kit goes together, and if you like if you like it then send us an email at and we can get you a price. Tawny Hargrave Feb. 12, 2020, 9:18 p.m.My crawlspace is similar to one of the gentleman who was seeking answers for his crawl, which involves hydronic in floor heating.What we’ve done so far:I’ve had the box ends and concrete walls spray foamed, the spray then meets up with a 13” overlap of 12mm poly on dirt floor. This is a ‘conditioned’ crawl I think?
A complete envelope?We are the new owners and were told the perimeter drain was newly completed. Unfortunately for us.
This was untrue.We currently have water pooling in corners( sitting on top of the poly) and just trying to get through the rainy season to sort out all the issues- starting with the obvious removal of water and fixing the perimeter drain.After these things are repaired, my intention is to air it out, dry it out, and re-poly. If a rainy season goes by without any issue, I was planning on pouring concrete over that poly.Thoughts?Any help is greatly appreciated as we are told so many things. Vent- NO vent.Insulate the floors for the hydronic floors to be more effective, etc.The hydronic system is above the sub floor and covered with a finished concrete FYI.Thank you in advance for any advice you may have!!Tawny. March 7, 2020, 8:48 a.m.Hi DeniseIf the batts are starting to fall down you could remove them and re-insulate between the joists from below. If it's really low to the ground and there isn't much air flow you could also lay down a 6-mil poly membrane right on the ground and put some rocks on top of it to hold it in place, making sure it doesn't become a problem by allowing water to pool. That would reduce any moisture if that was a problem.You could also spray foam it from below, that would give you an air seal and plenty of insulation, so you'd be much warmer for sure.If you were looking for a DIY solution you could put new batts back in, but that wouldn't do anything in terms of providing an air seal, do you find it drafty? If there is a plywood or OSB subfloor and floor boards on top then you may not be too leaky, but if there is nothing but floor boards then you'd be best to seal air leaks someway, that's where the spray foam does a really good job.If you did batts, I might choose Rockwool rather than fiberglass as they are more solid and would probably stay in place better.
You would also be wise then to nail up some diamond lath metal sheets to hold it up and prevent access for critters. Jacques Lafrance March 15, 2020, 3:33 p.m.My house is 11 years old and has a partial crawl basement. Built on piles with 2’’x6’’ walls 30’’ high. When this was built, my thinking was that this crawl space would be warm and thus keep the floor warm. This has not been the case. There are heat ducts running in that space.The walls are well insulated with 2’’ foam insulation added inside, the joist spaces stray foamed, there is hard foam insulation all over the very uneven ground floor (badly done) and a vapour barrier all over the whole ground floor and attached to the walls.
(not sealed) You would think that would do it but no. The soil outside only comes to about 4’’-5’’ from the bottom of the pony wall. What might be happening is that with the Manitoba cold, the frost goes down into the ground outside and then it comes up inside the crawl space?? Also, there is the mouse and squirrel problem with them always managing to find their way underneath especially when the ground starts to separate from the wall.
(The mice have found their way beyond the vapour barrier into the house) How high should the ground come up to the outside wall and does insulation need to be buried in the ground to prevent frost from going down so close to the wall? Should have built a full basement to spare me those problems. Mike Reynolds March 17, 2020, 12:17 p.m.Hi Jacques, that's a lot going on there for sure.
To recap just to make sure I'm getting it right - walls are insulated, floor insulated, insulation between joists but heating ducts running through the space?Rigid insulation on an unever surface is for sure not going to perform well, though the vapour barrier is likely helping a lot.There are a couple of options I'd consider depending on what budget you have available. Installing spray foam on the dirt directly would solve a lot of problems, you could go up the wall a bit as well to meet the interior insulation, because you are correct - cold from the exterior is coming up from underneath I believe.Another solution depending on how easy it is to accomplish, could be to add a couple of inches of EPS rigid insulation to the exterior vertical portion of the wall and back fill it. For sure if most of the wall is exposed then R8 or so of insulation isn't a lot for Manitoba. An exterior horizontal (laid flat) skirt of insulation buried under the dirt would also stop a lot of heat loss if you were going to go that route of insulating and backfilling.Rodents is a whole other issue that you for sure would want to deal with first, here is our page on, there may be some info there that could help. Unfinished crawlspaces really are a source of moisture and mold, that’s why its so important to keep the damp down to mitigate heat loss but also protect air quality. They are also a good source of questions for us!
This page below is a good place to start for you -An inch of foam on crawlspace walls is good, but 2 inches would be better. Think about the returns – you’ll be doing the same amount of labour but you will double your insulation value. A few questions do come up from this side, what do you mean by ‘seal’ the floor?
If it is cement, I would be thinking about laying as sheet of 6 mil poly and then laying insulation boards on top. It’s not the worlds most durable surface, but if you rarely need to walk on it, it should last a long time. That would stop the moisture but also stop heat loss. If you like that idea I’d for sure go with 2 inches, not just for heat loss but for durability, if you do need to walk on it on occasion it will be less likely to get damaged.Here are a couple of other relevant pages you may want to check out:. And for house shopping in case you ever move.And about venting crawlspaces, that can be a problem depending on where you live.
The foundation walls will be cool in summer, so drawing in warm air can lead to condensation on those cold surfaces, I’d consider closing it up and running a dehumidifier. What climate zone are you in Dave? That may help us help you more. The first thing to mention is that, so venting is good for now but I would think of a longer term solution. The whole Ottawa Valley area of Ontario is unfortunately a real hot spot for radon gas in homes, so see our pages on, including, in case you dig a well in the future.Venting a crawlspace is not a great idea since it can be very cool down there and when you draw in warm, humid air in the summer, it is at risk of condensing on the cool surfaces. So I would consider a radon gas venting solution and then close the vents.
Once you've done that, keep an eye on the humidity levels and keep a dehumidifer running down there if necessary.Applying spray foam to the dirt floor of your crawlspace may be one of the easiest and most effective solutions, and if so, then you would be best not to insulate the joists over your head and just heat that space instead., and please feel free to ask more questions if you are still stumped on what is the best solution. At the very least, laying a 6 mil poly vapour barrier will keep the moisture down.For the addition that is on concrete piers, if that means air (and wildlife) are free to travel underneath it, then you could consider spraying the underside of that if you have a spray foam contractor there anyway.
We would recommend you look for an installer than has switched to the. Spray foam will act as an air and vapour barrier but it it is pretty easy for critters to dig into it, so you may also want to tack up something like a diamond lath underneath to keep rodents out.As for your radon gas concerns, is that just your common sense or have you had the radon tested and found it to be high? I had high radon gas in by basement and so I installed a. The most likely cause of your problem is actually the inclusion of ventilation, which is a fairly common mistake. In most regional climates across Canada, ventilating a crawlspace will not reduce moisture problems, it will add to them as warm and humid summer air can condense on the cooler surfaces.
Another possible cause of the moldy insulation is if you didn’t include a vapor barrier on the warm side of the insulation, meaning between the joists before the insulation. And due to the stack effect, this air will also rise into the conditioned living space above. Rather than inviting in new humid air in a crawlspace with ventilation hatches, you’d be better keeping them closed and using a dehumidifier.Solutions:The first thing we would recommend is removing the wet and moldy fiberglass insulation.
Fiberglass is quite susceptible to moisture damage and when it is wet it offers very little in insulation value. You’d be better with an insulation like foam or Rockwool (Roxul) that is not affected by moisture, so it’s much safer to have in a potentially humid environment like a crawlspace.
Insulating between the floor joists is not the best way to reduce heat loss in a crawlspace as you will have created two separate environments in terms of temperature and humidity. We normally recommend insulating and sealing the crawlspace walls and floor instead, and having it moderately heated to keep any pipes from freezing. If insulating between the joists is your chosen method, be sure there is a vapor barrier included on the warm side of the insulation.Here is a page that further explains what is mentioned above -This is also a good time to see if you have high levels of radon gas, and to deal with it if so, read more here.