Insulating in crawl space

The living room in our house is built over a crawl space about 3 ft high. The foundation of the addition extends about 4ft down and is uninsulated poured concrete.

The crawl space is connected to the rest of the basement through a 3ftx3ft opening.

In really cold weather the pipes in the crawl space have frozen.  The wood floors tend to be cold.

The floor is insulated, but the walls of the crawl space are not.

I am looking for suggestions on the best strategies to improve comfort in the living room.

The living room is over the crawl space you speak about?

> "floor insulated..."
How?

What is the situation in the crawl under the rest of the house? Pipes OK?

As a first thought, fully - and sufficiently - insulating the floor of the living room would seem the most direct approach. If those pipes that froze could be on the warm side of any insulation, they wouldn't freeze so often. Normally it's more expensive to heat (ie insulate) a space unnecessarily; that's why crawl spaces are not insulated as a rule - we usually don't need, or at least want, to pay for heating an unused area.

You might also try sticking a thermometer into the ground at various places in the crawl and to various depths, up to a couple feet. Ground temperatures can be much higher than outdoor temperatures. That can give a little indication if the ground is contributing much to the coldness in the crawl. It may  not be, in which case you can look to sealing the air leaks from outside and maybe applying  foam to the inside of the walls in the crawl to help keep the outdoors outside. However, consult local real estate people or building inspectors about the possibility of radon gas in your area before sealing under-house spaces tightly. Depending on ground conditions in your area, come summer you may want to look at blocking moisture rising from the ground by placing polyethylene sheet over the ground and sealing it to the walls.

Or, you could ventilate the crawl fully, after moving the pipes to the warm side of the insulation. That might require some carpentry and plumbing but the ventilation would help reduce any possible moisture problems. If the insulation is some kind of bat, it needs to be mostly air tight to avoid "wind washing" which kills its insulative properties.

The usual problems in a crawl are moisture, vermin, insects and poison gas (radon). When designing solutions, take account of those common issues so you can avoid creating more.

Rufus

Insulating the perimeter of the crawspace down 2'-4' is one of the best upgrades for most crawls. The insulation of the floor (good on rufus) might be very thin insulation or it could be heavy.... the difference in temp between the living space and crawlspace will move heat rapidly through thin insulation as the surface area is large. If 5he detail at the perimeter and floor insulation is not correct the edges will be cold. Sheeting, joists, foundation and wall plates and studs conjoin there making a thermal bridge that is hard to nix without good detail.

Rigid construction grade foam is likely best, spray has great coverage, but can be a toxic nightmare.

Double bubble reflective sheet is easy to apply and moisture proof.

My dream foundation and wall detail is 12" concrete from basement (or tall crawl) to eaves, 6" rigid foam on the outside from footing to eaves and sided with fieldstone and or old grey wood. Doorframes steel, poured in place. Commercial aluminum window frames with bullet resistant glass and window quilts!

Couldnt resist.

A very common mistake is to insulate a floor of a basement/crawlspace and not the walls, when in reality the cold comes in from the sides. A lot of people make the assumption that insulated floors make warm floors but that is just not so. The laws of thermo dynamics come into play here, and no insulation ever invented is going to stop the laws of stacking. All insulation in a basement or crawlspace does is keep cold floors cold, and give rodents a nice place to live while increasing the cost of building the home. Worst yet, after a few years of moisture condensation, removing the nasty insulation ladent with rodent feces and urine will not be a fun job, or expensive if it is hired out. There are a few exceptions to this, but mostly in split level homes.

The great news is, you may be able to get out of this pretty cheaply.

Drop down into the crawlspace and take a look at the rim joist. If this does not have insulation, IT NEEDS IT! Thankfully, that may be all you need.

A lot of people think hot air rises, but this is actually incorrect, cold air is more dense then hot air, so it sinks. This is a huge difference, especially in your home.

A house is heated via a few different ways, but mostly by convenction. Think of this as a rolling swirl. Cold ALWAYS goes to warm, so as the air around your ceiling is warmed, it is stopped from rising by your attic insulation, BUT now cold wants to go to warm so a vaccum is present. Without insulation in your rim joists, it is sucking that cold air from outside, under your walls and then up through the floor and into your home. This then starts stacking up, cusing that swirling effect. The more air iniltration in your walls and crawlspace, the faster this swirl happens. Just keep in mind, this vaccum is present 24/7 during the heating system so any way cold air can get in (not warm air getting out) can make your home harder to heat.

In your case, your home is "stacking" cold air down at the floor level, and in your crawlspace freezing your pipes when it is really cold.

You need to keep the cold air from coming in, but that is done at the walls in the crawlspace, and via two ways. Insulation (and your rim joists may just be enough), and air infiltration. Think plastic, caulking, really anything to stop air from coming in. This includes in the living space around any penetration that goes outside; doors, windows, pipes, around outlets, etc.

Sadly your floor is covered in concrete because a dirt floor lets in a lot more "heat". I put heat in quotes because the ground here in Maine anyway, always stays 57 degrees so it really is helping heating a house compared to the fridgid cold outside. As I type this, it is 20 degrees outside, but my dirt floor, fieldstone basement is 41 degrees because of what I say is happening. But you have what you have and that is fine, no need to rip out the concrete.

So I would insulate your rim joists, which should be really inexpensive since you are not doing entire walls. If that is not enough, you might consider "banking the house" which is what we call it here in Maine. I did this yesterday, putting hay all around the edge of my house to stop the wind and cold (but I have a fieldstone foundation too). If that is not to your like for asthethic reasons, you can insulate your walls by furring out with strapping and insulation.

Thanks for the great  responses.

Some clarifications.

Living room is above the crawl space.  The living room is currently heated by electric baseboard.

The floor joists are insulated with the pink bats.  A layer of chicken wire was nailed in to help support the insulation which is sagging in some places.   There are signs of rodents.

The plumbing is on hanging in the crawl space on the cold side of the insulation.

The other parts of the house have a 5' basement there is a 3'x3' opening between crawl space and basement.

The crawl space has a dirt floor.

There are places where additional insulation could be added  along the rim joists.

I think what Travis meant about insulating the rim included _sealing_, making it airtight - not simply putting batt insulation against the rim. One way to do this is using hard foam of pretty much any thickness from the box store, cutting it to fit loosely in the joist space at the rim and then using canned spray foam to seal all four edges - at the floor, joists and the plate the joists are sitting on. The plate itself is often source of breezes because the stem wall isn't very flat and there are spaces under the plate. Thus, the plate also needs to be sealed to the stem wall, caulked, to stop cold air coming in. That is assuming you want a closed crawl, which is a good workable method.

But the rodent problem is a PROBLEM. Vermin destroy building structure and can make interiors very unpleasant. It's seriously important to get them out and keep them out and it's not a trivial task, especially in old buildings. _All_ holes larger than a pencil size need to be blocked and sealed to keep little mice out. Rodents inside the building need to be trapped; from what I've read and experienced, snap traps do the most efficient job. And a cat can be a big help if it's a good mouser. Unfortunately, that's not a given, but if you have any likely candidates, be sure not to feed them much and _for sure_ don't "open feed" them.

The plumbing piping _might_ depending, on your building details, be helped, once the vermin are gone  and the the crawl is sealed (again, check the local authorities regarding radon gas before sealing a space) by dropping the ceiling of the crawl and installing another layer of insulation under the existing joists; the pipes will be on the warm side of this layer of insulation. That is, once all else, including making sure existing insulation is _properly_ installed, is taken care of. If the crawl is sealed well,  the pipes may actually be safe as they are.

Regards,
Rufus

Amazing how a month can pass by.  I have been trying to research and better understand all of the conflicting information regarding the best way to insulate.

Here is what I am planning to do, I am interested in all critiques of my plan, so please continue with your appreciated advice:

Firstly I have installed the device to measure if radon is an issue in our situation.

I plan to remove all of the the existing insulation.

I would like to insulate the rim joists and the walls of the foundation in order to maintain a warmer climate in the crawl space.  I am looking at 2 different approaches.

1 - use of a spray foam product to provide a complete air sealing and insulation in one application.  I understand that there are environmental concerns with respect to these products, so I have some reservations about proceeding with this option.  It is also expensive at about $3 / ft2 for a 2" application.  Are there alternative products available that are more environmentally friendly?  Are the energy savings worth the use of this product?

2 - Individually insulate the rim joists and walls with a rigid board product and substance to seal each are of the rim joists and seams.  If I am going to go with this option, I need to identify the best product(s) for this application, so I am looking for recommendation to consider.  In our local hardware stores they sell rigid rock wool based boards that could be used, which seem to be a better option to the typical foam products, but I am not sure that these are actually a more environmental option.

I saw a post that I am having trouble locating again, where there was a mehthod to insulate rim-joists with some type of board and a lime based (maybe hemp based?) product was used to complete the air sealing around the board.  I also cannot remember what the "board" material was.

I am interested in opinions on both the most effective and economical options, so if there are other alternatives that I should be considering please let me know.

The recommendations in Canada also include insulation of the floor of the crawl space, but I am not planning to do it at this time but will evaluate how effective my first attempts at insulating are performing.

Hopefully these interventions will improve the comfort in the living room and prevent the pipes from freezing...I plan to monitor the temperature in this crawl space and will add space heating if required to prevent freezing.

Spray foam is the highest performance available, you will need to heat the crawl good for a couple days before having it done. The contractor may provide the service. There is a potential for a permanent health safety nightmare involved if it cures improperly, plus fore retardants....

Sheet foam is diy friendly and much better performance than batts. Fire retardants.....

Rockwool is a hazardous material, flat out dangerous for workmen and anyone disturbing it later on.

I like construction grade closed cell sheet foam, it is easily applied, nearly impervious to the environment in the crawl and is high performance. Does have fiberglass and care should be taken with dust and particles from cutting and installing.

I pile straw bales around mine.  It keeps the crawlspace warm and I use the bales in the garden in the spring.

I'm assuming the crawlspace is not ventilated to the outside?  What kind of foundation wall is it?  Is the crawlspace floor deeper than the outside grade?  How old is the building?

I insulated my rim joists by cutting styrofoam rectangles to be 1/4" undersized.  I popped them in and caulked around the perimeter to seal them.  Actually, I caulked the rim joist first, then put in the styrofoam and then caulked that as well.

I believe rodents love the white expanded polystyrene but not the extruded polystyrene (pink).  My dad put up 1" expanded on our garage walls and covered it with some paneling.  10 years later he took it out and the polystyrene looked like a huge ant farm.  Mouse tunnels were all over through it.

Insulating the walls of the crawl space will keep the cold air temps from sucking heat through the wall and cooling down the air under the floor.  That's a good thing (I believe).  The frozen ground just outside the foundation can transfer heat through the foundation and from the dirt in the crawlspace, then you're losing heat into the floor.  I think the best solution would be to insulate the foundation (on the inside or outside) down as far as you can reasonably go (ideally to the code required frost depth).  Then the dirt in the crawlspace will be heated by the deeper earth temperatures instead of wicking the heat through the foundation to the frozen ground outside.

Trace's and Travis's suggestion of straw/hay bales around the building adds a lot of insulation to that foundation wall and potentially keeps the cold air from freezing the soil right against the foundation.  So it acts a bit like buried insulation against the foundation even though it's above grade.  I hope my rambling makes sense...

Adding hay to the outside of the foundation, and insulating the rim joists can really make a difference.

I did that to this house we are in now, and the last few nights it has dipped down to -3 below zero (f), and without heat down there, it has stayed a consistent 35 degrees. That means my pipes do not freeze which is the goal.

Hi Tom,

I just saw your post for the first time.  You have gotten some great suggestions here and I think your plan is sound.  The high density foam is a great product (I know about the environmental stuff, but sometimes we cringe a bit and pull the trigger), I used it on the roof f my garage workshop and what a difference from last year.

One trick you might try in your crawlspace is something that Mike Oehler suggested in his passive greenhouse book is to dig a cold well.  This puts the laws of thermodynamics back on your side.  if you pick a corner near the least used wall of the room above and dig a trench 3 feet deep and a couple feet wide.  Spread the dirt over the rest of the area.  This will provide a well for the cold are to fall into.  Mike successfully used this and insulation with appropriate solar heat to have his greenhouse function in Idaho with no supplemental heating.

I haven't heard this approach used before in this type of application but i think it will definitely help along with the insulation.  It will also allow the heat that is there to stratify a bit and keep the heat closer to the pipes and the cold the down in the hole.

I like the sprayed on foam myself.  The foam can compensate for bad floor framing details at the rims and typar if any was even installed. As previously mentioned heat up the space before hand for best setting and adhesion. At a thickness of 2 inches you should not get curing problems. Is your installer using the high density non porous foam? At $1.50 per board foot that is a little pricey but if its a smaller space probably about right. When I've worked out pricing materials plus labour rigid sheets has always been more then sprayed. I believe it is the best option when you work in energy savings down the road. It comes at an environmental cost now but mitigates much greater enviro costs down the road for the lifetime of the structure... Don't forget ventilation. Your crawl space has probably been getting by without since it leaks air. Seal it up and you must give it a way to refresh itself.
Cheers,  David

Spray Foam has two other advantages too: rodents cannot burrow through it, and it provides 40% structural rigidity to what it is adhered too. It is just expensive to do.

But insulation once versus heat loss and busted pipes constant.

Travis Johnson wrote:Spray Foam has two other advantages too: rodents cannot burrow through it, and it provides 40% structural rigidity to what it is adhered too. It is just expensive to do.

But insulation once versus heat loss and busted pipes constant.

The structural rigidity is of course only with the high density foam.  It is a very useful property when installed on am outside wall or roof, as those surfaces are exposed to wind, etc. I am not sure the structural rigidity is much use on a flour over a crawl space unless it is currently squeaky.  ;-)

Tom

You're looking at three main points. In order of importance:
- eliminate moisture in the crawl
- seal out drafts, prevent uncontrolled air moving in/out of the crawl to the outside
- insulate the crawl

The first two are much more important. By keeping it dry, you allow it to be sealed w/out incurring moisture issues To maintain raised temperatures, you want to reduce/eliminate ventilation in the crawl in winter. The third, insulation, varies in importance.

You can seal the rim with cheap 30yr caulk. Using a couple cartons of the stuff and smearing it in/over _all_ the joints and cracks will get you 85-90% sealing for 10% of the cost. There are "better" ways, but cheap and fast counts for something. It won't prevent going for the gold plate solution later. Per a suggestion above, a step up would be cutting solid foam sheet (the pink stuff is probably perfectly good), of any thickness pick your price range, to fit loosely at the rim in each joist space; caulk or foam around the edges to seal thoroughly. Seal the plate to the concrete/stone/whatever. Seal the "long" sides (parallel to the joists); this could easily the the hardest, a royal PITA because it might be only 6" or even less access - or it could be wide open, full joist bay.

If you will have stuff like hay or manure (or even reliable snow drifts) to stack against the outside stem walls each year, like Travis did, that will serve for free, or rather for the price of your time to do it each  year. As Travis noted, the crawl does not need to be "room temperature". As long as your pipes remain healthy, that's about the sum of it. To keep the house upstairs warmer, insulate the ceiling of the crawl; it will be a lot more effective once the air in the crawl stops cycling in and out taking away the heat and bringing in cold breezes.

Rufus