I am in the process of working with a client on insulating a crawl space on an addition to a house in central Indiana. I looked through the archives and have found a variety of opinions on how best to do this. The wide variety of opinons has me a bit stumped and I am not sure how to proceed in this circumstance and was hoping the group could help.
The addition was built several years ago and my client complains of the room being cold (he just moved in so I don’t know if it also hot in summer, but I would assume so). The rest of the house is on a basement. There is foamboard on the inside walls (looks to be 1″) with nothing on the crawl space ceiling. I had one insulation sub say to spray uretahne on the walls and leave the ceiling bare. Another sub said to leave the walls as is and put batts to fill the cavities in the ceiling. The crawl space is vented and the joists are 2 x 10.
TIA.
Paul
Replies
Is there a good vapor barrier (at least 6mil poly overlapped and taped) on the crawl space floor, and lapped up the walls? If not, consider installing one and close up the vents, both summer and winter.
I have extensive crawl spaces (cold climate SE MN) and my research indicated sealed up crawl space with VB on floor and walls, batts in joist space underneath floor.
paul.... the type of heat you have will have a bearing on the solution... if it's baseboard... you could go either way..
if it's hot air and the ducts run thru the crawl... then i'd lean towards insulating the walls..
if it's electric heat.. i'd probably insualte the floor..
if it's new construction... i'd make sure it is dry... and insulate the walls.. and use hot air heat
Mike Smith Rhode Island : Design / Build / Repair / Restore
Mike: It is hot air, ducts through the crawl. The ducts are insulated, although the insulation looks a bit ragged. Do you say this because insulating the walls will enhance the insulation of the ducts? Is additional foamboard a viable way to insulate the walls, or would the urethane be better?
Paul
paul.. if the ducts are in the crawl.. then insulating the walls with EPS will turn the whole crawl intoa conditioned space... making for warmer floors..
if you insulate the floors.. any duct loss will be wasted into the crawl
we would make sure it is going to stay dry.. then order 3"EPS PerformGuard with a 1/2 gypsum skin for fire code.. the panels would sit on the 6 mil poly vapor barrier on the floor of the crawl.. and extend to the bottom of the subfloor... the box formed at the band joist would be insulated with cellulose blown in after the panels are installed
anyways .. that's the way we would do itMike Smith Rhode Island : Design / Build / Repair / Restore
Mike,
Would the EPS/gypsum skin configuration of the walls of the crawl have any bearing on the fix?
My walls are only above ground about 3" below the bottom of joists,and floor of crawl is 36" below grade. The ducts are in the crawl.
We are essentially in a desert ,(CO) so there is not much moisture. is the 6 mil vapor barrier still de rigour? Crawl is sealed to the outside, altho there is leakage to the furnace room in a basement next to the crawl.
Great info, Thanks!!!
Bud
bud.. i don't understand your question....
<<<<Would the EPS/gypsum skin configuration of the walls of the crawl have any bearing on the fix?>>>>>>
by configuration do you mean thickness...or R-value?
i think the vapor barrier would still be part of it..
one reason we went to this is because of the years of crawling around in crawl spaces we've done..
the ones with insulation between the joists are usually cold floors,, the insulation is hanging down, the ducts are losing heat to the crawl space anyway.. and that heat is wicked out to the foundation wall.. which increases the heat loss of the duct by increasing the delta-T..
if the duct is in a conditioned space... the loss will be less.. and since the crawl is conditioned... the floor will be warmer..
i would still use an insulated duct of course.. especially since it will propbably be doubling as your A/C duct in the summer..
moving air in and out of the crawl by means of controlled duct supplies and returns will also allow you to control the humidity of the crawl.. another reasonto keep the poly vapor barrier...
i wonder what the true moisture content of the earth below a crawl is even in a desert ?Mike Smith Rhode Island : Design / Build / Repair / Restore
Mike, you are correct , my question did not make any sense.
The question intended was, will the wall insulation make any difference, since the walls are almost completely below grade. there is only about 3" above outside grade. plus the 9" of the floor joists. I suppose a shot with the infrared thermometer would be in order. Then we would know the temp differential.( Damn, I might be learning something!)
The ducts are not insulated,(yet, untill my knees recover from another project).
There are two seperate crawls on two sides of a basement. One of them has no ducts and is sealed. the dirt is stone dry, down at least 2 feet. Although who knows what is migrating thru it.
Paul, good idea about isolating the furnace room, will be real easy. Got some good ideas from your e book. Found 2 out of 8 boots that were leaking most of their air.
Great thread Guys, and thanks very much for the input!
Bud
RE: leakage to furnace room...I assume you have a combustion burner in that furnace room. It would be helpful if you could isolate the room from air path to rest of basement and supply dedicated air to the furnace room. Other wise, you are sucking in outside air through out the basement. And, if you have other burners, such as a gas water heater, you could be pulling negative pressure in the house with potential backdrafting down flue...think carbon monoxide... PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
I'm thinking of sealing of my crawl space. It has a concrete floor (a little rough on the knees). It stays dry all year but there are 4 vents around the outside. My plan is to lay very thick poly or tu-tuff over the whole area, taped and laped where required. Glue to the walls to grade level (do I need to go that high?). Close off the vents and seal. Have foam sprayed around the outside walls and install the floor mats that link together like jigsaw pieces to protect the poly. What do you think?
My present floor is insulated with fiber glass but has many cold spots. The heating ducts also run through the crawl space. With the vents closed is is "warm" down there so there is a lot of "lost" heat. The heating duct to the second floor were run up the outside wall (dumb idea).
Don't run the plastic to the sills, or you may encourage rot with migrating condensation. Other wise the closing off should be ok with a few ifs:
* You have do not have any combustion appliances that are dependant on crawl air
* Check code regarding foaming the walls. You may need a sheet rock barrier over the foam.
* Seal the return duct work well so that you are not pulling crawl air into the system.
How well are the penetrations between floor and crawl sealed?
In reality, you will be making the crawl space into a low overhead basement. It should improve the house efficiency in both heating and cooling seasons, especially if in a high humidity area.
How much area are you considering for the interlocking floor mats?
Is the headroom high enough for the crawl space to be functional?
PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
its a crawl around crawl space. No items draw air from the space. I was thinking of the whole area to be covered with the mats.
Mike: Thanks for the help, I greatly appreciate it.
paul did i read your post correctly? you said the crawl space is vented and there is no insulation between the joists that support the subfloor, and the homeowner is complaining the room is cold?
first you have to decide whether or not to vent, and then what to insulate and how. venting the crawl space to the outside and not insulating the floor that covers the crawl space will never work. its like trying to fit an elephant in a shopping bag.
how do you fit an elephant in a shopping bag you ask? well first you have to get the biggest brown paper bag that they make from safeway, and it has to say safeway on the side. then all you do is take the "f" out of safe. then you take the "f" out of way. c'mon your not playing along take the "f" out of way. whats that you say, they're is no "f" in way.......
Yeah, you read it right. Someone was cutting corners when they built the addition. For cost reasons, I am planning on keeping it vented and not sealing it entirely, at least at this point. Just trying to detemrine if best to do the walls or to do the ceiling of the crawl. Thanks for your thoughts.
Paul
From what I've read, the problem isn't likely the lack of insulation in the floor and the venting of the crawl.
I go through a lot of crawl spaces in a very similar climate, many with no foundation insulation, and they are a lot warmer than you would suspect.
The most likely causes of the addition (one room?) being cold are (i) poor heat distribution into the addition and (ii) poor wall and ceiling insulation.
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ok now yer killin me, it does no good whatsoever to insulate anything but the ceiling of the crawl space if it is vented to the outside. cmon you guys think about it. air provides instant thermal transmission. if it is vented to the outside it doesnt matter what you do to the walls or the ground the air moves in through the vents and the temperature in the crawlspace is exactly the temperature of the outside air. the only place insulation will do any good is at the building (conditioned space) envelope, which in this case with the vent to the outside is the ceiling of the crawl space.
you guys keep tryin to fit that elephant in that shopping bag though, i think its hilarious
They should close their vents in the winter. That's why the room is so freekin' cold. First hand experience-my Wisconsin house has a crawl space.
I would insulate the walls (cold is on the outside) and insulate the ground (cold is down). This way the crawl space will be warmer in the winter. The disadvantage is that it will also be warmer in the summer resulting in the use of A/C more. Run the vapor barrier over the insulation up the side wall. Throw some sand over it to protect the vapor barrier.
Tim, why would you insulate the walls of a vented space?
Why would a crawl space be warmer in the summer if it had insulated walls when air conditioning? Just looking for some clarification ?
Paul HaydenEnergy Consultant and author of Practical Energy Cost Reduction for the Home
They should be closing those vents during the winter. Leaving them open is like leaving a window open. With the vents closed, this puts the walls in a "semi" conditioned space. The outside of the wall is in direct contact with the cold and there is no thermal break in the concrete block. To make things worse, the block is a excellent conductor of heat...or cold depending on how you want to look at it. I also suggested insulating the ground as that also is a major source of energy loss. If the ground is cool and the air warm, obviously there will be a energy transfer.
Now, during the summer, the vents should be open. This is to help control the humidity. It also is helpful to get a little air movement through there. Earth is very stable in temperature. It doesn't change a whole lot (other than the top couple of feet outside, but it won't freeze in the crawl space). That cool earth will help keep the crawl space cool during the summer by stabilizing the temperatures. Insulating the ground will cancel that effect and cause the space to heat up faster. It's kinda like the old all brick building staying hot for days after a warm spell and staying cool after a cold snap. Think thermal mass. The warmer comment in the summer has nothing to do with the wall insulation, it's in relationship to the ground insulation. The wall insulation is only there for the winter.
So what will keep the space cool during the summer and warm in the winter is the exposed (with a vapor barrier) earth. But the criteria was to make it warmer. Because the ground is a heat sink I recommended insulating the ground too. I guess the easy method would be to insulate the floor only, but it's hard to put a vapor barrier on the warm side of the insulation-especially with existing construction. Assuming a heating climate the vapor barrier would need to be under the sheathing, not under the joist. No matter what happens there still needs to be a vapor barrier on the ground. There is just way too much moisture moving through it.
Edited 1/9/2004 9:29:58 PM ET by Tim
Tim, I agree with the vapor barrier on the ground, and it should extend up every wall and pier and be caulked (pl-300 is good) to the block. That said, if the vents are then closed, and kept closed, there is little reason to open them in the summer in a cooling climate to let in 80-90% hot humid air. If they are opened, and the house is in A/C mode, then condensation on ducts, boots, air handlers, flooring where boots pass through etc., takes place. Also, the humidity is pulled through the floor into the house.
Some where early on, the statement was made that the vents were staying open...which begged the question as to why insulate walls if the "windows" are open. If the crawl was not designed to be sealed, sole plate, all penetrations, then I would spend the $$$ on sealing and insulating the underside of the floor, and perhaps stapling a layer of tyvek to serve as an air barrier across the floor joists.
Of course, combustion appliances need an air supply, hopefully isolated and never causing negative pressure.
For any ducts, plenums,trunk lines or air handler, I would seal all seams (mastic backed aluminum tape)and then add flex insulation or foam board to the flat surfaces.
I have seen a number of wet, moldy air handlers the "sweated" all summer, and the seams and duct leaks let the mold get pulled into the house air. Paul HaydenEnergy Consultant and author of Practical Energy Cost Reduction for the Home
>>Tim, I agree with the vapor barrier on the ground, and it should extend up every wall and pier and be caulked (pl-300 is good) to the block.
On an older house with little clearance between the framing and grade and without PT sill plates, do _not_ extend the VB up the walls - it can lead to rotted sills.
>>Some where early on, the statement was made that the vents were staying open...which begged the question as to why insulate walls if the "windows" are open.
Theories are fine. And crawl vents do look like open windows.
When you go through 5-10 crawls a week, however, you'll find that the practical reality is that even with the vents open, a insulated crawl is warmer than than an uninsulated crawl. Crawl vents just don't ventilate all that well
Seal the returns; let the distribution side leak some (or seal it but be sure to add a register or two, depending on the size and configuration of the crawl.)
Choose your crawl strategy (i) based on climate and (ii) after reading about crawls at the Building Science Corporation site
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The first donation just arrived! Thanks and God bless!
Bob, I agree re; do not extend to the sills. Only meant to not leave flat, but turn up so the the seal to the wall can be made. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Therories aside...these are things that I know from my house. If I keep the vents open it's very cold down there. Proably just a little warmer than the outside air temps. With them closed and no insulation the temps hang around 40 in winter. When the temps get down to around 0, the crawl space temperature gets close to freezing. I installed a duct run with a thermostat and a motorized damper that will turn on when it gets colder than 38. It doesn't raise the temps, but it also doesn't allow them to drop below the mid 30's. Must be the thermal mass thing again.
During the winter there is very little moisture that moves through the ground. If we get a good rain, there will be a wet spot or two, but otherwise things will remain dry. During the summer though, the ground is always damp. If it rains really hard, there will be some standing water. I'm right on the river, although there is no high water mark, my gut says that there has been significant water down there. Now, I'm the poster boy for needing a vapor barrier, but I must get the grade cut down first. They backfilled it with clay and the stuff is like a rock. Then I need to start chasing after those rotted joists. Sure wish pressure treated sill plates existed way back when. :(