Last year when we bought our house, one of the recommendations by the home inspector was to insulate the crawl space under the house. So I undertook this project went to HD and bought a bunch of insulation they only sell insulation with vapor barrier on it. I thought nothing of it and put it in. Now last week some one came over to the house said I probably should remove the vapor barrier. Is this advisable, or should I leave it as is?
Appreciate any thoughts.
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Replies
Where do you live? What kind of vapor barrier is on the insulation? Is the vapor barrier on the top or the bottom of the insulation?
I live in California, SF Bay Area. The vapor barrior is against the house. HD completely wraps it's insulation in a pretty cheap and flimsy plastic with one side being a vapor barrier.
The vapor barrier should be against the floor sheathing (to the warm side of the envelope).
.......................Iron Helix
I did that one right. thanks.
If he is insulating a crawlspace there won't be any insulation against the floor sheathing. It will be against the crawlspace walls.
Locally, at least....F/G insulation is stuffed in the joist bays and crawlspace walls are covered with EPS/DowFoam. ......Iron Helix
On the crawlspace walls can i use insulation between the studs or should i use the foam? Right now i am cutting insulation to fit but if the foam is better i can switch easily enough.
Locally the construction habits have the crawlspace walls made of concrete block or poured concrete. And then the EPS is attached directly to the block/concrete. No framing needed.In our "mixed/wet " building environment framing below the sill plate is avoided.
What is the floor of the crawlspace.....dirt, gravel, concrete?
Do you have a framed treated wood foundation?
California is a different building climate......with different methods.
............Iron Helix
Edited 6/24/2004 6:53 am ET by Iron Helix
The crawl space is dirt.
The house is 61 years old and it does not appear to be preasure treated wood. The house is at the bottom of a hill, so near the back of the house there is about 6 to 8" of framing before the floor joists and near the front it is up to 24" before the joists. I put insulation between all of the joists and then was going to put insulation inbetween the studs on the framing. What do you think?
An unusual situation....but I would insulate the short walls with the vapor barrier to the warm side...to the inside. And insulate the concrete/masonry wall with EPS.
............Iron Helix
I am sorry if I do not understand the climate dynamics here but may i ask, why do i put the vapor barrier against the house between the joists and put the vapor barrier on the short walls in the crawl space facing away from the house, or facing into the crawl space?
Yea the situation is a but unique, but it is logical if you look at it, the house was built into the side of a hill. So at the back of the house i have about 1' ~ 2' of foundation, while at the front of the house and on one side i have about 7' of foundation and on the other side about 4'. So the oddity of the foundation, due to the hill, requires the short walls in the crawl space to even everything out. It is actually nice because i have a ton of easy access storage space.
Thanks.
The vapor barrier side of F/G insulation is usually placed to the "warm side" of the framing structure.
The warm side of the joist bay is the floor sheathing, hence the vapor barrier goes up against that surface.
The warm side of the crawlspace walls is the crawlspace itself, hence the vapor barrier faces the inside of the crawlspace rather than the exterior wall.
The reasoning for this centers around condensation of moisture on a cool surface versus a warm surface.
If you would install the insulation with the V/B toward the crawlspace and as the house's water vapor migrates into the joist bay cavity the placement of the vapor barrier on the bottom of the floor joist will allow for entrapment of the moisture inside the joist bays. If the crawlspace cools down then the coldest surface inside the insulated bay would be on the inside of the vapor barrier where it may condense and be trapped/absorbed by the fiberglass insulation.
With the insulation installed with the V/B against the floor then that V/B surface is too warm to condense any water vapor.....and any moisture in the insulation is free to migrate into the crawlspace. The vapor barrier's job is to keep the warmer moist air in that warmer compartment.
In the perimeter crawlspace walls the coolest surface will be the exterior sheathing and the warmer more moist air is to the crawlspace side. Placing the V/B to the exterior wall will allow the crawlspace air to migrate to the cold surface where it will condense and saturate the fiberglass, thus losing the R value and creating a water problem.
With the V/B toward the warm side of the crawlspace the moisture is restricted from migrating to the cooler surface.
Now to put a new twist to this scenario..... it is now suggested that the building envelope be extended to include the crawlspace into the living space envelope. And to condition the air that moves through that area.
Basically to seal and insulate the crawlspace walls and box sill and heat and A/C it to control moisture and moderate temperature.
Check out http://www.buildingscience.com for more info.
Perfectly clear......as mud maybe
.........Iron Helix
Yep, clear as mud, but I think I better understand it now. Thank you.
What you say about heat and cooling the crawl space is interesting and logically makes sense now that I have a little explanation. FHB had an article about a year ago on sealing the crawl space with a 20mil plastic if I recall. That maybe something to consider as well.
Maybe cheaper and easier though would be to install a vent fan, like in a bathroom, with a humidity control on it. If the humidity builds the fan switches on, what do you think about this? Similiar to the atic fans removing excess heat.
Our local climate, which has a lot of humidity, would not allow for power venting the crawlspace because the make-up air would probably be of higher humidity than that which was vented.
Check on the link I gave you for the proper crawlspace environmental control with your local climate conditions.
.............Iron Helix
Sorry I am so late in the discussion, but, (everyone has one), Why insulate a crawl space in a place where it probably never gets below 30 f????Payout has to be several lifetimes...
Because even though it does not typically get below 30 here, it still gets cold. I had the same thoughts and the first winter i had my house I did not insulate and noticed how cold the floor got as we do not wear shoes in my house (when all you have is a pair of sox on between you and the floor you notice how cold it gets). Second winter I insulated under one room and noticed a difference. So I did the rest of the house.
Besides insulation is not that expensive if you are willing to do the work yourself and even if I never recoup the cash, the comfort you get lying on your floor in the winter is nice.