Return to the Old House Forum | Post a Follow-Up

 o
Vapor Barrier on cellar dirt floor

Posted by fredwe (My Page) on
Sun, Sep 2, 12 at 22:38

Hello, my situation is ca. 1770 house in Mass. with rubble foundation (joints only partially chinked), and dirt floor. To reduce water vapor infiltration, I have so far:
1. Installed 30mil MDPE 'pond liner' on top of geotextile (the latter to protect MDPE from punctures due to stones underneath). This barrier is fitted around chimney bases, pump sump, and MANY lally columns. Joints are lapped by about 6" and poly runs up foundation walls 6-12".
2. Installed dehumdifier, draining into sump. Not surprisingly it costs about $500/yr in electricity when set to 60% RH.

Ok, now my question: to further lower water vapor entry, what is the next most important step to take, for example:
- Seal the edge of MDPE to the rubble foundation wall, perhaps with a butyl-adhesive based membrane like "Ice & Water Shield."
- Seal the lally column openings, maybe with rubber flange typically used for plumbing stack going through a roof.
- Apply a vapor retarder to the rubble foundation.

Many thanks for your advice.


Follow-Up Postings:

 o
RE: Vapor Barrier on cellar dirt floor

I'm sure you're not going to want to hear this after all the expense and labor youve already expended, but a concrete floor and an interior coating of concrete (or spray on insulation) on the interior walls is likely the best solution. My own foundation is exactly like yours. Had the walls (floor was already concrete) sprayed with shotcrete several years ago which made a real difference. Modern spray on insulation may be a better choice today.

Foundations like these from the 18th and 19th century were designed to allow water to enter then exit quickly via a gravity drain.Make sure the work you have done has not blocked the passage of water to the exit point and that the drain is not clogged. They will always be humid to some degree because seepage takes place more or less constantly. Keeping them closed up rather than opening the windows, bulkhead, whatever in summer as many people do will help. Warm humid air always moves toward colder areas. Grading away from the foundation from the outside is also important.

Not sure how long you've been running the dehumidifier, but it may not be a good idea. Old house foundations tend to adapt over the years to the conditions they encounter. Radically reducing the humidity through artificial means can cause shrinking and cracking that are potentially worse problems than humid air.


 o
RE: Vapor Barrier on cellar dirt floor

I have a 200 year old cape in Maine and work with an old home contractor. He is of the same thought as akamainegrower, vapor barriers aren't a good idea as it can cause areas for dampness to accumulate and hasten rot.

What we should have done by now (and, I swear, we'll do next year) is to ensure all land slopes away from the house. We'll dig a 4' channel at the granite wall around the house and provide a slope away from the house at the base of the channel. From the foundation and down the lowest part of the channel, we'll run ice and water shield to ensure all water runs away from the house (we don't have gutters). If we didn't have such great earth, which drains wonderfully, we would install drains at the lowest part of the channel to further move the water away from the house.

This will help with the damp in our basement.

Now, will someone tell me how to keep the spiders in the basement and out of my house?


 o
RE: Vapor Barrier on cellar dirt floor

Thanks to both of you for responding!

Curious about both shotcrete and spray on insulation. How did you notice an improvement after shotcrete? Was it straightforward to have it sprayed on the rubble? Bonding agent required, I would guess. And does spray on insulation perform well as a vapor barrier (R-value of same probably not important for me).

A few more details prompted by your posts...AFAIK there is no gravity drain. I have spent more hours than I wish to admit, down there working in all parts of the cellar. Typically for 10 months of the year, there is no visible water in the cellar. We get water in late winter / early spring due to seasonal high water table. Otherwise it takes 3+ inches of rain in one day, to cause water to appear.

Years ago I performed my version of the "Big Dig" by digging foot-deep trenches from 5 points around the cellar, leading to a central sump with two pumps (one for backup). Trenches have 6" perf pipe wrapped in filter fabric and filled back to grade with 1" stone. The pump keeps the water level below grade in almost all of the cellar and now has a long duty cycle because the trenches serve as a reservoir.

I appreciate the pointer about keeping warm humid air OUT of the cellar (a good reference is http://www.co.hunterdon.nj.us/health/FLOODING/ventilate_basement.pdf). Any downside of reducing RH in the cellar in our case was less an issue than reducing mildew and off-odors in our living quarters. And just to clarify, I'm stumped as to why vapor barriers are NOT a good idea, at least where I've placed mine - confining the vapor to the interface between soil and underside of the poly.


 o
RE: Vapor Barrier on cellar dirt floor

It's very unusual for a house of this vintage to have a cellar with no gravity drain, but if there's no visible water for all but 2 months, perhaps it was felt to be unnecessary because of the natural slope of the land, soil conditions or some other factor(s).

My cellar has rubble walls up to grade, then brick. The shotcrete treatment was done primarily to reinforce the brick which had begun to deteriorate in several places. No bonding agent was used, but metal mesh was put on the walls before the spray was applied. This is not a neat process. Anything you do not wish to have a coating of shotcrete needs to be covered before spraying. I attribute the decrease in humidity primarily to sealing the brick and below grade areas with continuous coating. I don't know enough about spray insulation to offer any advice or opinion, but I know it's being done frequently in old houses currently. Unlike shotcrete, however, it does not provide any structural reinforcement.

I didn't suggest that vapor barriers are a bad idea. I just don't know. My comment was about using the dehumidifier. If you're still getting mildew and odors in the living area after all you've done if you don't run the dehumidifier, I am more than a little mystified about where the moisture is coming from. Perhaps if the dirt floors remain saturated beneath and because of the vapor barrier, enough is escaping from the inevitable openings however small they may be.


 o
RE: Vapor Barrier on cellar dirt floor

My understanding of maintaining old homes is that they have survived for this long because of their ability to shed water and breathe. Removing that ability can cause rot (dry or wet) and mold to develop.

I only know what I have experienced with this home and am no expert, only an armchair old home owner.

Have you consulted a contractor who specializes in old homes?


 o
RE: Vapor Barrier on cellar dirt floor

I'm no expert, either, but Maine_Mare's comment about the reasons for longterm survival of old buildings is in my view absolutely correct. I've seen more than a couple horrible examples of rot in 19th century houses which had vinyl siding installed. The current - very understandable - mania for "energy efficiency" may very well quickly destroy old houses if not done with great care and expertise.

In my own circa 1810 house, the cellar remains wet by modern standards, but the water flows in, collects in a perimeter gutter system and exists through a cellar drain. The sills are 8x8 spruce heartwood that are so solid it's nearly impossible to drive a nail into one. The joists are 6 to 8" diameter cedar logs with one face squared off. They're as sound as the day they were installed. Old time builders knew exactly what they were doing. Even the rubble walls had the advantage of flexing with frost rather than cracking.


 o
RE: Vapor Barrier on cellar dirt floor

Regarding my lingering humidity problem, I'm about as stumped as akamainegrower. I have tried researching online the permeability of rubble foundations (chinked and unchinked) and have come up empty-handed. Likewise the effect of incomplete sealing of, in this case, a dirt floor. For sure water vapor will migrate from high dewpoint to low dewpoint, but can't find a formula to estimate the effect.

Re: vapor barriers, it seems to me their value depends entirely on where they are placed. Vinyl siding likely a no-no, along with the stupid move some house painters inflicted on us, by caulking under each clapboard for a "better look" and (they didn't mention) quickly failing paint. Boy were we rubes then (hopefully a bit less now). OTOH vapor barrier behind plaster or drywall has, AFAIK, no disadvantages at all. Damp insulation is not much better than no insulation.

Finally I think "dry rot" is sometimes misinterpreted (see for example http://www.waltersforensic.com/articles/civil_engineering/vol1-no9.htm). The organisms that cause rot (and also allow opportunistic "sqatters" such as carpenter ants), MUST have a damp environment.

If I ever get someone local to give me an informed prescription what next to do, I'll try to follow up on this excellent forum.


 o
I have more questions than advice on this topic

One of my concerns about putting a vapor barrier down on the dirt floors in my old house's cellar has to do with the risk of creating a super-saturated zone right at the foot of my dry-laid walls (some rubble, some much more carefully selected and laid, but all w/o more than chinking mortar.)

The vapor barrier, in my view, is there to stop the inexorable rising of water vapor from the soil. (It rises due to constantly changing atmospheric pressures that no one can do anything about.) Blocking it at the cellar-floor surface level won't stop it rising, but it could channel it all outward to the edges of the barrier. If the barrier is tightly sealed to walls (as it ought to be) then where does all that accumulated water vapor go? It seems to me it will create a lot of sogginess in the soil at a very bad place: where the foundation of my house rests on what I assume was undisturbed soil at the time of construction c 1845-ish.

I think it's important to differentiate between free water that comes in during periods of high soil water or the result of poor local drainage from roofs, flooding, etc, and moisture that comes from rising soil moisture vapor.

The free water part may be containable, managable, or mitigated, but soil moisture vapor is probably not something you can stop.

Moisture arising from the soil in very old houses may be a natural phenomenon that we have lately defined as a problem, or that has become problematic because of material changes we have made to our buildings by installing central heat, insulation, double-glazing and even running water. It may also be that our expectations have changed to cause something previously deemed "normal" to be seen as a problem in need of action to eliminate.

Before there was electricity and air-conditioning technology I doubt that people were much pre-occupied with removal of air-borne humidity by dehumidification. But the fact that we can do it, may now make us feel that we have to do it.

I also disagree with the notion that keeping cellar rooms closed up during the warm months is the best course of action. I do see the logic that keeping warm, summer, moisture-laden air away from the soil-cool stones of a foundation avoids condensation on the walls. But I am less concerned with condensation coming from warm-air atmospheric moisture, than with venting soil moisture vapor to the outside of my building envelope. Old people around here who lived in old houses like mine have told me of the careful attention they paid to opening up the cellar and airing it out after the winter. Since most of them lived and worked on the farms they were at home to attend to this and paid close attention to the direction of the wind so to maximise the flow-through pathways by opening different windows, doors, etc. I practise this as much as possible and it results in a dryer cellar, even though I still get some condensation on the walls, especially in the early Spring. In the years when I can pay the most attention to active cellar ventilation, my cellar - and consequently the rest of my first floor - stay the driest. But it often takes multiple changes during the course of a day, and I have to have my whole outdoor cellar stairway open all the time (during the day, it's generally closed at night to avoid dew-laden night air), which many people couldn't or wouldn't do out of fear of intruders.

My cellar walls show evidence of multiple layers of white-wash (quick-lime and water). This is an effective preventive, curative and aesthetic disguise for dampish stones. It does nothing to reduce humidity in the air (adds to it for a few days as it dries off), but it makes the cellar seem less grungy.

I struggle with this issue, a good deal, because I think a lot of the best-advice from old house "experts" may not be the best for the building's long-term survivabality.

Info dump: My house is located in northern, NY. Foundation as described above, otherwise timberframed, two-story, wooden structure with its original plaster walls intact. Wall cavities are mostly filled with two separate layers of backplastering on wooden lath. Two layers of 5/4" X 10" T&G sheathing with clapboards nailed on top. Slate roof. Still no central heat, though now only two modern, more-effective stoves rather the original 4-6. Electrified (but not in every room) just before WW II; minimal indoor plumbing installed in 1960. In short, a oddly long-term survival of 19th technology, which I am slow to alter.

If you're going to put vapor barrier down, and going to the trouble of sealing it properly, you should use material specifically intended for the purpose, not construction poly.

I haven't solved this problem to my satisfaction, yet.

Lately, I have been thinking that I should undertake a more active course of observation (recording indoor and outdoor temps, humidity and wind direction and speed) along with a program of trial openings and closing to gather better information to form a more thought-out moisture vapor reduction program. (I expect this was all empirically known a hundred years ago, but even old timers now have forgotten the details, alas.) This summer has been dryer than normal so perhaps this would be a propitious time to start.

There is a guy, an engineer, (located in eastern MA, I think) who owns an old house and he has basically sealed up his entire cellar walls and floors from within. I'm drawing a blank on his name, but a frequent poster, Worthy, often posts links to his work so if you search for Worthy's posts on this forum you should turn up the link. I have read this guy's writing on his website, but remain unconvinced that it's what I should do with my old building. I don't think he's a crank, or anything - and he may be right - but what he does is essentially non-reversible. That irreversability is what's stopping me.

L.


 o
RE: Vapor Barrier on cellar dirt floor

Of course, just as I posted I remembered the engineer's name: Joseph Lstiburek. He bills him self as a green building technologist, which he is because he is very concerned with energy-saving methods. Whether they are also old-building-protection/conservation techniques is a more complex question.

My personal definition of green building technology does not stop at better energy conservation. If buildings' useful lives are substantially shortened by energy-saving efforts then I think proposals need a second look, or two.

But, as I said this guy is not a crank, and more to the point as you can see from his site, he has done this to his own 19th c. building, not just pontificate about it.

HTH,
L.

Here is a link that might be useful: Lsitburek's website


 o
RE: Vapor Barrier on cellar dirt floor

I appreciate your additional thoughts on this issue, but (no offense) you have not persuaded me to halt my pursuit of a drier cellar. It is unfortunate that there appears to be little fact-based information on this issue.

Your concern about redirecting water vapor to the foundation is, IMHO, a bit over-stated, considering that the outside of the foundation is in constant contact with soil (and has been for centuries, in the case of my house).

Each homeowner is free to manage their old house in the era of its construction, meaning avoid central heat, storm windows and doors, insulation, and so on. OTOH, it's not disrespectful of an old building, to strive for a compromise among longevity, energy conservation, health, and comfort. Preserving our planet by producing less CO2, is just as important as preserving a structure.

BTW I had already found http://www.buildingscience.com/documents/insights/bsi-041-rubble-foundations. It's an extreme approach but impressive in its thoroughness.


 o
RE: Vapor Barrier on cellar dirt floor

"e is very concerned with energy-saving methods. Whether they are also old-building-protection/conservation techniques is a more complex question."

They do not.

And there have already been no end of problems created by tightly sealed houses before anyone noticed the lack of ventilation and make up air.

Now you know why heat recovery ventilators are included on even newer tight houses.

Moisture control was not an issue before central cooling and energy efficiency.

The houses leaked a LOT of air.

Throw another log on the fire, or use a larger boiler or furnace.


 o
RE: Vapor Barrier on cellar dirt floor

Grace does make a butyl-based self-adhering flexible underlayment/flashing called Vycor Butyl primarily intended for high temperature conditions like in the desert but Grace Ice & Water Shield is a modified asphalt-based product that should not be used indoors nor will it readily adhere to porous irregular surfaces.

Closed cell spray foam is a good sealer but it must be protected from fire by a layer of drywall.


 o
RE: Vapor Barrier on cellar dirt floor

I agree with much of liriodendron's post, especially the suggestion that we need to consider the potential lifespan of buildings in our pursuit of "energy efficiency". The example of thousands of perfectly good, repairable old windows dumped in landfills in order to replace them with new "energy efficient" ones which will not last more then 20 years at best is, imho, one of the greatest consumer frauds of the last several years.

As to the original basement issue, let me suggest the following. Installing an impermeable vapor barrier on a below grade dirt floor may be less effective in reducing moisture than the traditional concrete over gravel surface. The concrete is not totally impermeable and allows moisture to slowly migrate from below to the air or drain away through the gravel layer to a drain. The trouble with the vapor barrier appoach is that it really doesn't do anything to naturally reduce the moisture content of the underlying soil. It's as if the dirt floor becomes a giant sponge with no way to dry out.

Conincidentally enough, one of my neighbors has just within the last two days embarked on a solution to the wet basement in his 19th century house. The contractors involved, who I have known for years, have installed a perimeter drain system using plastic pipe and gravel, created a gravity drain connecting to the storm sewer and installed a a concrete surface over the small area that had previously been dirt. No new rec room, but a much drier basement without a sump pump or dehumididfier will be the result.


 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!


Return to the Old House Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.


Learn more about in-text links on this page here