GREETINGS AND HAPPY NEW YEAR FROM FANCY GAP, VIRGINIA
Although a builder/renovator and avid F/H reader for 20 years, I’m just now beginning to enter the 21st Century (on-line). From all I’ve seen this afternoon, it appears that I’m in very good company. My question today concerns damp-proofing the crawl-space of a manufactured home with brick underpinning. What is the current school of thought on how best to combat MOISTURE and ODOR that are seemingly forever present in these little hells-on-earth? Thanks for any and all suggestions.
Replies
Happy new to you too.
I'm afraid I can't help with this one since all the mobile homes I've dealt with requirerd ventiation under them. It sounds like you are trying to seal the space tight.
Just for speculastion, I supose I would need tp starty with pouring a slab over a VB, level the home into place, then buil;d the walls up and spray them from inside with a polyurethene foam or just tape in some Astrofoil around the perimiter.
There is still a prblem with that though, in that some weind driven rain will still enter, and likely be trapped, so the slab would need to be crowned to drain to edges asmd weeps made in the wall, or a mechanical system like a de-humidifier used on an auitomatic setting. I would think this might add too much heat to the spacve in summer though
BTW, this ois a very active forum. For future ref, it is not necessary to post twice in different areas. That can actually be quite confusing, unlike other similar forums where folks don't migrate aropund as much and you can wait for a week for a reply.
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Thanx Piffin. In all the time I spent inspecting this hell-hole the other day, I missed the obvious--ventilation. Now that I think about it, this structure has the "automatic" style vents, which in my experience always manage to automatically freeze in either the open or closed position. Maybe the total abscence of even the hint of light should have been a tip off. Must have missed that one, since I was too busy trying to find the source of an extremely unpleasant odor that has recently made it's presense known inside the home. Also, thanks for correcting my ettiquette, but after I made my first posting, I was unable to find it and assumed I'd done something wrong, so I tried again. You know, the whole patience thing. Later.
By default you only see UNREAD messages.So after you have seen the one that you posted you won't see that thread again until someone post a new message to that thread.But you can go back and look at previous threads. Look on the left side above the index, SHOW DISCUSSIONS.You can select Show High Interest. Those are ones, that by default, you have posted to. Also you can set the High Interest flag by selecting the Thumbs Up at the bottom of the page and clicking Apply.You can also use Recently Seen. Also ALL and keep paging through the list. They is a show 50 more at the very bottom of the index.
Thanks BillHartmann, but I don't have a SHOW DISCUSSIONS tab or button anywhere on my screen. Do you have any idea why?
Look to the left under the banner you have 5 buttons (Start, etc)
Below that links for New Message and Advanced Search.Then a Show Discussions drop down window with a Go button below it.The the index of messages.You might be in Basic View.At the bottom of the message window mine has this link"Is this too complicated? Switch to Basic View" to switch to basic view. If you are in basic then it will be an option to switch to advanced view.PS I just checked and in basic view you don't have the discussion option.You will have this at the bottom." Choose your own font size - Advanced View"Click on it and you will get the Show Discussion (and other options).
Edited 1/1/2006 4:49 pm by BillHartmann
From what i've read, it seems i'm in good company when I say, "seal them and condition them".
I've read articles in Builder magazine that back me up on this. Just consider a crawlspace. If you vent it, you allow moisture in, but theres no positive way to evacuate the moisture.
When I build a crawlspace I treat it like it were a basement. Would you vent your basement?
Good Point!
What you say sounds good, but... A guy I know built a small home on a crawl space here in dryland southern Colorado. When the home was sold only three or four years later the BCI joists were almost entirely covered with mold. There were no vents at all and he had not put vapor barrier on the ground (he says the building inspector told him NOT to vent the crawl space). The owners had vents cut in and hired someone to wash down the joists with something to kill or slow down the mold, then VB was installed.As to "would you vent your basement?", if there is any heat ducted to your basement then the air would be circulating with the rest of the house, even if more slowly. That coupled with the common complaint of "damp basement", either the basement needs to be heated and thus dried out OR very good measures need to be taken to keep moisture out. In some locations I doubt if moisture could be kept out, even though I opted for keeping moisture out in the home DW and built recently.Life and suffering are inseparable.
I didnt say simply seal it up. I suggested conditioning the crawlspace. By this I mean heat it. I also install a vapor barrier on the floor and rigid insulation on the walls with scrap drywall over it for fire protection.
Yes if you simply seal the thing whatever moisture is there will be trapped and create mold problems.
Hasbeen:
It's really pretty straight forward if you look at it from the right perspective. The things that need to be considered are the moisture levels relative to each other (inside to outside). First, you do everything that you can to eliminate moisture in the crawl space by applying waterproofing and using a vapor barrier. Then you look at the humidity in the crawlspace relative to the outdoor air. If the average moisture level of the outdoor air is higher than in the crawlspace after you have applied the waterproofing and the vapor barrier, bringing it into the crawl is going to cause problems as it condenses on all the cooler surfaces of the crawl. If however, you are lucky enough to live someplace where the relative humidity is low enough (the desert?) then bringing this dry air in to the crawl will be a good thing.
I have only lived and worked in NY and New England and I have never come across a situation that I thought would be helped by venting. In new construction I treat the crawl as conditioned space. I waterproof the foundation walls, insulate them on the interior surface to R-19 (I insulate on the interior so that I can insulate all the way up to the plate with minimal increase in the risk of termites etc.). We use a 6-mil poly vapor barrier under the entire slab and insulate at least 2' in from all the exterior walls with 2" of foam. We also use a strip of sill seal all the way around the slab to allow for expansion and contraction as well as providing a thermal break. If the house has forced hot air we usually bleed off a little bit of conditioned air to maintain the temperature of the crawl above the dew point. I was a little concerned in the beginning about mixing the crawlspace air with the living space air (odors etc) but it has not been a problem yet although given the right conditions I am sure it could be. So far, the BI has not had any issues with the procedure and all the crawls are still dry and usable.
Retrofitting existing construction is trickier, more expensive and a more unpleasant job but can still be done. We begin by cleaning everything out of the crawlspace, including the insulation in the floor joists. We make any necessary repairs and then apply a mold inhibitor to all exposed surfaces. Waterpproofing is applied to all the interior foudation walls in the form of 2 coats of Drylock paint, then a layer of 2" foam is installed with all the vents getting plugged with foam plugs that are caulked in to place. We dig a trench along the foudation walls so that we can get the foam-board down below the surface as far as practical. Ideally you'ld want to go below the frost line but sometimes there is simply not enough room to pile the dirt and still work so we function on the premise that every little bit helps (insulating from the exterior might be more effective in these situations but you have to consider existing landscaping and the insect issue as well). Two layers of 6 mil poly applied to the floor of the crawl, running in different directions and taped to the foam at the walls, are used to eliminate moisture coming up from underneath. We then re-insulate the floor system, install a low-temp dehumidifier with a pump for the condensate. Again if there is forced hot air we try to bleed off some conditioned air however, the risk of odors etc being drawn up in to the house is usually much greater in retrofitting than in new work so you have to be extremely carefull. The potential issue, at least here in Mass is that if the crawl is not conditioned (heated/cooled, the dehumidifier doesn't count) then it must be vented so we will use removeable foam plugs in the vents in those situations.
All of this work is useless though if you don't also deal with landscape moisture at the same time. Water from the downspouts, sump-pumps, etc must be lead away from the foundation. Any irrigation must be adjusted so that it does not apply excess water against the house (Drip irrigation seems to be the best near the foundation) and the soil must be graded away from the structure and provide for proper drainage.
These methods have served us well so far but I'm also sure that the other members here will have their own take on things as well as ways to polish these methods even further.
Good Luck, BILL
"Then you look at the humidity in the crawlspace relative to the outdoor air. If the average moisture level of the outdoor air is higher than in the crawlspace after you have applied the waterproofing and the vapor barrier, bringing it into the crawl is going to cause problems as it condenses on all the cooler surfaces of the crawl."Yes, but it is a little tricky.You need to look at absolute moisture levels or dewpoint. RH alone won't give meaningful information. You can use RH and air temp with a psychometric calculator to get the dewpoint.
Bill:
Absolutely correct, the concern is, at what point will that moisture condense in the crawl. I was just trying to point out that you don't want to ventlate the crawl with air that brings in more moisture than is already in there.
Best, BILL
I get your point. Our outdoor humidity level here is typically between 20% and 45%... so different than most of the other places I've lived.Life and suffering are inseparable.
Here in LA it's very different. SOP is that crawls are vented. Ours is extremely dry all year. The ground in there is mostly as hard as really bad concrete. It takes a Bosch hammer to do any digging, except for the top half inch, which is a very fine dry powder.
-- J.S.
David:
Welcome to the "21st century." Try this link for some ideas http://www.crawlspaces.org.
I actually just gave copies of these articles & reports to my local building inspector following a discussion that we had on keeping cralspaces dry.
BILL
Thanks for the tip Bill. In scanning the site you sent me to, I noticed that some of the information mentions NC specifically which, coincidentally, is where this particular home is located. Have a great and prosperous New Year, and remember to bang the nails, not the fingers!!