Partial Crawlspace Encapsulation

[wrw103]

I have a 106 year old with a basement that is open to a crawlspace. I recently talked with a contractor about encapsulating the crawlspace, and they said they could do most of it, however, the crawlspace under some additions is too tight to install the encapsulation. They suggested encapsulating the accessible areas and sealing off the portions that can't be accessed. There are no existing vents that would allow the addition crawlspace to breathe, I'm afraid that closing off the crawlspace under the additions might cause more problems that not encapsulating at all.

I'm considering encapsulating the accessible areas, but not closing off the addition crawlspaces to help them breathe a little. Would this completely defeat the purpose of the encapsulation or would I still get some benefit?

[Sailfast]

What do you want to accomplish with encapsulation?
What does too small mean?

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[teddy bear]

Get 10 mil plastic on as much of the earth as possible. Even extending the plastic with a pole to cover the earth and some gravel on top of it will dramatically reduce moisture evaporation of moisture from earth.
Leave the space open and add enough dehumidification to maintain <60%RH. Check out the heavy duty Santa Fe dehumidifiers that have extra capacity durability needed for this type of application. If you are in a green grass climate, avoid outside infiltration/ventilation because of moisture in the mild seasons outside air.
Monitor the %RH in the space to avoid mold and high moisture in the home.
Keep us posted.
Regards Teddy Bear

[wrw103]

The crawlspace height is very short ~18". The contractor thought it would be tough to get in there. I crawled up there the other day though, and I think you could at least do as Teddy Bear suggested and lay some plastic down. It might be tough to attach securely to the walls though.

There's also another section that can't be accessed at all. There are footings all the way around it. The only access is a few penetrations for piping. They must have installed all the piping from the topside during construction.

My main goals are to reduce the musty "basement" smell and prevent any future mold/rot issues. The house subfloor currently has fiberglass insulation installed on it, and, from what I've read, that's not good to have if there is moisture in the air.

I'm lucky that the previous owner installed a sump and a sani-dry dehumidifier. Overall it doesn't seem to be too humid down there even when it rains. I guess the dehumidifer is doing it's job.

From Teddy Bears response, it sounds like it might be worth encapsulating what I can, not sealing off the unaccessible areas, not installing new vents in the unaccessible ares, and keeping the dehumidifer working.

[teddy bear]

The Sanidry is good dehumidifier. l Covering earth is more critical than attaching to the wall.
The last issue maybe fresh air change in the living area. Measuring the CO2 levels when occupied will tell us the amount of fresh infiltrating and exfiltrating the home. Ideally a fresh air in 4-5 hours when occupied will purge indoor pollutants, including any odors, and renew oxygen.
$100 CO2 meter from CO2.com is one of the tolls to monitor CO2. 650 ppm CO2 is 30 cfm per occupant.
During winter with max stack and winds, you will have plenty of air change. During the calm winds and moderate outdoor temps, your air change will decline to an air change +12 hours. Odors will be noticeable and Oxygen levels will decline.
Not Ideal. A fresh air duct connected to a small whole house dehumidifier with 70-80 cfm of fresh air operating when occupied is a way of doing ventilation and humidity control. The Sanidry could be modified or an Ultra-Aire 70H will do the job.
Keep us posted.
Regards Teddy Bear

[Sailfast]

The crawlspace height is very short ~18". The contractor thought it would be tough to get in there. I crawled up there the other day though, and I think you could at least do as Teddy Bear suggested and lay some plastic down. It might be tough to attach securely to the walls though.

There's also another section that can't be accessed at all. There are footings all the way around it. The only access is a few penetrations for piping. They must have installed all the piping from the topside during construction.

My main goals are to reduce the musty "basement" smell and prevent any future mold/rot issues. The house subfloor currently has fiberglass insulation installed on it, and, from what I've read, that's not good to have if there is moisture in the air.

I'm lucky that the previous owner installed a sump and a sani-dry dehumidifier. Overall it doesn't seem to be too humid down there even when it rains. I guess the dehumidifer is doing it's job.

From Teddy Bears response, it sounds like it might be worth encapsulating what I can, not sealing off the unaccessible areas, not installing new vents in the unaccessible ares, and keeping the dehumidifer working.

How big is the unacessable area? How tall? Might want to add a trap door or something to get to it.

What kind of shape is the rest of the house in?
Insulation?
Happy with your utility bills?
Comfort?

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[Sailfast]

What part of the country do you live in?

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[wrw103]

The completely enclosed crawlspace is about 20'x10'. It's also pretty short ~18". I like the idea of adding an access door, but I'm not sure how it'll affect the stability of the footing or if there's enough room. I'll have to do some investigation to see what is possible.

The rest of the house is in pretty good shape. There is some sagging of the main beam in the house, and I'm looking at shoring/leveling it. We're also upgrading the knob and tube wiring and the HVAC system.

The floors are insulated from the crawlspace and the attic has blown in insulation. I can't say if the walls are insulated or not, but some of them are plaster which I hear is a better insulator than sheetrock.

I just purchased the home, and I haven't received a utility bill yet. So I can't say what the heating/cooling costs will be.

I haven't moved in yet since we're doing some renovating, but, from the time I've been there, the heat seems to do pretty good. I haven't cranked the AC on yet. We're also upgrading the HVAC system to one that is properly sized and balanced so that should only help it get better.

I live in the southeast (Tennesse) with hot and humid summers and pretty cold and wet winters.

[Juan Madera]

You need to cut a "trap door" in the floor of the 10x20 crawl space, and better to do now while remodeling than when something breaks down there in the middle of the night during a 3 day weekend.... Plus you can assess the structure.

I'm betting that with no ventilation and wet humid climate, there will be mold, mildew and wood rot.

[Sailfast]

The completely enclosed crawlspace is about 20'x10'. It's also pretty short ~18". I like the idea of adding an access door, but I'm not sure how it'll affect the stability of the footing or if there's enough room. I'll have to do some investigation to see what is possible.

The rest of the house is in pretty good shape. There is some sagging of the main beam in the house, and I'm looking at shoring/leveling it. We're also upgrading the knob and tube wiring and the HVAC system.

The floors are insulated from the crawlspace and the attic has blown in insulation. I can't say if the walls are insulated or not, but some of them are plaster which I hear is a better insulator than sheetrock.

I just purchased the home, and I haven't received a utility bill yet. So I can't say what the heating/cooling costs will be.

I haven't moved in yet since we're doing some renovating, but, from the time I've been there, the heat seems to do pretty good. I haven't cranked the AC on yet. We're also upgrading the HVAC system to one that is properly sized and balanced so that should only help it get better.

I live in the southeast (Tennesse) with hot and humid summers and pretty cold and wet winters.

Ok. Be VERY careful that the AC is not over sized.... Will not dehumidifier if oversized.... and if cost is not a factor plan to possibly inject REAL polyurethane foam, not Water mixed foam into the walls... before you select a new hvac system.
You may be able to use Aeroseal to deal with the inaccessible crawlspace, check for a local dealer.
And like he said, add a trap door in the floor somewhere.

The completely enclosed crawlspace is about 20'x10'. It's also pretty short ~18". I like the idea of adding an access door, but I'm not sure how it'll affect the stability of the footing or if there's enough room. I'll have to do some investigation to see what is possible.

The rest of the house is in pretty good shape. There is some sagging of the main beam in the house, and I'm looking at shoring/leveling it. We're also upgrading the knob and tube wiring and the HVAC system.

The floors are insulated from the crawlspace and the attic has blown in insulation. I can't say if the walls are insulated or not, but some of them are plaster which I hear is a better insulator than sheetrock.

I just purchased the home, and I haven't received a utility bill yet. So I can't say what the heating/cooling costs will be.

I haven't moved in yet since we're doing some renovating, but, from the time I've been there, the heat seems to do pretty good. I haven't cranked the AC on yet. We're also upgrading the HVAC system to one that is properly sized and balanced so that should only help it get better.

I live in the southeast (Tennesse) with hot and humid summers and pretty cold and wet winters.

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[billygoat22]

they make this thing called a "shovel". candyman contractor needs one, and 18" is NOT a tight crawl. 10" I'll give you some wiggle room for whining. really? I've run duct in 10" crawls before.

I work on one house that has trenches dug in crawl to access the equipment and ducts, unless your house is set on solid granite, can make a few inches if want access by digging. And you won't have anyone else whining about access to run piping, wiring, etc.

Agree on getting access hole to other crawl, you will need it eventually, if only for termite treatment.

[hvacker]

18 inches, no problem. In that Tennessee is one big cave, go to the local NSS Grotto and hire some seasoned lads and they will have it done in no time.
The insulators were seemingly able to work so access is possible.
I agree most of your problems can be fixed cheap. Lay down the plastic. attachment to the wall is not so important as some pea gravel will keep it against the wall.
I wouldn't expect plaster is any more a benefit than drywall as insulation goes. Both are rocks. Plaster is just harder. Any benefit of one over the other is not worth considering compared to the other load factors.
With an old house, keep an eye out for icicles. Old homes have this problem because eve venting wasn't done and icicles are an indicator. Need to fix that as rafter rotting can happen.