Encapsulate or Vent 100+ Year Old Crawlspace

I have read much discussion whether it is better to ventilate a crawlspace or encapsulate. I live in North Carolina where it is humid, seemingly, all of the time. I have a humidistat in the crawlspace and during this time of year the humidity reading often ranges from 80% to 55%. When compared to the outside humidity, the crawlspace is generally 10-15% higher.

I know these readings are high, but how can I possibly expect a 40% RH reading when the outside air is often at 70% or higher? I have added a vapor barrier, some vent fans, and increased ventilation by making the three crawlspace doors vented as well. Plus, when I bought the house in October there were no gutters. The first thing I did was install gutters and run the downspouts out into the yard.

I have debated trying to seal the crawlspace, but the house was built in the 1890's and far less than air tight. Also, there is no subfloor in parts. The floor boards are very thick, but they are attached directly to joists.

The moisture level in the wood framing is about 16-18%.

The house has been standing for over a hundred years - so I have to imagine something is working in the crawlspace.

Is it worth/possible to encapsulate the crawlspace? Or given the region, are those RH readings at this time of year normal?

Thanks!

Welcome to the site.
There has been a few discussions here on the issue. Like you said if it ain't broke it must be working. You do want a good poly in the crawl space to control ground water and insulating water pipes to limit condensation.
If you seal it up you should condition the space also.

Here are a few threads you might find interesting. There are others too, if you use the search box at the top of the page. i just typed in 'crawlspace' and got pages of posts.

http://www.houserepairtalk.com/showthread.php?t=18447&highlight=crawlspace
http://www.houserepairtalk.com/showthread.php?t=17610&highlight=crawlspace
http://www.houserepairtalk.com/showthread.php?t=18152&highlight=crawlspace

Great. Thanks for the links. I really don't know how feasible it is to truly encapsulate my home. It is actually so old that parts of it don't even have a subfloor....it's just the floor boards attached to 4x6 joists that are sitting on rock piers. I would have to totally seal everything to encapsulate. I am afraid that if I took the floor boards up they wouldn't go back down since they have been settling for 100+ years. I did consider putting sheets of plywood between the floor joist from below in the crawlspace. It wouldn't be a true sub-floor - but it would at least seal the floor.

Until I get to that point I think I may just add some additional fans below to keep the air moving.

chippedtooth said:

Great. Thanks for the links. I really don't know how feasible it is to truly encapsulate my home. It is actually so old that parts of it don't even have a subfloor....it's just the floor boards attached to 4x6 joists that are sitting on rock piers. I would have to totally seal everything to encapsulate. I am afraid that if I took the floor boards up they wouldn't go back down since they have been settling for 100+ years. I did consider putting sheets of plywood between the floor joist from below in the crawlspace. It wouldn't be a true sub-floor - but it would at least seal the floor.

Until I get to that point I think I may just add some additional fans below to keep the air moving.

Click to expand...

It was common not to have a sub floor when the floor boards were a full inch thick. You really should have poly on the dirt in the crawl space and on old houses it is a good ideal to crawl around down there and plug or cover all holes that go up into the house.

Yeah...I was amazed at how thick the floor boards were when we re-did the bathrooms. They were also fastened with square cut nails. I kept one just to have.

I spent the winter filling gaps between floor boards with caulk (we heat with propane...so any heat loss was pricey). That's why I think maybe putting plywood between the joists and then adding insulation back might be a good idea. I've just never heard of it before.

The first thing I did when we bought the house was add a vapor barrier to the crawlspace ground and add gutters (with extensions for the downspouts that run to the yard). I also built crawlspace doors with the ability to close or leave open with screens to increase ventilation.

You can insulate the floor with batts but that wants to breath below that so use something with holes in it to hold it up. Do not use paper backed batts.

chippedtooth said:

Yeah...I was amazed at how thick the floor boards were when we re-did the bathrooms. They were also fastened with square cut nails. I kept one just to have.

I spent the winter filling gaps between floor boards with caulk (we heat with propane...so any heat loss was pricey). That's why I think maybe putting plywood between the joists and then adding insulation back might be a good idea. I've just never heard of it before.

The first thing I did when we bought the house was add a vapor barrier to the crawlspace ground and add gutters (with extensions for the downspouts that run to the yard). I also built crawlspace doors with the ability to close or leave open with screens to increase ventilation.

Click to expand...

Are the screens only available when the doors are open?

slownsteady said:

Are the screens only available when the doors are open?

Click to expand...

Before anyone here insulated the floor it was common to close the vents in winter, not a good idea.

In other words, the venting should be available all the time?

slownsteady said:

In other words, the venting should be available all the time?

Click to expand...

I don't know if the same applies everywhere, but I think so. Same as an attic, air behind insulation.

Yes...when doors are open the screens let air pass. When doors are closed it is air tight.

I've heard to close vents in winter to keep pipes from freezing.

I always heard to close the vents in winter to keep pipes from freezing...

Insulate the pipes. If you isulate the floor the crawlspace will still freeze with the door closed

Pipes are insulated and currently have batts in between joists. We still had one pope freeze last year it got so cold (for North Carolina).

A few things can be done.
Closing the doors when it gets really cold may help for a while but with an insulated floor it may still freeze if cold lasts a long time.
Add some framing around the pipes and lower the insulation so the pipes are on the warm side.
Wrap the pipe with heat tape.
Running a little water will bring slightly warmer water from deeper underground, you could set a toilet to run a little continuesly when it is really cold, just a drible.

Great. Thanks for all of the tips. The water dribbling trick is what we did growing up outside of Buffalo. Simple but effective.