subfloor crawl space

[rscho]

I've had to remove a few T&G floorboards near some walls to replace rotten joists in a cavity brick house. In order to get underneath the boards I had to dig out about 6-8 inches of rubble (bricks, mortar and clay soil) making a space of about 1'4" so I could crawl around. Having replaced the rotten joists (and fixed the drainage problems that caused them) I don't know whether to return the rubble, replace with a cleaner & easier draining (and less smelly!) fill like crushed rock or leave it cleared. The ground level underneath the house is now about 5" lower than that outside the house.

Any suggestions would be appreciated.

[Rick]

I have always left mine clean and empty when I have cleaned them out so I can gain access.

If nothing else, it saves cleaning it all out again next time.

Rick

[Bob]

Because the ground around the home is higher, the ideal thing to do is to provide good water run off. Do not back fill under the home at all, because the more air circulation, the better it will be. If water gets down there, it will not only rot the wood, but can cause mold. Install a submersible sump pump in the lowest spot, with some kind of access door for maintenance. If you back fill, and the dirt gets wet, it's much harder to dry it out.

[calhoun]

Spread it out and cover the entire ground area with a sheet of 6mil poly before you close it back up.

[Stretch]

Where you are located has a bearing on the answer. Here is a link to an article on drying out crawlspaces:

Crawlspace problems:

Stretch

[tbasc]

You're correct to be concerned about the difference in level between inside and outside. You don't say what "the drainage problem" was. Certainly, as Rick says, it's a good idea to leave the working space below the floor. As Bob notes, the problem is to keep water out of the space. As long as you think you can keep the crawl space dry, you are o.k. In addition to directing roof run off well away from the house, sloping the yard surface away from the house, sodding for improved run off, and making sure of the water table height, you might consider directing some conditioned air into the crawl space. This can be done with passive registers or a fan. In the South East, outside air is often too humid to be useful in lowering the relative humidity in crawl spaces. TB

[raden]

It also allows better airflow

I ended up with some rot after the previous owners of my house made a though lounge and left the wall under the floorboards

[Bill Gill]

The crawlspace under my house has always been lower than the outside yard. When I first moved in I had a moisture problem, but I figured out where it was coming from and corrected it and now have a dry crawlspace. The main thing is to make sure where any moisture is coming from and try to keep it out. Sometimes this is easy, mine was, and sometimes it isn't. It can involve extensive sculpting of your yard to redirect rain flow, or french drains, or something of the sort.

The main thing I am saying is that having the crawlspace lower than the outside is not necessarily a bad thing.

Bill Gill

[Jay Stootzmann]

Check out

for more info on crawl spaces

[Stretch]

Don't run AC into the crawlspace. It will pull the main house into a negative pressure which will suck crawlspace or outside air into the house. This will reduce performance of the ac and heat serving the house. It can also backdraht a flue and kill you. Far better to put a dedicated DEhumidifier in the crawlspace and close the vents after you put plastic on the ground. To try to condition the crawlspace with the vents open is like running the ac in your house with the wimdows open.

Stretch

[rscho]

Thanks for all the info,

The drainage problem was a blocked storm water drain caused when whoever put up the fence drove a post through it and then set it with concrete. This allowed the roof run-off to overflow and enter the crawl space. Judging by the age of the fence it must have been at least 20 years ago. The previous owners seemed to go to considerable lengths to control the resulting rising damp (its an old house with inadequate or no damp course) but never seemed to attend to the drainage problem.

The average afternoon relative humidity here is about 55% (SE Australia). Closing the crawl space really goes against the grain as everything I've come across regarding rising damp or rot suggests increasing ventilation but I guess if the outside air is carrying more moisture than the crawl space air it makes sense! In any case I will never be able to get access to all of the crawl space (without ripping up all the floors) to lay poly effectively so I'm thinking of relying on low voltage sub-floor ventilation fans that turn on and off depending on the atmospheric conditions eg. turn on if outside air is drier than the crawl space air.... or perhaps let natural ventilation take it course and move on to the next project..

thanks again everyone!

Jay Stootzmann wrote:

[Dave Fawthrop]

| Don't run AC into the crawlspace. It will pull the main house into a | negative pressure which will suck crawlspace or outside air into the | house. This will reduce performance of the ac and heat serving the | house. It can also backdraht a flue and kill you. Far better to put a | dedicated DEhumidifier in the crawlspace and close the vents after you | put plastic on the ground. To try to condition the crawlspace with the | vents open is like running the ac in your house with the wimdows open.

Utter and complete Rubbish.

--=20 Dave Fawthrop

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