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shtoink 12-03-2008 11:25 PM

Filling in large openings in concrete foundation
Hi folks

As some of you may know, I am rebuilding my house that I had moved (by truck and by barge) to an island just over a year ago. During the house moving process, the house was temporarily set down on two large steel I-beams on top of wooden cribbing until a concrete foundation was poured beneath it. After the forms were stripped, the house was finally set down on the foundation.

Here is a photo of the house on the I-beams, before the foundation forms were built:

Consequently, the foundation now has 4 openings in it where the I-beams protruded. Two of the openings are in the front, two are in the back. Each opening is about 24" wide and 18" high. I have temporarily framed each opening with 2x6s and built removable wooden hatches to cover them. The picture below shows the two openings in the front.

The two openings in the back are identical.

Underneath the house is a crawlspace with about 4 feet of headroom. Each opening is spanned by the rim joist. I want to seal up these openings and I intend to install a small vent in one of the front openings and one of the rear openings.

Here are my questions:

1. Should I seal the openings with concrete? If so, how should I construct forms and how would I get concrete into such an awkward spot? How should I prep the existing concrete to get a good bond with new concrete?

2. For crawlspace ventilation, how big should the vents be? If I were to use concrete, how would I accommodate vents?

3. Is sealing these openings with wood an option? If so, should I use P/T lumber? How would I seal the openings adequately using wood?

I look forward to your expert opinions...


yesitsconcrete 12-04-2008 06:13 AM

i'd set conc block & finish w/vertical patch,,, should have cross-ventilation & i like humidity-controlled fans but we're in ga & sc,,, 8 total measuring 4"x12" should work fine.

the only option i can see would be gunports to defend against indian attack :laughing:

Able Hands 12-04-2008 06:42 AM

I would not seal them up. Venting the foundation is extremely important.

Given what I see in the pictures provided, the four holes will be the only venting you can offer the house. Moisture accumulating in the crawl space over time can/will create serious issues with mold. Depending upon where you are geographically that may take years, or months.

If it were my place I would build and install louvered vents with screening on the inside to keep out bugs. Make them hinged or removable to allow access to the crawl for repairs. While inconvenient to enter, a four foot space under the house would allow for some storage opportunities. Think root cellar.

By the way, nice house, and I love the setting!!

Shamus 12-04-2008 06:47 AM

I'd leave one as a crawl space opening. You never know when you need to get under there. Put one vent in that one. Another vent, as you mention in the front.

These are not structual so all your trying to do is close them off. Just use concrete block and mortor them in. For the top/last block you might consider a cement bag to squeeze in mortor if your not handy with a trowl. If you set the block back a half inch you could parg mortor over them to blend in with the rest of the foundation. As mentioned, a 4X12 vent would be fine.

Nice set-up you have with some effort for sure. Well worth it I'd say.

yesitsconcrete 12-04-2008 07:20 AM

remember a matthew schnurbusch but he was from conklin !

Termite 12-04-2008 07:50 AM

I agree with Able Hands in full on this. You need as much ventilation as you can get, and this is a great oppurtunity to get it. Two vents is probably inadequate...Ideally you have them at all corners.

Another consideration is access to the crawlspace. You need to be able to get in there for whatever reason, so a combination vent/access door might be in order.

shtoink 12-04-2008 11:09 AM

Thanks for all the input so far.

I am considering concrete blocks and mortar. I will have to get information about venting requirements in this climate. The house is on one of the Gulf Islands on the west coast of BC, Canada. The damp Pacific Northwest climate may require me to convert all four openings into vents.

I have a 4' x 4' opening (with a temporary door) into the crawlspace on the right side of the house, so I won't need to use one of the smaller openings for access.

yesitsconcrete 12-04-2008 01:27 PM

forgot this earlier,,, you are one UGLY man if that's you in the picture :laughing:

shtoink 12-04-2008 01:51 PM


Originally Posted by yesitsconcrete (Post 193786)
forgot this earlier,,, you are one UGLY man if that's you in the picture :laughing:

Well, if the women don't find you handsome, they should at least find you handy.


yesitsconcrete 12-04-2008 02:43 PM

long live red greene, eh ?

Able Hands 12-04-2008 04:03 PM


Originally Posted by yesitsconcrete (Post 193634)
remember a matthew schnurbusch but he was from conklin !

One and the same... Send me a PM. I would send one to you but I can't cuz I don't have 20 posts yet.

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