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The previous homeowner had a deck. Then he enclosed it. Then he dug out underneath it about 3-4 feet, cut into the foundation, and put a door from under the basement to under the deck. It's about 7ft high under there. I'm not sure if it's legal, or if he paid fines for it when he had to get it permitted to sell the house. It also has an entrance to outside, and has lattice work on the sides. We use it to store bikes, pool chemicals, shovels, and in the winter, firewood. We don't have any water issues with it, as he built up a stone and concrete wall around the area he dug up.

Porch Under Porch

He also installed a patio that's not doing too well. I want to break it up and replace it with a deck. As an added bonus, I want to use underneath it as an extension of that storage space... But I'm not sure how much foundation is allowed to be exposed, or if this is safe at all. I will, of course, pour a concrete floor and walls for the underground portion of this.

Patio Issue Proposed Deck

This is Massachusetts, by the way... pretty sure I'm not on bedrock, and I know there's gravel and pipes underneath the basement floor if that information is pertinent. Part of the exposed foundation may end up being garage foundation, which may not even be as deep as the house foundation.. I'm not sure, though.

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You packed a lot of info into that question. Maybe break it into a couple of questions. Regardless, the main question is about the excavation next to the foundation. I can't say for sure if that is a code violation in your area of Mass. I will say that in the Northeast, it is important to bury at least 4 feet of foundation or footings into the earth to prevent movement from frost. Depending where you are in Mass, the frost line probably runs from 2 to 4 feet below grade. The other problem with having a well entrance to a basement is the introduction of water, or the buildup of snow and ice in the well. I seriously doubt any permit was pulled for such a modification. Had this reduction in the frost wall depth been done at the time of a building inspection, I think it would have been frowned upon. usually extra depth of the frost wall and some type of drainage would be recommended.

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I would think the biggest concern here is where the footing is in the midst of all this. In Maryland the frost line is 30" where I am. In Massachusetts I am sure it is much lower. Code requires the footing to be at or below the frost line for an area, otherwise the freezing ground will heave the wall and start bad things. @shirlock, I know you may know this already, I am just getting it out there for others. –  Jack Mar 11 at 23:30
    
Exactly right Jack. I mentioned, but maybe not well enough, that they need to be 4 feet under grade. –  shirlock homes Mar 11 at 23:43
    
@shirlockhomes So if I was to dig down to the bottom of the foundation to see how deep it went, I would just have to make sure to maintain 4ish feet? (I will contact the building department, of course, for a more accurate depth) Regarding the entrance to the basement, see the photos I added. We have never had water come through the door, but that's not to say adding a drain is a bad idea for when I do this. –  kavisiegel Mar 12 at 23:59
    
The pics help. the excavated area for the door isn't as deep or dramatic as I expected. Although not an optimal design, I think there is probably still a good couple of feet of concrete then a footing under the door. I'm all about practical when it comes to old houses. If you haven't experienced any serious shifting, stress cracks in the concrete close to the door etc, then there is probably enough under grade. The fact that the door area is sheltered helps with keeping water from flowing under the door. If you are going to add a deck, a permit may be required in your area. –  shirlock homes Mar 13 at 8:46
    
I really don't think the door is going to be a major issue when the inspector sees it. You don't need to dig it up to tell the depth, do it with a little math and measurements from the inside wall dimensions. I'm not your inspector, but i think this one can slide. Installing drains is a whole different issue. That could be a bit more complicated tieing into the drain tile. Would need to know a lot more about the existing foundation drainage system. –  shirlock homes Mar 13 at 8:51

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