New addition foundation question


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Old 10-19-16, 11:17 AM
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New addition foundation question

I'm adding an addition to my home and I don't want to cover up the two existing foundation windows because they are the only source of natural light in my finished basement. Therefore, I'm thinking an elevated wooden foundation would be the way to go (basically a room on top of wooden posts and joists). Considering the space above will be conditioned space, is this okay to do or will it be an energy efficiency nightmare? Climate is northern VA (single digits in the winter and upper 90's and humid in the summer). There will be no plumbing in this room. Just electrical and one duct/register. Seems like it would be okay as long as I install thick enough insulation in the floor.
 
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Old 10-19-16, 12:59 PM
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While a raised deck above those windows won't cut out all the light - it will reduce it significantly. Any time you have open air under a room that room will be harder to keep warm in the winter. IMO you are better off with more lighting in the basement and forget about those windows.
 
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Old 10-19-16, 01:06 PM
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What kind of addition...... bedroom ?

That area under the addition will be impossible to manage and keep clean.
Unless it's a tiny addition.... most of the light will be gone anyway.

Put it on the ground and be done with it.
 
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Old 10-19-16, 01:08 PM
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You're effectively creating a crawlspace under the room and then the question becomes whether you enclose it or vent it. Lots of threads about that on the site....
 
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Old 10-19-16, 01:08 PM
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Need some pictures.
I agree 100% those windows will be useless with an addition over the top of them.
 
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Old 10-19-16, 04:29 PM
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Yes, your addition can have an exposed foundation or underside. It's done in mountainous or steep terrain. It is not cheap and as others have pointed out it will block a considerable amount of light and create an odd space underneath. One thing adding to the cost is non-standard construction method part of which is that the underside of the addition will need to be enclosed to protect the insulation from birds and rodents. Basically you'll be adding a new face to the house that needs to be finished.
 
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Old 10-19-16, 08:57 PM
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The addition I am adding will have a garage in the front part and a dining room in the rear part. The dining room portion is the area I'd like to have elevated. I realize not much light will make it into the basement windows, but it would be better than nothing. With the completely blocked, the basement will feel like a dungeon. The dining room addition (expansion of the existing dining room) is 9' wide by 20' deep, so not a huge space. It would be five feet off the ground at the highest point, and I would enclose the area with lattice. It would actually be a nice place to store some things (lawn mower, wheel barrow, yard tools). I'll snap a photo tomorrow and post it so you can see what I am talking about. I should add that the entryway to the dining room expansion will be approximately 10' wide by 10' high, so it will have adequate circulation from the core of the home. Plus my propane heater (supplementary heat) is adjacent to the room so it would keep it toasty. As long as I insulate real well around the rim joists and between the floor joists, I don't think it will be too bad. I could use 12" lumber for the joists to allow for more insulation.
 
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Old 10-20-16, 05:03 AM
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How will the floor level of the addition correspond with the rest of the house?
Spray foam is said to be best for floors like you propose .... but it isn't cheap
 
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Old 10-20-16, 05:18 AM
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It will be the same level as the adjoining room. Why do you ask?
 
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Old 10-20-16, 05:45 AM
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You mentioned both having the room on a slab and raised off of the ground.

I re read the thread - I guess it was someone else that mentioned a slab
 
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Old 10-20-16, 09:05 AM
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Sorry for the confusion. I suppose "slab" was not the proper term. The grade from the front to the back drops about five feet. The garage portion will have a poured foundation around the perimeter and (obviously) a concrete floor. The dining room portion will either have a poured concrete foundation or be a raised wooden structure supported by posts. Benefit to poured foundation is cohesiveness, strength, and insulating properties, but I lose the natural light in the basement, and the benefit to the raised design is I maintain some natural light in the basement, but then have to be concerned with adequately insulation the floor, and the structure wouldn't be as solid.

Another option I hadn't thought of...I suppose I could do the poured foundation and excavate the entire area under the dining room, then blow out a 10 ft section of the existing foundation wall to extend the finished basement into that area. That way I could put windows on the exterior wall, and at the same time increase the size of my basement. As opposed to windows, I could make it a walkout like I've been wanting to. I imagine that could get pricey though.
 
 

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