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photograph lowering basement floor 2
- Wallpaper: lowering basement floor 2
- June 8, 2017
Second in an occasional series in which designer Dina Holland walks readers through the process as she undertakes a major renovation of her home. With two boys under the age of 6, the daily struggle for order among the growing LEGO collection was real. Raucous games of superhero tag around the dining room table and dinner preparations while dodging street hockey passes in the kitchen were the norm during our long Boston winters. My husband and I dreamed of finishing our basement and creating a bonus room/playroom the boys could call their own, but very low ceilings (under 6 feet) and occasional flooding after a hard rain meant finishing that space was just a fantasy. Or was it? As we interviewed various builders early on in our renovation plans, one of them proposed something we’d never even considered — digging out the existing basement to create additional height — turning it into actual usable living space. This seemed like the perfect (albeit slightly terrifying) idea. With a narrow lot and tight setback constraints, our expansion potential for the footprint of the house was limited. Lowering the basement floor would allow us to recapture the space we’d written off at a much lower cost than adding square footage. This part of the project would cost us $30,000, and we were sold. While our project also includes doing an addition on the back of the house, making the basement finishable space would give us nearly 1,000 square feet more living space within our existing footprint. This was key to keeping the addition smaller and allowing us to preserve more of our precious green space. Terms like “foundation undermine,’’ “water table,’’ “ledge,’’ and “slurry wall’’ became part of our daily vernacular as we anxiously prepared for this part of the project. Now that this phase is nearly complete, I’d like to share what we learned in case you want to reclaim your basement, too. What is down there? Do you or your neighbors have basement flooding? If so, this could be a sign of a high water table, and you won’t be able to achieve the desired headroom without some serious water-management solutions. The other headache you hope to avoid? Hitting ledge. Say hello to granite, the most common rock in New England. While not a deal breaker, it will certainly add time and cost to your project as you determine just where and how you will blast past it. Cue the jackhammers. If your neighbors recently built an addition, ask them what they found when they excavated. Their experiences could give you the confidence to proceed (or proceed with caution). Regardless, make sure your builder has a plan for how to address whatever pops up. Our biggest fear was hitting water. We already had a sump pump that would go off occasionally, and a few days of rain would turn into puddles on the basement floor. Before we started, our builder dug a hole toward the back corner of our existing foundation. About 24 inches down, we were still dry. When we went another foot, things started to get muddy. That told us just how far we could go. To keep future flooding at bay, a French drain system was laid out to redirect ground water, and we added two new sump pumps (both on backup batteries). Make room for the not-so-fun-but-necessary stuff Basements are by definition utility spaces meant to house things like boilers, water heaters, and the other mechanicals of your house. How much of your existing basement square footage do you hope to reclaim, and how much will you have left once you account for sewer pipes, sump pumps, and other mechanicals? For most people undertaking a dig out, the answer is probably “as much as possible.’’ Since our project also involved renovating the rest of the house, we were able to relocate most of the mechanicals to one corner of the basement, leaving the rest of the space for use at our discretion. Be sure to account for necessary-but-sometimes-inconvenient things like lally columns and beams when designing the new space. A good builder should have a vision for how to run sewer pipes, ductwork, etc. and hopefully be able to hide them between ceiling joists and walls to minimize the use of soffits and loss of headroom. How will you use the reclaimed space? What are your priorities? Do you envision a media room and stocked bar for entertaining or just an open playroom? If you think you’ll want to add a bathroom later, it’s a good idea to have the plumbing roughed into the location during the dig-out process and save yourself the cost of retrofitting later. We did just that, spending a bit of time thinking through the layout and planning for a future bathroom in a tucked-away corner. We were hoping to get dry storage and a playroom in our basement, but with the increased headroom, even my 6-foot-plus-tall husband can do jumping jacks comfortably. Suddenly an exercise room is a possibility. First we removed all the horsehair plaster and the radiators and gutted the kitchen and a bathroom. We had planned on it all going anyway, but our builder felt it was important to remove any unnecessary weight from the house before starting to undermine the foundation. After the demo was complete on the main living floors, a crew cut a Bobcat-sized hole in the back of our foundation, and our own personal Big Dig commenced. More than once I thought What if the whole thing falls down?, but my capable and experienced crew assured me that wouldn’t happen. Working in alternating 6-foot sections, they carefully dug down along the inside basement foundation wall about 30 inches. They added rebar to the bottom of the old foundation and poured a new lower wall alongside the now-exposed dirt up and over the rebar, essentially securing the new wall to the old. They worked their way around the perimeter over the course of a week, giving each 6-foot section ample time to cure before moving on to the next. All in all, it took about two weeks of heavy equipment and dirt moving to dig out our basement. Lesson learned In this crazy real estate market, every square foot of the space you have — above and below ground — is valuable. Explore your options and educate yourself about how to make the most of it. Before we started this process, we had no idea something like this was even feasible. A few weeks ago, they poured the new foundation floor, and my husband and I stood there and marveled at our now 8-foot-plus ceiling height. We’re so excited to enjoy this space as a family and can’t believe we almost wrote it off entirely. Dina Holland also writes the Ask the Designer column in the Boston Globe’s Address section. Send comments to Address@globe.com. Sign up for our free newsletter, Address, at pages.email.bostonglobe.com/AddressSignUp.
In a "look-out" basement, the basement walls extend sufficiently above ground level that some of the basement windows are above ground level. Where the site slopes gently and is insufficient for a walk-out basement, a look-out basement tends to result. Sometimes, a look-out basement is deliberately constructed even on a flat site. The advantage is that the basement windows are all above grade. The disadvantage is that the main floor entry is above grade as well, utilizing stairs to access the main floor. The raised Bungalow design (known as a split-entry home in much of the US) solves this by lowering the entry halfway between the main floor and basement to make a dramatic, high-ceiling foyer. It is a very economical design because the basement is shallower, and excavation costs are reduced.
A daylight basement or a walk-out basement is contained in a house situated on a slope, so that part of the floor is above ground, with a doorway to the outside. The part of the floor lower than the ground can be considered the true basement area. From the street, some daylight basement homes appear to be one storey. Others appear to be a conventional two storey home from the street (with the buried, or basement, portion in the back). Occupants can walk out at that point without having to use stairs. For example, if the ground slopes downwards towards the back of the house, the basement is at or above grade (ground level) at the back of the house. It is a modern design because of the added complexity of uneven foundations; where the basement is above grade, the foundation is deeper at that point and must still be below the frost line.
The concrete floor in most basements is structurally not part of the foundation; only the basement walls are. If there are posts supporting a main floor beam to form a post and beam system, these posts typically go right through the basement floor to a footing underneath the basement floor. It is the footing that supports the post and the footing is part of the house foundation. Load-bearing wood-stud walls rest directly on the concrete floor. Under the concrete floor is typically gravel or crushed stone to facilitate draining. The floor is typically four inches (100 mm) thick and it rests on top of the foundation footings. The floor is typically sloped towards a drain point, in case of leaks.