Walkout Basement

Of the roughly 133 million houses in the United States, about 37 million were built on a basement, giving the homeowner more space. In many of those cases, the homes were built without the basement being finished, either to use that space as storage or to hold in reserve for additional living space, sometime in the future. Those with the foresight to have their home built on an unfinished basement provide themselves with the ability to gain more living space at a much lower rate than adding on to their home.

The twin drawbacks to building living space in the basement are the lack of natural light and the limited access to the basement from the outdoors. The lack of natural light can be rectified with electric lights or by making the windows and corresponding window wells larger. Access is a bit trickier; but it is possible to add an outside access to almost any basement. Basements with windows that open to the outdoors are commonly called “daylight basements,” while a walkout basement gives direct access to the outdoors through a doorway.

Of course, the easiest basements to turn into a walkout basement are those built on a hill, where one wall of the basement is exposed, above ground. In this case, the work is mineralized, requiring only cutting a hole in the wall for the door, adding a steel lintel above that doorway, putting a concrete pad outside the doorway and installing a door.

But most homes require more work than that, as the home isn’t built on a hillside. This puts the floor of the basement below ground level, requiring excavation to put the entryway in. We’ll look at this process, as it includes everything necessary for completing the simpler installation of a door into a home where one wall of the basement is exposed, eliminating the need for extensive excavating.

Figure Out the Drainage First

One major consideration for installing an entryway into a basement is drainage. Unless the walkout is able to be built without any excavation, there’s a good chance that water will collect in the stairwell every time it rains. The real question is how much rain will collect and how often it will happen. Drainage of some sort must be provided as part of building the walkout.

A typical 3’ wide stairwell, with a 3’x 3’ landing at the bottom, equals just shy of 38 square feet. Assuming no other rain falls into the stairwell, all the rain that falls into those 38 square feet will end up in the 3’x 3’ landing at the bottom. So, one inch of rainfall will turn into 4.2” of standing rain on that slab. If the slab isn’t far enough below the level of the doorsill or there isn’t sufficient drainage, that stairwell is going to end up becoming an access point for water to flood the basement.

There are several ways of handling this problem. Which one is used depends a lot on how much rainfall there is in the area. It isn’t sufficient to build it to accommodate the average rainfall, as that will still leave an opportunity for water to leak in when there is more severe rain. The stairwell and the drainage associated with it must account for the worst expected rainfall in that area.

The first thing that can be done and should be done in all cases is to make the landing at the bottom of the stairwell below the level of the basement floor. It is customary to build it 4” to 6” lower, creating a drain sump for the water. Angle the floor towards the center, putting a drain in the center.

In places where there is little rainfall, a French drain can be installed below the landing. This requires excavating a couple of feet deeper and then filling the hole with large gravel, before pouring the slab at the bottom of the stairs.

Crushed gravel leaves about 40% air space when placed in a pit like this; so two feet of French drain will be able to hold 40% of that in water or about 9.6” of water. Added to the 4” of water that can sit on top of the slab, before the basement starts to flood, that equals just over 3” of rain, before the basement starts to flood. Increasing the French drain to 3’ deep would increase the capacity to 4-3/8” of rain.

If that’s not enough drainage to cover the worst-case incident, then it will be necessary to install a sump and sump pump, either under the slab, where the French drain would otherwise be or inside the basement, under the floor, with a pipe connecting the French drain to the sump. This is better, in that the sump can be covered by a removable cover, in case the pump needs maintenance. However, it must be done by digging underneath the footer, without damaging it. Damage to the footer could result in serious foundation issues down the road.

Roofing over the Stairwell?

Another option to help keep the stairwell from flooding the basement when it rains is to build a roof over the stairwell. This is normally something that’s done after the stairwell is built, but some contractors will build a temporary lean-to style roof to cover it during construction, especially if they are expecting inclement weather. It’s easier to build a temporary roof, than it is to constantly pump out the excavation or try to work in the mud.

A roof doesn’t have to be fancy, to be effective. All that’s required is a framework and corrugated metal or plastic roofing. It needs to be mounted high enough so as to protect people from banging their heads, while at the same time provide the necessary protection from the rain. That might mean providing sufficient overhang to prevent rain from getting in or in cases where the predominant wind comes at that side of the house, walling off the outside of the roof covering as well.

Making the Stairwell

Before digging, it is important to lay out the stairwell, making sure it will fit in the intended area. Some people have the stairwell stick straight out from the wall, but it is more common to bend the stairwell 90 degrees so that it runs alongside the wall of the home. A few people go a step further; putting a small patio at the bottom of the stairs and having the stairway go up the side of the patio wall.

One of the big advantages of building the stairwell alongside the basement wall, besides it not being as big a trip hazard, is that it can eliminate the need to build a wall on both sides of the staircase, if properly planned and executed. The big thing is making sure the stairs themselves butt up against the wall well, without a crack and that the seam is filled with an expansion joint material. With that in place and the concrete wall cleaned up, there’s really no reason to spend the time and money building a wall on that side of the stairway.

Another decision that has to be made is what material the stairwell is to be made from. There are two basic possibilities: poured concrete or cinder block. For the do-it-yourselfer, it is easier and cheaper to build with cinder block than to put up forms and pour concrete. Paying the cost for the material to make the forms is unrealistic for a one-time project. Even so, some concrete will be needed for the landing at the bottom of the stairs and the surface of the stairs themselves. The cinder blocks would be used for the walls.

It is easiest to dig out the stairwell with an excavator, although for those so inclined, digging it out by hand could make for a great day or two of upper body workout. Either way, the hole needs to be dug wider and deeper than the actual stairwell, allowing space for access to the outer side of the wall. Avoid digging out too much where the stairs themselves go, sloping the floor to the approximate angle of the stairs. Once the wall is built, this extra space will need to be backfilled with some of the dirt that is removed, packing the dirt down, so that it doesn’t sink over time.

With the hole excavated, lay out the door opening, checking it from the inside as well, using windows or whatever other reference points are available, so as to ensure that the door excavations are in the right place. Patching a hole in the basement wall and making another doorway is an expensive mistake to make.

Installing the Landing

The first thing to build is the French drain or sump, as that is the Lowest point in the project. If a sump is to be installed inside the basement, then it might be necessary to cut the door out at this point; but if not, it’s best to wait until the stairwell is complete.

The landing slab cannot be poured directly on top of the gravel used for the French drain, so one of two things has to be done. The first is to install a stormwater pit, to be used as a French drain and the second is to fill the pit with gravel and then cover it with corrugated metal, with a drain hole in the middle. A short piece of pipe would need to be placed in this hole, with the idea that it can be cut off so that the drain will end up flush with the surface of the concrete.

Before pouring the slab, install rebar in a grid pattern or remesh to strengthen the concrete against breaking. Concrete, like any rock, is strong in compression but not in tension. That’s why stone and concrete can be broken with a chisel. The rebar or remesh provide strength in tension, helping to keep the concrete from breaking. Some sort of standoffs should be used, to hold the rebar or remesh up 2” off the ground, so that it will end up being in the middle of the slab, rather than at the bottom.

It is best to do a monolithic pour here, rather than just a slab, although most people use just a slab. While a slab will work, the edges of that slab will have to support the weight of the walls being built onto them. That’s a lot of extra weight for the slab to support. Digging down a foot around the edges to form an integral footer and adding rebar all the way around, a couple of inches up off the bottom of that trench, will help ensure that there will not be any need for future replacement of the slab.

monolithic slab, wall, drain, drain pipe to sump, french drain
Monolithic slab

Adding the Stairs

With the foundation in place, it’s actually possible to start building walls; but that’s not necessarily advisable. The only wall that could be built is the lower part of the wall that encloses the landing. Where that has to interface with the wall for the staircase, the wall would have to wait until the staircase is in place.

Professional contractors who work with concrete all the time would pour the stair as one unit; building a form that allows the concrete to flow downhill, filling in each step along the way. This can be tricky to work with, especially to someone who is unaccustomed to working with concrete. Therefore, I would recommend pouring each step, one at a time. That allows the form for each step to be constructed separately and the step poured flush with the top of that form. Once set, the form can be removed and reinstalled for the next step.

The steps themselves need to be 4” thick, just like the slab at the landing. They will also need to have rebar installed in them. That rebar should come up through the back of the step, forming a pin that will be embedded into the next step, tying the two of them together. Ideally, the rebar should be bent into an “L” so that the same piece runs the depth of the step tread and then runs up into the stair above, but if the necessary equipment to bend the rebar is not available, then tie the two piece together with baling wire when installing them.

stairs, rebar, landing
Stairs

Notice in the picture above that the dirt has been dug out in a stair-step pattern, to match the concrete stairs being poured on top of it. Concrete is expensive, so it is important to avoid wasting concrete in the process. Digging the dirt out in this manner allows the 4” slab thickness to be maintained for both the step tread and the riser, without wasting concrete. If too much dirt is dug out, the excess space can be filled back up with packed dirt, gravel or scrap wood.

Building the Walls

The walls themselves are fairly easy to build, if they are being built out of cement blocks, or cinder blocks. These are stacked in an offset manner, just like a brick wall, with mortar in between the blocks. The only difficulty is in taking time to ensure that the wall remains straight and level while it is being built. Running a string from corner to corner is normally used for that, as the string provides a ready reference as to where the top outer edge of the blocks should be.

Installing the Door

In most cases, it’s a good idea to wait until the stairwell is installed, before cutting through the basement wall and installing the door. The actual cutting needs to be done with a diamond-bladed saw, which most do-it-yourselfers would have to rent or a masonry saw blade, mounted to a circular saw. Take care to keep the blade from overheating, as that will cause excessive wear on the saw. It will probably be necessary to score the concrete wall on both sides and then break out the middle part with a sledge hammer. A grinder can be used to smooth out the middle part of the wall, where the blade from the saw didn’t reach. The door opening must be 2” wider than the door frame and 1” taller.

If the basement walls were made of concrete block, instead of poured concrete, there will be some voids showing up in the edges of the cutout. These can be filled with sections of 2”x 4”, glued in place with construction adhesive. The surface of these blocks must be installed flush with the cutout.

A steel lintel will need to be installed in the top of the door opening, to support the remainder of the wall above the door opening. This usually requires cutting horizontal slits into the wall, at the top corner of the opening, so that the weight the lintel is supporting can be transferred to the wall on either side of the opening. The lintel should fit into these and rest snugly up against the concrete or concrete block above the door opening. Use mortar to hold the lintel in place.

Both wood and metal door frames can be installed into a concrete mall, although it is typical to use metal frames, rather than wood. In either case, it will need to be a door frame designed for use in masonry walls and will need to have a jamb depth equal to that of the wall thickness.

Set the frame in place and mark where the mounting holes need to be drilled. With metal frames, this is done by inserting the anchors into the frame and then hitting their heads with a hammer, allowing the point of the fastener to make a dent in the concrete. With wood frames, a punch needs to be used. Drill the holes in the sides of the door frame and set the door frame back in place, shimming it as necessary and attaching it with threaded anchors.

With the door frame in place, all that remains is to hang the door and install the lockset. Caulk around the edges of the door frame, between it and the concrete. If a wood frame was installed, brick mold should be added, snug up against the masonry, nailing it to the door frame.

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