Evaluating a Basement

 While it’s impractical to add headroom in a basement, there are some ways of working around the requirements. You can often move Ducts and pipes, and beams and other obstructions can be incorporated into walls or hidden in closets or other uninhabitable spaces. Also, some codes permit lower ceiling heights in rooms with specific purposes such as recreation rooms. If headroom is a problem, talk to the local building department before you give up on your dream room.

A well-built basement is structurally sound and provides plenty of support for finished space, but before you cover up the walls, floor, and ceiling, check for potential problems. Inspect the masonry carefully. Large cracks may indicate a shifting around the foundation; severely bowed or out-of-plumb walls may be structurally unsound. Small cracks usually cause moisture problems rather than structural woes, but they should be sealed to prevent further cracking.

Contact an engineer or foundation contractor for help with foundation problems. If you have an older home, you may find sagging floor joists overhead or rotted wood posts or beams; any defective wood framing will have to be reinforced or replaced.

Understanding My Basement

Basement Anatomy

To ensure that your basement will be secure and dry, start by gaining an understanding of how it was constructed. The drawing below shows a fairly typical construction for a basement, plus framing for the floor above. Poured concrete walls (or walls made of block or stone), which are often 8 in. or 10 in. thick, rest on concrete footings that are often 10 in. thick and reinforced with steel.

A poured concrete floor is often 3 in. or 4 in. thick and reinforced with metal. If the concrete walls, footings, or floor are not strong enough, or if they rest on soil that is not firm, then walls and floors can sag. Here drainpipe (often referred to as “drain tile”) runs around the exterior of the house at the bottom of the wall. The pipe is encased in gravel, so seeping water can easily enter the drainpipe and flow away from the basement.

If a basement does not have this drainpipe, it should have tile running under the basement floor on the inside. The tile should run into a sump pump. In this example, there is a massive beam running through the centre of the basement ceiling, to support the joists (which are ceiling joists for the basement and floor joists for the first floor).

The beam is supported with large posts, which rest on deep concrete footings. This beam is often needed if the width of the basement is too long for joists to span and remain strong. However, if the basement is not very wide, or if engineered joists are used, then the beam may not be needed. During a remodel, the posts are often removed. In order to do this, the wooden beam is replaced with a very strong steel I-beam, which can span very long distances. A “bearing” wall can take the place of a massive beam but will limit floor-plan options. A “curtain” wall is not needed for support and can be removed.

The joists (which again serve as floor joists for the first floor and ceiling joists for the basement) rest on a sill, which rests on top of the basement wall. This sill should be made of pressure-treated or other rot-resistant lumber. The rim joist, which rests on the sill and runs around the room, should be carefully protected from moisture with building paper and siding.

In this example, one side of the basement has outside soil grade near the height of the basement wall. The other side is a walk-out basement, with the outside grade at floor level. Many basements have walls that rise above grade by a couple of feet or more. In that case, windows can allow light in, and the basement is said to be at “garden” level.

Wall And Footing Materials

Most basements built after World War II have walls made of poured concrete or concrete block. Basement walls in older homes may be stone, at least at their bottom 4 ft. or so, and perhaps brick or block atop the stone.

Poured concrete

Poured concrete walls usually present a fairly monolithic surface. At their bottoms, they rest on a poured concrete footing, which is typically 4 in. or so thicker than the walls.

If they were poured correctly, with metal reinforcing bar (called rebar in the trades), concrete walls will be very strong. And if a solid waterproof coating was applied to the outside of the walls before they were backfilled with soil, the walls should successfully resist water infiltration, unless hydrostatic pressure is very strong (see p. 28). However, some concrete walls were poured or reinforced incorrectly, and this can lead to moisture and structural problems, as the following pages show.

Concrete block

Often referred to as “cinder blocks,” structural blocks are actually made of concrete poured into molds. They are typically 8 in. wide by 16 in. long, with open spaces called “cells” inside.

The blocks are stacked on top of each other in a running bond pattern (which means each block rests on two blocks below, rather than just being stacked in vertical rows).

Block basement walls usually rest on a poured concrete footing. For strength, the walls should be reinforced in three ways, as shown in the drawing: with horizontal ladder-type reinforcing mesh every two or three courses; by filling at least some of the cells with grout (which is actually a type of concrete); and with vertical rebar embedded in the grout fill every other block or so.

Unfortunately, not all block walls are created equal, and some lack sufficient reinforcement-making them susceptible to cracks that need to be sealed and perhaps repaired as well.

Many older homes have a foundation and a lower wall made of natural stone assembled with mortar joints. Many of these walls remain strong and level for centuries because of their massive size (often 2 ft. thick), the durability of boulders, and the old-world skills used in their construction. Often, a brick wall is installed on top of the stone wall.

These walls were likely installed in the days when people didn’t think of living in their basements, and so they may not be very waterproof. Some can stay surprisingly dry but inspect yours carefully after heavy rainfall for any signs of moisture. If moisture is a problem, consider having the outside of the wall waterproofed.

In this older home, mortared stones were used to make a footing and about 3 vertical feet of wall. If your house has a wall like this and the mortar between the stones is eroding, the wall has likely been exposed to moisture.

Most brick homes built before World War II were constructed so that the bricks actually form the structure of the house. (Most brick homes built more recently use brick only as a veneer; the foundation and basement walls are most likely poured concrete, and the house’s structure is made of wood.) Usually, the basement wall is three wythes, or thicknesses, of brick. There is typically little if any metal reinforcement. Instead, the bricks are laid in an interlocking pattern. The brick wall is shown here, which rests on a stone foundation, was built in 1882. Its walls are almost perfectly plumb, and it is, overall, no more than 1⁄4 in. out of level.

How to Evaluate Your Basement

Your basement’s mechanicals is another important consideration. The locations of water heaters, pipes, wiring, circuit boxes, furnaces, and ductwork can have a significant impact on the cost and difficulty of your project. Can you plan around components or will they have to be moved? Is there enough headroom to install a suspended ceiling so mechanicals can remain accessible? Or, will you have to reroute pipes and ducts to increase headroom? Electricians and Heating Ventilation and Air Conditioning (HVAC) contractors can assess your systems and suggest modifications.

  • Trace plumbing lines and note locations of shutoff valves on supply lines, which are natural points for adding new pipes or redirecting old pipes. If you are considering a bathroom or kitchen addition, also trace drain lines back to the main drain stack, and take measurements to determine if adding new drain lines is feasible.
  • Evaluate headroom in your basement, paying particular attention to ductwork that is mounted below the bottoms of the floor joists. In many cases, you can reroute the ductwork so it runs in the joist cavity.
  • Look for asbestos insulation, usually found on hot air supply ducts from the furnace. Asbestos removal is dangerous and closely regulated, but it in many cases you can do it yourself if you follow the right prescriptionsè. Check with your local building department or waste management authority for more information on asbestos abatement in your area.
  • Identify sources of standing water and visible leaks. If water comes into the basement on a regular basis through the foundation walls or floor, you’ll definitely need to correct the problem before you begin your basement project.
  • Inspect foundation wall cracks to see if they are stable. Draw marks across the crack and take measurements at the marks. Compare measurements for a few months to see if the crack is widening. If the crack is stable you can repair it. If it is moving, contact a structural engineer and resolve the problem before you begin your remodelling project.
  • Probe small cracks in poured concrete walls and floors with a cold chisel to evaluate the condition of the concrete. If the concrete flakes off easily, keep probing until you get to solid concrete. If the crack and loose material extend more than 1″ or so into the wall, contact a structural engineer.
  • Check the mortar joints on concrete block foundation walls. Some degradation is normal, but if gaps wider than 1/4″ have formed, you should have the wall repaired before you begin building.
  • Check for bowing in basement walls. Water pressure in the ground often causes concrete walls to bow inward over time. As long as the amount of bowing is less than 1 or 2″ and the bowing is not active, you can usually address the problem by furring out from the wall with a framed wall.

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