When we think of the word “crippled”, we often think of it as disabled. However, cripple walls have nothing to do with it. Now, what is a crippled wall? Let us know more about the cripple walls definition and other details
What is a Crippled Wall?
Definition: Cripple walls are the little vertical framing, also known as stud walls made of wood that surround a crawling area (which holds electricity, water lines, etc.) beneath the first floor of a house, in touch with the soil gradient to assist the end of the floor joists.
It is a type of raised foundation, which is usually between 14 inches to 4 feet. The walls that connect the floor living area of the home to the mudsill, also known as the sill plate. The mudsill is a wooden member that attaches the building to its foundation. These walls and/or studs that link the home to its foundation are known as the cripple wall. Essentially, the cripple wall is the part of the foundation that handles the entire weight of the building.
Because of the cripple wall’s load-bearing capacity, this area can become compromised in the event of a large earthquake, causing damage to the foundation and/or total collapse.
Why is it Called a Crippled Wall?
Crippled walls originate from the “crippled zone” since it is the most fragile link in times of seismic event. For this, earlier it was thought that houses must have a space so it gets crushed to protect the rest of the property from being damaged. It is obviously the first section of the home with direct contact of soil so it is the fundamental element in building the frame of the house
These kinds of walls are seen commonly on homes built before the 1960s by the sloped hillsides. Therefore, it is very old-fashioned to have it these days. It started losing fame after the year 1980 due its intrinsic structural susceptibility to seismic activities like earthquakes. If the cripple wall fails, the living area of the home falls
to the street level, causing the property to slide off its foundation. So, the amount of risk calculated made its usage lesser with years ahead.
Although it is quite commendable, how it takes such imagination to construct a house on a slope of the hilly area but crippled walls have the ability to cause vast issues depending on whether they are retrofitted and anchored precisely.
Problems of a Cripple Wall
Some of the problems related to a cripple wall are given below:
1. Influence of Gravity:
Cripple walls rely mainly on gravity and compression to bear the construction- the load of the structure compressing the cripple wall between the house and the foundation. It is pressed between them without being properly binded. The weight ranges between 80,000 to 160,000 pounds.
2. Structural Integrity:
Cripple walls are often too weak to support the loads they are intended to carry. It is often poorly constructed, with inadequate reinforcement and poor connections.
3. Easy to catch fire:
Cripple walls could easily catch fire due to being associated with wood.
4. Attract Insects:
Since cripple walls comprise of wooden stud walls and so it can be infested with termites and other wood-destroying insects.
5. Damage by seismic events:
Natural catastrophic events such as earthquakes, landslides, high winds etc. can prove to be extremely detrimental for cripple walls. During an earthquake, these walls if not braced to resist horizontal movement, can snap or slip out from inbetween the home and foundation, the home having nowhere to go but down.
Solutions to Secure a Cripple Wall
There are quite a few solutions to secure a cripple wall. Some of the most used ones include:
Installation of plywood or metal sheathing:
Cripple walls are short walls that frame the space between the floor joists and the mudsill. They are typically found in homes with a crawl space. To install plywood in order to secure a cripple wall, it required to first measure the breadth and height of the wall and then cut plywood panels to fit these dimensions. Then pre-drill holes in the plywood panels and lastly secure the plywood panels to the cripple walls with screws.
Installation of foundation anchor bolt system:
The first step is to excavate the area where the foundation anchor bolt system will be installed to a depth of at least 2 feet or 12 inches. Then we place the foundation anchor bolts in the excavated area and secure them to the cripple wall with washers and nuts. The bolts should be spaced evenly and installed at a depth of at least 18 inches. We install the foundation anchor bolts around the perimeter of the foundation wall, spaced at least every 2 feet. And proceed to install a second row of foundation anchor bolts above the first row, spaced at least every 2 feet. It is to be repeated till 6 rows and lastly have to backfill around the foundation wall, being sure to compact the soil around the anchor bolts. Once the anchor bolts are in place, we have to install the cripple wall bracing. The bracing should be installed on both the inside and outside of the foundation wall. Finally, the cripple wall is secured bracing to the anchor bolts using nuts and washers.
Installation of horizontal/diagonal bracing:
There are a few ways to do diagonal bracing, but the most common is to use 2x4s or 2x6s placed at an angle from the bottom plate to the top plate. At first we start with measuring the length of the wall that we will be installing the diagonal bracing on and then two pieces of lumber for the appropriate length for the wall needs to be cut down. These will be our top and bottom plates. Now the top and bottom plates are to be nailed to the studs on the wall, making sure that they are level and flush with the wall. We have to use hurricane ties to secure the diagonal braces to the studs. Then we can Install plywood sheathing over the cripple wall, and then toenail the diagonal braces to the plywood. It is important to use Simpson Strong-Tie hurricane straps to secure the diagonal braces to the studs. Lastly installing OS remains. OS is for "over-stressing."The type of OS required for installing diagonal bracing will vary depending on the specific project requirements. However, some common OS options for this purpose include OSB (oriented strand board), plywood, and lumber.
Installation of hurricane straps or clips:
There are some ways to install hurricane straps or clips to secure a cripple wall. In order to install hurricane straps, you will need the following materials:
- 1/2" x 10' galvanized hurricane strap
- 1/4" x 1 1/2" lag bolts (8)
- 1/4" washers (8)
- Drill -1/4" drill bit
- Measuring tape
At the very beginning, the width of the cripple wall is to be measured and then the hurricane straps are to be cut to size, making sure to leave a few extra inches on each end. It necessary to pre-drill holes for the lag bolts at each end of the hurricane strap. Then we place the hurricane strap over the cripple wall, aligning the pre-drilled holes with the studs. And finally, secure the hurricane strap in place by threading a lag bolt through each hole and attaching a washer. The bolts are to be tightened strongly. We must drill pilot holes for the lag bolts, screws or nails and countersink them so that the heads are flush with the surface of the foundation We should apply sealant to the lag bolts, screws or nails to prevent water infiltration.
The process is to be repeated at the other end of the cripple wall as we have to use hurricane straps or clips to secure all four corners of the cripple wall to the foundation. There must be space in the clips evenly along the length of the cripple wall. The clips are to be installed at the top and bottom and longer straps at the corners of the cripple wall.
Installation of the foundation reinforcement system
The installation process varies depending on the specific foundation wall reinforcement system being used. However, in general, the installation process will involve first by excavating the area around the foundation wall to a depth of at least 2 feet or 8 inches. Next, we install a layer of gravel around the perimeter of the excavation and proceed to install a layer of perforated drain pipe on top of the gravel. After that we install a layer of filter fabric over the drain pipe and then backfill the excavation with soil, tamping it down as you go and then install a row of horizontal reinforcement bars (rebar) around the perimeter of the foundation wall, at least 2 feet above the ground. It is required to install vertical reinforcement bars every 2 feet along the length of the foundation wall. Then we pour concrete into the excavation, filling it to ground level. The concrete is to be vibrated to remove any air pockets. Allow the concrete to cure for at least 24 hours before proceeding and install a layer of stucco or brick veneer over the foundation wall. Once the system is securely attached to the wall, it will need to be properly braced and supported in order to provide the desired level of reinforcement.
Installation of waterproofing membrane:
We begin by preparing the surface of the cripple wall. This may involve cleaning off any dirt or debris, and then applying a primer. Once the primer is dry, it's time to install the waterproofing membrane. This can be done by either taping or gluing the membrane to the surface of the wall and when the membrane is in place, you'll need to apply a sealant around the edges which will help to ensure that no water can get underneath the membrane and cause damage to the wall. Finally, you'll need to install a drainage system and this may involve installing a French drain or a sump pump. This ensures that any water that does get under the membrane is quickly removed before it can cause any damage.
Installation of drainage system:
The process of installing a drainage system to secure a cripple wall will vary depending on the specific situation. However, some tips on how to install such a system include ensuring that the system is installed properly and securely, and making sure that any potential drainage problems are taken into account. The first step is to excavate around the perimeter of the cripple wall to a depth of at least two feet. Next, installing a perforated drain pipe along the base of the excavated area. And covering the drain pipe with gravel or other drainage material. Lastly, the excavated area is to be backfilled with soil and compacted firmly in place.
Installation of insulation:
Using an exterior form of insulation is necessary to protect the cripple wall.This will help to keep the cripple wall from shaking and collapsing in an earthquake. There are a few different types of insulation that can be used for this purpose. One is called shear wall insulation. This is a type of rigid foam insulation that is installed between the studs of the cripple wall. It helps to keep the wall from moving and shaking in an earthquake. Another type of insulation that can be used is called base isolation. This is a system that is installed under the foundation of the home. It helps to isolate the foundation from the rest of the house so that it can move independently in an earthquake. Installing insulation in a cripple wall is not a difficult task. However, it is necessary to make sure that it is done correctly to ensure its effectiveness. To install insulation, we measure the height and width of the space, then cut the insulation to fit and proceed to install furring strips on the foundation wall, then attach the insulation to the furring strips with screws or nails. If you are not sure how to install insulation, you should hire a professional to do it for you.
Installation of weatherproofing sealant:
Some tips on how to install weather proofing sealant to protect a cripple wall include: making sure the surface is clean and dry before beginning applying the sealant evenly, using a brush or roller and apply a top coat of paint or sealant to further protect the wall from the elements. Lastly, allow the sealant to dry completely before exposing the area to weather conditions.
Structural risks of a cripple wall
There are several structural risks associated with a cripple wall. Some of them are presented below:
- It may be load-bearing, and if it is not built correctly, the entire house could collapse.
- It may be made of materials that are not compatible with the rest of the house, and this could cause problems down the road.
- It may settle unevenly, causing crack or buckle if it is not properly reinforced.
- It may be damaged by water or insects.
- It may be too weak to support the house in high winds.
- It may not be able to support the house in an earthquake.
- It may be damaged by fire.
- It may be poorly insulated, leading to heat loss and higher energy bills.
- If the cripple wall is not built correctly, it could void the warranty on the home.
- It may leak if it is not properly sealed.
Cripple Wall Failure
Cripple wall failure is when the wall collapses due to the weight of the house or other factors which can result in serious injuries or even death for those inside the building at the time of the collapse. Cripple wall failures are often preventable with proper design and construction methods. However, when they do occur, they can cause extensive damage and loss of life. Cripple wall failures are a serious concern for engineers and architects when designing and constructing buildings. Proper design and construction of cripple walls are essential to the safety of those who will occupy the building.
Cripple Wall Retrofit
A cripple wall retrofit is an efficient and cost-effective way of reinforcing or replacing the framing of a wall that is considered to be structurally weak. This is usually done in order to enhance the strength and stability of the wall and to prevent it from collapsing in the event of an earthquake or other catastrophic/seismic events. Retrofitting your cripple walls can help to strengthen them and make them more resistant to damage. It can also improve the energy efficiency of your home by sealing up any gaps or cracks in the walls. The process is a relatively simple and inexpensive project that can make a big difference in the safety and security of your home. It is especially important to consider retrofitting your cripple walls if you live in an area that is prone to earthquakes. Cripple wall retrofits can be done by a professional contractor or it can be done by yourself if you are handy with tools and have some basic carpentry skills. The most important thing when retrofitting your cripple walls is to make sure that the walls are securely fastened to the foundation of your home. There are a few different ways to retrofit your cripple walls so if you are considering retrofitting your own home, it is crucial to do some research and consult with a professional before beginning the project for determining the best method for your home. Cripple wall retrofits are far more budget-friendly solution for repair, rather than a total foundation replacement or dealing with destruction from any natural disaster.