Why is my sofa sagging?

Furniture Upholstery is just about fabric, right? 

Nope. Upholstery fabric is only the skin that covers a complex interior.

The “foundation” or the system of springs or webbing inside the sofa, is what gives it its bounce and shape. Without a foundation, a sofa is just a wooden frame. 

When you want to repair a sagging sofa, you may find that the problem lies deeper than the padding or cushions. That under-cushion couch support you see online may not help. Replacing the cushions may not even do anything. 

The foundation itself might need to go to an upholstery shop to be repaired. 

The foundation types you might encounter are:

• 8-Way Hand Tied
• S-Springs
• Webbing
• Drop-in Springs
• Marshall Coil Spring Units
• “Trampolines”

The foundation can depend on the age, style, and size of your furniture. 

What kind of foundation system does your sofa or chair have? 

Have you noticed any changes in how your sofa feels? 

Main Foundation Systems

8-Way Hand Tied

Many older pieces of furniture rely on 8-way hand tied springs. Even today, very well-made, higher-end furniture tends to have 8-way hand-tied springs. 

This foundation is called 8-way, hand-tied because a thick piece of twine is attached to 8 points around each spring. This creates a kind of circuit. As each spring expands or compresses, the attached strings pull the neighboring springs along with it. These connections distribute weight along the length of the couch or chair, which makes it more comfortable for the sitter. 

This foundation system has existed since the mid-19th century. These springs offered support at a time when padding consisted of thinner materials, such as horsehair or down. 

Because these large springs are meant to last for decades, they provide comparatively firm support. A properly-secured 8-way hand-tied foundation will not allow you to sink down as if you are on a cushion. Instead, it will feel more like a medium-firm mattress. It is particularly effective for regularly-used furniture, as it will maintain its shape well. 

The bottom foundation of these springs can be attached to a metal frame or sewn to webbing.

8-way hand tied springs are very heavy, due to the amount of metal involved. Anyone who has had to carry one of the pieces can attest to that fact! 

Eight-way hand tied foundations offer excellent support and last for years, but it takes time and expertise to create them. For this reason, modern furniture manufacturers prefer to cut costs (and often quality) and use other foundation systems.

Additionally, post WWII-synthetic materials allowed for thicker cushions, so large springs were no longer necessary to ensure a comfortable seat.

Eight-way tied springs last for many years, but if this foundation does fail, it is most likely because the twine holding the springs together has broken.

If this happens, call upholstery shops near you to ask if they can repair 8-way hand-tied foundations. This skill is increasingly rate, so not all upholstery shops can accommodate this kind of repair. 

When you find a good upholsterer, they can remove the upholstery, retie the springs, and then replace the original upholstery.

Since 8-way hand tied springs do last so long, when this foundation fails, the couch’s upholstery is generally worn and faded after decades of use. Many customers elect to replace the upholstery and re-tie the springs.

S-Springs (aks sinuous, serpentine, or zig-zag springs)

These springs are more easily installed than 8-way hand-tied springs, as they do not involve individual springs that require meticulous preparation. 

Instead, each S-Spring is pulled across the sofa, from front to back, and secured. 

S-Spring foundations do not have springs that compress vertically, so they offer a firmer seat than 8-Way hand-tied. Many modern pieces of furniture feature S-Springs to economize both material costs and production time. 

S-Spring foundations are especially useful in thinner pieces of furniture that can not accommodate the bulk of an 8-way hand tied foundation. 

This does not mean that S-springs are inferior, however! They offer good support, are durable, and can last for many years. 

If your S-Spring foundation has failed, it may be because the wood the spring is attached to has deteriorated and allowed the spring to pull loose. 

The upholsterer will make the necessary wood repairs to the chair or couch frame  and then reattach the hardware and springs.

Webbing

Webbing is present in both new and old furniture.

Older furniture tends to use webbing as a support system for springs. 

In modern furniture production, the webbing supports thick foam cushions. 

No matter the additional system–whether foam or springs–upholsterers recommend that children be discouraged from jumping on furniture with a webbed foundation, as this will wear the webbing system out faster. 

To the right is an example of a fresh foundation of jute webbing.

You'll notice an example of the old, degraded webbing displayed in the foreground.

Webbing Materials

Webbing can come in the form of traditional jute or more modern, synthetic materials.

Jute webbing is a traditional webbing material and has little to no elasticity, which provides a firm foundation.However, it is a natural fabric and therefore does tend to relax over time. This means that it may eventually sag. 

Elastic webbing is popular in inexpensive furniture as it is easily attached and costs the manufacturer comparatively little. It is “bouncier” than jute webbing, but will wear more rapidly.

Nylon webbing has no elasticity and is stronger than jute webbing. This makes it especially popular for modern furniture that must offer durability in addition to comfort. 

Modern webbing can now include elastic and nylon, as shown in the photo to the left.

Webbing quality

High-quality webbing has comparatively little stretch, which allows it to function for decades. Its durability prevents sagging and ensures that your couch or sofa will last.

Although this inflexibility makes it more challenging to secure to the sofa frame, good upholsterers still recommend it over flexible webbing. 

Lower-quality, elastic webbing is easy to install as it is can easily be stretched across the chair or sofa frame easily. Unfortunately, its elasticity makes it prone to sagging and more frequent replacement. 

As lower quality webbing tends to indicate less conscientious production, factories that use low-quality, flexible webbing also skimp on the amount of webbing. So, the webbing’s quality and quantity are both lacking.

Additional Foundation Systems

There are three main systems, but they aren’t the only ones out there! 

From vintage alternatives to modern replacements, furniture makers have always experimented with easier or more economical foundations.  

Drop-In Springs

Modern production methods have created an alternative to the 8-way hand-tied spring system:  drop-in springs.

A drop-in spring system is a set of metal springs sandwiches between a set of metal frames. Each frame is a grid that supports the springs from the bottom and presses them down from the top. The frame is not tied to the couch or chair, but is instead screwed into the furniture frame. 

Because of the extra metal, a drop-in spring foundation may be noisier than other foundations. The wood these frames are screwed into can sometimes deteriorate and allow part of the frame to come loose.

As with an S-spring repair, the upholsterer will repair the couch or chair frame and reattach the spring frame.

Marshall Spring Coil System

The Marshall Coil Spring Unit consists of a series of springs individually wrapped in cotton or other fabric. Each wrapped coil is attached to its neighboring coil via a small hog-ring. An upholsterer can adjust the size of this spring unit by opening hog rings to detach as many springs as needed. 

The Marshall Coil Spring Unit can be more durable than some foams, but is lighter and less sturdy than other foundation systems. 

It is most suitable for small pieces of furniture that do not receive considerable wear.

In the photo below, you will see two examples of the Marshall Coil Springs.

This will provide a side and top view of this light-weight foundation.

"Trampoline” Foundations

This is a relatively new, inexpensive form of foundation in which the manufacturer does not install ANY springs or webbing. Instead they simply place a large piece of acrylic/rigid plastic where the springs would ordinarily be. 

This acrylic sheet can not support weight well and soon begins to sag. 

A couch with a trampoline foundation can have the plastic replaced with springs, but the cost of the work may be greater than the sofa itself. Since these sofas are unlikely to be sentimental pieces, the owner may prefer to simply buy a new sofa (or a new-to-you antique/vintage sofa).

The Finishing Touch for Modern furniture

The heyday of horsehair and down is long past.

Foam is king of the modern upholstery world.

This thicker material has allowed for lighter, more-streamlined foundations. Sofa cushions today are light, bouncy, and comfortable. 

Upholstery foam has become increasingly durable and resistant to sinking, but it does still have its limits.

Without a good spring system, foam has no internal support. This makes it more likely to sink quickly and noticeably, at which point it must be disposed of and replaced. 

As this synthetic material is not recyclable, it must go into a landfill. This clashes with the greener sensibilities of modern furniture buyers.

Higher quality furniture will tend to have a combination of springs and high quality foam that has a relatively high-density.

The combination of foundational support and more resistant foam material will ensure that your chair or sofa lasts for many years!

Mumford Restoration: Your Upholstery Expert

There might be alternative foundations, but there is no alternative for expertise. 

Mumford Restoration’s upholsters have spent decades perfecting their craft and have seen every foundation system there is. 

From drop-in springs, to webbing, to 8-way hand tied, they know their craft! 

Mumford is here to help if you have a challenging or rare reupholstery issue–or if you just want your sofa or chair to have a beautiful, tailored upholstery job! 

Call our consultants today and or fill out an online form to find out how we can help with your upholstery repair! 

Come see the Mumford Difference!