How to fix a sagging mattress with plywood [Definitive Guide]

Whether you’re moving your mattress or just want to give it a boost, plywood under mattress is an easy solution for sagging mattresses. It’s also the cheapest and most accessible material on the market! This how-to will walk you through how you can fix a saggy mattress with help of plywood.

What are the main reasons for a sagging mattress?

First of all, we should find out the possible reasons for a sagging mattress. This will help us to prevent them in the future and also to understand if plywood will help us fix this.

Reason 1: Mattress quality

The mattress can be too soft, too thin, or it can be made of materials that are not durable enough. Latex and memory foam mattresses are more durable while pillowtop mattresses are more likely to sag.

However, please pay attention that each type of mattress can be made of more durable or less durable materials. The quality and durability of materials is a critical factor here.

Reason 2: Lack of support

If your mattress is installed on slats that are too soft, the slats will not provide enough support and the mattress can sag a little bit. It is also possible that your mattress rests on only one side of the slats while the other side hangs in midair.

Even the most durable mattress can start sagging in this situation because of how it rests on the slats.

A platform bed also does not provide support to your mattress from the sides. This can lead to sagging.

Before we start: check your mattress warranty

You can save time and money right now. Many mattresses have a warranty that covers sagging as well. All you have to do is call the manufacturer and they will usually send a technician to fix the problem or completely replace the mattress.

If your mattress does not have a warranty that covers sagging, keep reading!

How plywood can help you to fix a sagging mattress

Plywood is a solid and affordable material that can be used to provide support to your mattress.

You can use plywood for two purposes:

  • Use plywood as a bed board that supports whole mattress
  • as a brace that supports only a part of the mattress

Both methods are almost identical and involve one or two sheets of plywood for mattress support.

Please, follow the instructions below:

How to fix a sagging mattress with plywood: step by step instructions

Step 1: Check if your mattress is sagging

You need to measure how much the mattress is sagging.

To measure this, you can use a carpenter’s level or any other type of tool that will give an accurate measurement for each side in inches. If the difference between mattress thickness in the middle and near the edges is more than 0.2 inches — the mattress is sagging. Otherwise, it’s not.

Step 2: Find out the reason for a sagging mattress

Put your mattress on the floor and measure how much it is sagging once more.

If the difference between mattress thickness in the middle and near the edges is more than 0.2 inches — then the reason is low-quality materials. In this case, plywood won’t help because it won’t fix the problem. In this case, it’s better to replace your mattress or buy a new one. Make sure you will pick one of the best mattresses that won’t sag. Mattress topper can be a temporary solution.

If your mattress is not sagging on the floor — then the reason is lack of support and it can be resolved using plywood. Proceed to the next step.

Step 3: Measure your mattress

Measure the width and height of the mattress. The total rectangular area of the plywood should replicate the size and form of your mattress.

Step 4: Calculate how many plywoods are required

The most common size for a sheet of plywood is 4 x 8 feet.

This table will help you to find out how many plywood sheets are required to fix your sagging mattress:

SizeSize A, inSize B, inSize A, cmSize B, cmNumber of required plywood sheets
Plywood sheet4896121.92243.84
California King7284183213.52
King7680193203.52
Olympic Queen6680167203.52
Queen6080152203.52
Full XL5480137203.52
Full5475134.5190.52
Twin XL388096.5203.51
Twin387596.51881
Small Single307576.2190.51
Crib27.255169.2129.51

As you can see:

  • 2 standard size plywood sheets are required to fix a California King sagging mattress.
  • 2 standard size plywood sheets are required to make a plywood base for a King size bed.
  • 2 standard size plywood sheets are required to fix an Olympic Queen sagging mattress.
  • 2 standard size plywood sheets are required to make a Queen size mattress board.
  • 2 standard size plywood sheets are required to fix a Full XL sagging mattress.
  • 2 standard size plywood sheets are required to fix a Full sagging mattress.
  • 1 standard size plywood sheet is required to fix a Twin XL sagging mattress.
  • 1 standard size plywood sheet is required to fix a Twin sagging mattress.
  • 1 standard size plywood sheet is required to fix a Small Single sagging mattress.
  • 1 standard size plywood sheet is required to fix a Crib sagging mattress.

Step 5: Cut the plywood

You need to cut the plywood into a rectangle that is the same size as your mattress. Your plywood bed board will consist of one or two plywood sheets depending on the size of your bed.

Step 6: Make the holes in the plywood

To improve the air circulation, make holes in the plywood. The size of one hole should be at least 0.5 inches. The distance between holes should be 4 inches.

Step 7: Put the plywood on top of bed slats

Now it’s time to fix the sagging mattress. Place the plywood on top of your slats and put it in place if necessary with hinges or screws. It should be sturdy and as stable as possible.

Alterternative:

Alternatively, you can completely replace bed slats with plywood at this stage. All you have to do is remove the slats and put the bedboard on the frame instead.

Step 8: Put the mattress on top of the plywood

You should feel the difference instantly: the mattress will be more stable, the sagging should stop.

Step 9: Test the mattress

Please, avoid jumping on your mattress right away. Test how it feels by just sitting on the edge of your mattress. Then you can gently push on the center of the mattress with your arms and see if you feel any sagging. If not, congratulations! You have successfully fixed the problem with plywood under the mattress!

Alternatively, you can use plywood as a brace that supports only a part of the mattress. All you have to do is measure the dimensions of the sagging part of the mattress: height, width, and depth.

The plywood should have the same height and width and thickness that is equal to the sagging depth. After this, you can do steps 4…9.

Downsides of using plywood for bed support

The wood under the mattress will isolate the mattress from below and will prevent airflow. This can lead to increased sweating and can cause a bad odor from bacteria accumulating.

Also, in a long-term perspective, this may lead to mildew growth. Mildew will not only be unpleasant, but it can also damage the mattress and lead to further sagging.

To prevent mildew and increase air circulation, you should make a set of holes in the plywood using a drill and turn the mattress regularly.

The best types of plywood to fix the mattress sagging

1. 7-, 9-, or 13-ply plywood

This is an optimal amount of layers to support the mattress. The plywood should not be too thin or too thick.

2. Softwood plywood

It’s a good choice that would help the mattress last longer because it does not warp or crack easily. Also, this type of plywood is likely to produce less noise. For these reasons, softwood plywood is considered the best plywood for under the mattress.

3. Hardwood plywood

Hardwood plywood will provide better support, however, it can warp and crack.

Plywood vs alternative methods to fix sagging

Plywood vs mattress toppers

While plywood is fixing the problem of lack of support, the mattress topper is a temporary fix that will provide insulation. A Mattress topper can be a temporary solution for a sagged mattress that was sagging due to low-quality materials.

Also, mattress toppers will never offer the firmness that can be achieved with plywood.

If you are looking for a little more longevity, then using plywoods will work better than mattress toppers that may only offer short-term relief from sagging mattresses.

Plywood vs pillows

Sure, you can put pillows on the sagging area in order to make it feel more comfortable. However, plywood will hold the mattress up for a longer period of time and can be used as a permanent fix if you are looking to improve your sleep quality.

Again, I can not say that plywood is a solution that will last for years, but it is more sustainable than using pillows which can only offer short-term relief.

Plywood vs a new boxspring

Also, you can purchase a new boxspring that will replace the slats.  This may sound like a more expensive option. However, it is not always necessary to purchase an entirely new boxspring. A used boxspring can cost not more than plywood and become an easier solution. While plywood is a temporary solution, a new boxspring is a more decent investment that will last longer.

Plywood vs mattress helper

Mattress helper is a specialized solution designed to offer additional support for your mattress. It is a good option if you do not want to have plywood under your mattress but still need some extra support and comfort. The main benefit of the mattress helper is that it is a complete solution and no extra work is required. The main downside of the mattress helper is that it can be higher priced than plywood.

A wood board under mattress

Sure, you can use a wooden board instead of plywood. But it is more prone to warp and crack. Also, this option will cost more and at this point, you might consider purchasing a new box spring or mattress instead.

Plywood is a temporary solution only

Please, keep in mind that this is only a temporary solution. Only use plywood if you have no budget for a new mattress. It will come with its own set of problems, but it is an option. Some types of plywood can be hazardous to sleep on and in long term, this may become a reason for allergies and respiratory diseases.

And your mattress is likely to sag again in 6-12 months.

Plywood under mattress instead of box spring

Yes, the plywood under the mattress may be an alternative to a box spring. If your mattress was sagging because of the lack of support, it will resolve the problem. However, you should have a mattress for a platform bed.

Otherwise, the lack of support from the sides will cause harm to your mattress and it can get worn out very fast.

Frequently asked questions

How to make a mattress firmer with plywood?

Place the plywood under your mattress on top of a rails system to achieve a low-key effect. If you want to make your soft mattress significantly firmer, you can place plywood on top of your mattress and then place a mattress topper on top of the plywood.

What thickness of plywood to use between mattress and box spring?

0.5-0.8 inches is an optimal thickness of plywood. On one hand, if you want a low-key effect, use plywood of 0.25 inches thickness or less to achieve this result. But if your intent is to make the mattress firmer, it’s best to choose thicker plywood with at least 0.8 inches in thickness.

How does plywood on box spring make mattress firm?

Actually, it does not make the mattress firmer. The plywood provides additional support for the mattress and prevents it from sagging. If the slats were too soft or not in a good shape, the plywood will compensate for this.

Where do you get a plywood mattress support board?

You can find plywood almost in any hardware store. They are usually in the building materials section and come in a variety of thicknesses, sizes, and grades so you can find one that is perfect for your needs.

  • lumber yards
  • home improvement stores
  • furniture shops

Does putting a board under mattress help?

Yes, if your mattress lacks support, a plywood board will resolve this issue and prevent the mattress from sagging.

At the end of the day

Plywood is one of the most versatile construction materials you can find. It’s inexpensive, easy to work with, and is a great solution for how to fix a sagging mattress without the need for any sort of foundation or frame underneath it.

Plywood boards are lightweight and sturdy enough that they won’t sag under your weight. Putting a board under the mattress really works if your mattress lacks support.

There is a number of alternatives to plywood that have been discussed. But ultimately plywood is the best solution to how to fix a sagging mattress problem without spending too much money. Now you know how to make your own sagging mattress support board fast.

However, please keep in mind that it is only a temporary solution so you’ll need to get a new mattress eventually.

If you have any questions, comments, complaints, or concerns, please email me or leave a comment.

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