It could be the soil. It could be a poor construction. Either way, a sagging deck is a pain to deal with. So, how do you fix a sinking deck? It’s an involved process that’s best to bring in professional help on. Always reach out if we can help, but I will walk you through what’s involved so you can better understand the process.
Issues That Cause Decks to Sink
Before you jump into fixing a sinking deck, you need to know some potential contributors to the problem. Soil erosion is one of the main factors that causes decks to sink. The deck foundation fails when underground water flow or poor drainage or rain washes away the soil beneath the footings, which causes the deck to sag.
And then there’s the contractor who does not do a thorough job. Decks break down when untreated wood is used, and the footings are not poured deep enough. The supports will eventually fail.
Moisture also plays a key role. The base area of wood posts exposed to damp conditions will rot and soften. The support system becomes compromised when the settlement becomes uneven.
The structure of decks can experience destabilization through the periodic movements of the soil. On the East End, for example, the silt and clay soil can move around. The continuous movement of the structure can cause a well-built deck to experience both leaning and section dropping over time.
Identifying the root cause of the issue leads to repairs that become both durable and long-lasting.
RELATED: The Beginner’s Guide To Decks
How to Spot the Warning Signs
The sooner you can spot that your deck is starting to sag, the better. It can save you from harder renovation work (and that saves you time and money).
Here are some of the signs you might see:
- An irregular incline: One telltale sign is a slant or an irregular incline on the deck’s surface, which may cause furniture to sit unevenly or lead to water pooling on your deck.
- Spaces between the deck and your home: An installed deck should fit snugly against the wall of your home; if you notice gaps and alignment issues, that’s a problem.
- Soft spots: If you’re walking along and notice a place with some give, it could mean the underlying supports are damaged or have moved significantly. Also, keep an eye out for cracks in the wood.
RELATED: Resurfacing vs. Installing a New Deck
Make sure to check the stability of the railings and stairs, as their alignment with the ground, to see if there are any signs of shifting or movement underneath.
Being mindful of these indicators not only helps avoid accidents but also safeguards the durability of your deck.
Tool List to Fix a Sinking Deck
Now that we’ve talked a bit about what causes a deck to sink and how to spot the warning signs, let’s talk a bit about the tools and materials you’ll need for this type of project.
List of Tools
- Hydraulic jack
- Post level
- Cordless drill
- Circular saw
- Shovel and digging bar
- Safety goggles and gloves
The tools have particular functions that are essential for deck sinking repair. The hydraulic jack enables safe elevation of sagging sections, and the post level provides vertical accuracy. The cordless drill and circular saw enable efficient removal and installation of components. The process requires digging tools to access or replace footings and protective gear to keep you safe as you repair your deck.
Materials List
- Treated lumber or replacement posts
- Concrete mix
- Gravel for drainage
- Galvanized hardware (post anchors, bolts)
- Wood preservative or sealer
While you may not need all the tools and materials listed here, these are the general items to get the job done safely and correctly.
Sinking Deck Repair – The (General) Steps to Follow
Each deck repair job is different. Don’t think you’ll be able to take the steps here and fix a sinking deck with no issues. But these steps represent a high-level view of what goes into a basic job.
Assess and Prepare the Deck for Repair
Before jumping in, go over every point of your deck. You’ll want to identify any sagging areas and damage to beams, posts, or footings. Never take on a job you can’t handle. If you’re feeling overwhelmed with the amount of work, reach out to a professional.
Once it’s go time, make sure you have your deck cleared. All furniture, obstacles, and decorations should be removed.
Raise the Deck and Fix the Footings
It’s time to break out the hydraulic jacks and raise the deck. Your attention will most likely be on the footings. They are normally the main reason for sinking. The original footings require complete replacement because they are too shallow or have deteriorated. You should remove the existing footing and inspect the hole depth. Standard building codes usually state that the lowest point of footings should extend beneath the frost line — for many places, it’s around 36 inches deep (always check local building codes).
RELATED: Town of Babylon Deck Requirements
The construction of new concrete footings should be done using either a prefabricated form or a basic wooden mold. Place a drainage layer of gravel at the bottom of the hole before pouring to limit the amount of space water has to get in. A post anchor should be embedded in wet concrete to create a solid post-to-anchor connection.
If your soil is unstable, you’re going to need helical piers, also called screw piles. These set a really solid foundation. They’re huge galvanized steel shafts with screw-like flanges. You can’t DIY these. Not even a chance. You need specialized machinery.
Concrete footings are easier to DIY (but not always easy). It takes a minimum of 24 to 48 hours for the curing time before they can support any weight. Properly set reinforced footings act as the essential foundation for any deck structure, so ignoring this step will result in the same issues from coming back up.
Fix the Deck Posts and Beams
After the footings, it’s time to move on to the posts and beams. They help secure footings. Posts need complete replacement instead of repair when they demonstrate signs of rot or cracking or when they lean. Installing ground-contact rated pressure-treated lumber requires exact measurements for post heights.
Make sure you have structural support for the post and beam connection, using galvanized bolts to provide long-lasting strength.
Inspect your beams as well. You will likely need to add another, identical beam to the sagging one to increase its strength. (FYI, this is called “sistering”). The sagged beam and the new one should be connected using structural screws or bolts for a secure bond.
Before finalizing the installation, check that all posts are straight vertically and beams are perfectly horizontal. Verify the alignment by taking measurements from multiple points to prevent the structure from twisting or sloping before your final fastening.
Adjust and Re-level the Deck Surface
After fixing the footings and posts, you need to tackle the deck surface levelness issues. Start your inspection with the horizontal joists that support the deck boards. A level tool allows you to detect any irregularities in the deck surface. The joist-beam interface can be adjusted using shims when things aren’t lining up like they should.
Some joists require replacement because they have become warped or damaged. The deck boards must be removed first from the affected joist before you can unfasten them from the frame. The replacement process requires using identical pressure-treated wood sections, which you need to install and then secure properly.
Verify that deck boards maintain proper spacing and direction after performing structural modifications. The replacement of warped boards requires deck screws for re-fastening or complete board replacement. The deck surface becomes safer while water drainage improves, and the deck’s appearance is enhanced when properly leveled.
Check the deck alignment through a complete length and width run of the deck. When you perform these surface-level adjustments,, the structural fix becomes complete so the deck becomes ready for safe extended usage.
Quick Summary
A sinking deck is a safety issue and certainly doesn’t look good. While fixing it is probably best left to the pros, I did want to help you better understand the process.
I’ve shown you how to identify the warning signs of a sagging deck and the typical reasons why decks begin to sink. The general process is usually pretty straightforward. It’s not easy work, but it’s not something you can ignore.
