Underpinning a deck is a crucial step in ensuring its longevity and safety. It involves supporting the deck structure from below, typically with concrete or other materials, to prevent sagging, warping, or even collapse. This guide will walk you through the process, from planning to execution, to help you underpin your deck like a pro.
Before we dive into the step-by-step process, it's essential to understand why underpinning is necessary. Decks are exposed to various elements, including moisture, temperature changes, and heavy loads. Over time, these factors can cause the soil beneath the deck to shift or erode, leading to instability. Underpinning reinforces the deck's foundation, distributing its weight evenly and preventing these issues.
Planning and Preparation
Before you start underpinning your deck, you need to plan and prepare the site properly. This step ensures that you have the right materials and tools and that you understand the process thoroughly.
First, assess the condition of your deck. Check for signs of sagging, warping, or other structural issues. If the problems are severe, you may need to consult a professional before proceeding. Once you've determined that underpinning is the solution, gather the necessary materials and tools.
Materials and Tools
Here's a list of materials and tools you'll need for the project:
- Concrete mix (ensure it's suitable for your climate and soil conditions)
- Gravel or crushed stone
- Plastic sheeting
- Shovel
- Wheelbarrow
- Concrete mixer (if mixing concrete by hand)
- Concrete forms (if using)
- Tape measure
- Level
- Gloves and safety glasses
Site Preparation
Once you have all the necessary materials and tools, prepare the site for underpinning. Clear the area beneath the deck, removing any debris, vegetation, or other obstacles. If the soil is wet, allow it to dry out before proceeding.
Next, measure the dimensions of the deck and calculate the number of piers or footings you'll need. A general rule of thumb is to place a pier or footing every 6 to 8 feet along the deck's perimeter and under any interior support posts. However, this can vary depending on your deck's size, load, and local building codes.
Underpinning Methods
There are two primary methods for underpinning a deck: using concrete piers or a spread footing. The choice between the two depends on your deck's size, the soil conditions, and local building codes.
Concrete piers are typically used for smaller decks or when the soil is stable. They involve creating individual concrete columns beneath each support post. Spread footings, on the other hand, are used for larger decks or when the soil is unstable. They involve creating a continuous concrete foundation beneath the deck's perimeter and any interior support posts.
Concrete Piers
To create concrete piers, dig a hole beneath each support post, ensuring it's at least twice as wide and deep as the post's diameter. The hole should extend below the frost line, if applicable, to prevent heaving in cold climates.
Fill the bottom of the hole with a layer of gravel or crushed stone, creating a base for the concrete pier. Wet the gravel and compact it using a tamper or the handle of your shovel. Cut a piece of plastic sheeting to fit the hole, creating a form for the concrete. Place the plastic sheeting in the hole, ensuring it extends above the ground level.
Spread Footing
To create a spread footing, dig a trench along the deck's perimeter and beneath any interior support posts. The trench should be at least twice as wide as the deck's beam and extend below the frost line, if applicable.
Fill the bottom of the trench with a layer of gravel or crushed stone, creating a base for the footing. Wet the gravel and compact it using a tamper or the handle of your shovel. If desired, create concrete forms along the trench to contain the concrete. Place the plastic sheeting in the trench, ensuring it extends above the ground level.
Mixing and Pouring Concrete
Mix the concrete according to the manufacturer's instructions, ensuring it's a consistent texture and color. If mixing by hand, use a wheelbarrow and shovel to combine the ingredients. If using a concrete mixer, follow the machine's instructions for proper mixing.
Once the concrete is mixed, pour it into the pier holes or trench, filling them to the desired level. Use a trowel or shovel to smooth the concrete and remove any air pockets. Allow the concrete to cure according to the manufacturer's instructions, typically for 24 to 48 hours.
Finishing Touches
After the concrete has cured, remove any forms or plastic sheeting. If necessary, backfill around the piers or footing with soil, ensuring it's well-compacted and sloped away from the deck to prevent water accumulation.
Finally, inspect the underpinned deck to ensure it's level and stable. Make any necessary adjustments, such as shimming or leveling the support posts. Once you're satisfied with the results, your deck is ready to enjoy for years to come.
Underpinning a deck is a rewarding project that adds value and longevity to your outdoor living space. By following this comprehensive guide, you'll have the knowledge and confidence to tackle the task like a pro. Don't forget to consult local building codes and obtain any necessary permits before beginning the project. Happy building!