In looking at constructing a new basement or converting an existing one, it is crucial that the underlying land and the land your property is on are viable for the work. The last thing that you want is to start a project and then discover halfway through that it cannot continue.
One of the common questions we are asked is “Can I add a basement if my property is on marshy land?”
The answer is – it depends. It is certainly doable to add a basement to a property on marshy land, but it is not always straightforward and should only be done if all the initial checks on the land suggest it will be safe and viable to do so.
There are a number of ways that basement builders can deal with the challenges of basement construction on marshy land.
1. Use a bituminous layer and polythene sheet
This involves constructing a retaining wall, applying two coats of plaster to the exterior face of the wall, applying the cement slurry, adding a bituminous layer on the exterior face of the wall, and then immediately adding a polythene HDPC sheet (1mm thick recommended. This method is believed to be more effective than pitching.
2. Provide external drainage
The key here is to remove water from the ground/below the surface, and sub-surface measures are able to do this. These include tiling and backfilling, locating the groundwater, and providing drainage through the footings (potentially with an impaction strip over the footings if needed).
3. Ensure the basement floor is effective
Before placing the basement floor, we excavate a minimum of 6 inches of soil in order to place the rock or gravel. We then grade the excavation to a low corner and provide at least one and preferably more floor drains. We ensure the basement floor is sloped toward the drains.
4. Use the right concrete
Any basement builders should use low-water concrete mixture in basementconstructionon marshy land. Weaker concrete cracks more easily and voids allow water to seep. It is best to use air-entrained concrete with a minimum 28-day compressive strength of 3,000 psi, a minimum cement content of 520 pounds per cubic yard, and a maximum slump of 5 inches.
5. Use piling
Piling is the most effective method for resisting hydrostatic uplift pressure. A pile is a slender structural element made from steel, concrete, or wood. Examples of piles that can be used in marshy land include: end-bearing piles, friction piles, unreamed piles, sheet piles tension piles, and compaction piles.
Expert basement builders
We are experts in everything to do with basement construction, including knowing what is viable and what isn’t. So if you are unsure whether what you want to achieve is viable because of the land, why not give us a call today to talk through your plans with one of our experts?