Building a Basement

What’s the best method of basement construction?

Basement construction is a popular trend as people try to make the most out of the square footage of their property. Home gyms, playrooms, wine cellars, swimming pools or car parking facilities are just a handful of the uses people find for digging downwards.

It’s interesting to note that costs will usually double for a basement than for a loft conversion.

Obviously, it’s far simpler to build a basement when you’re constructing a house from scratch, but even if you don’t need to worry about the complexities of excavation, there’s still a lot of factors to think about.

The big things that need to be considered are:

  • The structure - What are the shell and core made out of and what footings do they sit on?
  • Soil removal - if you can’t reuse it elsewhere on site, how are you planning to get rid of it?
  • Waterproofing - This can be achieved through a combination of membranes, water-resistant materials, drainage cavities and pumps
  • Lighting - There’s often a desire to get natural light into basement rooms via light shafts or walk-on glazing
  • Fit out - A construction team is unlikely to get involved in decoration, but floor and wall finishings and built-in storage or seating may become part of the job
  • Maintenance - A tough element estimate up front, but something that needs to be factored in, especially if pump drainage systems are in place

Not every site is suitable for a basement and checking the ground conditions for the following elements is essential before you begin to avoid having to backtrack halfway through a project.

  • High water table soil - the biggest risk for basement projects
  • Sloping sites - putting undue pressure on one side of the structure
  • Unsuitable bedrock - something you can check for in preparation studies
  • Existing structures - Not disturbing the foundations of other walls or buildings
  • Existing services - having to work around or redirect pipework

It’s rare, but archaeological finds may also have a major impact on your planning, and throw your project timescales into turmoil.

Basement building materials

When it comes to foundations and structure, concrete is a common choice, with three methods to select from:

  • Masonry walls
  • Precast panels
  • Poured concrete walls

Which you go for depends on your budget, the site conditions, soil type and whether you’re building your basement below an existing structure.

Your choice will also come down to how much you need to consider insulation and waterproofing. While all concrete structures can be engineered to become both dry and warm, it’s far easier and more cost effective to factor this in when you’re building rather than having to add something later on.

Effective basement waterproofing

Damp issues and flooding are part of the perils of having a basement. They’re unnatural structures built directly where lands was — and wants to be — so despite all the planning, preparation and preventative measure you put in place, there’s always a danger the elements will work their way back in.

Basement waterproofing options come in three flavours:

  • Type A - Waterproof materials or membranes sitting inside or outside of the basement structure.
  • Type B - Structurally integral protection where water-resistant concrete is used to provide the waterproofing protection.
  • Type C - A water management system that allows water to penetrate the structure in a controlled way.

These methods are often combined to counteract the weaknesses of each other. For example, Type B requires perfect joints and pours to avoid seepage, so a Type A membrane may be necessary to double up the protection.

The quality of the products you use in basement construction is essential. This is not a time to cut corners and go for the cheapest option. Concrete isn’t inherently waterproof without additives, so when selecting the concrete mix for your basement, ensure the specifications suit the waterproofing you’re hoping for.

While basement floor sealers can be effective for waterproofing, arguably the most effective method is for a waterproof foundation in the form of a cavity drainage system. This is a floor (and sometimes wall) membrane that channels water towards a safe point where a sump chamber and pump system can be installed.

Depending on the heating, ventilation, and air conditioning (HVAC) methods being used in the interior, it’s possible to incorporate the excess water from the membrane into that system for a seamless setup.

Any below-ground installation needs to be thoroughly checked by inspectors so factor in checkpoints within your plan where the structure is exposed to allow them to effectively carry out their work.

What are the best basement flooring options?

Once you’ve constructed your basement foundations and effectively waterproofed them, choosing the correct flooring is more than just a simple aesthetic decision.

Generally, it’s better to opt for inorganic materials such as tiles, polished concrete or vinyl over organic options such as hardwood. Even the best waterproofing systems cannot avoid all elements of damp, and because moist, humid air is heavy, you may need to consider what’s coming from above as well as what’s below your basement.

You’re better off opting for a material that’s not going to be affected by this.

  • Vinyl offers the easiest installation but requires a perfectly smooth slab to avoid any bumps or imperfections showing through.
  • Tiles come in all shapes, sizes and colours, and can be used as effectively on basement walls as well as floor to create a seamless design.
  • Engineered wood is an option if you want the look of a hardwood floor without the difficulties that come with it.
  • Laminate flooring may be preferred depending on the intended use of the space, for example, a gym where heavy equipment may be prone to scratching.
  • Concrete can be finished by painting, staining or polishing to provide a natural look finish to the basement.

While it may appear to be a complex project fraught with risk, it’s important to consider that any costs involved in the construction of building a basement are usually offset in the overall increase in house price. Basements can very often pay for themselves.