Types of foundation

A concrete strip foundation is a type of foundation that is used to support load-bearing walls. It consists of trenches that are dug below the level of the ground where the walls will be constructed. The trenches are then filled with concrete, typically to just below ground level to protect the concrete from frost. Concrete blocks are then built up on top of the concrete to the desired level above ground. The log walls and stud walls are then built on top of the blockwork loadbearing foundation walls.

There are two main types of concrete strip foundations:

• Strip foundation with slab-on-grade floor: These foundations have a concrete slab that rests directly on top of the compacted soil. The slab serves as both the foundation and the subfloor for the house. Insulation is then placed on top of the slab.

• Strip foundation with suspended timber floor: These foundations have a ventilated cavity between the ground and the bottom of the floor joists. This cavity helps to prevent moisture from rising into the house and also helps to improve insulation. Insulation is placed between the floor joists.

A slab foundation for a residential house is a solid concrete slab with steel reinforcement that rests directly on the ground. It is the simplest and most common type of foundation, and is most often used in warm climates where the ground does not freeze.

Slab foundations are typically 100-150mm thick in the center, with thicker edges to help support the weight of the house. The concrete is poured over a prepared bed of compacted sand and gravel, which helps to improve drainage and prevent the slab from cracking.

Slab foundations offer a number of advantages, including:

• Cost: Slab foundations are relatively inexpensive to build, making them a popular choice for budget-conscious homeowners.

• Speed: Slab foundations can be built quickly, often in just a few days.

• Durability: Slab foundations are very durable and can last for many years.

• Low maintenance: Slab foundations require very little maintenance.

However, slab foundations also have some disadvantages:

• Cold floors: Slab foundations can be cold to the touch in the winter, especially in colder climates. Insulation can be installed on top of the slab before the finished floor is installed, or underneath the slab, and around the edges to provide a fully insulated slab with no cold-bridging.

• Plumbing and electrical work: Plumbing and electrical lines must be installed in the slab before it is poured, which can make repairs more difficult.

• Ground movement: Slab foundations can be more susceptible to damage from ground movement, such as frost heave and earthquakes.

Overall, slab foundations are a good choice for homeowners who are looking for a cost-effective, durable, and low-maintenance foundation. However, it is important to weigh the pros and cons carefully before making a decision.

Blockwork pier foundations are a popular choice for residential timber buildings because they are relatively inexpensive and easy to install.

To construct a blockwork pier foundation, a series of holes are dug into the ground to the desired depth generally at 2m intervals along the lines where the load bearing walls will be constructed. The holes are then lined with gravel or coarse sand and backfilled with concrete. Once the concrete has cured, concrete blocks are mortared together to build a pillar on top of the concrete pad to bring the top level of the foundation up to the desired height above ground.

Blockwork pier foundations are typically used to support the perimeter and interior load-bearing walls of a residential building. A timber ring beam will then be constructed on top of the blockwork piers to join them together and provide a base for the load bearing walls to be constructed on. The number and size of the piers will depend on the weight of the building and the soil conditions.

Here are some advantages and disadvantages of blockwork pier foundations for residential buildings:

Advantages:

• Relatively inexpensive as they require less concrete and fewer blocks than a strip foundation

• Easy to install

• Durable and can last for many years

• Versatile and can be used on a variety of soil conditions

• They are particularly suitable for building on uneven ground due to the material savings.

Disadvantages:

• Not suitable for heavy buildings e.g. ones built from stone

• Are only suitable for building on stable ground with good load bearing capacity

• The holes may require additional waterproofing measures before filling with concrete in areas with a high water table

Overall, blockwork pier foundations are a good option for timber residential buildings in areas with good soil conditions and they only require a moderate level of support.

If you’re considering using blockwork pier foundations for your residential building, it’s important to have a ground investigation carried out by a qualified surveyor to assess the load bearing capacity of the soil on your site and recommend the appropriate foundation design.

Screw pile foundations have gained popularity due to their unique advantages.

Let’s explore the benefits of screw pile foundations:

1. Quick Installation:

o Screw piles can be installed rapidly, whether manually or using lightweight drilling machines.

o No need for heavy specialized machines like piling/drilling rigs.

o Each screw pile can take as little as five minutes to install, making large projects feasible in a short amount of time.

2. Low Labor Intensity, Low Stress:

o Typically, only two people are needed to install screw piles. No labour intensive concrete shuttering to install, no deep trenches to be dug, no stressful concrete pour. No need for bricklayers to build time consuming dwarf walls.

3. Weather Independence:

o Unlike concrete foundations, screw piles can be installed regardless of weather conditions (rain, shine, heat, or cold).

4. Minimal Site Disturbance:

o Ground screws cause very little site disturbance, low noise levels, and minimal vibrations.

o Ideal for building in sensitive areas, e.g. near tree roots.

o No excavator/digger required for constructing house foundations; your site won’t get churned into mud by heavy machinery

o No mountain of excess subsoil to dispose of.

5. Immediate Load Carrying:

o Screw piles are ready to carry their load immediately after installation.

o Accurate load testing is carried out to ensure the ground screws have been installed correctly and confirms your foundation has been constructed to meet the structural engineer’s technical specifications.

6. Versatility and Adaptability:

o Modular design allows easy adjustments – additional screw piles can be added to increase load-bearing capability or added for an extension in the future simply and quickly.

o Building on sloping ground is achievable in a cost effective way – ground screws with longer shafts above ground are used on the downhill side. This allows a flat ground floor platform to be created with ease and the minimum amount of materials.

7. Installation in Challenging Conditions:

o Screw piles can be installed in various soil types (sand, clay, chalk) and easily extended to screw down into good load bearing ground if the top layers of ground are too soft.

o Challenging sites with high groundwater are not a problem with screw piles – no need to worry about foundation trenches filling with water that could collapse the trench walls, or need pumped out before concrete can be poured.

Disadvantages of Screw Pile Foundations:

Soil Restrictions:

While ground screw piles work well in various soil types, they are not suitable for rock, gravel, or other soil types that contain large rock obstructions. A ground investigation of your site needs to be carried out before the foundations are designed to determine what types of foundation are suitable for your particular house plot.

In summary:

Screw pile foundations are efficient, adaptable, and can be the most cost effective solution for many sites, but they do have limitations related to specific soil conditions. It’s essential to have the results of a geotechnical site investigation that’s been carried out by a suitably qualified engineer to ensure we have accurate ground condition data for the proposed house plot. From this data, the right foundation type can be chosen for your project. Ground screw pile foundations are particularly advantageous when quick installation, minimal site disturbance, and immediate load-bearing capacity are essential considerations.