Types of Concrete Slabs for Houses: A Complete Guide

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Have you ever wondered what slab options you have when building a house? Well, stick around because, in this article, I’m going to share the three most common types of concrete slabs for houses and when and why you would use each.

Then, moving forward, you’ll be able to reference this nifty little article when it comes to slab selection time on your next residential development project.

You’ll understand the various slab types and thickness requirements for these residential builds.

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Let’s get into it.

It is important to note that your concrete slab is a big-ticket item and one of the more costly parts of your project.

Suppose you get your selection incorrect. It can cost you significant time and money.

Different engineers will specify different types of concrete slabs for houses, and not always for the right reasons.

It isn’t uncommon for them to lean a specific way because it’s what they are most familiar with.

As the property developer, it is your responsibility to know what options you have and when and why you would use each.

You must understand that one size does not fit all.

The type of concrete slab that you select will come down to your site and its specific environmental conditions.

And as I say all the time on this channel, you need to do your own research. Never assume you’re your providers and suppliers are doing the right thing.

It is incumbent on you to have the required knowledge to hold them accountable. Otherwise, you could be costing yourself a lot of money, and you don’t even know it.

Slab Types

When considering types of concrete slabs for houses on flat sites, there are generally three main options. One of these isn’t exactly a slab, but it’s a genuine option nonetheless.

• Raft Slab
• Waffle Slab
• Sub-floor with Strip Footings & Stumps

Looking at it simplistically, selection would be based on the proposed structure type, soil conditions and finished floor levels.

Raft Slab

The raft slab has been in use for a long time. They consist of edge and internal concrete beams formed like a grid pattern, integrated with the above-ground slab.

Raft slabs are suitable for most soil types and site conditions and have been used widely over a long period of time.

As the raft slab beams penetrate the ground and are found onto the natural soil profile, the raft slab generally offers better soil movement resistance than the other footing systems.

Therefore, you can use a raft slab for any soil classification.

As the reactivity increases, the concrete beam depth increases and the grid spacing decreases to make the slab stiffer to resist soil movement due to the seasonal moisture variations.

Waffle Slab

Relatively speaking, waffle slabs are new compared to raft slabs.

And generally speaking, waffle slabs are considered most builders preference, especially in the new estate developments where there is fierce competition among the builders offering competitive building contracts.

This is mainly because no beam excavations are required in the waffle slab preparation process, which allows builders to estimate the required concrete quantity accurately.

Waffle slabs are particularly useful if the finished floor level needs to be raised 600mm above the existing ground level and the client wants a concrete slab.

In a scenario like this, the waffle slab becomes a more economical option than the raft slab.

It means that the concrete and excavation can be accurately estimated. The builder can then provide a more accurate quote, giving them the best chance to win the project.

Now, as the slab sits on the ground, extreme care should be taken during and after construction.

If there are flooding or water leaks from downpipes, water can seep under the slab, making the soil soft and losing its bearing capacity, ultimately resulting in slab failure.

If the plumbing excavations under the slab haven’t been backfilled correctly, they will be numerous, which may also lead to slab failure.

Unfortunately, these problems are hard to detect. As a result, there have been many issues in new estates.

Strip Footings and Sub-floors

This is a super old construction method. Almost every old house in Melbourne consists of either strip footings or stumps or a combination of both.

This method is useful, mainly when the finished floor levels are much higher than the ground levels.

It is also very laborious. And nowadays, builders choose not to use strip footings or sub-floors unless the clients request it’s the engineer’s recommendation due to site conditions.

This method is also generally suitable and economical for sloping sites.

Wrapping Up

At the end of the day, it’s going to come down to who you have engaged in working with. Also, consider sustainable building practices.

You need to connect your project with a quality engineer who appreciates their choices’ financial implications.

As a residential property developer, you need to be confident in the decisions made by your contractors, particularly on big-ticket items such as the type of concrete slab.

If you aren’t on top of this, your engineer will give you a one-size-fits-all solution.

I promise you that in most cases, it’ll be the wrong call, negatively impacting your project and, ultimately, its bottom line.

Filled under: All Building