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.

Let’s get into it.

It is important to note that your concrete slab is a big-ticket item, so it is 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 for no other reason than it’s what they are most familiar with.

types of slabs for houses

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.

types of concrete floor slabs

Slab Types

For the most part, there are three main options for a flat site when considering types of concrete slabs for houses, one of which isn’t exactly a slab as such, 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

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

types of concrete slabs

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 the soil movement due to the seasonal moisture variations.

Waffle Slab

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

waffle 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.

types of concrete slabs australia

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.

waffle slabs australia

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. So the builder can 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.

Also, there will be numerous plumbing excavations under the slab if these haven’t been backfilled correctly. This may also lead to slab failure.

Unfortunately, these problems are hard to detect. There has been a lot of issues in new estates due to such issues.

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.

strip footings and sub floors

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.

strip footings

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 to work with.

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 these bigger ticket items, such as the type of concrete slab.

If you aren’t on top of this, you will end up with a one size fits all from your engineer.

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