What Is Oversite? Concrete Base Explained for Homeowners

Oversite is one of those construction terms that gets thrown around — but most homeowners have no clue what it actually means.

If you’re building an extension, garage, or new floor slab, you’ve probably heard the term… but is oversite just concrete? Does it go under your house? What’s it for?

Let’s break down exactly what oversite is, when it’s used, and how ShellCo installs it properly.

🧱 What Is Oversite?

Oversite is the layer of concrete that forms the ground-level floor in domestic builds. It’s laid inside your foundations and typically poured after footings and walls are in place.

It forms the solid base your flooring (and sometimes insulation) will sit on.

⚙️ What Goes Into an Oversite Slab?

A standard oversite prep includes:

1. Excavation and hardcore (MOT Type 1)

2. Blinded sand layer

3. Damp-proof membrane (DPM)

4. Insulation layer (Celotex or similar)

5. Reinforced concrete pour

That gives you a strong, insulated, and moisture-protected base that’s ready for screed or floor coverings.

Want a deeper dive? Read our full Block and Beam blog here →

⚠️ What Can Go Wrong With Oversite?

If not done properly, you’ll get:

• Slab cracking or dipping

• Damp rising through floor

• Cold floors or energy loss

• Failed building control checks

✅ At ShellCo, we:

• Compact every layer

• Install proper DPM overlap and insulation

• Ensure correct depth and mix ratios

🧱 Where Oversite Is Used

We install oversite bases for:

• House extensions

• Garden rooms & outbuildings

• Domestic garages

• Internal refurbishments

• Utility or kitchen slab replacements

Each job is done to building regs standard, with optional reinforcement for heavy-load floors.

📍 Where We Install Oversite

We install oversite slabs across:

Stevenage, Hitchin, Royston, Welwyn, Harpenden, Biggleswade, Shefford, Cambridge and more.

See all areas we cover →

📞 Need an Oversite Quote?

We offer full slab packages including prep, pour, and insulation.

No fluff — just reliable, flat, and solid results every time.

➡️ Get in touch with ShellCo to book a quote or site visit.