Suspended vs Concrete vs Beam & Block: Understanding Your Floor Type

Your floor type affects almost everything in a renovation: how you insulate, whether you can add underfloor heating, how much the work costs, and what problems to watch out for. Yet most homeowners have no idea which type they have—until a builder tells them mid-project.

Here's what you need to know before work starts.

The Three Main Floor Types in UK Homes

Most UK homes have one of three ground floor construction types. Upper floors are almost always suspended timber or concrete (for flats), but it's the ground floor that varies most and causes the most renovation decisions.

1. Suspended Timber Floors

This is the classic Victorian and Edwardian floor. Wooden joists span the ground level with floorboards nailed across them. Underneath is a void—a gap between the floorboards and the earth below, usually with air bricks in the external walls to ventilate it.

How to Identify It

• Floorboards run in one direction with a slight bounce or flex underfoot
• You can hear footsteps clearly from underneath (if there's a cellar)
• Air bricks visible at low level on external walls (little terracotta or concrete vents)
• House is pre-1960s — suspended timber was standard until solid concrete became common
• Lift a floorboard: you'll see joists and a void below, not solid ground

The Underfloor Void

That void exists for a reason: it ventilates the timber and stops it rotting. This is critical. If the airflow is blocked—by insulation fitted badly, debris, or air bricks being covered during landscaping—the joists can rot within years.

Insulating a Suspended Timber Floor

The standard approach is to fit rigid insulation between the joists from above (by lifting boards) or from below if there's a crawlspace. Typical options:

• Rigid PIR insulation fitted between joists — cost-effective, good performance. Boards are supported on battens or netting so there's still airflow below. This is the most common approach.
• Spray foam between joists (from below) — fast and fills gaps well, but it makes future access almost impossible and can complicate mortgage valuations. Many surveyors flag it as a concern. Avoid unless you have a very specific reason.
• Loose mineral wool between joists — cheap but needs support netting and doesn't perform as well as PIR.

Underfloor Heating on Suspended Timber

This is more complicated than on concrete. Your options are:

• Electric UFH mats under new floor finish — the simplest option. Lay electric mats on top of the existing boards, then overlay with new flooring. Adds some height. Running costs are higher than water-based.
• Water-based UFH with overboard system — specialist aluminium-spreader plate systems can be laid on top of the existing suspended floor, with pipes running through them. More expensive but achieves water-based running costs. Floor height increases by 40–60mm.
• Full concrete slab conversion — dig out the void, pour a new concrete slab, then install UFH in the conventional way. Expensive and disruptive but gives you the best long-term result.

For most suspended timber floors, electric UFH or an overboard water system is the practical choice. A full concrete conversion is only worth it if you're already doing significant structural work.

2. Solid Concrete Slab

From the 1960s onwards, solid concrete ground floors became the standard in new builds. The ground is compacted, hardcore is laid, then a concrete slab is poured — typically 100mm thick. A damp-proof membrane (DPM) sits either below the slab or between the slab and any screed above.

How to Identify It

• No flex or bounce underfoot — it feels completely solid
• No air bricks in external walls at low level
• House was built between the 1960s and early 2000s
• If you knock out a section of skirting board, you may see the edge of the concrete slab
• Tap the floor: a dull thud rather than a hollow sound

The Damp-Proof Membrane

This is the silent guardian of your concrete floor. It stops ground moisture rising into your home. In older concrete floors, it can degrade or may have been inadequate to start with. If you smell dampness or see moisture at floor level, the DPM is the first suspect.

When disturbing a concrete floor for any reason, always check the DPM and replace or patch it before reinstating.

Insulating a Solid Concrete Floor

You have two choices:

• On top of the slab — lay rigid insulation boards (usually PIR, 75–100mm), then a new screed or floating floor on top. This raises your floor level by 100–140mm including the new floor finish. You'll need to sort door heights, step thresholds, and skirting boards.
• Below the slab (dig out) — rarely done unless you're already excavating. Insulation goes below the DPM as part of a full floor rebuild. Much more disruptive but doesn't raise floor level.

Raising the floor level is the most common approach and the realistic one for most renovations. It's disruptive but doesn't require digging.

Underfloor Heating on Concrete

Concrete is the ideal base for water-based UFH. The process:

1. Insulation layer laid on existing slab (100mm PIR minimum)
2. UFH pipes clipped or railed on top of insulation
3. Liquid screed or sand/cement screed poured over the pipes (65–75mm over pipes)
4. Floor finish laid on top once screed has cured

The concrete's thermal mass works in your favour: once the floor warms up, it holds heat for hours. This pairs brilliantly with heat pumps and smart scheduling.

3. Beam & Block Floors

Beam and block (sometimes called "beam and pot") has become the standard ground floor construction for new builds since around the 1990s and is now almost universal in new residential construction. Pre-cast concrete beams are laid across the foundations, with hollow concrete blocks (or polystyrene "pots") filling the gaps between them. A thin sand/cement slurry is brushed over to bind everything together.

How to Identify It

• House built after approximately 1995
• Floor is solid underfoot but with a slightly different sound to a poured slab — sometimes a faint hollow resonance
• No air bricks (the blocks provide the structural ground floor without needing a void)
• Builder's drawings or NHBC certificate will confirm — worth checking if you have them

Why It's Used

Beam and block is faster to install than pouring a concrete slab and avoids the wait time for concrete to cure. It's also structurally very strong and can span moderate distances without needing a solid compacted fill. For builders, it's efficient. For homeowners, the result is similar to a concrete slab in terms of renovation options.

Insulating a Beam & Block Floor

The approach is the same as for a concrete slab — insulation goes on top, then screed or a floating floor. The beam and block surface is suitable to accept insulation boards directly in most cases. Some installers also use expanding foam or mineral wool between the beams from below if there's a void, but this is less common and less effective unless the void is accessible.

Underfloor Heating on Beam & Block

This is arguably the easiest floor type for water-based UFH. The flat surface accepts insulation and pipes cleanly, the structure is rigid (no movement), and screed bonds well. Most modern new build UFH installations sit on beam and block.

How Your Floor Type Affects Renovation Decisions

Underfloor Heating: Quick Guide

Damp Issues

Each floor type has its own damp risks:

• Suspended timber: Damp from blocked ventilation (rotten joists) or rising damp. Check air bricks are clear; inspect the void if you can.
• Concrete slab: Rising damp through a failed DPM. Often shows as tide marks on walls at low level, or a musty smell. Requires DPM repair or an overlay system.
• Beam & block: Similar DPM risks, but less common in newer construction. Check the horizontal DPC (damp proof course) at wall base is still continuous.

Floor Height Implications

Adding insulation and screed to any floor type raises its level. This is one of the hidden complexities of renovation:

• Internal doors may need trimming or replacing (typically lose 20–40mm of clearance)
• Thresholds between rooms become steps if you're only doing part of the ground floor
• Skirting boards need to be removed and re-fitted, or new taller ones added
• Stairs — if the hallway floor rises, the bottom step effectively gets shorter, which affects building regs compliance
• Existing vs new floor levels — a common issue where an extension floor is higher than the existing house floor. Should be planned at design stage, not discovered during build.

Screed: The Right Choice for Each Floor

Once insulation and (if applicable) UFH pipes are laid, you need screed or a floating floor system on top. For each floor type:

• Liquid screed (anhydrite or calcium sulphate) — flows into all gaps, gives a very flat finish, ideal over UFH pipes. Suitable for concrete and beam & block. Needs 24–48 hours before light foot traffic, 21–28 days before UFH can be turned on.
• Sand and cement screed — traditional, stronger, but requires more labour to level. Can be used over any floor type. Slower to cure.
• Floating floor panels (chipboard or cement board) — for suspended timber floors or where you can't use screed. Quicker but adds more floor height and can be noisier underfoot.

How to Find Out Which Floor You Have

If you're not sure, here are the quickest ways to check:

1. Look for air bricks on the outside of your ground floor walls. Present = likely suspended timber. Absent = likely concrete or beam & block.
2. Tap the floor through a small area of skirting board. A hollow sound = suspended. A dull solid thud = concrete or beam & block.
3. Check when the house was built. Pre-1960 strongly suggests suspended timber. Post-1990s strongly suggests beam & block. 1960–1990 is typically solid concrete.
4. Lift a small section of flooring (e.g. at a doorway threshold where a board may already be loose). If you see joists and a void, it's suspended. If you hit screed or concrete immediately, it's not.
5. Ask a surveyor or structural engineer. If you're buying or planning significant work, get a proper survey — this will flag the floor type and any issues.

Track Your Renovation Costs by Floor Area

Insulation, screeding, UFH installation — floor work adds up fast. Ted helps you log costs as you go so you always know what you've spent and what's left in the budget.

Quick Summary: Which Floor for Which Situation

You have suspended timber and want UFH:

Electric mats under a new floor overlay are the most practical option. Water-based is possible with spreader plate systems but expensive. Only worth a full concrete conversion if you're doing major structural work anyway.

You have a concrete slab and want UFH:

Water-based is ideal — this is the textbook scenario. Lay insulation, pipes, and screed. Plan for 100–150mm of floor level rise including the floor finish.

You're building an extension:

Beam and block or concrete slab will be specified by your structural engineer or architect. Either way, plan UFH from the start — adding it now costs a fraction of the cost later.

You have damp at floor level:

Identify the floor type first, then address the root cause — ventilation (timber), DPM failure (concrete/beam & block), or external drainage issues. Don't just cover it up.