Laying an Insulated Concrete Floor

This type of floor construction differs from the garage floor. A thick insulation slab is added either under or on top of the concrete followed by screed layer to conform to bulding regulations. As I found when trying to level the concrete on the garage floor, it would be almost impossible to get a perfect finish on such a large area without using loads of self levelling compound. This time a screed layer is vital.

The construction I went for:

1. 100-150mm hardcore
2. 50mm building sand
3. 1200 gauge damp proof membrane
4. 125mm Polystrene insulation
5. 100mm concrete slab
6. 50-75mm screed

From the expereince I gained whilst working on the garage floor I made sure the hardcore was wet enough to allow for better compaction with less runs of the compactor. A rough layer of sand was then compacted to fill any voids for a final layer of sand.


Walking on the sand left voids so I used a ply board to step on. I precut the DPM to 4m, the join will have to be bang on in the middle this time. I had to throw the sheets into place move them around using a stick. Walking on the insulation sheets carefully did not damage it much.


I left a 300mm overlap and again used double side tape to join and hold it place. Once it was joined, I cleaned up any sand and sealed using the 75mm tape to make the end water tight. I could not do a triple seal like the garage as I had no room to get under for another seal.


Around the edges a 25mm sheet is used to prevent any cold bridging from the outide. I done this all around, perhaps it is only required on outside walls.

2014-04-01 13.36.30

Cutting the 25mm sheets was easier than using a saw. With a a slight cut with a sharp blade it would snap off.


I cut the sheets 10mm wider using a hand saw and then forced them down. It made them fit nice and snug.


I used my self levelling laser to compare the floor heights in the lounge and kitchen. The differences were about 20mm so I cut the 25mm sheets 50mm higher just in case above the DPC. I will have to screed all floors at roughly the same level later on and trim this insulation down.

2014-04-04 12.16.07

With the laser in the centre of the room I drew a line where the concrete should finish. You can see the width of the brick is 100mm and shows the line approx 100-120mm in some places. I will keep the concrete slightly below this line when pouring.

2014-04-04 12.15.03

I used Hep20 for all my heating pipes, althouigh there are many types that do the same job out there. For the 2 radiator heating pipes, I ran them thorught conduit approx 1m from the edge of the outside wall. It would be nice to sit on a sofa and have slightly warmer feet in these areas. I also added another conduit to allow me to run any cables such as internet or TV. I did not place any sharp bends in the conduit as it make it alot easier replacing pipe if they need to be .


Concrete came 2 hours late at 3pm. 4 guys this time. They took it nice any easy. Gave me more time to check and adjust the level. As I will be laying a 50-75 screed on top I did not mind if it was out in a few places.