Removing concrete floor in 70s build

I'd much prefer digging out the existing floor and is what I did on my 1979 house. We had circa 75mm screed on 25mm of insulation on top of the concrete subfloor. We had a split level house and had almost three meter ceilings in one area so removed the screed, kept the existing sub floor, put down radon, 150mm of insulation and a 100mm polished concrete floor on top of this. This meant all doors were now 150mm to low. I had a massive concrete ring beam above the front door and had to hack off a large chunk of this to keep the front door height. That was harder than removing the floor. The heights of the one other internal door was also raised. Also put in under floor heating. Outside I'm still trying to fix the outside steps as an extra step is now required (ran out of money / next years problem).

In the other area where we only had 2.4 meter high ceiling we removed everything including the sub floor and dug down another 200mm approx below that. We then put back a new sand binding, radon, concrete sub floor, insulation and the polished concrete. The advantages of this were we included a radon sump (although not in a high radon area). This was also the new kitchen area so ran waste pipes to an island and new sink and dishwasher locations. The original floor level was retained which was important due to the ceiling height but also we have a large slider that goes out to the garden and is level with the patio without any steps.

While retaining the sub floor was less work in digging out and one less concrete pour there are other issues like door and window heights that need to be fixed, outside steps or no longer having a level access for child buggies / wheelchairs. It doesn't work out as big a saving as you'd expect. Advantages in removing the sub floor include the ability to add loads more insulation, a proper radon membrane and sump, flexibility in locating ducts and waste pipes, etc.

Another thing to check is if any internal load bearing walls are built off the sub floor. The load bearing wall at the change in level had its own foundation so could be retained but another load bearing wall was built off the sub floor. Obviously you can't remove the sub floor and dig down while retaining a load bearing wall floating in mid air. This needs to be propped and gets very messy. Can you check the neighbors house (which I presume is the same as yours) and see if he has any load bearing internal walls and if they sit on the sub floor or have their own foundation? That would be very useful and important to know before beginning.

You could have lowered it but in my case it wasn't practical due to the outside ground level. In your case it shouldn't be an issue. You will have to lower the entrance door which isn't a big problem. It's a lot easier than raising the height. Just make sure you wrap the new Radon barrier up to wherever the DPC layer in the wall is.

Looking at this from another viewpoint...

We renovated a 70's bungalow with a solid concrete uninsulated floor. For various reasons, we decided to leave the floor alone and externally insulate the walls ensuring that the ewi went down approx 1m below the ffl. Worked a treat in the sense that you wouldn't know from feel or touch that the floor had no insulation.

Poor, the official BER is C1 (but I pay no attention to it as I do not believe in the system of rating for existing housing which results in the BER ... but that's another story).

However:

We maintain a constant (24/7) 20 degC living area and 18 degC bedroom area during the heating season. I measure all energy inputs and monitor the internal temperatures etc. When all inputs of energy actually consumed are calculated and converted back to primary energy usage over the last 7 years, it performs at between 26 & 29 kWhr/m2/yr or A2 BER depending on the actual year in question.

Yes attaining a B2 is one way of complying but there are other ways where attaining a B2 is not feasible... perhaps worth exploring!

I would not recommend raising the Ground Floor level under any Circumstances whatsoever.

What I mean is do not under any circumstances raise OR lower the level of a Ground floor. Never.

it will cause many problems.

I Recommend that if you intend to insulate your existing concrete Ground floor, you should engage a Registered Building Surveyor or Chartered Building Engineer, etc. to carry out a survey of the existing house and advise the best way forward. It will cost a lot of money to insulate an existing concrete ground floor. Ensure it is done correctly and certified in accordance with the Building Regulations.

You can however leave the floor as is.

lf it is decided to insulate the ground floor (GF) it must be done in accordance with the Building Regulations (BR). The Technical Guidance Documents (TGD) give advice on how this must be done.

The 5 purposes of the BR are for the Health Welfare and Safety of Persons, Access for people with disabilities, and Conservation of fuel & energy.

These are very complicated and you need a professionally qualified person to survey, advise, supervise and certify when the works are completed. This Certificate of Compliance with the BR is very important when you go to sell the property.

What I would normally Specify for an existing house - if it is possible-

Powerfloat finished minimum 150 mm concrete on 100 mm hi-density insulation, on 1200 gauge DPM (or) Radon Barrier (RB) on 25 mm sand blinding on minimum 150 well compacted hardcore with Radon sump/s and pipes under the DPM/RB.

In an existing house there will be many problems and many scenarios. Therefore you must retain a professional, specialising in house renovations.

Regards

CE.

Houseyhouse. Thanks for your kind words.

Take a look at what Micktheman said above.

If a budget is a problem then don’t insulated the floor at this time. Use the money to insulate the walls, double glazing and insulate the ceiling in the roof.

There is very little heat lost through a solid concrete floor.

I would not invest money on insulating my floor which is 100 concrete on 1” (25 mm) aeroboard.

You could put laminate on 6 mm approved underflooring insulation on your ground floors.