New Extention, Raised or Concrete Floor ?

[smithy99]

Hi

I am currently building a new extention, basically knocking down the old draughty conservatory and replacing it with a proper extention with pitch slated roof etc to keep the heat in.

At the moment, the existing house has suspended wooden floor (around 6" thick and a gap of about 300mm to the dirt below). I have kingspanned the entire house and this has made a huge difference to the general warmth.

However, in the extention part, am I as well to do the same or would it be just as warm to have a damp proof sheet and concrete on top. What are the cost / insulation implications of either.

I must admit I somewhat like the idea of the wooden joists as it makes cable runs and central heating pipes a doddle.

Many Many thanks

Smithy

 

[Onemoreandyouroff]

I had a similar question when renovating the basement of my house last year. My mind was made up when we found dry rot in some of the floor joists so it was concrete all the way for me.
I don't think it worked out much more expensive and with a bit of planning you can sort all the wiring out either through the roof or walls. Also has the added bonus of being able to add underfloor heating for not too much more - which is fanastic.

 

[tony1851]

If you want to do a timber floor, you really need a height difference of about 12" between outside ground level and your new floor level. This is to allow adequate space below the floor joists for efficient air flow.
Concrte floors, if done properly, have a warmer feel because the mass of the concrete acts as a heat sink, retaining warmth. If you go for a concrete floor, the polythene damp-proof membrane goes down first on the hardcore; put 4" Kingspan board on this, and then a minimum of 4" concrete. Make sure the dpm is effectively sealed to any dpc in the walls.
You have to allow sufficient time for the concrete to dry out before applying any moisture-sensitive finish.
Also, make sure any airbricks to your existing sub-floor space are not obstructed by the new concrete floor. You can use 4" dia. pipes laid under the concrete, going to air bricks in your new wall, to duct air through to the existing air bricks. Don't forget this very important point because if you have a dirt floor, any blocked airbricks will cause dry rot.