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I am choosing my timber frame company for my modern bungalow in Cambridge. One respected company has offered a floor made of eco-joists rather than the usual reinforced concrete passive slab I had assumed. I am worried about the floor sounding hollow and making the whole dwelling feel flimsy and insubstantial: Anybody have experience of a ground floor made with joists? Could I perhaps screed such a floor to give it a more solid feeling (and create a space for UFH)? I wonder if such a construction would be cheaper than a passive slab. Any guesses? Any other pros or cons to using joists for ground floor? Overall what do people think, joists or slab? (My foundation system is screw piles. The build will be near passive.) (By the way, with joists I know I would lose the ability to use a slab as a thermal store).

Hi We have been asked if we would consider using "Thermal Bead Screed" on the ground floor, it's an Italian product, real name Politerm Blu 110. It appears to be a lightweight screed with insulation beads used as aggregate. My original ground floor build-up gives me a respectable U-Value of 0.14 and is as follows; 100mm Sand & cement screed with UFH pipes embedded 3mm Polythene 125mm Thermafloor TF70 insulation boards with hot & cold water pipes embedded 3mm Raydon barrier 150mm dense concrete sub-floor The key to reaching the U-Value of 0.14 is that the boards are installed correctly without gaps or voids. The "Thermal Bead Screed" approach appears to remove the risk of gaps & voids and the floor build-up is as follows; 50mm Liquid Hemihydrate screed with UFH pipes embedded 3mm Polythene 175mm "Thermal Bead Screed" with hot & cold water pipes embedded 3mm Raydon barrier 150mm dense concrete sub-floor This won't give me as good a U-Value, I've been told 0.16 by the company selling it to me and 0.18 by an independent energy assessor. Have any of you used "Thermal Bead Screed" or know anything about it?

In our renovation of a Victorian end terrace, we have been replacing the lounge floor beams as they had been rotting where they sat on the cellar wall, which is reasonably damp most of the time. In most cases there was no dpc. as can also be seen, as we removed the flooring, the chipboard was quite damp too with mould. The make up of the floor was as follows: beams, with rockwool insulation squashed between and in some areas, around the front door and alley wall, the rockwool was wet. tongue and groove chipboard - some of which was damp. upside down gripper rods - to hold the insulation in place. foil backed insulation sheets. pine tonge and groove. In two areas, the chipboard was quite rotten and could be pulled away with fingers. So we have removed all the flooring and the old beams, fitted a new extra thick beam across the whole floor and then put in new joists. We have sat them on dpc, with engineering bricks, slate and strong cement used to level them to the correct height. Then we have laid new 18mm T&G chipboard across the whole floor. My question is how to insulate the floor to provide a comfortable lounge without any draughts while avoiding any future damp issues? This house is to sell so we do not want to spend too much yet still want to do a reason job. We want to lay bamboo flooring above the chipboard. but do we need any membranes? and how best to insulate? The cellar could always have damp issues, particularly in that corner, although we have added an airbrick to the front so there is now a cross flow of air to the other airbrick under the bathroom. so if we just add Earthwool between the new joists, will that get damp and eventually rot the new joists and chipboard? Or would a thin insulation go on top of the chipboard before the bamboo? We dont have much head room, only 2.1m in the lounge, so do not want anything that will reduce the height further. Any suggestions/advice.