bmj1

Very tight. ~120mm total for insulation + screed (to include underfloor heating)... I managed to pick up 75mm phenolic for £20/sheet from Secondsandco (link), so I think that's the best result I can hope for given the situation.

What screed did you use? I'm planning 40mm liquid screed to maximise heat transfer

Insufficient in terms of sap calcs? Or the house feels cold/is costly to heat? Are you using a heat pump ?

Ok fab. Out of curiosity, how thick did you go ?

Sure. Only thing is it isn't PIR, it's the phenolic product. K103 So not quite sure how it behaves !

Hi wise people, Was planning to do underfloor heating with liquid screed over kooltherm phenolic insulation. Kingspan advise that this insulation should not get wet, so plastic sheet above. So how do we do the clips for underfloor heating without piercing the insulation ?

Thanks, makes sense. DPM below and above then. I've grabbed some 75mm Kooltherm from Seconds and Co.. (£400 / pallet of 20 sheets). Can't go wrong at that price. My max was 90mm, but that was pushing it on tolerance. This is much more comfortable. Gets us a floor u-value of 0.157, which we'll compensate for with solar PV. I'd rather have the extra ceiling height than a slightly more energy efficient house.

Yes, London Clay

I'm a bit confused by the K103 product: K103 insulation is designed for floor insulation in floor buildups. You can install K103 phenolic foam boards in block and beam, solid concrete, suspended ground floors and timber floors. The insulating core is surrounded by glass tissue facings. Why do they surround it by glass tissue facings ?

Our GF build up is: Beam & block DPM PIR insulation Liquid screed Floor finish Should the PIR insulation layer be foil or tissued faced? One-side or both sides ? Or should we be putting a plastic membrane between the PIR and liquid screed, in which case tissue facing is fine ? Thank you in advance.

I think you need to remove the foundations to save the vat with a new build

Thank you all for the advice ! Does having MVHR help at all with the condensation risk flagged ?

Hi all, I've got a flat roof problem to solve. Roof is already built and sealed watertight. Was spec'd as 125mm above / warm roof. Built as 100mm above / 25mm between rafters. Architect wants us to rip out and add above. Building control says it's fine if the insulation between is pressed up against the bottom of the plywood, to form 1 layer. All insulation is as 0.022. Options 1) Rip off roof and rebuild 2) Remove the insulation between the rafters 3) Something else ? Advice gratefully received ! Many thanks in advance.

Are you saying that as a good thing that it sucked up the moisture ?

How about this ? https://www.ready2pour.co.uk/liquid-floor-screed/gypsol-ts-15/

We will be dry lining our exterior walls with insulated plasterboard, to bring up u values. Can we wet plaster the interior ones, or is that madness and we should use plasterboard throughout ?

Hi all, So I'm all pleased with our velux CVU units.. .. But, it's been pointed out to me that we need access to the roof, and they don't open fully. Any recommendations for a rooflight to fill an opening 120cm x 90cm, that opens fully? Ideally not made of plastic, triple glazed and with option for built in motorised black out blinds. Thank you in advance.

I mean that all the steps are not tall enough. Simply due to the previous builder not following the drawings. We'll lose a little ceiling height on the first floor, but will still have 2470mm or so FFL to FCL, which I think is plenty for a bedroom floor.

Yes! Big sigh of relief ! What about using sand/cement screed to build it up ?

Ok, so spent some more time on site this morning...! Good news mostly. We've got space for 140-150mm or so of PIR. We'll be okay here. But - our staircase was built wrongly. It's solid concrete (cast in-situ), but not enough height on each step, we probably need to add ~80mm to the height of each step. Any thoughts on the best way to build this up ? The staircase will be finished with hardwood treads and risers. I.e. we could cast more concrete in a mesh and build it up that way, just wondering if there is a more sensible solution ?

We've got B&B upstairs, but none of the internal walls are structural, upper floor sits on steel posts at the perimeter, and steel beams running across the floor span.

Hi all, Our build-up is: 1. Concrete floor (beam/block) 2. PIR 3. Screed / underfloor heating 4. Engineered wood 15mm Please can I ask this forum: what is the very thinnest screed option available? That will be effective and durable.

I'll need to review the walls above. We've done concrete blocks for the walls above, so might not be totally unnecessary!

Agreed. We will work through it

London. Load bearing walls are all on the perimeter. I wonder if they over ordered the T-Beams and didn't have anything else to do with them..