Renovating 30s bungalow - underfloor insulation?

crashd_3

We're in the throes of adding a loft conversion and a rear extension to this property. We're also renovating/modernising bits as we go. We're thinking about what to do regarding the existing ground floor flooring situation. Our plan is to lift the cheap click flooring + underlay, pull the floorboards up (some of which will definitely need replacing as there's a certain damp smell in the kitchen/bathroom) and insulate underneath then lay overboard UFH and new flooring on top.

 

Our builder suggested that if we take up floorboards completely and instead lay down floor grade TNG board, underlay, overboard UFH (the Wunda board system) and then new flooring, and it's all done correctly, we'd save money on labour + materials and wouldn't notice the difference. I feel like this is probably an ok solution but seems like the 'easy out' from our builder - what do you all think?

 

We'll also be putting in EWI, new boiler, double glazing etc... for reference.

FreeBear

If you are lifting more than 25% of a floor in each room, building regulations kick in - This would require something in the region of 75mm Celotex type insulation under the floor if it is technically possible. Without that, the underlay & Wunda board is unlikely to meet the required target. But.... If your floor is anything like mine, skinny little 3x2 (75x50mm) joists, there is precious little room for insulation without compromising under floor ventilation.

crashd_3

FreeBear said:

If you are lifting more than 25% of a floor in each room, building regulations kick in - This would require something in the region of 75mm Celotex type insulation under the floor if it is technically possible. Without that, the underlay & Wunda board is unlikely to meet the required target. But.... If your floor is anything like mine, skinny little 3x2 (75x50mm) joists, there is precious little room for insulation without compromising under floor ventilation.

Oh this is good to know! So it might be better to lay insulation + TNG board + wunda + new flooring then?

FreeBear

crashd_3 said:

FreeBear said:

If you are lifting more than 25% of a floor in each room, building regulations kick in - This would require something in the region of 75mm Celotex type insulation under the floor if it is technically possible. Without that, the underlay & Wunda board is unlikely to meet the required target. But.... If your floor is anything like mine, skinny little 3x2 (75x50mm) joists, there is precious little room for insulation without compromising under floor ventilation.

Oh this is good to know! So it might be better to lay insulation + TNG board + wunda + new flooring then?

My mantra is insulate, insulate, and then insulate more". But as mentioned above, the practicalities may well limit how much insulation you can put down. With a 1930s floor (on the assumption that it is 3x2 joists), 25mm of Celotex may be the limit without compromising the underfloor ventilation. Even 25mm will make a worthwhile improvement.

My plan of action would be - Fit 25mm of Celotex (other brands available) snugly between the joists just below the floorboards. Use battens to stop it dropping down, and fill any gaps with expanding foam. If the original boards are still in good condition, reuse them, or sell (they will have value on the s/h market). T&G chipboard if you must, just make sure it is screwed down rather than nailed, and holes drilled for the screws. Fit your Wunda boards, and plumb in the UFH (it is a wet system you are going for, yes ?). Finish with flooring to suit your taste.

crashd_3

FreeBear said:

My mantra is insulate, insulate, and then insulate more". But as mentioned above, the practicalities may well limit how much insulation you can put down. With a 1930s floor (on the assumption that it is 3x2 joists), 25mm of Celotex may be the limit without compromising the underfloor ventilation. Even 25mm will make a worthwhile improvement.

My plan of action would be - Fit 25mm of Celotex (other brands available) snugly between the joists just below the floorboards. Use battens to stop it dropping down, and fill any gaps with expanding foam. If the original boards are still in good condition, reuse them, or sell (they will have value on the s/h market). T&G chipboard if you must, just make sure it is screwed down rather than nailed, and holes drilled for the screws. Fit your Wunda boards, and plumb in the UFH (it is a wet system you are going for, yes ?). Finish with flooring to suit your taste.

Thanks for this, really useful. Yeah it's a wet UFH. Hopefully this will make tis a lovely, warm place to live!