Kingsman or Celutex

As part of the kitchen refurbishment I am looking to insulate the floor whi ch at present is a suspended T&G floor on 100mm joists. I am looking at fix ing 25 X 25 battens to the bottom of the joists and dropping 75mm foam insu lation in between the joists. Any advice regards preferences between Kingsp an or Celutex or is it just a case of whichever I can get at the best price ?
Richard

On 31/07/2020 08:20, Tricky Dicky wrote:
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it is just a case of whichever you can get at the best price.
No need for the battens either - just wedge the sheets in place and use expanding foam to fix and fill any gaps. Remember to foil tape over the joists as well..

On 31/07/2020 08:31, The Natural Philosopher wrote:
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I used Quinntherm in 70mm thickness because they all seemed to have a consistent thickness, essential if you have a floating floor. The sheets of Celotex in Wickes had a slight undulating thickness.

On Fri, 31 Jul 2020 00:20:32 -0700 (PDT), Tricky Dicky wrote:
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The insulation is very light and when cut to be an interference fit all the battens are for doing is acting as a stop. 20 x 6 lath will do that and be easier to fix. I'm assuming that the crawl space under the joists is not big enough to squeeze through to shove errant sections of insulation back up.
Provided the boards are a tight fit with no big gaps they don't need to be foamed in, tapping will be fine. However as they are 25 mm below the top of the joists taping the internal 90 degree joint might be a challenge.

On Fri, 31 Jul 2020 12:15:20 +0100, Robin wrote:
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need
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might
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But with the joints taped there can be no "leakage up the sides of the joists". I did think about the gap betwixt insulation and flooring and sort of decided that a bit of warm side ventilation wouldn't be a problem.
25x25 batten at the bottom and sides of the joists wouldn't be too tricky to fit. I'd use a jig to set the postion though not rely on the joists and/or insulation actually being the dimensions they proport to be.

On 31/07/2020 13:51, Dave Liquorice wrote:
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Well yes it *is*, actually. If there is any exposed joist, that is *precisely* where condensation will happen. The foil doesn't just seal, it is impermeable as well. You MUST ensure that the no-longer-ventilated cold joists are taped over. It so happens that is simpler if the insulation is flush with the joist tops.
Underfloor ventilation in an insulated scenario has no purpose: You wont get condensation where its warm.
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Make up battens with slotted holes so you can get the batten the depth of the insulation below the joist top, then screw in more screws to stabilise.
Insulate, foam in any air gaps, and tape over.

On 31/07/2020 14:27, The Natural Philosopher wrote:
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Nonsense. The void below the insulation and flooring joists still needs to be ventilated.
There must be no gap(s) between the insulation and the floor.

On 31/07/2020 13:51, Dave Liquorice wrote:
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You may be able to achieve perfection but it is rarely within my grasp :( Especially perfection that has to survive thermal cycling and movement over the years.
But I can't swear that flush fitting is not just a myth that manufacturers et al have bought into.

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Can't comment on foaming but Cellotex has a surface release agent which needs to be cleaned off for reliable sealant tape fixing:-(

On 31/07/2020 18:22, Tim Lamb wrote:
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then there's how to clean the joists to get the tape to stick to them reliably...another one that's beyond me

On 31/07/2020 21:34, Robin wrote:
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It is not necessary that the tape sticks to the joists. It is simply carrying an impermeable layer from one sheet of foil-covered insulation to another.

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Hand held or bench circular saw, then finish the cut with a hand saw.

On Sat, 1 Aug 2020 09:19:40 +0100, Tim Lamb wrote:
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Power tool to cut celotex type rigid foam board? Seems a bit OTT.
A hand saw will do it but generate a lot of bits that'll be great fun with any static electricity (but probably not as fun as the bits from expanded polystyrene). Deep score with a stanley knife 'n snap works for 25 mm not tried that on thicker boards. For thicker borads I'd try a scallop bladed knife, possibly with some thin wedges to keep the cut open.

On 01/08/2020 09:47, Dave Liquorice wrote:
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I found that slow with 75mm boards
Anyone tried a 100mm blade in a multi tool?
https://www.toolstation.com/smart-trade-insulation-blade/p62092

On 01/08/2020 10:12, Robin wrote:
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I used these
https://shop.bosch-professional.com/gb/en/accessory/t-313-aw-special-for-soft-material-jigsaw-blades--2592808
They were a lot cheaper when I bought mine (usual pack of 4)

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I read that score'n'snap may not give a straight edge on thicker boards. So you would likely have gaps where the insulation is thinner, and harder to butt pieces together or have a tight fit against joists.
You can get special insulation hand saws: (Amazon.com product link shortened)
For power tools there's this sort of thing, but it ain't cheap: https://www.festool.co.uk/products/sawing/cordless-insulating-material-saw/574820---isc-240-li5,2-eb-plus-gb If you have a big job to do, I wonder if they might be hired?
Theo

On 01/08/2020 09:19, Tim Lamb wrote:
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Which will shower you with PIR dust !!!.
Bosch make a special 4 inch cutting blade with a smooth knife edge that fits any compatible jig saw.
Or sharpen the back of a hacksaw blade into a knife, stick a handle on one end and cut them carefully.
Lay some fine guage chicken netting over the joints and loop down so that the PIR board is held tighly up against the flooring.

On 01/08/2020 09:19, Tim Lamb wrote:
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Yes.
panels between woodwork, foil tape over the top of it all. Its just to stop vapour getting to cold joists, that's all
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almost anything if you fill any gaps with expanding foam :-)

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Far and away the easiest I've found is an old (but still sharp) non-serrated kitchen knife, 9" or so blade. Makes a neat job of anything up to 50mm (at least - that's the thickest I've tried).

On Friday, 31 July 2020 08:20:34 UTC+1, Tricky Dicky wrote:
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hich at present is a suspended T&G floor on 100mm joists. I am looking at f ixing 25 X 25 battens to the bottom of the joists and dropping 75mm foam in sulation in between the joists. Any advice regards preferences between King span or Celutex or is it just a case of whichever I can get at the best pri ce?
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whatever brand you find in the nearest skip.