Kingsman or Celutex

[Tricky Dicky]

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

[The Natural Philosopher]

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..

[Dave Liquorice]

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.

[tabbypurr]

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?

whatever brand you find in the nearest skip.

[John Rumm]

With the caveat that kingspan as a brand covers things like expanded polystyrene insulation as well as the foiled polyisocyanurate foam as well, so make sure you are comparing like with like.
(The PIR foam is a better insulator and typically foil faced. Its also quite a bit more rigid and easier to work with).

[Dave Liquorice]

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.

[The Natural Philosopher]

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.

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.

[Peter Parry]

Either, or similar such as Xtratherm or Ecotherm. See for a cheap supplier as long as you are using quite a lot. Small amounts only make sense if collecting from Presteigne in Powys or Stirling.

[Robin]

I can't recall if you've mentioned the age of the house but I forgot to mention last time that retrofitting insulation to older houses can lead to rot from loss of ventilation. Eg if you have joist ends built into solid external walls without proper damp courses the underfloor insulation /might/ tilt the balance. Knowing just when it will or won't is beyond me.

[Robin]

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.

[Brian Gaff (Sofa)]

Are they flammable at all? Brian

[harry]

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?

An important thing to remember is not to "insulate" any wiring that carrie s significant current. (Ring main, cooker, immersion heater etc.) You might have to move it.
Wiring can overheat, especially in a loft where the ambient temperature can get quite high.

[harry]

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?

Burn test.

[Tim Lamb]

In message , Robin writes

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

[Tricky Dicky]

which at present is a suspended T&G floor on 100mm joists. I am looking at fixing 25 X 25 battens to the bottom of the joists and dropping 75mm foam insulation in between the joists. Any advice regards preferences between Ki ngspan or Celutex or is it just a case of whichever I can get at the best p rice?

The house was built in 1975 with cavity walls already insulated with blown fibre. Joists only stretch between the inner walls.
Richard

[Tricky Dicky]

which at present is a suspended T&G floor on 100mm joists. I am looking at fixing 25 X 25 battens to the bottom of the joists and dropping 75mm foam insulation in between the joists. Any advice regards preferences between Ki ngspan or Celutex or is it just a case of whichever I can get at the best p rice?

ies significant current. (Ring main, cooker, immersion heater etc.) You mig ht have to move it.

an get quite high.
Wiring and pipework will only pass through the thickness of the foam as it disappears under the floor so should not pose too much of a problem unlike a loft where whole lengths could be buried under insulation. In my loft all wiring is secured above the insulation.
Richard

[Robin]

then there's how to clean the joists to get the tape to stick to them reliably...another one that's beyond me

[The Natural Philosopher]

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.

[Tim Lamb]

In message , Jimk writes

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

[Dave Liquorice]

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.