Suspended floor insulation odd spacing

[svouts]

I want to insulate under ground floor. It is a suspended floor with wooden beams. I have access form the crawling space so I wanted to use rockwool. The problem is the distance between the beams. It varies between 61-64 cm so the standard 60 cm rockwool boards are not wide enough for tight fit. If I cat them across then I either have a lot of leftover material or it gets difficult to squeaze and fit it between the beams two pieaces.

Any ideas how to make easy insulation between the 61-64 cm distance beams?

 

[JP_]

Solid boards + expanding foam - although might be harder to get into crawl space.

 

[JohnD]

If you use loft quilt, it is quite squashy so you can push it into irregular gaps between the joists. if the gap is too big you can push an additional slice, or offcuts, in easily.

And is cheaper. The modern brown variety, treated with Ecose, does not shed irritant dust and fibres.

It is much easier than trying to cut foam to fit.

On an unrelated note, mineral wool is non-flammable and produces no toxic gases in a fire.

Foam slab isn't

Since Grenfell I would not want it inside my house.

 

[JP_]

This is interesting ...

PUR
PUR is combustible. However, it forms a char layer which tends to inhibit further combustion. The char layer is relatively fragile. It may break off to expose fresh combustible foam. PUR also contributes to fire growth in a fully-developed fire, giving off black smoke and toxic fumes, including hydrogen cyanide above 850oC.

PIR
PIR, a variant of PUR having improved fire properties, is difficult to ignite and exhibits a pronounced charring which enables it to withstand fire for longer, but is ultimately combustible.

Phenolic Foam
Phenolic foam (which manufacturers such as Kingspan use) is difficult to ignite. It chars, gives off fumes and burns with black smoke, but flame spread, smoke and toxic fume generation are moderate.

Rockwool
Rockwool mineral fibre, inorganic rock fibres bonded together with small amount of combustible binder, is non-combustible.
https://www.homebuilding.co.uk/fire-safety-self-builders-renovators/
​

I have been using a combination of Kingspan and rockwool, although bathroom and my bedroom are kingspan only.
I never knew Kingspan was different to other PIR boards - I only use as MKM Builders Merchants sell it and deliver for free.

I think that if I have a fire it will most likely start above the floor and by the time it gets to the kingspan it will have already burned the roof down anyway!

 

[^woody^]

60 cm rockwool boards are not wide enough for tight fit

That's irrelevant as you need to support the insulation in any case.

 

[svouts]

I am going to install the insulation from the crawiling space, this is my only access. I would prefer rockwool panels to squeeze between the joists, I have done it before and it was easier to first fit the insulation and then support it with chicken wire.

I have found some rockwool panels for floor insulation with 2-4 cm thickens. Do you think I can cut and use long strips of these panels? I can then squeeze vertically the 2-4cm stripes with the horizontal 60cm panels for the odd 61-64 spacing. Will stay in place until I will then install the chicken wire underneath...?

Would I be able to staple the 2-4 cm rockwool stripes along the joists to reduce the spacing to 60 cm, I have a 15mm stapler...?