Insulation between joists

[mylittlehouse]

Hello All
i am nearly ready to insulate between my floor joists on my suspended timber floor
i read that celotex ga range is the right one to use and put batterns under it to suspend the insulation.
what thichness should i use?
also i am going to put timbermate underlay on top of the joists to dampen the sound and stop as much draft as possible.
what is your recomendation on the thickness of insulation as i read that only 10% of heat is lost through the floor.
Any tips welcome (is there a cheaper effective insulation?)

 

[freddiemercurystwin]

Rockwool is cheaper but not as effective so you need to use more (in theory) are you doing this to meet Building Regs (ie as part of a renovation that will be inspected) or just getting the floor a bit warmer? If not doing it to regs then use two layers of Rockwool (assuming your joists are deeper than 100mm) suspended with chicken wire stapled to the underside of the joists, ensure there are no gaps beneath the floor boards so pack the Rockwool in rather than being sparse with it but no so as its tight. If you cannot get under the joists to staple the chicken wire beneath them then staple it to the sides to create a basket of chicken wire between each joist if you get the gist. Obviously we assume the void beneath the floor will remain well ventilated with air bricks.

 

[mylittlehouse]

hi there
i am not doing this to meet building regs just to be as "green" as i can and keep my bear reclaimed floors as warm as possible (or should i say less cold)
my joists are 100mm deep and i thought by putting celotex in between i could make it air tight to stop drafts.
then i was going to put Timbermate Excel on top of the joists and lay the new reclaimed pine.
is the general concensus that rockwool is just as effective to reduce heat loss through the floor and keep the cold air underneath from making the floor extra cold?
and oh yes the void will be open as it alwasy is to allow the house to breath, i am also going to cleaner up quite a bit of the old rubble and cables from under the floor to remove any obsticales.
your thoughts would be great.

 

[mylittlehouse]

also i want to keep as much sound in the room as possible so i dont upset next door when im watching films

 

[freddiemercurystwin]

You need about 300mm of Rockwool to match 100mm of Celotex so it won't be as warm if you just use 1 layer of 100mm Rockwool, its a poor insulator compared with the likes of Celotex. Its not a consensus but a scientific fact.

If it were me and I had the budget I'd be looking at fitting something like 60mm+ Celotex or 100mm of Polystyrene fitted tightly between the joists either with battens or nails if you can get under the void to knock them in. Then seal any gaps with expanding foam. Make sure the top of the insulation is up to the same level as the top of the joists so no air gap between the top of the insulation and underside of the floor boards.

 

[mointainwalker]

Freddy

It astonishes me that you can work in building as you do and still be wrong about major elements that are requirements for meeting building regs.

Celotex is 60% more efficient thant fibre -wool, not 300%.

OP if I were you, I would fill between the joists with either fibre-wool roll insulation or fibre-wool sound-deadening batts to minimise sound transmission.

Neither will insulate as well as Celotex but will be cheaper and absorb sound better.

keep my bear reclaimed floors

P.S. Was the bear upset when you took his floor ?

 

[mylittlehouse]

hahaha i wondered what you meant but after reading my post back i see "bear" lol

i looked at Rockwool RWA45 74mm on ebay.

so realistically celotex is the better option for heat loss and i will need perhaps 75mm celotex or i can use rockwool and stuff it in between on chicken wire.

if i need to get in the floor in the future celotex will be better as i can pull a piece out without cutting chicken wire.
all in all if i fill the spaces between joists in rockwool i suppose i will need to spend quite allot on buying enough to fill the void or i could spend the same / maybe less on celotex 50-75mm

I think i will use the Celotex GA4000 range on batterns as its cleaner and easier to get in the void in the future if i ever need to.
the timbermate excel should help with the sound reduction.
What is the best size to use as big as possible?
your advise is really valuable

 

[mointainwalker]

I don't want to hammer this to the n'th degree but the floor is not a major source of heat loss by radiation/convection as warm air rises and so the walls and roof are far more important per m2.

What is important with a floor is preventing cold air penetrating from the underfloor as cold moving air is :

1) Noticed and perceived as very uncomfortable ( cold feet/ankles)
2) Very efficient at carrying away warm air.

Whichever you choose, ensure that there are no gaps/leaks in the insulation that let air in.

 

[mylittlehouse]

excellent point taken so i will spend more time working on air tight than heat loss.
thanks so much for your input.

 

[freddiemercurystwin]

Freddy

It astonishes me that you can work in building as you do and still be wrong about major elements that are requirements for meeting building regs.

Frankly I have never bothered to check the exact difference between the two. I spec one or the other whichever is most suitable for the situation and work out the thickness required to meet the regs. I don't have a need to compare them like ofr like as inevitably one is more suitbale than the other in any given situation. If I was doing the drawings for a refurb and was specifying the ins for a suspended timber floor it would be Celotex end of.