Insulating between/under joists Help

[richo106]

Hi 

 

We will completely renovating/extending our 1960s bungalow, currently our ground floor is tongue and groove floorboards on 50 x 100mm joists with around 450-600mm (maybe more in places)

 

The kitchen currently (4 x 3m) is concrete floor...that's uneven and need levelling

 

The whole of the ground floor will either tiles or wood flooring

 

My plan is to rip up all the floorboards and insulate between the joists, I am not sure which insulation to use. The options I was thinking is:

 

1. Use 100mm kingspan/celotex and fitted tightly between each joists

2. Rockwool insulation fitted between each joist

 

I have been reading about a DPM barrier, where would this be installed

 

Would 18mm 8ft x 2ft floorboard be suitable to relay on top of the joists and tile directly onto? I am just worried about the floor being solid so it doesn't bounce (and damage grout/tiles)

 

I have been trying to look into this online but struggling to find any definitive answers. We may also want UFH for about half the area

 

I am happy to pay for expert advice on this on to how to go about it

 

Many Thanks

[ProDave]

I would look at say 50mm of PIR strapped UNDER the joists (hard work fixing it from below, hope you have enough crawl space) then 100mm between the joists.

 

18mm flooring is only good for 400mm spacing, if your joists are 600mm centres you need 22mm.

[ToughButterCup]

5 hours ago, richo106 said:

....

I am happy to pay for expert advice on this on to how to go about it

...

 

Then please do that.

We are but interested (not to say nosey) amateurs. While some may draft posts that sound  authoritative, we aren't.  @ProDave's post above makes good common sense; but any reply we might write lacks detailed knowledge of your house design, and so we can only make an educated guess. I have it on good authority that Dave is educated (some say ?).

Before you engage anyone to advise you, please do your Due Diligence 

[markc]

I have just done an old floor with 150mm joists. Even from above was a pain because all the joist spacing varied slightly. Can’t imagine how hard it would have been from below in a 4ft high crawl space.