Insulation between bedroom ceiling joists &

[Bryera]

Hay guys and girls not been on here for a long time and I have moved since and remember how helpful people was on here ? I have just got up all the very old insulation from the loft and binned all the old stuff and started laying that kingspan stuff between the joists where I have put a new bedroom ceiling in. Now I want some of the fleecy stuff to lay on top of the kingspan for more insulation what's best to go for ???

 

I will also at some point be doing in between the joists where the roof is and was thinking more kingspan but keep seeing the foam stuff they spray but see a lot of mixed reviews on it just wanted to know what's best ??? 

 

Thanks again guys and girls this is something new to me so learning along the way so any help or advice you have is much appreciated 

[Conor]

You shouldn't use kingspan between the joists as you'll have condensation issues behind the plasterboard. You should have 100mm mineral wool between joists and 200-300mm layed across the joists. You should also put all of you insulation on either the ceiling joists or under the roof rafters- not both.

 

Are you planning on using the attic space for storage or anything more? Looks to be a decent size. If you just want storage space, get those stilts so you can lay loft boards above the insualtion. I see you've no roof felt under your slates so that would mean no to any sort of spray insulation.

Edited December 1, 2020 by Conor

[A_L]

@Bryera  It looks like your timbers are at 400mm  centres, the most important thing is to find insulation rolls which are already partially pre-cut into 3 x 380mm sections, then find a thickness compatible with the remaining timber depth. The question then is do you use 'cheap as chips' loft roll with a thermal conductivity of 0.044 or premium Frametherm32, thermal conductivity 0.032 at about three times the price. If you intend to add more insulation above this I would not bother with the premium stuff, just use (150-200mm)  more loft roll.

 

There will be no problem with condensation on the underside of the Celotex if it has silver foil there, it acts as a vapour barrier layer. The additional insulation will keep it warm and there will be no problem with interstitial condensation

[Cpd]

I put 70mm of kingspan under my shed rafters and 200+mm frametherm or something similar.... above it and was surprised at just how much heat wast trapped between them, it was toasty warm on the back of the kingspan ! It was a reminder that on general you can’t have to much insulation. Where there was just kingspan it just felt like the ambient temperature and one would assume it was working great as it was not warm but that was only because the heat from the room must instantly disperse into the air as there was no secondary insulation layer to trap it. I taped all the insulation sheets on the front so it acted as the VCL.  

[Bryera]

Thanks all of you for the advice ? yer the insulation I have down has the silver on both side so not so worried about moisture hopefully ? have been looking at this stuff to lay on top  ? Or is that to much ? Any more suggestions or where I can get stuff from much appreciated ?

 

So with having no felt under lay under my slate that foam stuff would be no good so thinking doing something like I did in my van conversion ? silver foil then some 50m kingspan would keep a lot of heat in the house and rooms I hope ??

[A_L]

@Bryera, If you intend more than one layer of insulation then you need to just fill the remaining depth of the timbers first, so you probably need a 100mm roll. The same site/warehouse has

 

Quote

Knauf 100mm Space Bottom Layer Loft Roll Insulation - 8.3m2

 

at about 1/3 the price for the same total amount of insulation.

 

I do recommend a pre-split roll as it make life in a loft easier, e.g.

 

https://www.insulationsuperstore.co.uk/product/loft-insulation-multi-roll-44-by-superglass-100mm-1212m2-pack.html it is incidentally marginally cheaper again.

 

10 hours ago, Bryera said:

So with having no felt under lay under my slate that foam stuff would be no good so thinking doing something like I did in my van conversion ? silver foil then some 50m kingspan would keep a lot of heat in the house and rooms I hope

 

Multiple layers of loft roll (300mm) will be sufficiently insulating would make this unnecessary and uneconomic. If there is any ventilation in the loft it would also be ineffective. 

[Sandybay]

Hi, 

I have an insulation question, hoping to start my Icf bungalow build next year, was planning to spray icynene inside of slated roof, around a 220 sqm roof was quoted £7000,but have now thought I could save quite a bit by using 140mm celotex between trusses and foam them in place for a good seal. 

Is this almost as good as spray insulation? 

Thanks. 

[Conor]

3 minutes ago, Sandybay said:

Hi, 

I have an insulation question, hoping to start my Icf bungalow build next year, was planning to spray icynene inside of slated roof, around a 220 sqm roof was quoted £7000,but have now thought I could save quite a bit by using 140mm celotex between trusses and foam them in place for a good seal. 

Is this almost as good as spray insulation? 

Thanks. 

How deep are your roof trusses? You need to leave a decent air gap. In our build, we're doing 100mm celotex between 150mm rafters, air tightness membrane under rafters, another 50mm celotex, 25mm service void made with batons, then plasterboard. Issue with spray insulation is consistency... Hard to get even coverage and hears of some horror stories.

[Sandybay]

Hi, will be 150mm deep trusses, sarking and water proof membrane under slate, 

Not planning to use loft, at moment but would have potential to provide extra space/ rooms at some point. 

[A_L]

1 hour ago, Sandybay said:

Is this almost as good as spray insulation?

 

Celotex has a thermal conductivity of 0.022W/m².K  and the usual open cell Icynene has a thermal conductivity of 0.039W/m².K. This means that 100mm of Celotex has the same insulating effect as 177mm of Icynene.

[Sandybay]

That's interesting, Thanks.