Loft boarding and insulation - space board/jablite/celotex?

[johnny124]

Hi all,

Have done plenty of reading but can't find firm answers to the following - any help much appreciated!

8 year old house, insulation in loft only goes up to top of joists - some more thrown here and there, but not consistently. I'd like to board up most of the loft for storage, and to have enough boarded to be able to move about easily. However, through the reading I've done so far, simply putting B&Q style loft boards down is not going to get me the 270mm of insulation I need!

I can do common sense DIY, cut loft boards to shape etc, but don't fancy raising the joists with counterbattening. Space boards looked attractive, but then I read that jablite premium and celotex (even more so) were more effective (and that I'd need 2 layers of space boards..). However, I liked the idea of having (non compressed/squashed) insulation in the joists, covered by space boards screwed down, covered by chip board screwed down - tidy, and a smart wooden surface. However, given I can only see space boards at wickes, and jablite premium and celotex I've read give better insulation, I wouldn't mind using those instead if it gets me better insulation for a ball park similar cost, and a similar amount of my time installing.

However, I can't see a clear answer as to whether I can fit them in the same way - standard "pink" insulation in joists, jablite/celotex resting on top of joists and screwed in, chipboard on top screwed through jablite/celotex into joist? Would the thickness of the jablite (2 options?) or celotex (many more thicknesses?) cause an issue?

Or would I have to have the chipboard resting on joist, with the jablite/celotex on top? And if so, I assume I could readily walk across it when moving storage about?

And can I cut jablite/celotex readily without issue? Jablite it looks like yes, celotex seemed foil wrapped?

All help really appreciated - its our first year with our first child, so heating is on a lot more than normal!

 

[headworx]

Hiya,

As you've yet had a reply, thought I'd share my point of view.

I'm doing the same thing as you really and thought about the best way to do it, battening etc. but didnt want too much weight in the roof.

What I'm ending up doing is having the space blanket 200mm along with the rafters, then across the rafters going to use the space board with the chip board flooring above this.

After that, I might actually lay some more glass fibre insulation over this and then place my storage boxes.

I did look at celotex as its slightly cheaper and I'd imagine better as foiled both sides, but opted against it as the celotex compression strenght was nearly 1/2 of the space board and as I didnt want them sinking onto the joists opted for stronger.
I suppose you could put the celotex where I've put the space blanket, but dont think it would be as good? It would be a hell of a lot dearer anyhow.

I've yet to fit it but so far bought 10x lots of each (so cost me approx £110 so far) will fit and see how much it covers.

Hope this helps.

 

[johnny124]

Hi
Thanks for the reply - much appreciated.

Are you putting 200mm down, then space board on top, then chipboard? Are your joists high enough to allow the 200mm before hte chipboard/space board, or are you compressing it?

Noticed this on the website for space board, making me think I need to double layer it:

"Two layers of Space Board laid over boarded ceiling joists with 100mm Space Blanket or Space Loft Roll (formally known as Space Combi-Roll) between the joists, will achieve a U-value of 0.16 W/m2K."

 

[headworx]

Hiya,

Yes, doing exactly as you said, think it may have to compress a tad but not much - I know it effects it a bit but not worried that much.

I'm not doing 2x spaceboards as would need massive screws and didnt wanna raise the floor any higher than it will be.

Roughly if you doubled it up it would be 122mm with the chipboard, so thats raised by about 5"

Each to their own I suppose but as I said, the cost will increase a lot using double Space board.


Another way to look at it, you supposed to have 270mm of glass fibre stuff down. Ive got 200 of that and also 50mm of the PIR space board making 250, but as the PIR stuff is a better product then it should easily hit the 270mm needed. Hence no need for the double boarding.

I'm no expert but just done a little reading on it and am happy with what I've planned.
Good luck.

 

[johnny124]

Thanks - I've seen it instore, but the cost without a promotion put me off a bit. Do you know when the next promotion is due?

Also, just to confirm - this goes on top of the joists, both insulation and chipboard? That's what it looked like on the installation instructions?

Thanks again to both.

 

[mointainwalker]

@headworx

If I have understood your post correctly - and I did find it rather difficult - you may have wasted time and money.

What I'm ending up doing is having the space blanket 200mm along with the rafters, then across the rafters going to use the space board with the chip board flooring above this

First of all, do you really mean rafters or maybe joists ? There is a rather big difference .


Anyway if the ceiling ( loft-floor ) is insulated, then the amount of heat getting into the loft is significantly reduced. The loft is unheated , therefore very cold and the incremental heat from below will scarcely raise the temperature. I wouldn't even expect 1 C in total.

The insulation you have added at rafter level will therefore retain a percentage of 1 C - maybe, but since it is important to allow free air-flow to the rafters, it is unlikely that will be achieved.

 

[headworx]

Oops sorry, my mistake.

Everything I'm talking about was on the floor of the loft (joists).

Thanks for correcting me as dont wanna be giving inaccurate or misunderstood info.

Yeah, I didnt see a point in sticking it in the loft roof - rafters, as not gonna be a livable space so only need to do the floor.

If I was gonna have a conversion the insulation would have been in the roof of the loft instead.

Cheers again.