Loft insulation, squished or not squished?

markin

Keeping your Energy thread in mind, Forget storage and have as much insulation as you can fit!

is 140kwh-of-gas-a-day-normal

ohdarn

m0t said:

ohdarn said:

I'd rather not use the loft legs as their weight ratings seem quite poor, 50kg per square metre which means I wouldn't be able to stand on any of it.

There's the option to build it up with timber I guess, but very expensive.

And either option will mean having to extend the electrics so they're not buried under the insulation.

The other thing to note is the the roof is split into two halves, this is one side and the other is smaller that we're not storing things in.

Maybe we put a thicker layer in the other side, although we haven't looked up there yet to see what's already installed (probably a horror going by what we've already found).

Your loft joists are designed to carry the weight of the ceiling below, the 50kg m/2 is to prevent bending of the joists/cracking of the ceilings and not a limit of the legs themselves.

That may be the case, but since I weigh a considerable amount, I'd prefer the chipboard to be resting on something a little more substantial before I walk around on it.

ohdarn

markin said:

Keeping your Energy thread in mind, Forget storage and have as much insulation as you can fit!

is 140kwh-of-gas-a-day-normal

Unfortunately the storage space at this new property is in short supply so loft storage is a must.

FreeBear

If you use (for example) the loft boards from B&Q, they measure 1220x330mm. And if your joists are around 340mm centres like mine, you'll be using quite a few legs. They'll end up close to 320mm apart, so any load you place on top will be spread over a fairly large area.

casper_gutman

ohdarn said:

That may be the case, but since I weigh a considerable amount, I'd prefer the chipboard to be resting on something a little more substantial before I walk around on it.

If you go up to the unboarded loft and walk around on the joists your entire weight will be supported at a point on a joist under your foot.

Boarding it with loft legs will only help: stand between two legs and your weight will be shared between them, reducing the load at each point on the joists beneath.

Stand directly above a leg and the leg won't crush, it'll just transfer the load straight down to the joist below, where it would have been in the unboarded loft anyway. 

The joist will be the weakest linkwhether the loft is boarded or not. If youare concerned about the ability of the joists to carry your weight, you need to strengthen them, which mean adding timber on top of them (with lots of screws).

ohdarn

I'm not concerned about the joists carrying the weight as I've been up there working on them but I would be concerned about chipboard perched on top of legs, supported in less places than if they were laid on joists, when I know there's up to a six metre drop below me if something fails.
And I don't want to raise the electrics further to make them accessible.
In short, I ain't using loft legs.

scottishblondie

ohdarn said:

I'm not concerned about the joists carrying the weight as I've been up there working on them but I would be concerned about chipboard perched on top of legs, supported in less places than if they were laid on joists, when I know there's up to a six metre drop below me if something fails.
And I don't want to raise the electrics further to make them accessible.
In short, I ain't using loft legs.

The loft legs are perfectly capable of being walked on.  We installed them in our old house, and myself, my husband and my father were up there (all at the same time) plus all the stored stuff with no issues.  And none of us are exactly slim.  The legs were rock solid.  Nothing is "perched" it's all screwed securely in to place.

If you squish the insulation you're taking all its insulation properties away, and putting pressure on the lathes supporting the ceiling below.  If you don't want to use loft legs use timber to build up and install a decent amount of insulation.  250mm of the fluffy stuff is recommended.

casper_gutman

ohdarn said:

I'm not concerned about the joists carrying the weight as I've been up there working on them but I would be concerned about chipboard perched on top of legs, supported in less places than if they were laid on joists, when I know there's up to a six metre drop below me if something fails.
And I don't want to raise the electrics further to make them accessible.
In short, I ain't using loft legs.

You need to use something, otherwise you'll either have inadequate insulation or damage the ceiling, as @scottishblondie says.

If you don't like the basic loft legs, then you can use timber, but as you say, it's more expensive.

Alternatively there are options like this: https://www.loftzone.co.uk/product/storefloor/ which might make you feel more confident? They're not cheap, but the way timber prices have gone over the last year or so they might be more cost competitive than they were when I did my loft!

ohdarn

I'm just going to put 100mm loft insulation down then put boards on top of that, directly on to the joists.
I'll use the 200mm stuff for the roof that's not used for storage and in the roof that is used for storage, around the edges of the boarding.

aoleks

we did it as 300mm. 270mm insulation, not squashed + 30mm gap, boarding (18mm) on top. did this with additional structural joists, rather than legs and now you can walk around the entire loft, store anything you want and it feels sturdy. we also insulated the loft hatch and some material was fixed to the sides to prevent drafts.