Insulating a boarded loft

[eazilyled]

I recently decided to re-insulate my loft, and and I found that there was already approx 100mm width of existing insulation between the ceiling joists. The existing insulation looked quite old, and the joists were completely boarded over.

As the loft space isn't paticularly useable for storage (it is quite pokey and the access hatch is tiny), and partly due to laziness, I decided to lay new insulation (170mm width) over the top of the boards.

My question is: Should I add another layer of insulation (100mm width) over top of the

170mm layer to bring it up to the recommended width of 270mm, or is this unecessary due to the presence of the old insulation beneath the boards, i.e. do layers of insulation need to laid directly on top of each other for them to be effective?

Cheers, Rick

[Guy King]

The message from [e-mail] contains these words:

Yes, and no, in that order.

[Codswallop]

I assume you mean should I add another layer of insulation (170mm thickness) over the top of the 100mm layer to bring it up to the recommended thickness of 270mm. I would say yes, and leave the boards where they are.

[eazilyled]

Sorry, my message was a bit confusing.

I have already added 170mm on top of the boards. So the current situation in terms of layers is (from top to bottom):

170mm Boards 100mm

Should I make it:

270mm (by adding 100mm to 170mm) Boards 100mm

or is this po> wrote:

[Codswallop]

I make that 370mm thickness of insulation. The recommended thickness is about 250mm, boards or no boards. I don't know whether it is worth having

370mm in the UK.

[EricP]

Probably. Someone did some nice calculations in here ages ago illustrating the diminishing returns on more and more insulation.

But to be practical, the stuff is almost given away to the DIYer, and so, what harm can shoving another layer in cause? It will make you happy and might cover a deficiency in the existing layers missed so far.

[Dave Liquorice]

270mm of insulation plus the thermal resistance of the boards. No more insulation is required.

How ever is there a gap between the top of the lower 100mm and the bottom of the boards? That isn't a good idea as it'll allow air flow and thus removal of heat. Rather than add another layer of insulation make sure there is no gap.

[mike. buckley]

In message , Dave Liquorice writes

This is all very well, however I only have room for 100mm of insulation in the gap between the loft boards and the ceiling. I can't put insulation on the top of the boards as it's used for storage. So I'm a bit stuffed as far as the 270mm recommendation goes. I suppose I could get the inside of the roof sprayed with insulation material, but that would take too long to pay back.

[The Natural Philosopher]

wont work on a vented roof anyway.

several options

1/. use 100mm of kingspan etc under boards. Best although the joists will bridge it.

2/. remove borads and lay some 170mm joists across existing, fill with more rockwool amd reboard..

3/. Lay polystyrene floor slabs (or celotex) over the boards and put storage on top of that.

[zikkimalambo]

And failing that........

We're getting extra Rockwool laid over the existing rockwool and joists. (Free! due to my daughter getting disability living allowance).

They want the loft emptied and the boards removed before they start.

The salesman's suggestion with regard to storage was to put some lengths of 2x2 or 3x2 crossways over the joists on top of the new insulation, and then put the boards down on top of them.

What does the team thnk of this idea?

[Guy King]

The message from [e-mail] contains these words:

It's exctly what I did in the same situation. Only I used 4x2 'cos that was the lift I needed.

[Roger]

The message from Guy King contains these words:

New timbers on top of the insulation? Or on top of the original joists with the insulation between the new timbers?

[Guy King]

The message from Roger contains these words:

Right angles to the old timbers. I had to split the new insulation to make space for them but in most cases it conicided (not surprisingly!) with an existing split.

[Dave Liquorice]

Not a good one. The crossways timbers will compress the new insulation not only at the intersects with the ceiling joists but in the spaces as well. Remove the boards put in the crossways timbers, have the freebie insulation fitted then board over the top. The height of the crossways needs to be the same as the nominal thickness of the new insulation.

The fitters will like it if you ensure that the spacing of your crossways timbers is the same as the width of their insulation rolls.

[marvelus]

The new insulation shouldn't be squashed down by the boards or 'crossways' or you wont get the insulation you should be.

[zikkimalambo]

In the first instance I went for a bit of leteral thinking.............

Layed some insulation batts (rockwool??) 2 or three deep over one of the other lofts

And put boards down on them. Feels a bit like i'm at see when I walk on them, but they don't seem to compress too much. I managed to get most of the rarely accessed stuff up there, and managed to haggle with SWMBO to keep more of my wood pile :=))

I am now wondering whether to do the same sort of thing on a section of the main loft for the other storage requirements. ie lay batts down and put the boards on them rather than put down timber bearers to sit the wood on. Either putting this on top of what the contractors lay, or moving theirs to the side to make some areas of the loft ridiculously well insulated and putting it down instead

What does the team think of the merits/demerits of each scheme?

Anyone got any Kingspan/Cellotex that's surplus to requirements??

I'd be after enouth to cover about 64 square foot.

[zikkimalambo]

Bad form to reply to my own post I know, but there you are....

Latest update!

The insulation people are coming this afternoon, I have just managed to get the last of the existing boards down from the loft after emptying it, and my daughter (she who is in receipt of the disability living allowance had a fall yesterday and broke her femur :=((((((

House of course was/is in complete chaos due to the contents of the loft being spread across every horizontal surface.

I think it's going to be a question of getting the insulation put down, putting the boards down on top of that and putting the junk back temporarily, and adding some Kingspan type stuff either under or over over the boards at a later date.

[cpvh]

Just in case anyone is still reading/interested.......

The cowboys - sorry, contacters came at around 5 yesterday and covered the loft in stiffish rockwool.

Not as firm as the insulation batts I used in the other loft, but certainly much firmer than the candy floss type stuff i've seen on rolls before.

They then kindly lifted the boards back up for me and laid them on the top of the rockwool.

Not ideal, but it will do for now, and I can start the joyous task of getting the bags of clothes and "special things" boxes back up there a little later and hopefully restore some order before my daughter gets back from hospital (if they ever find her a bed!!)