Alternatives to 18mm Chipboard?

NewtoDIY

I need to board and insulate my eaves space and as it's an old house, the weight of 18mm Chipboard is too heavy. I want to lay Celotex GA4000 but they have told me that this needs to be sandwiched inbetween chipboard in order for it to be strong enough.


The joist centres measure 31cm so Styroloft isn't going to be an option because I'd have to cut every single board and it would be a massive waste.


So my question is, are there any other loft boards that are as strong as 18mm chipboard, but weigh considerably less?

mart.vader

"So my question is, are there any other loft boards that are as strong as 18mm chipboard, but weigh considerably less?"

Not that I know of, but most people use 18mm flooring grade chipboard as it's made for the job. Who told you that 18mm chipboard would be too heavy and wouldn't be strong enough?

Jonesya

Have a look at 18mm softwood plywood, I think that's somewhat lighter than chipboard.

Also - I'm struggling to visualise where you want to insulate so that you need to sandwich insulation between sheet. Is it just the eaves you're insulating or the loft space in general?

vaio

I'm guessing the OP wants to lay insulation board on top of the joists, when it does need to be sandwiched between two sheets of chipboard or similar.

OP.......easier solution might be to cut the sheets and lay them between rather than on top of the joists, then you'd only need one layer of chipboard. It wouldn't be particularly wasteful as you use the off cuts at the start of the next sheet.

For example...you joists are 310 centres (you sure? seems too small) so 260 gap. Take your 1200 wide sheet and cut it into four 260 wide strips which will leave a 160 wide offcut. Take the next sheet and cut a 100 strip off it to use with the 160 wide offcut and then do another four 260 wide strips.......repeat as necessary.


use these strips to fit between the joists, lay chipboard on top of joists (screw rather than nail) and the job is done

NewtoDIY

mart.vader wrote: »

Who told you that 18mm chipboard would be too heavy and wouldn't be strong enough?

Have read lots on this and a builder who worked on the property said it would be suitable for light storage. Chipboard is very heavy. Add to this my weight + the stored items and lath plaster ceilings, I'd rather be cautious.

NewtoDIY

Jonesya wrote: »

Have a look at 18mm softwood plywood, I think that's somewhat lighter than chipboard.

Also - I'm struggling to visualise where you want to insulate so that you need to sandwich insulation between sheet. Is it just the eaves you're insulating or the loft space in general?

The eaves area in a cold roof room at the top design. The two eaves spaces either side of this room are the only dry storage areas we have. Loft space is insulated with regular insulation as there's only 80cm head height.

NewtoDIY

vaio wrote: »

I'm guessing the OP wants to lay insulation board on top of the joists, when it does need to be sandwiched between two sheets of chipboard or similar.

OP.......easier solution might be to cut the sheets and lay them between rather than on top of the joists, then you'd only need one layer of chipboard. It wouldn't be particularly wasteful as you use the off cuts at the start of the next sheet.

For example...you joists are 310 centres (you sure? seems too small) so 260 gap. Take your 1200 wide sheet and cut it into four 260 wide strips which will leave a 160 wide offcut. Take the next sheet and cut a 100 strip off it to use with the 160 wide offcut and then do another four 260 wide strips.......repeat as necessary.


use these strips to fit between the joists, lay chipboard on top of joists (screw rather than nail) and the job is done

I wasn't able to insulate as you suggested between the joists in the eaves as they were all non-standard sizes. - approx. 27.5cn wide. So what I've done is insulated with loose fill (I think warmcell) up to the height of the joists. I didn't want to place anything of weight directly on these lath plaster ceilings so the loose fill was the best option.


My plan was to board out completely and buy 18mm chipboard to lay on top of the joists followed by 100mm Celotex. But as you noted and as they said to me on the phone, Celotex can only be walked on if it is sandwiched between a firm surface.


The soft plywood idea sounds interesting - I'll look into it.

Gloomendoom

Do you really mean 'eaves'?

The eaves are where the roof overhangs the outside wall.

NewtoDIY

That's a modern construction diagram. This house has a room in attic design (hence only 80cm head height). Either side of the top room the are hatch doors which lead to the eaves spaces. These spaces measure 1.42m x 3.95m.
The roof is sloping as you enter these spaces but you can still stand in there.

Jonesya

If you're just boarding out your loft and looking to insulate over the joists/under the boarding, have you considered cross-battens or loft legs?

You've got some weight in the battens but they do help spread the load over several joists and then you only need a single layer of boarding.

[Edit] If you've got clear access to the walls at both ends you might even be able to hang the cross battens and shift some of the weight onto the wall.

NewtoDIY

Jonesya wrote: »

If you're just boarding out your loft and looking to insulate over the joists/under the boarding, have you considered cross-battens or loft legs?

You've got some weight in the battens but they do help spread the load over several joists and then you only need a single layer of boarding.

[Edit] If you've got clear access to the walls at both ends you might even be able to hang the cross battens and shift some of the weight onto the wall.

I did think about cross battens but they would need to be 3.95m long and I'd have no way to get them into that space. Also I don't know how to secure them to the walls correctly?

Loft legs are no good as they would compromise head height, hence my use of pir insulation instead.