Options for loft insulation AND storage please

[Ecohouseconvertor]

Options for loft insulation AND storage please

Hello there, I am in the process of insulating the loft in my Victorian house. But I also need to use the loft for storage. I'm interested in people's opinions on how to achieve this please.

Here's what I know:

- I am going to use 270mm of mineral wool or rockwool insulation, as it is cheap and easy
- I know that you mustn't compress the insulation once laid, as squashing it stops it working as well (obvious really!)
- So I am not going to put boxes directly on top of the insulation, nor am I going to screw boards down at joist height. But I need to find a way to store these boxes in the loft. They are not heavy, but there are lots of them and I don't have the space elsewhere.

I've looked online and my options seem to be:

- to raise the joists with timber to above 270mm and cross-batten, but I'm worried this will add quite a bit of extra weight in the loft and I don't have easy access to get all the timber in? What do people think about this extra weight?
- not use mineral wool or rockwool but instead use PIR boards (eg Celotex, Kingspan). But this works out much more expensive to get the same insulation value. I've also heard of condensation issues when you put boards directly above solid insulation? Have people come across this problem?
- use some new products I've seen, like Loft Stilts (http://loftstoragestilts.com) and StoreFloor (http://www.loftzone.co.uk) , which both provide a raised platform above the insulation. Has anyone tried these? What do you think of them?

Any advice gratefully received, thanks!

 

[Perry525]

All forms of insulation use air as the object that slows the

passage of heat to cold. Mineral wool/rockwool transmits heat

along its fibres, it also allows warm air and water vapour to

pass though it. The water vapour can and does freeze inside

and when it thaws makes the insulation wet, wet insulation is

useless. Cheap but inch for inch not very good.

Polystyrene brought to market 51 years ago, is pockets of air

trapped inside thin plastic balls laid out in sheet form. It is wind

proof, waterproof and if thick enough water vapour proof.
If it is underwater or covered in ice it still works.

You can pay a lot of money for proprietory brands of

polystyrene, there is also the generic forms available from

Wicks and other people that are cheaper. Inch for inch and

price its about as good as it gets....and it is available.
You can cut polystyrene with a sharp knife, a saw or a hot

wire.

Fitting sheets of polystyrene as a push fit between the joists

will provide a better result than rockwool, it will also enable you

to fit floorboards, walk about safely and store your boxes with

compromise.

You may or may not have a ventilated roof, but note, the

passing wind creates an uplift effect above and down lee of a

house which pulls your expensive warm air out, tight fitting

insulation stops this and will save you money.

 

[tony1851]

Cheap but inch for inch not very good.




.

Eh? Sorry, but inch-for-inch, expanded polystyrene board is no more thermally efficient than the average mineral wool quilt.

 

[JohnD]

passing wind creates an uplift effect above and down lee of a house

 

[Ecohouseconvertor]

Perry525, thanks for taking the time and trouble to write your post. But Tony1851 is right, expanded polysytrene is about the same as mineral wool in insulation terms. So I'd need about 270mm of it, just like mineral or rock wool. And mineral or rock wool is much cheaper. (Which is probably why not many people use polystyrene!),

So I've still got the dilemma of the options I posted originally: raised joists, Celotex or a raised loft floor with Loft Stilts of StoreFloor. Does anyone have any views on these please?

 

[Perry525]

Perry525, thanks for taking the time and trouble to write your post. But Tony1851 is right, expanded polysytrene is about the same as mineral wool in insulation terms. So I'd need about 270mm of it, just like mineral or rock wool. And mineral or rock wool is much cheaper. (Which is probably why not many people use polystyrene!),

So I've still got the dilemma of the options I posted originally: raised joists, Celotex or a raised loft floor with Loft Stilts of StoreFloor. Does anyone have any views on these please?

=========================
Tony. Is wrong!
Not only is polystyrene better inch by inch it is wind proof and water proof.
It can be under water or covered in ice and it still works. You cannot say that of rockwool. You can also pile things on it without it deforming and lowering its insulation value.
Put simply....go on the net compare the figures!

 

[Ecohouseconvertor]

Here is a good guide to insulation values. Polystyrene is on page 5. You can see it has roughly the same insulation value as mineral wool.
http://tinyurl.com/8hjtcmu

The lower the k value, the better (it's the thermal conductivity). Expanded polysytrene is about 0.038. (Not 0.38, that would be terrible, and is a typo) Mineral wool is about 0.035. Google other sites if you want to confirm the figures, they all say about the same.

I appreciate you can store things on top of 270mm of polysytrene, but I don't want 270mm of polysytrene. Especially as it is flammable! Really, this forum post was about storage options above mineral wool, or possibly PIR. I didn't really want it to get turned into a discussion about insulation materials.

Does anyone have views on the storage options I mentioned in my original post please?

 

[freddiemercurystwin]

Perry525, thanks for taking the time and trouble to write your post. But Tony1851 is right, expanded polysytrene is about the same as mineral wool in insulation terms. So I'd need about 270mm of it, just like mineral or rock wool. And mineral or rock wool is much cheaper. (Which is probably why not many people use polystyrene!),

So I've still got the dilemma of the options I posted originally: raised joists, Celotex or a raised loft floor with Loft Stilts of StoreFloor. Does anyone have any views on these please?

=========================
Tony. Is wrong!
Not only is polystyrene better inch by inch it is wind proof and water proof.
It can be under water or covered in ice and it still works. You cannot say that of rockwool. You can also pile things on it without it deforming and lowering its insulation value.
Put simply....go on the net compare the figures!

EPS is better but only marginally.

50mm Celotex has an R Value of about 2.35
50 mm EPS (polystyrene to the OP) has an R Value of about 1.25
50mm Rockwool Roll (the kind used in lofts) has an R Value 1.14

Depending on the sources you believe it is believed that phenolic foam insulation (like Celotex and Kingspan) leaks its gas over a period of about 10 years when it ends up no better than polystyrene. Though manufacturers will tell you that whilst this was an issue it is now resolved.

But @ the OP and his original question, for my money I'd be fitting 150x38mm joists perpendicular to the originals and squeezing in a couple of layers of 100mm mineral wool. The stilts don't spread the load as joists will. There are hundreds of threads on this in the Floor section, this is the same old route that most end up going down.

 

[Perry525]

Freddy, while manufacturers like to make their product read the better buy, in real life situations, not in the lab, it is impossible to make rockwool an air tight fit.
In real life you have warm air rising through and round the product.
I have seen lofts where the insulation has been so badly fitted, that where at first glance the loft floor appeared to be covered, when fitted correctly the insulation covered less than half.
Warm air does not pass through polystyrene, heat does but attenuated.
Because polystyrene can be compressed, and it springs back to size, careful fitting does make a difference.

 

[freddiemercurystwin]

Yes OK Poppet whatever, cos they'll be so much air movement in a 150 void with 200mm of mineral wool insulation won't there? And getting your polystyrene to tuck into all the tricky areas round the eaves would be good to watch too. Muppet!

 

[Perry525]

Freddy, you are supposed to come back with an erudite reply.

 

[freddiemercurystwin]

No need, a simple answer for a Simpleton.

 

[Perry525]

Freddy, surely you can try to offer something useful?

 

[freddiemercurystwin]

I have done so already, I put you in your place and gave a comprehensive answer to the OP.

 

[tony1851]

[

It can be under water or covered in ice !

I don't know if polystyrene 'works' (whatever that means) under water, but that is hardly likely to be relevant to the environment in the OP's loft.

OP; the only practical way I can see you getting any cheap insulation and storage is to ;1. put full-depth (ie 3" or 4") glasswool between the ceiling joists; 2. put some 4" x 1 1/2 " joists over the existing ceiling joists, at right-angles (perhaps steadied by small angle-brackets).
3. put a further 4" quilt between those
4. board over with 1/2" sheathing ply.
Obviously this doesnt give you 270mm, but it would be a considerable improvement.
And dont worry about ice in your loft, or 'the passing wind creating an uplift up and down' or whatever it was.