Easiest way to fix polystyrene sheet to struts?

[Lusi83]

I'm insulating an existing room in the eaves - it is plasterboard strut wall and is a bit of a mess - lots of uneven noggins, boards fixed to the plasterboard, odd shaped bits... pipes go through etc...
I'm fixing 25 mm and 50 mm polystryene sheets between the struts (making 75 mm thickness where possible) so it is level with the struts, filling the odd gaps with expanding foam...
Ideally I want to then fix 25 mm polystrene over the top of the struts to stop cold spots...
It is a storage area -so I don't need to plasterboard and it would be a nightmare to fit it with the pipes and odd shapes, limited access (I have to crawl!) - even just hardboard would be difficult...

So could I use something like 'no more nails'? Or another type of glue or fixing? I do intend to seal between the sheet edges with expanding foam...

 

[PrenticeBoyofDerry]

Staple them
Do you have any electrical cable in the stud walls you are insulating with polystyrene?
Two reasons I ask this question, both regarding safety!

 

[Lusi83]

Hi
Don't think my (cheap) staple gun has big enough staples...do they normally?

There is some cable - I've read about polystyrene and PVC cables - it is only a problem if they are actually touching each other???
I have pulled them away from the struts and intend to get some type of plastic ducting for them to run across the top of the polystyrene - which I believe should be sufficient? Was going to look more into which kind of ducting to get etc once the boards up ...(taking up huge amount of space right now and children enjoying making 'snow' with them...)
Also thought that if I had to put wooden batons across I could run the cable along that???
Any advice about that as well would be appreciated...

 

[Lusi83]

Ahhhh - just realised I think you can get some staple things you knock in with a hammer???
(memories of 'helping' putting up fencing as a child on my grandparent's farm...)
Are they the kind you mean....

 

[PrenticeBoyofDerry]

Staple using one of these
http://www.screwfix.com/prods/10110/Hand-Tools/Staplers-Riveters/Staplers-Nailers/Staple-Nail-Gun.
Lots easier and quicker than messing about with anything else.

The PVC sheathing on some cables reacts with polystyrene causing marring, which will make the PVC brittle.
If you run cables in conduit, it could well reduce the the current carrying capacity in that cable, lighting circuits on 6 amp MCBs and 5 amp fuses are normally okay, but any other power circuits such as sockets, showers, cookers etc... will need to be calculated and factored in.
So your best option would be to form a barrier between the cable and polystyrene, this would be best if plastic, plasterboard or wood etc.. but not metalic unless you connected the metalic barrier to earth.
The other problem would be if you used a diffent type of insullation as this will also effect the current carrying capacity, if the cable was surrounded by it.

 

[foxhole]

http://www.wickes.co.uk/Insulation-Fixings/invt/510007?source=123_4
Something like this to fix over the timber .Staplers simply won't do it.

 

[PrenticeBoyofDerry]

I do apologize, my head must be up my arse
For some reason, I thought you were installing the polystyrene sheets then putting polythene sheets over them as a vapour barrier!
That's why I suggested the staples, to staple up the polythene sheets to the timbers, therefor not only an added vapour barrier but will also hold the polystyrene back.
But if you cut the 50mm polystyrene sheets, so it's nice and tight between timber studs, it should stay put.
Then you can lay the 25mm sheets over the studs and trap these in with some some roofers lathe, nailing or screwing in to your stud work.
Sorry for the confusion, one of them days

 

[Lusi83]

Thanks - Feel like I'm getting into more and more of a mess (this minor refurbishment is turning into a major nightmare...)

First the plastic things from wickes - what do you do with them - hammer them into the struts through the polystyrene? Look like the easiest - if more expensive option ...otherwise the roofers lathe route ...


I didn't think I needed a vapour barrier - because it is into what is basically a sideways on loft space...(and there is lots of ventialtion - had to take down rafter insulation - looked like my roof was leaking but roofer thinks it is just condensation ) Please don't tell me I'm wrong...

And the cable - I could staple up polythene sheeting and put the cable over the top? or even just a piece of wood...there are 2 major looking cables but the rest are the two lights in there and the switch...
The feed for the lights comes down the sloping roof bit - I have put it on the top of that bubble wrap foil insulation stuff which is over a polystryene sheet....hope that is ok ( foil bubble wrap won't conduct electricity will it?)

 

[PrenticeBoyofDerry]

Sounds like your roofer has given you the correct advice regarding the insulation causing condensation, it will do if ventilation is not offered between the insulation and your roof tiles.
Providing the cables are clipped securely every 300mm you should be okay.
The plastic fixing for insulation should just tap/push in, I think they will fit the two layers of polystyrene sheets together, you can get simular types that will fit your poly sheets in to wood and stone.
with regards to the Vapour check barrier, polystyrene sheeting does have water resistant qualities, so I don't see an issue with using it in this instance, just me getting confused with your original post, for some reason got it in to my head that you was also installing polythene sheeting
But just in case we are missing something.
What exactly is wall and what purpose is it serving?

 

[Lusi83]

There was an approx 5cm gap between the insulation and roof (mine is wooden boards covered with felt and then tiles - a scottish thing I think) it was wet in one patch a rafter width so I assume it had just been pushed in around there ... but there was some mould growth and it must have been like that some time - pure luck that I noticed it before any serious damage (looked ok from the inside) and I don't think it worth the risk to keep the rest up...
(BTW I was very aware of the need for ventilation - I paid a company to insulate the rafters of the rest of the house a few years ago and they did a really really bad job - I think I'll post it in DIY disasters- in the end I took it down and now I really realise just how damaging it could have been it...)

The wall is from a bathroom extended into the eaves...I posted about insulating it before then I realised that the rafter insulation had to come down..(general DIY "insulating a room in the eaves")...so now I'm doing the best I can on the walls...

Thank you for the help and advice...