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insulation board. what way round should foil side face?

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woodworm2009

from United Kingdom

Joined: 17 Aug 2009
Posts: 22
Location: Herefordshire,
United Kingdom

PostPosted: Thu Dec 17, 2009 3:15 pm Reply with quote

I am using insulation boards which have foil on one side.

which way should the foil face? facing into my room or facing out?

I am using the insulation boards directly onto the walls of my trailer.

The walls of trailer consist of outer aluminium skin, rockwool (i presume) insulation inside and a 3mm plywood sheet to enclose.

this is not warm!

I have bought sheets of insulation board and am attaching directly onto wall with no gap and then boarding over with hardboard.

Does the foil side need to be against the existing wall or the hardboard side facing into the room.

Do i need an air gap between wall and insulation board?

I have no damp on the walls.

any advice would be great.

thanks
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mointainwalker

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PostPosted: Thu Dec 17, 2009 6:01 pm Reply with quote

Insulation board is impermeable to water vapour and so the foil serves no purpose unless it us as a tiny amount of insulation. It doesn't matter which way you fit it.

You don't need to leave any gap, but what you DO need is a vapour-barrier to prevent the warm-moist air inside penetrating in to the rockwool and condensing becuse of the severe cooling effect of the outer-skin.

The easiest thing to use would be large poly-sheets from DIY sheds which are sold as protection when decorating.

However I'm farly certain that this is the scenario that you currently have i.e. no vapour-barrier fitted on warm-side of insulation because of the difficulties of doing so will all ribs etc.

If this is the case your existing insulation will be wet. The result is not simply that it is wet, but that it has lost all its insulating properties as water is a superb conductor of heat.

If I were you I would remove a small panel of the plywood to check on the original insulation. If it's wet there is little pont in further insulation until it has dried out and you install the vapour barrier to stop the problem re-occuring.
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woodworm2009 (18 Dec 2009)
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noseall

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PostPosted: Thu Dec 17, 2009 6:22 pm Reply with quote

Foil to the warm side. Foil tape all joints.
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woodworm2009 (18 Dec 2009)
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mointainwalker

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PostPosted: Fri Dec 18, 2009 11:45 am Reply with quote

@noseall

What difference does it make which way the foil is ?

The board is impermeable and so the foil is only adding a tiny incremental amount of insulation and it will do that, I believe, equally on either the warm or cold side.
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woodworm2009 (18 Dec 2009)
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woodworm2009

from United Kingdom

Joined: 17 Aug 2009
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Location: Herefordshire,
United Kingdom

PostPosted: Fri Dec 18, 2009 2:11 pm Reply with quote

mointainwalker wrote:

If I were you I would remove a small panel of the plywood to check on the original insulation. If it's wet there is little pont in further insulation until it has dried out and you install the vapour barrier to stop the problem re-occuring.


I cant remove the wall to look in the cavity but i presume it is as minimal as it is in the roof ( when i put wood burner in i can see there is the ali outer skin a thin layer of fluffy insulation stuff and then the layer of 3mm ply making my interior ceiling)

The insulation board i have has foil on one side and some kind of white almost fibreglass matting like stuff on the other side. (foam stuff in between)

Do i really need to put plastic sheet on the wall inbetween?

I am now wondering if the foil should face onto the existing wall, so facing outwards from the room, would this be a 'radiant barrier'? - keeping heat out if hot outside, keeping cold out if cold outside.

I am confused that if the foil is facing in will it just make my room into a cool box if the room is cold etc.

but will the foil touching the existing plywood wall cause it to get wet and thus damp and rot?

I am not a professional and am trying to do this quickly as its freezing.
its only a rented static trailer so i cannot afford to get a pro in.

Thanks
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noseall

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PostPosted: Fri Dec 18, 2009 5:21 pm Reply with quote

mointainwalker wrote:
@noseall

What difference does it make which way the foil is ?

The board is impermeable and so the foil is only adding a tiny incremental amount of insulation and it will do that, I believe, equally on either the warm or cold side.


There are always gaps. Ever tried to cut this stuff for a perfect snug fit? So, the thinking is, tape all joints and keep the 'skin' continuous.
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mointainwalker

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PostPosted: Fri Dec 18, 2009 6:46 pm Reply with quote

Of course I agree with you, but what does that have to do with whether the foil is facing in or out ?
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noseall

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PostPosted: Fri Dec 18, 2009 6:51 pm Reply with quote

mointainwalker wrote:
Of course I agree with you, but what does that have to do with whether the foil is facing in or out ?


..begs the question, why do inso' companies bother withn a foil covering at all. Maybe you are missing something Mountainwalker.

...use the force....mo..er..walker.
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woodworm2009

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PostPosted: Fri Dec 18, 2009 7:00 pm Reply with quote

If i appear to be asking same thing i appologise but i am confused.

I have a static mobile home.
The walls are made of the outer skin (aluminium) then in the gap is some kind of insulation, then there is a 3mm sheet of plywood. Thats all my outer walls are made from.

I have bought insulation boards from a seconds place so i don't know what type they are and have no instructions.

The boards have foil on one side, some kind of expanded foam stuff and a white matted sheet (feels a bit fibreglass like but not sure what it is) completing the board.

I have put the board white paper side against the existing inside plywood wall, then put hardboard over it (on foil side) and then screwed it in the corners to the wall.

I have gaffa taped the edges of the board to enclose the foam stuff from being exposed at the sides.

Is what i'm doing just completely wrong?

It is a rented trailer so i cant glue the stuff to the walls as it needs to be removable if the next tenant or landlord wants it gone.

I have just finished being a student and have no job so am trying to insulate as cheaply as possible. Also i dont want to spend loads as its not MY home.

Do i need to have the foil facing into the interior of my room or facing outwards thus up against the plywood wall?

Do i need to have an air gap?
if so can i just put a baton across the top and bottom of wall and screw into that?

The plywood walls are not wet in my home but when my clothes in the cupboard touch up against it they get damp...

I have unscrewed a bit of the insulation that has been up for a week now and the plywood wall feels incredibly cold and its hard to tell if its wet or not... it is not visibly wet but its so cold it feels like there might be moisture there.

I desperately want to make my home warmer but i dont want to accidently wreck it and cause a damp problem and rot the plywood walls.

Please please can anyone offer me some advice and way of sorting this out in a very basic explanation as i am getting lost on some of the abbreviations and professional terminology.

Thank you.
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mointainwalker

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PostPosted: Fri Dec 18, 2009 7:24 pm Reply with quote

If you want to be warmer, then what you have done is fine and will help you, although to be honest a caravan, given space limitations is going to be cold .

I don't think it matters which way round the foil is, but you see there is not unanimity so you choose.

It is in any case of very minor significance in insulation terms compared to the board. What type and what thickness have you got ?

As I wrote before a vapour barrier - either a plastic sheet as I suggested or taping as noseall says - will stop moisture condensing in the little original insulation that exists and this will then keep you warmer ( a bit )

No you don't need an air-gap. Fill the available space with your insulation-boards.

As for your clothes, I'm sure they will always feel damp in the mornings because there will be a lot of condensation on the windows, roof/ceiling etc and the humidity is easily taken up by textiles.

How are you heating currently ? If it's by gas or parafffin you should know you are creating hue amounts of water-vapour. It's always quoted that one litre of paraffin creates one litre of water-vapour when burned, although that has always seemed enormous to me.
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woodworm2009 (18 Dec 2009)
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mointainwalker

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PostPosted: Fri Dec 18, 2009 7:32 pm Reply with quote

@noseall

I don't know why insulation cos. foil-coat their boards.

I could believe that it is solely for marketing reasons to combat the multi-foils as potential buyers see both products are shiny and think they are both usung the same "technology"!

It is quite possible I am missing something and I would be happy ( well, a litle bit anyway) to be enlightened, so please tell me ?
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woodworm2009

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Joined: 17 Aug 2009
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Location: Herefordshire,
United Kingdom

PostPosted: Fri Dec 18, 2009 7:58 pm Reply with quote

Thanks for reply.

I am currently just using an electric oil filled heater, i will be using my wood burner once i have extended the flu pipe (not enough draw).

So i should not worry about the coldness of the plywood wall against the foam insulation board? There wont be any damp?

Or am i just being dim and do i need to get the polythene sheet and put it inbetween the plywood wall and the insulation board?

Or do i put the poly sheet in between the hardboard and the insulation board (foil side).

I am not opening the existing wall in any way so the insulation board is going on the existing wall internally.

thanks
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woodworm2009

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Location: Herefordshire,
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PostPosted: Fri Dec 18, 2009 8:01 pm Reply with quote

Oh forgot thickness is on one wall about 30mm maybe a little more and on other wall its about 15mm.

The boards were seconds bought on a pallet so various thickness but i have stayed consistant size on each wall!
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woodworm2009

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Location: Herefordshire,
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PostPosted: Fri Dec 18, 2009 8:08 pm Reply with quote

mointainwalker wrote:


You don't need to leave any gap, but what you DO need is a vapour-barrier to prevent the warm-moist air inside penetrating in to the rockwool and condensing becuse of the severe cooling effect of the outer-skin.


Do i need to put the plastic inbetween the insualtion board and the plywood wall?
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woodworm2009

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Location: Herefordshire,
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PostPosted: Fri Dec 18, 2009 8:35 pm Reply with quote

found this bit of info at http://www.viking-house.ie/Insulation-facts

An uninsulated wall usually has the Dew Point at the centre and the inner wall face is warmer than the external face. If you dryline you move the Dew Point to where the insulation and the wall meet and the wall now becomes a cold wall. With the new Airtightness regulations there will now be less airchanges so the air is your house will have higher water vapour levels. The joints between insulation backed plasterboard are never sealed and with high air pressure inside the house, water vapour will get in behind the insulated plasterboards and condense on the Cold Wall causing fungus and mould growth. The only way to avoid this is to leave an airflow between the insulation and the drylining. This means that the combination of a partial fill cavity wall with drylining isn't possible as the ventilated cavity behind the drylining messes up the U-values. External Insulation moves the Dew Point to the outside which is much safer.
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