loft foil insulation

[lofthelp]

HI IF I STAPLE FOIL INSULATION ACROSS MY ROOF BEAMS INSIDE MY LOFT IS IT OK TO PUT PLASTER BOARD RIGHT ON TOP OF THIS OR NOT?

I KNOW PEOPLE USE WOOD BLOCKS ON TOP OF FOIL TO ATTACH PLASTER BOARD BUT CAN I JUST PUT THE PLASTER BOARD against IT ?

 

[lofthelp]

ANYONE GOT ANY ADVICE ON THIS YET?

 

[mointainwalker]

All the insulation foils I have read about all require an air-gap on both sides of the foil to achieve their (IMO) vastly-exaggerated performance.

Since the 25 mm that they normally require provides a certain amount of insulation itself, fixing it directly to pb will diminish the overall effect, but I can't guess by how much.

I hadn't heard of it being done, but presumably this (25 mm gap ) is the reason for the blocks.

 

[lofthelp]

your probabley right . but if anyone else no's more on this please let me know thanks.

see my problem is that i can just about only stand up in my loft now and by the time plaster board is up it will touch my head so if i use blocks to i will be walking around on my knees.

 

[noseall]

Building control will only sanction this stuff in conjunction with trusted insulation products such as kingspan celotex rockwool etc.

Do not expect it to comply when used on its own.

 

[lofthelp]

so will kingspan boards be better between the rafters then puting that foil roll right over the rafters.?

will it cause damp if i uses the foil roll with plaster board on top

 

[lofthelp]

is ther any roofers out there who can anwser my question .

 

[lofthelp]

someone out ther must no about this.

dont be shy and help me out.

THANKS

 

[eddylyons]

this all seems like a huge grey area to me as im in similar boat to you and have not found much help on the subject, what i have found is that with tri iso's and superquilt u do need the air gap betweenfoil and plaster, it should also be ok with condensation coz of the foil back, just makesure you overlap the joints correctly on your tile side so any build up runs off. im struggling as my house is old and has slate with no felt and have been asking similar questions, shall i use kingspan type stuff inbetween rafters or foil, or even kingspan backed plasterboard?? alot of people say tri iso is best?? i think im gonna go with it.

 

[lifesagasman]

i'm thinking of using double foil myself but agree i can't see a great insulation value. (if i board over i'll use battens). however it's simple and lightweight and will prevent condensation which are important factors for me as i will be carting it to France. i've seen the multiple layer stuff in use and it does appear to work well, but it also costs an arm and a leg, so it's OTT for my purpose.
i'm just a DIYer in this area, so keeping it simple is sufficient.
manufacturers websites are helpful and they've answered e-mails, too

 

[mointainwalker]

@lifesagasman

When you say "it will prevent condensation " do you mean by acting as a vapour-barrier ?

If yes, you would save money by just buying a roll of plastic sheet.

I'm not sure if you are referring to a specific product when you speak about " double foil " but you should do some checking before importing foil to France as this is where the idea originated and still has the biggest producer - Tri-Iso.

A couple of big shed sites are:

www.castorama.fr
www.leroymerlin.fr

 

[lifesagasman]

cheers, M, get back to you in a few minutes..

 

[lifesagasman]

hi, M. looked on castorama, the nearest equivalant would be a multicouche thermo-reflecteur, but these are a superior grade to what i'd thought of using, with a much higher price tag! double foil is 2 ali foil layers with thin iso between. low insulation value but i can get 60 m2 for £100 so cost effective.
i'm hoping it will keep out some of the cold (and heat) in the loft area though it's not a living space. it won't be that much dearer than vapour barrier but i only noticed that the slates were damp as i was insulating above the ceilings and warm air was getting into the loft space. and it was about -10C at the time!
should kill 2 birds with one stone, but neither problem is a serious one. my only niggling doubt is - will the 'loirs' eat the stuff? i caught one of them eating expanded poly foam- yes , literally eating and swallowing it!
i know they chew it and nest in it, but as a ready meal- i was surprised!

 

[mointainwalker]

Yes, it's amazing what the wildlife will eat. I'm putting expanded metal around the edge of my floor to try and keep them out.

If you are really interested in this foil, there is a French manufacturer called XLMat who make a product called XL Bulles which is foil-coated bubble-wrap , 3 mm thick total. haven't found any prices for it.

 

[lifesagasman]

great minds...i've put the foam-backed plasterboard on some of the external walls and closed the bottom edge with galvo mesh. strange how these ideas develop. they were 2.7 boards for a 2.9 height so i've used a 200mm infill at the bottom and run cables and pipes behind, covered by the galvo. now all the first fix is hidden and if i ever need/want to make changes i will only damage the infill. skirting is screwed and plugged onto the board.

edit-- as a detail, i think i folded the galvo into the floor/wall corner first, then fixed pipes/cables on top of that. that way any intruders from the ceiling void can't get to the cables. the galvo was stapled to the wall then dotted and dabbed for the board. i'm hoping that if i get round to changing the floorboards i will have enough space just by removing the skirting.
since the iso boards now stand 50mm proud of the original wall plane, it's a theory which may or may not work in practice.
as a cosequence of using iso board i've noticed that the walls don't breathe so easily and i get a bit more condensation on the singleglazing. i guess for every action there is a reaction...