loft rafters and insulation ... or not

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i have now fully boarded the loft floor and am about to start on the "walls" my question is do i ned to actually insulate between the rafters or can i staple a breathable membrane across and plasterboard straight on to that? the reason i ask is that the rafters are very old and only the thinnest insulation would be able to leave the 50mm void for ventilation. my idea was to leave them as they are without insulation on the basis that the membrane followed by plasterboard would be enough of Insulator and would also allow me to install halogen downlighters (spots).
 
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i think the answer to this question depends very much on the answer to the question : "what do you intend to do with the loft once it is finished?" as plasterboard and membrane have no real insulating effect, compared with say 270mm of rockwool or 140mm of cellotex.

Doing it your way will leave you with a very cold loft!
 
it's ultimately going to be a "den" of sorts for the son's Xbox and hifi etc.
So ... of i fill between the rafters with "fibre" insulation leaving a gap between that and the roofing felt and then staple the membrane over that and then Plasterboard would that be right? if i'm fitting downlights into the plasterboard though, i'm presuming there would need to be some "space" left in the insulating material around the transformer and lights themselves?
 
If you want to achieve a decent amount of insulation using fibre insulation, you are going to have to use 50mm of mineral wool slabs between the rafters and then about 130mm onto of the rafters then boarded over.

I would somethink like Kingspan or Cellotex between the rafters, say 25mm if thats all you can fit, then another 80-100mm of cellotex bonded to plasterboard ontop.

This is what you would use for a loft conversion to comply with the regs concerning insulation (i think- an expert may be along in a minute to tell me i am completely wrong :oops: )

Any less than this and the loft will be very cold, and all the heat from your house will escape.
 
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an expert may be along in a minute to tell me i am completely wrong :oops: )
The experts on here are sometimes reluctant to post on the subject of dubious loft conversions, that's not to say they may not support such activities privately, just are reluctant to add professional advice on potentially dangerous conversions especially where kids are concerned.
 
an expert may be along in a minute to tell me i am completely wrong :oops: )
The experts on here are sometimes reluctant to post on the subject of dubious loft conversions, that's not to say they may not support such activities privately, just are reluctant to add professional advice on potentially dangerous conversions especially where kids are concerned.

Fair point, well made!

As you can probably tell I am no expert, so any advice is given as such!

On a side note- check out CE184 from the the energy saving trust. They give some good advice on how to insulate.
 
Why is Ben the lawyer (charging £250 per hour) not having a full loft conversion done?

Andy
 
Why is Ben the lawyer (charging £250 per hour) not having a full loft conversion done?

Andy

Hiya Benlawyers is the name of the first mountain i climbed (i.e. i'm not a lawyer ;) )

my son is only with me once a week and every other weekend and has a bedroom at mine. the loft is too small for a conversion but now that the floor is boarded, there is enough space for a bean bag, TV, etc. As the crap that was up there certainly outweighs any strain he's gonna put on the floor by sitting on it. it seemed to make sense to give him a teen den and a nicely finished loft space. there are also 2 velux windows which were already installed so all i'm loking at really is making a comfortable temporary space rather than a full blown "room"
 
You must insulate otherwise your child will freeze, however the specific circumstances you outline give options other than the full 270 mmm or equivalent.

How deep are your rafters and how much height can you afford to lose in current space ( not forgetting that your child will grow ! )
 
You must insulate otherwise your child will freeze, however the specific circumstances you outline give options other than the full 270 mmm or equivalent.

How deep are your rafters and how much height can you afford to lose in current space ( not forgetting that your child will grow ! )

i'd need to measure again but i think 6x2 there is plastic sheeting behind roof tiles and Felt in some areas. now that i have exposed all the rafters i am definitely looking for an insulator. i'm installing LED downlighters to minimise heat from lighting within the insulation. i would like to use fibre insulation (same as between flooring joists. then a breathable membrane stapled across the rafters then Plasterboard. just concerned whether that'l give me enough circulation. as far as space is concerned, i can't really add anything to rafters without encrouching too far. it's not a "walkabout room" more of a sit and crash but still would like to retain what height it's got.
 
The rafters in my house are 100mm deep and I want to add insulation as the loft is used for model railways and will never be converted so no plasterboard will be used.

The felt is breathable and fairly new. Would an air gap of 25mm be acceptable if using polystyrene sheets of 75mm thickness? What screws/fixings do you use to attach the polystyrene to the additional battons I will add along the inside of the rafters?

Thanks!

Tom
 

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