loft insulation + nightmare access - advice please!

22 Jan 2004
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United Kingdom
Hoping for some advice .... Please forgive the very long post. I've tried to research this but am now stuck and really need others' input.

We have a 1950s chalet bungalow with 3 dormer windows across two attic bedrooms. See plan View media item 53907
Hopefully the plan shows that a narrow triangular attic space runs all round the two rooms with access through a small door in one of the the dwarf walls. The space is partially boarded out but the joists are really deep so there's probably about 15cm of insulation where it's been laid. The outer dimensions of the attic space are 6m 30 x 9m 30 and the slope of the roof is about 2m long. There's an average 35 cm gap tween rafters which are 75mm deep.The roof is tile with breathable felt.

This side marked A on plan (turn head) View media item 53899 of the attic is the widest because there's no dormer and it's fairly easy to clamber around: but the other sides are a bit of a nightmare crawl through - and I'm 160cm tall. pic taken from C: (turn head)View media item 53903
Loft insulation appears stuffed down to eaves in most places but light does come through in the odd spot - ( I pulled some insulation out here: View media item 53904) in any case should there be more ventilation here with the current set up? (there doesn't appear to be a condensation problem)

The dwarf walls in the attic/bedrooms are made of single thickness concrete blocks (apparently load bearing) which rest on the pretty deep joists and wooden floor (you can see this detail here, marked C on the plan: View media item 53902. These dwarf walls aren't insulated at all.

The dormer window sides are made of wood and can't be insulated from the inside because the existing (poor) double glazing fits the dormers exactly, leaving no space for insulation on the roof or triangular sides. External pic of dormers here: View media item 53898. Our long term plan is to either replace the double glazing with smaller windows (and add 150mm insulation to the walls and roof) or strip off the tiles and insulate on the outside of the dormers. Before we moved in we had 150mm of celotex installed on the inside of all sloping rooves within the bedrooms and the skeilings replastered.

Our real dilemma is with regards to the attic space and how to insulate that better. The bedrooms get very cold in winter and very hot in summer - in a previous post the suggestion was to add ventilation for the summer which we are still looking to do. But there obviously needs to be more insulation in the attic itself.

So Should we make the attic a warm loft or a cold loft? ( ie I think I'm right in saying that means should we insulate the floor and dwarf walls in the attic space or the roof itself?)

As we want to knock through to make kneehole cupboards in the bedrooms, have awkward water pipes running through the loft and also use the attic for storage, I'm leaning towards a warm loft. I think this means taking out all "floor" insulation and insulating the roof ideally between the rafters after leaving 50mm space for ventilation???

The rafters are only 750mm deep and as access is such a pain for measuring, cutting and fitting celotex, would it be a stupid idea to staple that Triso bubble sheet stuff e.g to the rafters instead? And if so, which is the best make?

If we did install king span/celotex, i dont think theres actual room to get 150mm in there and still be able to crawl round the attic. So what thickness would be worth it/effective for all the labour involved?

Of course the bubble wrap stuff won't be as good as celotex but is it better than nothing?

And what about the existing loft floor insulation - should I then remove it to allow warm air to rise from the rooms below? Or should we just bite the bullet and try to cut and fit one sheet of celotex a week for the next year (and then remove the loft insulation??)

Argh!!! Advice please!!!

A billion thanks in advance

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Sorry! Thank you for letting me know my post was indigestible! :)

Short version: if i want to create a "warm" loft, given our attic space access issues and the cramped working conditions would using thick foil blanket material be an ok compromise rather than cutting and fitting celotex/kingspan. If so, which blanket do you recommend and does it have to have a dead airspace on both sides? if celotex is really the only solution what's the minimum thickness required to make it worth a week's full time labour to fit it?

And once having installed some roof insulation should I then remove all loft floor insulation (especially as it seems to be stuffed down into the eaves)?

Thanks again for thoughts

That's better.

Space blanket is generally a waste of time (and space) because you need an air gap both sides.
Just use the rigid foam boards,, say 50mm betwen rafters and 50mm below, and then plasterboard. Make sure there is sufficient ventilation by leaving a 25 air gap above the insulation, and ensure eaves and ridge vents are present and clear.

(Just one "thankyou" would do; I dont need a centillion like that other guy!)

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Space blanket is generally a waste of time (and space) because you need an air gap both sides.


Tony, Isn't space-blanket fibre insulation inside a polythene envelope ? Don't believe it is foil-type.
Thank you guys for your advice. But what about the access issue? there's only a small door (located in my two year old's bedroom) to access the attic space and really only crawl space once youre inside. Measuring, cutting and fitting all that celotex and plasterboard is going to be a very time consuming job i fear. I figured the blanket would be easier and quicker to fit and be less of a health hazard ...? I know it wouldnt be as effective from an insulation perspective but would it provide something? In a worst case scenario, could the breathable felt under the tiles act as one side of the 50mm air gap, staple the blanket 50mm from the felt and then add batons to make up the final 25mm gap (rafter depth = 75mm).

Going the celotex/kingspan route (which i know woukd privide better insulation but am dreading as a project) do you have any tips on how to make the cutting, fitting process easier given the access issues?

Also, once the job of insulating the roof is done, should i get rid of the floor (loft) insulation?

Sending out a hundred thanks for this one :)

I would use iso 10 foil in your case or something similar. You could get a new roof and insulate that way.
Check out comments on thin-foil insulation It is very controversial and not AFAIK approved for use on its own in areas where BC are demanding certain values.

My opinion is that it is a total rip-off delivering only about 30% what it promises.
I am only going on practical experience, my friend did his loft conversion with it, and he uses it as his office which always feels warm when I go in there.

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