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PostPosted: Fri Oct 20, 2017 8:11 pm 
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The new rafters have been spec'd (sort of) as 125mm deep (sistered to 75mm truss rafters)
Its tar paper/felt, so a 50mm air gap has been allowed, then 75mm cellotex, then 32.5 insulated plasterboard over the lot, so a total of 100mm of insulation.

Putting that into a U value calculator, i get a calculated U value of 0.24w/m2k.

Bit confusing these U values, from what i can make out, its acceptable? but could be better... higher the number, the better?
I suppose thicker insulated plsterboard would help.

This still needs to visit BC, but I could do with a little more understanding.

If the 75 is okay'd, can i put in 25mm, then 50mm, or do i need to just cut out the bit where the trus rafter encroaches on the space the insulation takes up on one side...?

Insulation seems a pain at the moment, ive been pricing it up at 75mm, but long lead times on it, local merchant quoting me 5-6 weeks :roll:


Foil blankets... perhaps id be better looking at that too?

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PostPosted: Fri Oct 20, 2017 8:28 pm 
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We’ve just did a loft conversion and that’s the same amount of insulation we used. The vertical wall we built under the rafters tho,had 100mm then insulated board and we used velux windows. Gable wall was 90mm stud,90mm insulation then insulated board. I think the whole rooms u values is calculated within the entire houses if you know what I mean.
You can add tri-iso super quilt foil on top of rafters to hike the u value up but it’s expensive.
We put 300mm of fibre insulation in the small ceiling void as well.



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PostPosted: Fri Oct 20, 2017 8:38 pm 
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Cheers Stevie,

What p/board did you use, 25 or 50 insulation?
Im a bit pushed for space on one gable, i was hoping to dot and dab staright onto the thermalite... reckon i'll get away with that? :lol:

Theres 200mm fibre going on the flat section, much more and itll impede the vented ridge tiles.

Was the 100 on the verticals just because thats the sixe of the stud timbers? I suppose it could help a bit.

Its a fair whack of boards I need, think its virtually 40 8x4s

Can it be layered Steve, or will i have to notch the edge of the board do you know?

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PostPosted: Fri Oct 20, 2017 9:36 pm 
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Hitch wrote:

Insulation seems a pain at the moment, ive been pricing it up at 75mm, but long lead times on it, local merchant quoting me 5-6 weeks :roll:


Celotex have stopped supplying so it's caused chaos with insulation supply at the moment. Appears to be a knock on issue from the Grenfell tragedy.

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After careful consideration, we have taken the decision to temporarily suspend supply of some of our 5000 product range in light of a recent and unexpected test result. This relates to Celotex FR5000, Celotex CG5000, Celotex CF5000 and Celotex SL5000 which share the same insulation core and facer.

We recognise that this decision could have some practical implications for some of our customers for which we apologise. We hope in the present circumstances which are explained in further detail below, that customers will understand the reasons behind our decision.

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PostPosted: Fri Oct 20, 2017 10:20 pm 
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darrenba wrote:
Hitch wrote:

Insulation seems a pain at the moment, ive been pricing it up at 75mm, but long lead times on it, local merchant quoting me 5-6 weeks :roll:


Celotex have stopped supplying so it's caused chaos with insulation supply at the moment. Appears to be a knock on issue from the Grenfell tragedy.

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After careful consideration, we have taken the decision to temporarily suspend supply of some of our 5000 product range in light of a recent and unexpected test result. This relates to Celotex FR5000, Celotex CG5000, Celotex CF5000 and Celotex SL5000 which share the same insulation core and facer.

We recognise that this decision could have some practical implications for some of our customers for which we apologise. We hope in the present circumstances which are explained in further detail below, that customers will understand the reasons behind our decision.



Apparently its a shortage of the main ingredient of the PIR foam, only a few types of the cellotex have been stopped i'm told, but i guess others have been used as a substitute.

Enquiered at 4 places today, few odd boards in stock, but nothing for bigger orders. :roll: :roll:

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PostPosted: Fri Oct 20, 2017 10:47 pm 
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We notched the boards,the timber apparently has a u value so the bc don’t mind us doing it.
We used the insulated boards with plasterboard attached that were approx 38mm thick. You can cover with 25mm insulation then clad 12mm plasterboard on top also. This is more time consuming tho.
The stud wall under the rafters were specified at 95x45 c16 as support and 90mm insulation was specified too. We also put a vapour barrier on prior to boarding.
We were told to use kingspan or celotex but we use rectocel or any other generic rigid board,they are way cheaper.
Every loft conversion we do differs slightly regarding insulation specs depending on which architect has done the drawings tbh.



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PostPosted: Tue Oct 24, 2017 10:29 pm 
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Not sure Rectocel is the right spelling Steve... just googled it :lol:

Have found it though :lol:

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PostPosted: Wed Oct 25, 2017 7:25 am 
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Just a note on the supply problems:
There was a fire at a factory in Germany a year ago which was one of 4 places in the world where a key ingredient for PIR boards called MDI was made.
Further to that there were 2 more problems, one in Germany, one in Belgium, these related to one of the other raw materials for the boards.
On top of that there is Grenfell, for which Celotex have now pulled out all of their 5000 series boards from manufacture while fire testing is carried out.
I've just found out all about it yesterday while trying to source enough boards for a small side extension we are doing (relatively small amount) and there is very little of the stuff around..... None in any Jewsons, Travis or Parkers branches in the whole of the South East.... I drove all around the county buying from 3 different places to get what we needed. One was a Jewsons who were waiting for the lorry from France carrying PIR boards which were all sold before even unloading it. They had been waiting 2 weeks for that order and the next won't be for another 2 weeks...... Not a good situation for any of us...... Luckily I got in on this delivery on the phone in the morning and they held me some back.
All in all this doesn't look good for us for the forseeable.... I think it is time for the space blanket roll types to shine now, and also go back to using the old fibre glass stuff.

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PostPosted: Wed Oct 25, 2017 9:59 am 
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There is a certain irony in that 'There was a fire at a factory in Germany a year ago which was one of 4 places in the world where a key ingredient for PIR boards called MDI was made.' :lol:

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PostPosted: Wed Oct 25, 2017 1:57 pm 
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We can get boards no problem in Scotland.
We use generic boards tho,celotex and kingspan are too expensive.


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PostPosted: Wed Oct 25, 2017 7:42 pm 
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steviejoiner74 wrote:
We can get boards no problem in Scotland.
We use generic boards tho,celotex and kingspan are too expensive.


Same as you Steve, we never use the real thing (ie Celo), we use Recticel, Quin therm, eco therm, or whatever else they come up with, but they all use the same chemical filling which came from the factory that blew up, so all the makes have been hit now.

Good to hear you've got them in Scotland though, that's weird coz there's none down 'ere

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PostPosted: Wed Oct 25, 2017 7:58 pm 
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Just a thought.... if you have got access to a lot, and I mean a LOT, then why not get a few lorry loads and drive them down here?

We were just talking today about shipping some in from China to sell here ....!

It's pretty serious, there are no boards in the South East .... big market ...

120mm boards are fetching over £80 in Wickes who it seems are the last place South of London to have any at all.... God knows what I've just paid for the 90mm, 150mm, and 25mm boards I picked up from Jewsons yesterday, but I'll let you know when I get the invoice.. it will be crazy money for sure...

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PostPosted: Wed Oct 25, 2017 8:18 pm 
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Handyman in Sussex wrote:
Just a thought.... if you have got access to a lot, and I mean a LOT, then why not get a few lorry loads and drive them down here?

We were just talking today about shipping some in from China to sell here ....!

It's pretty serious, there are no boards in the South East .... big market ...

120mm boards are fetching over £80 in Wickes who it seems are the last place South of London to have any at all.... God knows what I've just paid for the 90mm, 150mm, and 25mm boards I picked up from Jewsons yesterday, but I'll let you know when I get the invoice.. it will be crazy money for sure...


My mrs. works in shipping... 4 weeks at sea from China. plus getting the insulation to the port in China, another couple of days for clearance at the port in the UK then onward delivery to the site in the UK sooo about 6 weeks just from the shipping point of view.

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PostPosted: Wed Oct 25, 2017 8:52 pm 
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This is getting interesting...

My nearest Travis Perkins today were waiting on a lorry of it which "should" arrive in the next few days, BUT the whole lot is pre sold before it even touches the ground, and most of their next delivery after that is pre sold which should be in the UK in the next 2 weeks..... All the merchants are being allocated only a certain amount of deliveries in any 2 week period now and they can't increase the order as all the other merchants are in the queue for it.

Travis are now quoting 5-6 week lead times for any boards at all.

There's a big market out there just now..

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PostPosted: Wed Oct 25, 2017 9:13 pm 
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Have you tried seconds and co



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