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14-11-2019, 14:38   #1
magnethead
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Thinest insulation for inside of Velux

I have a skylight popping up out of the roof quite a bit, about 5"....
I want to run some insulation on the inside of the trimmer, I see Kingspan do 25mm sheets, do you know anybody doing anything thinner?

Thanks
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14-11-2019, 18:52   #2
BryanF
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Aerogel
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14-11-2019, 19:06   #3
magnethead
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They are practically giving the stuff away

http://www.buyaerogel.com/product-category/airloys/


Even the thermal wrap at 6mm for these applications is mad money

http://www.buyaerogel.com/product/thermal-wrap/

interesting stuff though!

Last edited by magnethead; 14-11-2019 at 19:17.
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14-11-2019, 19:20   #4
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What about a 15mm foam sheet? Would this be pointless under plasterboard or better then nothing?

https://www.efoam.ie/foamsheets.php
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14-11-2019, 21:02   #5
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Sorry, I assumed by ‘thinner’ that the purpose was still to insulate the rooflight/roof junction?
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14-11-2019, 21:33   #6
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I have 30mm on the inside of the rooflight trimmer, 12.5mm will be taken up by plasterboard going up into that slot in the rooflight, which leaves me with 17.5 mm, to add insulation between the wood and the plasterboard. This is all on the inside of the Velux window. because this 18" velux trimmer is popping out of the roof a terrible distance. It's what the zinc roofer said was code.
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14-11-2019, 22:24   #7
BryanF
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Show us the detail?
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16-11-2019, 09:58   #8
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Not sure but maybe areogel spacetherm wall board which would replace the plasterboard?
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16-11-2019, 15:46   #9
SC024
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Quote:
Originally Posted by magnethead View Post
I have 30mm on the inside of the rooflight trimmer, 12.5mm will be taken up by plasterboard going up into that slot in the rooflight, which leaves me with 17.5 mm, to add insulation between the wood and the plasterboard. This is all on the inside of the Velux window. because this 18" velux trimmer is popping out of the roof a terrible distance. It's what the zinc roofer said was code.
28mm insulated plasterboard, rebate the insulation so that the top of the slab slides up into the grove on the window frame. you can go for the plasterboard with the K15 bonded to the back of them.
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16-11-2019, 21:33   #10
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Thanks @SC025 that sounds like a proper solution
Here is the velux I have in a 9*2 trimmer frame, coming out 4" from the roof, I'm going to stick another 9*2 trimmer under this one..
but the insulated plaster board up the side, seems like a good / only option



I found the stuff at Goodwins (looks like I only got 27mm, will search for 28mm as every mm counts LOL)

https://www.goodwins.ie/products/Ins...tml?filter_set[]=1413,1419



Thanks lads
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16-11-2019, 23:40   #11
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What's the roof buildup? I'm curious as never seen anything like that.
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17-11-2019, 00:20   #12
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So all of the insulation <25mm is inside timber trimmer, butted up to the window?
1. Is there a ventilation requirement outside, ie Is it slates with breathable felt outside trimmer?
2. Where is the the air-tightness/vapour barrier layer? It should be warm side of the insulation
3. Have you considered the BER and thermal bridge requirements of part TGD L? What psi value do you need to achieve?
4. What does the skylight manufacturer’s roof install detail show? And is the warranty intact if the roofer deviated from it?

Roof-lights are a pain to detail to eliminate cold bridges, the manufacturers should be doing more to address roof junction insulation detail.
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18-11-2019, 11:30   #13
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Panjandrums, This roof is from a Kerry Company called thermohouse, you can see their roofs on their website. It's basically large tongue and groove EPS panels slotted together with steel beams running through them for reinforcement.

Thanks Bryan, There is metal going on the outside, I already have a penny gap boarding roof deck screwed to the outside. Velux has a plastic looking sheeting for a vapor membrane. I might use that.
I was thinking of using tec 7 to seal the edge where the velux meets the trimmer
The manufacturers detail is vague enough, it just shows a picture on a wooden trimmer cut into the roof as I've already done.
Without the membrane hanging down the side of course
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18-11-2019, 11:39   #14
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Is that not breathable membrane velux supply?

I would advise against using the trimmer for air-tightness

Are you not putting a membrane inside the EPS?
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18-11-2019, 11:47   #15
magnethead
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no the membrane is Tyvek, I put it across the whole roof. I'll have some blower proof membrance across the inside of the EPS panel, or maybe those bitumen sticky sheets, I'll have to run a few screws up into the panel to attached batons.
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