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Thinest insulation for inside of Velux

  • 14-11-2019 2:38pm
    #1
    Registered Users Posts: 429 ✭✭


    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


Comments

  • Moderators, Home & Garden Moderators Posts: 10,135 Mod ✭✭✭✭BryanF


    Aerogel


  • Registered Users Posts: 429 ✭✭magnethead


    They are practically giving the stuff away :rolleyes:

    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!


  • Registered Users Posts: 429 ✭✭magnethead


    What about a 15mm foam sheet? Would this be pointless under plasterboard or better then nothing?

    https://www.efoam.ie/foamsheets.php


  • Moderators, Home & Garden Moderators Posts: 10,135 Mod ✭✭✭✭BryanF


    Sorry, I assumed by ‘thinner’ that the purpose was still to insulate the rooflight/roof junction?


  • Registered Users Posts: 429 ✭✭magnethead


    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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  • Moderators, Home & Garden Moderators Posts: 10,135 Mod ✭✭✭✭BryanF


    Show us the detail?


  • Banned (with Prison Access) Posts: 82 ✭✭Bdjsjsjs


    Not sure but maybe areogel spacetherm wall board which would replace the plasterboard?


  • Registered Users Posts: 567 ✭✭✭SC024


    magnethead wrote: »
    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.


  • Registered Users Posts: 429 ✭✭magnethead


    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

    velux.jpg?raw=1

    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/Insulated-Plasterboard-29mm-8x4-ft-.html?filter_set[]=1413,1419



    Thanks lads


  • Registered Users Posts: 398 ✭✭Panjandrums


    What's the roof buildup? I'm curious as never seen anything like that.


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  • Moderators, Home & Garden Moderators Posts: 10,135 Mod ✭✭✭✭BryanF


    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.


  • Registered Users Posts: 429 ✭✭magnethead


    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 :)


  • Moderators, Home & Garden Moderators Posts: 10,135 Mod ✭✭✭✭BryanF


    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?


  • Registered Users Posts: 429 ✭✭magnethead


    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.


  • Moderators, Home & Garden Moderators Posts: 10,135 Mod ✭✭✭✭BryanF


    Tyvek? Didn’t know they did air-tightness product, they are traditionally known for garden matting and more recently breathable roofing membranes.


  • Registered Users Posts: 429 ✭✭magnethead


    It is a breathable roof membrane, the carpenter installing the velux, pulled it through when he was wedging the trimmer into place


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