Green Building Forum - Insulating ceiling - cheapest fluffy product (ideally non itchy) Wed, 26 Aug 2026 09:15:58 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Insulating ceiling - cheapest fluffy product (ideally non itchy) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306064#Comment_306064 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306064#Comment_306064 Wed, 19 Jun 2024 10:18:49 +0100 Huwblut
The ceilings are down on my little bungalow renovation and I’m thinking hard about how to re insulate them. I think the electrician would appreciate it if we’re all gone while he’s working from underneath.


Previous posts recommended a fluffy product of some description. I’ve seen this advertised on marketplace local to me for £30 per roll : Rockwool Therma insulation roll 100/200. Any opinions please?

Question is there something similar / less expensive & possibly less itchy out there?

I’m keen to reuse the existing stuff despite it being a horrible job to remove, store and re install. Seems a shame to send it landfill.

Suggestions greatly appreciated

Huw]]> Insulating ceiling - cheapest fluffy product (ideally non itchy) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306075#Comment_306075 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306075#Comment_306075 Wed, 19 Jun 2024 20:59:46 +0100 owlman ]]> Insulating ceiling - cheapest fluffy product (ideally non itchy) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306076#Comment_306076 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306076#Comment_306076 Thu, 20 Jun 2024 01:59:05 +0100 Peter_in_Hungary Posted By: owlmanWhenever I've done awkward between rafters/joists esp. from underneath I've used Rockwool batts, in one form or another. You're able to cut them fairly accurately and hence jam them between the timbers and they stay there unlike the " Fluffy Stuff ".https:///newforum/extensions/Vanillacons/smilies/standard/smile.gif" alt=":smile:" title=":smile:" >
+1
However fluffy stuff is usually cheaper than batts. If your ceilings are down can you wait with the insulation until the ceilings are back and then put fluffy stuff on top. You are unlikely to get a good enough U value by stuffing either fluff or batts between the rafters, more will be needed over the top (Minimum recommended loft insulation for UK is 270mm)

If you are rewiring then it is better to have any wiring in the loft above the insulation or de-rate the wiring to allow for the insulation (reduce the size of the MCB or increase the diameter of the cable). Your electrician should know about this and best to discuss your insulation plans with them to avoid issues later.

In your position I would put the ceilings back and then put fluff between the joists and more layers over laid so that the joins do not coincide.

Rockwool or equivalent is (much) less of an irritant than glass wool.

edit to say if you are relying on eaves ventilation for the loft don't block the flow with insulation.]]> Insulating ceiling - cheapest fluffy product (ideally non itchy) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306077#Comment_306077 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306077#Comment_306077 Thu, 20 Jun 2024 09:40:22 +0100 GreenPaddy
I always spec Kanuf earth wool, as it's the least itchy of any wool. As PiH above, run cabbles above the insulation top level. I always get my sparks to clip cables at 500mm above the ceiling level, onto rafters/trusses, and then there's just single vert drops to lights or into stud walls. That keeps the cables mostly above the insulation, which I usually lay 3 layers of 140/150.

If there's space, I also run some "cat walks" from the hatch to each gable end, by adding some short lengths of 4x2 horizontally, and fixing any leftover sarking/flooring boards, to give paths to crawl for access, over the insulation. Otherwise, any future access will tramp over and wreck the loft insulation.]]> Insulating ceiling - cheapest fluffy product (ideally non itchy) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306078#Comment_306078 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306078#Comment_306078 Thu, 20 Jun 2024 11:44:03 +0100 Huwblut
Thanks for the information. It's a it of an odd set up...There's some makeshift rooms in the attic so adding insulation from above isn't mostly feasible.

Appreciate that insulating the floor / ceiling isn't usually enough but the rooms above are plaster boarded and insulated with foam boards of some kind so it's mot just a plain attic. There's two small radiators up there as well which are turned down to almost off and 3 small Velux windows which can be left open a tiny but for air movement.

If i run my hand between the Celotex and the roof there appears to be a gap so I'm hopeful that if I don't stuff the wool too tight to the eaves then there'll be air movement there too.

'll start pricing up Knauf Earth Wool and will have a chat with the electrician about keeping the cables on top or above the insulation.

Appreciate your help!]]> Insulating ceiling - cheapest fluffy product (ideally non itchy) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306079#Comment_306079 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306079#Comment_306079 Thu, 20 Jun 2024 15:52:02 +0100 Peter_in_Hungary Posted By: GreenPaddyThat keeps the cables mostly above the insulation, which I usually lay 3 layers of 140/150.
But dropping cable through insulation also requires derating

Table 4.5 - Derating factors (CI) for cables up to 10mm² in cross-sectional
---------------- area buried in thermal insulation.
Length in insulation (mm) Derating factor (CI)
50mm 0.89
100mm 0.81
200mm 0.68
400mm 0.55
500 or more 0.50]]> Insulating ceiling - cheapest fluffy product (ideally non itchy) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306087#Comment_306087 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306087#Comment_306087 Fri, 21 Jun 2024 08:09:53 +0100 GreenPaddy Insulating ceiling - cheapest fluffy product (ideally non itchy) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306096#Comment_306096 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306096#Comment_306096 Fri, 21 Jun 2024 16:17:58 +0100 Peter_in_Hungary Posted By: GreenPaddyDon't think I suggested de-rating was not required,
I don't think you were either but

Posted By: GreenPaddyworth pointing out for others reading this.

it often forgotten that when there is a substantial amount of loft insulation the drop down cables through the insulation can warrant derating according to the above table (either derate the cable or up the diameter)

And too often I have suffered contractors either stamping all over insulation or throwing it to one side never to be fitted back properly.

Having a walk way the length of the loft above the insulation is worth the effort.]]> Insulating ceiling - cheapest fluffy product (ideally non itchy) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306099#Comment_306099 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306099#Comment_306099 Fri, 21 Jun 2024 20:17:32 +0100 djh ]]> Insulating ceiling - cheapest fluffy product (ideally non itchy) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306490#Comment_306490 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18147&Focus=306490#Comment_306490 Sun, 18 Aug 2024 23:15:19 +0100 wookey
There are lots of good natural products too (hemp batts, blown woodfibre, cellulose) but you'll generally pay about 3 times the price of glasswool.]]>