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Posted 20 November 2023
3 for 2 - Knauf Insulation Loft Roll 200mm - free C&C
£6 ·
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Dominic_Saneria
Joined in 2020
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Good deal on loft insulation at home base, 3 for 2 on loft insulation on both 100mm and 200mm perfect for a winter DIY job.
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Edited by a community support team member, 20 November 2023
68 Comments
sorted byI've a building control certificate for mine. Cost £60 and didn't need extra ventilation but I needed to install 40 felt slot vents into my other house and it just about ventilates it along with the existing eave slot ventilation.
Loads of DIYers out there doing nice damage with roof insulation, your nose will tell you soon enough though (moulds/fungus).
Dew point shift is relevant where the ceiling is vapour permeable, for example lime and lath, or poor fitting loft hatches, fans vented lazily into the roof space, loose downlighters etc. A well ventilated loft will be full of external air with a very low dew point, the dew point isn't relevant.
Higher dew point humid air comes from living areas. Insulating or not insulating doesn't change the requirement for ventilation. If you do have a leaky ceiling however, it will trap condensation. That's not dew point shift though.
[image] (edited)
This stuff makes a real difference.
I have a boarded section in my
loft not sire what to do there
The recommendation is to install to the depth of your joists/truss then install more in the opposite direction. If you need to board it, install loft legs and allow 10mm clearance to the underside of the board. You want to be aiming for 400mm+ insulation to be affective
The joists are 100mm deep and not exactly even height. One company that specialises in insulation/boarding has said they will run wooden beams across the joists to increase the height and can take it up to 300mm (+-100mm). A couple of builder family friends reckon this is an absolutely okay method to go about it. I.e. loft legs are not needed. The company says it can board (tongue & groove) 70% of the loft and have quoted 15sqm of boarding at £705 + insulation at about £300-£350 (300mm).
Price seems about right to you? Unfortunately I don't have the know how or time to do this myself, and as it's for my parents, I want to get it done properly
Is there any need to go beyond 300mm?
And, if we can afford it, should I go for rock wool rather than this one which is glass wool? Sound insulation, fire resistance or pests are not an issue.
Thank you! (edited)
15m2 is about 15 packs of board, which are £15 each. So there's some profit/labour in there. (Understandable)
Insulation isn't a terrible quote either...
My concern would be the additional loadings to the timber and roof structure using 200mm timbers to increase the depth. Would they be on load bearing walls? Loft legs weigh hardly anything, and can be levelled without the worry on uneven joists. however they are expensive.
There's no mention of cost of timber in the above quote? Make sure you don't get stung after!
300mm is better than nothing and would make a noticeable difference. The Thicker the better. Hope that helps