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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthormarsaday
    • CommentTimeMar 5th 2021
    I am working on a flat i will be renting out. Doing a full strip out of electrics and fit new windows, wall insulation etc.

    It is a 1890 semi and divided into 7 flats. There is no insulation at all between all the floors. The conversion was done in 1982.

    Because i am ripping it about a fair bit i thought i would get some insulation between the 9" deep floor joists (i cant insulate above, just my own floor).

    So from reading a bit the best bet is rockwool RWA45 as it is denser. They make a 100mm slab so was planning on using that.

    Anyone know of other products which may be good ?

    Also am i breaking any regs by doing this work ? It seems a bit weird if i was, but understand this maybe the case.
    Yes higher density insulation is better but I don't believe rockwool's any heavier than 15/20kg per m3?
    Consider soft materials between hard materials and decoupling the floor from the ceiling with staggered timbers.
    A second plasterboard reduces sound transmission by 5dB as does 100mm of rockwool.
    • CommentAuthormarsaday
    • CommentTimeMar 5th 2021
    I cant change the ceiling with a false one. I can only add insulation between these joists. Carpet and underlay is an option, but i will be having some area of exposed flooring in the kitchen and bath areas.
    • CommentTimeMar 6th 2021
    I think you're saying that you can only alter either the floor under your flat or the ceiling above but not both? And I think you're saying only the floor beneath? (I'm not sure why you can't change the ceiling?)

    Yes, acoustic rockwool is a fine material. It must be fitted with a space above it, rather than tight, and as VH says the denser materials above and below it are as important. There are additional acoustic screed type materials that can be incorporated as well. Best to look at the specialist sound insulation websites to get an idea.
    • CommentAuthormarsaday
    • CommentTimeMar 6th 2021
    Yes i can only alter the floor in my flat as all carpets are up and i will be taking up a large amount of the timber flooring to do new electrics and install new heating as not got any.

    The ceiling in the main lounge area is 3m tall and has this amazing huge cornice all the way around it. Plus the sash windows go up to the ceiling. So i will loose the cornice and the windows will need to be altered. So doing all that work is not an option really.

    The flat above is also renovating so i may ask him if he wants to put in the same insulation in his floor (my ceiling).

    I will check out the websites selling this stuff.
    Theres not going to be too much difference between different types of mineral wool insulation. Although some are higher density than others, the overall mass they add to the floor is pretty insignificant (their purpose acoustically is to reduce the cavity resonance - various open-celled insulation materials will basically do the same thing). But putting insulation in the cavity should make a difference - provided all holes and gaps in the floor and ceiling are well sealed.

    If you want to make a bigger improvement without changing the floor or ceiling you'd need to add more significant mass to the void (structure permitting!). Traditionally 'pugging' used building materials - sand, rubble etc. but there are some proprietary options, e.g. Hush-Fill 60 by Hush Acoustics.

    Carpet and underlay will make a big difference to footfall etc, but not so much to airborne sound - speech, hifi etc
    • CommentAuthormarsaday
    • CommentTimeMar 10th 2021
    Thanks for the info.

    I am working on the electrics at the moment. So i have lots of boards up. Getting rockwool into place is going to be tougher over a roll of insulation. I think it will be easier to pull the softer rolls between boards taken up. The rockwool looks like it will be less forgiving, but i may be wrong.

    My joist spacing is around 350mm (actual gap) so i can see the soft insulation is going to be easy to fit inside.

    My joist depth is 220mm, so i want to use a 170mm depth roll.
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