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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.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorXT600
    • CommentTimeMar 25th 2019
     
    I'm building a small extension, cavity block with a 100mm cavity. I was planning to use a PIR type insulation, 90mm 'fullfill' but am now wondering if it's worth its cost. Given that over a time pir loses its insulation values, and often shrinks leaving air gaps, can the cheaper polystyrene sheets be used instead?
    • CommentAuthorjfb
    • CommentTimeMar 26th 2019
     
    have you looked at glass fibre or rock wool full fill cavity batts?
    • CommentAuthorneilu
    • CommentTimeMar 26th 2019
     
    'Standard' polystyrene cavity wall insulation, like standard PIR insulation, is only suitable for partial fill applications not full fill. And I'm pretty sure that partial fill polystyrene wouldn't achieve the building regs U-value of 0.28.
    The polystyrene and PIR insulations that are suitable for 'full fill' situations have a profiles plastic face on the outer side, this is what makes them expensive, eg Jablite Jabfill HP is a polystyrene full fill.

    As jfb says, you will be best advised to use a glass fibre/mineral wool insulation that are suitable for full fill applications. Knauf, Superglass, Isover and Rockwool all do these types of insulation. Knauf have the best range in terms of performance. I would suggest that you ring the technical department of one of these companies and run through your intended construction and they will advise which one of their products to use.

    Using lighter weight blockwork will allow you to use a poorer grade of insulation to achieve the U-value of 0.28. But some builders don't like using this blockwork because it's not as robust as denser blocks.
    • CommentAuthorneilu
    • CommentTimeMar 26th 2019
     
    Or try a calling a partial fill PIR manufacturer such as Xtratherm or Celotex. I think Celotex have an online U-value calculator.
    • CommentAuthorPetlyn
    • CommentTimeMar 28th 2019
     
    How about using an expanded glass bead which has all the advantages of polystyrene beads but none of the disadvantages - it does not degrade, take on water, is non-flammable and with a thermal conductivity of W/(m-K) 0.066. If you have conventional brick ties in your wall build, the beads can be poured in around these leaving no gaps.

    What part of the country are you? We have some left over from our self-build in Norfolk and would send a sample if it is something that might be of interest?
    • CommentAuthorXT600
    • CommentTimeMar 28th 2019
     
    <blockquote><cite>Posted By: jfb</cite>have you looked at glass fibre or rock wool full fill cavity batts?</blockquote>

    I have to admit, I didn't think glass fibre was suitable for full fill. I'll take a look, thanks.
    • CommentAuthorXT600
    • CommentTimeMar 28th 2019
     
    Using lighter weight blockwork will allow you to use a poorer grade of insulation to achieve the U-value of 0.28. But some builders don't like using this blockwork because it's not as robust as denser blocks.</blockquote>

    I have thought about building the inner skin from thermal blocks, but having used a calculator (can't remember now which website I used) it made so little difference to the values it was not worth the extra cost. The inner skin will be supporting floor joists and I'm not convinced the lightweight blocks have sufficient compressive strength.
    • CommentAuthorXT600
    • CommentTimeMar 28th 2019 edited
     
    <blockquote><cite>Posted By: Petlyn</cite>How about using an expanded glass bead which has all the advantages of polystyrene beads but none of the disadvantages - it does not degrade, take on water, is non-flammable and with a thermal conductivity of W/(m-K) 0.066. If you have conventional brick ties in your wall build, the beads can be poured in around these leaving no gaps.

    What part of the country are you? We have some left over from our self-build in Norfolk and would send a sample if it is something that might be of interest?</blockquote>

    I'm in Cornwall, so probably too far away to pop in and have a look :-) However, something I can pour in as I build sounds like an attractive proposition. What is the name of the product you used? Do you know what the U value will be for 100mm cavity?
    • CommentAuthorXT600
    • CommentTimeMar 28th 2019
     
    One of my reasons for choosing the PIR insulation was that it has a reflective metal foil. Because I have insulated the main house with this on the internal walls, and multifoil used above the ceilings upstairs it has done a fantastic job of blocking out phone and wifi signals. Although certain members of the family don't approve, I quite like the idea of not being constantly surrounded by this 'noise' while at home. While choosing the wall insulation for the extension, I just have to weigh up the cost difference and whether it's worth the extra cost. I can always use some cheap foil backed plasterboard on the inside perhaps :-)
    •  
      CommentAuthordjh
    • CommentTimeMar 28th 2019
     
    Posted By: XT600I can always use some cheap foil backed plasterboard on the inside perhaps :-)

    Or just wear a tinfoil helmet? :bigsmile: :bigsmile: :devil:
    • CommentAuthorgravelld
    • CommentTimeMar 29th 2019
     
    Posted By: PetlynHow about using an expanded glass bead which has all the advantages of polystyrene beads but none of the disadvantages [...] a thermal conductivity of W/(m-K) 0.066.
    Sounds like a good product, but 50%ish higher lambda is quite a significant disadvantage, especially with builders grumbling about cavity widths.
    • CommentAuthorrevor
    • CommentTimeMar 31st 2019
     
    Depending where you are I would be vey cautious of doing fulfil in Cornwall. If your location is subject to some very harsh south westerly's as I am here in Anglesey then there is a great risk of problems. It is well reported that the programme promoted by the government for companies like BG to fill cavities has gone pear shape in some regions due to condensation and damp ingress as a result of no cavity. It is costing more to rectify the problems than the cost of doing the work in the first place. I am aware of external walls being removed to take out the insulation.

    BC here require a 75 mm clear cavity if you are using facing brick and 50 mm if you are rendering. When I built our extension I opted for a 150 cavity with 100mm t& G PIR externally rendered blockwork. The pir has not shrunk as exampled by some I have had in store for nearly 10 yrs but another make I used in floors does show shrinkage. Thing is to avoid the cheaper PIR makes.

    Have you considered the wider cavity option and use a decent grade of PIR.

    When I said to the architect what I wanted to do he was very negative saying it was going to be very costly, in the end it was not and now lintels and wall ties are fairly standard off the shelf items for a 350 mm wall. Labour is the same, blocks and mortar the same and about 8% extra concrete for the foundations i.e 650 vs 600 mm.

    I achieved 0.18 u value when all reckoned up for the walls.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 1st 2019
     
    Looked at Bldg Regs Part C 5.15? There's a complete ban on full-fill cavity insulation in more exposed areas of the country, depending on whether the wall is facing brick, or rendered, or has cladding. Absolutely not, west of Exeter, unless rendered.
    • CommentAuthorXT600
    • CommentTimeApr 3rd 2019
     
    <blockquote><cite>Posted By: revor</cite>Depending where you are I would be vey cautious of doing fulfil in Cornwall. If your location is subject to some very harsh south westerly's as I am here in Anglesey then there is a great risk of problems. It is well reported that the programme promoted by the government for companies like BG to fill cavities has gone pear shape in some regions due to condensation and damp ingress as a result of no cavity. It is costing more to rectify the problems than the cost of doing the work in the first place. I am aware of external walls being removed to take out the insulation.

    BC here require a 75 mm clear cavity if you are using facing brick and 50 mm if you are rendering. When I built our extension I opted for a 150 cavity with 100mm t& G PIR externally rendered blockwork. The pir has not shrunk as exampled by some I have had in store for nearly 10 yrs but another make I used in floors does show shrinkage. Thing is to avoid the cheaper PIR makes.

    Have you considered the wider cavity option and use a decent grade of PIR.

    When I said to the architect what I wanted to do he was very negative saying it was going to be very costly, in the end it was not and now lintels and wall ties are fairly standard off the shelf items for a 350 mm wall. Labour is the same, blocks and mortar the same and about 8% extra concrete for the foundations i.e 650 vs 600 mm.

    I achieved 0.18 u value when all reckoned up for the walls.</blockquote>

    Although in Cornwall, my terraced house is very well sheltered by higher ground behind, and I don't anticipate any such problems with driving wind/rain etc. The walls will be rendered. I'm stuck with a 100mm cavity because of space restrictions, and needing to maximise the space available to extend between the neighbours. What PIR do you consider to be the 'cheaper' brands? I've seen examples of shrunken Celotex, although this was some time ago.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 3rd 2019
     
    In Part C, rendered, 100 cavity, built-in full-fill is OK in Cornwall but not if it's above a non-renderd facing brick panel.
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