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    • CommentAuthorSnikom
    • CommentTimeJul 6th 2009
    Hello there

    This question is from a confused and frustrated newbie to building.

    I am having an extension built on my house. We are planning a 200mm cavity full filled with insulation (rockwool or similar) which will hopefully achieve a u-value of 0.18

    I am trying to research some non-thermal bridging wall ties which will cover a 200mm cavity. The only quote I have so far seems (to me at least) to be quite expensive, about £8 per square metre of wall. They also don't have certification so I would have to get approval from my local building control, which could be irksome.

    Do theramally broken cavities make a significant difference on a 200mm cavity and are there any availiable that are already regularly used and have been certified by whoever certifies these things.

    I need to get this sorted fairly quickly as the builder is nearly up to the level where he starts the cavity and I have yet to make a decision :confused:

    Thank You
    • CommentTimeJul 6th 2009 edited
    • CommentAuthorCWatters
    • CommentTimeJul 6th 2009
    Does the rockwool also need insulating fixings?
    • CommentAuthorSnikom
    • CommentTimeJul 6th 2009
    Thank you for the quick responses

    The ties I have a price for are the same ones as used in Tony's house (only 200mm cavity not 300)

    As far as I can tell they seem to make a far larger % improvement in 300mm cavities as opposed to 200mm


    I don't believe that rockwool or similar will need insulation fixings. My original idea was to use celotex but advice from everyone (including here) is that it is difficult to get right and any benefit may then be lost.
    • CommentTimeJul 6th 2009
    no problem.
    shouldnt need fixings unless going more than a couple of storeys.
    my advice for tony was to stagger the insulation so that rather than 3 layers of 100mm going in together have the middle layer sit short to create a horizontal and vertical tongue n groove effect
    you can see on his project photos
    • CommentAuthorSnikom
    • CommentTimeJul 6th 2009

    I think the term is aaaahhh!

    Is there any flex in the composite ties?

    We are using metric blocks but imperial (73mm) bricks to match the existing house. So the builder was planning to bend the ties a bit to make them fit between the different height of the courses.

    As a further note when I asked for a price on steel ties for a 200mm gap they have come in at more than composite ones as they are two pieces.
    • CommentTimeJul 6th 2009
    i'm sure tony will be on here before long and will give a rundown of his experience with them. i believe it will need a more open minded team of bricklayers to get it to work properly when tying in blockwork to brickwork.
    • CommentAuthortony
    • CommentTimeJul 6th 2009
    The ties are best built in as you go and not left poking out when raising one leaf at a time. They dont bend but they can be built in with a slight fall outwards. I would use them again even though they are expensive -- It is worth careful counting how many you need -- I have three spare from my whole house.

    There were some for sale in offers and wants a while back.

    If I were trying to do what you are I would be building in courses of splits or brick sized blocks -- most manufacturers make these now.

    hope that helps
    • CommentAuthorCWatters
    • CommentTimeJul 6th 2009
    Posted By: ali.gillno problem.
    shouldnt need fixings unless going more than a couple of storeys.

    ..and I forgot that with rockwool you can fully fill the cavity (I think).
    • CommentAuthorSnikom
    • CommentTimeJul 8th 2009
    Thank You for your help

    But (why is there always a but)

    What are "course of splits" I have contacted our two local builders merchants and both have said blocks only come in standard metric sizes. (both originally said that you only got metal wall ties too :))

    Thanks again
    • CommentAuthortony
    • CommentTimeJul 8th 2009
    For instance I but brick size pieces of block -- same as the blocks but same size as a brick -- very useful.

    Splits are often used with beam and block floors -- even thinner bits than bricks

    If it comes to it get a cutter and make your own :smile:
    • CommentAuthorSnikom
    • CommentTimeJul 8th 2009
    Cheers Tony

    I had suggested using coursing blocks which it seems are similar but thicker. My wife was told that the extra mortar between the additional courses would adversely affect SAP (although which aspect of SAP I am unclear)

    Magmatech are sending out a sample tomorrow and we are going to try knocking it into a block and then fixing with resin and/or mortar. Is there anything I should be worried about with this approach.
    • CommentAuthorSnikom
    • CommentTimeJul 8th 2009
    BCO just gave us a plain old "no you can't use them as the have no BBA certification" via e-mail, he is out tomorrow I hope. How do I convince him to change his mind or better still is there a BBA approved thermally efficient tie?
    • CommentTimeJul 8th 2009 edited
    TeploTie is currently being tested and accessed for a BBA certificate. While this process is ongoing TeploTie can be used in projects. Local Authority Building Control will consider the ties based on the test data collected as part of the BBA process. Please contact us for further details on how you can start to use TeploTie.

    Paragraph on page 2 specifically states LABC positon in relation BBA Cert

    if you're having problems just get a different bco.
    or shove this up his nose
    • CommentAuthorSnikom
    • CommentTimeJul 8th 2009
    Cheers Ali

    I have also been in contact with Ben who has provided me with lots of information.

    Now all I have to do is convince a building inspector, I don't really want to tell him to stick anything up his nose as he has been very helpful so far. Heres hoping he sees things better tomorrow.
    Try changing the design of your construction - life can be a lot simpler - as a 200mm cavity will bring its own problems when it comes to structural stability - you could consider the following:

    100mm Face brickwork - (sacraficial layer to the elements U value not necessarily of any importance, whereas weathering properties, longevity and ease of maintenance are of importance)

    50mm cavity +
    50mm PIR insulation
    125mm Thermalite Turbo Blockwork Inner Wall
    65mm Thermaline Super (sandwich insulation board with plasterboard finish on adhesive dabs).

    Overall thickness of construction - 400mm - U value less than 0.18w/m2K

    • CommentAuthorsydthebeat
    • CommentTimeJul 17th 2009

    have you done a dynamic condensation risk analysis on that make-up... because it would send alarm bells going in my opinion...
    • CommentAuthorSnikom
    • CommentTimeJul 17th 2009
    Hi Onceuponatime

    I have just played with ubuild with your design, but I only get down to 0.23.
    Also wouldn't this isolate/lack thermal mass?

    My original idea was for PIR insulation in a 125-150mm cavity but advice from the professionals onsite was that this was hard to get right and a 200mm cavity full filled would be easier/simpler (I guess on it being simpler/easier at least they were wrong :confused:)

    The BCO will NOT sign off without a BBA cert for the wall ties (Otherwise he is happy with the construction and the 200mm cavity). I cannot find a wall tie with a BBA cert that is capable of spanning a 200mm cavity.

    Current plan is to build with the teplo ties as there BBA cert is due very soon, so we have started building an outer leaf.

    The plan is to drill and glue (with resin) the ties into the outer (imperial brick wall) and then fill with insulation and build the inner leaf. This does mean the ties will be poking out but I couldn't find a better solution.
    • CommentTimeJul 17th 2009
    tonys already given you a better solution - i suggest you pay him a visit for a 'live' explanation

    also double check that the insulation you spec is suitable for full fill
    • CommentAuthorbeelbeebub
    • CommentTimeJul 17th 2009

    Have you tried these?


    i think they are certified but check, they also seem to be two part so that would make building easier.
    • CommentAuthorSnikom
    • CommentTimeJul 17th 2009
    Hiya Beebleebub

    It is me trying to build the wall not ali.gil

    I have phoned ancon and they said that they don't hold a bba certificate for over 150mm. They do hold a certificate for ties upto 150mm.
    • CommentAuthorbeelbeebub
    • CommentTimeJul 17th 2009
    @ snikom


    That's annoying, I'm looking to build a 200-250mm cavity wall.

    What's the deal, people make the wall tie's, they comply with NHBC and BS (according to their catalogue) so why can't they be used? What's so special about the BBA cert? How come some people have built a wall with a wide cavity (e.g. tony or BEDZED) and some can't get sign off? Is there no consistency? Either a product works or it doesn't, it can't work in some parts of the country and magically not in others (extreme wind loading and rain penetration aside)

    We may well get structural calcs done by a structural engineer. Surely the building control officer has to sign off on that?

    Or am I being naive?
    • CommentAuthorSnikom
    • CommentTimeJul 17th 2009
    Well here in East Lindsey the BCO was very clear no BBA Certificate at the end of my build and he will not sign off (I am gambling on one being there by sign off time, a situation I don't like as I am normally anything but a gambler) . Now it could be there is another wall tie for a large cavity with a certificate out there but I couldn't find it on the net in general or at http://www.bbacerts.co.uk/.

    As to an engineers report being good enough to sign off, I don't know. I have seen people say you don't even have to use building control but I am an amateur at this and don't really want to move too far from the norm (extra insulation excepted)

    So thats the bad news, the good news is

    1. Your BCO or area may be more lenient
    2. The ties that Tony used and are mentioned earlier in the thread (I am trying not to turn this into an advert) are hopefully going to get there certificate through in a few weeks.
    • CommentAuthorbeelbeebub
    • CommentTimeJul 17th 2009
    Ahhh, I've just looked up BBA and it looks like they are just an accreditation and standards body like BSi or Moodys International.

    So effectively a BBA certified part (tie, block etc) has been tested and the manufacturer and their processes inspected to ensure they have quality control etc in place.

    Did Ancon say if they were going for BBA? If BCO's don't accept anything without a BBA cert then how can anything without a BBA cert be sold?

    It also seems like a bit of overkill to not approve anything except within the limits of a BBA cert when the work is being done by (pardon the generalisation) less than meticulous people (builders).

    It's a bit like having to inspect and certify every single part in a car but allowing it to be assembled by unskilled labourers in field? (I'm going to catch it for this one) :bigsmile:
    Hi Snikon

    You should never fill a cavity, as minimum it goes against the building regs (or at least it used to a short while ago), at worst you could have some regrets. Problem with filling the cavity is that the insulation will get damp on the external face when the external brickwork is soaked by persisant rain, was going to say saturated but that would be to extreme.

    The purpose of a cavity is to allow the walls to breathe and dry out otherwise moisture gets retained and the insulation gets weater and weater and its effectiveness in some cases becomes nigh on useless, and even worse it may cause damp problems inside the building.

    The beauty of PIR board is that it is pretty vapour resistant and you won't get problems with condensation especially if you have some PIR insulation material on the warm side of the construction as the warm air will be kept in the room and by the time the warm air meets the cavity its temperature will have been so reduced that condensation either surface or interstitial will be significantly reduced and the cavity will again come to the rescue. This assumes that people are aware that warm air holds more moisture than cold air, and when the temperature of the warm air drops the warm air becomes saturated and any further cooling will lead to condensation which can occur as either surface and/or interstitial condensation.

    Years of experience have shown that a 50mm cavity is about right. Also to get the best out of the insulation you want it on the warm side of the construction as PIR is so thermally efficient it will keep the warmth where it is most needed (that is in the room) rather than keeping internal walls warm. Some people reckon putting thermal insulation on the external of the building reduces its effectiveness by around 20%

    Going to the calcs which I had not intended doing, but hey lets do a comparison!

    Thermal Conductivity (TC) W/mK Rsi + Rso = 0.18; 100mm face brickwork = 0.125; Cavity = 0.18; 50mm PIR Insulation = 2.08; 125mm Thermalite Super = 1.13; 65mm Gyproc thermal super = 1.8 + allow a bit for air gap caused by dabs say 0.12 Total thermal conductance = 5.615

    U value = 1/TC = 1/5.615 = 0.178W/m2K

    Best Regards
    • CommentAuthorbeelbeebub
    • CommentTimeJul 18th 2009 edited

    Edit: Added picture and found Gyproc is vapour barrier

    I was under the impression that full fill cavities had been approved and there were several types that were considered to be waterproof (glued beads or some rockwool bats).

    I was originally going to go with PU/PIR boards due to their much better insulation values. I had a plan involving double layer of 60mm ( to give 120mm) laid with staggered and taped joints to make it air and water tight. a 50mm air gap on the outside then a rainscreen or some blockwork/render or brick (planner dependent).

    Effectively this was external wall insulation.

    My main concern was the work on thermal looping. If there is any gap behind the insulation it causes a major loss in thermal performance. The minimum gap size is around 5mm or less. This could be very hard to prevent. Also the superior thermal performance per unit thickness of the PU/PIR is slightly mitigated by the need for a 50mm air gap. A 120 PU/PIR wall is not far off a 170mm EPS wall(.21 vs .2).

    I'm tending to come round to a fill fill cavity using blown in EPS beads with a glue bonding agent. In theory it's simple, build a wide cavity wall (assuming wall ties are available), then call the contractors up and fill the wall. The result is a fully filled cavity of whatever thickness you want (best laid plans and all that ). :bigsmile::bigsmile:

    As a side note the wall you mention appears two have two layers of insulation. Is there not a potential problem with condensation in the layer between the gyproc and the PIR? I assume the Gyproc should act as a vapour barrier but if there is a hole (say a small gap between the boards or a service entry) then any water that does get in will condense and find it difficult to escape.

    I did a little analysis and the line between no condensation and condensation id fine. At 20C 50RH no condensation, at 20C 60RH condensation starts to happen. I would say that those conditions could happen in a bathroom or kitchen in the winter.
    Hi Guy's (that includes any Gal's)

    Your not going to have any problems with condensation except in the cavity, which is why you need the cavity in the first place (to let the construction breathe - call it old hat thinking).
    Even if you fill the cavity with insulation you are still going to get thermal bridging which will cause interstitial condensation to form somewhere between the outside wall and within the insulation material, not to mention surface condensation at the interface between the insulation and the external brickwork.

    The problem that then arises will be saturation of the brickwork in winter conditions, as there will be no cavity to assist in drying out of the external bricks. The external face of the brickwork will then be open to frost attack and over a few years you could easily find the face of the brickwork delaminating. Possibly the reason that you won't find filled cavities in the building regs.

    Best Regards
    • CommentAuthorbeelbeebub
    • CommentTimeJul 19th 2009
    I agree that PU/PIR offer fantastic insulation values. In fact my first stab at a wall used a similar system to onceuponatime but with all the insulation in the cavity (100block, 120PU, 50cavity,100block).

    My main worry with PU/PIR boards is the dependence on no gaps between the inner blockwork and the PU/PIR. The work on thermal looping shows reductions in insulation values of around 30% for a 5mm gap, rising to 200% for 10mm with gaps at top and bottom.

    I can't see a way that a traditional cavity wall can be built (by building both inner and outer leaves at the same time and stuffing insulation in as you go) with that degree of accuracy.

    This lead me to a solid wall with external insulation, nice for inspection of the wall and the insulation before rendering the outside. But difficult to get in the UK, the Germans seem to know how to do it but the average UK builder is a bit flummoxed by it.

    This lead me to look at full fill cavities, 200mm wall ties aside, the rest seems to be standard UK practice so should be easy to get someone to build. The only question is what filling? At the moment I'm leaning towards glue bonded beads. i am told they are considered waterproof if over 50mm thick so that should be ok in 200mm.

    I have to admit my only fear with a full fill cavity is the moisture penetration issue, although I will be using block and (waterproof) render and overhanging eaves should keep the wall fairly dry.

    I think you may be mistaken that the building regs mandate against full fill (see attached pics from Part C of building regs).
    • CommentAuthorbeelbeebub
    • CommentTimeJul 19th 2009 edited
    also table 4 or Part C gives exposure ratings for various constructions (i've chopped it up to get it all on one page)

    A 150mm full fill is roughly equivalent to a 100mm clear cavity and a 100mm residual cavity in a partial fill.
    Full cavity fill is obviously an option but on a personal note only I would avoid such a detail, the insulation may be waterproof, but it will mean that the external brickwork will become saturated and with no cavity it will rely on evaporation from the external face, which will leave the face of the brickwork open to frost attack.

    No building element is absolutely vapour resistant and a certain amount of warm air will travel towards the external face of the structure, when this warm air meets cold air or a colder surface condensation is likely to occur.

    As a safeguard, it would be best to carry out an analysis of the construction detail to determine whether or not there is a condensation zone and if so its location - as mentioned earlier by beelbeebub - which brings me to mention that there would be no problem with condensation between the PIR board and the Blockwork as the temperature drop between the back of the PIR board and the face of the blockwall will be insignificant and the temperature will be above the dewpoint of the air.

    I have taken the time to calculate the dewpoint profile for the proposed construction model, not that anything is set in stone, please see attachment (here's hoping it works!!

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