Am I right in thinking that with a partial fill cavity wall it doesn't matter what the external leaf is made up off?

[PeterW]

It's one of the reasons I'm planning to use a blown bead full fill as they can just concentrate on keeping the cavity clear.... 

[jack]

28 minutes ago, ProDave said:

That picture is quite shocking Jack. It shows the builders regard fitting insulation as a "box ticking" exercise, rather than actually giving any thought to making it well insulated.
 

 

In defence of the builder, none were perfect, but this one was much worse than all the others.

 

My mate is really, really happy with the work that's being done.  I just bite my lip when he shows me around, same as I've taken to doing with just about every other recent extension I've been shown around by various friends over the last couple of years.  This is also a rare case of me raising insulation for discussion.  I've learned that people don't know and quite literally don't care, and indeed, get defensive if you try and discuss improving insulation and airtightness.  The attitude seems to be that it's fine if you want to build an "eco-house" like we did, but that all that stuff isn't relevant for an ordinary build.

 

All anyone seems to care about is how big the kitchen is and how wide a set of bifolds they can get away with. 

[ProDave]

1 hour ago, ADLIan said:

 

 

Sorry ProDave but I do not see any meaningfull approval, i.e. BBA or similar, on the link and your detail is not supported by TRADA (see Timber Frame Construction, 5th Ed), NHBC Standards or Building Regs. The fact that BC accepted it may simply mean a lack of undertsanding here. It is not a condensation issue but an issue with rain/moisture penetrating the render system and then having ready access to timber and wood based materials - the drained/vented cavity avoids this problem and is shown by the mainstream insulation manufacturers in TF systems.

 

Ian

 

All that matters to me is building control have accepted.the design drawings and as long as it's built to the drawings will sign it off for completion.  I am not using the services of nhbc so if they don't like it, that's too bad but not a problem.

 

i don't want to stay in the past and am happy using a modern building method that's been in use on the continent for some time.

 

[ADLIan]

Hi ProDave

 

It's not just BC sign off - the wall has got to last long after your BC has lost interest. The recomendation from TRADA etc is there for a reason. From past experience they note this type of system causes problems in the longer term - if you are happy to accept this risk then fine.

 

I note that a woodfibre product, Diffutherm, had BBA certification for your exact application but it has now lapsed or been withdrawn.

 

Ian

 

 

[Gimp]

50 minutes ago, ADLIan said:

Hi ProDave

 

It's not just BC sign off - the wall has got to last long after your BC has lost interest. The recomendation from TRADA etc is there for a reason. From past experience they note this type of system causes problems in the longer term - if you are happy to accept this risk then fine.

 

I note that a woodfibre product, Diffutherm, had BBA certification for your exact application but it has now lapsed or been withdrawn.

 

Ian

 

 

Sure, but if it lasts 30-40 years or so everyone's long since moved on or no longer around  Like you say probably not good long term though, sounds to me like the problems had with timber frame in the 60s & 70s with major problems or replacement being needed after 20 years or so due to rot, guess there's no telling how long ProDave's will last though.

[ADLIan]

PeterW - problem with blown bead (or fibre) is you never know if the cavity is filled correctly and without voids - the estimate of product usage and target installed density is VERY approximate. This may be OK with refurb where anything is better than nothng but not, in my view, in new build.

 

At least with a built in product you can see if it's installed correctly or not!

 

Ian

[PeterW]

We've got 3 walls that are refurb with cavities from 65-100mm and then a pair of single story extensions that have a 150mm cavity. 

 

The 65mm wall will get filled and  IWI, the rest get full fill graphite bead and I do get the point about getting them full - given the option I would go with TF and Warmcell but as its two extensions and a conversion it's proved impossible to get a decent price. There is also some internal detail that needs steelwork and TF becomes even more complex at that point. 

[ProDave]

2 hours ago, Gimp said:

Sure, but if it lasts 30-40 years or so everyone's long since moved on or no longer around  Like you say probably not good long term though, sounds to me like the problems had with timber frame in the 60s & 70s with major problems or replacement being needed after 20 years or so due to rot, guess there's no telling how long ProDave's will last though.

Well it's nice to have the doom sayers telling me my house is not approved and will rot and fall down in no time.

 

Yes, I appreciate the render is what keeps the rain out. So attention to detail is important, as is keeping en eye on it. So if in the future I see cracks then I will need to fix them. With a masonry wall you can let the render blow and half of it fall off and apart from looking tatty, nothing much will happen. With my build it will be more important to repair any defects quickly.

 

Having had a good look at and spent a lot of time working with this wood fibre board, it is actually very surprisingly resistant to water. The outer layer has coating that makes it waterproof. I have had some bits left exposed while waiting for the renderer, and rainwater just runs off. compare that to bare timber where the water soaks in and wicks deep into the timber.

 

The firm that dis the design on my house have just built some flats in town using this method, so the housing association involved are happy with the risk.

 

As to vapour barrier. the condensation analysis and approved drawings show just the OSB layer as the vapir and air tightness layer. But when I do the interior I am likely to also include a air tightness / vapour membrane on the inside. 

 

[Declan52]

2 hours ago, ADLIan said:

PeterW - problem with blown bead (or fibre) is you never know if the cavity is filled correctly and without voids - the estimate of product usage and target installed density is VERY approximate. This may be OK with refurb where anything is better than nothng but not, in my view, in new build.

 

At least with a built in product you can see if it's installed correctly or not!

 

Ian

When you are building the blocks you leave out a few half bricks at different heights so you can see if the beads get to these points. Same goes at the of your cavity, leave of some of the slate/asbestolux that you have closed the cavity with so you can see if the beads are right to the top. Have some squares of timber cut so once you see the beads coming out you can wedge the timber in. Other than that a thermal camera will tell you if it's done fully.

[Declan52]

I am sure whatever system Dave has used he done his research and found it to be fine. Like most renders it will have some sort of water proofer built in and the same goes for the wood fibre boards. 

How long were the wood fibre  boards exposed to the elements before you got the render on and did any show signs of water damage. If they didn't let water in uncovered I doubt they will when the render is on top.

[Construction Channel]

7 minutes ago, ProDave said:

Well it's nice to have the doom sayers telling me my house is not approved and will rot and fall down in no time.
 

 

You can only go on what you are advised to do at the time, My money says you will be fine and the house will probably outlast the grandchildren,

 

But as you said all that matters at this moment in time is being able to get it signed off by BC so you can get on with living in it. worst comes to worst there are always remedies, 

 

[ProDave]

The wood fibre board is rated by the manufacturer to be exposed to the weather for 3 months before being covered. I have not exceeded that yet. However the roof (which is also covered with wood fibre) was closer to 6 months with only the breathable roof membrane protecting it without leakage before I got the tiles on.  In fact the garage roof has only just been tiled and that is a year since it was put up, again only the breathable membrane protecting it.  Not a drop of leakage inside.
 

[PeterW]

32 minutes ago, Construction Channel said:

 

You can only go on what you are advised to do at the time, My money says you will be fine and the house will probably outlast the grandchildren,

 

But as you said all that matters at this moment in time is being able to get it signed off by BC so you can get on with living in it. worst comes to worst there are always remedies, 

 

 

A lot of the new "guidance" is actually thinly veiled arse covering by the warranty companies and the likes of NHBC and others. Why disrupt the status quo if it's been working for 30 years ..??

 

I remember looking at some products in Iceland that would be great in the UK but aren't certified by BBA or others so can't be used - cost of certification far outweighs the benefits. 

 

@ProDave I think your system is used in a  lot of German builds with no issues however it's not been fully certified for UK use which is barking mad ..!! Makes no sense as the last time I checked, rain was rain and frost was frost no matter where you were !!

[ADLIan]

Not meaning to be negative just trying to advise on accepted good practice within the timber frame and insulation industries backed by British Standards and BRE work.

 

if you are happy with the system and your BCO is willing to sign off then fine.

 

Ian

[PeterW]

41 minutes ago, ADLIan said:

Not meaning to be negative just trying to advise on accepted good practice within the timber frame and insulation industries backed by British Standards and BRE work.

 

if you are happy with the system and your BCO is willing to sign off then fine.

 

Ian

 

Ian I don't think anyone sees it as negative - what's disappointing with the "industry" is its lack of investment in new methods. The UK seems to be 5-10 years behind the rest of Europe on construction technology and even the basics have to be imported. Look at the Window industry for an example and it's just driven to a bare minimum to meet regulations. 

 

I I was talking to Quinn at length at Ecobuild about their construction methods and even they said the update into mainland UK was going to be minimal - there wasn't or isn't the need for change. 

 

I remember many years ago the development of a plastic wall tie by my fathers company. It far exceeded the thermal bridge requirements we have now, but it's strength could not compete on a stretch test with steel - the BS standard test. 

 

To prove a point, they set a plastic and a metal tie into mortar and let it set for 28 days and then retried the test. The smaller surface area of the metal loop tore out the mortar joint - the plastic stayed intact. But that's not the test they use for strength - they test the component !

 

In Australia and South Africa  they are widely used and walls don't fall down ..! But as it doesn't meet the BS testing regime, then it is deemed inferior.

 

I do get the use of standards but sometimes we need to get off the fence and try some new things - and it's sad that mostly it's the self builders who are doing that as the volume builders are just set in their ways. 

[Crofter]

Is there no international recognition of building standards and certifications at all?

[Gimp]

Sounds like not venting a cavity masonry wall is the way to go then, the weep holes will probably do anyway to suffice in air change over time without being overboard I'm thinking. I'm guessing heavy/medium density blockwork is used on the outside for strength against wind load and also security as anyone could saw through into your home if it were aerated block outer, sounds a bit extreme I know, but was watching a programme a year or two back and some thieves had done just that, but through an aerated block wall into a commercial premises. Thinking perhaps a medium density block then u-value not too bad but still fairly dense but early days yet. 

[Declan52]

8 minutes ago, Gimp said:

Sounds like not venting a cavity masonry wall is the way to go then, the weep holes will probably do anyway to suffice in air change over time without being overboard I'm thinking. I'm guessing heavy/medium density blockwork is used on the outside for strength against wind load and also security as anyone could saw through into your home if it were aerated block outer, sounds a bit extreme I know, but was watching a programme a year or two back and some thieves had done just that, but through an aerated block wall into a commercial premises. Thinking perhaps a medium density block then u-value not too bad but still fairly dense but early days yet. 

If burglars round your way would rather go through a wall than pop a door or window I think they have too much time on there hands.

What ever the cheapest block is put it on the outside. 

[Temp]

Just a reminder that walls have to meet Parts B (Fire) and E (Sound) and that this may affect the make up of the outer leaf.

[Gimp]

22 hours ago, Declan52 said:

If burglars round your way would rather go through a wall than pop a door or window I think they have too much time on there hands.

What ever the cheapest block is put it on the outside. 

It would keep me awake at night, particularly when away

 

[Gimp]

2 hours ago, Temp said:

Just a reminder that walls have to meet Parts B (Fire) and E (Sound) and that this may effect the make up of the outer leaf.

Yeah, been looking into Part B regs at the moment with regard to unprotected area of the wall to the boundary. I'm guessing block walls would be real fire resistant so would pose little problem in this respect whereas timber walls less so. Sound I think should be fine on this front also with all the cavity in between partial or full fill.

[Gimp]

A couple of interesting sources here I've found about weep holes & venting the cavity:

 

https://masonrysolutions.wordpress.com/2011/03/29/what-are-weep-holes-and-do-i-need-them/

 

http://www.labc.co.uk/news/renders-weep-holes-are-you-using-them-correctly