Larger Cavity Widths

M

Musk

Registered User
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13
Was thinking of increasing cavity width to 120mm and going with full fill bead insulation.Somebody has since told me that once you exceed 110mm in cavity width you need to alter your standard foundations and they now need to be of a higher spec.
Has anybody gone with these wider cavities and does it add much expense?Am I just better coming back to 110mm?
Any help or advice at all is greatly appreciated.
 
Built with cavity 150mm and full filled with beads. I dont think the raft spec needed to be changed but check with your engineer.
 
extopia said:
What kind of dpc in walls?
Click to expand...

The normal kind.

Only problem I had was getting wall ties that were long enough (11 inch i think). Had to order them via Brooks and they were a little more expensive. I told the blocklayer to put in more than is normal too.
 
What is certified - the beads or the DPC. Interested to know more details, thanks.
 
First: have you found a certified tie, that long?

I was also told - but please check - that Homebond won't stand over any non-standard cavity widths. This came up on a project in Galway that the client was thinking of doing what you're thinking of, last year. Architect checked with Homebond, and subsequently architect would not stand over that detail, due to non-availability of a tie.

I do have to ask, though, why you think it's a good idea?

You are also introducing a lot of other work/costs associated with that detail - bigger reveals, window boards, cills, questions about window/door frame location.
 

Neither my blocklayer or the windows people or the carpenter doing the window boards had any problems. I dont think the costs were much greater than if I had gone for 100mm. The engineer thought it an excellent idea and had signed off previous houses with the same specification. I dislike dry-lining and so far I have found the heat retention in the house to be excellent.
 
If using a standard foundation and footing you will end up building an extra 100mm block on edge of which you will only use 50mm.
 
Hey
I looked at this briefly before. Doubkle check but if I recall correctly bead insulkation doesnt give as good a u-value as PIR board or similar, so in other words you mighte be better with a standrd cavity and 60mm board than 120mm bead!!!!

or if going for a120mm cavity you can have an 80mm board
 
its worth noting that several studies have shown that a partial-fill cavity insulation does not often work in practice to its 'design' u-value.

The following link may be of interest in this regard:



If any other system is being considered, however, make sure it is IAB certified. BBA certs may also be acceptable in some circumstances if your architect/engineer is willing to sign off on it.
 

Interesting document that, esp with hindsight. Interesting too that the picture on the cover shows why that whole model of wall build is so poor - gaps all over the place, etc, referred to in the document under Thermal Looping.

However, don't get hung up on IAB or BBA certs - if the system you're looking at has a corresponding approval from anywhere in the EU, there should be no issue. It'd be daft to think a German certification, for example, would not be accepted here......
 
The DOE will not accept German certification only Irish and maby British with an Irish cover letter at a push
 
slates is sadly correct, it is near to impossible to get the DOE to accept anything which doesnt have an IAB or at a push BBA certs. They really make you jump through the hoops if you are proposing anything 'off-homebond' standards..
Homebond have a lot to answer for as well in not accepting anything which does not appear in their (mostly useful) 'homebuilding manual'.

As far as off standard wall ties go, i have used 'eurobead' in the past, they seem to be able to source the off standard wall ties for you. they are expensive if you intend to move towards 'passive' u-values howeve.
 
I was at the recent Self Build show in Belfast and a number of speakers said they were impressed with a full fill (well almost) cavity board.

The boards are made of Neopor and come in the following dimentions:

120mm + 10mm
140mm + 10mm
(see link below to see where the +10mm comes from)


Here's the relevant link although the spec is out of date (I spoke with the company rep and they confirmed this): [broken link removed]

The advantage I can see for this product is:
  • boards will fit tight as they are the same width as the cavity
  • means the builders have to be tidy, otherwise boards won't fit into cavity
  • have K value of 0.030 (not quite as good as Kooltherm but ok)
  • tongue and groove so good fit all over
  • BBA approved
Anyway has anyone ever used this product and if not has anyone any comments?
 
the springvale link looks interesting, although it falls between two stools for me...either there is a cavity or their isn't... also how do they get around the thermal looping issue?
they should get irish approval if they're serious about using it 'down south', although in the current climate whey might not want to do to the expense!

something else comes to mind re. partial fill insulation, i saw a house under construction in blackrock a year ago, where they used cavity walls. however, they build the inner leaf first with wall tiles protruding, then fixed the insulation firmly to this leaf using mushroom-head fixings, then built the external leaf (of brick, as it happens).
this would seem to get around most of the problems noted in the link posted above, but i'm not sure how it worked out on a cost level...
 
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