full fill cavity

fiacsher

Just getting ready to commence a new build. Does anyone have any suggestions on if it is more cost effective to full fill a 150mm cavity with beads or go up to a 200mm cavity?

fclauson

The answer is it depends
what is your foundation detail
how are you limiting thermal bridging where the walls meet the foundation
what is your window detail
what is your roof detail
have you looked at each and every thermal bridged and worked out how you are going to build it

my advice - do not start until you know all of the above as this stuff is really hard to work out on site - make sure you have detailed drawings of everything

kieranhr

But the short answer to your question - a 150 mm cavity full-filled with graphite bonded bead is roughly equivalent in u-value to a 150 cavity with 100 mm of rigid PIR board, namely 0.2 W/m2K. The extra insulation in the full-fill is cancelled out by its higher thermal conductivity. For my money though, the full-fill is a better construction as it cuts down on thermal looping within the cavity.

beyondpassive

I'd go with 200 (or even 250/275) You can then use stainless steel wall ties which are more robust than basalt ties and glue. 250 silver bead fill has a conductivity of 0.33W(mK) giving a U-Value of about 1.45 corrected for wall ties to about 1.6W(m2K).

Edit. giving a U-Value of about D'oh 0.145 corrected for wall ties to about 0.16W(m2K).

fiacsher

i'll take it u mean 0.16, where can i locate 200 ties, aint they very expensive?

beyondpassive

fiacsher wrote: »

i'll take it u mean 0.16, where can i locate 200 ties, aint they very expensive?

There is an Engineering Company in Vartry in Wicklow.

dfader

beyondpassive wrote: »

There is an Engineering Company in Vartry in Wicklow.

Beyondpassive,
Have you any pictures or details you wouldnt mind sending on of the easiest/simplest way to close a 250mm cavity at the reveals and heads (reducing termal bridging and air leakage offcourse). I've seen several ways of doing this now and would like to know whats simplest on site. PM if you wish.
Thanks,
dfader

sydthebeat

dfader wrote: »

Beyondpassive,
Have you any pictures or details you wouldnt mind sending on of the easiest/simplest way to close a 250mm cavity at the reveals and heads (reducing termal bridging and air leakage offcourse). I've seen several ways of doing this now and would like to know whats simplest on site. PM if you wish.
Thanks,
dfader

do you not think that this kind of information would come with a fee attached? just wondering...........

dfader

sydthebeat wrote: »

do you not think that this kind of information would come with a fee attached? just wondering...........

Well thats BP's decision. Also why I said pictures not necessarily details.

beyondpassive

dfader wrote: »

beyondpassive wrote: »

There is an Engineering Company in Vartry in Wicklow.

Beyondpassive,
Have you any pictures or details you wouldnt mind sending on of the easiest/simplest way to close a 250mm cavity at the reveals and heads (reducing termal bridging and air leakage offcourse). I've seen several ways of doing this now and would like to know whats simplest on site. PM if you wish.
Thanks,
dfader

The ties are 400mm long stainless steel with a vertical twist and cost €70 per hundred with 4 needed per meter and doubled up at the opes and top of cavity.

The wide cavity details are specific to each individual project and would need to be coordinated with your Str Engineer and Architect. Window placement is critical and again depends on the type of window selected, the installation thermal bridge at the sill and threshold, the air tightness benchmark and the design aesthetic.