Bonded Beed vs Cavity Board

rsheehan

Hi All

My first post!

Im planing to build a new house starting next year. I was wondering about which of the two methods for insulating a 150mm cavity wall would be better?

Would fully filling the cavity with bonded bead insulation provide a better U value then using a 140mm cavity board that the manufacture claims can give a U value of .20.

I also plan on using a lightweight thermal block for the inner side of the wall.

The house will have a very high airtightness rating (done by trusted professionals)

Is this a sensibleness option for a wall

NickTellis

Hi and welcome to the forums. I think you'll find that the jury is still out over bonded bead insulation - many swear by it, while many say that an air gap should always be present in a cavity wall and to fully fill it with beads is a big no-no.

Hope this was a sensibleness answer.

RKQ

IMO a cavity wall is a tecnology developed out of a need to prevent damp walls. To fill the cavity destroys the safe guard of this construction method.

To depend on an external render to keep your walls dry is IMO risky. If you have clay brick fascade, brick quoins or brick soldier arches - then expect wet damp walls!

Surely a aircrete internal block with say 110mm foil + 40mm air gap will meet your requirement?
Others no doubt will have other ideas - just ask yourself why was cavity construction developed?
Good luck

topcatcbr

I have to agree with RKQ about the air cavity. I prefer a min 80mm foil backed urethane board in min 120 cavity with 62mm urethane/gypsum slab inside. This will reduce thermal bridging to a min.

sydthebeat

topcatcbr wrote: »

I have to agree with RKQ about the air cavity. I prefer a min 80mm foil backed urethane board in min 120 cavity with 62mm urethane/gypsum slab inside. This will reduce thermal bridging to a min.

have you done any condensation risk analysis on this??

id be hesitant to specify internal drylining over 0.5 times of that in the cavity.... especially where it may occur in a non vented cavity....

This is just a query, im not challanging the spec...

topcatcbr

sydthebeat wrote: »

have you done any condensation risk analysis on this??

id be hesitant to specify internal drylining over 0.5 times of that in the cavity.... especially where it may occur in a non vented cavity....

This is just a query, im not challanging the spec...

to be honest i wouldnt know how

sydthebeat

topcatcbr wrote: »

to be honest i wouldnt know how

http://www.builddesk.co.uk/our+software/builddesk+u/download

a very very handy free tool.....

rsheehan

Thanks for the info in the posts.

sydthebeat the link to the building software program was good, will take me a little while to figure out how to use it but its good that you can get such hands tools for free:).

A lot of people say that moisture in the cavity could be a problem but i haven't herd of any cases and hopefully a good quality, well finished render on the out side will keep every thing dry.

DustyBin

Hi All
Regarding rsheehan's initial post does anyone know if the remaining 10mm of air is enough of a gap to stop water penetration?
I am currently trying to acheive a similar u-value without using insulation backed plasterboard on the inner face if possible.
Also, I think I read somewhere that Homebond don't like anything above 150mm cavity?
Thanks

RKQ

40mm is consider the recommended clear air gap / cavity. IMO 25 or 30mm is absolute minimum.

There are many methods and ideas at the moment. Only the easiet to construct will survive. These are interesting times!

Homebond may have to change or update that opinion soon. We are all in the process of change... 150mm overall cavity makes sense

DustyBin

Many thanks for speedy reply RKQ