Air tightness with Blocks

Hi,

Why would you need an airtightness detail for hanging kitchen units on an internal wall?? Where is the air going to escape to ?

Don't forget that you will lose lots of air/heat every time that you enter/exit the house. I say build your house & heating system around how you live. Rural/Urban, kids/no kids, pets/no pets, single/not, both work/one works etc etc. With regard to passive house I firmly believe in the law of diminishing returns.

Naux

DeeJunFan wrote: »

My main focus was on Block build but i have recently began a second prong of research on Timber Frame passive building. In a discussion on another forum a user raised a good point. Assuming Sand/Cement plaster is your air tightness barrier in a block build and any hole made in that layer eg Raw plugs etc would compromise its effectiveness.

Think about it. You drill a hole in the sand/cement plaster, insert rawl plug and then screw fix the fitting in place. The original drilled hole is now "plugged" (combination of rawl plug / screw) and therefore AT barrier is still intact.

hi fclauson,

would you mind telling us how you dealt with penetrations to the external wall air tightness layer on your build? e.g. power sockets, light switches, wall hangings, curtain rails, blind fixtures etc.

slip

slipstream wrote: »

hi fclauson,

would you mind telling us how you dealt with penetrations to the external wall air tightness layer on your build? e.g. power sockets, light switches, wall hangings, curtain rails, blind fixtures etc.

slip

You need to firstly minimise penetrations - so a service void is useful keeping all electrical cables etc inside the airtight layer.

Where you have to penetrate
a) membrane going upwards - in one place in the centre of your house put in a piece of ply and drill through it with the number of cables which need to make their way into your loft space - thread each cable through and seal around each one. This worked very well.
b) wall sockets - external wall - and within 1M of a T off the external wall - chase , bond chasing with "pink" plaster and push socket box into pink bonding to seal. You will still have to check each socket when you do your air tight check as not all worked out perfectly for me. The chasings going up the wall as per the above then go into the service void and hence you do not need to puncture the membrane for each socket cable.
c) doors within 1.5 M of T off external wall - bond around the door frame (as well as scratch coat all the walls) as air will go around the architrave and through the block work to the out side.
d) pipes etc - seal every one with combination of tape and airtight mastic
e) hanging things on external wall - put a little of the air tight mastic on the screw as it goes in.

Never let ANY dill on site without briefing the user about how to maintain air tight layer.

Be eagle eyed and vigilant - many trades say "achh its only a small hole" - remember you are only allowed a hole smaller than an A5 sheet of paper across the whole fabric

slipstream wrote: »

thanks; it is very helpful to find out what worked on a project that achieved results like yours.

what is pink plaster and would you use it if you were doing it again or something else?

the skin coat you use a final plaster finish

did you bury the cables directly in pink plaster in the chase or use a plastic cover or conduit?

I think they have to be in conduit to comply with regs

did you use this as well as or instead of wet plastering? was the same air-tighness finish applied to internal and external walls?

thanks again,

slip

Plaster & sand and cement is airtight so you can use which ever - the final pink plaster coat is just easier and thinner to apply - so you can mix and match - but you do need to coat any surface which has a chance of leaking air externally

lownhard wrote: »

How do you plaster an airtight membrane into a block wall to avoid the sand cement plaster falling off the membrane?

There are tapes with a "nap" and you can also cover the membrane with wire mesh
check out the manufactures instructions

DeeJunFan wrote: »

Thanks for the input fclauson,

turns out you are a celebrity in the Passive house world!

I am currently struggling against the tide of indifference in my build. My architect thinks going for a wider cavity is a waste of time. He said the difference between a 150mm and 200mm cavity will only save the same heating costs as running a light bulb.

God only knows what he will say when i ask him to design some thermal bridge free junctions. I already have a number of details to choose from but it would be interesting to see what he comes up with.

Thanks again
Damian

If the Dr cannot see you disease then change doctors don't ignore the disease

Hi flcauson, a few quick questions if you dont mind in relation to your very helpful post above:
1. Did you use special socket boxes (i.e. with grommets/gaskets) or did you find that preparing the chases with bonding/skim was sufficient?
2. Is there any precedent/testing/guidance on the 1m and 1.5m distance from external walls or is this a new standard you have set for the rest of us?!!!
Thanks
PK