Air tightness with Blocks

DeeJunFan

Hi All,

I am in the planning stages of a Self-build (Maybe partly contracted partly direct labour)

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.

What would you recommend as an air tightness detail say for hanging kitchen units etc on a sand/cement plastered internal wall?

My initial thought is to ensure that any holes made by trades be back filled with and Air-tight sealer (Can't name products) and then insert plugs/fixings.

Would this work?

Are there any other areas where there are not specific products available ie tapes or membranes?

Thanks
Damian

Naux

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

Well its not only kitchen units i'm thinking of.

Any puncture holes in the block, so any screws, pipes, wires, conduits etc.

As far as door openings i will be using internal doors to reduce heat loss.

I do understand your point about building the house to suit your lifestyle but there are so many large investments for a low energy home and if you get the details wrong then you can waste an awful lot of money!

Thanks
Damian

Naux wrote: »

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

MicktheMan

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.

fclauson

MicktheMan wrote: »

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.

not wholly true - one of the leaks in our house was around kitchen cabinets attached to external wall - it cracked/damaged the plasterwork and air got out through this - might not be much but remember across a whole build you can only have a hole about the size of a 4inch pipe - and across say 1000sqm of external wall thats not much

slipstream

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

bertie 56

Butyl tape ?

Usually used under roofing battens when nailed through a membrane, but some are double side and sticks in masonry and blocks.

fclauson

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

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

fclauson wrote: »

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.

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

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

fclauson wrote: »

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.

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

fclauson

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

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

fclauson

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

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

fclauson

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

acehigh76

MicktheMan wrote: »

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.

I have to agree with Mick. plus if your wall is 100 mm use 80 mm plugs.if your wall cracked because of using plugs then air tightness is the least of your worries

PROJECT K

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

fclauson

PROJECT K wrote: »

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?

what we did was chase wall, pink plaster bond the chase and push the metal socket box into the pink plaster bonding. The cables go up to ceiling level but are kept inside the thermal envelope. This worked ok - but still some leaked so we had to go back around with air tight mastick to fix those which still leaked.
If you have cables which need to go into the roof (TV etc) then in once central place put a 1ft/1ft square board - secured to the airtight membrane and then drill a hole through for each cable and seal around. You will never get a bunch of cables airtight easily.

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

Not that I know about - it was on advice of beyondpassive who is a member of this board