Airtightness catch 22

soldsold

Here is the problem:

To do an airtightness test in a block house with hollowcore first floors you need to scratch coat the block walls.

To scratch coat the block walls you should have ceiling plasterboard fitted first.

To repair any leaks above the suspended ceiling you need access to tape up the leaks, so plasterboard will get in the way.

So whats the best sequence to follow?

beyondpassive

scratch coat without plasterboard installed, why not?

sas

A very pertinent one to myself at the moment too.

The airtightness guys I've spoken to all state that typically the scratch coat is brought right up to the hollowcore slabs.

This is all well and good but as you said you need the ceiling slabs fitted at this time.

What a friend of mine (who pulled a 0.5 N50 incidently) did was as follows:

Starting with raw block work and membrane held in place below hollowcore with expanded metal:

1. Mark a line approx 4 inches below where you expect the ceiling line to be
2. Sand and cement plaster from this line up to the underside of the hollowcore. For the area above the ceiling line you can put one a good thick layer of sand and cement plaster. This should deal with any damage that was done that you aren't aware of.
3. Have the suspended ceiling guy fit his rails etc at this point.
4. Fit your plaster slabs.
5. Scratch coat the walls up to the plaster that is already in place. You may be able to overlap at this point depending on thickness of the plaster in place.

As I see it you either risk:
(a) have a crack in your ceiling\wall junction if you leave the plasterboard to last until scratch coat is complete
(b) having to rip back the plasterboard if you have a big leak

Note: I believe "Bonding" could be used for step 2 above instead of sand and cement. You would potentially get a better join in step 5 if you went this way.

It was suggested that I plaster the outside of my blockwork to contribute to airtightness which would avoid this problem altogether. However, my PHI engineer has advised against this. The approach I have described is what I currently plan on doing.

I am open to other suggestions that would make this easier.

sas

beyondpassive wrote: »

scratch coat without plasterboard installed, why not?

Risk of crack around the joint between wall and ceiling according to plasterers I've spoken with. Same advice given to the friend I reference above.

I figure SoldSold is being told something similar based on his question.

soldsold

sas wrote: »

Risk of crack around the joint between wall and ceiling according to plasterers I've spoken with. Same advice given to the friend I reference above.

I figure SoldSold is being told something similar based on his question.

Yes, more than one plasterer have advised to put the boards up first, also the plasterboard gives a straight line to work to. I had considered cutting strips of plasterboard about 100mm wide and putting these up at the perimeter but it would probably cause more trouble than it's worth.

Will probably tape the area above the metal suspended ceiling under the hollowcore as best I can and put the plasterboard up

MicktheMan

Consider the following.
The official airtightness test is performed at the end of the build (thus when all finishes are in place) and is therefore too late to do any major repair work.
What I recommend to clients and works quite well is to have two tests performed. One when the airtightness membranes are complete but before any slabbing is started. Okay, you probably wont get a very good result with this test as the walls are unplastered but any good airtightness tester will be able to identify the weaknesses in the airtightness work already carried out. This is generally highly informative for both the client and the tradesmen and helps prevent the membranes from being punctured by the trades later in the build as they can see what airtightness is all about! Proceed with slabbing, plastering etc when weaknesses are sorted and then do the final test towards the end of the build.

soldsold

Good man mickthe man,
that sounds like a plan!

Viking House

sas wrote: »

However, my PHI engineer has advised against this.

Did she give a reason? I'm curious!

sydthebeat

Viking House wrote: »

Did she give a reason? I'm curious!

as a guess id suppose because it doesnt afford a reasonable key for the polystyrene EWI glue??

sas

MicktheMan wrote: »

Okay, you probably wont get a very good result with this test as the walls are unplastered but any good airtightness tester will be able to identify the weaknesses in the airtightness work already carried out.

I'm told unplastered block work leaks like a sieve. Airtightness work of a reasonable standard in theory then should be tighter than the block work and hence I don't see how a test at this stage will provide much value. The majority of the airtightness layer is missing if no scratch coat is in place.

The advice I have been given is that you first test once you have the airtightness layer in place but not covered up. In a masonry house this means scratch coated but not skimmed. Final test once house is complete.

This is the crux of the issue for soldsold. The completion of the airtightness is difficult before some of it is hidden.

sas

sydthebeat wrote: »

as a guess id suppose because it doesnt afford a reasonable key for the polystyrene EWI glue??

No, sorry syd. ALthough I have a call in with an EWI supplier on this as that was what struck me initially too.

Viking House wrote: »

Did she give a reason? I'm curious!

Wasn't huge amount of discussion to be honest. This may be specific to my home.

My house has been designed to have the internal plaster work as the airtightness layer.

If I plaster the outer layer I am introducing an additional airtightness layer.

When you test the house you can't be sure whether the internal or external layer is the tighter layer.

You therefore risk getting moisture into the structure and associated problems.

The junction between the floor slab and outer plaster layer in my case wouldn't be easily made tight based on what's already in place.

Viking House

sas wrote: »

If I plaster the outer layer I am introducing an additional airtightness layer. When you test the house you can't be sure whether the internal or external layer is the tighter layer. You therefore risk getting moisture into the structure and associated problems. The junction between the floor slab and outer plaster layer in my case wouldn't be easily made tight based on what's already in place.

When you externally insulate with the amount you are using, both sides of the concrete wall will end up being about 18-19 degrees, so no temperature drop in the wall means no condensation so no moisture problems.

I'm going to use a bucket with the airtight lid to explain this point!
The lid is the inside of the plastered wall and the base of the bucket is the outside of the plastered wall, there's a hole in either the base or the lid but the air pressure test can't detect which one. I don't think its so important because if there is a hole in the lid the air won't get past the base, if there's a hole in the base the lid will stop the air getting in.

If you externally plastered why would you be worried about connecting to the slab when it now becomes an internal junction? I'd be more worried about the detailing around your girders to be honest.

What type of roof are you building? Have you or Syd any wall/roof junction details drawn up?

sas

Viking House wrote: »

When you externally insulate with the amount you are using, both sides of the concrete wall will end up being about 18-19 degrees, so no temperature drop in the wall means no condensation so no moisture problems.

I'm going to use a bucket with the airtight lid to explain this point!
The lid is the inside of the plastered wall and the base of the bucket is the outside of the plastered wall, there's a hole in either the base or the lid but the air pressure test can't detect which one. I don't think its so important because if there is a hole in the lid the air won't get past the base, if there's a hole in the base the lid will stop the air getting in.

If you externally plastered why would you be worried about connecting to the slab when it now becomes an internal junction? I'd be more worried about the detailing around your girders to be honest.

I'm not disputing what you are saying. I can see the logic in it. I am however paying for advice so it makes sense to follow it.

Viking House wrote: »

What type of roof are you building? Have you or Syd any wall/roof junction details drawn up?

We had a detail drawn up which involved alot of rockwool. Specifically to keep the price down. As time went on I got a little concerned that my idea was going to be difficult to execute on site. Then circumstances changed for us recently and I have a small bit more wiggle room in the budget. So I took a look at softboard again.

Had herself run a u-value on 100mm softboard with cellulose in 225mm rafter. Approx 0.15 taking fixings into account which apparently covers me. The service cavity could be insulated should compensation for an unexpected cold bridge be needed later.

sinnerboy

Ok , I have not actually used this product before . It is applied to only 6mm thickness . So assuming that plasterers are typically concerned that a crack may arise between the ceiling board and the wall skim coat .... because the wall plaster does not overlap much with the ceiling boards ... try -

1. 6mm of Airtite plaster applied to wall - from lower slab edge to upper slab edge ie the whole wall surface
2. Ceiling boards
3. 12-16mm wall finishing plaster ( wet or boards+skim)

You get the same wall plaster overlap to the ceiling as per "the usual way"

I don't talk from experience here - but I should expect this to work

.

sinnerboy

sas wrote: »

It was suggested that I plaster the outside of my blockwork to contribute to airtightness which would avoid this problem altogether. 7

https://www.youtube.com/watch?v=i4rx53ZUd3U

Listen carefully around 4 minutes in . The airtightness layer can only be to the internal .

soldsold

Airtite plaster will go behind insulated slabs fine, but not behind sand and cement plaster. It gives a very powdery finish and the plaster will fall off.

It also wont work over quinnlite blocks as it dries out and cracks like a dried up river.

I used it behind a dry stone internal wall and its an easy DIY material to put up.

Bonding should work well instead, I believe you can put a sand and cement coat over this, maybe someone could confirm?

sinnerboy

soldsold wrote: »

Airtite plaster will go behind insulated slabs fine, but not behind sand and cement plaster. It gives a very powdery finish and the plaster will fall off.

It also wont work over quinnlite blocks as it dries out and cracks like a dried up river.

I used it behind a dry stone internal wall and its an easy DIY material to put up.

Bonding should work well instead, I believe you can put a sand and cement coat over this, maybe someone could confirm?

You have hands on experience so - fair dues .

But why try to finish with sand and cement - why not gypsum plaster - or plasterboard + dabs ?

soldsold

I might be mixing up what your post suggested, by lower slab edge I assume you mean the ground floor and upper slab edge the first floor ceiling?

So by the "whole wall area" you mean just that - the whole wall?

If so, plasterboard on dabs will work fine but neither sand/ cement screed will work, or a skim coat as this doesnt stick to airtite plaster either according to the gypsum rep who did a demo I attended before I used the stuff.

So its:

Airtite plaster followed by plasterboard (insulated or not) on dabs or mushroom fixings, or
Sand/ cement screed followed by skim coat, or
Bonding followed by skim coat within a short time - 24 hours max I think, definitely not more, might be less.

Why use sand/ cement? My understanding is to give a more solid finish than plasterboard with a skim, easier to hang stuff off, greater thermal storage.

sas

sinnerboy wrote: »

Listen carefully around 4 minutes in . The airtightness layer can only be to the internal .

He never states that the airtightness layer can only be to the internal. He implies it by describing the risk of condensation damage to the structure.

In a TF build up this makes perfect sense.

In an externally insulated masonry house, one could argue (VH is saying this) that the internal face of the external insulation IS suitable for the airtightness layer.

I'm going to quiz my adviser a little more and see if I can get more on this.

sinnerboy

Not going to get into semantics ( "states" vs "implies" ) . Keep it simple - keep the warm vapour laden air - within the internal environment . Thus the air tight line is determined .

sinnerboy

soldsold wrote: »

I might be mixing up what your post suggested, by lower slab edge I assume you mean the ground floor and upper slab edge the first floor ceiling?

So by the "whole wall area" you mean just that - the whole wall? .

Yes the entire surface of the raw blockwork as seen before the ceiling slabs go in

soldsold wrote: »

If so, plasterboard on dabs will work fine but neither sand/ cement screed will work, or a skim coat as this doesnt stick to airtite plaster either according to the gypsum rep who did a demo I attended before I used the stuff.

thanks for sharing your real life experience here - useful clarification

soldsold wrote: »

So its:

Airtite plaster followed by plasterboard (insulated or not) on dabs or mushroom fixings, or
Sand/ cement screed followed by skim coat, or
Bonding followed by skim coat within a short time - 24 hours max I think, definitely not more, might be less.

Yes - the point of suggeting the Airtight is that it the affords the relatively thick finishing boards over to overlap the the ceiling boards .

soldsold wrote: »

Why use sand/ cement? My understanding is to give a more solid finish than plasterboard with a skim, easier to hang stuff off, greater thermal storage.

All perfectly valid .

Of course another way to deal with the wall / ceiling junction is to use covings - not suitable for interiors mind you

sas

This is what it breaks down to.

The inside of the house will be plastered anyway. So logically it makes the most sense to have the airtightness layer there too.

Details around sockets are all pretty easily resolved (on paper albeit, execution is a difference matter) and hence this is why the internal surface is the recommended airtightness layer.

In an externally insulated masonry house, there would be no particular harm in having 2 airtightness layers i.e. internal and external faces of blockwork plastered. It is basically a waste of time and materials is how it was put.

So I will stick to the current plan which in my case is to make the house tight at the internal plaster layer.

Carlow52

sas wrote: »

I'm not disputing what you are saying. I can see the logic in it. I am however paying for advice so it makes sense to follow it.
.

Only if you believe it and don't get better advice subsequently.

Taking bad advice because you paid for it is not a sensible approach

In any wall construction the airtight membrane is positioned on the warm face of the structure which is generally the inner face of the wall.

However in an externally insulated house as VH has pointed out the temperature drop, and associated dew point risks, will really only start at the insulation and thus if the make up of the external insulation process provides an air-tightness layer by default then internal layer may be unnecessary.

On when to test, I concur with Micktheman that the intermediate /early test, when done by a competent tester, combined with good smoke testing can be very beneficial.

Viking House

Hi SAS

We airtightened an externally insulated timber frame extension and 2 QL extensions from the outside, and from a builders viewpoint we found it way easier and we will do this in future to all new builds.

If you speak to Cyril Mannion he will tell you of the month he spent pulling out his hair when the plumbers and electricians were in, he had to stand over them constantly, when his back was turned for a minute they had holed drilled everywhere.

The Germans were no better in our Foxrock project, we spent a month ripping out plasterboard because they used inferior tape that peeled off under pressure and left out some membranes, we ended up with 0.8 airchanges there because we couldn't afford to spend any more time on it.

We got to 0.58 with my brothers timber frame house but he didn't want to spend the money to get it certified, we spent 2 weeks getting it from 1.1 to 0.58 so its not easy, the Rathdrum energy plus renovation took nearly a month of work to get it down to 0.8, Arty will do a final test next week so fingers crossed.

If you can imagine plastering your house with a 1-2mm coat of external insulation glue @ €1.50/m2 plus labour. Then fit the windows and fill the house with smoke from Archie's disco ball and turn on the fans. You will see the smoke billowing out through the holes from the outside which you mark and plaster when the pressure goes down.

I've spent weeks on building sites doing airtightness and I can easily see that this takes all the headaches out of it, you can walk away then for 2 weeks and let the plumbers and sparks do what they want without worrying.

But you gotta do your own thing!

Roof's
We're presently doing a Passive standard extension from QL blocks, we used a layer of plywood on top of the 150mm rafters as the airtightness line and put 150mm of EPS on top of the ply. The plywood overhangs the wall and has a few 2 x 2 stiffners on top. The plywood is taped to the external plaster where they meet. We used silicone between the plywood sheets to save money on tapes. We will use rockwool between the rafters and then plasterboard on the rafters with no vapour control membrane, the spots can go into the plasterboard just like before without airtightness boxes and the likes.

Comments please!

sas

Carlow52 wrote: »

Only if you believe it and don't get better advice subsequently.

Taking bad advice because you paid for it is not a sensible approach
.

Agreed. I tend to forget that not everyone knows how I'm going about this. My house is being detailed by PHI directly. Hence, by and large what they say should trump everything else when building a PH.

I do like the idea of plastering the outside too. If I fell short of the standard I'd be very ticked off I didn't do this when I was made aware of it. What I'd like to confirm is whether there is a risk of problems of adherence when the EWI isn't attached directly to the block work.

sas

Viking House wrote: »

If you speak to Cyril Mannion he will tell you of the month he spent pulling out his hair when the plumbers and electricians were in, he had to stand over them constantly, when his back was turned for a minute they had holed drilled everywhere.

The Germans were no better in our Foxrock project, we spent a month ripping out plasterboard because they used inferior tape that peeled off under pressure and left out some membranes, we ended up with 0.8 airchanges there because we couldn't afford to spend any more time on it.

We got to 0.58 with my brothers timber frame house but he didn't want to spend the money to get it certified, we spent 2 weeks getting it from 1.1 to 0.58 so its not easy, the Rathdrum energy plus renovation took nearly a month of work to get it down to 0.8, Arty will do a final test next week so fingers crossed.

If you can imagine plastering your house with a 1-2mm coat of external insulation glue @ €1.50/m2 plus labour. Then fit the windows and fill the house with smoke from Archie's disco ball and turn on the fans. You will see the smoke billowing out through the holes from the outside which you mark and plaster when the pressure goes down.

I've spent weeks on building sites doing airtightness and I can easily see that this takes all the headaches out of it, you can walk away then for 2 weeks and let the plumbers and sparks do what they want without worrying.

But you gotta do your own thing!

This is going to sound like a "dig" but shouldn't be taken that way.

I know 2 people personally that recently had their first blower tests done on their homes.

1. TF built by small custom company. It was delivered as a standard open frame, not a closed panel system. TF company did airtightness details that must be done during construction e.g. middle floor detail. Remaining work was done in conjunction between a specialist approved installer for ECBs system and the home owner (approx 70% work himself). First test obtain 0.24 N50 (this is not a typo). After some additional work they got it down to 0.19 N50.

2. Masonry PH by and large identical in planned spec. for mine. First test was 0.5 N50.

There was no cheating on these e.g. badly sealed windows with masking tape during test.

I have always fully believed that the airtightness was going to be a massive task based on stories such as the ones you've posted.

The success of my friends however suggests that it's about being careful with your choice of tradesmen and getting good advice on your detailing.

Direct labour self builds should not be out performing contractor builds. The anecdotal evidence suggests they very much are however.

I should underline that the 2 owners in question have spent an awful lot of time researching the specific details on their homes and paid well for good advice (based on their results). Neither are construction professionals nor are their careers in anyway related to the construction field.

Viking House

The point here is not who got the best airtightness result, but which way is easiest and most idiot proof so that it can be adopted by most of the building industry. I personally would find it much easier spending €5/m2 externally plastering a house than going around with a microscope looking for pin holes on the inside.
What is your budget for airtight sockets and airtighness tapes and membrtanes SAS?
What is your budget for the labour involved in airtightness work?
Were you planning on lining your roof internally with OSB?

sas

Viking House wrote: »

The point here is not who got the best airtightness result

The point of this discussion was to determine how to make the house most airtight. I wasn't discussing it from a cost point of view because the aim is absolute airtightness in theory. On the houses you plastered outside, what results have you had with them on the blower door?

Viking House wrote: »

, but which way is easiest and most idiot proof so that it can be adopted by most of the building industry.

I'm not concerned with the building industry, only my own home. I share here so that people considering doing what I'm trying get some non-biased info. (if such a thing exists) on how easy\difficult the task is.

Viking House wrote: »

I personally would find it much easier spending €5/m2 externally plastering a house than going around with a microscope looking for pin holes on the inside.

You would need an awful lot of pin holes for them to make any meaningful difference based on the experiences of my friends. When you do use the internal plaster layer you can recover if issues exist. If you get it wrong on the outside it's buried behind the EWI and your only fallback is tackling the inside.

Viking House wrote: »

What is your budget for airtight sockets and airtighness tapes and membrtanes SAS?

Don't have one, it will cost what it costs. Airtight sockets aren't required. The 0.5 house didn't use them. The taping (except at the hollowcore membrane detail) will be require equivalent effort\quantities regardless of the detail chosen. The membrane is only needed inside the roof. I will look at the cost of each (intello vs osb) when I'm at that stage. I don't fancy a blind fill on cellulose in the roof however so intello would have to be alot more expensive to get eliminated.

Viking House wrote: »

What is your budget for the labour involved in airtightness work?

Don't have one, it will cost what it costs. This stuff ain't rocket science so I'll tackle some of it myself. Window installers will fit tapes during installation. We're only looking at the roof space then which is pretty straight forward and is why I fancy doing it myself. The roof airtightness work will be the same too regardless of whether I plaster inside or outside of blockwork anyway.

Viking House wrote: »

Were you planning on lining your roof internally with OSB?

See above. Haven't decided basically.


A thought.

Given the fixing pattern for EWI, I would argue that it effectively makes the blockwork airtight at the outside anyway.

- I'm working on the assumption that the EPS boards themselves are airtight.
- There is a solid band of adhesive around the perimeter of each board.
- The bands from adjacent boards are in contact with eachother.

A final thought.

If your approach is the way to go for the reasons you specified, why isn't it the recommended approach?

Viking House

Its not my method, its a standard method used in externally insulated Canadian timber frame houses. The build programme would go like this; build the blocks, put on the roof, plaster externally, put in the windows and then do the airtightness test. When the test is good you insulate the roof, externally insulate and then do the electrics and plumbing without worries.

Then you have all the options that regular clients have, you can drill holes in the wall, you can put spots in the bedroom ceilings, you can move the position of a door or a wall at a later date without too much worry.

Cellulose over OSB isn't a blind fill the good installers use cameras to check the voids for obstructions and they always insert the hose to the bottom of the void.

Oh and EPS wouldn't be airtight enough, you can blow through it.

Out Of Order

sas wrote: »

Details around sockets are all pretty easily resolved (on paper albeit, execution is a difference matter) and hence this is why the internal surface is the recommended airtightness layer.

sas wrote: »

Don't have one, it will cost what it costs. Airtight sockets aren't required. The 0.5 house didn't use them. The taping (except at the hollowcore membrane detail) will be require equivalent effort\quantities regardless of the detail chosen. The membrane is only needed inside the roof. I will look at the cost of each (intello vs osb) when I'm at that stage. I don't fancy a blind fill on cellulose in the roof however so intello would have to be alot more expensive to get eliminated.

Can I ask what is the method of resolving air leakage at the sockets?

I'm trying to decide my own roof detail at the moment.
Intello/DB+/Vario would be a lot cheaper, faster, and easier work to install.
I would also be happier to be able to check the consistency of the cellulose fill by just pressing the membrane at random areas of the roof.
The other pros are that you would have less weight on your roof, you need less tapes, and I'd also be concerned about the glues used in the OSB.
The cons are that you have less racking strength and it might be harder to press down on the tape to make a seal on the areas between the rafters.

sas

Out Of Order wrote: »

Can I ask what is the method of resolving air leakage at the sockets?
.

You can bed the metal backing boxes for the sockets in "bonding" and run the electric cable into it through the bonding also. This worked for the house that got the 0.5.

There are backing boxes available from ECB (though not strictly designed for masonry) that will accomadate a doulble socket for about €3 each.

Out Of Order wrote: »

I'm trying to decide my own roof detail at the moment.
Intello/DB+/Vario would be a lot cheaper, faster, and easier work to install.
I would also be happier to be able to check the consistency of the cellulose fill by just pressing the membrane at random areas of the roof.
The other pros are that you would have less weight on your roof, you need less tapes, and I'd also be concerned about the glues used in the OSB.
The cons are that you have less racking strength and it might be harder to press down on the tape to make a seal on the areas between the rafters.

Fitting osb will be hard going from a labour point of view i.e. big heavy sheets working over head etc. Fitting membrane will be easier from a weight point of view but definitely awkward in alot of other senses. If I go with membrane I'm not going to do it myself, I'll work along side an installer.

My advice on cellulose comes from a german gentleman that is a cellulose installer in Ireland. His familly established one of the first cellulose factorys in germany years ago. He is very knowledgeable on the installation. He will pump behind OSB no problem but prefers intello because the client can actually see the finished job. This part I like. He also believes fully in intello in terms of its ability to aid the dying of your roof so would recommend it from that point too.

The idea of the use of a racking board on roofs in Ireland is very new so I don't think I'd be put off by the lack of one.

I don't believe that you'd try to seal along the joins between rafters. I assume you'd cut it back to align on a rafter. This I'm open to correction on.