Air tightness advice required for masonry build

[ruggers]

I'm looking to achieve the best air pressure test result I can on my 200m2 masonry self build. Under 2M3/hr/m2 @50 PA I'm about to install the 1st floor joists & would like advice on sealing the block outer walls. All of the walls, or focus only on the area directly behind the masonry joist hangers, which once installed, I can't get behind them.

 

A little about the build & what I've considered.:

Masonry cavity wall 100 dense block, 100mm Tongue & groove PIR fitted by myself with most joints taped, 50mm air gap, 100mm facing brick.

MVHR to be installed (Zehnder Q350)

*First floor installed using 250mm deep masonry hangers - These will be tight to the blocks so i'd like to seal the blocks before the hangers are installed.

Windows, doors, ceilings etc will all be sealed & taped including airtight loft hatch.

Walls will be dot & dabbed with perimeter edge picture framed in dab then boards skimmed. Wet plastering isn't gonna happen.

 

For sealing the air permeable block work before dabbing, options are:

• Do nothing.
• Brush sand/cement slurry over all internal walls, which many seem to say that parge coating is now a waste of time, why?
• Cover all block work in liquid membrane like passive purple, blower proof membrane, Soudal soudatight. (Expensive but effective).
• Use liquid membrane but only around key areas like DPC level, around the hangers & wall plate junctions?
• Aerobarrier - Too expensive from what I've seen, over £2k not in my budget.

 

They say if water can get through blocks, air definitely can.

 

 

 

[Nickfromwales]

29 minutes ago, ruggers said:

All of the walls, or focus only on the area directly behind the masonry joist hangers, which once installed, I can't get behind them.

Use wall plates and hang off those? No need to punch into the blockwork a load of times and create work afaic. I believe the Tony's Trays are the weapon of choice, if you do choose to turn the house into a colander. If not then you just tack a ribbon of AT membrane to the wall and then fix over it, but see my last for why none of this is necessary if you use one's noggin.

 

29 minutes ago, ruggers said:

Under 2M3/hr/m2 @50 PA

So under 1ACH. Not a bad target, but better is doable, and the rewards are there for the taking if you strive for better.

 

29 minutes ago, ruggers said:

100mm Tongue & groove PIR fitted by myself with most joints taped, 50mm air gap

Why not pump the gap full of bonded EPS beads afterwards and fully insulate?

 

29 minutes ago, ruggers said:

MVHR to be installed (Zehnder Q350)

Buy a perfectly comparable Brink and save 4 figures. Then....

29 minutes ago, ruggers said:

Aerobarrier - Too expensive from what I've seen, over £2k not in my budget.

....use the money not wasted on the Bugatti of MVHR to get the best AT solution you can. If £2k for AT isn't in your budget, then neither in a Zehnder MVHR . I know where my priorities would be here, plus if you get the unit bought ASAP, then Air-Haus.co.uk have a massive discount on these atm. I've nudged a few clients to buy the systems/units now to save money.

 

29 minutes ago, ruggers said:

• Brush sand/cement slurry over all internal walls, which many seem to say that parge coating is now a waste of time, why?
• Cover all block work in liquid membrane like passive purple, blower proof membrane, Soudal soudatight. (Expensive but effective).
• Use liquid membrane but only around key areas like DPC level, around the hangers & wall plate junctions?

All negated by Aerobarrier............ Which means if you take some simple advice, you'll come out with a better result, executed faster, with less trades involved, and it'll cost you less.

 

Take this from someone who's doing this for a living.

[ruggers]

1 hour ago, Nickfromwales said:

Use wall plates and hang off those? No need to punch into the blockwork a load of times and create work afaic. I believe the Tony's Trays are the weapon of choice, if you do choose to turn the house into a colander. If not then you just tack a ribbon of AT membrane to the wall and then fix over it, but see my last for why none of this is necessary if you use one's noggin.

I don't like the Tony tray for 253mm joists, looks ok for 225mm joists. Too late now joists are ordered and hangers are here.

I like the timber ledger plate with timber hangers, but couldn't get the S.E to agree to it with it spaced off the wall 20mm to allow for services.

1 hour ago, Nickfromwales said:

 

So under 1ACH. Not a bad target, but better is doable, and the rewards are there for the taking if you strive for better.

 

Why not pump the gap full of bonded EPS beads afterwards and fully insulate?

Already at 1st floor height using T&G PIR. Got a direct load of it. EPS can't be used in our area with facing brick and cat 4 or 5 wind driven rain. I agree its a much quicker and easier way of getting consistent results, but I've never heard of a single person in the county who's used it. Trying to get architects and others on board in the early days was hard work. They all live by cavities need to breath.

1 hour ago, Nickfromwales said:

 

Buy a perfectly comparable Brink and save 4 figures.

Never heard of Brink, I'll look into it. Any certain model to rival the Zehnder with preheater? I was going with a company to refine my on design, supply and commission. I'll self install. I've spent too long studying everything else & against the clock now so don't want to design & calculate my own.

Not many trades will be involved once built. I'll be doing or involved in 80% of the rest other than plastering & windows.

I don't have extra for aerobarrier so it would need to come from a saving elsewhere as you mentioned. Unfortunately family bereavement now means theres a set amount to complete the project with no real way to add more.

Edited August 2 by ruggers

[Nickfromwales]

17 minutes ago, ruggers said:

I don't like the Tony tray for 253mm joists, looks ok for 225mm joists. Too late now joists are ordered and hangers are here.

I like the timber ledger plate with timber hangers, but couldn't get the S.E to agree to it with it spaced off the wall 20mm to allow for services.

Already at 1st floor height using T&G PIR. Got a direct load of it. EPS can't be used in our area with facing brick and cat 4 or 5 wind driven rain. I agree its a much quicker and easier way of getting consistent results, but I've never heard of a single person in the county who's used it. Trying to get architects and others on board in the early days was hard work. They all live by cavities need to breath.

Never heard of Brink, I'll look into it. Any certain model to rival the Zehnder with preheater? I was going with a company to refine my on design, supply and commission. I'll self install. I've spent too long studying everything else & against the clock now so don't want to design & calculate my own.

Not many trades will be involved once built. I'll be doing or involved in 80% of the rest other than plastering & windows.

I don't have extra for aerobarrier so it would need to come from a saving elsewhere as you mentioned. Unfortunately family bereavement now means theres a set amount to complete the project with no real way to add more.

Ah, ok, I didn't appreciate you we're this far in, sorry. Your posts probably state this, but I've likely missed it or my brains used the spare disk space for things more fundamental lol.

 

18 minutes ago, ruggers said:

Never heard of Brink, I'll look into it. Any certain model to rival the Zehnder with preheater? I was going with a company to refine my on design, supply and commission. I'll self install. I've spent too long studying everything else & against the clock now so don't want to design & calculate my own.

Most decent ones have the pre-heater, it's not unique to Zhd'r. Ping me a PM and I'll help you push this along. I'm owed a few favours.

 

23 minutes ago, ruggers said:

I don't have extra for aerobarrier so it would need to come from a saving elsewhere as you mentioned

If you go AB and ditch all the other things you mention, which I assume you do have a budget for as you don't state otherwise, then you will save money overall, and time, and hair loss.......

 

 

[Nick Laslett]

My airblower door test guy had just tested a house that had the AeroBarrier treatment and he was amazed with the results. 
 

To paraphrase him, “it was a no brainier.”
 

My approach has been to keep it simple, if you can. The less steps, less trades, less materials, less things that can go wrong. 
 

Despite all the taping, sealing, foaming you do yourself, it is hard not to still fret about if you’ve done enough, or if the work is good enough. I have an ICF build, so the actual walls didn’t need any extra considerations, but all the junctions soon mount up. The material costs too. 

Edited August 2 by Nick Laslett

[MortarThePoint]

I've used Passive Purple quite a lot

 

Aero barrier looks interesting, but I'd worry about my windows getting covered in gloop

Edited August 2 by MortarThePoint

[Nickfromwales]

2 hours ago, MortarThePoint said:

I've used Passive Purple quite a lot

 

Aero barrier looks interesting, but I'd worry about my windows getting covered in gloop

They spend the majority of the visit masking up. Some more time doing the obligatory checks for what Joe Bloggs has missed, including taping up of ducts etc etc, and then they do the application / treatment. 
 

They specifically said to me that you only need to foam around doors and windows, no tape needed there either, just that you did a good job of it and that it was cut back flush / recessed slightly ahead of their arrival. You don’t want them to come and go, and then you remove something that’s been sealed by their wizardry. 

[Tony L]

3 hours ago, MortarThePoint said:

Aero barrier looks interesting, but I'd worry about my windows getting covered in gloop

 

I'd worry about my lungs.

 

Do the AeroBarrier team zero rate their invoice, @Nickfromwales?

[Nickfromwales]

Just recommended PassivePurple to another client for a masonry build we’re getting airtight to PH level or better.
 

PP is a liquid airtight membrane (for anyone wondering) which can be bought as a sprayable liquid, or as a thicker product that you apply by hand with a brush. Get some disposable gloves, decorators coveralls, and some cheap as chips brushes. Easier to throw these away then clean and reuse as the PP starts to go off on the brush and the brushes get mangled on masonry / woodcrete ICF anyways.

 

Theres a few products in the range which can be used, so when we were challenged getting a VERY complex ICF superstructure airtight to PH+ levels, this stuff came in super-handy.

 

If anyone needs info on this, Adam White from Intelligent Membranes is a top chap and extremely helpful tbf. He came out to meet me on site without hesitation to recommend the correct products and to demonstrate how I best applied them to get the great results we attained there. 
 

https://www.intelligentmembranes.com

 

For context, an ICF company I worked alongside previously applied this against the recommendation of myself, and used a boatload of PP, and the AT score was just over 3ACH after £thousands got spent. Poor workmanship will

always yield poor results. 
 

So, you MUST sequence getting AT measures into your construction phase at the design / pre-commencement stage or no amount of Barney-juice will save the day. Sadly for that client it was 💷🔥, but for the one where I drove the AT works it was a game changer. Client thought above 1 ACH, I said lower. First test was 0.88, and I said it can be better, so we went and tweaked doors and windows, and found some nooks and crannies that needed more foam, and then 0.66 ACH which even the clients couldn’t believe.

 

Now, if we’d have known about AeroBarrier back then, the combination of the two products / systems would have got this to around 0.3-0.4 I reckon. Client was happy with 0.66 obvs, but I had got 0.27 previously so like to aim for <0.3 ACH wherever possible. This allows for any degradation over time of AT measures (imo), so more belts and more braces the better. 

[Nickfromwales]

3 minutes ago, Tony L said:

 

I'd worry about my lungs.

 

Do the AeroBarrier team zero rate their invoice, @Nickfromwales?

They should as it’s supply and fit.

 

Just ping them an email, they were super helpful when I rang them for technical info and method statements etc.

 

You’d not need to worry about your lungs!!

 

You’ll be stood outside when it’s being done lol. Water based product so pretty inert afaik. 

[Tony L]

I should think you're right.  Email sent.  I'll report back.

[ruggers]

@Nick Laslett Do you still use any kind of tapes or liquid membrane when going to use aerobarrier, or just use aero barrier only?

 

@MortarThePoint How much passive purple did you use. Full walls, or just key areas or walls and joints?

[Nickfromwales]

Just remember that with AB they want the entire 1st fix done for M&E, all known penetrations through slab / superstructure done, and then they do their thing.

 

For current masonry project, I’ve asked the client to instruct the builder to do a 200mm ribbon of parge at the top of each external, internally, and then to PP that. 
 

The AVCL that comes down the posis on the roof will be cut long, to have about 100mm of skirt left hanging down there, then a 75mm AT tape will fix the AVCL to the PP. That’s over breeze block.

 

AB will go from there, penetrating the porous elements of the masonry and finding the bits the builder / client missed.

[ruggers]

30 minutes ago, Nickfromwales said:

The AVCL that comes down the posis on the roof will be cut long, to have about 100mm of skirt left hanging down there, then a 75mm AT tape will fix the AVCL to the PP. That’s over breeze block.

 

AB will go from there, penetrating the porous elements of the masonry and finding the bits the builder / client missed.
 

If you come down the wall 100mm with the AVCL, how do you D&D the boards to the walls with a perimeter edge seal. The board dab would then only be adhered to the AVCL at the top, not the wall?

[Nickfromwales]

21 minutes ago, ruggers said:

If you come down the wall 100mm with the AVCL, how do you D&D the boards to the walls with a perimeter edge seal. The board dab would then only be adhered to the AVCL at the top, not the wall?

Hence it only being 100mm   Dab over the PP and half over the tape etc reduces that down to only missing ~50mm of ‘mechanical’ adhesion. 
 

PB of wall gets scrim taped to PB coming down the ceiling = winner winner 🐓 dinner. 

[Nick Laslett]

3 hours ago, ruggers said:

@Nick Laslett Do you still use any kind of tapes or liquid membrane when going to use aerobarrier, or just use aero barrier only?

I didn’t use AeroBarrier.  Not sure if they were operating when I was making these choices. 
 

I have an ICF build so the walls and floors already have good airtightness. My air test will be happening soon, so wish me luck!
  

For my window installs I used Illbruck TP651 compriband tape, Illbruck FM330 foam and Siga Fentrim tape. 
 

I have Thermohouse roof boards, so used Illbruck FM330 foam and Siga Wigluv tape for the board joints. I used Siga Fentrim for the wall/roof junction. I have a steel frame roof structure, where the Thermoroof boards are fixed to the timber on top of the steel ridge beams, I used Siniat Foil Roll Intumescent Acoustic Sealant.

 

For MVHR inlet and outlet, I used Illbruck FM330 foam and Triton TT Vapour Membrane paint. 
 

We have two dormer windows. For the dormer cheeks I used Pro Clima Intello membrane, with Siga Wigluv tape. 

 

 

[SteeVeeDee]

17 hours ago, Nickfromwales said:

Use wall plates and hang off those? No need to punch into the blockwork a load of times and create work afaic. I believe the Tony's Trays are the weapon of choice, if you do choose to turn the house into a colander. If not then you just tack a ribbon of AT membrane to the wall and then fix over it, but see my last for why none of this is necessary if you use one's noggin.

 

So under 1ACH. Not a bad target, but better is doable, and the rewards are there for the taking if you strive for better.

 

Why not pump the gap full of bonded EPS beads afterwards and fully insulate?

 

Buy a perfectly comparable Brink and save 4 figures. Then....

....use the money not wasted on the Bugatti of MVHR to get the best AT solution you can. If £2k for AT isn't in your budget, then neither in a Zehnder MVHR . I know where my priorities would be here, plus if you get the unit bought ASAP, then Air-Haus.co.uk have a massive discount on these atm. I've nudged a few clients to buy the systems/units now to save money.

 

All negated by Aerobarrier............ Which means if you take some simple advice, you'll come out with a better result, executed faster, with less trades involved, and it'll cost you less.

 

Take this from someone who's doing this for a living.

 Great reply and very interesting. 

[Tony L]

2 hours ago, Nick Laslett said:

...so wish me luck!
 

 

Good luck, @Nick Laslett, & thanks for your airtightness details.  You certainly sound as though you know what you're doing, so I have saved a copy of your post in my "Airtighness" folder, which I will hopefully remember to look at when I start to select (or others start to propose) which products will be used in my build.

[MortarThePoint]

17 hours ago, ruggers said:

MortarThePoint How much passive purple did you use. Full walls, or just key areas or walls and joints

 

Key areas as we wet plastered the walls. If we'd gone for and dab I'd have fully covered.

 

We have a membrane on top of precast concrete GF subfloor so I painted from that up about a block's height (225mm). The FF is hollow core (HCF) so painted about a block's worth down from that to encompass the ceiling void. Focused on joints between HCF at walls, perhaps should have sealed along whole joint.

 

On FF painted up from HCF about a block's worth and down from top of wall plate about 150mm.

 

Also painted up floor to ceiling all wall corners.

 

I used Intelligent Membranes tape on windows followed by Passive Purple and then their Pink Grip.

 

+1 for Adam being a top bloke.

 

We don't have MVHR and am not aiming at PH standard, but did want to do a reasonable job of air tightness.

[VikG]

So after completing self build air tightness for external walls I found fairly easy to achieve unless in areas where joists were built into the wall itself. Over here we ended up using a lot of expandable foam (not the most eco friendly). One consideration that I still am unsure about (even though our build is finished) is where the internal leaf of wall meets the rafters of the roof. Since we had a warm roof this area was very difficult to make airtight. We extended the PIR behind plasterboard vertically as far as we could go (to the OSB holding the roof above but as you can imagine this created potential leaky points every 400mm where the roof rafters were. There seems to be no issue with thermal imaging, but would be nice to know if there is something else people use to seal the internal area when using an MVHR. We are currrently building the inlaws home in derbyshire and would be nice to get it right. Also when window fitters come ensure there are plenty of foam guns for them to use, they're terrible for leaving gaps all around the windows and where the cavity wall is exposed needs cavity closers.

[Nickfromwales]

On 03/08/2025 at 06:52, MortarThePoint said:

We don't have MVHR and am not aiming at PH standard, but did want to do a reasonable job of air tightness.

Words I never thought I'd see in the same sentence on here, but hey ho lol.

 

So airtight, and then trickle vents in all the windows and extractor fans I guess? 

[Tony L]

On 02/08/2025 at 12:07, Nickfromwales said:

They should as it’s supply and fit.

 

Just ping them an email, they were super helpful

 

Just confirming AeroBarrier is indeed zero rated for new builds.  & their responses to two emails I sent were very helpful, although they weren't prepared to say, "If we come along & your building is already at x ACH, we'll guarantee to get it down to 0.6 or better.".  That's not a big surprise really, although a guaranteed result would certainly mean I'd be more likely to go ahead with them.

[Nickfromwales]

1 hour ago, Tony L said:

 

Just confirming AeroBarrier is indeed zero rated for new builds.  & their responses to two emails I sent were very helpful, although they weren't prepared to say, "If we come along & your building is already at x ACH, we'll guarantee to get it down to 0.6 or better.".  That's not a big surprise really, although a guaranteed result would certainly mean I'd be more likely to go ahead with them.

Thanks for confirming.

 

I doubt they want to go around shooting their toes off, lets be honest, so nobody would say that in reality as no two tests/treatments will ever be the  same.

 

The solution is great for anyone with an overly complex or DIY build, but also I will consider them for any projects where I am coordinating/consulting on M&E (and have made sure the manual AT measures are already super-robust/identified and addressed to suit) as for the price I think this is an excellent set of braces to compliment the belt.

 

Something to make your house more comfortable (for the rest of your life) and that also makes the MVHR efficiency max out, is a no brainer afaic.