What air tightness should I be targeting for brick and block build?

[mads]

Hello all,

the architect has forwarded me a response from the SAP consultant and wanted to gauge what target (and actual) people have had for air tightness in a traditional block and brick masonry build?

what the SAP consultant said…

Quote

I have attached the Energy Report for the proposed dwelling with an air tightness score of 2.2.

As you can see, currently the dwelling has achieved net-zero with an EPC rating of 114A.  Due to the proposed masonry build, I would recommend that the design air tightness score is not <1. I have allowed for a healthy margin of 2.2 which should be easier to achieve on site with the use of correct preparation and multiple air tests throughout the project.

 

Edited July 30 by mads

[Nickfromwales]

21 minutes ago, mads said:

what the SAP consultant said…

Has anyone mentioned mechanical ventilation or trickle vents to you, or the ideal which is installing MVHR, or do you already have this planned? You're building to (N)ZEB?

[mads]

12 minutes ago, Nickfromwales said:

Has anyone mentioned mechanical ventilation or trickle vents to you, or the ideal which is installing MVHR, or do you already have this planned? You're building to (N)ZEB?

 

Hey Nick, I will be installing MVHR throughout and removing trickle vents from the windows. There is no letterbox though there is a catflap planned (https://www.thepetflap.com/passivhaus-pet-door/) 

 

Not intentionally building to NZEB but there is a desire to build to the best standards we can afford. Already have a 30Kw PV array, solar batteries, ASHP, MVHR, UFH planned. The cavity is 150mm.

[Nickfromwales]

6 minutes ago, mads said:

 

Hey Nick, I will be installing MVHR throughout and removing trickle vents from the windows. There is no letterbox though there is a catflap planned (https://www.thepetflap.com/passivhaus-pet-door/) 

 

Not intentionally building to NZEB but there is a desire to build to the best standards we can afford. Already have a 30Kw PV array, solar batteries, ASHP, MVHR, UFH planned. The cavity is 150mm.

Ok, thanks.

 

Have you heard of AeroBarrier UK? Probably ideal for you to get <1 ACH.

44 minutes ago, mads said:

Due to the proposed masonry build, I would recommend that the design air tightness score is not <1. I have allowed for a healthy margin of 2.2 which should be easier to achieve on site with the use of correct preparation and multiple air tests throughout the project.

This is a bit of a cop-out afaic..... <1 should be achievable if you know where to focus your attention during the early part of the construction phase. I've done builds down as far as 0.27 ACH, and with not a huge amount of additional time/money etc, just attention to detail and a bit of experience/tenacity. Most of my M&E projects have been new builds, ICF and TF, but there are a few on here who have gone down the traditional masonry route and done very well.

 

At 3 ACH I would tell you not to waste your money on MVHR, for context.

[mads]

3 minutes ago, Nickfromwales said:

 

Have you heard of AeroBarrier UK? Probably ideal for you to get <1 ACH.

This is a bit of a cop-out afaic..... <1 should be achievable if you know where to focus your attention during the early part of the construction phase.

 

Yes I have and have put it in the tender spec. However, I don't want the MC to be using it as a get out of jail free card and actually get to as low as possible before we apply it.

 

Also, I agree with you about it being a bit of a cop out so thought I would ask the collective wisdom here as to what has been targeted/achieved before I respond back and ask the SAP consultant to try harder.

[Mr Punter]

I just had an air test done on brick and block flats and they were just under 4.  No mastic or sealing as I did not want to get less than 3 and certainly did not want MVHR ducting.

[nod]

2.2 is easily achievable Most of the site houses are aiming for 2 

They seem to be done as a desktop survey Though they have probably altered this to 3 with the new regs 

Our Sap guy put ours as 9 and we were dead on 2 Old regs so no need for MVRH 

[Nickfromwales]

43 minutes ago, Mr Punter said:

I just had an air test done on brick and block flats and they were just under 4.  No mastic or sealing as I did not want to get less than 3 and certainly did not want MVHR ducting.

Erm, so basically zero comparison lol  

 

15 minutes ago, nod said:

2.2 is easily achievable Most of the site houses are aiming for 2 

They seem to be done as a desktop survey Though they have probably altered this to 3 with the new regs 

Our Sap guy put ours as 9 and we were dead on 2 Old regs so no need for MVRH 

Did you fit normal extractor fans though?

[Mike]

There are currently 67 new-build masonry homes in the UK certified to the PassivHaus standard of <0.6 ACH, so no doubt many more that have achieved that that aren't in the database. As you want to build to the best standards, that would be the obvious target. Air tightness is also one of the least expensive and most rewarding upgrades, if you're planning MVHR.

 

Edited July 30 by Mike

[Nickfromwales]

2 minutes ago, Mike said:

Air tightness is also one of the least expensive and most rewarding upgrades

+1  

[nod]

22 minutes ago, Nickfromwales said:

Erm, so basically zero comparison lol  

 

Did you fit normal extractor fans though?

Yes 

trickle vents on windows 

and normal extractor fans for bathrooms Loos etc 

[nod]

To be fair If you hit below 3 without MVR I would imagine the tested would right it up as 3 They are not there to fail you 

Someone on here recommended a company that did an air test without visiting the build 

 

[Mr Punter]

33 minutes ago, Nickfromwales said:

Erm, so basically zero comparison lol  

 

 

The OP "wanted to gauge what target (and actual) people have had for air tightness in a traditional block and brick masonry build?"

[FarmerN]

Brick and Block construction , wet plaster and a builder who wasn't really intested. Only one air test done at end of construction. Air Test 1.9.

Should have been and easily could have been lower.

Edited July 30 by FarmerN

[Andehh]

2.7 for us, but then we have a few sliding doors which suck(!) for air tightness. 

[Mr Punter]

3 hours ago, FarmerN said:

wet plaster and a builder who wasn't really intested. Only one air test done at end of construction. Air Test 1.9.

 

This plus plumbers and electricians not just mutilating the airtight layer.  Unless you are doing MVHR with the associated install and maintenance issues I am not convinced that anything less than 3.0 is worthwhile, especially on a smaller property in the SE where mains gas is available.

[Nickfromwales]

5 hours ago, Mr Punter said:

 

The OP "wanted to gauge what target (and actual) people have had for air tightness in a traditional block and brick masonry build?"

Sorry. A knee jerk response, as you have a sealed compartment wrt roof above/floor below, ergo far less to detail vs a domestic residence.

[Nickfromwales]

1 hour ago, Mr Punter said:

This plus plumbers and electricians not just mutilating the airtight layer.  Unless you are doing MVHR with the associated install and maintenance issues I am not convinced that anything less than 3.0 is worthwhile, especially on a smaller property in the SE where mains gas is available.

Doesn’t that promote an ethos of “why bother”?

 

If you run your site properly and educate the trades then you’ll find the majority are receptive. If people on your site are performing less than admirably, then I attribute this to poor leadership. 
 

Explaining that poor results or ignorance/slovenliness have consequences to them will address this quite significantly and reduce the problem. Also, telling trades to work slower and more meticulously, and that you accept the marginal uplift in costs for this to be observed, yields far better results imho.

 

1 hour ago, Mr Punter said:

Unless you are doing MVHR with the associated install and maintenance issues

Can you elaborate please?