Airtightness

[matthyde83]

I’m looking for some general advice…

 

Due to start the main part of our build in February.  I’ve had to push the architect thus far and tbh he’s not that knowledgeable on airtightness etc. So I’m working a lot out myself. Have a builder on board to shell stage then I’ll take over and work out with subbies  (this is 3rd time I’ve built but not for a good few years and this is now forever family home). 
 

So far.  I’ve increased cavity to 150mm and planning on blown EPS beads.  200mm floor.  Have dormers, vaulted ceilings so will need warm roof detailing there but then 400mm loft roll elsewhere. 
 

Windows and doors I’m considering ply boxes as per Denby Dale ph.  

Everything I’m reading on here talks about the difficulty with getting airtightness. I’m probably being naive so forgive me, but my plan:

 

Tape window/door frames to ply box, boxes to wall

Membrane before boarding ceiling on 2nd floor (1st floor also?), taped to wall

Walls taped to concrete floor (below insulation and screed)

Airtight paint behind boxes, channels etc for 1st fix

Grommets and or seal wherever wires, pipes, ducts enter the envelope

Parge coat (including before fitting/inbetween joists), overlapping all taped joins

Wet Plaster

Decent loft hatch

 

Anything I’m missing here??

[nod]

You don’t need to Parge coat to achieve airtightness You definitely don’t need Parge if you are wet plastering 

Though acoustic sealing all perimeter edges of plasterboard is necessary 

A airtight membrane on the underside of the trusses lapped onto wall will seal the loft off Then pretty much what you have highlighted Frames sockets switches etc 

Edited January 1, 2022 by nod

[Iceverge]

27 minutes ago, matthyde83 said:

Tape window/door frames to ply box, boxes to wall

 

I did this. Used 18mm OSB. Worked fine. Airtight paint + airtight sealant to connect to walls that had been parged. Tape might have been easier. We followed the Golcar window positioning. It's much easier to build. 

 

 

29 minutes ago, matthyde83 said:

Membrane before boarding ceiling on 2nd floor (1st floor also?), taped to wall

 

Membrane to bottom of trusses. 88mm service cavity for MVHR and wiring on 2nd ceiling, then plasterbaord. It's tricky to detail around the back of conduits from the wall chases into the service void.  Here's what I came up with. It made it easy for the membane to be cut back and not interfere with the chase. 

 

 

41 minutes ago, matthyde83 said:

Walls taped to concrete floor (below insulation and screed)

 

I used airtight paint. Dilute coat first and then proper layer x2. 

 

43 minutes ago, matthyde83 said:

Airtight paint behind boxes, channels etc for 1st fix

 

Yes, you can see the chases above. again a dilute course first. I found lots of leaks here when blower testing. Used airtight silicone to seal. 

 

44 minutes ago, matthyde83 said:

Grommets and or seal wherever wires, pipes, ducts enter the envelope

 

 Airtight silicone and paint again. Where cables ran through the ceiling membrane I drilled individual holes in a 300x300mm square of ply and siliconed each wire one by one. I found those grommets expensive. You can make a pretty good seal with airtight tape too. 

 

48 minutes ago, matthyde83 said:

Parge coat (including before fitting/inbetween joists), overlapping all taped joins

 

We had a disaster with our "tony tray around the precast concrete slabs. I ended up sealing every room individually . Not ideal. I would use the denby dale detail and timber floors if doing it again. 

 

49 minutes ago, matthyde83 said:

Wet Plaster

 

Yes. 

 

49 minutes ago, matthyde83 said:

Decent loft hatch

 

Hard to find. I bought a passivhaus approved one and it leaked. I would be tempted to use a window with an insulated panel instead of glazing. 

 

52 minutes ago, matthyde83 said:

Anything I’m missing here??

 

 

Don't forget that blockwork is very leaky . I was careful to make sure any walls abutting external walls were sealed within 1m of the external wall Including the tops of the internal walls on the first floor. 

 

 

 

Building a DIY blowerfan made all the difference in finding leaks.

Tested 0.31ACH50 in the end. 

 

Do you have a robust detail for the threshold? 

 

 

Re insulation, we have 200mm EPS in the floor. 250mm EPS Beads in the wall and 400mm cellulose in the wall.

If we could do it again 300mm EPS floor. 300mm cavity wall. Would have added less than €2k which starts to look like small money considering it will work forever unlike a boiler or heat pump.  

 

Maybe mineral wool batts instead of EPS beads. The jury is out.  

 

 

Good luck! 

 

 

[matthyde83]

This is excellent thanks both.  Really helps me visualise how to do it!

 

@Iceverge few questions…

 

What’s the outside detailing on the windows?  I’d be worried about OSB being exposed? Also how do you seal cavity behind osb for damp and fire? What’s Golcar window positioning?

 

I think I’m following the ceiling detail.  So you are sealing bottom of trusses then creating a void for services, avoiding needing to take them through the seal?  So why the OSB?  How do you create the void dropping the ceiling that far?  

 

Good tip on sealing the top of walls where they meet external, not sure I’d have thought of that. 

Don’t have a detail for threshold yet and have a few of them!  Front door, 2x back doors, 2x French doors and Bifolds!

[matthyde83]

52a1 h.pdf 53a1 f.pdf

[nod]

Stopping the air getting to the block work is the main thing

Parge is a waste of time and money 

As a business I’ve used 1000s of m2 Mainly as a sound coat Even the housing associations have stopped including it for airtightness 

[Iceverge]

5 hours ago, matthyde83 said:

What’s the outside detailing on the windows?  I’d be worried about OSB being exposed? Also how do you seal cavity behind osb for damp and fire? What’s Golcar window positioning?

https://www.greenbuildingstore.co.uk/golcar-passivhaus-windows-doors/ this shows the Golcar project. 

 

Our windows were supported underneath buy the concrete window sill built into the outer leaf and bolted to the outer leaf with angle brackets.  We used these sills which have a thin upstand. 

 

The OSB is overlapping the windows by about 5mm and concrete screwed to the inner leaf. It requires care by the bricky to set back the sill and header the right amount although nothing would stop you building too big and packing it out. The window was installed first. Then the OSB sill and head and finally the reveals. All had to be cut to measure. It was slow, but once screwed in place with brackets was quite rigid. We drilled the OSB to pump eps beads into the area below the cavity tray and under the sill. 

 

 

As you can see the OSB is still about 50mm back from the outer leaf so doesn't get damp and allows the EPS beads to press against the edge of the window. 

There is an alternative and maybe easier to build method here but I preferred the use of OSB to membranes for robustness 

https://www.edmondodonoghue.com/build-it-better-window-door-detailing/

 

Re damp and fire. As I understand it the issue with fire is from the inside the house into the cavity. The plasterboard and skim take care of this. Mineral wool batts are better than EPS beads for fire.

 

Regarding damp I'm surprised there's not more leaks with plastic dpc used as cavity trays. It's so vulnerable to being damaged during building. In fact,  I would build an angled PVC profile only half way across the cavity into the outer leaf  if doing it again and dispense with the full cavity tray. I sealed the windows to the outer blockwork reveal with airtight sealant and carefully(ish) airtightpainted the PVC windows to the outer blockwork reveals. This was mainly to keep the cavity windtight but has a dual purpose of sealing the window to the outer render in a fashion that won't crack and let water blow in. 

 

 

5 hours ago, matthyde83 said:

I think I’m following the ceiling detail.  So you are sealing bottom of trusses then creating a void for services, avoiding needing to take them through the seal?  So why the OSB?  How do you create the void dropping the ceiling that far?  

 

Yes and put 44x44mm battens x 2 to create an 88mm service cavity.

It was a good bit of work but I didn't want to penetrate the ceiling membrane. With the benefit of hindsight, as I did the MVHR myself I would trust myself to seal around the ducting and plenums if it was done in the attic and use a 22mm service void with 22x75mm strapping for the electrician.

 

Not sure what you mean re the OSB?

 

5 hours ago, matthyde83 said:

Don’t have a detail for threshold yet and have a few of them!  Front door, 2x back doors, 2x French doors and Bifolds!

 

Greenbuildingstore's threshold is as good as any. I bought GRP grating. I did a post on this somewhere recently. 

 

Bifolds. "Sucks through teeth..........."

 

It can be done. Greenbuildings store achieved 0.18ACH with https://lacunaofdenmark.com/en/lacuna-folding-doors/ . I imagine they're pricey however. 

 

However MOST of them are tragic. if you can live with french doors or tilt and sliders instead it'll be much much cheaper and perform better.  Sliding or brush seals belong in the bin. Compression seals X 3 for every opening. 

 

 

 

 

 

 

 

 

 

 

 

Edited January 2, 2022 by Iceverge

[Iceverge]

Looking at your plans you'll really need to take care with the thermal bridging. 

 

It's a nice design, in effect its a smaller second story on top of a larger ground floor. The external upper block walls being supported by steel will be the main source of your issues as these will bridge the continuous thermal envelope.  Steel is a tremendous conductor so you could end up with condensation as well as energy loss and discomfort if not attended to. 

 

Is that a chimney in the Study?  I would bin it unless you're far from neighbours and have ready access to free wood. 

 

Is it possible to include an accessible shower and on the ground floor. I recently listened to a heart-breaking documentary about a woman who went from hale and hearty to dead in the space 7 months with motor neuron disease. 

 

 In the middle of the worst of it there was a discussion with care workers where the woman in point was faced with the choice of builders coming in to rip up her home to make it suitable for her condition or being carted off to a convalescent home mid covid. A few lines on a piece of paper now is cheap and easy in comparison. 

 

 

[matthyde83]

1 hour ago, Iceverge said:

The OSB is overlapping the windows by about 5mm and concrete screwed to the inner leaf. It requires care by the bricky to set back the sill and header the right amount although nothing would stop you building too big and packing it out. The window was installed first. Then the OSB sill and head and finally the reveals. All had to be cut to measure. It was slow, but once screwed in place with brackets was quite rigid. We drilled the OSB to pump eps beads into the area below the cavity tray and under the sill. 

Ok so you didn’t use the OSB to support the windows then, just for airtightness.  Could you reach in to the cavity to paint the seal to the outer (I’m assuming from the inside? Unless you mean from the outside in which case ours is a brick finish not render).  I like the drilling of the board to pump in EPS under the cavity tray. 
 

One thought I had on the OSB / ply was the ability to build precise openings meaning windows can be ordered up earlier rather than waiting for structure completion given lead times. 
 

1 hour ago, Iceverge said:

It was a good bit of work but I didn't want to penetrate the ceiling membrane. With the benefit of hindsight, as I did the MVHR myself I would trust myself to seal around the ducting and plenums if it was done in the attic and use a 22mm service void with 22x75mm strapping for the electrician.

Yep I’m thinking of installing MVHR myself so this sounds like a good solution.  Did you have MVHR designed separately or by supplier.  I’ve had a quote from a renewables company that would design, supply and install MVHR, ASHP, UFH and 1st fix plumbing.  But it’s a pretty penny. 
 

Like the look of the Lacuna.  It’s a balance with what we’re trying to achieve on the ‘look’ of the house and its performance. 

[matthyde83]

28 minutes ago, Iceverge said:

It's a nice design, in effect its a smaller second story on top of a larger ground floor. The external upper block walls being supported by steel will be the main source of your issues as these will bridge the continuous thermal envelope.  Steel is a tremendous conductor so you could end up with condensation as well as energy loss and discomfort if not attended to. 

Yup it’s occupying a lot of my thoughts without really having a solution atm.  I’m waiting for structural engineer to complete his bit before I then try to work it out / ask for help!!

 

29 minutes ago, Iceverge said:

Is that a chimney in the Study?  I would bin it unless you're far from neighbours and have ready access to free wood

Again this is more about look of the house than performance.  I love a log burner too but reality I think will be different.  Especially as it’s going to be in my study now (we’ve played around with floor plan a bit, and still are!)

 

31 minutes ago, Iceverge said:

Is it possible to include an accessible shower and on the ground floor. I recently listened to a heart-breaking documentary about a woman who went from hale and hearty to dead in the space 7 months with motor neuron disease. 

We’re mid 30’s so it hasn’t been front of mind BUT we’re still playing with the laundry room piece and having an accessible bathroom or at the very least plumbing in place is a good thought.  We’ll use stuff walls for everything outside of the three structural components so reconfiguring wouldn’t be awful if we allow for plumbing…

[matthyde83]

Some 3D renders I had done on Fiverr to bring it to life for the other half…

[SteamyTea]

2 minutes ago, matthyde83 said:

Some 3D renders I had done on Fiverr to bring it to life

You were not hoping to fit PV with that roof were you.

[Iceverge]

3 minutes ago, matthyde83 said:

Ok so you didn’t use the OSB to support the windows then, just for airtightness

Correct. 

 

3 minutes ago, matthyde83 said:

Unless you mean from the outside in which case ours is a brick finish not render

 Yes from the outside. An alternative might be using a proprietary system like that from Illbruck. I've heard good reports. 

https://www.illbruck.com/en_GB/solutions/window-installation/brick-block/

 

5 minutes ago, matthyde83 said:

One thought I had on the OSB / ply was the ability to build precise openings meaning windows can be ordered up earlier rather than waiting for structure completion given lead times. 

 

Yes. Beware protecting the window boxes whist exposed however. 

 

6 minutes ago, matthyde83 said:

Did you have MVHR designed separately or by supplier

 

Did it myself. 

10 minutes ago, matthyde83 said:

 It’s a balance with what we’re trying to achieve on the ‘look’ of the house and its performance.

 

Of course. If you're going to compromise with doors etc you're probably wasting your time painting chases etc. They're really the finishing touches as you aim for passive levels. 

 

 

[matthyde83]

17 minutes ago, SteamyTea said:

You were not hoping to fit PV with that roof were you.

Nope - although we’re east facing, garden west. So south elevation is more simple but not huge. 

[matthyde83]

17 minutes ago, Iceverge said:

Of course. If you're going to compromise with doors etc you're probably wasting your time painting chases etc. They're really the finishing touches as you aim for passive levels

The plan is to do everything we can and push as much as practical but not aiming for ph standard.  I think doors are definitely going to be the key thing and clearly need to make some decisions, including on spend here. 

[Iceverge]

13 minutes ago, matthyde83 said:

 I’m waiting for structural engineer to complete his bit before I then try to work it out / ask for help!!

 

 

Eeek! Maybe discuss this with them now. It might avoid a costly redesign. I'm trying to come up with a detail out of interest. I'll see how I get on. 

 

 

16 minutes ago, matthyde83 said:

having an accessible bathroom or at the very least plumbing

 

 

I've had this fight a couple of time on here. DO IT BEFORE YOU NEED IT.  It's less than 1m2. You can use it to store junk once it's done but for heavens sake build it while you can. 

 

Documentary On One - I'll Send You Butterflies (rte.ie) Listen for 2 minutes from 21:21 about this very discussion.

 

Anyway without the gloom of succumbing to a nasty disease it's perfectly possible you'll need to avoid stairs for a week. I did a couple of years ago when I came off my road bike and bashed my knee. Washing yourself with a cloth in the sink soon gets old. 

 

The house looks beautiful by the way. 

[matthyde83]

11 minutes ago, Iceverge said:

Eeek! Maybe discuss this with them now. It might avoid a costly redesign. I'm trying to come up with a detail out of interest. I'll see how I get on

Thanks. Will do. Plenty of opportunity, they’re visiting 13th Jan to inspect trial holes for foundation design.  Will bring it up with them before that (may even email them right now!).  Would be interested in what you come up with.  I’m assuming we need some kind of thermal break between the steel and outer leaf or at least wherever the outer leaf exits the thermal envelope. 
 

13 minutes ago, Iceverge said:

I've had this fight a couple of time on here. DO IT BEFORE YOU NEED IT.  It's less than 1m2. You can use it to store junk once it's done but for heavens sake build it while you can. 

Makes a lot of sense. 
 

13 minutes ago, Iceverge said:

The house looks beautiful by the way.

 
Thank you!  It’s been a journey getting this far, taken about 4 years.  We’ve actually completed the garden and the garage first.  Just still have a bungalow in the middle atm!  Now all I need to do is build the house ?

[matthyde83]

1 hour ago, Iceverge said:

Looking at your plans you'll really need to take care with the thermal bridging. 

What about something like this??

 

 

[matthyde83]

On 02/01/2022 at 15:17, Iceverge said:

 

Eeek! Maybe discuss this with them now. It might avoid a costly redesign. I'm trying to come up with a detail out of interest. I'll see how I get on. 

 

 

 

 

I've had this fight a couple of time on here. DO IT BEFORE YOU NEED IT.  It's less than 1m2. You can use it to store junk once it's done but for heavens sake build it while you can. 

 

Documentary On One - I'll Send You Butterflies (rte.ie) Listen for 2 minutes from 21:21 about this very discussion.

 

Anyway without the gloom of succumbing to a nasty disease it's perfectly possible you'll need to avoid stairs for a week. I did a couple of years ago when I came off my road bike and bashed my knee. Washing yourself with a cloth in the sink soon gets old. 

 

The house looks beautiful by the way. 

 

So I've now received structural calculations.  I think I can decipher some of it but in a 90 page document I'm struggling with a lot of it!

What is evident is although I've brought up thermal bridging there is nothing in here mitigating it.  We have steel connections penetrating the wall for the balcony, steel posts going down to foundations etc.

What next?  I'm not sure who's responsibility it now is to take the structural calcs and turn them into something we can build from.  Do I really need to pay for construction drawings form the architect etc.?  Also whoever that is I now need to take on the journey with thermal bridging...

 

HELP! (please!)

[markc]

50 minutes ago, matthyde83 said:

 

So I've now received structural calculations.  I think I can decipher some of it but in a 90 page document I'm struggling with a lot of it!

What is evident is although I've brought up thermal bridging there is nothing in here mitigating it.  We have steel connections penetrating the wall for the balcony, steel posts going down to foundations etc.

What next?  I'm not sure who's responsibility it now is to take the structural calcs and turn them into something we can build from.  Do I really need to pay for construction drawings form the architect etc.?  Also whoever that is I now need to take on the journey with thermal bridging...

 

HELP! (please!)

Structural calcs are there to show what is needed to keep the structure up, how it is done and the nitty gritty details are something else.

balcony support calcs will show what you need, then you need to look at how these can be aesthetically pleasing (or acceptable) and broken thermally broken etc.

same with posts and founds.

don’t think of it as one pig picture, break the structure down into components and taking a look at each of these is much easier and less daunting.

Edited January 19, 2022 by markc

[freshy]

On 02/01/2022 at 14:54, matthyde83 said:

Some 3D renders I had done on Fiverr to bring it to life for the other half…

 

 

Renders look great! Who did you use on Fiverr and how much do they charge?

[matthyde83]

3 hours ago, freshy said:

 

Renders look great! Who did you use on Fiverr and how much do they charge?

 

Yeah I'm really pleased with them!

Tharindudhan168 was the name.  I paid £250 all in and have about 20 images.  Really useful to help visualise things with the oh etc.

[Iceverge]

10 hours ago, matthyde83 said:

So I've now received structural calculations.  I think I can decipher some of it but in a 90 page document I'm struggling with a lot of it!

What is evident is although I've brought up thermal bridging there is nothing in here mitigating it.  We have steel connections penetrating the wall for the balcony, steel posts going down to foundations etc.

What next?  I'm not sure who's responsibility it now is to take the structural calcs and turn them into something we can build from.  Do I really need to pay for construction drawings form the architect etc.?  Also whoever that is I now need to take on the journey with thermal bridging...

 

HELP! (please!)

 

I did my own thermal detailing and the builder was happy to follow it. Normally it would be a part of the job of the architect+team. The structural engineer's main concern will  be to ensure the building doesn't fall down. If you want to get a professional to undertake it I would seek out a passivhaus architectural technician. 

 

Have you considered the option of external insulation, ICF or timber frame. These methods make it easier to cope with any thermal bridges etc but you will need brick slips or similar for the facade/

 

If you choose to stick with masonry cavity walls a couple of things might make it easier to deal with the steel bridging. 

 

1. Proprietary insulating connections for balconies +columns etc. 

2. Using precast concrete beams in place of steel ( cheaper and less than 10% as conductive) 

3. Using Marmox thermoblock, perisol or similar as a thermal break above the beams and outer walls. 

 

Beware most of those 90 pages will be standard issue not specific to your house. As for the construction drawings I can't be much help as we have a different process re BC etc in Ireland.

 

Good luck! 

[matthyde83]

27 minutes ago, Iceverge said:

 

I did my own thermal detailing and the builder was happy to follow it. Normally it would be a part of the job of the architect+team. The structural engineer's main concern will  be to ensure the building doesn't fall down. If you want to get a professional to undertake it I would seek out a passivhaus architectural technician. 

 

Have you considered the option of external insulation, ICF or timber frame. These methods make it easier to cope with any thermal bridges etc but you will need brick slips or similar for the facade/

 

If you choose to stick with masonry cavity walls a couple of things might make it easier to deal with the steel bridging. 

 

1. Proprietary insulating connections for balconies +columns etc. 

2. Using precast concrete beams in place of steel ( cheaper and less than 10% as conductive) 

3. Using Marmox thermoblock, perisol or similar as a thermal break above the beams and outer walls. 

 

Beware most of those 90 pages will be standard issue not specific to your house. As for the construction drawings I can't be much help as we have a different process re BC etc in Ireland.

 

Good luck! 

 

Yep I think it's where I'm getting to tbh.  I think I have my head around where the thermal bridging issues will occur and will just solve them with the builder and suppliers.

I've looked at different build methods but for various reasons we've stuck with masonry and are quite a way down the line.

Thanks for those suggestions, I've been looking at 1&3 and will now look at 2!

[matthyde83]

On 19/01/2022 at 18:36, Iceverge said:

 

I did my own thermal detailing and the builder was happy to follow it. Normally it would be a part of the job of the architect+team. The structural engineer's main concern will  be to ensure the building doesn't fall down. If you want to get a professional to undertake it I would seek out a passivhaus architectural technician. 

 

Have you considered the option of external insulation, ICF or timber frame. These methods make it easier to cope with any thermal bridges etc but you will need brick slips or similar for the facade/

 

If you choose to stick with masonry cavity walls a couple of things might make it easier to deal with the steel bridging. 

 

1. Proprietary insulating connections for balconies +columns etc. 

2. Using precast concrete beams in place of steel ( cheaper and less than 10% as conductive) 

3. Using Marmox thermoblock, perisol or similar as a thermal break above the beams and outer walls. 

 

Beware most of those 90 pages will be standard issue not specific to your house. As for the construction drawings I can't be much help as we have a different process re BC etc in Ireland.

 

Good luck! 

So I’ve taken to drawing it up prior to chatting through with builder… thoughts? (Ignore some of my dodgy scaling eg courses not lining up)