Airtightness steps and tips for success

[SuperJohnG]

There is another thread like this...butnit deals mainly with a brick and block home. 

 

Link here: 

 

 

However I wanted to capture basic logical steps for success and glean some wisdom of things that became hard before I start with the airtightness inside. 

 

I'm just finishing up outside of our SIPS house fitting the cladding and plan to move inside to start in around 4 weeks. 

 

It's a SIPS kit so naturally less junctions that are difficult to deal  E.g where you would have trusses meeting blocks walls etc. I have SIPS panel screwed to sip panel, whilst not airtight hies a long way to close uo gaps.

 

I fitted a tony tray during the kit erection, basic plastic sheet but all I could get on a Sunday but will hopefully simplify that step around joists. 

 

I have 900m2 of Intello VCL and 40 rolls of tescon vana on hand but before I start that I was thinking along the steps which seem basic but worth checking.

 

Starting bare house internally OSB:

 

1) go round and fill all holes (there are some despite it being SIPS) with airtightness foam. 

 

2) fit PIR internally over any ridge beams that are exposed and causing big thermal bridges. 

 

3) Fit extra layer of PIR internally (still debating this) in ceilings

 

4) Fit VCL. Start from the bottom, staple to wall above laps. Should I tape the top of that layer to wall? Or should I just get the layer above on and then tape the lap? 

 

Penetrations - I havent put anything through the walls yet. I really should've done them prior to putting on renderboard and cladding but just hasn't happened.

 

There are some big penetations for MVHR and stove direct air feed and ASHP pipes. The rest are small cables and all drainage goes out through the slab with no roof penetrations.

 

How best to do these? Ideally I'd have done them earlier and I'm aware it'll damage the VCL doing after but I haven't decided absolutely where the final locations are and I dont have the MVHR unit, stove or ASHP yet. I know where they go roughly but would struggle to place these just now. I assume I can just put them through later and then just seal around with airtightness tape easily enough. 

 

What other tips and bits and I missing. What can I do before I crack on to ensure success and take the best approach. 

 

 

 

Edited February 21, 2022 by SuperJohnG
Shoddy spelling and grammar

[ProDave]

My No 1 tip, since you didn't mention it, is a service void.

 

So as you line your entire house, with the air tight membrane, and all joints taped, you fix vertical battens at 600mm centres.  This gives you a void to run cables and pipes without any of these penetrating your air tight layer.  Only services that must exit the building penetrate the air tight membrane and are sealed where they do so.

 

Some examples:

 

 

 

[SuperJohnG]

5 minutes ago, ProDave said:

My No 1 tip, since you didn't mention it, is a service void

Ah yes - I have one. After VCL exactly that next step, I was actually considering the electrical first fix then battens but the joiners want battens then just say to cut out the cable ways for the safe zones but does concern me as the VCL might get damaged at thats point. I see you have yours cut out there Dave during battening ?

 

Also that you have 25mm battens I thiughtbthese would be too small for a service void for cables...isn't fitting cables in a 25mm deep box a nightmare for ring main? 

Edited February 21, 2022 by SuperJohnG

[ProDave]

1 minute ago, SuperJohnG said:

I was actually considering the electrical first fix then battens but the joiners want battens then just say to cut out the cable ways for the safe zones but does concern me as the VCL might get damaged at thats point.

Tell the joiners to stop being lazy.  CUT the battens and leave gaps at 450mm above FFL and 1150mm above FFL as you can see in my first picture.  Those are socket height and switch height are where you are most likely / be allowed, to run cables horizontally.

 

Cutting battens as you fit them and leaving that small gap gives space for cables, and no danger of damaging the VCL when drilling the battens.  and if the gaps end up not being used then no harm is done.

 

It also makes it easy to use all your battens with no waste.

[Thorfun]

12 minutes ago, SuperJohnG said:

Also that you have 25mm battens I thiughtbthese would be too small for a service void for cables...isn't fitting cables in a 25mm deep box a nightmare for ring main? 

this is exactly what I was going to ask! I remember @ProDave saying that 25mm battens plus the 12mm plasterboard fits a 38mm backbox perfectly. am I misquoting  you Dave?

 

But I also note that many others have used 38mm x 50mm battens.

 

as an electrician @ProDave which is best (or your preference) and why?

[ProDave]

I used 25mm battens almost everywhere.  25mm battens and 12mm plasterboard is a near perfect match for a 35mm back box.  I even managed carefully to run 15mm copper pipe in a 25mm service void.

 

I only used 45mm battens in the utility room where I had 22mm copper pipes to fit, and those, with fittings, simply would not fit a 25mm void.

[LA3222]

@SuperJohnG don't overthink it bud, it's as easy as you say, tape and seal away to your hearts content. Need to make a hole, make a hole then seal the membrane to the pipe/cable etc with tape.

 

I had loads of silicone left over from the SIP people so the missus went around and ran a bead along every panel to panel join - worked really well, (I did it all pretty much one man band), where the soleplate meets floor etc - every join. Not too difficult as the panels are big so not overly onerous.

 

Seal the membrane to the floor slab - I ran a bead of orcan f first, pressed membrane to that then taped with the tescon.

 

I did bottom sheet first and used the double sided tescon stuff to hold it in place, also chucked a bit of the tape on here and there. Lap top sheet over it then sealed top to bottom.

 

Get the battens up in good order else things start sagging - a day or two is generally OK. The Double sided tape holds it all taught to the wall without having to staple the shit out of it. The battens trap it there.

 

I did my 180mm mvhr ducts after the brick skin went up - stupid but the way it worked out  generally because I wasn't sure exactly where stiff would go. I havent used any proprietary grommets etc to seal, just orcon f in places and tape.

 

My air test was 0.24m3/hr/m2 - it's easy enough, just be reasonably diligent. I'm sure I have holes and bits I missed in the membrane  easily done but I looked at this as a compound effect. SIP is good for airtightness anyway, silicone the joins = better, fit insulation and tape all joins so another layer, fit vcl and seal up - in my head, cumulatively it would give a good result and it did.

 

I used 38mm battens and 47mm back boxes - useful if you have a lot of two way switching. I do, wanted most lights to be switchable from multiple locations and some of the back boxes are horrendously clogged up. 

 

 

 

 

Edited February 21, 2022 by LA3222

[JohnMo]

Slightly different approach.

 

Parge coat, service battons screwed to Durisol through parge coat, used a hybrid sealant at all screws.

 

Made plates at top of wall for electrician to run wiring, same for where plumbing was running so all clips were secured to OSB, instead of direct to the wall.  Below bottom horizontal battons, foam filled and airtight paint.  50mm battons everywhere.

[Nick Laslett]

Hi @SuperJohnG, @Russell griffiths mentioned in another thread recently that you can DIY an air blower to do your own preliminary searching for leaks.
 

 

It was a bit scant on details , but I think if you have seen an air test being done you can work out what is required. I only mention it here, because this might be a better place to keep the details. 

[ProDave]

This was my DIY air blower test, an old office desk fan, some cardboard, a few bits of OSB and a roll of duct tape.

 

 

You won't gat a calibrated result from it, but you will be able to go looking for leaks and fix them before it all gets covered up.

[Nick Laslett]

Of course this topic has already been tackled by the dedicated Buildhub members. Most of my building searches lead me back here. 
 

Lots of options for the fans, those used for bouncy castles is one idea, this is something you might already have cluttering up your shed! My kids are both at college, so the bouncy castle hasn’t been out for nearly 10 years. I wonder if the fan still works?
 

https://www.amazon.co.uk/ZWLE-Inflatable-Bouncer-Powerful-House-null250W/dp/B0992BTR4P/ref=asc_df_B0992BTR4P/?tag=googshopuk-21&linkCode=df0&hvadid=534946035793&hvpos=&hvnetw=g&hvrand=12472028111365706287&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1006886&hvtargid=pla-1411141262321&psc=1

 

Once you have the door fan set up to create some kind of positive or negative pressure, then you need a smoke pencil to detect the leaks. This appears to be a piece kit used by Chimney sweeps. 
 

https://www.chimneysheep.co.uk/product-category/smoke-pencil-draught-detector/

 

Or a thermal camera might work. 
 

https://www.test-meter.co.uk/blog/using-thermal-imaging-with-the-blower-door-method-for-airtightness

 

N.B. This is in no way a substitute for a professional test. Just a backstop whilst still in the build process to check for things when they can be easily remedied. 

 

Edited February 22, 2022 by Nick Laslett

[joth]

We did our preliminary test using a pipe though a sealed hole and then had a 1.5kW wet&dry vacuum sat outside sucking the air out the house.  

 

 

[SuperJohnG]

19 hours ago, LA3222 said:

Seal the membrane to the floor slab - I ran a bead of orcan f first, pressed membrane to that then taped with the tescon

Got the Orcan F already - did you do it on the first floor too or just tape down onto the tony tray but stil on the wall?

19 hours ago, LA3222 said:

silicone the joins = better

The silicone I wasn't planning - thinking that that VCL covers these anyway?

 

Thanks for all the good ideas on home made blowers - was going to do a proper test prior to close up but that will make it much easier. 

[WWilts]

Membrane to membrane join, overlap. 

Will Tescon duplex tape give an airtight join?