Airtightness Membrane....same as above ground?

[Thorfun]

I'd rather over-engineered than under-engineered! plus, I'm not an engineer so unless I then pay for a second SE to double check the work of the first SE I have to trust the engineer. and I chose a very well respected on this forum SE and I am very happy with their work and support.

[SimonD]

On 16/05/2021 at 17:11, Thorfun said:

thanks and glad it's not just me! I could potentially bring the insulation up past the sole plate but it'll have to somehow have a cutout for the osb. I'll have a think about it and what it might impact and, maybe, speak to the architects. but maybe it's just a detail too far. ?

 

standard external detail tbh. frame, osb, breathable membrane, battens, cladding.

 

I wouldn't lose any sleep over it. As long at the frame retains sufficient vapour control to avoid excessive moisture ingress, it's unlikely you'll suffer condensation problems. Standard stick build timber frames typically have up to 15% repeating cold bridges due to all the studs, top plate and sole plate, which is why the frames nowadays often have an additional layer of insulation either to the inside or outside of the frame. Does your drawing show an internal layer? However, even if it doesn't, there are numerous frames just like it around the world, many in far harsher environments that have performed and survived just fine.

 

As it is, you're probably better focusing as you are on airtightness and vapour control detailing.

 

 

Edited May 18, 2021 by SimonD

[Thorfun]

19 minutes ago, SimonD said:

 

I wouldn't lose any sleep over it. As long at the frame retains sufficient vapour control to avoid excessive moisture ingress, it's unlikely you'll suffer condensation problems. Standard stick build timber frames typically have up to 15% repeating cold bridges due to all the studs, top plate and sole plate, which is why the frames nowadays often have an additional layer of insulation either to the inside or outside of the frame. Does your drawing show an internal layer? However, even if it doesn't, there are numerous frames just like it around the world, many in far harsher environments that have performed and survived just fine.

 

As it is, you're probably better focusing as you are on airtightness and vapour control detailing.

 

 

thanks and there are many other things I can lose sleep over. ?

 

we are having an extra layer of insulation internal to the timber frame. planning on 140mm mineral wool between the timbers and 80mm PIR internally all covered in VCL/airtight membrane. seems to be a pretty standard make up for self-build TF these days.

[Thorfun]

On 17/05/2021 at 11:02, Bitpipe said:

Airtightness fabric, which is about 4m wide was used and taped to the airtightness board on the inside of the frame wall and to the concrete of the basement wall.

@Bitpipe qq. do you remember which airtightness fabric you used?

[Thorfun]

I found this https://passivehousesystems.co.uk/product/scrim-reinforced-airtight-membrane/ online. this seems like the right thing to use around the block and beam and the stats show a much greater tensile/tear strength.

 

anyone used it?

[Bitpipe]

2 hours ago, Thorfun said:

@Bitpipe qq. do you remember which airtightness fabric you used?

 

Nope, all I know is that it was bright yellow!

 

MBC took care of it, my interior wall was an airtight board and the fabric was only used in between floors and on the warm roof.

 

It was secured to the concrete wall and airtightness layer above with green / yellow airightness tape.

Edited May 21, 2021 by Bitpipe

[HerbJ]

Hi  

MBC probably used the same membranes as for my build, which was a couple of months ahead of @bitpipe.

They used  some AMPATEC DB90  but  mostly SIGA-Majpell -5 to wrap the joist ends and between floors and, for mine, they used SIGA-Majpell -5 for the walls and roof.  ( the airtight board was introduced after my build) - see photos.

 

 

 

[Thorfun]

9 minutes ago, HerbJ said:

Hi  

MBC probably used the same membranes as for my build, which was a couple of months ahead of @bitpipe.

They used  some AMPATEC DB90  but  mostly SIGA-Majpell -5 to wrap the joist ends and between floors and, for mine, they used SIGA-Majpell -5 for the walls and roof.  ( the airtight board was introduced after my build) - see photos.

 

 

 

thanks, that's good to know. it seems that airtight membrane all seems to do a very similar job and it's hard to know if the really expensive Proclima stuff is worth the extra cost over the cheaper alternatives. more research is required!

[Bitpipe]

13 minutes ago, HerbJ said:

Hi  

MBC probably used the same membranes as for my build, which was a couple of months ahead of @bitpipe.

They used  some AMPATEC DB90  but  mostly SIGA-Majpell -5 to wrap the joist ends and between floors and, for mine, they used SIGA-Majpell -5 for the walls and roof.  ( the airtight board was introduced after my build) - see photos.

 

 

 

 

 

 

Yes - it was the yellow Ampetex. I think my build was their first with the green airtight OSB board, we had the company rep come out to look and take pics. 

[Thorfun]

1 hour ago, Bitpipe said:

 

Nope, all I know is that it was bright yellow!

 

MBC took care of it, my interior wall was an airtight board and the fabric was only used in between floors and on the warm roof.

 

It was secured to the concrete wall and airtightness layer above with green / yellow airightness tape.

thanks. I'm still thinking about using the airtight board instead of fabric to be honest. the architect has detailed for the airtight board as I said I was going to use it but I can easily swap it out for normal OSB if I choose to go with the membrane instead. will need to run the costs in a spreadsheet for that one but will definitely have the membrane between floors.

[Bitpipe]

On 21/05/2021 at 16:23, Thorfun said:

thanks. I'm still thinking about using the airtight board instead of fabric to be honest. the architect has detailed for the airtight board as I said I was going to use it but I can easily swap it out for normal OSB if I choose to go with the membrane instead. will need to run the costs in a spreadsheet for that one but will definitely have the membrane between floors.

 

IIRC, MBC said that the board was much quicker to install as I believe the other system still needs an OSB layer to form the inner wall.

[Thorfun]

3 hours ago, Bitpipe said:

 

IIRC, MBC said that the board was much quicker to install as I believe the other system still needs an OSB layer to form the inner wall.

makes sense as I wanted OSB anyway so combining the two seemed to make sense. only small concern is the osb would be good for screwing things in to the wall but I'd be worried about penetrating the airtight board whereas OSB over a membrane would give a little extra potential protection from making a hole in the airtight layer.

[SteamyTea]

On 16/05/2021 at 20:56, Thorfun said:

assuming you're talking about the MBC twin wall system?

I never understood the design from sketches and drawings until I went to Jeremy Harris' place, the  it all made sense.

Can't remember the finer details now, but it works.

I know there was some toing and froing with Kingspan about their soleplate detail and the condensation risk. @saveasteading Maybe look up that detail and see what they do now.

[Bitpipe]

19 hours ago, Thorfun said:

makes sense as I wanted OSB anyway so combining the two seemed to make sense. only small concern is the osb would be good for screwing things in to the wall but I'd be worried about penetrating the airtight board whereas OSB over a membrane would give a little extra potential protection from making a hole in the airtight layer.

 

You can penetrate it (otherwise how would they fix it to the structural ribs) and it self seals but if you subsequently withdraw the fixing then you should seal the hole with airtightness tape. I doubt one or two holes would make a difference but lots will.

 

MBC put a 50mm service batten over the airtight board, aligned with the structural ribs, and for any load bearing elements like TVs or sinks etc, I just put in additional noggins or ply where required within the service cavity.

 

The electrician also took care to fix back boxes to the service battens (or on noggins spanning them). Where penetrations were required (e.g. outside light) he put a duct through, angled downward, and sealed with tape to the face of the board. When the required cable is pulled through the duct is sealed with silicone and another bit of tape on the inside.

[Thorfun]

1 hour ago, Bitpipe said:

 

You can penetrate it (otherwise how would they fix it to the structural ribs) and it self seals but if you subsequently withdraw the fixing then you should seal the hole with airtightness tape. I doubt one or two holes would make a difference but lots will.

 

MBC put a 50mm service batten over the airtight board, aligned with the structural ribs, and for any load bearing elements like TVs or sinks etc, I just put in additional noggins or ply where required within the service cavity.

 

The electrician also took care to fix back boxes to the service battens (or on noggins spanning them). Where penetrations were required (e.g. outside light) he put a duct through, angled downward, and sealed with tape to the face of the board. When the required cable is pulled through the duct is sealed with silicone and another bit of tape on the inside.

guess that's decision made then! ?

[Thorfun]

hi all. I've been doing a bit more reading on basement airtightness and vapour control (I know the thread subject heading is about airtightness but I think that airtightness and VCL seem to go hand-in-hand) and it looks like with insulation on the outside of the basement a VCL shouldn't be used in the basement.

 

this article:

 

https://www.buildingscience.com/documents/digests/bsd-103-understanding-basements

 

says:

 

"If basement wall systems are designed and constructed to dry to the interior – regardless of where insulation layers are located – interior vapor barriers must be avoided."

 

so, can anyone who is much smarter than me confirm or deny this? it seems to me that I can wrap the ends of the block and beam flooring in airtight membrane/VCL and then stick that to the basement concrete walls and NOT take it any further down the wall. The external Type A waterproofing membrane won't let moisture in and so the basement is, afaik, designed to  and constructed to dry to the interior and, therefore, no VCL should be used on the basement walls.

 

comments on this please?!

[Thorfun]

On 17/05/2021 at 11:16, Bitpipe said:

EPS70 was applied to the exterior walls when the basement casting was complete.

hey @Bitpipe. sorry if you've answered this elsewhere but how did your EPS get attached to the basement walls? I know you didn't have an external membrane so didn't have to worry about penetrations in that Type A waterproofing but did you use fixings or some form of adhesive? if adhesive what did you use? 

 

I need to make sure the groundworkers use the correct adhesive to attach our EPS to the type A membrane without using mechanical fixings!

[Bitpipe]

16 hours ago, Thorfun said:

hey @Bitpipe. sorry if you've answered this elsewhere but how did your EPS get attached to the basement walls? I know you didn't have an external membrane so didn't have to worry about penetrations in that Type A waterproofing but did you use fixings or some form of adhesive? if adhesive what did you use? 

 

I need to make sure the groundworkers use the correct adhesive to attach our EPS to the type A membrane without using mechanical fixings!

 

Soudal LE foam, the type that needs a gun. Simply wet the EPS and the wall with hose and then do a nice big squirty pattern on the EPS and offer up to wall. May need to prop it until the foam goes off. You can then go round and foam up the joints.

 

Always wear gloves as it sticks to your skin and is a bugger to get off.

 

I then dressed the exterior of the EPS with 3mm corex, the stuff you use to protect floors when building. It's the same size as the EPS sheets. Just to give some protection during backfill.

 

Tried stapling that but gave up and just pushed in old nails (had millions lying around from the formwork). 

[Thorfun]

9 minutes ago, Bitpipe said:

 

Soudal LE foam, the type that needs a gun. Simply wet the EPS and the wall with hose and then do a nice big squirty pattern on the EPS and offer up to wall. May need to prop it until the foam goes off. You can then go round and foam up the joints.

 

Always wear gloves as it sticks to your skin and is a bugger to get off.

 

I then dressed the exterior of the EPS with 3mm corex, the stuff you use to protect floors when building. It's the same size as the EPS sheets. Just to give some protection during backfill.

 

Tried stapling that but gave up and just pushed in old nails (had millions lying around from the formwork). 

thank you! just the information I needed. appreciate it. :-) 

 

[Bitpipe]

2 hours ago, Thorfun said:

thank you! just the information I needed. appreciate it. ?

 

 

I did it as a DIY job as the ground worker was not experienced in using EPS so just left it to me. Only took a few days to do this (I also had lightwells to install from MEA). Only fiddly bit was cutting the EPS to have the correct height at the top to interface with the timber frame - annoyingly it need to be exactly 80mm higher than the concrete wall itself to match the Kore profile.

 

I also used the EPS to form concrete corbels to support doors (sliding and fixed) that would not sit entirely on the basement wall but would straddle the insulated layer also. This was easy enough, the crew drilled and resin fixed stubs of rebar into the required area, braced with rebar at 90^o and I chopped out a 100mm wide, 200mm deep channel on the EPS which they backfilled with concrete - worked great. SE obv signed off this design detail.

 

[Thorfun]

hi all,

 

just to resurrect this thread briefly as our coursing blockwork is starting tomorrow.  The groundworker is now proposing that we run the membrane as follows:

 

 

so with the VCL membrane going outside the block and then in on the underside of the coursing brick and then up to join the timber frame walls internally (previously I had the membrane on the inside of the block running between the hollow core/block and beam and the block).

 

anyone with a better knowledge of physics able to tell me if this new solution is an issue? I can't think of it being one but thought I'd check on here first