Airtight Membrane

[Johnny Jekyll]

I'm researching MVHR and airtightness. I'm not going for Passive House but buying into making the house airtight. We are using block and block with render.

I believe wet plaster will make it airtight to a degree, but I'm wondering if using an internal airtight membrane to envelope the building (walls and ceilings with a cold loft) would be cheaper and actually better over time (cracking and all that)?

The Pro Clima Intello Plus looks like a great product. Has anyone had experience with it? I have questions like:

- Can Intello be installed directly against thermalite blocks? Or does there need to be a gap?
- How would it install around the posi joists at the joints to the walls, using joist hangers perhaps?
- I'd like to batten and plasterboard over the top of the membrane if possible, and run pipes / wiring behind the plasterboard. That way I can do most of the work myself. But how are battens attached to the blockwork through the airtight membranes? Screws?

Anyone have experience / advice installing airtight membranes?

Thanks.

[scottishjohn]

technically your blockwork should be airtight -

so you could get air test done once windows +doors etc are fitted 

and fix any airleaks at that stage

-but you still need a vapour barrier  -which could be under plasterboard.

 

 

Edited November 23, 2018 by scottishjohn

[Declan52]

Parge the blocks. 

50mm insulation and 50mm battens screwed to the wall.  By using screws you can put packers in if the walls are slightly out. 

Membrane.  Intello is good but one of the most expensive but there are plenty other options. 

50mm batten to form your service cavity.  Not sure a 25mm batten would work as well with regards the  back boxes of sockets and switches. 

Plasterboard. 

Skim. 

You can form an envelope by bringing the  membrane up and over the ceiling.  Once all the membrane is in you can do an air test and  see how you stand. Fix any leakage and then board over knowing its done right. 

By using a service cavity you will drastically cut down the air leakage from around sockets and switches which will make your house nice and warm. 

[Johnny Jekyll]

Thanks guys. Just had a great phone call with the Green Building Store, very helpful actually. They explained that the Intello Plus membrane can be laid directly against the thermalite blocks (overlapping and taping all joints in the membrane of course), and the battens can then be used to hold the membrane in place against the wall. It's ok to screw through the battens and through the membrane into the wall as the batten pressure should create an airtight seal for the membrane screw hole, but I'll check this again at installation time because I can always add a qualified sealant around each screw to ensure at good seal at that time.

 

So this is how my walls are made up so far, what do you think?

3mm skim for finish
12.5mm normal plasterboard
50mm battens for services void, and some extra insulation
Pro Clima Intello Plus membrane held against the wall by the battens, this membrane will envelop the building
100mm 7.3N thermalite blocks
100mm cavity using Cavity Therm by Xtratherm as they can achieve under 0.2 U Value at this thickness
100mm medium block
15mm K Rend