Airtightness catch 22

Viking House

Out Of Order wrote: »

Can I ask what is the method of resolving air leakage at the sockets?
I'm trying to decide my own roof detail at the moment.
Intello/DB+/Vario would be a lot cheaper, faster, and easier work to install.
I would also be happier to be able to check the consistency of the cellulose fill by just pressing the membrane at random areas of the roof.
The other pros are that you would have less weight on your roof, you need less tapes, and I'd also be concerned about the glues used in the OSB.
The cons are that you have less racking strength and it might be harder to press down on the tape to make a seal on the areas between the rafters.

The glues in the OSB offgasing are not an issue if you have enough ventilation.

The Cellulose installers I've used are all well up on their game so I would have no need to personally see the cellulose behind a membrane that could pop at the staples from the pressure. The consistency is always good when you have a careful installer, we've even removed boards a few days after the cellulose was pumped and the fill was perfect.

I've personally gone off all those VCL membranes and see them as only trouble to be honest, a friend had a leaking flat roof lately onto an Intello membrane, the water pool stayed on the membrane for months causing moisture damage to the plywood and timbers, the whole roof had to come off, if there was no Intello membrane the water would have come straight in and could have been solved sooner and easier. So now we're put 12mm ply outside the rafters, using this as the windtight, raintight, airtight line allowing everything to sweat, breathe and leak to the inside and outside. The plywood has a 150mm sheet of Polystyrene on top and rockwool between the rafters and just plasterboard inside.

And SAS, if you decided to externally plaster you could paint external insulation primer onto the plaster to create a second line of defence from the weather.

sas

Viking House wrote: »

Its not my method, its a standard method used in externally insulated Canadian timber frame houses. The build programme would go like this; build the blocks, put on the roof, plaster externally, put in the windows and then do the airtightness test. When the test is good you insulate the roof, externally insulate and then do the electrics and plumbing without worries.

Then you have all the options that regular clients have, you can drill holes in the wall, you can put spots in the bedroom ceilings, you can move the position of a door or a wall at a later date without too much worry.

Cellulose over OSB isn't a blind fill the good installers use cameras to check the voids for obstructions and they always insert the hose to the bottom of the void.

Oh and EPS wouldn't be airtight enough, you can blow through it.

I'm to be convinced that 200mm of EPS is not airtight. Once it's rendered it definitely is so I will stick to my opinion that a properly installed external insulation system will contribute a meaningful amount to the overall airtightness strategy.

As much as I enjoy our discussions, for me this one has run it's course so I will leave it there.

Viking House

sas wrote: »

On the houses you plastered outside, what results have you had with them on the blower door?

I'm working on the assumption that the EPS boards themselves are airtight.

We haven't tested these houses because we have only used it for extensions so far. We got below 1 for a timber frame extension that was externally insulated though.

btw. you assumed EPS board was airtight not plastered EPS board. An external airtightness line can easily be punctured. The best and easiest method in my opinion is still to have an airtightness line in the middle of the wall out of harms way on the warm side of the dew point and let the wall sweat out and sweat in from that point. You have not convinced me otherwise so we will leave it at that.