Airtightness - Steel lintels over 215mm block on flat

Blak8

Hello

I am embarking on a new build. The design is 215mm block on flat with external eps insulation. I am trying to achieve best airtightness as possible.

I have a question on airtightness detail around the steel lintels (203 x 133 x 25kg) over the large door and window openings, plus the same type of steels for a corner window with a steel post. I am looking to plaster the external face of the block wall before placing the external eps insulation for the block airtight barrier.

Can anyone share how they achieved airtightness for two above arrangements? (1) steel lintels over doors/windows and (2) steels for corner windows.

You input would be greatly appreciated.

MicktheMan

Blak8 wrote: »

I am looking to plaster the external face of the block wall before placing the external eps insulation for the block airtight barrier.

Madness. Who advised the detail above?
Airtighten on inside i.e. internal face of external wall.

Blak8

Thanks MicktheMan, I haven't made a decision on the general block wall. I will take you views into consideration.

To keep on topic, do you have any thoughts on airtightness re: steel lintels?

MicktheMan

I haven't gone off topic! How you air tighten your lintels depends on where your air tight barrier of the wall is.
Specifying the external face of the solid wall as the airtight barrier tells me that whoever is specifying this doesn't understand much about the concept of airtightness. For example, how will the ground floor to wall airtight continuity be achieved? Or wall to roof?
Again, who has advised on this detail?

Btw, block on flat with ewi is, imo, an excellent spec but you must get the airtightness detail right.

Blak8

Understood. The spec does detail internal plaster but I have been advised (verbally) that external plaster can provide additional protection for airtightness with the block wall (i.e. dealing with services embedded in external walls).

I see there are two choices:

e.g. choice #1: plaster internally and take careful consideration of plastering behind electrical wiring, sockets etc

choice #2: plaster internally (and don't worry having plaster behind sockets perfect) but have another external plaster barrier for additional airtightness protection. Will having this extra airtight protection cause issues?

If choice #1 is followed, how would you handle the steel lintels?

MicktheMan

Option 1 and minimise all services on external walls. Where services are needed, then ensure chases are airtightened.
Forget option 2. A lot of extra expense for questionable, if any, benefit (every mech fixing of the ewi batts will damage this barrier).

MicktheMan

Blak8 wrote: »

If choice #1 is followed, how would you handle the steel lintels?

Airtight mastic, tape and membrane.