Air tightness silly question ??

moan 77

Hi All,

This may be a silly question. I'm going to try to have my story and half domer built as air tight as i can, so far i understand i will have a breathable membrane just under slates then i will have 100mm of rigid insulation foil both sides fitted between the rafters, then an airtight membrane fitted to the underside of rafter counter battened to allow for services and then foil back slab. Is there anywhere else i should be looking to use the airtight membrane, as my walls upstairs and down are standard 100mm concrete block which i plan to plaster, i have a precast concrete first floor so i will have a drop metal ceiling with foil back slab skimmed and painted. I also will have hrv fitted.

I have heard of putting the airtight membrane on the precast slab and then plaster it to the block wall ????, like wise where it joins the rafters to the wall allow this to plastered in or if wall is slab seal down to floor.

All or any help would be great.

RKQ

moan 77 wrote: »

I have heard of putting the airtight membrane on the precast slab and then plaster it to the block wall ????, like wise where it joins the rafters to the wall allow this to plastered in or if wall is slab seal down to floor.

All or any help would be great.

Moan 77 IMO there is no such thing as a "silly question". Everyone has to start somewhere, we all continue to learn.

There are 3 major manufacturers / suppliers of airtight tape & membranes in Ireland. Check out their web sites for details, specifications, photographs & advice.

Also look at Irish Dept of Enviro web site - Acceptable Construction Details http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/

The junctions of wall to floor are critical in airtightness, you are correct to be concerned about these areas. Timber joists and hollow core slabs need an airtight membrane installed. There are lots of threads on this subject in this forum.

moan 77

Thanks RKQ,

My biggest problem is getting good honest advice.
Could someone give a guideline as to what is proper practice when it comes to a concrete constructed house with 150 mm hollow core slab with 125mm rigid insulation covered with 125mm 30n20 screed with Underfloor heating on ground floor, then 100mm outer leaf then 50mm cavity then 100 rigid insulation then 100mm inner leaf.
First floor is 200mm hollow core slab with 25mm rigid insulation Underfloor pipes with 75mm 30n10 screed, then a cut roof using 175mm rafters. Where would the major points that would need treatment for air tightness starting at ground floor finishing at the roof with the slates. Please please can someone advise me.

RKQ

moan 77 wrote: »

Thanks RKQ,

Where would the major points that would need treatment for air tightness starting at ground floor finishing at the roof with the slates. Please please can someone advise me.

Every junction!
In simple terms :-

• where the grond floor joins the external walls,
• where the 1st floor meets the externals walls (floor & ceiling!!)
• Wallplate level.

All internal leaves of external walls require a scud coat of plaster to achieve air tightness. IMO 1st floor ceiling (underside of attic) requires an airtight membrane.

See Dept of Envirno web site
http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,18749,en.pdf

Also check out the 3 Manufacturers / Supplies in Ireland of tapes & airtight membranes. I used them on my house in 2003.