wrapping hollowcore

selfbuildsoon

Will be ordering prestressed slabs soon and have been reading up on how to wrap it for air-tightness. What would you recommend to wrap it in(roofing membrane, DPM, breathable felt etc.) and how is this done?

No6

Try wrapping it in airtight membrane!! You have to leave enough at the ends to lap up and down the wall and be plastered over, assuming you are plastering.

Radonman

No6 wrote: »

Try wrapping it in airtight membrane!! You have to leave enough at the ends to lap up and down the wall and be plastered over, assuming you are plastering.

Yea, that is the correct method. You need whoever is doing the intallation of your airtight membrane to be on site the day the slabs are being delivered in order to place the membrane on the proper wall (you only need to wrap the slab where is breaks / enters the cavity). Below the slab as abvove ensure you leave enough of a lap to allow the membrane to be fixed to the masonry with the sealant - this will all be hidden by the suspended ceiling I presume. The upper side is a bit more tricky as it depends on the floor construction and cleanliness of your builder, from our experience the membrane always gets damaged from concrete etc and you may be better off to put a strip of membrane (no more than 100mm) around the internal leaf of blockwork sealing the floor to wall joint.

BryanF

Radonman wrote: »

from our experience the membrane always gets damaged from concrete etc and you may be better off to put a strip of membrane (no more than 100mm) around the internal leaf of blockwork sealing the floor to wall joint.

can you elaborate on this, thanks

if the units are hollow core and you don't wrap the ends ends and seal to external air-tight membrane, then what's to stop air travelling through the units to some mid point location where unregulated air follow can enter the house?

if you mean place some membrane on inner leaf to protect the actual air-tight membrane i see your point..

Radonman

BryanF wrote: »

can you elaborate on this, thanks

if the units are hollow core and you don't wrap the ends ends and seal to external air-tight membrane, then what's to stop air travelling through the units to some mid point location where unregulated air follow can enter the house?

if you mean place some membrane on inner leaf to protect the actual air-tight membrane i see your point..

We are Wrapping the ends - The top of the hollow core where the the internal leaf of block work sits on the membrane, the lap on the inside is the area I'm refering to.

selfbuildsoon

Can anyone give me the names of some airtightness membranes that can be used?

MicktheMan

selfbuildsoon wrote: »

Can anyone give me the names of some airtightness membranes that can be used?

I don't mean to be critical but ...
who (i.e. professional(s)) is/are advising you on your build? Asking about airtightness membrane names is a sign that perhaps no professional input is being sought (or paid for). This is foolish in the extreme.
For instance, in my experience, airtightness details are something that should be worked out well in advance otherwise it can easily end up costing a lot more to install and the results won't be anywhere near as good as they ought to be.

Btw pm sent on airtightness membrane names.

No6

Mick I think the clue is in the his user name, its a self build!! In my opinion these will soon become a thing of the past as there's way too much regulations that need to be complied with, even good builders find it hard to keep up to date!!

selfbuildsoon

Mick what professionals are you referring to?
I have rang the local companies that do airtightness as well as a company in Dublin and have had no luck. None of them will do the job and all said there was no reason to wrap the prestressed slabs as they have no holes in the end. one said to use Primur to seal the junction of the hollowcore to the wall.

MicktheMan

selfbuildsoon wrote: »

Mick what professionals are you referring to?

Your architect/engineer, whoever specified the airtightness target.

Radonman

selfbuildsoon wrote: »

Mick what professionals are you referring to?
I have rang the local companies that do airtightness as well as a company in Dublin and have had no luck. None of them will do the job and all said there was no reason to wrap the prestressed slabs as they have no holes in the end. one said to use Primur to seal the junction of the hollowcore to the wall.

Ive seen this done several times and is not adequete, once the blow door test starts it pulls air from everywhere and even if they do a perfect job unless they seal where the slab butt against each other too air has complete access to your downstairs area - wrapping is fool proof and any other method is taking chances imo, from what ive seen the only time sealing the conc slab the wall and sealing where they butt joint is acceptable is where the builder/client had forgotten to wrap the slabs

MacConmhaigh

Hi wondering what is the best airtight membrane to use? i saw some used felt. is this felt breathable or non breathable? thanks